Cenozoic Sediment Dispersal Patterns Across Trinidad, West Indies
by
Hasley Vincent
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy
at
Dalhousie University Halifax, Nova Scotia July 2008
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IV Table of Contents
LIST OF FIGURES xiv LIST OF TABLES xx ABSTRACT xxii ACKNOWLEDGEMENTS xxiii CHAPTER 1 - INTRODUCTION 1
1.1 OVERVIEW 1 1.1.1 Nature of Research 2 1.1.2 Organization of Thesis 2
1.2 RESEARCH OBJECTIVES 4
1.3 REGIONAL SETTING 5 1.3.1 Location 5 1.3.2 Stratigraphy 8 1.3.2.1 Stratigraphic column 8 1.3.2.2 Overview of formations 8 1.3.2.3 Historical development of the Trinidad stratigraphic table 9 1.3.2.4 Modifications to Bolli's original scheme 16 1.3.2.5 Facies control onplanktonic foraminifera 16 1.3.2.6 Formations in the Trinidad Stratigraphic table 17 1.3.3 Regional Structure 19 1.3.3.1 Caribbean Plate evolution 20
1.4 OUTLINE OF METHODS 23 1.4.1 Sedimentological principles 25 1.4.1.1 Historical Development of Sedimentology 26 1.4.1.2 Basic Principles in Sedimentology 27 1.4.1.3 The Behavior of Transporting Fluids 27 1.4.1.4 Sediment entrainment 28 1.4.1.5 Sediment support mechanisms and grain settling 30 1.4.1.6 Sedimentary Structures and Flow Regimes 31 1.4.1.7 Definition of terms 33 1.4.2 Deep-Water Sediment Gravity Flows 35
v 1.4.2.1 Grain support mechanisms in sediment gravity flows 38 1.4.2.2 Depositional products of sediment gravity flows 40 1.4.3 Facies Associations in deep-water clastic environments 41 CHAPTER 2 - LITHOFACIES ASSOCIATIONS AND SEDIMENTARY PROCESSES OF PALEOCENE TO EARLY MIOCENE FORMATIONS 48
2.1 INTRODUCTION 48
2.2 CHAUDIERE AND POINTE A PIERRE FORMATIONS 49 2.2.1 Overview of the Chaudiere formation 49 2.2.2 Overview of the Pointe-a-Pierre formation 50 2.2.3 Facies of the Chaudiere Formation 52 2.2.3.1 Amalgamated pebbly sandstone (APS) 55 2.2.4 Facies of the Pointe-a-Pierre Formation 59 2.2.4.1 Tabular sandstone (TS) 59 2.2.4.2 Massive thick-bedded sandstone (MTBS) 60 2.2.4.3 Discordant sandstone and shale (DSS) 65 2.2.4.4 Lenticular sandstone (LS) 68 2.2.5 Facies Succession in the Pointe-a-Pierre and Chaudiere Formations 69 2.2.6 Palaeocurrents from the Pointe-a-Pierre Formation 71 2.2.7 Interpreted sedimentary processes 72 2.2.8 An alternative to hummocky cross-stratification 74
2.3 SAN FERNANDO FORMATION 76 2.3.1 Outcrop Distribution 77 2.3.2 Members of San Fernando Formation 78 2.3.2.1 Mount Moriah Sandstone Member (MMGSM) 79 2.3.2.2 Mount Moriah Calcareous Silt Member 81 2.3.2.3 Vistabella Limestone Member 83 2.3.3 Conglomerates of the San Fernando Formation 84 2.3.3.1 Plaisance and Marabella Conglomerates 85 2.3.4 San Fernando Formation at Soldado Rock 88 2.3.4.1 Sedimentary Processes at Soldado rock 94 2.3.5 Summary of facies in the san fernando formation 96
2.4 ANGOSTURA SANDSTONE MEMBER (CIPERO FORMATION) 98 2.4.1 Overview of the Angostura Sandstone 99
vi 2.4.2 Fades of the Angostura Sandstone 102 2.4.2.1 Bioturbated sandstone and siltstone facies assemblage 102 2.4.2.2 Massive thick-bedded sandstone (MTBS) ....110 2.4.2.3 Graded thick-bedded sandstone and conglomerates (GTBS) Ill 2.4.2.4 Cobble conglomerate (CC) 113 2.4.2.5 Organic debris 115 2.4.3 Petrophysical Log Facies and Facies Succession 117
2.5 NARIVA FORMATION 117 2.5.1 Overview of the Nariva Formation 117 2.5.2 Facies of the Nariva Formation (from outcrop) 121 2.5.2.1 Amalgamated pebbly sandstone (APS) 122 2.5.2.2 Massive thick-bedded sandstone (MTBS) 122 2.5.2.3 Parallel-laminated sandstone 127 2.5.2.4 Tabular sandstone (TS) 130 2.5.3 facies of the Nariva Formation (from Subsurface Core) 131 2.5.4 Petrophysical log facies 132 2.5.5 Facies Succession 134
2.6 MIDDLE CIPERO FORMATION (PLUM MITAN) 136 2.6.1 Lithofacies of the Middle Cipero Formation (Plum Mitan) 136 2.6.1.1 Symmetrical rippled sandstone 136 2.6.2 Palaeoenvironmental significance of the Plum Mitan outcrop 138
2.7 HERRERA SANDSTONE MEMBER 138 2.7.1 Lithofacies of the Herrera sandstone 141 2.7.1.1 Rippled sandstone and shale (RSS) 141 2.7.1.2 Rippled and graded sandstone (RGS) 142 2.7.1.3 Graded thick-bedded sandstone (GTBS) 145 2.7.2 Petrophysical log facies 148 2.7.3 Facies Succession 149 2.8 PALEOCENE TO EARLY MIOCENE FACIES SUMMARY 149 CHAPTER 3 - PALEOCENE TO EARLY MIOCENE DEPOSITIONAL ENVIRONMENTS 152 3.1 PALAEOENVIRONMENTAL INTERPRETATION FROM BENTHICFORAMINIFERA.... 153
3.2 SUMMARY OF FACIES ASSOCIATIONS 154
vn 3.3 DEPOSITIONAL ELEMENTS 159 3.3.1 Canyons and other large-scale erosional features 159 3.3.2 Channels 161 3.3.3 Lobes 163 3.3.4 Channel-lobe transitions 163 3.3.5 Overbank wedges or levees 163 3.3.6 Slope facies 164
3.4 FACIES SUCCESSION AND DEPOSITIONAL ENVIRONMENTS 165 3.4.1 Fining-upward succession of the Chaudiere and Pointe-a-Pierre formations 165 3.4.2 Chaotic facies association of the San Fernando Formation 172 3.4.3 Aggradational succession of the Angostura Sandstone 174 3.4.4 Fining-upward succession of the Nariva formation 177 3.4.5 Coarsening and thickening upward succession of the Herrera Sandstone 180 3.4.6 Cipero Formation (Plum Mitan locality) 182 3.5 SUMMARY 183 CHAPTER 4 - LITHOFACIES ASSOCIATIONS AND DEPOSITIONAL ENVIRONMENTS OF LATE MIOCENE AND PLIOCENE FORMATIONS 185 4.1 CRUSE FORMATION 186 4.1.1 Facies of the Cruse Formation at Morne Diablo 189 4.1.1.1 Discordant sandstone and shale facies 189 4.1.1.2 Massive thick-bedded sandstone facies 192 4.1.2 Lithofacies along the eastern Morne Diablo coastline 193 4.1.3 Synopsis of sedimentary processes at Morne Diablo 194 4.1.4 Depositional Environment of the Cruse Formation along the Morne Diablo coast 195 4.2 LITHOFACIES OF THE MORNE L'ENFER FORMATION (LATE PLIOCENE) 197 4.2.1 Overview of the Morne L'Enfer Formation 198 4.2.2 Facies of the Morne L'Enfer formation 201 4.2.2.1 Laminated Silts (LS) 201 4.2.2.2 Thickening-Upward Flaser-Wavy Sands (TUFW) 202 4.2.2.3 Grey, Bioturbated Silts (GBS) 208 4.2.2.4 Swaley Cross-Stratified Sands (SCSS) 209
viii 4.2.2.5 Trough Cross-Stratified Sand (TCSS) 212 4.2.2.6 Amalgamated Sigmoidal Cross-stratified Sands (ASCS) 215 4.2.2.1 Laterally Accreted Sands (LAS) 216 4.2.2.2 Transitional Silts and Shale (TSS) 219 4.2.3 Lithofacies Succession and Sedimentary Processes in the Morne L'Enfer Formation: Summary 220 4.2.3.1 Palaeocurrent orientation in the Morne L' Enfer Formation 221
4.3 SEQUENCE STRATIGRAPHY OF THE MORNE L'ENFER FORMATION 224 4.3.1 Recognition of flooding surfaces and parasequences 224 4.3.2 Recognition of unconformities 226 4.3.3 Sequences and Systems Tracts 226
4.4 SUMMARY OF LATE MIOCENE TO PLIOCENE SEDIMENTARY PROCESSES 227 CHAPTER 5 - ICHNOFACIES ANALYSIS APPLIED TO THE TRINIDADIAN STRATIGRAPHY 230
5.1 ICHNOLOGY, ICHNOFACIES AND SEDIMENTOLOGY 230 5.1.1 Evolution of the Ichnofacies Concept 231 5.1.2 Application of ichnology and the ichnofacies concepts 234 5.1.3 Shortcomings of the Ichnofacies concept 235 5.1.4 Ichnofacies and deepwater depositional environments 236
5.2 ICHNOFACIES APPLIED TO THE TRINIDAD STRATIGRAPHY 240 5.3 TRACE FOSSILS OF THE PIERRE POINT SANDSTONE MEMBER (POINTE-A-PIERRE FORMATION) 242 5.3.1 Description of trace fossils 244 5.3.2 Summary of trace fossil assemblages for the Pierre Point Sandstone Member 254 5.3.3 Ichnofacies of the Pierre Point Sandstone Member 256 5.4 TRACE FOSSILS OF THE ANGOSTURA SANDSTONE 258 5.4.1 Description of trace fossils 258 5.4.2 Summary of trace fossil assemblages for the Angostura Sandstone 261 5.4.3 Ichnofacies of the Angostura Sandstone 263 5.5 TRACE FOSSILS OF THE HERRERA SANDSTONE MEMBER (CIPERO FORMATION) 263 5.5.1 Description of trace fossils 264
ix 5.5.2 Summary of trace fossil assemblages for the Herrera Sandstone Member 272 5.5.3 Ichnofacies of the Herrera Sandstone Member 273 5.6 TRACE FOSSILS OF THE LATE MIOCENE AND PLIOCENE FORMATIONS 274 5.6.1 Trace fossils of the Manzanilla and Cruse Formations 274 5.6.2 Description of trace fossils 275 5.6.3 Trace fossil assemblages 279 5.6.3.1 Cruse Formation along the Morne Diablo coast 279 5.6.3.2 Cruse Formation at Point Radix 279 5.6.3.3 Manzanilla Formation near Point Paloma 280 5.6.4 Summary of trace fossil assemblages for the Cruse and Manzanilla Formations 280
5.7 ICHNOFACIES OF THE MORNE L'ENFER FORMATION 281 5.7.1 Description of traces 281 5.7.2 Summary of trace fossil assemblages by depositional environment 286 5.7.2.1 Laminated silts (Prodelta facies) 287 5.7.2.2 Thickening-upward wavy-flaser sands (Proximal delta front) 287 5.7.2.3 Grey, bioturbated silts (Distal prodelta/ lower shoreface) 287 5.7.2.4 Swaley cross-stratified sands (Wave modified delta/ middle to upper shoreface) 288 5.7.2.5 Trough cross-stratified sands (Coastal Plain distributary channels)... 288 5.7.2.6 Amalgamated sigmoidal cross-stratified sands (Estuarine/ marine incursion) 289 5.7.2.7 Laterally accreted sands (Sub and intertidal channels/ tidal flats) 289 5.7.3 Summary and ichnofacies interpretation for the Morne L'Enfer Formation 290
5.8 DISCUSSION 291 5.8.1 Ichnofacies interpretations 293
5.8.2 ICHNOFACIES AND DEPOSITIONAL MODELS 298 CHAPTER 6 - PROVENANCE OF CRETACEOUS TO PLIOCENE SANDSTONES 300
6.1 PART 1 -DESCRIPTIVE PETROGRAPHY OF CENOZOIC SANDSTONES 300 6.1.1 Introduction 300 6.1.2 Rationale for classification scheme 301
x 6.1.3 Modal detrital framework and provenance relationships 305 6.1.4 Heavy mineral composition and provenance relationships 308 6.1.5 Modern approach to heavy mineral analysis 311 6.1.6 Sample collection and preparation 313 6.1.7 Heavy mineral separates 314 6.1.8 Sampling constraints 316 6.1.9 Previous petrographic and heavy mineral studies in the Southeastern Caribbean 317 6.1.10 Chaudiere Formation 321 6.1.10.1 Petrographic description 322 6.1.11 Pointe-a-Pierre Formation 325 6.1.11.1 Petrographic description 329 6.1.12 San Fernando Formation 330 6.1.12.1 Petrographic descriptions 331 6.1.13 Angostura Sandstone (Cipero Group) 336 6.1.13.1 Petrographic description 339 6.1.14 Nariva Formation 342 6.1.14.1 Petrographic description 342 6.1.15 Plum Mitan outcrop (Cipero Formation) 343 6.1.15.1 Petrographic description 346 6.1.16 Herrera Sandstone Member (Cipero Formation) 348 6.1.16.1 Petrographic description 348 6.1.17 Late Miocene - Early Pliocene Sandstones (Cruse and Manzanilla Formations) 351 6.1.17.1 Cruse Formation 351 6.1.17.2 Manzanilla Formation 352 6.1.18 Late Pliocene Sandstones (Morne L'Enfer, Springvale and Moruga Formations) 355 6.1.18.1 Petrographic description 357 6.1.19 Summary of petrographic properties of Cenozoic sandstones 360 6.1.19.1 Changes in compositional maturity 360 6.1.19.2 Changes in textural maturity 361 6.1.19.3 Diagenesis 363
XI 6.1.19.4 Rock fragments 364 6.1.19.5 Quartz inclusions, silica overgrowths and extinction patterns 365 6.1.20 Heavy Mineral Analysis 369 6.1.21 Scotland Formation Heavy Minerals (Barbados) 372 6.1.22 Summary of descriptive petrography 373 6.2 PART 2 - PROVENANCE OF CENOZOIC SANDSTONES 373 6.2.1 Introduction 373 6.2.1.1 Dissolution effects on feldspar 374 6.2.1.2 Dissolution effects on heavy minerals 375 6.2.2 Potential sediment sources 380 6.2.2.1 The Guyana Shield 380 6.2.2.2 Late Cretaceous to Early Cenozoic sediment sources 383 6.2.2.3 Cenozoic uplifts 384 6.2.2.4 Igneous sources 385 6.2.2.5 Other potential sediment sources 387 6.2.3 Distinguishing between potential sources 390 6.2.4 Sediment Provenance Interpretations (Trinidad Basins) 394 6.2.4.1 Cretaceous 397 6.2.4.2 Paleocene-Eocene 398 6.2.4.3 Late Eocene through Middle Oligocene 402 6.2.4.4 Late Oligocene to Early Miocene 405 6.2.4.5 Early to Middle Miocene 406 6.2.4.6 Pliocene 407 6.2.5 Sediment Provenance Interpretations (Scotland Formation) 409 6.2.6 Summary of Sediment Provenance 410 CHAPTER 7 - CONCLUSIONS 414 7.1 CHANGING SANDSTONE ATTRIBUTES THROUGHOUT THE CENOZOIC 415 7.1.1 Sandstones of the Chaudiere and Pointe-a-Pierre formations 415 7.1.2 Sandstones of the SanFernando Formation 418 7.1.3 Sandstones of the Angostura Sandstone Member (Cipero Formation) 419 7.1.4 Sandstones of the Nariva Formation 421 7.1.5 Sandstones of the Herrera Sandstone Member 422 7.1.6 Sandstones of the Cruse and Manzanilla Formations 424
xii 7.1.7 Sands of the Mome L'Enfer Formation 425 7.2 LATE CRETACEOUS TO PLIOCENE BASIN EVOLUTION 426 7.3 IMPLICATIONS FOR THE STRATIGRAPHIC TABLE 434 7.3.1 Soldado and Boca de Serpiente formations 435 7.3.2 Conglomerate Members 436 7.3.3 Recommended Changes to the Stratigraphic Column 437 7.4 DISCUSSION 438 REFERENCES 444 APPENDIX 1 POINTE-A-PIERRE FORMATION SECTIONS AT MT. HARRIS 484 APPENDIX 2 CHAUDIERE RIVER TRAVERSE, MT. HARRIS 485 APPENDIX 3 SAN FERNANDO FORMATION LITHOLOGY 487 APPENDIX 4 REEFAL AND SHALLOW-WATER FOSSILS IN THE SAN FERNANDO FORMATION 490 APPENDIX 5 OLIGOCENE GUAICO CONGLOMERATES AT FOUR ROADS, TAMANA 492 APPENDIX 6 FACIES OF THE EOCENE-OLIGOCENE CHALKY MOUNT MEMBER OF THE SCOTLAND FORMATION, BARBADOS 493 APPENDIX 7 NANNOFOSSIL ANALYSIS 496 APPENDIX 8 POINT COUNT CATEGORIES 504 APPENDIX 9 GRAIN SIZE DISTRIBUTION BY RELATIVE WEIGHT PERCENT 505 APPENDIX 10 SOME RESULTS OF HEAVY MINERAL STUDIES IN TRINIDAD AND BARBADOS 506 APPENDIX 11 DETAILS OF PETROGRAPHIC STUDIES ON INDIVIDUAL SAMPLES 507 APPENDIX 12 ALL COUNTS ON SAMPLES 511 APPENDIX 13 HEAVY MINERAL COUNTS 514 APPENDIX 14 SAMPLE OUTCROP DESCRIPTIONS 515
xiii List of Figures
Figure 1.1 Location of the study area 6
Figure 1.2 One of the earliest cross-sections from north to south Trinidad 14
Figure 1.3 Location of outcrop and seismic dataset 24
Figure 1.4 Schematic illustration of transport mechanisms within fluid flows 29
Figure 1.5 Sediment entrainment and stability of sedimentary structures in quartzose sand 32
Figure 1.6 Sedimentary structures, flow types and major sediment support mechanisms involved in sediment gravity flows 36
Figure 1.7 Facies stacking patterns for deep-marine clastic systems 43
Figure 1.8 Updip to downdip cross section showing facies transitions for a
lowstand slope depositional system (Gulf of Mexico) 44
Figure 2.1 Geological map across the Central Range 53
Figure 2.2 Some characteristics of amalgamated pebbly sandstone facies 56
Figure 2.3 Graphic sedimentary logs of amalgamated pebbly sandstone facies of the Chaudiere formation 58 Figure 2.4 Graphic sedimentary logs showing facies and interpretations for sandstones within the Pointe-a-Pierre Formation 61 Figure 2.5 Facies characteristics of the Pointe-a-Pierre Formation at San Fabien Road 62
Figure 2.6 Tabular sandstone and lenticular sandstone facies of the Pointe-a- Pierre Formation 63
Figure 2.7 Strike and dip stratigraphic cross-sections from the San Fabien Road location 66
Figure 2.8 Graphic sedimentary logs illustrating lenticular and massive thick- bedded sandstone facies of the Pointe-a-Pierre formation with interpretations 67
Figure 2.9 Proposed facies succession for the Chaudiere and Pointe-a-Pierre formations 70
xiv Figure 2.10 Palaeocurrent measurements within Pierre Point Sandstone Member 72 Figure 2.11 Summary of sedimentary structures and interpreted bed divisions in the Chaudiere and Pointe-a-Pierre formations 73 Figure 2.12 Photos and line drawings of a variably cross-stratified interval and their suggested classification 75 Figure 2.13 Schematic illustrations of the most detailed lithological descriptions of the San Fernando Formation from published literature 80 Figure 2.14 Summary of stratigraphic contacts described at the top and base of the San Fernando Formation by various workers 82
Figure 2.15 Reinterpretation of Soldado Rock as a slope canyon fill complex 90
Figure 2.16 Sandstones of the San Fernando Formation at Soldado Rock 92 Figure 2.17 Contorted limestone and conglomerate of beds "10" and "11" on Soldado Rock 93 Figure 2.18 Oligocene to Middle Miocene rocks across the Central Range and Southern Basin of Trinidad 100 Figure 2.19 NW-SE seismic section in the eastern offshore area showing the subsurface distribution of the Angostura Sandstone 104 Figure 2.20 Representative graphic logs for Angostura Sandstone lithofacies from well Kairi-1 106 Figure 2.21 Facies fromth e Angostura sandstone in well Kairi-1 107 Figure 2.22 Facies fromth e Angostura sandstone in well Kairi-1 108
Figure 2.23 Conglomeratic and organic facies of the Angostura Sandstone 114 Figure 2.24 Gamma ray log calibrated with facies for the Angostura Sandstone derived from the cored interval in well Kairi-1 118 Figure 2.25 Representative interpreted seismic section showing NW-SE shortening and piggy-back stacking of thrust sheets in the Brighton Marine oilfield, southeast Gulf of Paria 123
Figure 2.26 Facies and facies interpretation of the Nariva Formation from Sandstone Trace 124 Figure 2.27 Facies of the Nariva Formation from Corbeaux Hill and Esmeralda Junction 125
xv Figure 2.28 Sandstone facies of the Nariva Formation 126
Figure 2.29 Organic-rich sandstones of the Nariva Formation 129
Figure 2.30 Facies of the Nariva Formation from subsurface core in well ABM- 44 133 Figure 2.31 Proposed facies succession through the Nariva Formation based on well ABM-91 from the Brighton Marine oilfield 135
Figure 2.32 Symmetrical rippled sandstone lithofacies of Middle Cipero Formation at Plum Mitan 139
Figure 2.33 Lithofacies of the Herrera Sandstone Member, Cipero Formation 143
Figure 2.34 Lithofacies of the Herrera Sandstone Member of the Cipero
Formation from subsurface core in well BP-347 144
Figure 2.35 Lithofacies succession in the Herrera Sandstone Member 147
Figure 3.1 Bathymetric divisions of the marine environment 155
Figure 3.2 Relative location, geometry, facies and stratigraphic profile of depositional elements common to deep-water systems 160 Figure 3.3 Schematic illustrating idealized slope channel-fill succession which is compared to the Chaudiere/ Pointe-a-Pierre and Nariva Formation successions 162 Figure 3.4 Schematic illustration depicting various depositional environments for Cenozoic sandstones of Trinidad 169
Figure 3.5 Schematic illustration to explain the coarsening-thickening upward stacking pattern of the Herrera Sandstone 181
Figure 4.1 Geological map showing Late Miocene to Pleistocene sediments across the Southern and Northern basins of Trinidad 187
Figure 4.2 Facies of the Cruse Formation exposed west of Morne Diablo fishing depot 190
Figure 4.3 Deformed slope canyon fill facies west of Morne Diablo fishing depot 191
Figure 4.4 Cruse Formation slope and (outer) shelf sediments 196
Figure 4.5 Geologic map of southwest Trinidad showing distribution of the Morne L'Enfer Formation and the locations of logged exposures for this study 199
xvi Figure 4.6. Representative graphic logs of lithofacies within the Mome L'Enfer Formation 204
Figure 4.7 Prodelta, shoreface and fluvial facies in the Morne L'Enfer Formation 206
Figure 4.8 Representative graphic logs of lithofacies within the Morne L'Enfer
Formation 210
Figure 4.9 Tidal and fluvial-estuarine facies in the Morne L'Enfer Formation 211
Figure 4.10 Lithofacies of the Morne L'Enfer Formation 214
Figure 4.11 Amalgamated sigmoidal cross-stratified facies 217
Figure 4.12 Palaeocurrent orientions and isopach map throughout the Morne L'Enfer Formation 223 Figure 4.13 Facies succession and depositional environments of the lower Morne L'Enfer correlated to subsurface gamma log signature with the aid of an outcrop gamma 225 Figure 4.14 Main sedimentary processes, thickness and sequence stratigraphy of the Morne L'Enfer Formation 228
Figure 5.1 Contrasting scales of observation and classification employed by ichnologists and sedimentologists linked by an ethological framework 232
Figure 5.2 The initial sequence of marine ichnofacies proposed by Adolf Seilacher 233
Figure 5.3 Schematic diagram illustrating bioturbation intensity for different substrates 243
Figure 5.4 Deposit-feeding and farming traces within the Pierre Point Sandstone Member 247
Figure 5.5 Feeding and dwelling trace fossils of the Pierre Point Sandstone Member, San Fabien Road locality 248
Figure 5.6 Dwelling and deposit-feeding trace fossils within the Pierre Point Sandstone Member 249
Figure 5.7 Deposit-feeding trace fossils of the Pierre Point Sandstone Member, San Fabien Road locality 253
Figure 5.8 Stratigraphic log from a section of the Pierre Point Sandstone Member at San Fabien Road showing the location of trace fossils 257
Figure 5.9 Trace fossils of the Angostura Sandstone from well Kairi-1 259
xvii Figure 5.10 Trace fossils within the Herrera sandstone from BP-347 core 266
Figure 5.11 Trace fossils in Cipero Formation shales at Tarouba 267
Figure 5.12 Trace fossils within the BP347 core 270
Figure 5.13 Outcrop examples of Psilonichnus upsilon and schematic interpretation of the burrow 282 Figure 5.14 Trace fossil summary chart for seven lithofacies in the Morne L'Enfer Formation 294
Figure 5.15 Composite stratigraphic section from Cedros Bay and Fullarton within the Lower Morne L'Enfer Sandstone Member 295
Figure 6.1 The sandstone classification scheme of Pettijohn et al., (1972) 303
Figure 6.2 Provenance domains discerned from modal detrital framework
analysis of sandstones 306
Figure 6.3 Classification of Trinidad sandstones 323
Figure 6.4 Ternary classification diagrams of individual Mesozoic and Cenozoic sandstones by formation, member or unit 324 Figure 6.5 Photomicrographs showing features of quartz arenites of the Chaudiere Formation 326
Figure 6.6 Quartz arenites of the Pointe-a-Pierre Formation 327
Figure 6.7 Photomicrographs of marls, sandstones and conglomerates of the San
Fernando Formation 334
Figure 6.8 Photomicrographs of sandstones from the San Fernando Formation 337
Figure 6.9 Calcareous arenites and sublitharenites of the Angostura Sandstone 340
Figure 6.10 Photomicrographs of Nariva Formation sublitharenites 344
Figure 6.11 Photomicrographs of sublitharenties of the Cipero Formation (citrus estate, Plum Mitan) 347 Figure 6.12 Photomicrographs of Herrera Sandstone Member sublitharenites and lithic arenites 349 Figure 6.13 Photomicrographs of calcareous sublitharenites in the Cruse Formation 353
xviii Figure 6.14 Representative photomicrographs of a lithic wacke from the Manzanilla Formation 356
Figure 6.15 Photomicrographs of sublitharenites of the Springvale, Morne L'Enfer and Moruga formations 358
Figure 6.16 Changes in textural maturity based on clay matrix content for successively younger Cenozoic sandstones 362
Figure 6.17 Increasing lithic fragments throughout Cenozoic strata 366
Figure 6.18 Detrital lithic fraction of Cenozoic and Mesozoic sandstones 367
Figure 6.19 Composite bar chart showing actual counts of translucent heavy minerals and their relative contribution to the total fraction 370 Figure 6.20 Yield quantity and composition of heavy minerals from Cenozoic sandstones in Trinidad and Barbados 377
Figure 6.21 Northern South America showing provinces of the Guyana Shield and the extension of the Caribbean Mountain belt to Trinidad 381
Figure 6.22 Compilation of modal framework and heavy mineral percentages from modern sands and ancient sandstones in north-eastern South America 388
Figure 6.23 Ternary plot of the relative abundance of minerals ascribed to the "Transport-limited", "High-grade metamorphic" and "Caribbean Mountains" provenance groups in individual samples from Trinidad and Barbados 396
Figure 6.24 Provenance of selected Trinidad sandstones from QmFLt Dickinson plots 399
Figure 6.25 Relative proportion of low grade (LGM) versus high-grade (HGM) metamorphic-derived heavy minerals within Cenozoic samples from Trinidad and Barbados 403
Figure 7.1 Summation of lithofacies associations, depositional environments, sandstone mineral characteristics and trace fossil assemblages described throughout the thesis 416
Figure 7.2 Schematic illustration depicting the changing sediment sources and basin settings during the Paleocene to Middle Miocene 428
Figure 7.3 Palaeogeographic reconstruction for Cenozoic sediments 430
Figure 7.4 Recommended modifications to the Trinidad Paleogene stratigraphy based on the nature of sedimentary contacts 439
xix List of Tables
Table 1.1 Trinidad stratigraphic column 10
Table 1.2 Listing of references cited in Table 1.1 B 12
Table 1.3 Summary of measured sections derived from outcrop and subsurface
cores for Cenozoic formations 23
Table 1.4 Some of the more common geophysical flows 29
Table 1.5 Bedform terminology and sedimentary structures that are mentioned in this thesis and an interpretation as to their genesis 34 Table 2.1 Collective facies and depositional processes for Cenozoic sandstones discussed in the text 151
Table 3.1 Palaeoenvironmental interpretations from benthic foraminifera 156
Table 3.2 Summary of facies characteristics and interpreted sedimentary processes for Paleocene to Early Miocene sandstones 157 Table 3.3 Facies associations and interpreted depositional environments for Paleocene to Early Miocene Formations 158
Table 3.4 Facies and facies association of Mutti and Ricci Lucchi (1978) for deep-water systems based on turbidite systems from the Northern Appenines 167
Table 4.1 Members of the Late Pliocene Morne L'Enfer Formation and interpreted depositional environments of various workers 200
Table 4.2 Summary of lithofacies, processes and sand dimensions of Pliocene sediments 222
Table 5.1 Characteristic diversity, intensity and interpreted ethology of trace fossils in popular marine ichnofacies 239
Table 5.2 Stratigraphic sections studied for biogenic sedimentary structures and discussed in this chapter 242
Table 5.3 Summary of trace fossils found throughout the CenozoicTertiary stratigraphy of Trinidad 296
Table 6.1 Idealized sedimentary cycle showing different mechanisms that can alter the ratio of mineral species from the parent rock to the daughter sediments 310
xx Table 6.2 Relative stability of non-opaque heavy minerals in weathering profiles 312 Table 6.3 Abbreviations commonly used in this chapter 325 Table 6.4 Metamorphic facies and mineral assemblages of representative terrains in the Caribbean Mountains of northern Venezuela and Trinidad 386
xxi Abstract
Cenozoic sediments in Trinidad record elements of pre- and syn-orogenic siliclastic deposition related to the deformation of a formerly passive, northern South American margin. Prior interpretations regarding the timing of pre- to syn-orogenic sedimentation suggest Late Cretaceous to Early Miocene changes based primarily on lithology and biostratigraphy. These interpretations vary from "rapid" changes in sea level during the Paleocene to Late Oligocene caused by tectonic uplift, to continuous passive margin sedimentation into the Late Oligocene, influenced by eustatic sea level fluctuations. The Paleogene was characterized by relatively uniform sedimentary processes and depositional environments, which continued from the Cretaceous and were associated with the delivery of coarse-grained, mature quartz arenites into deep-water basins along a passive margin. Sediments were sourced mainly from the stable South American craton to the south. Changing sedimentological characteristics suggest the incipient input of syn- orogenic sediments into the basin as early as the Eocene, although the onset of active syn- orogenic sedimentation occurred from Late Oligocene to Early Miocene coincident with deposition of the Nariva Formation and Herrera Sandstone Member. By the Pliocene, lithic arenites were derived from the uplifted Caribbean Mountains to the west and possibly the north and deposited in shallow-water and terrestrial environments. These changes in sediment dispersal patterns in the Trinidad basins were consistent with changes across northern South America related to the uplift of the northern Andean mountains, including the Caribbean Mountains. Formal stratigraphic units may be better represented when their associated depositional environments are considered. Enigmatic stratigraphic correlations are readily resolved as recurrent depositional events, not deserving of formal stratigraphic distinction. Recommendations are made for formal changes to Paleogene formations on the stratigraphic table of Trinidad.
xxii Acknowledgements
This document is the culmination of four years of fieldwork and research effort that was supported by persons and institutions who gave willingly of their time and finances. To my supervisor, Dr. Grant Wach, a sincere appreciation for the invaluable guidance and feedback provided, and for the many hours spent in the field collecting samples and laying the groundwork for this material. To the other members of my supervisory committee, Drs. Marcos Zentilli and Martin Gibling, thank you for your guidance and discussion on the issues that arose with this body of work. I also thank Dr. Yawooz Kettanah for his open-door policy and interminable assistance on aspects of mineralogy. My appreciation to the following organizations and companies that provided financial assistance and technical information: American Association of Petroleum Geologists; Geological Society of America; BHP Billiton, for providing access to necessary reports and cores; Petrotrin for accommodating sample request and access to their core house; and the Ministry of Energy and Energy Industries, Trinidad, for granting both time and data to pursue this study. I thank Dr. John Frampton, Barry Carr-Brown and Curtis Archie for their advice on outcrop locations and palaeontology. I am also grateful to Kirwin "wasp-sting" Ganga and Adrian "see-snake" Gibbs who provided invaluable assistance in the field. I am indebted to John Keens-Dumas of Petrotrin for reviewing segments of this work as it developed. I also thank Lorcan Kennan and Jim Pindell for their comments and intriguing questions. To Dr. Alexander Grist, Debra Wheeler, Chloe Younger and Gordon Brown and Sara Mason of the Department of Earth Sciences, thank you for your assistance beyond the call of duty. I also thank Drs. Mike Kaminski, Jason Crux and Gunilla Gard for providing palaeontological interpretations. I thank the Wach family and graduate colleagues for welcoming me into their homes and providing discussions outside of the geological realm. To the family that I left in Trinidad, I acknowledge your patience and support. Finally, I am eternally grateful to
xxiii my wife Wendy, without whom, none of this would have occurred. I thank her for her encouragement, patience and manuscript edits throughout the past four years.
xxiv Chapter 1 - Introduction
1.1 OVERVIEW
Trinidad's location in the southeastern Caribbean is unique in terms of Caribbean and South American tectonics, marking the eastern extreme end of exposed deformation along the northern South American continental margin. South of the island along the Guyana coast, lies a relatively undeformed passive margin, while to the west in Venezuela, there are highlands and basins attributed to the Caribbean Plate deformation. Different hypotheses for the timing of deformation of the Plate have been proposed. The island itself has a complex structural history, reflected in the stratigraphic correlations. Coarse clastic units have always been explored for their value as hydrocarbon reservoirs, but have received less study relative to more expansive shale-prone horizons, studied extensively for their biostratigraphic value. This is especially true for Paleogene to Middle Miocene sandstones as they are the least exposed and most structurally faulted on the island. This thesis studies these coarse clastic intervals for changes in composition, physical and biogenic sedimentary structures, and stacking patterns, to determine changes in basin setting and the history of deformation along the margin. This thesis attempts to resolve the onset of syn-tectonic sedimentation associated with deformation of the northern South American continental margin in the vicinity of Trinidad. This involves a review of changes in sandstone characteristics throughout the Cenozoic and inferences on the nature of deposition. A spectrum of environments is described ranging from deep-marine basin floor fans, slope and shelf deposits, with the final record of basin fill represented by nearshore environments during the Pliocene. It will be shown that these changing environments record specific phases of passive to active margin settings in the Trinidad basins throughout the Cenozoic stratigraphy.
1 1.1.1 NATURE OF RESEARCH
This thesis was developed to investigate the Cenozoic sandstones of Trinidad using an integrated sedimentological approach. The research involved extensive fieldwork within "unfriendly" forests and along coastal transects, from which sedimentological descriptions of physical and biogenic sedimentary structures, sandstone geometries and stacking patterns and rock samples provided the foundation for further analyses and interpretation. The descriptions and interpretations throughout this thesis required knowledge of sedimentary and biogenic structures, the ability to recognise significant stratal boundaries and geometries and the components of depositional systems, interpret sedimentary processes and the description, quantification and interpretation of provenance relationships from sandstone mineralogy. The rationale and basis for this approach are discussed in subsequent sections and chapters.
1.1.2 ORGANIZATION OF THESIS
This thesis is arranged in seven chapters each of which presents some aspect related to the thesis objectives. The chapters are arranged in order of the scale of observations, moving from the larger, outcrop-scale and bedding relationships, to microscopic examination of sandstones. Each chapter describes the concepts, methodologies and past research relevant to its content. Chapter 1 outlines the objectives of the thesis and the rationale behind the methods chosen to meet these objectives. An introduction to the regional geology and stratigraphic table used throughout this thesis is provided, along with a synopsis of the historical development of the Trinidad stratigraphy. An outline of sedimentological principles and processes, including sediment gravity flows and their products, ichnology and the facies approach to sedimentary rock analysis is provided, as these themes are recurrent throughout this thesis. The emphasis in Chapter 2 is on the description and interpretation of physical sedimentary structures, sand-body characteristics, stacking patterns and bedding relationships among Paleocene to Early Miocene sandstones. These features provide the
2 basis for the interpretation of sedimentary processes, which are also interpreted throughout the Chapter. A stratigraphic review of individual formations and/or sandstone units is provided prior to each description, which sets the context for the descriptions that follow. Descriptions are grouped in terms of common facies, and facies successions are proposed based on field relationships or correlations to subsurface petrophysical logs. The Chapter emphasizes the sedimentary processes that characterize different sandstone units and provides the basis for interpretations presented in Chapter 3. Chapter 3 groups the facies and facies successions described in Chapter 2 into facies associations based on similarities or interbedding relationships between individual facies. Facies associations formed the basis for recognizing particular depositional elements and the interpretation of sedimentary environments. Chapter 4 reviews facies and depositional processes of Late Miocene to Pliocene sediments. Facies associations are proposed and interpretations of depositional environments are presented. Collectively, Chapters 2-4 outline the changing depositional settings throughout the Trinidad Cenozoic interval. Chapter 5 describes the trace fossil assemblages throughout the Cenozoic strata, and proposes ichnofacies based on these assemblages. Comparisons are made between individual ichnofacies, the significance of changing ichnofacies is reviewed, and implications for palaeoenvironemental analysis are discussed. Comparisons are also made with palaeoenvironmental interpretations suggested from the facies associations outlined in Chapters 2-4. Chapter 6 describes the petrology of the individual sandstones and interprets provenance relationships. The chapter is divided into two parts. Part 1 provides the rationale behind the sandstone classification used throughout the thesis, as well as a discussion on the modern use of sandstone petrology in provenance determination. The rationale behind modal detrital framework and heavy mineral analysis is given together with limitations of these methods. Part 1 of the chapter also describes and quantifies the modal mineralogy of each sandstone unit investigated, including framework detrital grains, accessory minerals and heavy mineral attributes. The changing petrological characteristics among the different sandstones through time, in terms of compositional and textural maturity, diagenesis and changing lithic proportionsis then provided. These
3 descriptions formed the basis for the interpretations presented in Part 2, with the main emphasis being sandstone provenance. Potential provenance domains around the northern margin of the South American continent are reviewed and interpretations proposed based on actualistic sandstone models. Chapter 7 integrates the results of the foregoing chapters, and interprets the changing basin-scale geometries based on changing facies associations, ichnofacies and sandstone composition. The evolution of the margin is presented in a series of schematic cross sections and palaeogeographic reconstructions illustrating the tectonic controls on sediment dispersal through the Late Cretaceous and Cenozoic. In closing, implications for the stratigraphy of Trinidad are presented, and recommendations are made for future research.
1.2 RESEARCH OBJECTIVES
There are two primary objectives of this research: (1) To review the onset of active margin deformation and its effect on sediment dispersal patterns along the eastern sector of the northern margin of South America, in the region of Trinidad. This objective attempts to resolve whether a north-facing passive margin persisted in the Trinidad region throughout the Paleogene, and the effect on Cenozoic sedimentation patterns. An alternative hypothesis is that active margin tectonics and syn-orogenic sedimentation occurred since the Late Cretaceous. (2) To demonstrate that sedimentological analysis can provide resolution of some of the ambiguities associated with the Trinidad stratigraphic table, particularly among Early Cenozoic strata. The alternative is that stratigraphic relationships are sufficiently understood using primarily biostratigraphic data, and the evaluation of the coarser clastic content cannot provide any further stratigraphic resolution.
These objectives were based firstly on the premise that the timing of active deformation along the northern margin of South America is not resolved, and secondly, process-based, sedimentological studies have not been sufficiently employed to the
4 understanding of sedimentary relationships in Trinidad. The rationale for these is highlighted in the following discussions.
1.3 REGIONAL SETTING
1.3.1 LOCATION
Trinidad is located at the eastern edge of the northern margin of South America to the northeast of Venezuela (Figure 1.1 A). It is bounded to the southeast by the Eastern Venezuelan Basin. To the north and east lie the Caribbean Sea and Atlantic Ocean respectively, and the island of Tobago is immediately to the northeast. Trinidad lies at the southeastern corner of the Caribbean Plate although this island may also comprise portions of the South American plate towards the south (Weber et al., 2001a). The Lesser Antilles island arc system, Grenada back-arc basin, Tobago Trough and the Barbados accretionary prism, are all associated with Caribbean-Atlantic plate subduction, north of Trinidad. Numerous geologic and geomorphic elements are continuous between Trinidad and eastern Venezuela, although these are now separated by the Gulf of Paria (Salvador and Stainforth, 1968). The most prominent of these features are the Araya-Paria Peninsula and Northern Range mountain belt (Caribbean Mountains) that extends across the north of Venezuela and Trinidad. The area chosen for study lies south of the Northern Range mountain belt, and incorporates sediments from the Northern and Southern basins, Central Range and offshore extensions of these basins (Figure LIB). A brief review of geomorphic subdivisions in Trinidad will help to further define the study area.
The Northern Range
The Northern Range is an east-west trending belt of sedimentary and meta- sedimentary rocks that is an extension of the Caribbean Mountains continuous from
5 B
NORTHERN RANGE / • &£s&^-~^
\ NORTHERN BASIN ,•'* \ - GULF OF PARIA ( •/""^ I ""**'j/lK^^ | ^^S" SOUTHERN BASIN ^^^ A SoMado __*—' o C s* 0 4 "^Q Figure 1.1 Location of the study area. A) Relative location of Trinidad to northern South America and geological features of northeastern South America and southern Lesser Antilles (shaded area in inset indicates a passive continental margin). B) Geological provinces of Trinidad. Outcrop examples from this study are from the Northern Basin, Central Range, Southern Basin, Soldado Rock and other offshore areas (denoted by shaded squares; dots represent well locations used in this research). BAR: Barbados accretionary prism, LA: Lesser Antilles island arc. Map compiled fromsevera l sources. 6 northern Venezuela. The oldest exposed rocks in Trinidad lie within the Northern Range mountain belt (Late Jurassic Maraval Formation). Fission track and Ar°/Ar° ages date the uplift of the range to at least Miocene (Speed et al., 1993; Weber et al., 2001b). The degree of metamorphism decreases across the range from greenschist facies to prehnite pumpellyite to the east (Frey et al., 1988; Weber et al., 2001b). Gulf of Paria / Northern Basin The Gulf of Paria and Northern Basins represent the offshore-onshore continuation respectively, a transtensional basin attributed to Late Neogene structural deformation (Babb and Mann, 1999; Kennan and Pindell, 2007). Late Miocene and younger rocks rest on Lower Cretaceous basement across the basin. Central Range The Central Range is a northeast-southwest trending topographic feature of low hills that lie across the central portion of the island. The range is a Recent pop-up structure that was associated with Recent strike slip motion across the Warm- Springs/Central Range fault system (Babb and Mann, 1999; Weber et al., 2001a). The oldest rocks known south of the Northern Range are exposured in the Central Range (Lower Cretaceous Cuche Formation). Southern Basin The Southern Basin encompasses the entire island south of the Central Range and comprises mainly Oligocene and younger clays, marls and sands. These sands serve as the reservoirs for most of Trinidad's hydrocarbon reserves and have been actively exploited in the past 7 1.3.2 STRATIGRAPHY 1.3.2.1 STRATIGRAPHIC COLUMN The stratigraphic column of Saunders et al. (1998) will be followed throughout this thesis (Table 1.1 A). The column represents a modified version of Kugler (1959) and Saunders and Bolli (1985), and allows correlations to be made with outcrops and established biostratigraphic zonations. The time-scale has been updated to reflect the radiometrically-calibrated ages of Gradstein et al. (2004). This was done by a correlation of the schemes of Berggren et al. (1985) to the scheme of Saunders and Bolli, (1985) and Saunders et al. (1998). The calcareous nannofossil scheme of Martini (1971) is common to all schemes and provided the needed baseline for correlations. 1.3.2.2 OVERVIEW OF FORMATIONS Mesozoic stratigraphy Outcrops on the island of Trinidad range from the Upper Jurassic to recent (Carr- Brown and Frampton, 1979). The date of the oldest rock unit is based on Tithonian ammonites found at the base of the Maracas Formation within the Northern Range). The oldest sediments in the Trinidad subsurface are the Couva Evaporites, which likely record the initial separation of North and South American plates during the Early Jurassic (Algar, 1993; Burke et al., 1984; Pindell, 1994; Babb and Mann, 1999). Onshore, Mesozoic rocks crop out among the prominent highs of the Northern and Central ranges. Apart from the Sans Souci volcanics, Mesozoic sediments consist predominantly of pelagic shales, sandstones, limestones, argillite and metamorphosed sedimentary rocks1. These sediments were deposited largely within a passive continental margin following the opening of the Atlantic Ocean. The transition into the Cenozoic may be locally unconformable (Algar, 1993; Algar and Pindell, 1990b; Kugler, 2001). 1 This suite only describes onshore basins of Trinidad. 8 Paleocene to Middle Miocene stratigraphy The following provides a general outline of the pre-Middle Miocene stratigraphy. This is discussed in greater detail when each formation is reviewed in Chapter 2. The stratigraphy for this interval was determined by micropaleontology in fine-grained sediments. Paleogene sandstone intervals are typically less constrained, and lateral correlation with coeval shales was usually based on outcrop observations. The Paleocene-Eocene stratigraphy of Trinidad comprises coarse-grained elastics and limestone within the Chaudiere, Pointe-a-Pierre and San Fernando formations. The coarse elastics crop out along the northern Central Range (Figure LIB) and bioclastic sandstones and limestones in several other locations towards the south. They were contemporaneous with "deep-water" shales that crop out mostly towards the south and unconformably overlie sediments ranging from Upper Cretaceous "deep-water" shales to Lower Cretaceous neritic sediments of the Cuche Formation (Bolli, 1957a; Kugler, 1959, Tyson and AH, 1991). Eocene sediments are overlain by Oligo-Miocene conglomerates and deep-water elastics of the Cipero Formation (Table 1.1, Stainforth, 1948; Bolli, 1957b; Kugler, 1959; Suter, 1960). Eocene bioclastic sandstones and limestones occur as olistoliths (Kugler, 1953; Kugler and Caudri, 1975; Kugler, 2001) or in faulted contact (Liddle, 1946; Algar, 1993) with Oligo-Miocene shales. 1.3.2.3 HISTORICAL DEVELOPMENT OF THE TRINIDAD STRATIGRAPHIC TABLE Geological investigations in Trinidad can be traced to the 1860s with the writings of RJ.L. Guppy (Harris, 1921) who was employed by the colonial Government as an engineer and 'Inspector of Schools' (Waring, 1926) (Figure 1.2). The first official government survey was carried out during 1856-1858 and published in 1860 (Wall and Sawkins, 1860), which put forward the first stratigraphic column for the island. Since 9 Table 1.1 Trinidad stratigraphic column. A) The stratigraphy followed throughout this thesis is after Saunders et al., (1998) for all provinces except the Northern Range. B) Differences in the stratigraphic contacts and missing intervals from Saunders et al., (1998), as compiled from literature, subsurface well picks, and map data. The numbers refer to individual references that are listed in Table 1.2. Sandstone units described in the text are underlined. Table continues overleaf. Cdtoraws Planktonic foraminlfara namofossOs TRINIDAD STRATIGRAPHIC Time II EPOCHS | (Mw*nl 1971; zones (after Sauntlars and iGradsteln derived from Boi 1985; equaled to TABLE (Ma) SAUNDERS el al., 1998 et al 2004) zooaj Martini from Berggren 1985)i A B Hildas :ED?,:S FH tiwm n 1- PLESTOCEHG jGloborotalia L trucatullnoides 2- HI L SPRIMGVA1E FBI GlcborotaHa 1. ct, losaensis wiaippFOREST fBa ill I ——,/ 3- o u 4_ o MJIS.' Globorotalia imargarltaB —1 b NN13 5 - a. Neoglobotiuactrina dutertrol 6- IIANZAMIU FU CRUSE FH 7- 8- 1 9- Globorotalia acostartensls 10- HN9 IWSFJlf FH JLLa. NN7 £tobon>lalla1ahsi' rebusta 12- Globorotalia fahsl fohsi HI MNB „ z S lobora li (li I. 14_ M o PIN5 Praeorculina glomerosa — o 16- s NrU Gtobigerinatella insueta 18- " '• ...inf., E Globigerinila dssimilis 20- (Cat. tKsaimJs o/detQgren} IMN2 22- Globorotalia kugteri WH 24- Gtobigerina dperaensis NP2S clperoensis contfonwrates 26- L zUJ 1982, Bl«w — III 28- ApproxBmatt Itanil o NP21 al Ujrrtilb Globorolalia opirna opima canglamaraw*' (3o of Blow it al _i 30- (Dr. optoia oplnta) o Globlgerlna ampliap&rtura o^ fc & c •§. cJ & at a 2 •o T3 is 1s5 -Qs -2 ° 8 to •n CO CD efere n c Q: ir Q. 3 ct (11 CO a • <] 0) <\\ i DQ ''SF "iT 3~"*~ i Q i 1 1 i •e 1 E a 3 CO I 3 f kiborotaii a tr i a 1 11! in _j s 111 _J 2 UJ 9}B1 A|JBH 3003110 3N3003 3N30O3~IVd sno33v±3ao I I I I I I I I i 1 I ] I I I 1 i I I I I I I I I ] I I I I I 11 Table 1.2 Listing of references cited in Table 1.1 B. Arranged in numerical sequence Arranged in alphabetical sequence Reference AUTHOR Reference AUTHOR 0 Vincent, 2008, this study 1 Algar 1993 1 Algar 1993 2 Blow 1969 2 Blow 1969 30 Blow etal. 1968 3 Bolli 1957 3 Bolli 1957 4 Caudriin Kugler2001 26 Carr-Brown et al. 2002 5 Eamesetal. 1962, 1965 4 Caudriin Kugler2001 6 Kugler, 1996, Enclosure 10 27 Crux 2001 (Canteen 1) 7 Kugler, 1996, Enclosure 11 28 Crux 2003 (Kairi 1) 8 Kugler, 1996, Enclosure 12 5 Eamesetal. 1962, 1965 9 Harris in Waring 1926 6 Kugler, 1996, Enclosure 10 10 llling 1928 7 Kugler, 1996, Enclosure 11 11 Kugler (in Van Den Bold 1960) 8 Kugler, 1996, Enclosure 12 12 Kugler 1953 24 Kugler, 1996, Enclosure 8 13 Kugler 1956 35 Harper and Chambers, 2004 14 Kugler 2001 9 Harris in Waring 1926 15 Liddle 1946 10 llling 1928 16 Renz1942 11 Kugler (in Van Den Bold 1960) 17 Stainforth1948 12 Kugler 1953 18 Suter1960 13 Kugler 1956 19 Van den Bold 1960 21 Kugler 1959 20 Waring 1926 14 Kugler 2001 21 Kugler 1959 31 Kugler and Caudri 1975 22 Well data 32 Kugler and Saunders 1967 23 Saunders et al. 1998 15 Liddle 1946 24 Kugler, 1996, Enclosure 8 33 Punch 2004 25 Saunders and Bolli 1985 16 Renz1942 26 Carr-Brown et al. 2002 25 Saunders and Bolli 1985 27 Crux 2001 (Canteen 1) 23 Saunders et al. 1998 28 Crux 2003 (Kairi 1) 17 Stainforth 1948 29 Stainforth 1968 29 Stainforth 1968 30 Blow etal. 1968 18 Suter 1960 31 Kugler and Caudri 1975 19 Van den Bold 1960 32 Kugler and Saunders 1967 0 Vincent 2008, this study 33 Punch 2004 34 Wallis et al 2002 34 Wallis et al 2002 20 Waring 1926 35 Harper and Chambers, 2004 22 Well data Subsurface well references base Chaudiere Montserrat 1 base Chaudiere Calyx 1 base Chaudiere Marabella 1 (Algar) base Angostura Canteen 1 base Angostura Canteen 2 base Angostura Kairi 1 12 then, scores of geoscientists have contributed to the geological knowledge base. By 1935 alone, there already existed at least 156 publications on the geology and palaeontology of Trinidad (Vaughan and Cole, 1941). Key publications have been referenced in Waring (1926), Liddle (1946), and most recently in Kugler (2001). The scale of geological investigations ranged from government surveys to amateur field enthusiasts. Most of the surveys were sponsored by petroleum companies during exploration for oil in the early part of the 20th century (e.g. Waring, 1926; Ming's geological map of the San Femando-Naparima area; Ming, 1928). Waring (1926) acknowledged several early contributors to the Trinidadian geology, including other government geologists such as C. Craig, who published extensively on oil and coal resources on the island. The earliest constraints on the superposition of sediments were based on macrofossils, fossil flora and lithological correlations. Lithological correlations were hampered by the similarity of outcrops in the field. For example, the coarse elastics of the Chaudiere, Pointe-a-Pierre and Nariva formations appear similar in hand-specimen, and workers have noted the likelihood for mis-identification among these units (Algar, 1993; Kugler, 2001). Similarly, authors have also commented on the difficulties in differentiating the Late Eocene to Miocene shales of the San Fernando, Nariva and Cipero Formations (Ming, 1928; Bolli, 1957; Kugler, 2001). Lithological and faunal correlations have also been hampered by the complex structural and stratigraphic relationships combined with dense tropical vegetation, which obscures the exposures for most of the Paleogene stratigraphy. Stratigraphic relationships between outcrops are rarely observed directly, and other criteria must be employed on which to base correlations. Scores of workers contributed to the advancement of the stratigraphic table based on macrofossils (see references in Kugler, 2001), of which the extensive writings of R.L. Guppy (see Saunders and Bolli, 1985) and C. M. Bramine Caudri are prominent. However, outcrop correlations based entirely on macrofossils were subjected to the limitations described above. 13 HqS'JHa^qrcmvSection/ sTuwinythe- 0merd^Suc€MsU^^^^B4^in^Trinid€^ &6»*0W JEocen? Tttoten* &t*&mUtfrMUcen*> A' b % & 4 & w Figure 1.2 Reproduction of one of the earliest cross-sections from north to south Trinidad. The Northern Range is shown to the left of the section; "a" to "d" was referred to the "Caribbean Group"; "e" referred to as "compact limestone" and "f' to "h" were referred to as "secondary", "eocene" and "miocene" rocks (sic); "i" comprised the "post Pliocene series". From Guppy, 1877, Figure 3, referenced from Harris, 1921. Micropalaeontology eventually provided an excellent correlation mechanism for Trinidad sediments. Guppy (1873) was one of the first to recognize fossil foraminifera within Trinidadian sediments (Saunders and Bolli, 1985), and it was used in the mapping of the San Fernando area (Nuttal, in Illing, 1928). It was not until the 1940s that detailed study of planktonic foraminifera began in Trinidad as a stratigraphic tool for hydrocarbon exploration and Hans G. Kugler is often credited for this advancement (Bolli, 1957; Bolli, 1966; Stainforth et al., 1975; Saunders and Bolli, 1985). A chronological review of the development of the stratigraphic table from fossil fauna is provided by Saunders and Bolli (1985). The Cretaceous to Middle Miocene stratigraphy of Trinidad is currently based entirely on microfossil populations; post-Middle Miocene sediments (equates to the top of the Lengua Formation) contain too few planktonic foraminifera and index fossils to be useful, and detailed zonations of that interval must rely on alternative tools (e.g. Payne, 1991; Pocknall et al., 1999; de Verteuil and Johnson, 2003). Although numerous micropalaeontologists must be credited for the current knowledge of the Trinidad stratigraphy (see references in Kugler et al., 2001), a key contribution was made by Hans Bolli, a micropalaeontologist employed with Trinidad Leaseholds Limited between 1946- 19582 (later Texaco). Bolli's zonal subdivisions of the Lizard Springs, Navet and Cipero formations based on planktonic foraminifera (Bolli, 1957abc), gained worldwide acceptance and served as the standard for low latitude planktonic foraminifera zonations. Subdivisions based on planktonic foraminifera had a regional impact on stratigraphic correlations. They facilitated global correlations with Eastern Venezuela, Gulf Coast of the United States, Jamaica, Mexico, Mediterranean, Russia and Peru, for example (Bolli 1957abc; Blow, 1969). The wide-ranging spatial and temporal correlations afforded by planktonic foraminifera added to the credibility of Mesozoic and Cenozoic Trinidad stratigraphic correlations. These regional stratigraphic correlations led to the recognition of several fossil zones that are not recognized in Trinidad (eg. Globorotalia eugubina and Globorotalia psuedobulloides, Gr. Edgari, Globigerinoides ruber; PI,PI 8, P17 zones of Blow, 1969), and other potential stratigraphic gaps based on fossil appearances, extinctions and evolutionary trends (e.g. between the Lower and 2 (cushmanfoundation.org/awards/awardees/bolli.html, accessed 17 November 2007) 15 Upper Lizard Springs Formation). These gaps are interpreted as "hiatuses" by various workers (e.g. Saunders and Bolli, 1985; Blow, 1969; Saunders et al., 1998). 1.3.2.4 MODIFICATIONS TO BOLLI'S ORIGINAL SCHEME Modified versions of Bolli's micropalaeontological subdivisions are widely used today (Blow 1969; Bolli, 1966; Stainforth, 1975; Saunders and Bolli, 1985; Saunders et al, 1998), including the calibration of datum events to radiometric dates, (e.g. Berggren, 1969; Stainforth et al., 1975). Much discussion however, surrounds the detailed taxonomy of foraminifera species and their age ranges, and correlations have been actively debated within the biostratigraphic literature (Kugler, 2001 and references therein; e.g. Blow, 1969; Eames et al., 1962; Stainforth, 1968; Renz, 1942). These modifications have received varied acceptance. For example, the modifications of workers such as W.H. Blow and F.E. Eames (e.g. Eames et al., 1962; Blow, 1969) do not seem to be incorporated in the Trinidad stratigraphic table, although they published extensively on the Trinidad stratigraphy, and their biostratigraphic zones have been otherwise widely adopted (Harland et al., 1990; Berggren, 1969; Berggren et al., 1985) and calibrated to radiometric dates (e.g. Berggren et al., 1995; Gradstein et al., 2004). The history and reasoning for stratigraphic modifications, the differences between schemes, and their varied acceptance are beyond the scope of this study. 1.3.2.5 FACIES CONTROL ON PLANKTONIC FORAMINIFERA The absence of planktonic foraminifera biozones may not be associated with an unconformity. The spatial and temporal distribution of planktonic foraminifera is controlled by several parameters, which collectively affect the occurrence of species. These include oceanic currents, water temperature, salinity, turbidity, sea bottom substrate conditions and climatic variations. Collectively, these influence the distribution of zones independent of changes in sedimentation rate. The facies control on distribution is well documented from Tertiary outcrops in southern Russia, Syria (Bolli and 16 Krasheninnikov, 1977) and Trinidad (examples below), many of which are caused solely by changes in sediment type and are not associated with unconformities. Calcareous planktonic foraminifera distribution in Trinidad sediments appear to be strongly facies controlled. Several workers have commented on the relative distribution of planktonic foraminifera (Bolli, 1957; Renz, 1942; Blow, 1969; Stainforth, 1948). Foraminifera-rich zones occur within the calcareous shales of the Lizard Springs, Navet, Cipero and Lengua formations and are relatively absent in non-calcareous shales (e.g. Chaudiere, Nariva, Lower Cruse). The northerly transition from calcareous shales of the Cipero Formation into non-calcareous shales of the Nariva and Brasso formations, and a similar reduction in the planktonic foraminifera is well documented (e.g. Stainforth, 1948). Stainforth et al., (1975) suggested that the Cretaceous-Paleocene absence of Globorotalia eugubina and Globorotalia psuedobulloides biozones might be due to environmental stresses and not a stratigraphic unconformity. Similarly, Blow (1969, p. 224) noted the "strongly susceptible" nature of the marker species Globotalia kugleri to facies changes and as a result, the Globorotalia kugleri zone in the Cipero Formation is reduced relative to established global correlations. He suggested that local shallowing within this level of the Cipero Formation (Middle Cipero of Kugler 1959) as the cause for the variation. Similarly, according to Blow (1969), the range of the Globorotalia menardii zone as defined in Trinidad must be locally diachronous (as opposed to an "extinction" as defined by Bolli (1957b, p. 102), as the calcareous Lengua fauna is replaced upward by agglutinated forms because of local environmental changes within the transition from the Lengua to Cruse formations. The relative absence of planktonic foraminifera species in post-Lengua sediments is attributed to facies not favourable for planktonic species (Blow, 1969; Saunders and Bolli, 1985). Inevitably, the stratigraphic table has the most uncertainty where Bolli's zonations do not work, although other biostratigraphic techniques such as palynology have been applied to these strata (e.g. Payne, 1991; deVerteuil and Johnson, 2003; Vincent et al., 2007). 1.3.2.6 FORMATIONS IN THE TRINIDAD STRATIGRAPHIC TABLE The Trinidad stratigraphic tables in popular use (Kugler, 1959; Carr-Brown and Frampton, 1979; Saunders and Bolli, 1985; Saunders, 1998) represent the culmination of 17 numerous modifications throughout the 20 century (Waring, 1926; Kugler, 1936; Stainforth, 1948; Bolli, 1957abc; Barr and Saunders, 1968; Carr-Brown and Frampton, 1979). Stratigraphic terminology is reasonably consistent in current usage (Kugler, 1956; 1959) although informal stratigraphic designations exist among hydrocarbon exploration companies. Formation ages and boundaries are continuously being proposed (e.g. Algar, 1993; Carr-Brown, 1998; Jones, 1998; de Verteuil and Johnson, 2003), especially for Neogene Formations. It is apparent that the current representation of stratigraphic relationships between units may be an oversimplification. This is particularly true of the Paleogene interval with few exposures or small outcrops that are often faulted. A review of the geological and biostratigraphic literature reveals observations, inferences and interpretations of previous workers that are not represented in the stratigraphic table (Tables LIB and 1.2). It is difficult to assess the validity of some of these observations as most contain very little or no supporting data. Older publications tended toward general descriptions, and often, the distinction between evidence and conclusion was blurred, still, many of these interpretations were based on palaeontological data and were often published in reputable journals. Others were based on lithology described from outcrop (including trenching specifically to observe contacts, e.g. Illing, 1928), and others based on the interpretations of respected palaeontologists (e.g. Renz, 1942), while one recommendation for changes to the age range of an established formation was proposed based on radiometric methods (Algar, 1993). The collective observations of scores of workers highlight the complex relationships between many of the stratigraphic units. Some were perceived as "puzzles" (e.g. Boca de Serpiente Formation, Kugler and Caudri, 1975, p. 418) or described as "difficult" (Kugler, 2001, p. 215) when field contacts were not understood. The complex geology has already been alluded to and some of the relationships observed will unavoidably be as a result of faulting. There is no difference in the ages of rock units between the two tables presented in Figures 1.1 A and LIB). Table LIB however highlights the considerable amount of unconformities and missing time intervals between formations. One example is the disconformity of Paleocene Chaudiere Formation overlying Lower Cretaceous Cuche Formation that occurs across the extent of the Central Range (Kugler, 1959). Field 18 observations supported by palaeontological data also suggest significant disconformities associated with the San Fernando, Nariva, Brasso and Cruse formations. One sandstone unit, the Angostura Sandstone, is not represented on Saunders et al., (1998). It is shown in Figure 1.1 B, based on palaeontolgical control and this will be discussed further in relevant sections. Further details will be given on the ambiguities associated with formalized rock units in the Trinidad Cenozoic stratigraphy throughout this thesis. Many of the pioneering stratigraphic developments preceded the 1950s, and as a result, early palaeoenvironmental and palaeobathymetric interpretations relied almost entirely on faunal assemblages. It was not the norm that sedimentological processes be considered or the impact this may have had on faunal distributions. This thesis will demonstrate that an understanding of sedimentary processes in accordance with biostratigraphy and an understanding of the depositional environments can help to resolve some of these stratigraphic uncertainties. 1.3.3 REGIONAL STRUCTURE The Cenozoic geological history of Trinidad was governed largely by the interaction of the Caribbean Plate with the "Proto-Caribbean" oceanic crust and South American continental crust (Wielchowsky et al., 1991; Meschede and Frisch, 1998; Pindell et al., 2005; Higgs, 2006). Plate tectonic models for the evolution of the Caribbean Plate tend to agree on its eastward migration relative to the South American Plate during the Cenozoic (Meschede and Frisch, 1998). There is less certainty on the exact timing for the influence and arrival of the Caribbean Plate in the Eastern Venezuela/ Trinidad region and the associated Paleogene basin configuration. Several workers suggest the perpetuation of passive margin basin settings to the Oligocene and associated Caribbean Plate deformation thereafter (Pindell and Barrett, 1990; Algar, 1993; Erikson and Pindell, 1993; Pindell, 1994; Erikson and Pindell, 1998, Pindell et al., 2005). This model was modified to include Paleocene basement highs north of the South American margin related to flexure of South American crust above subducting Proto Caribbean oceanic crust (Pindell et al., 2005; Pindell, 2007). Alternatively, some of the 19 earliest ideas on Paleocene basin configuration hypothesized foreland basin geometries occurring south of a rising orogenic belt along the northern South American margin (Senn, 1940; Hedberg, 1950; Kugler and Saunders, 1967; Salvador and Stainforth, 1968) and this idea has been rekindled by more recent workers (Morris et al., 1990; Tyson et al., 1991; Tyson and AH, 1991; Wielchowsky et al, 1991; Higgs, 2006). Various reasons have been put forward for the Early Cenozic orogenic highs, including assumptions of a northern source for elastics, tectonic barriers between mineralogically-varied sedimentary domains, interpretations of tectonically-derived olistostromes and inferences for Paleocene Plate convergence. 1.3.3.1 CARIBBEAN PLATE EVOLUTION The Caribbean Plate is considered an oceanic plateau province consisting of layers of fractionated volcanic rocks. The water covered portion of the plateau is up to 6xl05 km2 though may have originally been more than twice that size (Condie, 2001). The thickness of the plate ranges from 5-20 km (Revillon et al., 2000). Ar40/ Ar39 dating suggests that at least 3 periods of magmatic extrusion led to the formation of the Caribbean Plate. A volumetrically significant event occurred between 87-90 Ma (Coniacian) was followed by a younger event at approximately 72-78 Ma (Kerr et al., 1998) and a possible third extrusion ranged between 55-69 Ma (Revillon et al., 2000; Sinton et al., 1998). The geochemistry of the rocks is consistent with a single-sourced plume-related oceanic plateau (Condie, 2001; Kerr et al., 1997; Sinton et al., 1998). The present day plate motion has been estimated at approximately 20cm/ yr in an easterly direction (Weber et al, 2001a). Many of the reconstruction models for the Caribbean region attribute its origin within the Pacific Ocean sometime during the Late Cretaceous. This is supported by plate margin structural components, biostratigraphic and geochemical lines of evidence. The following synopsis of Caribbean plate evolution was guided by Duncan and Hargraves (1984); Burke et al., (1984) and Pindell (1994). 20 140 Ma (Berriasian) Late Jurassic to Early Cretaceous rifting in the Gulf of Mexico and northern South America associated with deposition of the Couva Evaporites (in the Gulf of Paria, see figure 1.1 for location) which provides the only evidence of this phase of tectonism along northern South America (Burke et al., 1984). Sea floor spreading is associated with the "Proto-Caribbean" seafloor (Pindell, 1994) evidenced by Jurassic ophiolites (Puerto Rico and Desirade island) and redbeds (Yucatan peninsula), the Gulf of Mexico carbonate bank and failed rift arms in Guyana and Brazil (Burke et al., 1984; Pindell, 1994). 90 Ma (Turonian) Africa begins to separate from South America by 119 Ma and spreading along the "Proto-Caribbean" plate ceases. Subduction along Plate margins (Farallon Plate) leads to the creation of the Greater Antilles island arc and the Villa de Cura complex of eastern Venezuela. Deep-water shales, limestones and marls are the predominant sediments in Trinidad at this time, indicating continuation of passive margin deposition. 80 Ma (Campanian) A phase of basaltic extrusion onto proto Caribbean ocean crust occurred at 72-78 Ma (Kerr et al., 1998). The islands of the Greater Antilles and Villa de Cura mountains are being rotated in opposite directions towards the present day position. The Aves ridge (a currently extinct island arc complex located west of the present-day Lesser Antilles island arc) was then actively associated with subduction of the "Proto-Caribbean" seaway along its eastern margin. Passive margin sediments dominate the Trinidadian stratigraphy at this time as the influence of the Caribbean plate is still west of Trinidad. 53 Ma (Early Eocene) An oceanic plateau has been inserted in the vicinity of the northern Venezuelan islands of Curacao, Bonaire and Aruba and its arrival evidenced by the uplift along the northern margin of South America and nappe emplacement (Caribbean Mountains) southeastwards onto the Venezuela margin. The Aves Ridge island arc is now extinct. The Grenada Basin to the north of Trinidad is opened through north-south directed 21 extension (Pindell 1994). Trinidad sediments include coarse-grained clastic intervals (e.g. Chaudiere formations) that interdigitate with Paleocene deepwater shales. 38 Ma fLate Eocene) Present-day northern and southern transform boundaries of the Caribbean plate begin to develop related to eastward motion of Caribbean Plate with respect to the North and South American Plates. In the vicinity of Trinidad and the southeast Caribbean, coarse- grained clastic deposition continued into the Eocene with the Pointe-a-Pierre and Scotland formations. Eocene to recent The Caribbean Plate is presently moving in an easterly direction and converging with the Atlantic Plate at a rate of 20 cm/yr (Weber et al, 2001a). This has been the dominant direction of plate motion since the Eocene. Renewed convergence and subduction began approximately 21 Ma (Duncan and Hargraves, 1984) with the result being the Lesser Antilles volcanic island arc. Easterly displacement of the plate since Late Paleogene is between 1200-1400 km based on estimations along the northern plate boundary (Burke et al., 1984; Duncan and Hargraves, 1984). A much wider transform plate boundary zone exists at the south (Duncan and Hargraves, 1984; Robertson and Burke, 1989) which has also been affected by minor convergence with the South American plate boundary during the late Cenozoic (Burke et al., 1984). The easterly-younging direction of thrusting on the northern Venezuelan margin and progressive west to east development of transtensional basins along the margin such as the Falcon, Cariaco and Gulf of Paria have also been cited as evidence for the easterly translation of the Caribbean Plate (Pindell, 1994). The last 10 million years of deformation in the Trinidad area has been dominated by strike-slip motion along the southern Plate boundary (Pindell and Kennan, 2007). The main arguments against the interpretation of Caribbean plate evolution as presented here question the origin of the Caribbean Plate Oceanic plateau within the Pacific. Despite varying theories as to its place of origin, a fair majority of models agree 22 on significant amount of eastward translation of the Caribbean Plate as opposed to in- place plate development (Morris et al., 1990). This thesis investigates the sediment dispersal patterns associated with the deformation of a formerly passive margin along northern South America. The history of deformation should be recorded in the history of sedimentation and be reflected in changing sedimentary processes, sandstone mineralogy and depositional environments. It is likely that most of the deformation and sediment patterns in the vicinity of Trinidad since Paleogene time can be attributed to plate interaction between the Caribbean and South American Plate. 1.4 OUTLINE OF METHODS This investigation focused on the Cenozoic stratigraphy of Trinidad and included the study of siliciclastic and limestone beds across the Southern Basin, Central Range and Northern Basin of Trinidad, and the island of Soldado Rock located in the Gulf of Paria. Samples were also collected from Cretaceous rocks in the Northern Range to complement interpretations made from the Cenozoic intervals. The objective was to discern information about the mode of sediment entrainment, transport and deposition that would form the basis for the interpretation of depositional environment and basin settings. Approximately 1800 m of measured section from Cenozoic formations were obtained from 28 outcrops and subsurface cores across the Southern Basin and Central Range (Table 1.3 and Figure 1.3). Standard outcrop measurements were taken to discern Table 1.3 Summary of measured sections derived fromoutcro p and subsurface cores for Cenozoic formations. Pliocene Morne L'Enfer All members 1131 1131 8 "Moruga" Late Miocene Cruse 36 36 1 Middle Miocene Cipero Herrera Sandstone 210 210 1 Early Miocene Cipero "Middle Cipero" 10 10 1 Cipero Early Miocene Nariva Poonah Sandstone 61 25 86 4 Oligocene Cipero Angostura Sandstone 142 142 5 Late Eocene San Fernando Glauconitic Sandstone 3 3 1 Middle Eocene Pointe-a-Pierre Pierre Pointe Sandstone 181 181 6 Paleocene-Eocene Chaudiere "Pierre Pointe Sandstone" 40 40 1 Total 1839 28 23 stratigraphic and structural data including grain size variations, bedding character, and palaeocurrent orientations. Standard stereonet techniques were applied to palaeocurrent orientations in order to correct for structural dip, though the history of structural rotations across the Central Range is poorly understood. Descriptions from outcrop and subsurface cores included physical and biogenic sedimentary structures, textures (sorting, grain size, grain shape), colour (on dry samples), bedding contacts, geometries and the overall bedset character and stacking pattern of sandstones. Facies groups were defined based on the descriptions outlined above following the approach of Walker (1992), Reading (1996) and Posamentier and Walker, (2006). The significance of each facies was assessed in terms of their depositional mechanism and associated sedimentary processes and this was the first step in interpreting the Figure 1.3 Location of outcrop and seismic dataset that formed part of this study. 24 sandstones. Facies were subsequently grouped into "facies associations" where a genetic relationship could be established or inferred confidently between them. Facies associations provided the basis for recognizing depositional elements (Mutti and Normark, 1987) and the interpretation of depositional environments. An integrated approach was taken for this investigation. Samples were collected for heavy mineral, modal detrital framework and biostratigraphic analysis (nannofossil and benthic foraminifera). The latter served to discern relative ages, aid in outcrop correlations and provide independent palaeoenvironmental interpretations. The methods employed were complementary; petrography and heavy mineral analysis were useful in discerning between formations where field relationships were ambiguous, while interpretations from benthic foraminifera provided supporting information for the facies associations. Biostratigraphic analysis was carried out by Drs. Jason Crux, Gunilla Gard (nannofossils) and Michael Kaminski (foraminifera). Details of each analysis and further details on the methods employed will be given in the relevant Chapters and Sections. 1.4.1 SEDIMENTOLOGICAL PRINCIPLES One argument of this thesis is that an understanding of sedimentological processes can elucidate some of the ambiguity within the stratigraphy, because unconformities, cycles and palaeoenvironments, interpreted largely from faunal assemblages, should also be recorded in changes in sandstone facies, architectural elements and stacking patterns. It was not until the 1960s that several papers were published on Trinidad sediments that demonstrated a modern sedimentological approach (e.g. Kugler and Saunders, 1967; Saunders and Kennedy, 1968; Poole, 1968). This section provides a review of sedimentological principles regarding sediment entrainment, transport and deposition that form the basis upon which later interpretations are made. Most of the Paleogene sandstones examined display features characteristic of subaqueous "sediment gravity flows" and a review of this concept and related depositional environments and products also follow. 25 1.4.1.1 HISTORICAL DEVELOPMENT OF SEDIMENTOLOGY "Sedimentology" as a discipline within the geological sciences is the study of the genetic link between sediments and the "processes" responsible for their deposition (Reading, 1996). It involves the study of sediment characteristics from erosion or precipitation from solutes, to eventual alteration by low-grade metamorphism. On that basis sedimentological studies span the disciplines of geomorphology to metamorphic petrology. Sedimentary rocks are the products of climate, tectonics, eustasy, inorganic and organic modification of the substrate and time; sedimentology provides a framework for differentiating the relative roles of each of these variables. One of the earliest applications of sedimentological principles to sedimentary rocks was credited to H.C. Sorby's pioneering work during the latter half of the 19 century involving both the petrographic microscope and interpretation of sedimentary structures (Carozzi, 1975). Since the turn of the 20th century, further advances were made in petrography and the classification of sandstones credited to scientists such as Lucien Cayeux, Paul Krynine, Francis Petty ohn and Bob Folk (see Carozzi, 1975 for a reprint of papers by some of these scientists). The beginning of "modern sedimentology" however, was credited to the seminal paper by Kuenen and Migliorini (1950) (Carozzi, 1975; Reading, 1996, pg. 1), whose demonstration of turbidity processes as a major contributor of sediments to deepwater basins was a "milestone" in the conceptual understanding of sandstones (Carozzi, 1975, p. 14). Their paper demonstrated a process- oriented approach to the study of sedimentary rocks based on the integration of mathematical models largely performed by fluid engineers, flume experiments and outcrop geology. This process-oriented approach was continued throughout the latter half of the 20th century by scientists such as J.R. Allen (e.g. Allen, 1982) and G.V. Middleton (e.g. Middleton and Southard, 1984), and developed in parallel with the recognition and understanding of physical and biogenic sedimentary structures (e.g. Bouma, 1962; Harms and Fahnestock, 1965; Seilacher, 1967; Reinick and Singh, 1973; Collinson and Thompson, 1989; Dott and Bourgeois, 1982; Southard and Boguchwal, 1990). The evolving "facies" concept, for which Harold Reading (1996, p. xiii) credits Maurits de Raaf (Shell geoscientist) and which he later imparted to his own students such as Roger Walker and Trevor Elliot (G. Wach, pers. comm.), provided an organized 26 framework by which to study sedimentary processes. It is based on the grouping of genetically related and recurrent aspects of sedimentary rocks. Within modern sedimentology, the association or assemblage of facies provides the "architectural elements" (e.g. Mutti and Ricci Lucchi, 1978; Reading, 1996; Walker, 1992; Posamentier and Walker, 2006) which, when placed in a three-dimensional context, serve as a basis for recognizing the geometries and stacking of modern and ancient sedimentary environments. Though many of the principles on which modern sedimentology was based are now over 50 years old, the discipline continues to be an integral part of basin- scale studies where it has both predictive and historical value (e.g. delimiting hydrocarbon reservoirs and evolution of fold belts respectively). Allen and Allen (1990) is an example of a comprehensive text in this regard, integrating several aspects of modern sedimentology. 1.4.1.2 BASIC PRINCIPLES IN SEDIMENTOLOGY An understanding of how sedimentary particles move is fundamental to process sedimentology, particularly with regard to clastic particles or reworked chemical and bioclastic rocks. Sedimentology is partially concerned with the movement of solid matter (sedimentary particles) within a fluid (water) or gaseous (air) medium across the surface of the earth. The following discussion will highlight some of the basic principles involved in particle motion, though it pertains mainly to clastic particles within a 'fluid' medium (water, non-viscous solids). Many of the points discussed were derived from Allen (1982) and Leeder (1999), except where otherwise referenced. 1.4.1.3 THE BEHAVIOR OF TRANSPORTING FLUIDS Transporting fluids can be categorized into at least two classes based on their reaction to an applied stress. The first is characterized by Newtonian flow where the shearing rate of the fluid is linearly related to an applied shear stress by the formula: dU T = 77 27 where x = shear stress, r\ = dynamic viscosity constant (a function of temperature) and dU/dy is the rate of shear. Most natural fluids exhibit Newtonian flow and will deform immediately as a shear force is applied. The second class of fluids is classified as non- Newtonian flow that is characterized by an inherent 'fluid strength'. These fluids do not deform immediately upon application of a shear stress and instead, a particular yield strength (xcr) must be exceeded before this can occur. This behaviour can be expressed as: dU dy where r|a is an apparent viscosity that is dependent on the shear rate (Allen, 1982, p. 4). The yield strength is largely a function of internal frictional forces that are dependent on the character of sediment particles within the 'fluid' (e.g. grain size, cohesion, angle of repose). Segments of a non-Newtonian flow may move as a solid depending on the influence of boundary stresses on the velocity gradient within the flow. Examples of Newtonian flows include rivers, tidal currents, longshore drift and surge currents, while non-Newtonian flows include cohesive sediment flows such as slumps, slides and debris flows (Table 1.4). In reality, these flow types can be gradational and it is sometimes difficult to differentiate their products in the field (e.g. Shanmugam, 1996; Lowe and Guy, 2000). 1.4.1.4 SEDIMENT ENTRAINMENT A particle will be transported while the collective lift and drag forces acting on that particle exceed some critical downward force that will tend to keep the particle stationary (Figure 1.4). The downward force to overcome is usually gravity, although other factors (such as internal friction and grain cohesion) must also be considered. Once the opposing forces, or critical shear stress, exceed the downward component, a grain will be entrained into a flow. Allen (1982) calls this dimensionless value the "threshold of particle motion", although it is an idealized concept and difficult to define theoretically, 28 Table 1.4 Some of the more common geophysical flows. Their driving mechanisms, flow types and geographic occurrence along a terrestrial to deep marine profile. Compiled from Allen (1982) and Leeder(1999). Flow type and mechanics Environment Geophysical flow Driving Mechanism Flow type Terrestrial Coastal Shelf Slope |Abvssal Mass flows* Gravity/ Density Non Newtonian IPjfjffcfjf •MM Rivers Gravity Newtonian Tidal currents Gravity Newtonian Longshore drift Wind, Coriolis force Newtonian „^ v Surface waves Wind Newtonian iiiiiBN iW*W^!lM4 Storm waves Wind Newtonian Hyperpycnal Density Newtonian Hypoypcynal Density Newtonian Oceanic currents Gravity, Coriolis force Newtonian Non Newtonian Turbidity currents Gravity to Newtonian * includes rockfalls, creeps, slides and slumps Surface p Fluid density .-".*-' "Permanently" ', (',.;-!•' suspended fines '- *'',„'' *; h Menn flow velocity Flew depth Gravitational mass (mgr) Figure 1.4 Schematic illustration of transport mechanisms within fluid (and air) flows. Some of the forces mentioned in text are also shown. 1) Rolling induced by bedload or traction forces 2) Saltation 3) Suspended grains. Modified after Leeder (1999) Figure 6.8. 29 as the exact moment of particle motion is difficult to define in flume experiments (Miller et al., 1977). The threshold is a function of grain diameter, shape and density, position in the substrate, sediment sorting, flow velocity, fluid viscosity, fluid turbulence and gravity (Miller et al., 1977; Allen, 1982; Leeder, 1999). Assuming non-cohesive sediments, uniformity of grain size and initial plane bed conditions, it was experimentally and theoretically shown that finer grain sizes are entrained at lower fluid velocities (Komar and Miller, 1973; Miller et al, 1977). The calibre and quantity of grains entrained within a flow are defined by the competence and capacity of the flow, respectively. A relatively competent flow is capable of entraining larger grains and this is again dependent on boundary conditions (shear stresses and grain sorting), fluid velocity, density and viscosity. The general trend is illustrated in Figure 1.5 for well sorted sands although it may not apply with decreased sorting as the grain exposure (or degree of shielding) must now be considered in the shear forces acting on that grain (Blatt et al., 1980). Pebbles and cobbles are too large to be moved in currents just competent enough to move sand-sized grains (Blatt et al., 1980). The capacity of a flow is dependent on the mode of transport, sediment discharge and flow intensity. This is elaborated below. 1.4.1.5 SEDIMENT SUPPORT MECHANISMS AND GRAIN SETTLING Once entrained into a flow, grain movement occurs either as bedload propelled by boundary layer shear stresses or may be suspended into the body of the fluid by "turbulent shear" (Leeder, 1999, p. 127). Intermediate between these two is grain saltation where particles move by repeated 'jumps' from the substrate to a few grain diameters into the flow (Figure 1.4). A variety of sediment support mechanisms interact to maintain the capacity of a flow, each variably affecting the grain settling velocity. Although idealized for sedimentary grain flows, Stokes law theorizes that the falling velocity of a grain is proportional to the square of its radius (Allen, 1982); larger grains will have a higher settling velocity and be the first to return to the base of a flow. This idealized falling velocity is reduced within high grain concentrations, or more viscous (cohesive) flows, where settling is hindered by grain boundary effects and repeated grain 30 collisions (dispersive pressure) (Lowe, 1982). The latter typically occurs in fluid- sediment mixtures where grains are supported by intergranular, buoyant fluid forces that counter the downward-acting particle weights. Other factors that influence sediment transport include grain inertia (Sanders, 1965), intergranular cohesive forces (e.g. formation of colloids in clays) and eddies produced by fluid turbulence. The net effect is that finer grained particles, once entrained, form a large component of the suspension load while coarser grain sizes are limited to bedload traction and saltation. This can vary for high-capacity, turbulent suspensions where both fractions are entrained within the current, and leads to poorly sorted deposits once the capacity of the flow is reduced by a loss of turbulence. All flows represent a balance between grain erosion, entrainment and deposition. Deposition of grains will occur once the relative cohesive/gravitational forces exceed drag/lift forces. This may occur with a reduction in flow velocity, a decrease in fluid turbulence or an increase in fluid density, due to added grain concentration or changes in salinity. 1.4.1.6 SEDIMENTARY STRUCTURES AND FLOW REGIMES The entrainment, transport and settling of sediment grains represent a continuum of processes that is not equally represented in the rock record. Entrainment and transport largely reflect erosional processes that are preserved only as gaps in the rock record. It is the depositional processes that permit the study of ancient processes and environments, as they leave a record of "mechanical structures" (Allen, 1982, pg. 5) that can be readily studied and interpreted. The study of these 'mechanical' or sedimentary structures forms an integral and established part of modern sedimentology. The fundamental concepts discussed above were developed from flows within river channels in modern alluvial environments (Allen, 1982 provided several references). These concepts were related to sedimentary structures by the empirical concept of flow regimes, whereby particular structures are stable over a particular range of fluid velocities for a particular grain size (Simons et al., 1965b; Harms and Fahnestock, 1965; Southard and Boguchwal, 1990). This concept provided a 31 hydrodynamic basis for the interpretation of sedimentary rocks. Under increasing flow velocities for a particular grain size, the scale of bedforms increase from a plane bed to ripples, dunes, horizontal lamination and antidunes. Ripples and dunes are stable under lower regime flows while plane beds (horizontal laminated) and antidunes are stable under upper regime flows. The boundary between the two is gradational and is dependent on grain size (Figure 1.5; Simons et al., 1965). For a particular grain size, the suite of sedimentary structures will progress from large, dune-scale bedforms to ripples with decreasing flow velocity. This waning-hydraulic flow interpretation has been applied outside of flume experiments and terrestrial rivers, to sedimentary structures in both shallow and deep-marine environments (e.g. Harms and Fahnestock, 1965; Arnott and Southard, 1990; Duke et al, 1991). Flume experiments for dominantly oscillatory flows demonstrated a transition from plane bed to small, straight-crested and symmetrical ripples (18-25 cm/s flow velocity) to larger irregular-crested, symmetrical ripples with increasing flow velocity (40 cm/sec) and oscillation period (Arnott and Southard, 1990; Southard et al., 1990; Dumas A 1 F I I I I I I i—n—i i i i i MfflOWiES 13 . 12 • II - 10 - 9 • / J 6 5 3 Z ^L^^ & 0 i i •—r^Ti i i ,1,1 , ,,,,,, J. I l II 0.01 0J 1.0 DIAMETER, mm DIAMETER, mm Figure 1.5 Sediment entrainment and stability of sedimentary structures in quartzose sand. A) Initial movement and suspension fields within a flow at 20°C. U* = shear velocity/ stress at the bedding surface. Modified after Blatt et al. (1980), figure 4-6. B) Velocity-size graph showing stability fields for sedimentary structures based on a synthesis of published data normalized to 10°C equivalent. Ripples and dunes are stable within "lower regime" flows while plane bed lamination and antidunes occur within "upper regime" flows. Fr = Froude number. After Southard and Boguchwal, 1990. 32 et al., 2005). The larger ripple forms included the "hummocky cross stratification" of Dott and Bourgeois (1982). These bedforms are unstable even under a moderate unidirectional flow component (5 cm/sec) where they transition to asymmetric ripple forms and plane beds (Arnott and Southard, 1990; Dumas et al., 2005). Hummocky cross-stratification is typical for sediments deposited within fairweather or storm wave base upon shallow coastal or shelf environments. No mechanism for their formation has been offered in cases where deeper water environments were interpreted with these structures (e.g. Wild et al., 2005). 1.4.1.7 DEFINITION OF TERMS Bedforms do not readily fall into size classes with well-defined boundaries as they vary depending on such factors as grain size, scale of the flow, current flux, crest geometry and depositional environments (Simons et al., 1965; Harms and Fahnestock, 1965; Ashley, 1990; Southard and Boguchwal, 1990). The problem of distinction is compounded where their three dimensional aspect is not displayed in outcrop. The terms commonly used throughout this thesis to describe bedforms and some sedimentary structures attributed to changing flow regimes are listed in Table 1.5. They were largely guided by the bedforms described by Harms and Fahnestock (1965) from alluvial streams, but also related in part to structures described from deep-water deposits. Other terms that find common usage in the description of deep-water sediments (e.g. "traction carpets") will be referenced where used, although they can be attributed to at least one of the flow regimes and groupings described by Harms and Fahnestock (1965). 33 Table 1.5 Bedform terminology and sedimentary structures that are mentioned in this thesis and an interpretation as to their genesis. Data compiled from Harms and Fahnestock (1965) unless otherwise referenced. STRUCTURE/ BEDFORM FIELD IDENTIFICATION INTERPRETATION REFERENCES Bar forms Cross beds greater than 75 cm thickness Migration of subaqueous longitudinal, transverse or point bars Bedset Two or more superimposed beds that display similar Localized, relatively short term depositional conditions as Campbell, 1967 comosition, texture and sedimentary structures that a subset of a larger depositional setting differences them from adjoining beds Basal erosive surface; wedge-shaped or lenticular Long-term pathway for sediment tranport. Synonomous Collinson and geometry; fining upward fill of variable lithology; with "axial-flow"A Thompson, 1989 laterally discontinuous Dune-scale bedforms Cross beds up to approximately 75 cm thickness Migration of subaqueous dunes; no implication is meant Harms and as to the 3-dimensional geometry of the bedform; Fahnestock, 1965; synonomous with "megaripples" Ashley, 1990 Flaser bedding Mud laminae, continuous or discontinuous, within a Related to changing flow regimes and preferential Reineck and Singh, dominantly sandy horizon deposition of finer or coarser sediment load. Mud drapes 1973 are deposited at lower flow velocities and eroded at higher flow velocities; Good indicator of short-term changes in flow-regimes Decrease in grain-size from base to the top of a bed; Inverse grading will be explicity stated when applicable Hummocky cross-stratified Low-angled, approximately symmetrical cross- Related to high velocity, long period, oscillatory currents; Arnott and Southard, laminae sets with alternations of convex they are destroyed at relatively low unidirectional velocity 1990; Dumas etal., (hummocks) and concave (swales) laminae (0.05 m/sec) 2005 geometry Large-scale cross-stratificaiton Metre-scale cross-bed sets disconformabte over Produced by downstream migration of bar-scale bedforms Bridge, 2006 shale beds or other cross-strata. Orientation is or lateral accretion of point bars; usually associated with oblique to the general palaeoflow. Smaller bedforms channels (e.g. trough cross-beds) may be superimposed Lenticular sand bodies A Refers to lens-shaped bed or bedset geometry related to the bounding top and basal surface; differes from "channel" in that a basal erosive surface was not observed or is not implied Lenticular bedding Ripple-laminae, continuous or discontinuous, Ripple migration within a generally still-water environment Reineck and Singh, encased in a dominantly shaly horizon 1973 Massive "Structureless" beds (sand or shale); no discernable Rapid settling from suspension; post-depositionai Lowe, 1962; Tucker, sedimentary structures from outcrop observation liquefaction; extensively bioturbated beds 1991; Stow and Johansson, 2000 Parallel-stratified stratification parallel to lower bounding surface in Grain suspension-settling in finer-grain size fraction and sandstone, siltstone or shale* traction transport of sand-sized particles at upper plane bed flow velocities Planar cross-stratified Parallel or near-parallel, linear cross-stratification Lee presentation resulting from the migration of dune- sets. Bounding surface of sets are planar and scale, straight-crested bedforms parallel; dimensions up to 60 cm thick Ripple cross-laminae cross laminae in sets less than 6cm height in sand- Lee preservation resulting from the migration of ripplesa t or silt- sized material. May by trough or planar cross- lower-flow regime laminated Sigmoidal cross-stratified Lower and top of cross-strata tangential to lower and Modification of planar or trough cross-stratification by Kreisa and Moiola, top bounding surfaces respectively, forming toesets reversals in current direction, as can occur with reversing 1986 and topsets tides Swaley cross-stratified Low-angled, approximately symmetrical cross- Same as hummocky cross-stratified sets with preferential laminae sets with prominent concave (swales) preservation of swales related to water depth and energy laminae geometry regime Tangential cross-stratified Lower section of cross-strata tangential to lower Ripple and dune migration with reworking at base of lee Kreisa and Moiola, bounding surface, forming toesets face 19B6 Trough cross-stratified Trough-shaped (concave) cross-stratification sets, in Lee preservation resulting from the migration of dune- the sand-sized or coarser fraction. Bounding surface scale, lingouid-crested or lunate bedforms of sets may not be parallel; sets thicker than ripple cross-laminae and up to approximately 60 cm** Wavy-divergent laminae Laminae or laminae sets within bed are not parallel Associated with migrating ripples in the finer-grain size to lower bounding surface or each other fraction, viewed oblique to palaeocurrent direction Wavy-parallel laminae Each laminae within set parallel to lower bounding Associated with suspension settling in finer-grain size surface and each other fraction (silt, clays and very-fine sand) * combination of "horizontal" and "parallel" stratification of Harms and Fahnestock ** Differs from the 30 cm dimension given by Harms and Fahnestock for "large-scale" trough cross sets; Equated dimensions with "planar cross-stratified" as emphasis was on geometries during field investigations A Specific definition related to this study 34 1.4.2 DEEP-WATER SEDIMENT GRAVITY FLOWS It was Roger Walker's opinion that no other group of clastic rocks offers the same simplicity of interpretation as turbidite beds, and yet presents such a "scientific challenge" due to the inherent difficulty in directly observing the depositional processes (Walker, 1973, p. 2). As a result, the geological literature abounds with classifications, terminology, literary debates and definitions regarding the appearance and deposition of these flows. Considering this, the following discussion will outline some of the sedimentary processes associated with these deposits and establish the nomenclature and classifications used for this thesis. The term "sediment gravity flow" refers to the (re)-mobilization of sediment by density- and gravity-driven currents composed of varying sediment-fluid mixtures. Such a definition encompasses bedsets attributed to density- and gravity-driven currents over a wide spectrum of the sediment support mechanisms discussed above. A turbidite bed is but one product of sediment gravity flows. Its diagnosis in ancient and modern strata relies on a recurrent stacking and assemblage of sedimentary structures that were recognized from both flume experiments and outcrops (Kuenen and Migliorini, 1950; Bouma, 1962; Sanders, 1965; Aalto, 1976; Lowe, 1982; Arnott and Hand, 1989) (Figure 1.6). Within the modern definition, only a part of a "turbidite" may actually be deposited by a turbidity current which, by definition, relies on evidence of turbulent flow; other sections deposited by laminar flow or inertia-driven grain flows (e.g. Lowe, 1982; Shanmugam, 1996) are also included. Turbidites are differentiated from 'debris flows', which occur where a sediment- fluid mixture has inherent matrix strength (non-Newtonian) and as a result, exhibits a plug-like flow behavior, irrespective of grain size and composition (Figure 1.6 A). The evidence for debris flows may include contorted layers preserved by en masse freezing or zones of floating outsized clasts suggesting matrix strength (Shanmugam, 1996). The concept of "high" and "low density" flows has sparked much literary debate (e.g. Shanmugam and Moiola, 1995), especially concerning thick-bedded, coarse-grained massive sandstones that cannot be readily explained by purely turbulent processes or cohesive flows (e.g. "fluxoturbidites" of Dzuynski et al., 1959; also see Figure 1.6 B). 35 Figure 1.6 A) Sedimentary structures, flow types and major sediment support mechanisms involved in sediment gravity flows, after Lowe (1982). The "classical" turbidite of Bouma (1962) is shown for comparison. B) Two end-members of sediment gravity flow processes and examples of terms used to refer to deposits that do not clearly fit into either. This range of processes has been actively debated. C) Time versus flow velocity graphs illustrating the differences in flow duration. Hyperpcycnal flows are considered a quasi-steady flow, a =accumulative, d=depletive. D) Schematic illustration of the down-current geometry of turbidites resulting from quasi-steady and unsteady flows, which is very similar to the vertical turbidite profiles. Thicker intervals reflect a coarser grain size. 36 For this thesis, the terms 'low density' and 'high density' are used and considered relative measures. 'Low density' is used to refer to flows for which more dilute sediment-water mixtures were evident, reflected in finer grain size and better sorting, and likely associated with more muddy interbeds. Lowe (1982) associates clay to medium-grained sediment sizes with these flows. Higher density flows are associated with a wider range of grain sizes (clay to cobble-sized clasts, Lowe, 1982), thicker beds (typically greater than 1 m) and display a higher degree of sandstone amalgamation. No quantitative limits for percentage grain size composition are implied between the two categories as this is not adequately defined (Shanmugam, 1996) and the grain sizes are not mutually exclusive (Lowe, 1997). Also, unless explicitly stated, no implication is meant regarding the nature of the sediment source by using these terms. The established term "massive" will be used for beds that display no obvious sedimentary structures in outcrop, although the definition employed here includes sandstones less than 1 m thick, unlike that employed by Stow and Johansson (2000). In some cases, massive sandstones included evidence for dewatering, being the only evident sedimentary structure within the bed. The term is used in the same sense as "structureless" sandstones used by other authors (e.g. Posamentier and Walker, 2006). Bouma (1962) first recognized the sequence of sedimentary structures in deep water sandstones from the Peira-Cava area of the French Alps, and his descriptive classification has become the standard for dilute, lower density flows. Lowe (1982) included both a descriptive and genetic aspect to his classification of coarser-grained turbidites (Figure 1.6 A). He defined a sequence of sedimentary structures attributed to waning sediment gravity flows within this coarser grained category. His sequence was attributed to variable sediment support mechanisms, from fully cohesive flows (e.g. debris flows) to turbulent suspensions. Both of these classifications were used for turbidite sequences described in this investigation. Lowe's theoretical treatment of depositional mechanisms provides a plausible explanation for his sequence of sedimentary structures expected with transitions from non-Newtonian to Newtonian flows and changing flow regimes. His classification also incorporates changing grain sizes and the effect these can have on sediment support mechanisms (e.g. dispersive 37 pressure is more effective with coarser grain sizes and higher concentration). Observations that do not fit within these classifications will be referenced accordingly. 1.4.2.1 GRAIN SUPPORT MECHANISMS IN SEDIMENT GRAVITY FLOWS The transfer of sediment from the shelf to slope and basin plain environments takes place via gravity currents of varying scales and duration. The character of these gravity flows depends primarily on the grain size distribution and concentration of entrained sediment (Lowe, 1982; Kneller, 1995), which in turn impacts the sediment support mechanisms within individual flows. The latter occurs to varying degrees by buoyant fluid forces or grain collisions. Earlier models of sediment gravity flows envisaged a transfer of sediment largely via suspension currents ('turbidity') in which grains were supported by buoyant uplift (Kuenen and Migliorini, 1950; Bouma, 1962). Sanders (1965) recognized sedimentary structures within turbidite beds, which he attributed to traction-related processes. These processes and the resultant bedforms are now commonly recognized, partly as a result of flume experiments (e.g. Arnott and Hand, 1989; LeClair and Arnott, 2005). In general, high- and low-density turbidite beds preserve an upward transition from traction to suspension-related processes, with an intermediate suite of sedimentary structures indicative of simultaneous traction and sediment fallout (Figure 1.6 A). Turbulent suspension currents may be dampened by grain collisions in highly concentrated flows (Normark et al., 1991) whereas more dilute flows may be deposited entirely by suspension. The association of the latter with the distal or lateral margins of higher density flows underscores the transitional nature between flow types. Debris flows are considered an end member of high-density flows under which sediment is moved downslope within concentrated masses, likely initiated by a loss of internal cohesion (Kuenen and Migliorini, 1950; Kuenen, 1956). Such masses will move downslope as long as shear stresses acting on the sediment exceed the yield stress (xcr) of the matrix. Such flows are characterized by internal matrix strength and plug movement, capable of transporting sediments up to boulder dimensions. The main sediment support mechanism is provided by the matrix strength (cohesive or frictional) and dispersive 38 pressure resulting from particle collisions, with the entire mass undergoing cohesive freezing once the stress conditions change (Lowe, 1979; 1982). These chaotic, slumped masses of sediment are often associated with turbidites. The scale of sediment gravity flows is varied, ranging from delta-front slope turbidites preserved as millimeter-scale laminae within a fine-grained environment, to mass transport complexes several kilometres in length and hundreds of metres thick, preserved along continental margins. Early experiments and mathematical models for turbidite flows emphasized unsteady, catastrophic flows of short duration (Kuenen and Migliorini, 1950; Lowe, 1982) that may have evolved from large-scale slumps and debris flows. Recent publications have highlighted the role of longer duration (quasi-steady) flows in the geological record (Normark et al., 1991; Kneller, 1995; Mutti et al., 2003; Mulder et al., 2003; Plink-Bjorklund and Steel, 2004) as an explanation for sedimentary structures that do not fit easily into the established turbidite schemes (Figure 1.6 C). These include hyperpycnal flows attributed to density differences between two bodies of water, leading to an underflow of the more dense solution that is capable of carrying up to medium-grained sediment over long distances (Mulder et al., 2003). The difference in density is attributed to excess sediment load (as with sediment-gravity flows) and is often associated with flood river discharges into the saline ocean (Mulder and Syvitski, 1995; Mulder et al, 2003). The turbidite bed examined in outcrop represents only the final depositional process within what may have been a transitional current or slide (Mutti et. al., 1999). Whether unsteady or quasi-steady, the final deposit largely reflects decreasing flow velocities (Sanders, 1965; Harms and Fahnestock, 1965). With a decrease in velocity, all flows eventually lose their ability to carry the quantity and quality of sediments initially entrained in suspension or traction. Larger grain sizes will preferentially deposit first as flow competence decreases. This results in horizontally graded deposits with a coarser component at more proximal localities (Kuenen and Migliorini, 1950; Bouma, 1962; Lowe, 1982; Mutti et al., 1999). Simultaneous with velocity loss, a flow loses its capacity to carry the quantity of sediment initially entrained and begins to deposit its load irrespective of grain size, resulting in poorly sorted deposits. This can explain the occurrence of fine sand and coarse silt throughout dominantly coarse-grained sandstone, 39 or the presence of larger floating mudclasts and pebble grains throughout a fine-grained sandstone bed (Hiscott, 1994). Both the flow and related depositional processes of sediment gravity flow deposits result in a recognizable sequence of bed character and sedimentary structures that are exclusive to turbidite beds, simplifying field recognition of this lithofacies relative to other environments of deposition (Walker, 1973) (Figure 1.6 A,D). 1.4.2.2 DEPOSITIONAL PRODUCTS OF SEDIMENT GRAVITY FLOWS The finest grained component of the Bouma (1962) classification has been further refined by Stow and Piper (1984; 1991). Bouma's classification did not include conglomerates for which Walker (1975a) recognized three sequences attributed to inertia- driven grain flows into deep-water environments: normally graded, inverse-graded and disorganized. It is the range of grain sizes and sediment concentration between these two extremes that has invited the most debate. Higher density flows, with a greater component of coarse-grained sand to gravel-sized clasts display sedimentary structures and stacking patterns not recognized by either Bouma (1962) or Walker (1975 a). For the most part, these are incorporated by Lowe (1982) (Figure 1.6). Hyperpycnites (Mulder et al., 2003) are the products of hyperpycnal flows and their similarity to classical turbidites may have resulted in them being largely overlooked in the geological literature (Mutti et al., 2003). They develop along shelves and upper slopes at the distal end of flood-dominatedrivers , and are differentiated from classical turbidites by their association with other deltaic sediments, evidence for wave reworking (Mutti et al., 2003), inversely graded bed division (Figure 1.6 D), and abundant plant and wood fragments (Mulder et al., 2003). Massive sandstones are caused by several mechanisms, including gravity flows and bioturbation. For the former, they are produced by high sediment fallout rates that suppress the formation of traction-related structures (Lowe, 1982; Arnott and Hand, 1989). Plane beds (Tb), cross beds (Tt) and ripples (Tc) developed only when the downward sediment flux is insufficient to suppress the bedload migration of grains driven by the overriding turbulent currents. Thick, massive sandstones are therefore produced during the passage and collapse of unsteady, highly concentrated, liquefied gravity flows. 40 An alternative mechanism proposed by Kneller and Branney (1995) suggested that, instead of rapid sediment fallout, thick massive sandstones gradually aggrade during the passage of depletive quasi-steady flows of longer duration than surge type currents. With this mechanism, the thickness of massive sandstone beds is a function of the duration of the turbidity current and sediment supply. Stow and Johansson (2000) provided a useful review of the occurrence, associated facies, formation and significance of massive sandstones. For this investigation, emphasis was placed on the occurrence and succession of sedimentary structures in order to recognize these products of sediment gravity flows. This approach was found to be applicable particularly to Early Cenozoic intervals where the classifications of Bouma (1962) and Lowe (1982) provided a suitable basis for comparisons between sandstones. 1.4.3 FACIES ASSOCIATIONS IN DEEP-WATER CLASTIC ENVIRONMENTS Walker (1973), Normark et al., (1993), Reading and Richards (1994), Mutti et al., (1999), and Posamentier and Walker, (2006) provided details of historical milestones, debates, classifications and recent facies models for deep marine clastic systems. They typically included "slope", "inner", "middle" and "outer" fan components based on studies from both modern (Normark, 1970; 1978) and ancient environments (Walker, 1978; Mutti and Ricci Lucchi 1978). These are complex clastic systems, widely varied in morphology, stacking patterns and sediment calibre. Their eventual form and character depend on the geometry of the receiving basin, sediment supply and allocyclic controls in the source area (Shanmugam and Moiola, 1988; Richards et al., 1998; Prather, 2003). "Slope" is a morphological term that, in modern deep-water environments, can refer to the continental or localized basinal slopes both of which lead to the basin floor (Bouma, 2004). The continental slope is characterized by bathymetric gradients between 3-6° that grade imperceptibly into the continental rise and basin floor at the distal end (Stanley and Unrug, 1972). It is usually outboard of a coeval shelf. Slopes are 41 essentially structural entities that have been modified by sedimentary processes and occur in all tectonic settings with varied sediment-rates, -type and -delivery and, ultimately, variable bathymetric profiles (Stanley and Unrug, 1972; Reading and Richards, 1994; Prather, 2003; Flint and Hodgson, 2005). There is no particular facies restricted to slope environments though research on both modern and ancient slopes has identified several distinctive characteristics. They are best constrained from outcrop by delimiting the transition to coeval basin floor and shelf environments (e.g. Link and Welton, 1982; Chan and Dott, 1983; Dott and Bird, 1979; Pickering, 1984; Beaubouef et al, 1999; Plink-Bjorklund et al, 2001; Shultz et al., 2005). In terms of sediment distribution, it is convenient to divide slopes into an upper, middle and lower region. The relatively steeper upper and middle regions are sites of erosion, sediment instability and bypass. Clastics that accumulated on the outer shelf are transported basinward by sediment gravity flows through incised valleys, gullies and canyons that largely bypass the upper slope, to rest upon the lower slope and basin floor (Stanley and Unrug, 1972; Prather, 2003). This results in a general fining-upward succession from the lower slope towards the shelf-slope break (e.g. Lowe, 1972; Bruhn and Walker, 1997; Shultz et al., 2005) (Figure 1.7). There is also a down-slope transition from coherent slides and rock failures attributed to instability, to more viscous and turbulent flows. This results in large, internally coherent, allochthonous blocks being retained within more proximal slope and slope canyons, while debris flows and turbidites accumulate towards the lower slope and inner submarine fan environments (Figure 1.8; Stanley and Unrug, 1972; Nardin et al., 1979). This tendency is reflected in the high proportion of slumps and debris flows relative to turbidites that make up the fill of ancient slope canyons (Stanley and Unrug, 1972; Cook, 1979; Nardin et al., 1979; Shultz etal.,2005). In ancient slope systems, laterally confined coarse clastics tend to be associated with slope channels and other incisions where amalgamated bedsets of conglomerates and massive pebbly sandstones accumulate (e.g. Winn and Dott, 1977, Stanley et al., 1978, Dott and Bird, 1979; Morris and Busby-Spera, 1988; Camacho et al., 2002; Shultz et al., 2005). Away from slope incisions, a considerable amount of fines may be 42 delivered to slopes by contour and nepheloid currents and hemipelagic sedimentation, and in some distal ramp ramp fringe B uppar stopc • y lowflr slope - Figure 1.7 Facies stacking patterns for deep-marine clastic systems. A) Aggradational to progradational stacking of multiple-sourced, delta-fed submarine ramp model and B) Point-sourced, canyon fed submarine fan model. Modified after Heller and Dickinson (1985) and Mutti and Ricci Lucchi s. outer fan • (1978). 43 lowmsumm MIDDLE SLOPE UPPER SLOPE SHELF Mwaat mm .BUXKytpBXnE. SANDBQDfES BWMSS- 4^ -1^ •StOStONAL 'CHAHNELS- SHELF MARGSN •DEBRI8 FLOWS- ""'"" EAHJURE 'I^VEED'CHAMNCLS- vXUSk JgJELFflMftGm wm DELTAICS — _ — _ _ —SLUMPS ; — •CURRENT REWORKED • — - - Figure 1.8. Updip to downdip cross section showing facies transitions for a lowstand slope depositional system (Gulf of Mexico). After Yeilding and Apps, 1994, Figure 10. cases, these are the main contributors of sediment to the slope (Stanley and Unrug, 1972; Stow and Piper, 1984). Prather (2003) divides modern slopes into two types based on subsurface examples from the Gulf of Mexico: (1) above-grade slopes with intraslope "perched" basins caused by deviations from the ideal slope profile in response to mobile substrates, and (2) graded slopes which are very similar to the classical slope profile characterized by sediment bypass in the upper slope region to sediment accumulation at the base of slope. Prather's review highlighted different mechanisms of creating accommodation in the slope that included sediment ponding in "above-grade" slopes, slope readjustment after failure ("healed-slopes") and slope incision within incised submarine valleys and canyons. Sediments deposited on the lower slope coincide with models for submarine fans. These components are differentiated by facies associations, sandstone stacking and geometry, external fan geometry, abundance and nature of interbedded shale, depositional or erosional capacity of flows, and presence of other morphological elements such as channels, levees, suprafan lobes and fan valleys (Mutti and Normark, 1987). Submarine fans develop at canyon mouths (lower slope) where turbidity flows lose their transport capacity and begin to deposit any entrained sediment. Much of the sediment is delivered by turbulent and liquefied flows; grain flows and cohesive flows gradually reduce in importance from upper to lower fan environments (Mutti and Ricci Lucchi, 1978; Shultz et al., 2005). A transition also occurs from confined flows in the canyon mouth of inner fan levees to unconfmed flows, and this is reflected in the overall channel geometry (Posamentier and Walker, 2006). The down-current change in flow regime (elastic and viscous 'flows' to grain, liquefied and turbulent flows) is again reflected in the depositional elements. Coherent block slides and viscous debris flows that are volumetrically important in slope environments are replaced by high and low density turbidites in submarine fans (Stanley and Unrug, 1972; Nardin et al., 1979; Mutti et al., 1999). The change in flow regime is further reflected by a down-current change from massive sandstones to normally graded, "classical" turbidites reflecting the down-current sorting from suspension settling (Mutti and Normark, 1987). 45 Mutti and Ricci Lucchi (1978), Mutti and Normark (1987) and Shanmugam and Moiola (1988) described morphological or depositional elements that can be found in ancient deep-water systems and the facies that can aid in their identification. From these reviews, the main morphological elements of these systems include (1) channels, (2) overbank deposits, (3) lobes, (4) channel-lobe transition and (5) sheet sands. Channels are the main depositional pathways in inner fan environments and may or may not be contained within fan lobes which transition to the downstream end of the system (Mutti and Ricci Lucchi, 1978). Channels are dominant in more sand-rich systems and may be "braided" (Walker, 1978), with overbank deposits hindered by a lack of fine-grained sediment. The change from confined to unconfined flows is reflected in a transition from relatively narrow and lenticular turbidite fills, to broad and continuous turbidite sheet beds within the outer fan and distal basin floor (e.g. Schenk, 1970; Mutti and Ricci Lucchi, 1978; Walker, 1978; Lien et al., 2003; Wickens and Bouma 2000; Gardner and Borer, 2000). The location of that transition upon the fan depends on sediment supply and calibre, basin topography and other extraneous factors (Posamentier and Walker, 2006). Depositional elements will be further considered later in this thesis (Chapter 3). Stacking patterns and trace fossils also aid in the differentiation of submarine fan deposits. Prograding submarine fans characteristically produce coarsening/cleaning and thickening upwards successions, resulting from the tendency of distal fines to be overstepped by proximal channel fills (Figure 1.7; Mutti and Ricci Lucchi, 1978; Walker, 1978); though stacking trends must be interpreted with caution (Hiscott, 1981). Submarine fans are associated with numerous meandering and complex grazing traces (graphoglyptids) that typify the Nereites ichnofacies (Seilacher, 1967; Crimes, 1977; MacEachern et al., 2007; Seilacher, 2007) although this criterion must also be carefully applied due to taphonomic considerations and the establishment of uncharacteristic trace fossil communities (e.g. Heard and Pickering, 2007; Uchman, 2001). This is elaborated further in Chapter 5. Other studies and classifications have highlighted deviations from some of the traditionally accepted sedimentation patterns described above for slope and basin floor systems which mainly related to single-sourced, canyon-fed systems that have received the most attention in traditional models for deep-water environments (Mutti and Ricci 46 Lucchi, 1978; Walker, 1978). Recent classifications have highlighted the importance of multiple sediment feeders and the development of "clastic ramps" on the slope (Heller and Dickinson, 1985; Reading and Richards, 1994), and these have found applications in several basins (e.g. Steel et al., 2000; Plink-Bjorklund et al., 2001). It is also a common practice to distinguish between coarse-grained/sand-rich and fine-grained/mud-rich deep- water systems (Mutti and Normark, 1987; Reading and Richards, 1994; Richards et al., 1998; Bouma, 2000). Classifications also exist that differentiate submarine fans based on the character of the receiving basin (Mutti and Normark, 1987; Shanmugam and Moiola, 1988). The complexity of deep-marine systems was reiterated by Bouma (2000) who drew attention to the multiple factors that can influence the eventual morphology, stacking and internal connectivity of fan systems, and suggested caution in the application of end-member models. These models however provide a framework for the recognition of these systems relative to other sedimentary environments and a basis for comparisons between different deep-marine environments. They provide a starting point for the study of turbidite systems that can be tailored to suit individual basins (Bouma, 2000). The classifications and models discussed above, together with examples of facies from other basins, will be readdressed when facies from this study are considered. The themes and principles that were discussed in the foregoing section provide the framework for the interpretations that follow, particularly for Chapters 2 to 4 where the selected sandstone intervals are described. Chapter 2 describes Early Cenozoic clastic (and limestone) units ending with the Early Miocene Herrera Sandstone Member of the Cipero Formation. Chapter 3 presents an interpretation of depositional environments arising from the descriptions in Chapter 2. Late Miocene to Early Pliocene sediments are described and interpreted in Chapter 4. This dataset will be integrated and summarized in Chapter 7 where the changing sediment dispersal patterns throughout the study interval will be demonstrated and conclusions drawn on the general basin settings. 47 Chapter 2 - Lithofacies Associations and Sedimentary Processes of Paleocene to Early Miocene Formations 2.1 INTRODUCTION For Trinidad sediments, the role of sedimentary processes did not develop in parallel with biostratigraphic data, as previously discussed. Knowledge of sedimentary processes associated with clastic intervals lagged behind the local and global strides being made in biostratigraphy (Saunders and Bolli, 1985). Over the past 50 years several publications on Trinidad geology have attempted to address this gap but these largely benefited Neogene strata (Kugler, 1953; Barr, 1962; Kugler and Saunders, 1967; Poole, 1968; Saunders and Kennedy, 1968; Harry, 1992; Algar, 1993; Babb and Mann, 1999; Winter, 2006; Osman, 2007). This chapter reviews the previous interpretations of Paleocene to Early Miocene coarse clastic units and describes the range of lithofacies common to each. Coeval shale-prone environments are also discussed in part as they are important for age and bathymetric control. Interpretations will be given that either agree with, or amend the opinions of previous workers, but ultimately, provide possible solutions for ambiguities associated with interpretations arising primarily from micropalaeontological data. It will be shown that an appreciation of sedimentary processes can taper the emphasis placed on particular beds, bedsets or entire outcrops. These lithological units may prove to be no more than localized and recurrent depositional events common to the overall basin setting, and not associated with rapid shallowing and regional unconformities as often suggested in the Trinidad literature. The following descriptions and interpretations were derived from approximately 672 m of core and outcrop sections ranging from the Chaudiere Formation of Paleocene age to the Herrera Sandstone Member of the Cipero Formation of Early Miocene age (Table 1.1). The facies approach follows that of Walker (1992), Reading (1996) and Posamentier and Walker, (2006), and is described based on physical sedimentary structures, bedding geometry and stacking relationships (facies succession). Further 48 details on the general approach taken for the description of sandstone intervals were described in Section 1.4. Details of biogenic sedimentary structures are described in Chapter 5. Sandstone units will be described in relative superposition and a similar format will be followed for each, with the exception of the San Fernando Formation. For this formation, outcrop descriptions were combined with published literature because of the relative lack of exposures. For the other clastic units, descriptions and interpretations will follow a stratigraphic summary in which age ranges, stratigraphic contacts, and past interpretations (regarding palaeocurrents, palaeoenvironments and general basin setting) will be reviewed. Major facies characteristics and sedimentary processes will then be summarized and conclusions collectively drawn on the facies and sedimentary processes throughout the early Cenozoic. These provide the basis for the interpretation of depositional environments in the following chapter. 2.2 CHADDIIRE AND POINTE A PIERRE FORMATIONS 2.2.1 OVERVIEW OF THE CHAUDIERE FORMATION The geological history of the Chaudiere Formation is closely associated with the Paleocene Lizard Springs Formation as they are considered time and biofacies equivalents (Table 1.1; Bolli, 1957a; Suter, 1960; Kugler, 2001). The formation contains a formainiferal assemblage very similar to the Lizard Springs Formation and the uppermost Guayaguayare Formation (Maastrichtian) characterized by the species Rzehakina epigona (Bolli 1957a; Kugler 1959; 2001; Kaminski et al., 1988). The base of the Chaudiere Formation may even extend into the uppermost Cretaceous based on this similarity (Renz, 1942). Both formations (Chaudiere and Lizard Springs) also appear to have an interbedded relationship (Kugler 1953; 2001; L. Tyson, quoted by Algar, 1993). The Chaudiere Formation rests unconformably upon Lower to Upper Cretaceous rocks (Bolli, 1957a; Kugler, 1959) while the coeval Lizard Springs Formation is also 49 unconformable upon Upper Cretaceous rocks in more northerly exposures but conformable toward the south (e.g. Well Guayaguayare 163, Bolli, 1957a). The Chaudiere Formation has been considered the "neritic" facies of the Lizard Springs Formation (Barr and Saunders, 1968, p. 4), and comprises shales and quartzitic sandstone ranging from thin beds of "fine-grained grit" (Renz, 1942) to thicker graded beds. According to Kugler (2001), the extent and thickness of sandstone increase towards the top of the formation. Algar (1993) excluded the sandstones from his "Chaudiere Formation" and suggested instead that that they belong entirely to a much younger "Oligocene" Pointe-a-Pierre Formation and that their juxtaposition with the shales is fault-related. The formation was assigned a bathyal origin based on its arenaceous benthic foraminifera assemblage (Barr and Saunders, 1968), while agglutinated foraminifera within the Lizard Springs Formation were correlated with upper and middle slope assemblages from California (Kaminski et al., 1988). Kugler (1953) suggested a foredeep 'flysch' origin with associated slope turbidites and Cretaceous olistoliths. The total thickness for the formation was estimated at 600 m (Kugler, 2001). A northerly provenance was proposed for the Chaudiere Formation based on southward interfingering with shales of the Lizard Springs Formation and the assumption of a northern basement high (Senn, 1940; Kugler, 1953; Kugler and Saunders, 1967; Pindell et al., 2005; Higgs, 2006). Algar (1993) suggested that this interfingering merely represented the position of axial turbidity flows within shales of the Lizard Springs Formation with no implication for downstream proximity to source. He preferred a southerly source for the Chaudiere elastics, which was the South American craton. 2.2.2 OVERVIEW OF THE POINTE-A-PIERRE FORMATION The Pointe-a-Pierre Formation conformably overlies the Chaudiere Formation (Table 1.1; Suter, 1960; Kugler, 2001) and is divided into the Pierre Point Sandstone and Charuma Silt members (Kugler, 2001). The latter occurs at the top of the formation and consists of organic silts and shales, with local sandstone beds up to one metre thick 50 (Kugler, 2001). It grades into the Late Eocene Navet Formation (Table 1.1; Bolli, 1957c) with which it shares a greater similarity of fossil fauna than the underlying Pierre Point Sandstone Member (Kugler, 2001). The formation is also unconformably overlain by the Nariva Formation (Waring, 1926; Suter, 1960) and conglomerates of Oligocene age (Kugler, 1959). Thickness estimates for the entire Pointe-a-Pierre Formation range from 90 (Suter, 1960) to 305 m (Liddle, 1946). The basal sandstones of the Pierre Point Sandstone Member are quartzitic, flaggy to metre-scale, often displaying tabular bed geometries. Several workers have also mentioned coarsening and thickening upward bedsets among the sandstones (Illing, 1928; Liddle, 1946; Suter, 1960; Kugler and Saunders, 1967). Suter's (1960) designation of the Pointe-a-Pierre Formation as "controversial" is justifiable based on the different interpretations regarding lithology, depositional setting, provenance and age. A primary cause of this disagreement is the segmented nature of outcrops that have led to their inconsistent designation to the Pointe-a-Pierre Formation. It was not uncommon that beds claimed by earlier workers as part of the formation were later challenged (e.g. Renz, 1942; Liddle, 1946; Kugler, 1956). Individual outcrop segments have been variably interpreted as slumped blocks within younger Oligocene shales (Kugler, 1953; 2001) or as fault-bounded slivers (Liddle, 1946; Algar, 1993) deformed by Central Range thrust or strike slip faulting. There are two schools of thought regarding the depositional environment of the Pointe-a-Pierre Formation: (1) shallow water, shelfal origin (e.g. Illing, 1928; Renz, 1942; Suter, 1960; Algar, 1993) and (2) deeper water, slope to basin floor origin (e.g. Kugler, 1953; Kugler and Saunders, 1967; Tyson and Ali, 1991; Rohr, 1991; Algar, 1993; Kugler, 2001; Pindell et al, 2005; Higgs 2006). Very few workers have critically assessed the environments using lithofacies criteria and even among those (Kugler and Saunders, 1967; Algar, 1993), interpretations have differed. Similar to the Chaudiere Formation, both northerly (Kugler, 1953; Kugler and Saunders, 1967; Kugler, 2001; Pindell et al., 2005; Higgs, 2006) and southerly (Rohr, 1991; Algar, 1993; Punch, 2004; Pindell, 2007) sediment sources were proposed for the formation. Punch (2004) concluded that the sediments were derived from the Guyana Shield to the south based on their textural maturity, and Pindell (2007) used a similar reasoning in suggesting an 51 origin in the Quirequire area of eastern Venezuela, where rocks of similar lithology are found. Dating of the formation has been hindered by a sparse and non-diagnostic faunal assemblage (e.g. Renz, 1942; Van den Bold, 1960) and limited outcrop continuity (e.g. Illing, 1928). It has been variably dated as Cretaceous (Waring, 1926; Illing, 1928), Paleocene to Middle Eocene (Kugler, 1953; Bronniman referenced in Suter, 1960), Lower to Middle Eocene (Liddle, 1946; Van den Bold, 1960; Punch, 2004), Upper Eocene (Renz, 1942) and Oligocene (Algar, 1993). All dates were based on faunal assemblages except the latter, which was based on zircon fission track analysis. For this study, a Lower to Middle Eocene age is assumed for the Pointe-a-Pierre Formation (Table 1.1) constrained by the overlying and partly interbedded Navet Formation with a rich Middle to Late Eocene faunal assemblage (Bolli, 1957c). Outcrop samples for nannofossil analysis proved barren. It is likely that the top is diachronous based on the gradation into the Navet Formation and references that were made to Upper Eocene fauna (Renz, 1942). The following descriptions, figures and interpretations were published previously in Vincent and Wach (2007a). They are repeated here with only a few modifications as they arose initially from this investigation. Contributions by others will be acknowledged accordingly. 2.2.3 FACIES OF THE CHAUDIERE FORMATION Only one facies was recognized among the sandstones of the Chaudiere Formation. Representative sections were described in the eastern Central Range along the Cunapo Southern Road where a large conspicuous roadside boulder is called "Growing Rock" by locals (Figure 2.1), in reference to the supposed "growth" of the boulder over time. On the boulder is the engraving: 52 Figure 2.1 Geological map across the Central Range (light shading in both inset and map) showing Paleocene and Eocene outcrop locations examined for this study. From west: PaP = Pointe-a-Pierre (Bon Accord); SFD = San Fernando (Quenca Street and Mount Moriah); SFR = San Fabien Road quarry; CR = Caratal Road; MR = Morne Roche quarry; TBF = Tormos Brake Factory, Mayo; TBQ = Tabaquite sawmill; ALL = Allen Trace;FR = Four Roads conglomerates; LOS = Los Armadillo junction; MiR = Mitan River; GR= "Growing Rock"; PLM = Plum Mitan orange estate (not Paleocene-Eocene). Map modified after Saunders et al., 1998. 53 "This formation forms the backbone of the hills around Mt. Harris. The clays and sandstones yield an infertile, poorly drained soil, unsuitable for intensive cultivation. This boulder has come from sands that originally collected on an old sea floor, covering the area where you now stand\ The source for the inscription was not stated. Large blocks of very coarse to pebbly sandstone are scattered over the location, separated by several metres of vegetation and soil cover, the largest of which is approximately 15-18 m in height (Figure 2.2 A). It was not obvious whether they represented a continuous succession or a random scatter. Kugler (1953; 1959) interpreted these large boulders as Lower Cretaceous olistoliths into Chaudiere shales ("wildflysch" of Kugler, 1953). Several factors however, do not support these being olistoliths, and they may actually be part of a continuous succession deposited simultaneously with the Chaudiere Formation and later deformed by faulting. Firstly, seventeen planar orientations measured on the faces of seven sandstone blocks around the locality show three consistent groupings (Figure 2.2 E). Two orthogonal sets are interpreted to be structural in origin while the third is similar to one confirmed bedding orientation (25° azimuth—> 58°E). The apparent 'order' between the blocks suggests stratigraphic continuity; a more random orientation would be expected if these were olistoliths. Secondly, the mineralogy of the sandstones is similar to those of the Pierre Point Member of the Pointe-a-Pierre Formation (see Section 6.1.19.1), which supports a "transitional" contact between the two (Kugler, 2001). Thirdly, similar facies occur at other outcrops of Chaudiere Formation that were not mapped as olistoliths by Kugler (1959). 2.2.3.1 AMALGAMATED PEBBLY SANDSTONE (APS) Description This facies was distinguished by grain size, bed thickness, bed contacts and absence of shale. The lithology comprises very coarse to pebbly quartz (to 2cm) within a fine- to medium-grained sand matrix. Beds are typically massive and greater than one metre (up to five metres was measured) with highly irregular bases and localized scours (Figures 2.2 and 2.3). Some thicker beds display parallel stratification of similar appearance to traction carpets (Figure 2.2 D; Lowe, 1982; Hiscott, 1994) and one 55 Figure 2.2 Some characteristics of amalgamated pebbly sandstone facies (APS), (A, B). Photo and line drawing of thick, massive beds of pebbly sandstone. Bedding corresponds to 'c' on plot shown in (E). C) Erosive based, amalgamated pebbly sandstone beds. D) Thick-bedded sandstone with planar stratification at base (parallel to arrow) passing upwards into massive sandstone; 1.5m thickness shown. (E) Strike orientation of several planar faces measured using right-hand-rule from separated blocks across the "Growing Rock" locality. One confirmed bedding orientation is shown corresponding to 'C. 'A' and 'B' are interpreted as associated with conjugate fracture sets. All photos from "Growing Rock" locality except (C) taken from Caratal Road. See Figure 2.1 for locations. 56 instance of normal grading was seen in a 2 m thick bed. Discontinuous, decimetre-scale beds are also common and often truncated by overlying beds. Mudstone beds are either absent or were deposited as shale partings now preserved as millimetre-scale recessive breaks between sandstone beds. This facies was also observed in the Pointe-a-Pierre Formation along Caratal Road and Tormos Brake Factory in the western Central Range (Figure 2.1). Despite the pervasive tectonic fractures at Caratal Road, continuous bedding segments indicate similar facies attributes as observed at "Growing Rock". The lithology is dominated by pebbly to very coarse, quartzitic sandstone with rare interbedded shale. Beds are massive, considerably thinner (decimetre-scale) with highly irregular bases (Figure 2.2 C). At Tormos Brake Factory, pebbly to coarse-grained sandstone forms low scarps approximately 10 m high. The thickness of these scarps can be attributed to amalgamation of the coarse-grained sandstones although it is uncertain how much is juxtaposed because of localized faulting. Shale was not observed among the scarps. Interpretation The very thick beds of pebbly sandstone, rare traction-related sedimentary structures and massive nature of the bedding are similar to the products of sediment gravity flows ("pebbly sandstone" facies of Walker, 1978). These characteristics are comparable to Lowe's (1982) S1-S2 divisions for high-density turbidites, including the multiple irregular contacts interpreted as erosive surfaces and traction-related planar- stratification (interpreted as traction carpets). Lowe (1982) interpreted these divisions to represent deposition from high-density turbidity current through successive stages of sustained bedload traction (traction carpets), and traction plus suspension fall-out of the coarse sediment particles. The limited extent of the amalgamated pebbly sandstone facies, deep erosive surfaces (including scours) and high degree of amalgamation suggest that these are associated with highly erosive, laterally confined, axial flow events. 57 A 18m- FACIES INTERPRETATION Amalgamated pebbly sandstone fades (APS) S2 - S3 sequence. Fig. 2.2 Amalgamated, high-density grain flows deposited during passage of high velocity 2m- surge-type or quasi-steady currents. o-~i n B 12m-J LEGEND Wavy divergent laminae ->-/- Flute cast Wavy parallel laminae V Scour Parallel laminated ^ggr Slump fold Paleocurrent vector Contorted bed/ V m~ laminae Trace fossil •SSSl. Amalgamated pebbly & Planar cross beds sandstone fades (APS) I Fining upward M Mudclast Current ripple G Rotated block Climbing ripples ® Sample 5048 number Traction carpets """_•> Lenticular APS Fades acronym '.ZZ bed geometry Channelized I Bedding detail I sands 2m- missing section or outcrop Figure 2.3 Graphic sedimentary logs of amalgamated pebbly sandstone facies of the Chaudiere formation. Note thick, amalgamated, coarse-grained beds (A) and multiple erosional surfaces (B) that are characteristic of this facies. Both logs were derived from the "Growing Rock" locality. 58 2.2.4 FACIES OF THE POINTE-A-PIERRE FORMATION 2.2.4.1 TABULAR SANDSTONE (TS) Description This facies was distinguished by bed geometry, grain size and bioturbation. Nine metres of interbedded sandstone-siltstone-shale were measured at an abandoned quarry along San Fabien Road, western Central Range (Figures 2.1 and 2.4). Grain size ranges from silt to fine-grained sandstone within beds up to 80 cm thick. Beds display tabular geometry, with no changes in thickness over their exposed length. Thicker beds are massive with flute casts at the base (Figure 2.5 D) and are often capped by a few centimetres of parallel or wavy laminae. Thinner beds are either parallel or wavy laminated throughout, the latter occurring with higher silt content. Most beds are overlain by a silt drape that is commonly bioturbated. Lower bed contacts are either undulatory, indicating some amount of localized scouring, or planar. Shale occurs as thin, parallel-laminated beds often with interlaminated current-rippled sand. The sandstone-shale ratio of this facies at San Fabien Road is approximately 1:1. This facies is also common among beds at Mt. Harris in the eastern Central Range (Figure 2.1) where it is found in association with beds of the "lenticular sandstone" facies (described below) in a generally shale-prone interval (Figure 2.6 A-D). Sandstone bedsets occur with individual beds displaying planar bed boundaries and either separated by shale partings or with sand-on-sand contacts. There is no change in bed thickness over the exposed length of most of the beds. The lower bedset surface may show local erosional scours (Figure 2.6 A). This facies is commonly bioturbated and trace fossils are preserved in positive relief along bedding planes or within the thin silt drapes overlying sandstone beds (see Section 5.1). It was also recognized at other outcrops across the Central Range, including the grounds of the Geological Lab at Pointe-a-Pierre and Tamana Road Junction near Los Armadillos (Figure 2.1). 59 Interpretation The tabular sandstone facies is interpreted as low and high-density turbidites (Bouma, 1962; Lowe, 1982) as evidenced by bed transitions upward from massive to parallel and wavy laminae (Ta-Tb, Ta-Tc-Td of Bouma, 1962; S3 of Lowe, 1982). The flute casts and localized scours also provide evidence of turbulent flows. The lack of evidence for erosion at bed bases suggests that these beds are mainly "depositional" in character (i.e. not associated with significant erosion and bypass, Mutti and Normark, 1987) while the tabular geometry suggests relatively unconfined flow when compared to the amalgamated pebbly sandstone facies. The tabular sandstone facies is interpreted to represent a distal or off-axis facies relative to the amalgamated pebbly sandstones based on bed continuity, higher shale content, lower amount of bed amalgamation, finer grain size and degree of bioturbation. 2.2.4.2 MASSIVE THICK-BEDDED SANDSTONE (MTBS) Description This facies was differentiated by thick beds of massive and less commonly, gradational, coarse-grained sandstones. Bed thicknesses generally do not attain the dimensions of the amalgamated pebbly sandstone facies and grain size is not as coarse (mainly coarse-grained). It is typically found in association with other facies and commonly interbedded with shale. Two localities are now described. Seven metres of massive thick-bedded sandstones were measured at San Fabien Road quarry (Figure 2.4). These beds incise into the tabular sandstone facies and are also capped by them. Above the incision, individual beds up to 120 cm thick of poorly sorted, very coarse sandstone occur. Bed contacts are sharp with local evidence for scours (mud rip-up clasts). The top of one bed contains 15 cm of wavy-parallel, low-angled laminae overlain by trough cross-stratification. These sandstones continue on a strike for 30m before bed thinning, shale intercalation and deformed beds occur toward the margin (south) of the outcrop (Figures 2.4, 2.5 B and 2.7). The thicker coarse-grained beds are also associated with planar stratified, medium- and fine-grained beds, with individual 60 FACIES INTERPRETATION 17m S1 - S2 - S3 - Tt sequence. Deposited from high density grain and liquified flows. Low density turbidity currents were } Massive thick-bedded of lesser importance. sandstone facies (MTBS) Discordant sandstone Subaqueous slide and and shale facies (DSS) downslope creep with minor cohesive flows. Tabular sandstone As below facies (TS) Processes as described above with evidence for channelized flow. Massive thick-bedded sandstone facies (MTBS) Fig. 2.6 S3 - Tt and Ta-Tb-Tc-Td. High 2m- density fluidized flows and low Bioturbation index density turbidity currents. A=abundant Tabular sandstone Ocommon Interbedded high and low density R=rare facies (TS) turbidites. Figure 2.4 Graphic sedimentary logs showing facies and interpretations for sandstones within the Pointe-a-Pierre Formation. Two correlative logs (A - A') are shown that illustrate both intrastratal deformation and conformable strata as part of the complete succession. Also see Figure 2.7 for a wider cross section and Figure 2.3 for key to symbols. Section fromSa n Fabien Road locality. 61 Figure 2.5 Facies characteristics of the Pointe-a-Pierre Formation at San Fabien Road. A) Rotated, thick-bedded sandstone of discordant sandstone and shale facies (DSS). Shale wedges are highlighted. B) Dashed line separates massive thick-bedded sandstone (MTBS) channel fill above from tabular sandstone facies (TS) below. C) Folded strata. Fold limb (highlighted) goes from discordant to concordant with beds below. D) Flute casts on the base of a bed within the TS facies. 62 25m Figure 2.6 Tabular sandstone (TS) and lenticular sandstone (LS) facies of the Pointe-a-Pierre Formation. A) Tabular sandstone beds overlying silty, low-density turbidites. Only the lowest sandstone bed is erosive; note scour behind hammer. B) Thick beds of fine-grained turbidites with interbedded shale that likely represent amalgamation of lower density turbidites. C) Alternating thick and thin fine-grained turbidites with tabular bed geometries. D) Close-up view of parallel and ripple-stratified sandstone. E) Outcrop cross section illustrating lenticular geometries and oblique stacking of coarse-grained sandstones within the LS facies. A-D from Mt. Harris, E from Tabaquite Sawmill. 63 beds in the range from 1-7 cm; one bedset is up to 40 cm and comprises 11 thin beds with planar contacts, subsequently overlain by a 1 m thick massive sandstone bed (14-15 m in Figure 2.4). Laminated shale beds barren of microfossils, with thin, lenticular, rippled sandstones, are interbedded with the massive sandstone. One shale bed is intruded by decimetre-scale sand dikes sourced from the massive sandstone bed below. At Tormos Brake Factory, this facies occurs as very coarse-grained, quartzitic beds up to 2 m thick (Figure 2.8 C). Bed transitions occur from erosive-based, massive sandstone upward to parallel and cross-stratified sands. Some beds show no obvious gradation or internal amalgamation surfaces. Shale occurs both as thin (25 cm) silty mudstone between sandstone and as rip-up mudclasts at the base of beds. At all localities, bioturbation is rare and of a restricted trace assemblage along the tops of sandstone beds; this also distinguishes this facies from the amalgamated pebbly sandstones. Traces comprise a range of grazing and dwelling. This facies can also be studied at Allen Trace (3 m-thick bed) and eastern Mount Harris in the middle and eastern Central Range, respectively (Figure 2.1). Interpretation The assemblage of sedimentary structures and bedding character is comparable to that described for high-density suspension and grain flow turbidites (Lowe, 1982, S1-S2- S3-Tt divisions). This is evidenced by the coarse grain size and thick, massive beds. The sand dikes occurred in response to sediment loading by the overlying turbidites. The thin, planar-stratified beds are interpreted to be deposited from combined grain flow aggradation and suspended sediment fallout. They are analogous to the traction carpets described for the amalgamated pebbly sandstone facies. The incision below the thick- bedded, coarse-grained sandstones at San Fabien Road and their lateral thinning and deformation suggest that these are relatively confined turbidite fills, likely related to the axial portion of channels. Relative to the fine-grained tabular sandstones, the frequency of turbidite events was sufficiently higher to create a restrictive environment for organisms. 64 2.2.4.3 DISCORDANT SANDSTONE AND SHALE (DSS) Description This facies was distinguished by localized deformation among bedding adjacent to apparently conformable strata. Fifteen metres were measured at San Fabien Road quarry where discordant sandstone beds up to 3.75 m thick rest upon deformed shale (Figures 2.4, 2.5 A and 2.7). Shale-prone beds are wedged between the thick sandstones and contain both deformed shale laminae and thin sandstones. Two partially preserved localized folds are also associated with these beds. In one example, the fold limb displayed a transition from overturned to conformable (Figure 2.5 C). Both fold axes are oriented NE-SW, perpendicular to the palaeoflow direction inferred from flute casts (N- NW). The overfold direction could not be determined from the remnant fold limbs. The sandstone and shale beds of this facies show similar characteristics to other facies. The sandstones are quartzitic, very coarse-grained and massive with scattered mud clasts throughout. Flutes are present at their base along with traces of Chondrites and Planolites. Thinner (up to 50 cm), fine- to medium-grained sandstone beds associated with the fold limbs are of similar aspect to the tabular sandstone facies. Localized folds and deformed beds of this facies were also seen along the Mitan River traverse, just above the contact between Chaudiere Formation shales and Pointe-a- Pierre Formation sandstones (Figure 2.1, Appendix 1). There, thin and deformed sandstone beds and folded and overturned strata can be discerned among the poor exposure of Pointe-a-Pierre Formation elastics. A thin (<2 m) matrix-supported conglomerate with cobble-sized clast of coarse-grained sandstone is also exposed among the deformed beds. Interpretation Bed rotation and sliding is evidenced by the discordance between sandstone beds and deformed shale wedges at San Fabien Road. Together with the localized folds at Mitan River, they suggest substrate instability and downslope creep. The thick-bedded sandstone beds at San Fabien Road are likely not far removed, as they are similar to the massive thick-bedded sandstone facies nearby. The finer grained sandstone and 65 Figure 2.7 Strike and dip stratigraphic cross-sections from the San Fabien Road location. The inset map shows the relative location of measured sections (numbered on cross section) and the palaeocurrent orientation of the sandstones. Collectively, stratal relationships at the outcrop show coarse-grained turbidite channel fills (MTBS facies) incised into finer grained turbidites and shales (TS facies). Inter- stratal folding, deformed and rotated beds (DSS facies) provide evidence for gradient-induced instability and deformation. Note the change of scale between strike and dip sections. 66 27m- FACIES INTERPRETATION LEGEND £gs Wavy divergent laminae F^" Flute cast S3? Wavy parallel laminae -w Scour Parallel laminated *g%*-Slump fold Paleocurrenl vector Contorted bed/ V nss~ laminae fr Trace fossil **&. Planar cross beds ? Fining upward M Muddast .-rO Current ripple C* Rotated block ^-®- Climbing ripples Sample 5048 number ^Sl Traction carpets ,.- > Lenticular APS Fades acronym bed geometry Channelized ' Bedding detail 1 sands missing section or outcrop .---.--:;=©' 0 HV602B • Lenticular sandstone Ta-Tb-Tc-Td-Te (Bouma) with (LS) minor S2 - S3 - Tt (Lowe). Low density fluidized and turbidity currents with subordinate high- density grain flows. Non-amalgamated turbidites. «=.-:=.* Jit 8m- t& Massive thick- B (? Vbedded i!lIs J 'sandstone 5m— ^is^n (MTBS) Fig. 2.6E Lenticular sandstone 2m- 2m— (LS) Figure 2.8 Graphic sedimentary logs illustrating lenticular (A, B) and massive thick-bedded (C) sandstone facies of the Pointe-a-Pierre formation with interpretations. A) is a composite log from Chaudiere River, Mt. Harris. B) Lenticular sandstone from exposure at the Tabaquite Sawmill, Tabaquite. (C) Erosive-based graded beds and massive sandstones from Tormos Brake Factory, Mayo. See Figure 2.4 for interpretations of the MTBS facies. 67 laminated shale beds were likely in situ and provided detachment surfaces upon which the sandstone blocks moved, and was subsequently deformed by the sliding blocks. The orientation of the fold axes at San Fabien Road, perpendicular to the inferred palaeocurrent direction, suggests downslope slide movement. The matrix-supported conglomerates at Mitan River provide evidence for cohesive flows associated with this facies. The reference to "slump structures" among the "characteristic features" of the Pointe-a-Pierre Formation (Kugler, 2001 p. 191) suggests that other occurrences of this facies have been observed. 2.2.4.4 LENTICULAR SANDSTONE (LS) Description This facies is distinguished by the lenticular geometry of sandstones (Figure 2.6 E and 2.8). Seventy metres of section were measured on the southwest flank of Mount Harris (Figure 2.1). Sandstones are predominantly fine-grained with bed thicknesses up to 50 cm. Beds are typically massive or parallel laminated, some displaying an upward gradation to wavy ripple-laminae (Figure 2.6 C, D). Rare flute casts were observed at bed bases. Individual sandstone beds pinch-out laterally over a range of centimetres to tens of metres within shale-prone bedsets. These beds exhibit a lenticular geometry, irrespective of bed thickness (Figure 2.6 E). The sandstone-shale ratio for the measured section is 1:4. Grey, silty shale beds displaying parallel to gently wavy contacts are interbedded with parallel laminated, foraminifera-bearing3 shale. Shales are bioturbated with common Chondrites traces. This facies also occurs at the Tabaquite Sawmill, Tabaquite (Figures 2.6 E and 2.8 B) where lenticular, coarse-grained beds are encased in laminated shale. The thickest bed (2 m) thins to 0.25 m over a distance of 10 m overlying a non-erosive base. Above this bed, a second sandstone lens is obliquely stacked and separated by laminated shale. Benthic foraminifera was derived from shale samples in this facies; palaeobathymetric interpretations arising from these are discussed in Chapter 3. 68 Interpretation The massive and graded beds, flute casts and sequence of sedimentary structures iare interpreted to be low-density turbidites interbedded within fossiliferous shales. The beds are characteristic of Bouma Ta-Tb-Tc-Td intervals for turbidites. The laminated, fossiliferous shales represent background sedimentation more characteristic of Bouma's Te interval. The rapid lateral thinning of the lenticular sand bodies suggests that they were deposited from relatively confined flows although their non-amalgamated and non- erosive character does not suggest long-term and dedicated flow pathways (such as channels). The lenticular beds are interpreted as depositional in character, and their geometries and stacking (e.g. Tabaquite Sawmill) likely reflect the local pre-depositional topography. Individual flows simply draped and filled the local relief that was created by previous erosive episodes. With this interpretation, the associated flows are relatively unconfined and likely represent the distal or off-axis equivalent of more dedicated flow pathways. The tabular sandstone beds (TS facies) that are associated with this facies also display a depositional character but were likely associated with higher rates of sedimentation or closer proximity to the flow axis. 2.2.5 FACIES SUCCESSION IN THE POINTE-A-PIERRE AND CHAUDIERE FORMATIONS The lack of continuity between outcrops precludes a direct reconstruction of lateral and vertical facies stacking patterns. The amalgamated pebbly sandstone facies of the Chaudiere Formation must be assigned to the base of the succession by virtue of its age (Kugler, 1959; 2001) and according to Kugler (2001), this facies is transitional upwards into sandstones of the Pointe-a-Pierre Formation (Figure 2.9). This facies was observed below beds of the lenticular sandstones facies along the Chaudiere River traverse in Mount Harris (Appendix 2), although the structural dips between the two suggest a more complicated relationship that could not have been resolved with the existing exposure. The discordant sandstone and shale facies occurs above the contact between the Chaudiere and Pointe-a-Pierre formations along the Mitan River tributary 69 FACIES FACIES ASSOCIATION •Lenticular sandstone VII. Lenticular and tabular •Tabular sandstone sandstones •Tabular sandstone II. Channelized and deformed thick- • Massive thick-bedded bedded and tabular turbidites sandstone •Discordant sandstone and shale A o, conglomeratecongioi s •Amalgamated pebbly I. Granule-sized, amalgamated and sandstone thick-bedded sandstones Cretaceous olistostrome Figure 2.9 Proposed facies succession for the Chaudiere and Pointe-a-Pierre formations. The conglomerates were reported by Liddle (1946) while olistostromes were reported by Kugler (1953). These were not validated during this study. The facies associations consider field relationships between facies and are discussed in greater detail in Chapter 3 where depositional environments are considered. 70 (section 2.2.4.3 above; Appendix 1), overlying a shale prone Chaudiere Formation (several metre-scale blocks of quartzitic sandstone also lie along the riverbed within the Chaudiere Formation; it is unknown how many of these were in situ). This contact suggests that the discordant sand and shale facies may also occur relatively low in the facies succession from the Chaudiere to Pointe-a-Pierre Formation. Liddle (1946) reported cobble conglomerate beds similar to the Plaisance Conglomerate of the San Fernando Formation (discussed in Section 2.3.3.1) in the basal section of the Pointe-a- Pierre Formation and this may also be a characteristic feature near the base of the succession. At San Fabien Road quarry, discordant sandstone and shale facies are interbedded with massive thick-bedded and tabular fine-grained sandstone facies (Figure 2.7). The 34 m of vertical section at that outcrop demonstrate the interbedded nature of discordant strata (DSS facies) with channelized turbidite fills (MTBS) and the off-axis fine-grained sandstones (TS). The lenticular sandstone facies is the dominant facies in the youngest beds exposed near the top of Mt. Harris and may occur near the top of the succession on this basis. It is associated with tabular sandstone bedsets (TS) and a few interbeds of the massive sandstone (MTBS) within a shale-prone interval. It may also overlie the amalgamated pebbly sandstone facies based on the tentative relationship mentioned above. The facies succession proposed defines an overall fining-upward for the Chaudiere and Pointe-a-Pierre formations (Figure 2.9). 2.2.6 PALAEOCURRENTS FROM THE POINTE-A-PIERRE FORMATION Palaeocurrent measurements were obtained from flute casts, scours and ripple crests within the Pointe-a-Pierre Formation (Figure 2.10). Measurements derived from flute casts vary over a 72-degree azimuth and suggest palaeoflow towards the north and west. A more northerly component is favoured by flute cast measurements derived from the in situ massive thick-bedded sandstones (n = 3) (Figures 2.4 and 2.7). Measurements from longitudinal scours and ripple crests suggest palaeocurrents oriented approximately NW-SE. Collectively they suggest a northwest-directed palaeoflow. 71 Figure 2.10 Palaeocurrent measurements within Pierre Point Sandstone Member, San Fabien Road quarry. Arrows in each panel show the interpreted paleocurrent orientation. A) Flute casts suggest palaeoflow towards 347° azimuth if WNW reading is ignored (taken from rotated block); n=4. B) Longitudinal scours; n=2, one measured, one approximated. C) Ripple crests on top of massive sandstone bed. D) Slump fold axes; n=2. E) One of the flute casts (FC) referred to in (A) at the base of a massive sandstone bed. F) Longitudinal scour at base of massive sandstone bed referred to in B above. The value of these palaeocurrent measurements is limited by the poorly understood structural history of Paleogene sediments across the Central Range, but they still provide some constraint on the direction of sediment transport. On the assumption that rotations about a vertical axis were not in the order of 180 degrees, the measurements from flute casts suggest that a southerly to easterly source of sediments was more likely than a northern source. 2.2.7 INTERPRETED SEDIMENTARY PROCESSES The limited suite of sedimentary structures within the Chaudiere and Pointe-a- Pierre formations is consistent with sediment gravity flow models in deep water systems (Figure 2.11). Most sandstone beds are either massive or parallel laminated and 72 commonly capped by ripple cross-laminae. Thicker, coarser grained beds are comparable to S2-S3 sequences of Lowe (1982) in both character and scale, while upper bed segments are characteristic of Lowe's Tt interval (see Figure 1.6). Finer grained intervals range from massive to graded bases upwards to parallel laminated and wavy rippled character, overlain by non-fossiliferous, bedded shales, and these are comparable to the Bouma Ta-b-c-d intervals for turbidites (Bouma, 1962). Massive sandstone of a range of thicknesses and grain sizes is the most characteristic feature and was also recognized by previous workers (Kugler and Saunders, 1967; Algar, 1993; Punch, 2004). The sequence of sedimentary structures associated with coarse-grained massive sandstone intervals is comparable to the S2-S3-Tt sequence of Lowe (1982) for high-density sediment gravity flows. Lowe (1982) interpreted these sequences as evidence for high velocity grain flows at the base (planar stratified bedsets) followed by high suspension fallout rates and traction reworking of bed tops by waning turbidity currents. Matrix-supported conglomerates as seen at Mitan River provide evidence for cohesive sediment gravity flows characterized by internal matrix strength and plug-like movement, capable of transporting sediments up to boulder dimensions. The main sediment support mechanism is provided by matrix strength and the dispersive pressure resulting form particle collisions, with the entire mass undergoing cohesive freezing once stress conditions change (Kuenen, 1956; Lowe, 1982), as can occur with a reduction in slope gradient. Figure 2.11 Summary of sedimentary structures and interpreted bed divisions in the Chaudiere (A, B) and Pointe-a-Pierre (C-F) formations. Divisions are based on Bouma (1962) and Lowe (1982). See Figure 2.8 for key to symbols. 73 2.2.8 AN ALTERNATIVE TO HUMMOCKY CROSS-STRATIFICATION Algar (1993) did not consider the assemblage of sedimentary structures to be "classic turbidites" and suggested that storm and shelf related processes might have been active during deposition of the Pointe-a-Pierre Formation. He recognized similar features to Kugler and Saunders (1967) in addition to channelized scours, dewatering features, sand dykes, symmetrical ripples and dune-scale cross bedding. He concluded that storm and shelf-related processes were dominant for three of the outcrops he reviewed and sediment gravity flow processes for one. Storm-shelf processes were attributed to the "interlaminated" nature of sandstones and mudstones, textural maturity as evidence of reworking, Thalassinoides traces, symmetrical-rippled sandstones and an occurrence of low angle cross laminae within coarse sandstone, interpreted as hummocky cross- stratification (HCS). These provide insufficient support for active storm or shallow water processes within the Pointe-a-Pierre Formation. The most convincing evidence was the abundant symmetrical ripples and trough cross-stratified sandstones described from Plum Mitan, a locality to the southeast of Mt. Harris (Figure 2.1). That outcrop, however, is not part of the Pointe-a-Pierre Formation (see Section 2.6). Correlation of Algar's section at San Fabien Road quarry (Algar, 1993, Figure 2.49 at 3.8 m) with sections from this study (see cross-beds below datum horizon in Figure 2.7) allowed a review of the HCS horizon. The correlative horizon contained low- angled, wavy- and trough-cross-stratification at the top of a massive sandstone bed within fine- and coarse-grained sandstone (Figure 2.11 and 2.12). HCS is a very unstable structure in the coarse sand size range where they form within a narrow orbital velocity window and are unlikely to be preserved with waning currents (Dumas et al., 2005). This likely explains why they are found primarily within silt to fine sand-sized sediments in ancient environments (Dott and Bourgeois, 1982). Structures of similar appearance are however common to turbidite sequences in deep water environments formed by other processes. They exist in turbidites of the northern Apennines, Italy, where they likely resulted from high velocity tractive currents and antidune bedforms (Mutti and Ricci Lucchi, 1978). Eschard et al. (2004) identified similar undulating laminae sets with 74 ^-JU-- ==^""\ j i S3 1 D Figure 2.12 Photos (A, B) and line drawings (C,D) of a variably cross-stratified interval and their suggested classification. Both images provide a different view of the same interval, tens of centimetres apart. Cross-stratified sets include trough, parallel and wavy laminae. The cross-stratification is equated to the Tt division of Lowe (1982) and was likely related to the passage of high-density turbidity currents as opposed to storm processes (HCS) as previously suggested (discussed in text). Grain size is shown for 'A'. 75 metre-scale wavelengths at the top of massive and normally graded sandstone in the Pab Sandstone, Pakistan. They termed the structures "pseudo hummocky cross-stratification" and differentiated this from normal HCS beds on the basis of poor sorting, absence of associated oscillatory ripples and its coarse grain size. Larue and Provine (1988) found similar structures within "outer fan" to "basin plain" turbidite facies of the Scotland Formation of Barbados, which they attributed to "fluidization". The bed described by Algar (1993) is analogous to "pseudo hummocky cross-stratification". It overlies massive, coarse-grained sandstones formed by suspension settling and grain flow from collapsing turbidity currents. The top of the bed was more likely reworked by boundary stresses associated with the passage of this current and not by oscillatory storm currents, for which no other associated structures were seen. The interlaminated nature of sand and shale is insufficient evidence to support a shallow water interpretation, and Thalassinoides traces have a wide palaeoenvironmental occurrence, not restricted to shelf environments. There is no conclusive evidence for shallow water wave reworking within the Pierre Point Member of the Pointe-a-Pierre Formation. 2.3 SAN FERNANDO FORMATION The San Fernando Formation is arguably the most enigmatic of the Paleogene formations and is unique in many respects. Apart from the wide variation in lithology, the stratigraphic relationships between its members and their palaeoenvironmental significance have been actively debated in the biostratigraphic literature (Eames et al., 1962; Jenkins, 1964; Eames et al, 1965; Blow et al., 1968; Stainforth, 1968). It has a wide variety of faunas relative to other Paleogene formations including abundant reworked foraminifera and shallow water reefal assemblages (Vaughan and Cole, 1941; Bolli, 1957c; Eames et al., 1962; Jenkins, 1964), all bounded at its top and base by bathyal shales with rich planktonic foraminifera assemblages. Inevitably this has led to assumptions of basin shallowing and emergence in the Trinidad area (Illing, 1928; Liddle, 1946; Stainforth, 1948; Kugler, 1953; Van Den Bold, 1960; Stainforth, 1968; 76 Kugler and Caudri, 1975; Algar, 1993; Kugler, 2001), although there has been some debate on the timing of such an occurrence (Eames et al., 1962; Blow et al., 1968; Stainforth, 1968). Can these assumptions and interpretations of rapid emergence and subsidence be sustained? Most workers considered the "shallow-water" sediments to be autochthonous, although there are some indications that this may not be the case. All of these factors have contributed to the enigma that is the San Fernando Formation, and it is unfortunate that the formation is also among the least exposed and accessible for study. The lack of exposure meant that a thorough review of the literature was necessary to critically assess the lithological variations, sedimentary processes, ages and palaeoenvironmental significance of the formation. The discussion that follows is not intended to be an exhaustive review, as the formation is described in great detail by Kugler (2001) and references therein. Instead, the discussion will expand on some of the topics mentioned above with a bias towards the stratigraphic and lithofacies character of the formation and its members. This will be supplemented by descriptions from one of the exposures along with faunal and mineralogical analysis from various lithological units (Section 6.1.12). These form the collective basis for the conclusions that follow, regarding the sedimentary processes, facies relationships and palaeoenvironment associated with the formation. 2.3.1 OUTCROP DISTRIBUTION Apart from the Late Eocene Navet Formation, the San Fernando Formation has among the smallest mapped outcrop extent relative to other Paleogene Formations, being restricted to its para-type4 locality at Mount Moriah in the western Central Range along the northern flank of San Fernando Hill (Figure 2.1, Appendix 3). Other 'exotic' outcrops also occur in the western Central Range (Plaisance Conglomerate and Morne Roche Limestone) and on Soldado Rock, an island off the southwest peninsula of Trinidad (see Figure 1.1 for location). These 'exotics' are either the "rootless masses" of 4 Kugler (2001) refers to the Mount Moriah outcrops of the San Fernando Formation as a "para-type". A para-stratotype is designated to illustrate features of a formation that are not evident at the original type section (Salvador, 1994). The abbreviated form "para- type" will be used as done by Kugler, 2001. 77 Kugler (1953, p. 244), ascribed a sedimentary origin, or are bounded by faults (Waring, 1926; Algar, 1993; 1998) within Oligo-Miocene shales. The para-type section lies within the densely urbanized area of San Fernando where exposures allowed only for the collection of samples (details are provided in the relevant sections). Similarly, the 'exotic' outcrops are now either depleted from mining or covered by vegetation. It is possible that there are correlative outcrops of the San Fernando Formation toward the east of the Central Range as suggested by Bramine Caudri (cited by Kugier, 2001, p. 207), and stratigraphic equivalents have been drilled in the subsurface both to the east and west of the Central Range (Dempsey, 1971 (Well Pointe-a-Pierre-1); Carr-Brown et al., 2000 (Kitchener-1); Kugler, 2001, p. 211 and 177; Evans and Mettes, 2002 (Crapaud- !))• 2.3.2 MEMBERS OF SAN FERNANDO FORMATION The base of the formation is unconformable over the Navet and Lizard Springs formations at its para-type locality (Waring, 1926; Bolli, 1957c; Kugler, 1996, Enclosure 10; Kugler, 2001), but conformable contacts occur away from the town of San Fernando (e.g. Well Rochard-1, see Blow, 1955). A conformable contact with the Pointe-a-Pierre Formation was also reported by Liddle (1946). The formation is overlain by the Cipero Formation where both unconformable (Liddle, 1946; Kugler referenced in Van Den Bold, 1960; Eames et al., 1965; Saunders et al., 1998) and conformable (Stainforth, 1948; Bolli, 1957a; 1957c; Stainforth, 1968) relationships were reported. At least 245 m (800 ft) of the formation was drilled in well FW 214 southwest of Mount Moriah (Kugler, 2001, p. 177), and this is the largest reported thickness for the formation. It is divided into four members based on lithostratigraphic criteria, while several lithologic units have been assigned to the formation based on their ages, lithology and faunal content. The members of the formation are: Mount Moriah Glauconitic Sandstone, Mount Moriah Calcareous Silt, Vistabella Limestone and Vistabella Marl. Lithologies include glauconitic clays, quartzitic and glauconitic sandstones and conglomerates, fossiliferous 78 and calcareous silts, orbitoid-lepidocyclina-nummulitic beds and reefal limestones (Kugler, 1936; Vaughan and Cole, 1941; Stainforth, 1948; Suter, 1960; Kugler and Caudri, 1975). Much of the uncertainty that surrounds the formation stems from the range of ages for its members derived from faunal assemblages. There was a general consensus that the Mount Moriah Glauconitic Sandstone Member is of Late Eocene age, but the ages of the Mount Moriah Calcareous Silt Member and conglomerates associated with the formation were contentious (Eames et al., 1962; Blow et al., 1968; Stainforth, 1968; Van den Bold, 1960; Kugler, 2001). For this study, the nannofossil assemblage derived from a sample of calcareous shale on Quenca Street in San Fernando (Southern Medical Clinic building) (Figure 2.1, Appendix 3) indicates a late Middle Eocene age (NP16-NP17, Martini, 1971) for the formation. This was based on the co-occurrence of Cribrocentrum reticulatum and Chiasmolithus grandis (late NP 16 - NP17) and the presence of Campylosphaera dela, whose extinction point may be close to the NP 16 - NP 17 boundary (analyses by Jason Crux (2006) of Biostratigraphic Associates, Canada). The Middle Eocene age derived from calcareous nannofossils suggests equivalence to sandstones of the Pointe-a-Pierre Formation, although the nannofossils could be reworked specimens, as this commonly occurs in the San Fernando Formation. 2.3.2.1 MOUNT MORIAH SANDSTONE MEMBER (MMGSM) The Mount Moriah Sandstone Member5 (Saunders et al., 1998) was described from its para-type section at Mount Moriah. Kugler (1996, Enclosure 10) provided the most detailed description of the member where a total of 25 m (83 ft) of section was measured, of which 13 m (43 ft) was described (Figure 2.13 C). From Kugler's descriptions, the Member consists primarily of thin-bedded, friable or indurated, glauconitic and calcareous sandstone. Grain size ranges from fine- to coarse-grained with occasional pebble-sized clasts of calcareous mudstone (marl). Intrastratal "slumping", "massive" intervals and "undulating bedding plane" were also noted. 5 "Mount Moriah Glauconitic Sandstone Member" of Kugler, 2001. 79 Figure 2.13 Schematic illustrations of the most detailed lithological descriptions of the San Fernando Formation from published literature. All are from the para-type locality, Mount Moriah. Collectively, the illustrations demonstrate 'fining-upward' lithologies unconformably overlying Paleocene-Eocene bathyal shales. Their descriptions suggest that multiple conglomerate horizons exist, and may be gradational into sandstones. It is not known how fer apart these descriptions were made. The thicknesses and names shown are from the original authors, except where in brackets. Kugler's descriptions contain no indication of cross bedding, ripples or other traction- related sedimentary structures. Waring (1926) also described sandstones from the same locality under his "Mt. Moriah Formation", a term that is now obsolete (Kugler, 1956). He noted the fine grained, quartzitic nature and compared the sandstones to finer grained beds of the Pointe-a-Pierre Formation (Figure 2.13A). Illing (1928) mentioned the laterally discontinuous nature of sandstones, "variable" thickness of sand beds (one described as "six feet thick") and "patchy" basal conglomerates with Cretaceous boulders. This also matches the interpretation of "rapid variations of sedimentation both laterally and vertically" of Blow et al. (1968 p. 176) for the same locality. 80 The basal contact at the para-type location consists of a sandstone bed in unconformable contact with marls of the Navet Formation. "Pebbles and fragments" of Paleocene-Eocene Navet and Lizard Springs formations are present within the basal strata (Kugler, 2001). The top of the member is unconformable below conglomerate beds of the Marabella Conglomerate Member (Figure 2.13 C). Collectively, these descriptions suggest the existence of fine-grained, lenticular sandstones and massive sandstone beds, some attaining considerable thickness, in the Mount Moriah Sandstone Member. These beds appear to be of similar lithology to beds of the Pointe-a-Pierre Formation. 2.3.2.2 MOUNT MORIAH CALCAREOUS SILT MEMBER The Mount Moriah Calcareous Silt Member was described from borehole cores in the vicinity of Mount Moriah. It consists of dark grey, calcareous, sandy siltstone (Waring, 1926; Bolli, 1957c) and some workers divide it into lower non-calcareous and upper calcareous zones (Van Den Bold, 1960). Interbedded glauconitic sand lenses and "thick layers of friable sandstone" (Kugler, 2001) also occur. Lenticular "orbitoid masses" may also be a common component of the silts (Figure 2.13 A, B). It is apparent that the Mount Moriah Calcareous Silt Member is a recurrent lithology throughout the formation, but referenced by a variety of litho- and stratigraphic names by different authors (Figure 2.14). North of Mount Moriah, the base of the siltstones rests unconformably upon lower Navet Formation (Figure 2.14 D) but this simple relationship is complicated where other lithologies also occur. According to Eames et al. (1962, p. 78), the "Mount Moriah silts" overlie the "San Fernando conglomerates", while other descriptions suggest that the siltstones may overlie the Mount Moriah Sandstone Member (Waring, 1926; Illing, 1928). The top of the member is similarly varied with its fauna and lithology transitioning into silts of the overlying Cipero Formation (Stainforth, 1948; 1968; Bolli, 1957c; Eames et al, 1962), while an unconformable relationship was proposed based on a "block conglomerate" interpreted to represent the base of the Oligocene Cipero Formation. (Figure 2.14 E). The member is rich in calcareous and arenaceous planktonic and benthic foraminifera, although their distribution is variable among the abundant shallow water 81 EPOCHS PtanMonle foramtfinefa zones Time (Gradslsln el. a/., (after Saunders and Bollj, CONFORMABLE UPPER CONTACT UNCONFORMABLE UPPER CONTACT 1B85; equated to Martini torn (Ma) 2004) Befggren, 1985). Kugterto EameseM, (1962:1965; 1968) WaKCatyx-59 Van den Sold, (19601 Kugter(1996, Bdfl(1957b,c) • Van DOT Bold (I960) • SWardrth (1966) I (Kuoler, 2001) glow (1969): Eamee I glow, (1966] enclosure 10) Saunders eta/.. {1998) 22- GbborotaHa kugleri 2 lit 24- GkMgerma AA ciperoensis Mount Moriah Silt Mbr. cipemensis 26- Non-deposition may extend into CIPERO GROUP theAouitanlan 28- Gbborotalia opima VMarabeBa . congtamerate • op/ma Cipero "Unver Cipero... CIPERO SUf GROUP 30- \ Cipero s "Mount V ** San Fernando ^ (Gtobfferina aropfaperturaj Moiiah v Formation "Upper N CIPERO GROUP sat % Mount MoriahSBT > Mount ^ "Block Member" X (calcareous) Morton N, conglomerate" 32- Cassigerinella Calcareous chipdensis/ snt Hasligerina micra ML Moriah sat Mbr. 00 Vistabalfa Hmestone "Conglomemtes, 34- San Fernando Formation Ml Moral) Globomtalia san*tor!«...biohermal Silt Mix V^belSmiestone^'^^ •Lower Mount Mortal, SIT cerroazulensis limestones! * Ml Moriah Sandstone Mbr. (non catcsreous) >*•»*•* Plalsance ••*.».£fti» 9 *w% conglomerate Mbr. 36- Navet Formation Globkjerinatheka Navet Formation semiiwohita Legend AA Eames and Bow (1965). The stratigraphy v Conformable contact position of the Vista Bella Limestone, Trinidad. V Position shown represents a maximum age s^\S\S Erosion surface suggested by the authors. The range Es shown by the arrow at right / //// Missing section * Mt Moriah silt rests on 'Gfobigefspsls kugteff •/*£ Conglomerates zone o* the Navet Fm. Figure 2.14 Summary of stratigraphic contacts described at the top and base of the San Fernando Formation by various workers. The schematic illustration is grouped into proponents for a "conformable" (A, B, C, D and "disconformable" (E, F, G, H) succession at the top of the formation. Note also the placement and significance of conglomerate beds; usually interpreted as overlying a hiatus that is variably placed in the formation. assemblages (Eames et al., 1962; Kugler and Caudri, 1975; Kugler, 2001). The Member was placed within the Globorotalia cocoaensis Zone of Late Eocene age (Bolli, 1957c; Kugler and Caudri, 1975) based on foraminifera assemblages. Van Den Bold (1960) also dated an "Upper" and "Lower" Mount Moriah silt from the Upper Eocene to lower Oligocene based on ostracod assemblages. Other fossils include abundant shell fragments, echinoid remains and fish teeth; common gastropods, molluscs and organic fragments; rare crab claws; and radiolarian and abundant shallow-water, larger foraminifera (Waring, 1926; Vaughan and Cole, 1941; Liddle, 1946; Kugler, 2001). From these descriptions, it is apparent that the Mount Moriah Calcareous Silt Member comprises interbedded siltstones, conglomerates and sandstones with a wide variation in faunal content. 2.3.2.3 VISTABELLA LIMESTONE MEMBER Two limestone beds will be described from the San Fernando Formation as they prove to be significant from a palaeoenvironmental perspective. These are the Vistabella and Morne Roche limestones of the Vistabella Limestone Member (Saunders et al., 1998; Kugler, 1996, Enclosure 12). These limestone beds once existed in the vicinity of San Fernando but have been completely removed by mining. The Vistabella limestone consisted of interbedded limestone and marls with lenticular glauconitic sands rich in orbitulinids (foraminifera), with lesser molluscs and echinoids remains (Kugler, 1996, Enclosure 11). The lithology is similar to the lenticular limestones described by Waring (1926) and Illing (1928) (Figure 2.13). The limestone was dated as Upper Eocene based on Hantkenina-beating marl at the top of the section (Kugler, 2001) and this date is reflected in the stratigraphic column of Saunders et al. (1998)6. 6 Eames and Blow (1965) proposed an Early Miocene (Aquitanian) age based on forms of Lepidocyclina and Pliolepidina foraminifera. If this age is correct, then these limestones do not belong to the San Fernando Formation. 83 The Mome Roche limestone quarry (Figure 2.1) was an upward grading succession from coarse elastics into limestone, a transition not elsewhere recorded in the Trinidadian stratigraphy. The following description was adapted from Kugler (1996, Enclosure 12). The clastic-limestone succession was approximately 17 m thick (60 m minimum according to Liddle, 1946) with the lowest beds comprising coarse-grained quartzitic sandstone with a resemblance to sandstones of the Pointe-a-Pierre Formation (Kugler, 2001). Earlier, this similarity led Lehner (1935, p. 697) to propose that the Morne Roche outcrop was interbedded with ("sont une intercalation dans") the Pointe-a- PJerre Formation. The quartzitic sandstone was upward gradational into coarse-grained, calcareous and fossiliferous sandstone with limestone lenses, to approximately 6 m of dense glauconitic limestone. The significance of this transition in the Morne Roche Member will be addressed further below. The entire succession was unconformably encased within clays of the Oligocene Nariva Formation, which prompted a "slip mass" interpretation for the Morne Roche deposit (Kugler, 1953, p. 244). The fossil assemblage found at Morne Roche includes Nummulites, Lepidocyclina, Operculina, Tubulostium and other foraminifera, oysters, pectinids and echinoids (Rutsch, 1939; Liddle, 1946; Kugler, 2001). The sediments at the quarry are also dated as Late Eocene based on several fossil specimens identified by Newton (1922) (referenced in Kugler, 2001) and G.D. Harris (in Waring, 1926). 2.3.3 CONGLOMERATES OF THE SAN FERNANDO FORMATION Much of the stratigraphic uncertainty in the San Fernando Formation is associated with the relative juxtaposition of conglomerate beds and "glauconitic sandstones" and "calcareous silts" typical of the Mount Moriah Sandstone and Mount Moriah Calcareous Silt members respectively (Figure 2.14). Conglomerates have been described at the base (Figure 2.13 A, B; Figure 2.14 C, G) and top (Figure 2.13 C; Figure 2.14 E-G) of the Mount Moriah Sandstone and Mount Moriah Calcareous Siltstone members that led to fundamentally different palaeoenvironmental and paleobathymetric interpretations for the formation. 84 For example, Eames et al. (1962; 1965) and Blow (1969) proposed an unconformity overlying the San Fernando Formation, with conglomerates-above- sandstones representing a basal Miocene (Aquitanian) trangressive deposit above the San Fernando Formation (Figure 2.14 F). Stainforth (1968, figure 6) also interpreted an unconformity below the conglomerates but differed in his placement of the conglomerates at the base of the San Fernando Formation (Figure 2.14 C). He argued instead that deposition within the San Fernando Formation is consistent with a gradual transition from shallow water facies to deeper water silts and marls of the basal Cipero Formation, based on consistent extinction and first appearance of foraminifera. All workers except Saunders et al., (1998) refer to one conglomerate horizon in the formation, which may not be the case, as with the Mount Moriah Calcareous Silt Member. It is questionable whether these conglomerates represent significant regional unconformities, with emergence and tectonic-induced uplifts (Eames et al., 1962) as proposed by those workers. Instead, they may have a restricted occurrence (e.g. Illing, 1928; Suter, 1960) with an entirely sedimentary origin. The discussion that follows will attempt to address some of these issues. 2.3.3.1 PLAISANCE AND MARABELLA CONGLOMERATES At least two conglomerate units have been formally named: the Marabella Conglomerate and the Plaisance Conglomerate members. The Plaisance Conglomerate Member was placed at the base of the formation (Kugler, 1996, enclosure 7; Saunders et al., 1998) while the Marabella conglomerate unconformably overlies the Mount Moriah Sandstone Member (Figure 2.14, F-H). The type locality for the Plaisance Conglomerate is at Pointe-a-Pierre, though lithological and faunal correlations have been made with other conglomerate beds across the Central Range (Waring, 1926; Lehner, 1935; Liddle, 1946; Suter, 1960; Kugler, 2001). The Plaisance Conglomerate consists of rounded pebbles and boulders of limestones, sandstones, quartzites and black shales within a coarse, siliceous, sandy matrix (Waring, 1926). Blocks of Paleocene coquinas are also incorporated in the matrix (Kugler and Caudri, 1975). The field sketches of Algar (1998, figure 9) from the type 85 section of the conglomerate display an interval 5 m thick with at least three normally graded beds, faulted against Oligocene beds. A few scattered boulders near the type locality display both rare grading of mainly pebble-sized clasts and disorganized intervals with cobbles, all supported within a coarse quartzose matrix. Crimson mudclasts are common throughout and this has led to the informal designation "cherry-cake conglomerate". At the type locality, the age of extrabasinal clasts ranges from Lower Cretaceous (Aptian) to Lower Eocene (Waring, 1926; Kugler, 2001). The Marabella Conglomerate consists of at least 3 m (10 ft) of rounded cobbles of dominantly Upper Cretaceous Naparima Hill, Paleocene and Eocene rocks within a coarse quartz matrix (Waring, 1926; Kugler, 1996, enclosure 10). Both of these conglomeratic units are unconformable over older rocks. Kugler illustrated the unconformable relationship between the Marabella conglomerates over the Mount Moriah Sandstone Member and Eocene, Paleocene and possibly Cretaceous sediments (Figure 2.13 C). If Waring's (1926) lithological correlation of conglomerates at Mount Moriah to the Plaisance Conglomerate Member is correct (Figure 2.13 A), then they also unconformably overlie Eocene and older rocks (the bedding relationship with the Plaisance Conglomerate and other lithologies at the type locality appears to be faulted (Algar,-1993; 1998)). There is a repeated association between these conglomerates and sandstones of the Pointe-a-Pierre Formation, though the nature of that association remains unclear. For example, Waring (1926, p. 45) noted that the conglomerates occur along "narrow strips along the northern border of the grits" in the Central Range, a relationship also demonstrated by Kugler (1996, Enclosure 7) in the western Central Range, although the rocks are not juxtaposed. The conglomerate also "seems to" directly overlie the "Pointe-a-Pierre grits" across the Central Range (Waring, 1926, p. 40); a direct contact at Pointe-a-Pierre was described as "difficult to understand" (Kugler, 2001, p. 215). Liddle (1946) also correlated conglomerates of similar lithology to his "lower shale member" of the Pointe-a-Pierre Formation from outcrops in the eastern Central Range (Mt. Harris). The association with the Pointe-a-Pierre Formation suggests either a recurring lithology that was not restricted to the Late Eocene, or that the incision below the conglomerates extended down to the Middle Eocene, a relationship already demonstrated at the para-type locality (Figure 2.13 A, C). 86 Although several correlations have been made between the conglomerate beds on lithological grounds (i.e. similar lithofacies), there has been little agreement and even literary debates on their relative ages. A common problem appears to be the reworked Cretaceous to Eocene conglomerate clasts and fauna. There is an abundance of reworked foraminifera within these conglomerates that precludes detailed subdivision into planktonic foraminifera biozones (Bolli 1957c; Eames et al., 1962; Jenkins, 1964). Yet, Kugler (2001) proposed an Upper Eocene age for the Plaisance Conglomerate at the type locality based on fauna found within the matrix. The age of the Marabella conglomerate is more conjectural. Eames et al. (1965, p. 163) placed the conglomerates "to any horizon from the bottom of the Oligocene to the Ciperoensis zone" (Late Oligocene), but preferred an Early Miocene (Aquitanian) age based on the foraminifera Pliolepidina tobleri, which they stated was not known before that time (Eames et al., 1962). They maintained these ages (Blow et al., 1968; Blow, 1969) even after objections were raised (Jenkins, 1964; Stainforth, 1968). If this age is correct for the Marabella Conglomerate, then Oligocene-Early Miocene conglomerates are unconformable upon Eocene and older rocks, a relationship that is well documented along the northern margin of the Central Range (e.g. Morne Brule, Kugler, 1959; see conglomerates just west of Los Armadillos in Figure 2.1) where the Oligocene Guaico conglomerates (Appendix 5) unconformably overlie the Eocene-Paleocene Pointe-a-Pierre and Chaudiere formations. These conglomerate beds are localized deposits, and either interbedded with, incised into, or laterally transitional into sandstones, siltstones and marls (Figure 2.14 A, B). They are disconformable everywhere, which has also led to assumptions of basin- scale uplifts and unconformities, but little agreement as to the timing of these events. One of the reasons for the apparent stratigraphic confusion may have been the significance placed on individual conglomerate beds. Collectively, they may be classified as either the normally graded to disorganized conglomerate facies of Walker (1975) or the inertia-driven, grain flow deposits (R3 division) of Lowe (1982); some may even be associated with more cohesive flows. It is apparent that these formally defined members represent a recurrent facies association within Middle and Late Eocene rocks (Pointe-a- Pierre and San Fernando formations) that may even extend into the Oligocene (Cipero Formation). Instead of the formally assigned conglomerates being correlatable in time 87 and space (as currently suggested on the stratigraphic table, (Saunders et al., 1998)), the beds or bedsets may have been associated with localized depositional episodes dictated by the larger depositional setting that may not have changed significantly throughout the time period associated with these beds. It is telling that where these conglomerates are not present, there appears to be little disagreement as to stratigraphic contacts, faunal content and dating, and a stratigraphic transition into deep-water siltstones of the Cipero Formation. This idea will be expanded upon when the larger set of Eocene to Oligocene facies and facies associations and the depositional settings have been considered. A similar example will be shown below (Section 2.3.4) where stratigraphic status has been assigned to what may have been no more than single depositional events. 2.3.4 SAN FERNANDO FORMATION AT SOLDADO ROCK Soldado Rock is a small, steep-walled island located approximately 10 km west of Icacos Point off the southwest peninsula of Trinidad (see Figure 1.1). The rocky topography of the island is made up primarily of Paleocene and Late Eocene rocks of the Soldado, Boca de Serpiente and San Fernando formations (Table 1.1). These outcrops have been extensively studied and sampled by paleontologists and the lithology is well documented (Kugler and Caudri, 1975; Kugler, 2001). Several facies within the San Fernando Formation at Soldado Rock were discerned both from the descriptions of Kugler and Caudri (1975) and a personal visit to the island on a very windy and rainy day in June 2007, accompanied by Dr. Grant Wach a,nd Mr. Rajendra Maharaj (geologist, Petroleum Company of Trinidad and Tobago). These lithofacies are discussed below. The significance of the Soldado Formation at Soldado Rock lies in its relationship with the San Fernando Formation. The following descriptions were derived entirely from Kugler and Caudri (1975). According to them (p. 373), the Soldado Formation comprises: "massive layers of... impure, glauconitic limestone containing scattered oysters...nests of comminuted shell fragments with streaks of 88 echinoderm breccia" and beds of fossiliferous sandstone, siltstone, foraminiferal and "sandy limestones". The Soldado Formation is represented by a 22 m-thick section interpreted as shallow- marine in origin (Kugler and Caudri, 1975). The top of this section is disconformable below pebbly silts of the San Fernando Formation, and although Kugler and Caudri stated that the base of the Soldado Formation is unknown, they illustrated a disconformable contact with silts of the San Fernando Formation on its northern, eastern and southern extremity (Figure 2.15). The "Soldado section" represents just one of several exotic 'clasts' that are encased within silts of the San Fernando Formation, others ranging from pebble "beds" to "chaotic" blocks larger than 10x10x7 m thick (see Kugler and Caudri's description of beds "3" and "4"). Collectively, they form an impressive "block" and "breccia" (p. 393-394) conglomerate more than 10 m thick (excluding the largest "Soldado Formation" section). The San Fernando Formation "matrix" comprises a sandy and calcareous silt with scattered quartz pebbles, and an "overwhelming" abundance of reworked Paleocene to Middle Eocene fauna (p. 385, 392). This matrix also contains "common interdigitations" of glauconitic sand and locally, is lithologically similar to the siltstones described from the Mount Moriah para-type locality of the San Fernando Formation (p. 393). The succession described above (beds 1 - 4) is in contact with beds "5" to "10" of the San Fernando Formation (Figure 2.15). The descriptions that follow are limited to beds "5" and "10" and were derived from a combination of outcrop observations and descriptions from Kugler and Caudri (1975). Bed "5" is a lenticular sandbody in direct contact with the block conglomerates described above and consists of non-calcareous, grey, quartzose sandstone approximately 5 m thick (Kugler and Caudri, 1975). From our observations (Figure 2.16), individual beds are also massive and topped with convoluted laminae. The thickest bed was measured at 45cm with irregular bed contacts and thicknesses along the exposed length. Sands are poorly sorted, with up to granule-sized grains within a fine-grained quartzitic matrix. Bed "10" of Kugler and Caudri (1975) is 1 lm thick and was dated at Late Eocene based both on planktonic and larger foraminifera. From their descriptions (p. 405, 406), the stratigraphic contacts are "abnormal" with the lower 4 m consisting both of "tests of 89 Figure 2.15 Reinterpretation of Soldado Rock as a slope canyon fill complex. Geological map (A) and cross section (B) of Soldado rock showing the relationships between the units ("beds") discussed in text and interpreted depositional mechanisms (italicized). Dashed line shows location of cross section. Map and cross section modified after Kugler and Caudri (1975) and ages shown also derived from same. Linear symbols in bed "10" assumed to indicate limestone (not explicitly labelled in the original source). 90 91 Figure 2.16 Sandstones of the San Fernando Formation at Soldado Rock. (A) Graphic log demonstrates irregular, massive beds of coarse-grained sandstone interpreted as the product of high-density sediment gravity flows (classification of Lowe, 1982). B) Outcrop photo of section shown in (A). Thick-bedded (C) and massive (D) character of sandstone beds. Scale in all photos is 15 cm long. orbitoids and calcareous algae... fine brecciated rubble of the same material and echinoids" and "rugged marlstone". The upper 7 m consist of "marlstone" of varying composition and thickness alternating with "glauconitic sand". They also described numerous "erratic blocks" of Paleocene limestone ("Ranikothalia" limestone), and quartzites and reworked specimens of foraminifera. The limestones and foraminiferal beds were assigned a shallow water origin (Vaughan and Cole, 1941). Our observations were made along approximately 80m of bed "10". The "erratic blocks" are up to boulder size and float within a convoluted matrix of calcareous mud and silt (Figure 2.17). Bedding planes are apparent along upper sections of the bed though much of the bed comprises this chaotic mass of sediment. A convoluted, calcareous matrix is present along its northeastern end associated with the large, floating boulders. The orbitoid tests and calcareous algae are amalgamated into thick intervals (minimum 4m) with no internal stratification. They appear to be localized although their true continuity is obscured by vegetation. Fossils identified from thin section include discocyclinids, nummulitids, coralline algae, mollusc and coral fragments and other foraminifera within a dolomitic 92 Figure 2.17 Contorted limestone and conglomerate of beds "10" and "11" on Soldado Rock. A) Southeastern end of bed "10" showing foraminifera limestone bed (L) overlain by stratified marl deposits (arrowed). B) Northern end of same bed showing large floating boulders (one circled) within a chaotic and contorted mass of calcareous mud (arrowed). Most of the exposed bed comprises this chaotic facies, interpreted as a debris flow event with rafted, internally stratified blocks as shown in (A). Bed "11", also known as the Boca de Serpiente Formation, comprises a blocky boulder conglomerate with Middle Eocene clasts. See Figure 2.15 for location and interpretations. 93 matrix (Appendix 4); quartz is absent from the calcareous framework (Kugler and Caudri, 1975). Collectively bed "10" has the character of a biohermal reef as interpreted by Kugler and Caudri (1975). Its association with contorted and deformed beds and floating boulders suggests however that it is an allochthonous mass resedimented by cohesive sedimentary flows to its current stratigraphic position. Based on these descriptions, the main lithofacies of the San Fernando Formation at Soldado Rock comprise lenticular sandstones and discordant limestones. Bed "10" is overlain by Bed "11" of Kugler and Caudri (1975) to which they assigned a Middle Eocene age (Boca de Serpiente Formation). Bed "11" consists primarily of glauconitic limestone boulders with the appearance of a boulder conglomerate (Figures 2.15 and 2.17). It was described as a "tumbled mass of semi- autochthonous and erratic blocks" and was interpreted as originally "fore-reef sediments (Kugler and Caudri, 1975, p. 414-415). It also contains clasts of Paleocene age. It is noted here because of its "breccia and boulder conglomeratic character" similar to that described for the San Fernando Formation. Unfortunately, weather conditions did not permit detailed examination during the traverse. Its significance will be readdressed when sedimentary processes and depositional environments are considered. 2.3.4.1 SEDIMENTARY PROCESSES AT SOLDADO ROCK Kugler and Caudri (1975) interpreted the field relationships between the Paleocene and Upper Eocene rocks to indicate erosion from a Late Eocene "transgressive" shoreline, where "steep" and "rocky" Paleocene cliffs were undercut and "collapsed" into the Late Eocene sediments. Hence, they envisioned a shallow water environment with active wave and shallow water currents as the main sedimentary processes. Some of the clasts (e.g. "Ranikothalia" limestone) are interpreted as slumped deposits that are not far removed from their original site of deposition. This interpretation does not adequately explain the field relationships between these rocks. There is no evidence of shallow water bedforms that would have been produced by wave (or even tidal) reworking along a shoreline. Similarly, beds of rounded clast-supported 94 conglomerates are a typical component of steep rocky shorelines pounded by surf action (e.g. Aalto and Dott, 1970), and this is not a recognized facies on Soldado Rock. At least two explanations must be considered. Firstly, the relationships may represent a fault melange. Faulting was preferred by Algar (1993; 1998) to explain the bedding relationships at Soldado Rock and this interpretation can be supported from the "indications of mylonite" observed elsewhere (bed "10" of Kugler and Caudri, 1975, p. 405). Similarly, Kugler once proposed faulted contacts between the Paleocene and Eocene of Soldado Rock, though later insisted that these are sedimentary contacts (Kugler and Caudri, 1975). During our traverse of Soldado Rock, deformation seams were noted in the vicinity of beds "5" to "9". Secondly, the relationships may represent a sedimentary origin based on the consistent occurrence of Paleocene clasts within an Upper Eocene silty matrix, the common rounded cobbles and pebbles and the orientation of sandstone lenses parallel to the structural strike (see Figure 2.15, beds 5-9); the 'order' suggested by the latter would not be expected with a fault melange origin. A sedimentary origin is the preferred explanation for the occurrence of extremely large blocks within the silty matrix (discordant limestone facies). A block fall and/or slide origin for the abundant Paleocene clasts is inferred, similar to the interpretation of Kugler and Caudri (1975). It must be assumed that the matrix moved as a cohesive flow that was capable of supporting the large, floating boulders, along relatively steep gradients to increase the gravitational force needed to flow. Alternatively, the blocks may not be far removed from their original source (e.g. the 22 m-thick limestone block and "Ranikothalia" limestone). Kugler and Caudri (1975) offer no interpretation for bed "5". The massive and poorly sorted bed "5" is similar in grain size and geometry to the "lenticular sandstone" lithofacies described for the Pointe-a-Pierre Formation, except with more irregular bedding contacts. The sandstones are interpreted as turbidites similar to the S3 sequence of Lowe (1982) (see Figure 1.6). This is evidenced by the massive bedding passing upwards to convoluted laminae at bed tops. The irregular bed contacts are also similar to the description of sandstones at Mount Moriah given by Illing (1928) and these suggest erosive flow events. Beds also show no evidence for traction-related reworking of sands such as wave ripples or cross beds. 95 Kugler and Caudri (1975) interpreted bed "10" as initially deposited in shallow water and later slumped as a rigid block into "quiet waters" (p. 430). Bed "10" is here assigned to the "discordant sandstone facies" analogous to the same described for the Pointe-a-Pierre Formation, except for the presence of mainly limestone blocks. The interpretation is similar to that of Kugler and Caudri. It is inferred to be an allochthonous mass rich in shallow-water fauna that was removed from its initial site of deposition by a combination of coherent block slides and cohesive debris flows. Clastic and carbonate boulders were transported downslope within a cohesive mass of fossil shells, algae, calcareous mudstone and glauconitic silt. The preserved bedding configuration represents cohesive freezing of the flow. Bed "10" has an abundance of shallow water fauna (Appendix 6; Stainforth, 1948; J.B. Saunders cited in Kugler and Caudri, 1975; Kugler, 2001) which supports interpretations of relative shallowing during deposition of the San Fernando Formation. The sediments likely originated within shallow water, but were subsequently resedimented into deeper water environments as a debris flow of considerable thickness (minimum 11 m height x 80 m length). The turbidite beds also suggest resedimentation and much of the glauconitic sand common to the San Fernando Formation (Kugler, 2001) may have been removed from the initial depositional site. The reinterpretation of bed "10" in the San Fernando Formation suggests that debris flows were also significant in redistributing shallow water sediments downslope into deeper water environments. Similarly, the chaotic block and breccia conglomerate of bed "11" also indicates resedimentation processes and was likely sourced from Middle Eocene rocks exposed along the outer shelf or slope canyon walls. This will be elaborated further in Chapter 3. 2.3.5 SUMMARY OF FACIES IN THE SAN FERNANDO FORMATION The lack of exposure within the San Fernando Formation was a hindrance to its direct study; emphasis was therefore placed on the observations of previous workers. This is not without its limitations, especially given that some were made over seventy 96 years ago. Today there is very little chance of validating some of these observations given that the para-type locality is within a densely urbanized area and most of the limestone units have been mined, however, there is still some merit to past publications. The San Fernando Formation has been extensively sampled for biostratigraphic purposes and the results have inspired some of the most active debates regarding Trinidad Paleogene formations (Eames et al., 1962; Jenkins, 1964; Eames et al., 1965; Blow et al., 1968; Stainforth, 1968). This includes exposures on Soldado Rock where all rock units have been extensively sampled dating back to the 1920s, even including rocks below the water line (Kugler and Caudri, 1975). Based on these past studies, there appears to be a general agreement on the relative ages of the formation and its members with few exceptions (Figure 2.14; Eames et al, 1962; Eames and Blow, 1965). It is the stratigraphic relationships between the various members and adjacent formations that show the greatest variance and it is here that an understanding of sedimentary facies, sedimentological processes and depositional environments can be of value. The recognized facies within the San Fernando Formation will now be summarized. The descriptions of previous workers suggest the existence of a localized cobble conglomeratic facies that is either gradational or unconformable with sandstones and silts. At least one of those horizons has been correlated with the Plaisance Conglomerate Member (Waring, 1926) and the other, the Marabella Conglomerate, is associated with a significant (in terms of time) amount of erosion at its base. Massive sandstones are known from Soldado Rock (Figure 2.16) and suggested from descriptions at Mount Moriah (Illing, 1928). Direct analogies have been made to the Pointe-a-Pierre Formation (Illing, 1928; Lehner, 1935) and traction-related sedimentary structures related to shallow-water processes are neither explicitly described nor implied in the descriptions of all workers. Instead, references to "massive" and "six feet thick" beds suggest massive sands. These sandstones are interpreted here as high- density turbidites analogous to the S3 - Ta sequence of Lowe (1982). Lowe interpreted these to result from combined suspension fallout and traction-related processes during the passage and collapse of high-density liquefied flows. Blocks of foraminifera and bioclastic limestone and calcareous mudstone several metres thick with abundant evidence for a shallow water origin (~50m water depth, 97 Vaughan and Cole, 1941) lie within zones of contorted bedding with large (>2m diameter) floating boulders of limestone and sandstone (Figure 2.17). This occurs below a thick bed (>10 m) of blocky conglomerate (Boca de Serpiente Formation). These relationships are interpreted to indicate a discordant sandstone, shale and limestone facies that resulted from block slides, slumps and cohesive debris flows. The entire succession of Paleocene to Lower Oligocene rocks in the San Fernando area contains numerous localized disconformities. The base of the Navet Formation at Mount Moriah is unconformable over the Lizard Springs Formation (Figures 2.13, 2.14) although these shale-prone formations are otherwise conformable over the Southern Basin (Bolli, 1957c; Saunders and Bolli, 1985; Saunders et al., 1998, Well Rochard-1). The San Fernando Formation is disconformable over Middle to Upper Eocene rocks, and where the conglomerate beds are present, another disconformity occurs below the Lower Oligocene Cipero Formation. Where conglomerates and sandstones are not present, a conformable succession into the basal Cipero Formation occurs (Figure 2.14 A-D). These relationships suggest that the "unconformities" interpreted throughout the formation were localized depositional surfaces and not regional surfaces of incision directly associated with eustatic or tectonic emergence. The significance of these facies will be returned to when facies associations are considered in Chapter 3. The facies described here will form the basis for the recognition of depositional elements and depositional environments, although these have been briefly alluded to in the paragraphs above. 2.4 ANGOSTURA SANDSTONE MEMBER (CIPERO FORMATION) The Angostura Sandstone is not displayed on stratigraphic tables for Trinidad (Kugler, 1959; Saunders et al., 1998), as it was unknown prior to 1999. The sandstone derived its name from its discovery exploration well, Angostura-1, drilled to test for Oligocene and Eocene petroleum reservoirs, which encountered approximately 300m 98 (1000 ft) of gross sandstone (Lerch et al., 2004). The sandstone is the primary reservoir in several hydrocarbon fields located along a northeast subsurface extension of the Central Range (Figure 2.18), including the Angostura field, named after the discovery well. The Angostura Sandstone has been studied extensively by the operators for the Angostura field development (Lerch et al., 2004), though relatively little has been published. As of 2004, six full-hole cores were taken in the sandstone from several appraisal wells (Lerch et al., 2004), and some of these cores were reviewed for this study. Core plugs from wells Kairi 1, Canteen 1 and Canteen 2 were also acquired for heavy mineral, petrographic and apatite fission track analyses, the results of which are discussed separately. 2.4.1 OVERVIEW OF THE ANGOSTURA SANDSTONE The sandstones are discussed as a member of the Cipero Formation on account of their age range and stratigraphic relationships with Oligocene strata. They are dated from Early to Middle Oligocene supported by biostratigraphic data (Lerch et al., 2004; Carr- Brown et al., 2001; 2002) while the palaeogeographic maps of Pindell (2007) suggest a similar Early Oligocene age of deposition. Age estimates for this study are based on nannofossil zonations (Martini, 1971) derived from subsurface core samples. The analysis was performed by Jason Crux of Biostratigraphic Associates (Canada) Ltd. (see Appendix 7). A lower age limit is restricted to the NP 16 Zone (Late Middle Eocene) based on the presence of Cribrocentrum reticulatum, Dictyococcites bisectus, Discoaster barbadiensis (Canteen 2, 4658 ft), Reticulofenestra hampdensis group, the tentative identification of Dictyococcites bisectus (Canteen-1, 5076') and Helicosphaera lophota (Kairi 1, 5395 ft). This lower limit is difficult to constrain because of the common reworking of older fauna (Carr-Brown et al., 2002) and it is possible that it is much younger. The sandstone lies above shales of the Navet Formation of the same age in well Canteen- 2 (Carr-Brown et al., 2002) although the amount of eroded section at the base of the sandstone is unknown. As a consequence, this age has to be considered a maximum. 99 Figure 2.18 Oligocene to Middle Miocene rocks across the Central Range and Southern Basin of Trinidad. Maps display the distribution of Oligocene to MiddleMiocene outcrops (A, B), outcrop and sample locations (A, B), and die the location of wells and seismic lines mentioned or illustrated in the text (A, B, C). Outcrop localities clockwise from northwest: Tar = Tarouba; SsT = Sandstone Trace; KHi = Kelly Hill; EsJ = Esmeralda Junction; CHi = Corbeaux Hill (2 outcrops); RR = Rock River, Bass Terre; Sol = outcrop of Soldado Formation at Marac quarry, Moreau Road; Mor = Moreau Road, Moruga; RRrd = Rock River Road. Geology and structure after Kugler (1959) and Saunders et al. (1998). 100 Canteen-1 KaW-1 Soldado Rock 0 10 20 c .^\ \ ABM-91*v ^ABM-44 \ \ A8M-92W I^-NN*'^^_ \ \ GU-99MP ~>-4» \f~^^ °""""~"5 I , i^K"""""1'" Earfy Miocene 1' BUI! BrawoFm IB Hsmm Sandstone- 2 ' jMULJim E H 00,cfoP* Lata Ollgacena Eaity OBgocwe £ Outcrops (sections & samples) 8P*« # WteB location ^^—*^ Fau(t9 *vS«smic section Late Oligocene (NP 25 zone) was the youngest derived age based on the identification of the Reticulofenestra hampdensis group (Canteen-1, 5076 ft) and the co-occurrence of Dictyococcites bisectus with Reticulofenestra samodurouvii (Kairi-1, 5395 ft). This age range (Late Middle Eocene to Late Oligocene (36-24 Ma)) indicates that the Angostura sandstone is a stratigraphic equivalent to at least the Cipero (Oligocene) and San Fernando (Late Eocene) formations. A correlation to the uppermost Navet (Late Eocene) is precluded by the poorly constrained maximum age. The sandstone lies within the deformed Angostura-Emerald belt east of the Central Range (Figure 2.19). Kennan (2007) estimated a structural translation of approximately 125 km towards the east-south-east of its initial depositional site by the Late Miocene. An outer shelf to upper slope environment is suggested by faunal content of the sandstone (Carr-Brown et al., 2002). A southwest provenance was proposed for the sandstones, sourced from the "Espino" drainage basin in Eastern Venezuela (Pindell, 2007). 2.4.2 FACIES OF THE ANGOSTURA SANDSTONE Lithofacies of the Angostura Sandstone were examined from 142 m of full-hole core from five wells (Table 1.3). At least four distinct lithofacies (including one assemblage) can be discerned from the cored intervals. These are: (1) Bioturbated sandstone and siltstone facies assemblage; (2) Massive thick-bedded sandstone; (3) Graded thick-bedded sandstones (and conglomerates) and; (4) Cobble conglomerates. 2.4.2.1 BIOTURBATED SANDSTONE AND SILTSTONE FACIES ASSEMBLAGE Description This facies assemblage is described from the well Kairi-1 (5397-5352 ft and 5447-5432 ft). It is differentiated from other facies by its relative abundance of fine grained sediments, lesser extent of sandstone amalgamation, common bioturbation, common traction-related sedimentary structures and heterogeneous character. The latter 102 is represented by at least three individual and interbedded facies that collectively define this assemblage: (la) fine-grained sandstone and siltstone; (lb) contorted shale and deformed mudclasts; (lc) subordinate coarse-grained sandstone beds. la) Fine-grained sandstone and siltstone facies This facies displays a uniform character with interbedded fine-grained sandstone and parallel or ripple cross-laminated siltstone and shale in intervals just over 1 m thick (Figure 2.20 B, 2.21 A). Sands occur as ripple-laminated beds up to 4 cm thick or as lenticular ripples in silts. Bed contacts can be planar or irregular, the latter resulting from bioturbation. Samples from this facies yielded several specimens of benthic foraminifera (Ammobaculites, Nodosaria, Lituotuba, Reophax and others; Appendix 8) and nannofossils (discussed below). This relatively uniform interval is intercalated with deformed and contorted horizons, described below. lb) Contorted shale and deformed mudclasts The contorted facies comprises beds of deformed pebbly mudstone and distorted sandstone and mudstone clasts floating within a shaly matrix (Figure 2.20 B, 2.21 B). These beds are up to 1.2 m thick. lc) Subordinate coarse-grained sandstone This facies displays a range of sedimentary structures and bedding styles. Grain size ranges from medium to coarse, occasionally pebbly, with bed thicknesses up to 60 cm. Dewatering structures, tangential cross-stratification, angular rip-up clasts and irregular basal contacts are characteristic. Both normally graded and massive beds occur, transitional upwards to parallel laminated sandstone (e.g. 5356 ft), or entire beds may display parallel laminae. Pebbly sandstone beds may be bounded within fine-grained sandstone (maximum 30 cm thick) with irregular contacts (e.g. 5330 ft). One burrow of Ophiomorpha nodosa was seen among the sandstones (Figure 2.20 B). Also typical throughout this facies assemblage are non-amalgamated, fine-grained sandstone beds up to 25 cm thick that display a range of laminae geometries ranging from parallel, wavy-divergent and tangential; the sets are either transitional into each other or 103 Figure 2.19 NW-SE seismic section (A) and (B) in the eastern offshore area showing the subsurface distribution of the Angostura Sandstone. The extent and thickness of the sandstone is constrained by wells (dashed line is projected) on which cored intervals are shown. See Figure 2.18 for location of section and wells. 104 6 6 Tf '6' rg-,r-g- ,•£• ,-g-'6 '6 '6 d'b'b'o'b'd'b o o o O o o o o 0 o o o o o o o o o o o o o o S N m ffi JT ffl S m o 1 I o <1 1 O t- N OOOOOOQT"*- o o o O o o *o! ^O o»! "O! t" r* *- r* odd 105 -3 .a j-« ft >4 (Hm)gsa9| I Figure 2.20 Representative graphic logs for Angostura Sandstone lithofacies from well Kairi-1. A) Graded thick-bedded sandstone and conglomerate facies. B) Bioturbated sandstone and siltstone facies. C) Massive thick-bedded sandstone facies. D) Cobble conglomerate facies interbedded with facies described in 'A'. Conglomerate symbols are schematic only. Trace fossil identification by Grant Wach; for bioturbation index, l=rare, 2=common, 3=abundant, 4=churned. 106 Figure 2.21 Facies from the Angostura sandstone in well Kairi-1. A) Parallel and ripple laminated fine sands and silts of the fine-grained sandstone and silt facies. B) Contorted pebbly mudstone facies. C) Fining-upward sandstone displaying components of the Bouma sequence (Tb-Tc-Td). Darker laminae are rich in organic matter. Thick-bedded, normally-graded sandstone facies. D) Massive sandstone with dish structures (Ta/S3) indicative of rapid sediment fallout from a fluidized flow. Underlying shale is deformed at the top suggesting loading from the overlying turbidite. Core depths are shown in feet. 107 h ••«! HI ! 7 « Figure 2.22 Facies from the Angostura sandstone in well Kairi-1. A) Erosive base of pebbly conglomerate incised into mudstone. Large angular clast is a mudstone fragment. B) Coarse-grained sandstone with dish structures (top of same bed as (A). (C) Normally graded sandstone displaying a partial Bouma sequence. Note the coarse grain size in the Ta/S3 division at the top which is the base of another turbidite. Also note the increasing concentration of organic particles (darker laminae) in the finer grained Tb-Tc divisions. D) Contorted sandstone with abundant mud rip-up clasts indicative of erosion associated with passage of high-density liquefied flow. Core depths are shown in feet. confined within discrete beds. Fine-grained sandstone beds are also cross-stratified, massive or normally graded, all transitional upward to parallel or wavy ripple laminae. Entire beds of parallel laminae also comprise a common sedimentary feature (comparable with the "parallel laminated sandstone" facies described for the Nariva Formation). Upper and lower bed contacts are often irregular and floating mudclasts occur among the ripple laminae sets. Organic matter is also common (discussed below) and silty intervals are commonly bioturbated. Interpretation The range and sequence of sedimentary structures within this facies assemblage is consistent with turbidites and this is interpreted as the main sediment delivery mechanism. Elements of the Bouma sequence (Bouma, 1962) include massive sandstone beds (Ta), upward to parallel (Tb) and wavy (Tc) laminated horizons. Normally graded, cross-stratified sandstones are similar to the Tt sequence of Lowe (1982) attributed to simultaneous traction and fallout processes. These structures are transitional upward into Bouma Tc-Td intervals reflecting the increasing role of suspension sediment fallout to produce these beds. Thicker (>20 cm) massive sandstones with dewatering structures were also deposited during sediment fallout from suspension currents in which traction- related currents were suppressed (Lowe, 1982; Arnott and Hand, 1989). Turbidite beds are not amalgamated, suggesting relatively unconfined deposition away from an axis of flow. The fossiliferous, uniform shale and siltstone beds represent background sedimentation fed by (hemi) pelagic dropout or low-density turbidites in relatively distal areas. The contorted shale and deformed mudclasts facies are indicative of more cohesive flows capable of suspending up to pebble-sized quartz grains within the fine grained matrix. They are suggestive of sediment instability, probably along localized slopes as inferred from the limited thickness (~60 cm) and interbedded nature with the uniform beds. Floating sandstone clasts in shale suggest a similar depositional mechanism while the irregular contacts between pebbly sandstone and finer grained beds may be attributed to more sandy debris flows (Shanmugam, 1996). 109 Among the cores examined, this lithofacies is the most distal or lateral relative to the main axis of flow on account of its lower sandstone/shale ratio, non-amalgamated turbidites and abundance of ripple cross-laminated sands (Tc). Possible depositional environments will be discussed in Chapter 3 when facies associations are considered in greater detail. 2.4.2.2 MASSIVE THICK-BEDDED SANDSTONE (MTBS) (Kairi-1, 5399-5432 ft) Description This facies comprises homogeneous bedsets of poorly sorted medium- to coarse grained, calcareous sandstone with floating mudclasts (Figure 2.20 C). Beds are typically massive and this differentiates this facies from other thick-bedded facies. Dish structures are common and current ripples are rare (Figure 2.21 D). Subtle breaks in the core suggest bed thicknesses in the order of 30-150 cm although thicker is possible; the true thicknesses are obscured by the high degree of bed amalgamation. Thin beds (5-10 cm) of silty shale with current rippled, lenticular sands form a minor component. Bed contacts are relatively planar when compared to the "graded thick-bedded sandstone" facies (discussed below). Organic fragments are common, either scattered as minute particles or as confined laminae within beds. Interpretation The massive character of these beds is attributed to sediment fallout from high- density suspension currents, modified by liquefaction. The interbedded shale beds were deposited either as pelagic fallout between turbidites or from the dilute ends of the high- density flows. Their uncommon occurrence is likely due to poor preservation potential related to high rates of sandstone amalgamation. The planar contacts between the two lithologies differ from the irregular contacts observed among the "graded thick-bedded sandstones" facies (discussed below) and suggest relatively less erosion during deposition of the thick-bedded sandstones. 110 2.4.2.3 GRADED THICK-BEDDED SANDSTONE AND CONGLOMERATES (GTBS) Interpretation This facies consists of normally graded, thick-bedded, pebbly conglomerates and thinner, coarse-grained sandstones (Figure 2.20 A). The following description pertains to cored intervals in well Kairi-1. The pebbly conglomerates are amalgamated into bedsets tens of metres thick. The lowest beds of these conglomerates are in sharp irregular contact with bioturbated sandstone and siltstone facies assemblage (Figure 2.22 A). They show coarse-tail grading and improved sorting upwards to very coarse-grained (still poorly sorted) at the top. An upward decrease in the size and quantity of rock fragments occurs until only mudclasts are evident near the top. Rock fragments include a mixture of limonitic clasts and bioclasts, the latter including bivalve, gastropod and calcareous foraminifera fragments (Westlake, 2002). Intraformational mudclasts 'float' throughout these beds and are of a variety of shapes (angular, elongated, rounded, deformed) and sizes. The long axes of elongated clasts are roughly aligned to bed bases (Figure 2.22 A). Thinner coarse-grained sandstone bedsets occur toward the top of the amalgamated pebbly conglomerates and define a general fining-upward relationship to this facies. They are differentiated from the lower pebbly conglomerates by mainly coarse quartz grains with rare pebbles (2 cm diameter) and generally thinner bed thickness (10s of cm). Sandstones range from massive, amalgamated beds with scattered mudclasts and dewatering structures (e.g. Figure 2.20, 5287 ft) to well-defined, normally graded bedsets that do not exceed 75 cm thickness (Figure 2.22 C). The latter grades from coarse-grained intervals with common mud rip-up clasts overlying erosive basal contacts, to fine-grained planar and ripple laminated tops. Within the graded beds, scattered organic particles transition upwards until concentrated within the ripple laminated horizons. Graded sandstones are capped by thin, bioturbated shale horizons with Planolites, Palaeophycus and cryptobioturbated laminae. The lithofacies was also identified from well Canteen-1 (5074-5139 ft; 1546-1566 m) where a few variations were noted. The thickest normally graded bed is 4.5 m (may extend to 5.5 m) and ranges from a basal pebbly sandstone (coarser grains up to 4 mm) to 111 cross-laminated fine sand at top. Mudclasts are typically restricted to the base of beds. Many other beds do not exceed 45 cm thickness and grade upward from massive pebbly sandstone to parallel laminated fine sandstone and occasionally to rippled tops. Most of these thinner beds however comprise amalgamated massive sandstones. Planar cross- stratification is rare and climbing ripples (sometimes tangential) are common, either in discrete beds or overlying parallel laminated sandstones. Thin beds (<30 cm) of pebble or mudstone conglomerate are also interbedded with the gradational sandstones and consist of angular, sub-rounded and deformed clasts of laminated mudstone up to 9 cm long (truncated at core edge). Shell fragments are rare among these coarser beds (the identity of these were not determined). Interpretation The grain size, erosive bed bases and thick-bedded character suggests relatively confined and high rates of sedimentation. The gradation and sorting observed are interpreted to result from decreased flow velocities associated with high-density grain and liquefied flows, traction and suspension currents, resulting in a characteristic sequence of sedimentary structures for turbidites (Bouma, 1962; Lowe, 1982). The facies is dominated by stacked Ta and S3 divisions (Bouma, 1962; Lowe, 1982) although all components of the Bouma sequence can be recognized from different beds. Near complete Bouma sequences was recognized in the coarse-grained beds of Kairi-1 where the sequence of sedimentary structures range from Ta-Td, with upper divisions likely eroded by subsequent flow events. The thin fossiliferous and bioturbated shale beds overlying gradational beds in Well Canteen-1 represent Td-Te Bouma sequences. The planar and tangential cross-stratification on the tops of beds are interpreted as the S3-Tt- Td sequence, resulting from the traction reworking of sediment that initially fell out of suspension from a liquefied flow (Lowe, 1982). The scattered and floating intraformational mudclasts are interpreted to result from either of two mechanisms. Firstly, decreasing turbulence and velocity within a waning suspension current decreases capacity of the flow to carry the quantity of sediment entrained. This leads to sediment fallout irrespective of grain size and results in very poorly sorted deposits (Hiscott, 1994). Secondly, it is theorized that thick-bedded 112 sandstones can be produced by continuous sediment fallout and amalgamation from quasi-steady flows (as opposed to surge-type flows, Figure 1.6). This model predicts that bed thicknesses are a function of flow duration and as a result, larger grains will not be restricted to bed bases. 2.4.2.4 COBBLE CONGLOMERATE (CC) Description A three-metre (10 ft) thick conglomerate is interbedded with the pebbly conglomerates and coarse-grained lithofacies described above (Figures 2.20 D and 2.23 A). The beds are very poorly sorted. The lower part of these beds consists of 1.5 m of disorganized (Walker, 1975) matrix supported cobble conglomerate. Here, a variety of clast types are present with the largest up to 10 cm (truncated by core edge) within a coarse sandy matrix. Clast shapes range from rounded to sub-angular to elongate and include various types of mudstone and siltstone, chert and bioclastic fragments. Sandstone and quartzite clasts may also be present (Westlake, 2002). A sharp contact exists with the upper 1.4 m (4.5 ft) differentiated by smaller clast size (up to 4 cm) and clast-supported texture with internal erosive surfaces. This interval exhibits coarse tail grading and an upward decrease in the size of the coarsest lithic clasts. 113 Figure 2.23 Conglomeratic and organic facies of the Angostura Sandstone. (A) Matrix- supported cobble conglomerate facies. (B) Organized organic facies with organic matter concentrated along parallel laminae sets within fine-grained sandstone. (C) Disorganized organic facies with scattered organic wisps within otherwise massive sandstone. (D) Recurrent organic laminae (arrowed) encased in massive sandstone without any obvious break in sedimentation. 114 Interpretation The matrix-supported, disorganized cobble conglomerate resulted from cohesive and grain flow processes likely induced by downslope gravity forces. Grain flows of such large clasts suggest relatively high flow velocities, probably within confined channels. The graded conglomerates suggest that sorting occurred upon deposition of the clasts or during transport; this may be due to grain flow combined with rapid fallout from suspension. This conglomerate may have been transitional from more cohesive flows similar to the underlying bed. The cobble conglomerates are capped by a normally graded turbidite bed typical of the normally graded thick-bedded sandstones and conglomerates facies; the association supports a resedimented origin for the conglomerates. 2.4.2.5 ORGANIC DEBRIS Description The organic content of the Angostura sandstone deserves special mention. Organic matter is not a common feature seen within earlier Paleogene sandstones, though they were observed at the type section of the Pointe-a-Pierre Formation by Kugler (1996). Organic matter is very common within sandstones of all the facies described above, where its occurrence ranges from a scattered, randomly oriented wispy fabric (disorganized facies) to interlaminated parallel or contorted particle concentrations (organized facies) (Figure 2.21 C, 2.22 C, 2.23 B-D). These two states may be mutually exclusive or transitional where beds display a consistent transition from disorganized bases to organized tops that coincide with changes in quartz grain size. Organic matter may also be concentrated among the parallel and ripple laminae of sandstone tops. Instances were observed where the organic matter was concentrated into cm-spaced wispy laminae that 'floated' within massive sandstone with no apparent break in sedimentation between the laminae (Figure 2.23 D). The significance of these will be expanded upon below. 115 Interpretation Organic particles were deposited by similar mechanisms as the enclosing quartz grains but if the relative settling velocities are considered, they provide additional insights that are not otherwise obvious. Nwachukwu and Barker (1985) gave a range of densities for terrestrial organic matter off of the Orinoco delta of 1.32 - 1.72 g/cm3. This range implies that organic matter has a hydraulic equivalence closer to clay particles and will naturally tend to settle with them in a standing body of water. If particle density is assumed to be the primary control on grain settling (i.e. the effects of particle shape, size and cohesion is assumed to be negligible ), organic particles are expected to 'behave' similarly to the clay fraction within an unsteady flow. This tendency can be observed in the organic facies, for example with the increasing concentration of organic particles towards the top of a normally graded bed simultaneous with a higher content of silt and clay-sized particles (Figure 2.22 C). Similarly, the disorganized organic facies are expected to occur among the massive and poorly sorted beds, and this does occur (Figure 2.23 C). The 'floating' organic laminae however, do not conform to an expected distribution for surge-type turbidity flows. The recurrent concentration within otherwise massive sandstones suggests that flow conditions (velocity and/or turbulence) changed sufficiently to allow concentration of organic particles into individual laminae and subsequently changed to favour the deposition of only the denser quartz grains. The absence of any obvious break between these recurrent laminae suggests prolonged waning and waxing flow velocities similar to the process described by Kneller (1995) for quasi-steady flows. The implication is that the sandstones were not only deposited by surge-type grain flows, but quasi-steady flows may have also played a role. This idea is further developed when sandstones of the Nariva Formation, with its higher content of organic matter, are considered. Organic particles are of a similar size within any particular bed or horizon (at least in two dimensions) and the effect of particle shape on drag/ lift forces is assumed to be constant. 116 2.4.3 PETROPHYSICAL LOG FACIES AND FACIES SUCCESSION The Angostura Sandstone is at least 300 m thick (Lerch et al., 2004) within the eastern offshore area of the Central Range (Figure 2.18). It attains thicknesses up to 450 m in the wells used for this study, although this may be due in part to structural repetition (Figure 2.19). Petrophysical log patterns (gamma ray) are consistently aggradational, with repeated "blocky" log patterns over the thickness of the sandstone. These blocky log patterns were correlated to the graded thick-bedded sandstone facies described above (Figure 2.24 C at 10 m). The finer grained, shale prone facies with non-amalgamated turbidites display a characteristic serrated log pattern, reflecting a greater heterogeneity over these intervals. These subsurface trends were useful when determining the succession of facies. The facies described above are interbedded within an aggradational succession that can be observed both in core and inferred from the petrophysical log signature. Metre-scale fining upward bedsets are a significant component within the overall aggradational succession and these were interpreted as channel fills. The finer grained bioturbated sandstone and siltstone facies assemblage account for a minor component within the overall succession and it is likely that much has been eroded by the coarse-grained flows. 2.5 NARIVA FORMATION 2.5.1 OVERVIEW OF THE NARIVA FORMATION The term "Nariva Formation" was first used by Kugler (1936) to refer to several rocks now known to extend from the Eocene to Early Pliocene. The Formation crops out across the extent of the Central Range (Figure 2.18). Its stratigraphic relationship with other formations is better defined than that of the Pointe-a-Pierre Formation, likely due to more extensive outcrops and many subsurface penetrations in the Tabaquite and Brighton Marine oilfields, where it is the main hydrocarbon producer (Figure 2.18). The formation can be distinguished by mineralogical and lithological character although several workers 117 Gamma rav (5170ft MD), Core grain size Fades Interpretation 70m Jtop_core ~~~[ Combined grain and cohesive (lows, plus IsSi)' fes^£« fallout from suspension. '£3 -?•=. 6(H Amalgamated turbidites. High density grain and fluidized flows, traction and suspension FACIES currents. Stacked Ta or S3 upward gradational to S3-TVTd 50- divisions and normally greeted ^] Gobble conglomerates beds. Amalgamated channel Ms Ta-Td- torWdiles Graded thick-bedded ?;y sandstone and conglomerates 40- Massive thick-bedded sandstone Bioturbated sandstone and siltstone assemblage 1a) Fine-grained sandstone and siltstone 30 Non-amalgamated turbidites and 1b) Contorted shale and deformed mudclast laminated lines. Combined traction plus suspension faHout 1c) Subordinate coarse-grained sandstone from high density fluidized flows and low density turbidity currents. Cohesive flows. Channel margin or overttenk deposits 20- Amalgamated turbidites produced from high rates of sediment fallout from suspension during the passage of 10- waning, high density fluidized flows. Grain flows are of minor importance. Proximal lower slope to inner tan robes 5 OmJ JIM.L.J (5520)* Figure 2.24 Gamma ray log calibrated with facies for the Angostura Sandstone derived from the cored interval in well Kairi-1. Collectively, they demonstrate an aggradational succession for these sandstones and conglomerates. Interpreted sedimentary processes are shown along with likely depositional environments that were interpreted from the "thick-bedded massive and graded turbidites" facies association (Chapter 3). The cored interval relative to the complete sandstone interval penetrated by the well is shown in Figure 2.19 B. Numbers in parenthesis are the measured log depth in feet. 118 have commented on the lithological similarity to the Pointe-a-Pierre Formation (Waring 1926; Liddle, 1946; Suter, 1960) as a cause for potential miscorrelations in the field (Illing, 1928; Algar, 1993; Kugler, 2001). Illing (1928) gave the first detailed lithological description of the Nariva Formation which formed his "Poonah Series" and part of his "Ben Lomond Formation", both of which are now obsolete terms (Kugler, 1956). The latter consists of micaceous shale beds with interbedded flaggy sandstones and localized coarse "grits" (Illing, 1928, p. 16). He also noted the abundance of leaf impressions and lignite beds. His description of the "Poonah Series" was made from 360 m (1200 ft) of exposure along Poonah road in the western Central Range. There, the sandy succession consists of coarse-grained sandstone beds gradational upward to sandy clays and, eventually, pure clays with rare sandstone beds. The lower coarse-grained sandstone bedset is up to 24 m (80 ft) with individual bed thicknesses typically up to 60 cm (2 ft). As with his "Ben Lomond Formation" lenticular layers of "lignitic material", typically less than 30 cm also occur among the coarser intervals (Illing, 1928; Kugler, 2001). It is apparent that the Nariva Formation also shales-out towards the southeast of the Central Range (Waring, 1926; Kugler, 2001). Kugler (2001, p. 170) also noted the occurrence of conglomeratic lenses with "well rounded black cherts and quarzites" as part of the lithological framework. Stainforth (1948) considered the Nariva Formation to be a biofacies within the thicker Cipero Formation, consisting of a predominantly arenaceous benthic foraminifera assemblage as opposed to the more calcareous planktonic assemblage of the Cipero Formation (Stainforth, 1948; Bolli, 1957b). Bolli (1957b, figure. 20) equated the formation to the lower "arenaceous Cipero", one of several arenaceous (bio)facies in the Cipero Formation (Kugler, 2001). Other fossils known in the Nariva Formation include reworked Lower Cretaceous to Eocene foraminifera, "koproliths", echinoid fragments, fish teeth and gastropods (Kugler, 1953; 2001). Apart from the faunal comparisons, the Nariva Formation shares an interfingering relationship with the Cipero Formation (Stainforth, 1948; Bolli, 1957c; Suter, 1960) and near its top, with the Brasso Formation as observed at Piparo (Suter, 1960). Based largely on these interbedding relationships, the age of the formation ranges from Late 119 Oligocene to Early Miocene (Table 1.1; Bolli, 1957b; Saunders et al., 1998) although Late Eocene ages have also been proposed (Illling, 1928; Renz, 1942; Stainforth, 1948; Bronniman in Suter, 1960). Kugler (1953; 1956) limited the Nariva formation to the Globigerina dissimilis and Globigerina insueta zones of the Cipero Formation (Early to Middle Miocene), again because of the interbedded relationship. Bolli (1957b) ascribed fauna of the Nariva formation to the Catapsydrax dissimilis zone, though he stated that it may range between the Globorotalia kugleri and Catapsydrax stainforthi zones (Late Oligocene to Early Miocene) (Table 1.1). The base of the Nariva Formation is unconformable upon many older formations. The type ection is at Nariva Hill (central Central Range) where the base rests on shales of the Cipero Formation (Kugler, 2001) while Illing's "Poonah Series" unconformably overlies the late Eocene-Oligocene San Fernando or Cipero formations (Illing, 1928; Kugler, 1956). It is also unconformable over the Eocene Pointe-a-Pierre Formation (Waring, 1926; Suter, 1960) and Cretaceous sediments (Kugler, 2001; Wallis et al., 2002; Harper and Chambers, 2004). The formation is unconformably overlain by conglomeratic beds including the diachronous Cunapo Formation as observed at Morne Brule (northern Central Range) (Table 1.1; Kugler, 2001; Suter, 1960) and according to Suter (1960), the Rio Claro boulder beds of the Lengua Formation (Table 1.1) along the southern Central Range. To the southwest of the Central Range (within the Gulf of Paria), the formation is unconformably overlain by Late Pliocene deltaic sediments of the Morne L'Enfer Formation. The top is not well defined where interbedding was observed with the Brasso and Cipero formations (e.g. at Chert Hill and along Brasso-Tamana road, Naparima area, Pointe-a-Pierre) (Kugler, 2001). Estimates for the thickness of the formation range from 500-2000 m (1750-6600 ft) (Kugler, 1953; 1956; Suter, 1960). Palaeoenvironmental interpretations for the formation are varied. Stainforth (1948; 1952) suggested that it represents turbid deposition within nearshore to "sublittoral" (greater than 60 m water depth, p. 1315) environments. A similar shallow- water environment was proposed by Algar (1993) who suggested deposition as shelf turbidites below wave base; he cited the abundant plant remains, absence of sedimentary structures and similarities with the Pointe-a-Pierre Formation as evidence. Suter (1960) 120 suggested foredeep-flych origin while Kugler (1953; 2001) suggested a tectonically active slope environment within a southerly migrating foredeep with plant remains rafted into deeper water. Kugler's interpretation was based largely on his "wild flysch" theory in which he interpreted blocks of Cretaceous to Eocene age (up to 600 m long by 100 m thick) within Nariva Formation clay beds to be "slip masses" or olistoliths (p. 249) associated with the orogenic uplifting of the Northern and Central ranges. Algar (1993; 1998) disputed the "wild flysch" origin for many of these blocks and instead favoured a tectonic origin. There appears to be a consensus that the Nariva sandstones were derived from a relatively proximal, northerly source. Waring (1926) and Kugler (2001) suggested that the sandstones were recycled from the Eocene Pointe-a-Pierre Formation while Stainforth (1948) suggested that they were eroded from a "Central Range high". Wallis et aL, (2002) interpreted the sandstones as turbidites derived from "the north", implying a relatively proximal source. 2.5.2 FACIES OF THE NARIVA FORMATION (FROM OUTCROP) Lithofacies of the Nariva Formation were examined from four outcrops along the western Central Range and full-hole cores from the Brighton Marine oil field in the southern Gulf of Paria (Figures 2.18 and 2.25). The subsurface cores were in a degraded state and as a result, they were used only to support lithofacies discerned from the outcrops. At least four lithofacies were discerned from outcrop and core: amalgamated pebbly sandstone, massive thick-bedded, parallel laminated sandstone and tabular sandstone. It will be shown that facies are similar to those described for the Pointe-a- Pierre Formation although they can be clearly differentiated by mineralogy. 121 2.5.2.1 AMALGAMATED PEBBLY SANDSTONE (APS) Description This facies is very similar to that described for the Chaudiere Formation and was best observed at Sandstone Trace and Corbeaux Hill (Figure 2.26 and 2.27 A). It consists of amalgamated bedsets of poorly sorted, pebbly sandstone. Individual bed thicknesses range from decimetre scale up to 2 m though amalgamated bedsets up to 4 m were measured (Figure 2.27 A). Beds are typically massive although one bed graded upward from a pebbly, massive base upward to sandy parallel laminae and silty current ripples (Figure 2.28 D). Irregular bed contacts are the norm for this facies. Organic matter content varies from locally abundant within the rock framework (e.g. Corbeaux Hill) to rare (e.g. Sandstone Trace). Where abundant, the organic matter is concentrated within decimetre-scale lens-shaped pods or mixed with the coarse sandstone. Shale is entirely absent within these amalgamated, coarse-grained bedsets. No evidence of bioturbation was observed. Interpretation Similar to the Chaudiere Formation, these beds are interpreted to be the result of high-density grain and liquefied flows similar to the S1-S2 divisions of Lowe (1982). The normally graded beds also suggest deposition and sorting from suspension sedimentation and traction currents. The amalgamated nature of bedding combined with the pebbly grain size and irregular (erosive) surfaces suggest confined flow along axial regions of turbidite channels. The organic matter is similar to the "disorganized facies" described for the Angostura Sandstone (Section 2.4.2.5) with scattered, chaotic fragments within the quartzose matrix. 2.5.2.2 MASSIVE THICK-BEDDED SANDSTONE (MTBS) Description This facies is also described from outcrops at Sandstone Trace and Corbeaux Hill and is similar to that described for the Pointe-a-Pierre Formation (Figures 2.26-2.27 A). 122 Figure 2.25 Representative interpreted seismic section showing NW-SE shortening and piggy back stacking of thrust sheets in the Brighton Marine oilfield, southeast Gulf of Paria. A) Seismic section without interpretation. B) Interpreted seismic section; all of the wells shown, except GU-990, drilled through the Nariva Formation below the Pliocene-Early Miocene unconformity. Gamma ray logs are superimposed to portray sandstone distribution in the Nariva Formation in the uppermost thrust sheet only. Well ABM-91 is magnified in Figure 2.31. The line was derived from a 3D seismic survey shown in Figure 2.18 A, C. 123 Sandstone Trace section I lis FACIES INTERPRETATION S1 - S2 - S3 - Tt sequence. -,*! Massive thick-bedded Deposited from high density sandstone grain and liquified flows. S2 - S3 sequence. Amalgamated, high density grain flows deposited during waning stage of high velocity surge-type or quasi-steady currents. LEGEND Fig. 2.28D p™™™™^^. fc& Wavy divergent laminae •; Organic matter * Amalgamated pebbly S==2 Wavy parallel laminae -wT- F sandstone Scour ' ' Parallel laminated M Load structure Post depositional fractures Contorted bed/ * ^S laminae Trace fossil & A Flame structure r Fining upward M Mudclast „-rt\ Current ripple Figure 2.26 Facies and facies interpretation of the Nariva Formation from Sandstone Trace. MTBS facies overlying APS facies defines a fining upward succession among these coarse grained sandstones. 124 Corbeaux Hill section Esmeralda Junction section A Ill§ mens ||s FACIES INTERPRETATION Massive thick-bedded sandstone Stacked Ta-Tb Parallel laminated Waxing-waning quasi-steady sandstone flows to upper plane bed velocities. Grain flows combined with suspended sediment fallout. Erosive flows. Parallel laminated sandstone m HW5010 Fig. 2.29 (A,B,F) Fig. 2.28 (B,C) i L i y Parallel laminated sandstone u =3 lim |Flg.2.28A Amalgamated pebbly sandstone Figure 2.27 Facies of the Nariva Formation from Corbeaux Hill and Esmeralda Junction. A) Corbeaux Hill section displays general fining-upward from basal APS facies. B) Parallel laminated and massive sandstone beds at Esmeralda Junction. 125 Figure 2.28 Sandstone facies of the Nariva Formation. (A) and (B) Parallel laminated sandstone facies at Esmeralda and Corbeaux Hill respectively. (B) comprises an amalgamated bedset 50 cm thick. (C) Massive sandstone with irregular base incised into parallel laminated sandstone. (D) Amalgamated pebbly sandstone facies exposed at Sandstone Trace. The lower bed (arrowed) is 2 m thick and overlies the pebble conglomerate shown in the inset. 126 It is differentiated from the amalgamated pebbly sandstone by the relatively finer grain size, although the two facies are gradational into each other. Sandstones are poorly sorted and comprise up to pebble-sized clasts scattered within a coarse quartz matrix. Individual bed thicknesses range from decimetre-scale up to two metres and may vary over the extent of the outcrop with irregular bedding contacts and basal mudclasts. Both massive and normally graded beds occur, some with dish structures throughout their bed thickness. Interpretation These beds are analogous to the S2-S3 divisions of Lowe (1982) deposited by the passage and collapse of successive high-density sediment gravity flows. Evidence for traction-related sediment reworking was limited to the top of a gradational sandstone bed. The massive bedding style is attributed to fallout from surge-type gravity flows. These were erosive events evidenced by the irregular bed contacts. 2.5.2.3 PARALLEL-LAMINATED SANDSTONE Description This lithofacies is described from outcrops at Esmeralda Junction and south of Corbeaux Hill (Figure 2.18) and is distinguished by the amalgamation of parallel- laminated sandstone beds (Figures 2.27, 2.28 A-C). Sands are up to fine-grained size within the amalgamated parallel laminated beds, with laminae highlighted by alternating layers of organic and quartz particles. The thickest 'laminae' are up to 4 cm. These thicker beds are massive, with a sharp top and base bounded by organic laminae. These laminated sandstones always occur together with beds of massive sandstone (up to 40 cm) with wavy, irregular bases, pinch-and-swell geometry, scattered organic fragments and up to medium-grained size (Figure 2.28 C). At least two stacking patterns were recognized between these two facies (massive and laminated). At Corbeaux Hill, the parallel-laminated beds amalgamate into metre-scale bedsets interbedded with the undulatory massive beds. At the Esmeralda Junction outcrop, sandstone beds are thicker (30-50 cm) and the two facies form distinct bedsets (Figure 2.27 and 2.28 A). Within the 127 lower bedset, sandstone beds with planar contacts and uniform thickness contain parallel laminae throughout, occasionally transitional upward to rippled laminae; there is no obvious change in grain size. These are separated from massive beds with both planar and way bed contacts where parallel laminae occur only near the tops of a few beds. Organic fragments are also abundant within this lithofacies. They occur as disseminated particles, concentrated laminae, lens-shaped lignite bodies or as variably preserved leaves or leaf casts within sandstone beds (Figure 2.29 D). The leaf casts indicate that abundant whole and broken leaves were scattered in random orientation within the fine-grained sandstone beds (disorganized organic facies). The lens-shaped lignite bodies are only partially preserved; most of the lignite was removed by outcrop erosion creating 'gaps' in the outcrop. They occur as an organized organic facies of variably sized lenticular bodies (maximum thickness up to 160 cm thick, width not discernible) with interbedded beds of fine-grained sandstone (maximum seen was 4 cm thick) (Figure 2.27 A at 3.5 and 9 m and Figure 2.29 A). One 'gap' in the outcrop showed a lateral transition to interlaminated fine-grained sand and organic matter. Additional sedimentary structures include flame structures and deformed wavy- parallel laminae below massive sandstone beds. One 70 cm-thick bed consists of sandstone clasts up to 10 cm diameter floating within a silty matrix with abundant organic matter. Evidence for bioturbation is limited to a rare grazing trace (Subphyllochorda) at the sole of a massive sandstone bed. Interpretation The amalgamated parallel laminated facies suggests quasi-steady flow conditions at upper plane bed flow regimes, with sediment aggradation occurring during waning flow stages, or with increased sediment load (loss of capacity). Where sharp breaks are obvious between laminae (or beds), shorter-duration, surge type flows may be responsible, and these beds may be considered analogous to the Bouma Ta division with organic drapes (Td). The associated and thicker massive sandstone beds, though 128 Figure 2.29 Organic-rich sandstones of the Nariva Formation. A) Photo and line drawing (B) of interbedded lignite and fine-grained sandstone at the Corbeaux Hill outcrop. All of the lignite overlying the sandstone was removed by recent erosion and a lenticular 'hole' now exists at the outcrop (see section in Figure 2.27 A). C) Organic particles form dark-coloured parallel laminae in this fine-grained sandstone. D) Leaves and leaf casts in random orientation within sandstones of the parallel laminated facies. One well-preserved specimen is shown in the inset (photo courtesy Curtis Archie). E) Pitted coarse-grained sandstone; the pits are due to the removal of organic particles mixed with the coarse quartz grains. F) Close-up view of lignite flakes shown in (A). Entire thickness consists of compacted leaves and other organic matter. All images are from Corbeaux Hill except (D), from Esmeralda Junction and Kelly Hill. 129 analogous to the Bouma Ta division, were also likely produced by quasi-steady flows that represent waxing flow stages (erosion at bed base) followed by rapid sediment fallout during a waning phase of fluid flow. At Corbeaux Hill, very little evidence was seen for flow waning below plane bed velocities (e.g. presence of ripples). Flame structures and wavy laminae below massive sandstone beds provide further evidence for rapid sediment loading from suspension. The concentration of organic matter within the lens-shaped lignite beds suggests proximity to an abundant source of organic matter. A similar interpretation was invoked for the organic facies described for the Angostura Sandstone, except that flows in the Nariva Formation were apparently of longer duration (greater degree of amalgamation). The geometry of these lignite beds and interbedded sandstone suggests that these are resedimented, deposited under similar flow conditions to the parallel laminated and massive sands. This is further supported by their lateral transition to interlaminated sand with organic matter and the absence of rooted horizons below these beds. The occurrence of floating sandstone clasts within silty, organic-rich matrix likely occurred under more cohesive flows capable of supporting the large clasts. These are interpreted to represent debris flows along an unstable gradient. The organic-rich source may have been a delta or coastal lagoon. The relative concentrations within the beds were likely due to environmental conditions at the sediment source. It is difficult to estimate the relative proximity to source based on the outcrops studied. There is no evidence for wave or other shallow water sediment reworking yet the distance to source was sufficient to allow the concentration of large amounts of organic matter into individual beds and preservation of entire leaf fragments (Figure 2.29 D). 2.5.2.4 TABULAR SANDSTONE (TS) Description This lithofacies is described from poorly exposed outcrops along the top of Corbeaux Hill (Figure 2.1) where sandstone beds are interbedded with mottled, grey shales. Grain size ranges from very fine to coarse within tabular sandstone beds with 130 planar tops and bases. Sandstone beds are up to 1 m thick although they are typically 30cm and display either normal grading or massive character. Thinner beds may be separated by shale partings. Common sedimentary structures include parallel laminations and current rippled laminae overlying more massive intervals. A sandstone-shale ratio of 1:3 is estimated for this locality. Organic matter is not as common to these beds relative to other lithofacies. Interpretation The assemblage and sequence of sedimentary structures are typical of turbidite beds in which partial components of the Bouma interval are recognized (Bouma Ta, Tb, Tc). This lithofacies is distinguished by the tabular nature of sandstone beds, which suggests greater lateral continuity relative to other lithofacies described. These beds may be representative of a more distal environment (perpendicular or parallel to flow axis) with lower rates of sandstone amalgamation and lower input of organic detritus. 2.5.3 FACIES OF THE NARIVA FORMATION (FROM SUBSURFACE CORE) The full-hole cores examined from the Brighton Marine oilfield (Figure 2.18) now consist largely of degraded rubble, attributed both to the friable nature of the sandstones and the age of the cores, many taken over forty years ago. The grain-size variations throughout the cores were logged along with sedimentary structures preserved in larger core fragments, some up to 30 cm (1 ft). Although no new facies were discerned from the cores, this served to extend the spatial range of those that were described from outcrop. The following facies description is from well ABM-44 in the Brighton Marine field from which 40 m of core were examined (Figure 2.30). Sandstone between 2937- 3029 ft core depth is predominantly fine- to medium-grained with occasional coarse grained intervals, more common towards the base. Many of the sandstone core fragments are either massive or parallel laminated and dish structures were apparent (Figure 2.30). 131 A few intervals of wavy-divergent laminae are indicative of current ripples. Also common are floating sandstone, mudstone and organic clasts within silty, sandy matrix. Organic fragments are also abundant; either as angular disseminated fragments within sandstone or concentrated along parallel laminae. The association of sedimentary structures is interpreted as partial Bouma sequences for turbidites. The massive sandstones and dish structures are indicative of rapid sedimentation, likely from the passage of high-density sediment gravity flows. Both suspension fall-out and concurrent sediment reworking by traction currents associated with the passage of the density current led to the deposition and preservation of parallel laminated sandstone. Similar to observations at Corbeaux Hill, intervals of floating sandstone, mudstone and organic clasts within a sandy matrix may be attributed to more cohesive flows; alternatively, these are rip-up fragments at the base of turbidite beds. A more conclusive interpretation is hindered by the limited core. The interpretation of the cored intervals is similar to that applied to outcrop. The abundance of organic matter suggest close proximity or direct access to an organic source although no evidence was seen to suggest reworking by shallow water processes. 2.5.4 PETROPHYSICAL LOG FACIES The Nariva sandstones are the primary hydrocarbon reservoir in the Brighton Marine field. The general structure across the field was determined for this study by interpretation of the 3D seismic survey that exists over the field constrained by several petrophysical well logs and formation tops used by past petroleum companies. The wells were 'tied' to the seismic using checkshot data from a well just south of the Brighton Marine field (AS-129). The main structure over the field consists of several piggy-back thrust sheets that verge towards the southeast. Early Miocene and older sediments are deformed and repeated within the thrust stack (Figure 2.25) and these are unconformably overlain by Plio-Pleistocene sediments. Away from the main field area, extensional faults were observed to the northeast and 'washout' zones on the seismic data are likely associated with intensely deformed areas. No attempt was made to resolve the nature of these deformation events except that they also deform the piggy-back thrusts and must 132 ABM-44 Depth TO Figure 2.30 Facies of the Nariva Formation from subsurface core in well ABM-44 (the cored interval is shaded in (A)). A) Petrophysical logs (SP, volume of shale and resistivity) demonstrate a fining-upward succession over the cored interval. B) Parallel laminated sandstone facies. C) Sandstone with abundant organic fragments. D) Contorted organic-rich, silty sandstone with floating mudstone and sandstone clasts. E) Core fragment of massive sandstone. F) Dish structures. For scale, the diameter of each circle is 2 cm. 133 be associated with a later deformational history. Similarly, no attempt was made to restore the structural section or determine the amount of shortening. The interpretation across the field provided a basis for evaluating sandstone distribution and stacking patterns within the Nariva Formation as continuous sections within individual thrust sheets could be isolated for study. Particular attention was paid to sections where the sand beds were not truncated by the thrust faults, which increased the likelihood of a continuous subsurface section. One of the better examples is shown in Figure 2.31. Within well ABM-91, the sandstones sharply overlie shale beds and show a fining-upward trend over 800m (2600 ft) until the uppermost shale interval is truncated by an unconformity. A similar sharp-based, fining-upward trend exists over the cored interval shown in Figure 2.30, though on a smaller scale. 2.5.5 FACIES SUCCESSION Direct reconstruction of the facies succession was hampered by the limited lateral extent of outcrops and the limited core coverage. The succession proposed below is based on the descriptions given above from outcrops, petrophysical well log signatures and information derived from the published literature. It assumes that the facies and trends recognized from these sources represent most of the formation, although this may not be the case for the finer grained intervals. The petrophysical log over an extensive section of the Nariva Formation in well ABM-91 suggests a fining upward trend to the sandstones. Similar fining-upward trends, though at a smaller scale, are obvious from the grain size variations noted from other sources: (1) the ABM-44 core, (2) at the Corbeaux Hill and Sandstone Trace outcrops and (3) Illings's (1928) description of the "Poonah Series" along Poonah Road. A vertical correlation of facies to the outcrop data is proposed in Figure 2.31 where the coarser grained facies are correlated to the lowest gamma-ray values. It is proposed that the pebbly sandstone facies is the dominant facies towards the base of the succession and is increasingly interbedded upwards with massive thick-bedded sandstone facies. This is then succeeded by fine-grained sandstones of the parallel laminated and tabular sandstone facies. It was obvious from outcrops that the facies are interbedded in part. 134 ABM-91 Gamma ray 2750ft Unconformity FACIES Parallel laminated & thick-bedded coarse-grained Thick-bedded coarse-grained & parallel laminated A Amalgamated pebbly sandstone Thrust fault 5600' Figure 2.31 Proposed facies succession through the Nariva Formation based on well ABM-91 from the Brighton Marine oilfield. The dashed arrows suggest transitional and interbedded facies contacts as apparent from outcrops across the Central Range. The rationale for the succession is discussed in the text. The section represents an unfaulted section through the Nariva sandstones as determined from 3D seismic interpretation (see Figure 2.25). The top and base of the section are unknown and as a result, this is considered a minimum thickness (850 m) for the formation and one possible facies succession. 135 The succession of facies demonstrated in Figure 2.31 represents a fining upward succession of thick bedded and amalgamated, channelized turbidites at the base to parallel laminated and tabular sandstones towards the top. The related depositional environments will be discussed when facies associations are considered in Chapter 3. 2.6 MIDDLE CIPERO FORMATION (PLUM MITAN) An outcrop of interbedded sandstone, siltstone and shale at Plum Mitan in the eastern Central Range (Figure 2.1) was initially described as a facies of the Eocene Pointe-a-Pierre Formation by Algar (1993). The outcrop occurs at a faulted contact between the Pointe-a-Pierre and 'Middle' Cipero formations (Kugler, 1959). Punch (2004) suggested that this outcrop was instead of Miocene age based on mineralogical differences with established Pointe-a-Pierre outcrops and biostratigraphic information. The immature composition of the framework detrital components of the sandstones appears to support Punch's assertion but the heavy mineral assemblage is similar to that of the Pointe-a-Pierre and other Paleogene sandstones (see Sections 6.1.15 and Figure 6.19). The outcrop is here assigned to the Cipero Formation, likely of Early Miocene age, based primarily on the striking difference in facies (described below), the equivocal mineralogical and biostratigraphic evidence and the mapped juxtaposition with that Formation. 2.6.1 LITHOFACIES OF THE MIDDLE CIPERO FORMATION (PLUM MITAN) 2.6.1.1 SYMMETRICAL RIPPLED SANDSTONE Description The distinction of the outcrop at Plum Mitan from the Pointe-a-Pierre Formation on mineralogical grounds also finds support from the lithofacies attributes because the outcrop shares no similarity to undisputed outcrops of the Pointe-a-Pierre Formation. 136 The 10 m of section measured at this locality consist entirely of interbedded wave-rippled sands and shale overlain by trough cross-bedded sands (Figure 2.32). Sandstones are up to fine-grained within beds that rarely exceed 30 cm thickness; thicker bedsets occur as amalgamated beds differentiated by internal rippled surfaces. Symmetrical wave ripples occur throughout the section and are preserved in three dimensions as straight crested or linguoid ripple forms. Asymmetric current ripples are less common and planar laminated sandstones are also interbedded. Bed contacts are sharp, though not erosive. The erosive contacts are limited to shallow localized scours within amalgamated bedsets. One significant scour occurs near the top of the section overlain by up to 4 m of trough cross-bedded sandstone that thickens laterally across the outcrop. The uppermost (exposed) beds comprise discontinuous, wedge-shaped sandstone beds, deformed along their length or exhibiting a 'pinch-and-swell' character. Load casts, load balls, planar cross-beds, symmetrical ripples and deformed clay beds are also characteristic of this upper interval. Trace fossils are rare and of low diversity. They are limited to millimetre-scale randomly meandering or straight grazing epichnial traces. Palaeocurrents were measured from the pitch of ripple crests (corrected for dip), which consistently show a north-south orientation (Figure 2.32 D). This indicates an east-west palaeoflow trend across the outcrop (this is of local importance only as the structural history is uncertain). There is a small deviation (43°azimuth) in the orientation of ripple crests when compared to sediments below the large scour, consistent with the change in depositional facies between the two intervals. Interpretation The abundance of symmetrical, oscillatory ripples throughout the interval indicates deposition above wave base while the symmetric ripples suggest combined unidirectional (current) and oscillatory flow (Dumas et al., 2005). The planar laminated sandstones hint at fairly high flow velocities, reaching upper plane bed conditions. The trough cross-bedded sandstones above an erosive base are attributed to migrating dune- scale bedforms (decimetre-scale relief); the fact that it thickens laterally suggests a 137 channelized geometry. The deformed and discontinuous beds above the trough cross- bedded sands make up the fill within this channel. 2.6.2 PALAEOENVIRONMENTAL SIGNIFICANCE OF THE PLUM MITAN OUTCROP The Plum Mitan outcrop marks a significant change in facies when compared to the Paleocene-Eocene formations described above. For the first time, there is clear evidence among the clastic component of in situ sediment reworking by oscillatory currents; above-wave-base deposition can be confidently inferred. In addition, suspension-sedimentation was absent and traction/bedload currents were the main sediment delivery mechanism. The Plum Mitan facies indicates that relative shallowing of the basin occurred at least by Middle Cipero deposition (Late Oligocene-Early Miocene) and this is further supported by numerous limestone units of the same age that were mapped by Kugler (1959) (Table 1.1). Potential driving factors for the relative shallowing will be discussed in Chapter 7. 2.7 HERRERA SANDSTONE MEMBER The Herrera Sandstone Member of the Cipero Formation consists of sandstone, conglomerates and shales that range between the Globorotalia fohsi fohsi and Globorotalia fohsi robusta biozones of Bolli (1957b) (Table 1.1). The member overlies clays and silts of the Cipero Formation and is gradational upwards into the Karamat Formation. At least four type locations are known along the Herrera Ridge, an east- northeast trending topographic crest along the Rock Dome Anticline (see Figure 2.18 for location). Current knowledge of the member was derived from several subsurface cores in oilfields where the sandstone forms a major reservoir (e.g. Barrackpore oilfield). The Member has been described in several publications (Liddle 1946; Bitterli, 1958; Poole, 1968; Jones, 1968; Higgins, 1955; Hosein, 1990; Kugler, 2001) and proprietary reports (e.g. Sprague, 1991). The most detailed publication was that of Poole (1968) who 138 Figure 2.32 Symmetrical rippled sandstone Scour lithofacies of Middle Cipero Formation at Plum Parallel laminae Mitan. A) Stratigraphic log of section showing Asymmetrical ripple abundance of symmetrical ripples. A channelized Symmetrical ripple fill occurs towards the top, different in o Ball and pillow sedimentological character and paleocurrents to (b Load cast sediments below. B) Bedding plane view showing v Wavy laminae straight-crested ripples. C) Cross-sectional view of Contorted bed/laminae symmetrical wave ripples. D) Ripple-crest 1m- orientations along outcrop section; individual (2) Ripple crest orientation ml(Bt-dtodtonrfpateocunents ) readings are shown in (A). An east-west paleocurrent orientation is inferred. Wedge geometry (D 139 provided a review of subsurface cores from the Barrackpore oilfield and divided the sandstone into nine lithostratigraphic units. Poole's detailed and well-illustrated descriptions compared the sequence of sedimentary structures to that shown by Bouma (1962) and concluded that the Herrera sandstones were deposited by at least 234 turbidite events. His descriptions are invaluable 40 years later as some of the cores have since deteriorated. The term "pepper and salt" is commonly used to describe the greywacke appearance and character of the sandstone (Bitterli, 1958; Jones, 1968; Poole, 1968; Kugler, 2001). The sandstone is typically dark grey in outcrop, well consolidated with calcite cement and grain size ranges from fine to conglomeratic. The most distinctive feature is the abundant lithic fragments (chert, limestone, organic matter) that enable differentiation relative to the older quartz arenites of the Nariva, Pointe-a-Pierre and Chaudiere formations. According to Bitterli (1958) and Jones (1968), both northerly (Northern and Central ranges) and southerly (western Venezuela, Guiana Shield) source areas were proposed for the provenance of the Herrera Sandstone. Jones (1968) favoured a southern provenance based on a correlation with the Freites and Oficina formations in Venezuela and other speculative evidence. Hosein (1990) depicted a Northern Range source in his depositional model for the sandstones. More scientific, yet inconclusive evidence was found in the grain-size variations and heavy mineral assemblage. Poole (1968) suggested that the typical bi-modal grain size distribution indicates two distinct sediment sources that became mixed within the Herrera sandstones. A similar dual-source origin was suggested by J.C. Griffiths (in Kugler, 2001, p. 60) who recognized from heavy minerals "the original source that supplied the earlier rocks" and an additional source supplying glaucophane, garnet and staurolite to the assemblage. Interpretations of the depositional environment are similarly varied, ranging from continental-deltaic (Jones, 1968; Sprague, 1991) to deep-water turbidites (Poole, 1968; Hosein, 1990). The following was compiled from the published literature: 1. The subsurface extent in the Southern Basin is confined to a narrow, fault-bounded, northeasterly trending zone (Bitterli, 1958; Jones, 1968; Hosein, 1990). 140 2. There is good lateral sandstone continuity in a northeast-southwest trend (Hosein, 1990). Progressively younger sandstones extend further south while all sandstones generally shale-out in this direction (Jones, 1968) and are thickest along the flanks of anticlinal uplifts (Kugler, 2001). 3. Associated shales are rich in calcareous and arenaceous foraminifera indicative of bathyal depositional environments (Bolli, 1957; Poole, 1968; Kugler, 2001). 4. Unidirectional current directions were discerned from current ripple laminae (Poole, 1968). 2.7.1 LITHOFACIES OF THE HERRERA SANDSTONE Even within Poole's (1968) invaluable descriptions of the Herrera sandstone, no attempt was made to discern the depositional environments other than passing references to "channels". The following facies description for the Herrera sandstone is derived from full-hole cores in well BP-347 of the Barrackpore oilfield. This well and others were examined by Poole (1968) and at least one of the facies described here draws from his work. The Herrera Sandstone is divided into three lithofacies based on core descriptions carried out at the Geological Services Laboratory at Petrotrin, Pointe-a-Pierre where 150 m of core was examined over two days. Most of the core is well preserved; where this was not the case, sections were 'reconstructed' from core fragments. 2.7.1.1 RIPPLED SANDSTONE AND SHALE (RSS) Description Most of the core examined falls within this lithofacies and consists of an approximately equal amount of sandstone and shale (Figure 2.33 B). Sandstone beds are up to 60 cm thick and commonly less than 10 cm. They are also up to fine grain size with the occasional thicker bed attaining up to medium-grained quartz. Some beds are normally graded and others are massive; bed contacts are planar or irregular and 141 internally, beds display current ripple and/or parallel laminations (Figure 2.34 A, B). Some sandstone beds are massive or contain only deformed laminae typical of dish structures. All of these sedimentary structures (current ripples, parallel laminae, massive beds) occur entirely within individual beds or they may be transitional into each other. Current ripples are the most numerous sedimentary structure while mud clasts and organic matter are rare, both scattered throughout the sandstone intervals. Shale beds are light grey in colour, and commonly contain deformed sand and silt laminae, some of which are attributed to bioturbation. The latter may be sufficiently intense to obscure the contact between the various lithologies. This lithofacies overlies a dominantly shaly interval and it is transitional upwards to the "rippled and graded sandstone" facies (discussed below). Interpretation Most of the sandstone beds in this lithofacies display a transition from parallel to current ripple laminae, or less frequently, the sequence begins with massive sands. The sedimentary structures are typical of the Bouma sequence for turbidites (Bouma, 1962) and are interpreted to representj^b-Tc, Ta-Tb or Ta-Tc transitions. Low-density turbidites were the main sediment delivery mechanism, further supported by the fine grain size and abundance of interbedded shale, some likely deposited at the tail ends of flows (Bouma's Td-Te). This interpretation agrees with that of Poole (1968). 2.7.1.2 RIPPLED AND GRADED SANDSTONE (RGS) Description This lithofacies also consists of interbedded sandstone and shale beds but with an increase in sand relative to the rippled sandstone and shale lithofacies (Figure 2.33 A). It is differentiated by thicker sandstone beds (up to 70 cm) that display a greater degree of amalgamation and normal grading. Sandstones are dominantly fine-grained although coarser quartz grains occur at the base of thicker beds, or as thin beds with irregular basal contacts. A similar suite of sedimentary structures exists as described for the RSS 142 Traca l MaJ m fossils ills! nlMA 10320") 8m— arc o EH! 7_ fcss TJ o 6 — * «S% = ! 5 — ® M %* i 4 — JT fag^ - & 1 3— j 1 1 2 — ! 1— T ftas: i 'Reconstructed' ' from core fragments * *ri 0m— | Measured section (9872') Approximate core LgQgNB depth (feet) Zoophyhcos Current ripple i Chondrites fcgs Wavy-divergent laminae <£SJ^ Rhizocorallium Parallel laminae nxc Scolicia Scour Palaeophycus •; Organic matter § Escape trace Mudclast igh intensity of WW Dish structure T traces Other unidentified £ traces XI Load cast r Normally graded bed Figure 2.33 Lithofacies of the Herrera Sandstone Member, Cipero Formation. A) Rippled and graded sandstone facies. B) Rippled sandstone and shale facies. C) Graded thick-bedded sandstone facies. Trace fossils are discussed in Chapter 5. 143 '« mi 4* Figure 2.34 Lithofacies of the Herrera Sandstone Member of the Cipero Formation from subsurface core in well BP-347. A) Current rippled sandstone interpreted as the Bouma Tc interval. Organic matter is preserved towards top of photo (Or). B) Parallel laminated fine-grained sandstone upward into a current rippled interval (Tb-Tc transition). C) Massive fine-grained sandstone (Ta). D) Massive, pebbly sandstone bed characteristic of the thick-bedded coarse-grained sandstone facies. Note the loose pebble in the core, also from this facies (S2-S3). Classifications after Bouma (1962) and Lowe (1982). All sandstones shown here are fine-grained except (D). Scales are in centimetres. lithofacies. Floating and rip-up mudclasts are also more abundant in sandstone beds and organic matter is similarly scattered throughout. The characteristics of shale beds and bioturbation are also as described from the RSS facies. Interpretation A similar sediment delivery mechanism as the RSS facies is inferred on account of the similarity in sedimentary structures and transitional nature between the two. The thicker sandstone beds, higher degree of amalgamation and greater content of mudclasts suggest a more energetic environment that may be associated with proximity to sediment source or axial flow. Successive turbidite events however, are still sufficiently spaced to preserve entire, normally graded, turbidite beds displaying Ta-Tb-Tc-Td transitions. This differentiates this lithofacies from the "graded thick-bedded sandstone" facies, which overlies it. 2.7.1.3 GRADED THICK-BEDDED SANDSTONE (GTBS) Description This lithofacies is differentiated by the occurrence of pebble conglomerates, pebbly mudstones, amalgamated sandstones and rare interbedded shale (Figure 2.33 C, 2.34 D). At the time of examination, much of the cored interval consisted of a 'continuous' set of disjointed core pieces up to 12 cm length. The pieces are not broken along shale partings (as occurred in other lithofacies from this core) and their irregular habit instead suggests that the breaks occur randomly, perhaps due to core handling. Collectively, they suggest bed thicknesses up to 150 cm (approximate) consisting of massive, fine- and medium-grained sandstone. Parallel laminae occur near the top of one bed while organic fragments up to 3 cm diameter are commonly scattered throughout. Grey, bioturbated shale, as described from other lithofacies, is absent and instead, pebbly mudstone beds up to 20 cm thick are interbedded with the amalgamated sandstone. Pebbles are rounded and attain diameters up to 1 cm. The top of this lithofacies contains the coarsest sediment observed throughout the core. Most of the interval now consists of rubble, but the lower 90 cm is preserved intact, 145 overlain by approximately 4 m of rubble. The interval consists of a pebbly conglomerate with clast size up to 5 cm in a fine sand matrix. Mudclasts are rare, unlike the rippled and gradational sandstones. Poole's (1968) core description and illustrations from well BP-347 included this facies, and a few points are worth repeating here. This facies is part of his "unit G" characterized by thick beds of normally graded, conglomeratic sandstones. It consists of gradational bedsets or "cycles" (Poole, 1968) with thicknesses up to 6 m. Each of his "cycle" grades from massive conglomerates at base (with erosive contact) to parallel and ripple-laminated, fine-grained sandstone. Contorted siltstones occur near the top of the bedsets and organic matter is abundant throughout Interpretation The erosive base of beds, high degree of sandstone amalgamation, coarse grain size and fining-upward bedsets are interpreted as channelized turbidite fills. The fills comprise beds of stacked, truncated turbidites (Ta-Tb); upper turbidite sequences (Tb-Tc- Td) and background shale were eroded by successive flows or never deposited. The large-scale fining upward bedsets record the overall filling and abandonment of the channel. Cohesive flows and soft-sediment deformation may have been a significant contributor to the channel fill once abandoned by turbidites, supported by two lines of evidence. Firstly, Poole (1968) noted contorted beds towards the top of his 'Unit G' and these are here interpreted as bed-collapse features from the channel margins. Secondly, this interval was also cored in well BP 344 and described by Poole (1968). His "Unit E" is correlated with the graded and thick-bedded facies and consists of 66 m of amalgamated bedsets of top-truncated turbidites with minor intervening shale. This unit is overlain by 10 m of matrix-supported mudstone conglomerate with chert, quartzite and limestone pebbles. Hence matrix-supported (cohesive) flows were active following channel incision and subsequent fill. 146 BP-344 BP-347 Gamma ray Measured Oammarai/ Measured Fades-units" I Correlative . DEPOSITIONAL - depth (feet) ENVIRONMENT uammaray^ depih(tept> of Poole (1968)| Fades (thisstudy) ^3500 F-H E GTBS \ i 'RGS & ,RSS D \ • RGS C t i RSS B > > 1 i A RSS Figure 2.35 Lithofacies succession in the Herrera Sandstone Member. A) Facies and facies interpretations fromthi s study shown against the gamma ray log for well BP-347. Facies are discussed in the text. Zoophycos ichnofacies discussed in Section 5.3. B) Facies from this study correlated to those described by Poole (1968) for well BP-344. Interpretations at top of core derived from his facies "F-H". See Table 2.1 for a summary of his facies. Dashed arrows suggest gradational facies contact; dashed correlation lines are drawn between diagrams. Depositional environment interpretations are discussed in Chapter 3. (B) modified after Poole (1968, Figure 5). 147 2.7.2 PETROPHYSICAL LOG FACIES The Herrera sandstone is a major hydrocarbon reservoir in the Moruga West, Barrackpore and Penal oilfields in the Southern Basin (Bitterli, 1958; Jones, 1968; Poole, 1968; Hosein, 1990), where hydrocarbons are produced from a series of stacked thrust sheets (Bitterli, 1958). Almost the entire sandstone interval was cored in well BP-347 where the sandstone is 250 m (750 ft) thick. Gamma ray (GR) wireline logs indicate an overall cleaning-upward character to the sandstone; at least three individual cleaning- upward cycles are superimposed on this general trend while the 'cleanest' sandstones display an aggradational (blocky) log character (Figure 2.35). Calibration with the core confirmed a coarsening-upward profile to the sandstones. The base of each cycle consists of 'rippled sandstone and shale' facies that grade upwards into the 'rippled and graded sandstone' facies. The coarsest grain size (lowest GR values) occurs at the top of the examined core (23 m below the top of the sandstone) and is calibrated to the 'graded thick-bedded sandstone' facies. The finest grained interval (highest GR values) coincides with shale-prone intervals assigned to the Zoophycos ichnofacies based on the assemblage of trace fossils (discussed in Chapter 5). A similar petrophysical log response exists in well BP-344 where approximately 300 m (1000 ft) of full-hole core represent most of the Herrera Sandstone (Figure 2.35 B). According to Poole (1968, p. 104-106), the cored interval transitions upwards from pure shale to interbedded "ripple- drift" and "parallel-laminated" sand and silt (his units A-C). This is overlain by 65 m of gradational "well developed" sands and pebble conglomerates (his unit E). His units ' A- C display a 'serrated' gamma ray log response, reflecting the heterolithic nature of sediments while unit 'E' displays a uniform, 'blocky' signature reflecting the more homogenous and amalgamated lithology. The lower units of Poole (A-C) are correlated to the 'ripple sands and shale' while the upper, homogeneous sands are correlated to the amalgamated, graded sandstone facies. 148 2.7.3 FACIES SUCCESSION The facies succession from the lithological and petrophysical facies assemblage indicates at least three coarsening and thickening upward 'cycles' for the sandstone. Cycles begin with a bioturbated shaly interval and grade upward to thin-bedded, rippled- sands and shale. This is succeeded by thicker, commonly graded turbidites displaying common Tb-Tc division and lesser Ta. The coarsest grains recorded in the system occur only in the uppermost cycle within thick-bedded, amalgamated and normally-graded turbidites. A heterolithic assemblage of graded turbidites, matrix and clast-supported conglomerates and rippled sandstones caps the succession. The coarsening and thickening upward cycles are analogous to the coarsening and thickening upward succession described for lobe deposits while the abundant current-rippled horizons are typical of overbank or channel-margin sediments (Mutti, 1977; Mutti and Ricci Lucchi, 1978; Walker, 1978; Mutti and Normark, 1987; Grecula et al., 2003). The relative merits of these environments will be elaborated when depositional elements are considered in Chapter 3. 2.8 PALEOCENE TO EARLY MIOCENE FACIES SUMMARY The facies described for Paleocene to Early Miocene formations are listed in Table 2.1. Collectively, a limited suite of facies exists for these sandstone units relative to that of younger sandstones (e.g. Late Pliocene Morne L'Enfer Formation). Most of the facies described are commonly related to sediment gravity flow processes and there is limited evidence to suggest shallow-water reworking by waves prior to the Early Miocene. The assemblage of facies is most characteristic of the outer shelf, slope and basin floor, produced by the combination of slope instability, deep-water accommodation and absence of secondary reworking by wave, storm and other shelf processes. The only evidence for the latter is suggested from the symmetrical-rippled sandstone facies within the Cipero Formation (Plum Mitan), and this equates in time with the occurrence of 149 shallow-water limestones (Table 1.1). Both indicate relative shallowing or local highs in the basin coeval with deeper-water resedimentation processes in the Nariva Formation and Herrera Sandstone Member. The high degree of sandstone amalgamation common to many of the sandstone intervals suggests common channelized deposits among them, and this was sometimes substantiated by common basal or interanal erosive surfaces. These were sometimes associated with discordant sandstone beds. Varied facies successions were also described although these can be divdied into at least three groups: (1) fining-upward successions of the Chaudiere, Pointe-a-Pierre and Nariva formations, (2) aggradational succession of the Angostura Sandstone and (3) coarsening-upward succession of the Herrera Sandstone Member. The related depositional features (depositional elements) and facies successions are discussed in greater detail in Chapter 3 where interpretations for depositional environments are also proposed. 150 Table 2.1 Collective facies and depositional processes for Cenozoic sandstones discussed in the text. Notice the traction-dominated shallow water facies associations of the Morne L'Enfer Formation relative to die gravity flow processes that dominated from the Paleocene to Middle Miocene (Chaudiere to Herrera). Shallow water transitions occurred in the Cipero, Cruse and San Fernando formations although the last was still dominated by sediment gravity flow processes. Decreasing age Key Discussed in detail Mentioned in text DOMINANT DEPOSITIONAL PROCESSES FACIES Cohesive, slides Discordant sandstone and and slumps, shale Cobble conglomerates Grain flow and Amalgamated pebbly bedload traction sandstone (and conglomerate) Massive thick-bedded sandstone Graded thick-bedded sandstone (and conglomerate)! iedload traction Parallel laminated sandstone and accretion from suspension Rippled sandstone and shale Rippled and graded sandstone Suspension settling Bioturbated sandstone and with traction reworking siltstone Suspension Laminated silts settling dominant Bioturbated silts Symmetrical-rippled sandstone . Thickening-upward wavy- flaser sands Traction/ bedload Swaley cross-stratified sands reworking Trough cross-stratified sands Amalgamated sigmoidal cross-stratified sands Laterally accreted sands Bioclastic facies Biohermal limestones Geometrical- Lenticular sandstones based facies Tabular sandstones Organic debris 151 Chapter 3 - Paleocene to Early Miocene Depositional Environments The previous chapter described lithofacies for the Chaudiere, Pointe-a-Pierre and San Fernando Formations and members of the Cipero Formation (Angostura and Herrera sandstones). Sedimentary processes were interpreted based on the physical characteristics and association of physical sedimentary structures, and some assumptions were made about sediment delivery based on the sandstone amalgamation or sand body geometry. Facies successions were suggested based on outcrop relationships, continuous core sections and petrophysical log properties. This Chapter will build on that framework with interpretations of specific depositional environments for these sandstones. This will be done by (1) considering palaeobathymetry and palaeoenvironment suggested from benthic foraminifera, (2) grouping of similar facies into facies associations, and (3) recognizing depositional elements from the facies and facies associations. The chapter will demonstrate that deep-water environments persisted in the Trinidad area throughout most of the Paleocene to Early Miocene. There is generally good agreement between the environments suggested by benthic fauna and the facies associations proposed, intervals of less agreement will be discussed and probable reasons put forward. The conclusions arising from this chapter establish both the facies associations and depositional environments that will be referred to in later chapters. Firstly, it provides a basis by which to compare sedimentary processes and environmental changes in Late Miocene and younger sands (Chapter 4); secondly, trace fossil intensity and diversity will be based on the established facies and facies associations (Chapter 5); and finally, it will be considered together with mineralogical characteristics (Chapter 6) in order to deduce any changes in sediment dispersal patterns (Chapter 7). 152 3.1 PALAEOENVIRONMENTAL INTERPRETATION FROM BENTHIC FORAMINIFERA A review of the palaeobathymetry associated with the Paleocene Lizard Springs Formation is a convenient starting point from which to review Early Cenozoic palaeoenvironments. Its rich planktonic and benthic foraminifera assemblage has been extensively studied for both age and palaeoenvironmental correlations to regions as far as the Gulf of Mexico, the Labrador Sea and sediments in the Polish Carpathians (Bolli, 1975a; Kaminski et al, 1988; Kugler, 2001). The formation is coeval with the Chaudiere Formation (Table 1.1). Kaminski et al. (1988) discussed the use of foraminifera assemblages as palaeobathymetric indicators and their variation among "flysch"-type environments. Their study correlated the foraminifera of the Lizard Springs Formation to the "Type-A" "flysch" assemblage of Gradstein and Berggren (1981) which is characterized by large, coarsely agglutinated and simple forms found on slopes in basins with restricted bottom water circulation and an otherwise restricted faunal assemblage. "Type-A" assemblages were correlated to palaeodepths ranging from 2500-3500 m (Gradstein and Berggren, 1981). Kaminski et al., (1988) also correlated the agglutinated Lizard Springs assemblage with upper to middle slope assemblages from Cretaceous sediments of southern California, and noted the similarity of the Lizard Springs fauna to 'flysch' sediments of the Polish Carpathians. From their study, they concluded upper to lower bathyal palaeodepths for the formation (Figure 3.1), with the deepest assemblage deposited below the carbonate compensation depth. For this investigation, fossil identification and palaeoenvironmental interpretations were provided by Dr. Mike Kaminski of University College, London, who previously studied the Lizard Springs Formation (Kaminski et al., 1988). Shale samples were collected from Paleocene to Early Miocene outcrops and subsurface cores including one sample from the subsurface well studied by Kaminski et al., (1988). The objective was to compare the palaeobathymetry and paleaeoenvironment indicated by the different faunal assemblages (Table 3.1). Most samples were derived from shales interbedded with the coarser clastic beds of the facies discussed in Chapter 2, and their ages 153 constrained by the geological maps in current use (Saunders et al, 1998). Only two samples were removed from these facies. A correlation was established for the first sample (HV6005, Tarouba Stadium site) based on the geological map (Saunders et al., 1998) and trace fossil similarities to studied intervals. The second sample (HV7024, Tamana Road Junction, Los Armadillos) was less certain. Although it lies within an area designated as Pointe-a-Pierre Formation and is located less than 100 m away from rocks similar to the tabular sandstone facies of the Pointe-a-Pierre Formation (Section 2.2.4.1), this sample was derived from a mud-supported conglomerate with metre-scale blocky and rounded boulders that may represent either a faulted or sedimentary (debris flow) origin. This uncertainty is compounded by the presence of Nariva Formation that was also mapped in the vicinity of the sample. The benthic faunal assemblage contains forms that were assigned to the Late Oligocene or younger (Alveovalvulinella, Valvulina flexilis) (M. Kaminski, pers. comm.). This was the only sample for which the ages suggested by the benthic assemblage were used. The palaeoenvironments indicated by the benthic assemblages suggest paleobathymetries ranging from outer neritic to abyssal water depths (Table 3.1) for periods ranging from Paleocene to the Early Miocene. Abyssal depths were interpreted for the Paleocene shales while later Eocene to Early Miocene forms were interpreted to represent outer neritic to lower bathyal. These will be correlated to the facies associations discussed below. 3.2 SUMMARY OF FACIES ASSOCIATIONS Some facies occur in more than one of the stratigraphic units described in Chapter 2 (Table 3.2). The assignment of facies associations were based on establishing a genetic link between facies. This was not straightforward given the different formation ages, modes of study (outcrop versus core) and degree of exposure. Facies associations were most confidently assigned where two or more facies were exposed at single outcrops. Where this did not occur, the individual facies was considered when discerning the various depositional elements. Within subsurface core, facies associations were assigned 154 from continuous cored intervals where facies were considered to be genetically related units (i.e. no evidence of unconformities in the section). On this basis, six facies associations and one of the individual facies groups were considered. These are listed in Table 3.3. DEPTH SEA-LEVEL '"m Figure 3.1 Bathymetric divisions of the marine environment. Modified after Berggren (1978), Figure 2. 155 Table 3.1 Palaeoenvironmental interpretations from benthic foraminifera. The Analysis was performed by Dr. Mike Kaminski (2008), University College, London. CCD = Carbonate Compensation Depth. AGE (Kugler, 1959 and Saunders FORMATION LOCATION SAMPLE NO. EQUIVALENT SANDSTONE FACIES PALAEOENVIRONMENTAL INTERPRETATION etal.,1998) Cipero Tarouba Stadium site HV6005 unknown Mixture of calcareous and agglutinated species; middle to lower bathyal; deeper more likely based on agglutinated forms. Early Miocene Cipero (Herrera Rock River, Basse Terre HV6012 Rippled and gradational sandstone Mixture of calcareous and agglutinated species; bathyal, Sandstone normal marine slope; upper part of the Oxygen Minimum Member) Zone. Cipero (Angostura Well Kairi-1 (5395 ft) AS1.16 Bioturbated sands and silts Agglutinated foraminifera assemblage. "Flysch-type" Sandstone) assemblage assembalge; "proximal" channel or fan; likely upper Late Oligocene bathyal depths. Pointe-a-Pierre San Fabien Road quarry GWHV14 Tabular sandstones Coarse agglutinated assemblage, low diversity; possibly outer neritic or upper bathyal setting Pointe-a-Pierre Tabaquite Sawmill HV5014 Lenticular sandstones Coarse agglutinated assemblage; possibly outer neritic. Middle to Late Eocene Pointe-a-Pierre Chaudiere River HV6027 Lenticular sandstones Agglutinated fauna recovered, no interpretation given. traverse, Mt. Harris Pointe-a-Pierre Chaudiere River HV6030 Lenticular sandstones Agglutinated fauna, deep-water, eutrophic, anoxic traverse, Mt. Harris environment; within lower part of the Oxygen Minimum Zone. Dominant deep-water agglutinated foraminifera; turbiditic enivronment, well-oxygenated, mesotrophic environment; Lizard Springs Paleocene Well GY-163 (4801 ft) HV5054 n/a lower bathyal to abyssal; close to the CCD. Unknown, possibly Tamana Road Junction, HV7024 n/a Upper to middle bathyal, few reworked Paleocene Nariva west from Los Armadillos specimens Late Oligocene or younger* * This age was suggested based upon benthic fauna. The age could not be conclusively determined from Kugler (1959) and Saunders et al. (1998). Table 3.2. Summary of facies characteristics and interpreted sedimentary processes for Paleocene to Early Miocene sandstones. The correlative facies of Mutti and Ricci Lucchi (1978) are shown for comparison. See Table 3.4 for a description of the facies of Mutti and Ricci Lucchi (1978). CORRELATIVE FACIES FACIES SEDIMENTARY FEATURES * SEDIMENTARY PROCESS OF MUTTI AND RICCI LUCCI (1978) 1. Discordant sandstone, shale Slump folds, rotated and displaced blocks, contorted strata, coherent slides, slumping, viscous flows. and limestone matrix and clast-supported conglomerates. 2. Cobble conglomerates Graded or disorganized cobble conglomerates, mudstone or Bedload traction, grain and inertia-driven quartzitic matrix; R2, R3, SI flows; cohesive flows. 3. Amalgamated pebbly Massive, amalgamated, rare normal grading, multiple erosive Bedload traction, grain and intertia-driven sandstone (and conglomerate) surfaces and scours, thick and thin bedscoarse to pebbly, high flows combined with suspension fall-out sandstone/ shale ratio traction carpets, organic matter in some, from high density flows; surge type or quasi- no bloturbation; SI, S2. steady. 4. Massive thick-bedded Massive, amalgamated, rare normal grading, thick-bedded (m- Bedload traction and accretion from A, B sandstone scale), mainly coarse-grained, dewatering structures, sand dikes, suspension fallout of high-density liquified load structures, trough and planar cross-beds, few shale flows, surge or quasi-steady interbeds, bioturbation limited to tops of beds or not bioturbated; S2, S3, Tt, Ta. 5. Sraded thick-bedded Common normal grading, fine-grained to conglomeratic, Inertia-driven grain and high-density A,C sandstone (and amalgamated m-scale thick bedset; floating mudclasts, fluidized flows; rapid fallout from conglomerates) multiple erosive surfaces, common to no bioturbation; inlcudes suspension induced sorting or quasi-steady "classic" turbidites; R3, S2, S3, Ta, Tb, Tc, Td. flows. Evidence for decreasing flow size and velocity upwards. 6. Tabular sandstone Massive, mainly fine-grained, cm-scale beds, flute casts at base Suspension fall-out from low - high density and rippled tops, shale interbeds and partings, planar tops and liquified, surge-type flows and subordinate bases, common bioturbation; mainly Ta, lesserTb-Tc. grain flows. 7. Lenticular sandstone Fine and coarse-grained turbidites, non-amalgamated, massive Suspension fallout from low and high and normally graded beds, thin and thick-bedden>ns-shaped density liquified flows. sandstone beds some "pinch and swell", shale-dominated interval, shale partings, planar bed bases; mainly Ta. 8. Parallel laminated Amalgamated parallel laminated sandstones, cm-scale bedding, High suspension fallout combined with high sandstone abundant organic matter, erosive-based massive sandstones, velocity traction currents; quasi-steady and flame structures, load casts, debris flows; Ta, Tb. surge type flows. 9A. Rippled sandstone and Thin, mm-cm scale beds, fine-grained sandstone, commonly Suspension fall-out, low-density turbidity C, D shale ripple and/or parallel-laminated, sometimes normally graded, currents and liquified flows. shale partings common, low sand/shale ratio, common bioturbation; Tb, Tc, Td. 9B. Rippled and graded Similar and gradational to "rippled sandstone and shale" but with Suspension fall-out, low-density turbidity sandstone higher sandstone/ shale ratio and thicker, graded sandstone beds;currents and liquified flows. Ta, Tb, Tc, Td. 10. Bioturbated sandstone and Laminated silts and muds, interbedded normally graded, cm-scale Suspension settling from low density C, F,S siltstone sandstones, few thick-bedded and coarse-grained; occasionally turbidites, minor cohesive flows and parallel laminated, pebbly and contorted mudstone, commonly slumps. bioturbated, relatively low sandstone/ shale ratio; Ta, Tb, Tc, Td, Te. 11. Symmetrical rippled Fine-grained, symmetrical and asymmetrical ripples, commonly Bedload reworking from oscillatory sandstone bioturbated. currents. 12. Organic debris Abundant disseminated or concentrated organic matter either as Turbulent and grain flows, quasi-steady and concentrated laminae, lens-shaped lignite beds or scattered wholesurge type; debris flows, and broken leaves. * Acronyms after classifications of Bouma (1962) and Lowe (1982). 157 Table 3,3. Facies associations and interpreted depositional environments for Paleocene to Early Miocene Formations. Interpreted depositional elements are after Mutti and Ricci Lucchi (1978) and Mutti and Normark (1987). INTERPRETATIONS CHARACTERISTIC 1. after Mutti and Normark (1987) FORMATION/ UNIT FACIES ASSOCIATIONS FACIES (Table 3.2) 2. after Mutti and Ricci Lucci (1978). (location or well depth) 3. ENVIRONMENT { discussed in text) I: Granular, amalgamated and thick- 3,4 1 .Depositional/ erosional channel fill, axial facies Chaudiere Formation (Growing Rock), Pointe- bedded sandstones 2.Inner-middle fan and slope associations a-Pierre Formation (Tormos, Caratal Road), Nariva (Sandstone Trace) 3.LOWER SLOPE CHANNEL FILL II. Channelized and deformed thick- 1.Depositional channel fills with finer-grained overbank Pointe-a-Pierre Formation (San Fabien Road, bedded and tabular turbidites and channel margin deposits Milan River) 11nner fan and slope facies associations 3.LOWER TO MIDDLE SLOPE CHANNEL FILL III. Thick-bedded massive and graded 2, 4, 5, 1 .Depositional and erosional channel fills, proximal lobes Angostura Sandstone (Kairi-1, Canteen-1) turbidites l.lnner to middle fan associations 3.AXIAL MIDDLE TO LOWER SLOPE CHANNELS AND OVERBANK AND PROXIMAL LOBES IV. Pebbly to fine-grained parallel- 3,4,8,12 1 .Mixed channel fill Nariva Formation (Corbeaux Hill) laminated sandstones 2.n/a 3.DELTA-FED UPPER TO MIDDLE SLOPE CHANNELS V. Coarsening and thickening upward 1,5,9 1.Depositional channels and thickening/ coarsening-upward Herrera Sandstone (BP-347 and BP-344) rippled to massive sandstones overbank wedge 2.Outer fan to distal basin associations 3.PROGRADING CHANNEL-OVERBANK BASIN FLOOR COMPLEX VI. Block slides, massive sandstones 1,2,7 l.n/a San Fernando Formation (Soldado Rock, and conglomerates Mount Moriah) 2. Slope association 3. UPPER SLOPE CANYON FILL VII. Lenticular and tabular sandstones l.n/a Pointe-a-Pierre (Mt. Harris, Tabaquite Sawmill) I.Slope association 3.MIDDLE TO UPPER SLOPE CHANNEL OVERBANK 3.3 DEPOSITIONAL ELEMENTS Stow and Mayall (2000, Figure 7) list at least eight depositional elements for deep-water sedimentary systems including several types of erosional features, channels, levees, lobes, mounds and sheet-like features. Some of the more commonly occurring were described by Mutti and Normark (1987); Normark et al. (1993); Mutti et al. (1999); Morris and Normark (2000); and Posamentier and Walker (2006). These include: (1) large-scale erosional features, e.g. slump scars, (2) canyons, (3) channels, (4) lobes, (5) channel-lobe transitions and (6) overbank wedges or levees. These depositional elements comprise specific features of the "inner", "middle" and "outer" fan as well as components of slope depositional systems described from classical models for deep-water sedimentation (Mutti and Ricci Lucchi, 1978; Walker, 1978). A few of these are illustrated in Figure 3.2 and a synopsis of their characteristic facies is provided below. 3.3.1 CANYONS AND OTHER LARGE-SCALE EROSIONAL FEATURES Large-scale erosional features also include slump scars and reentrants along the outer shelf and slope. They are associated with long-term sediment instability, and their location is usually a first-order control on sediment dispersal along slope profiles where they may either determine the pathways for sediment transfer into deeper-water environments, or create sites of ponding for later turbidites and debris flows (e.g. Prather, 2003; Shultz et al., 2005). The large scale of these features are better recognized from reflection and echo-sounding surveys but can also be delimited by the character of their fill and this is more applicable to this study. Canyon fills comprise a component of "slope facies" (Section 1.4.3). These fills usually comprise a high proportion of slumps, olistoliths and debris flows relative to turbidite beds (Stanley and Unrug, 1972; Cook, 1979; Nardin et al., 1979, Steel et al., 2000; Shultz et al., 2005), although channelized deposits are also common (e.g. Morris and Busby-Spera, 1988; Bruhn and Walker, 1997; Beaubouef et al., 1999; Camacho et al., 2002; Prather, 2003; Posamentier and Walker, 2006). 159 Figure 3.2 Relative location, geometry, facies and stratigraphic profile of depositional elements common to deep-water systems. (A) Illustration of the main depositional elements of a point-sourced, graded-slope to basin floor, deep-water system. These are discussed in text. (B) Schematic illustration depicting erosional base, lenticular geometry (one-half shown only) and nature of fill of two types of deep-water channels (discussed in the text). (C) Stratigraphic profile of levee-overbank system showing interbedded nature of shale with current-rippled sandstone. The thickening-upward profile indicates increasing proximity to the channel or crevasse splay. The related facies are discussed next to each diagram. (A) modified after Normark et al. (1993) and others modified after Mutti and Normark (1987). 160 3.3.2 CHANNELS Channels are a common depositional element to deep water systems as they are almost always associated with the transfer of sediments to the deeper parts of basins. They represent dedicated long-term pathways and often comprise the coarsest grain-size component of the system. They are commonly recognized by erosive surfaces below what can range from fine-grained muddy channel fills (e.g. Dott and Bird, 1979; Slatt et al., 2000) to conglomerate beds (e.g. Hein and Walker, 1982). The calibre and stacking of deep-sea channel fills have been extensively studied and a few trends have been recognized: (1) Within coarser-fills, a fining-upward trend is characteristic over the scale of metres to tens of metres reflecting waning flows resulting from either the abandonment or widening of the channel (Mutti, 1977; Shanmugam and Moiola, 1988; Clark and Pickering, 1996). (2) Variations from this fining-upward trend have been recognized where small- scale (2-4 m) thickening and coarsening upward packages were interpreted to result from lateral channel migration (Lien et al., 2003) or increasingly "depositional" (discussed below) character of the channel (Grecula et al., 2003). (3) Channels have been classified into erosional or depositional, largely related to the nature of their fill (Figure 3.2; Mutti and Normark, 1987; Clark and Pickering, 1996). The fill of erosional channels usually comprises coarse-grained and scoured turbidite facies, clast-supported conglomerates and debris flows. Distinctive facies include conglomeratic channel lags and mud-draped scours, as these provide evidence for bypass from which it is inferred that most of the flow was deposited further down-current. Depositional channel fills consist of thick, scoured, amalgamated and graded sandstone and pebbly sandstone beds, usually associated with the axial sections of channels. These may pass laterally into thinner, finer grained units separated by mudstone and eventually overbank sediments. Channels may contain a mixture of these two fill types. (4) Generally, channels become broader and less erosive downdip where they transition into unconfined, sheet-like sands typical of lobes (e.g. Beauboeuf et al., 1999; Slatt et al., 2000; Gardner and Borer, 2000). Channel fill facies can in part reflect the 161 position along this downdip profile. Mayall and Stewart (2000) proposed a model for slope channel fills based on three-dimensional seismic and core data (Figure 3.3). Their model included a basal gravel-lag facies overlying a prominent erosion surface. This is overlain by a chaotic facies comprised of muddy debris flows and slumps, which they interpreted to originate from higher reaches within the channel. This is in turn overlain by massive and amalgamated fine to pebbly sandstone facies with "individual channel facies" ranging from 1-10 m thick. The final phase of channel infill comprised fine grained sandstone and mudstones. These channels were "a few hundred meters wide" in extent. Their model demonstrates the associate fills of confined flows common to point- sourced slope settings as opposed to the broad channels and sheet-like sands of more distal fan environments (e.g. Schenk, 1970, Wickens and Bouma, 2000; Lien et al., 2003). This model is relevant to some of the interpretations presented below. Figure 3.3 Schematic illustrating idealized slope channel-fill succession which is compared to the Chaudiere/ Pointe-a-Pierre and Nariva Formation successions. Compare vertical profile with Figure 2.9. Modified after Mayall and Stewart, 2000 162 3.3.3 LOBES Lobes develop down current of channel and levee elements and tend to thin away from the sediment source (Figure 3.2 D). Within ancient strata, lobes are generally recognized by thick to thin-bedded, laterally extensive and non-channelized sand bodies (sheet-like sands) usually interbedded with muds in more distal settings; at their farthest reaches into the basin, "lobe-fringe" and basin plains contain regular and persistent thin- bedded turbidites (Mutti, 1977). They may display both thickening and thinning upward trends associated with lobe progradation or retreat respectively, or no trend may be apparent. Bed contacts are generally parallel to sub-parallel and internally, they may display better grading and development of vertical turbidite sequences than other sandy facies (Mutti andNormark, 1987). 3.3.4 CHANNEL-LOBE TRANSITIONS These are sites of simultaneous erosion and deposition usually associated with changes in flow capacity, as sediments are deposited from suspension and turbulent flows onto the proximal parts of lobes (Mutti and Normark, 1987). They typically comprise thick-bedded, amalgamated and conglomeratic sandstone with extensive evidence for scouring. Out-sized mudclasts are locally common together with common cross- stratified beds that resulted from reworking of the sediment by the tail end of flows, and contorted beds produced by the intense turbulence. The coarse sandstone beds can occur either within the proximal lobes or as isolated bodies within mudstone and lying between channel fill and lobe deposits. 3.3.5 OVERBANK WEDGES OR LEVEES "Levee" is a morphological term and usually depends on the recognition of mounded geometries (Normark et al., 1993). The term "overbank" is therefore preferred for this study. Overbank deposits result from the lateral spreading of sediment away 163 from the main body of a turbidite current and are always associated with channels (Mutti and Normark, 1987; Normark et al., 1993). The dominant facies includes thin-bedded, fine-grained, ripple-laminated or cross-bedded sands interbedded with mudstone beds reflecting the waning of flows and the important role of traction processes in fine-grained sediments that "spill" (Gardner and Borer, 2000) away from channel confines (Figure 3.2 C; e.g. Slatt et al., 2000; Grecula et al., 2003). Other associated features include common mudclasts, lenticular bedding, localized slumps, deformed beds and localized debris flows (Mutti and Normark, 1987; Posamentier and Walker, 2006). Overbank wedges may form persistent and thick (hundreds of metres) sediments that thin in a basinward direction. The character of overbank deposits (including wedges) can be indicative of the relative proximity of channelized sediments with coarser and thicker-bedded sediments reflecting a closer proximity (Figure 3.2 C; e.g. Grecula et al., 2003). 3.3.6 SLOPE FACIES Point-sourced slope models (Mutti and Ricci Lucchi, 1978; Walker, 1978) suggest a systematic variation of facies down-current from upper slope environments: (1) upper slope bypass and chaotic facies arising from the relatively steeper slope gradients, (2) lower to middle slope canyon fills (channel and overbank facies, channel-levee complex, debrites, block slides, conglomerates) and (3) lower slope to inner fan transition facies (debrites, mass transport complexes, channel-lobe transition). Variations are known from this idealized trend as slope facies may also include extensions from shelf- environments, as occur when fluvial or storm-modified deltas prograde to the shelf-edge and upper slope. Similarly, facies may include extensions "typical" of basin floor environments such as extensive sheet-like sands. Both are known to exist in delta-fed, slope-ramp settings (e.g. Heller and Dickinson, 1985; Steel et al., 2000) while the unconfined nature of basin-floor environments may be mimicked within intraslope basins (Prather, 2003). Facies variations from the idealized trend may also result from structural modifications of the shelf-slope-basin floor profile, as in the case of confined turbidite successions, which tend to develop aggradational profiles of thick-bedded and massive 164 sandstones (e.g. Sinclair, 2000; Comamusini, 2004). The variations in channelized elements were alluded to above. The following analysis of depositional elements from the Paleocene to Early Miocene sandstones will relate their facies and facies associations to those of point- sourced deep-water facies models, as these have been well-studied and repeatedly demonstrated (e.g. Beauboeuf et al., 1999; Shultz et al., 2005). Variations from this idealized model or facies that do not fit into that scheme will be addressed individually. Interpretations will firstly discern between the associated depositional elements, and secondly, attempt to place these within their relative location along a shelf to basin floor profile. The latter will incorporate both the interpreted depositional elements and stacking patterns of individual sandstone units, supported by facies correlations from different basins. This approach was thought to be necessary given the limited and/or discontinuous nature of 'exposures', which allowed for limited resolution of depositional elements. 3.4 FACIES SUCCESSION AND DEPOSITIONAL ENVIRONMENTS 3.4.1 FINING-UPWARD SUCCESSION OF THE CHAUDIERE AND POINTE-A-PIERRE FORMATIONS The Chaudiere and Pointe-a-Pierre sandstones are described as a continuous succession as transitional contacts have been reported between the two formations and they are interpreted to represent a continuum of facies and processes (Section 2.2.5). In addition, they are both distinguished by their mineralogical maturity relative to all other Cenozoic sandstones (Section 6.1.19.1). The benthic foraminifera assemblage obtained from samples in the Pointe-a-Pierre and Lizard Springs Formations suggests a bathyal to abyssal palaeobathymetry, respectively (Table 3.1). Benthic foraminifera from the Navet 165 Formation, overlying the Charuma Silt Member of the Pointe-a-Pierre Formation (Table 1.1) also suggests a bathyal palaeobathymetry during the Middle to Late Eocene (Stainforth, 1948). Granule-sized to pebbly, amalgamated and thick-bedded sandstones (facies association I, Table 3.3) are interpreted to lie at, or near the base of the Chaudiere/Pointe- a-Pierre succession (Figure 2.9). The erosive surfaces, scours, high degree of amalgamation, abundant pebbles and absence of shale are typical of the axial, "mixed" channels of Mutti and Normark (1987). The facies association also compares with the inner and middle fan facies association of Mutti and Ricci Lucchi (1978) as it is dominated by their correlative facies "A" and "B" (Table 3.4). The succession is interpreted as a lower slope, axial channel-fill in accordance with these comparisons, the palaeobathymetry suggested by the benthic fauna and the apparently restricted extent of facies association I. This is overlain by facies association II comprising thick-bedded channelized and rotated sandstones erosive into finer grained, tabular bedsets. The facies are similar to the depositional channels and channel margin deposits of Mutti and Normark (1987). It is also comparable to the inner fan to slope facies association of Mutti and Ricci Lucchi (1978) on account of similarities to their facies "A", "B" and "F" (Table 3.4). These are interpreted to represent middle to lower slope, depositional channel-fills on account of the generally finer grain size than the underlying facies association and evidence for sediment instability (discordant sandstone and shale facies). The tabular sandstone facies of the Pointe-a-Pierre Formation can also be associated with sheet sands and distal turbidites with rare and/or broad channels (e.g. Lien et al., 2003, Wickens and Bouma, 2000). This is not the preferred interpretation given the evidence for incision of these turbidites at San Fabien Road quarry (Figure 2.7). Facies association II is instead interpreted to represent a later stage of slope channel infill relative to facies association I (discussed further below). The lenticular sandstone facies caps the succession. These fine- to coarse-grained lenticular sandstones are best correlated to facies "G" and "E", which define the "slope association" of Mutti and Ricci Lucchi (1978). Their facies "E" is also common to outer fan environments (Mutti and Ricci Lucchi, 1978, Table 1), but this is less likely given the proposed stacking relationship. Middle to upper slope environment is interpreted, comprised primarily of 166 FACIES Types Sedimentary characteristics sum A Arenaceous-conglomeTate Modunt to coarse grained sandstones, pebbly conglomerates; thick-bedded (1 \WfM facies to upwards of 10m), high degree of sandstone amalgamation; limited lateral extant; abundant erosive surfaces and channels, near complete absence of mudsfones; massive or graded beds. mjm B Arenaceous fades Finer grain size *wi fades 'A' (coarse to fine sand) but commonly associated with it; better sorting; thinner, more confinuous strata; higher mudstone content; parallel and wavy-laminated sandstones. H3 C Arenaceous-pelitic facies Partial or complete Bouma sequences common in beds 50-150 cm thick; they show good lateral continuity; common sole marks; common mudstone TURBIDITE FACIES HI intsrbeds. 1*1 D Peliuc-arenaceous facies Laterally persistent (up to km scale), "plane-parallel" beds; higher mudstone cement than fades "C; fine-grained tocoars e silt grain-size; base-absent Bouma sequences; beds typically 3-40 cm thick. H E Pelitic^enaceous facies II Vary stellar to facies "D" except wMh a coarser gram size and lesser sorting; irregular bedding ("pinch-arid swell, flaseran d lenticular bedding"), both graded and massive sandstones; distinct separation between sandstone and mudstone bedsets. I G Hemipelagic sad pelagic Background, deep-water pelagic sedimentation; calcareous and fossiliferous facies shales. ASSOCIATED FACIES F Chaotic facies Localized folds, slumps, ollstollths, pebbly mudstones. ENVIRONMENT FACIES ASSOCIATIONS Slope G,A,E,F Inner fan (A,B),G,(E,D) Middle fen (A,B),D Outer fan C Distal bash Table 3.4. Facies and facies association of Mutti and Ricci Lucchi (1978) for deep-water systems based on turbidite systems from the Northern Appenines. Only an abbreviated summary of sedimentary characteristics is provided as well as the most commonly occurring facies within each. The most common facies association per environment is listed in order of priority under "facies association" (those in brackets have equal rank). Shaded polygon demonstrates increasing distance from axial flows either distal, or lateral; Pr = proximal, Di = distal. slope mudstones and isolated beds and bedsets of thick- and thin-bedded overbank sandstones and shales, marginal to slope channels and/or chutes. The lenticular geometry of the sandstones is interpreted to have resulted from the depositional topography created by upper slope erosion during periods of sediment bypass. The lenticular fill reflects periods of reduced flow capacity and deposition in more proximal environments, similar to that described by Grecula et al. (2003) for the Skeiding channel complex in the Permian Laingsburg Formation of South Africa. This interpretation implies a trangressive phase of basin fill during deposition of this facies. The facies associations and successions proposed here define an overall fining- upward sequence that is at least 300 m thick for the Chaudiere and Pointe-a-Pierre formations. A similar fining-upward facies succession is typical of single or multiple, point-sourced slope systems due to the tendency for slope erosion, bypass and downslope accumulation (Section 1.4.3; Mutti and Ricci Lucchi, 1978; Walker, 1978; Reading and Richards, 1994). Within these systems, the coarser-grained, lower to middle slope sediments are almost always channelized, as evidenced from similar facies described for slope successions in other basins. Shultz (2005) described amalgamated, thick-bedded (up to 10 m), pebbly sandstones upwards and lateral into thinner-bedded massive and gradational sandstones overlain by shale-prone facies from the Tres Pasos Formation of southern Chile. This was interpreted as a channelized middle to upper slope succession, constrained partly by overlying shallow marine sediments of the Dorotea Formation. Lowe (1972) described a 900 m thick fining-upward, channelized slope fill from the Pigeon Point Formation of western California with basal cobble-conglomerates, overlain in turn by massive sandstones and mudstone and lenticular-shaped, graded sandstone beds. The succession also contained slumps and debris flows and was capped by 300 m of shallow marine sandstones. Fining-upward and increasingly lenticular channelized slope successions have also been described by Klein et al. (1979), Morris and Busby- Spera (1988), Bruhn and Walker (1997), and Slatt et al. (2000) among others. The Chaudiere/Pointe-a-Pierre succession is similarly interpreted to represent a confined slope channel fill fed by fluidized and grain flows from a coarse-grained sediment source, analogous to the model presented by Mayall and Stewart (2000) (Figures, 3.3 and 3.4). Their "bypass" phase is represented by the amalgamated pebbly 168 SOUTH AMERICAN CRATON Figure 3.4 Schematic illustration depicting various depositional environments for Cenozoic sandstones of Trinidad. The succession of Paleocene to Early Miocene formations are represented in panels A-E and these can be compared with idealized deep-water succession of Mutti and Ricci Lucchi (1978). See the respective figure reference for further details on the succession. The ideailzed succession "D" is based on the descriptions given for the San Fernando Formation. Each succession is shown in their respective environment in the illustration above, which also includes "F" and "G" described in Chapter 4. 169 sandstone facies, which likely represents the "proximal" remnants of grain and fluidized flows, as finer-grained sandstones were transferred further in the basin to eventually be deposited upon basin floor fan lobes; these were located towards the north of these slope deposits as suggested by palaeocurrent orientations (discussed further below). Slumps and debris flows were a minor and localized component of this succession, represented by the overturned beds and matrix supported conglomerates (debris flow deposits) along the Mitan River (Section 2.2.4.3); this phase of channel evolution may also be represented by other references to "slump structures" in the Pointe-a-Pierre Formation (Kugler, 2001, p. 191). The overlying (and interbedded) sandstones of facies association II represents the stacked channel fill phase of Mayall and Stewart (2000). Axial sediments are represented by the massive and thick-bedded sands with erosive bases, while channel-margin sediments are represented by the finer-grained, tabular, sandstone facies as demonstrated from San Fabien Road (Figures 2.6 and 2.7). The latter supported a more diverse benthic community than the axial channels as evidenced by the trace fossil diversity and intensity associated with the interbedded sandstones and shales (Chapter 5). The eventual abandonment of the confined slope channel and progradation of the shaly middle to upper slope environments are reflected in the lenticular sandstone facies. The facies attributes and interpretations support the "deep-water" camp for deposition of the coarse elastics of the Chaudiere and Pointe-a-Pierre formations (Section 2.2.2 above), as no evidence for shallow-water reworking was observed, even from outcrops previously described as such. The various descriptions of stratigraphic contacts between the Chaudiere, Pointe-a-Pierre and other formations can be explained in a slope depositional framework. The Chaudiere and Pointe-a-Pierre formations are unconformable over Lower Cretaceous rocks across the Central Range (Kugler, 1959), and this may be as a result of large-scale incision of Cretaceous to Paleocene rocks along a slope profile. A continuous stratigraphic column to the Paleocene is otherwise preserved in several subsurface wells across the Southern Basin 8 (e.g. GY-163, Iguana River-1, Moruga East-15, Marabella-1), eastern offshore (e.g. Topaz-1, Crapaud-1) and southeast Gulf of Paria (e.g. ABM-1). The existence of Cretaceous olistostromes within the Chaudiere Formation shales as described by Kugler (1953) cannot be confirmed or 8 This is based on biostratigraphic age determinations within the well reports. 170 denied from this investigation, but may have been derived from the canyon walls or upper slope Cretaceous rocks. The Navet and Lizard Springs formations represent the pelagic and hemipelagic slope to basin floor shales into which these coarse elastics were introduced. For the Pointe-a-Pierre Formation, a transition back to hemipelagic sedimentation is represented by the silty and "organic" rich Charuma Silt Member that overlies the coarse-grained Pierre Point Sandstone Member. The overlying member appears to have sedimentological attributes similar to the Pierre Point Member ("one metre thick sandstone beds") but faunal attributes more synonymous with the Navet Formation (Kugler, 2001). In more axial regions along slope incisions, the sandstones may extend higher into the stratigraphy than the Middle Eocene age currently proposed (Saunders et al., 1998). This assumption is based on references to Upper Eocene fauna associated with the Pointe-a-Pierre Formation, and lithological correlations to the Late Eocene San Fernando Formation (e.g. Morae Roche, Plaisance Conglomerate; Illing, 1928; Lehner, 1935; Renz, 1942; Kugler, 2001; see Section 2.3.2). If the northerly source for these elastics (Senn, 1940; Kugler, 1953; Kugler and Saunders, 1967; Pindell et al., 2005; Higgs, 2006) is correct, there should theoretically be a coarse-grained lower slope to basin floor fan-equivalent to the Chaudiere/Pointe-a- Pierre slope succession, south of the Central Range. No such sediments have been identified to date, and instead, shale-prone Chaudiere Formation facies are known in this area. Algar (1993) first suggested that these coarse elastics represent axial flows within a shale-prone environment and the interpretations presented here support that assertion; the shaly Chaudiere facies towards the south of the Central Range represents a lateral facies to the confined slope turbidites, albeit now deformed. The challenge is to determine the orientation of the slope incision or channels, and in so doing, the trend of the palaeoslope. This is a difficult task given the faulted nature of exposures, but it is proposed that the coeval shelf was to the south - southwest of the current study area, and sediments were sourced from the South American continent. This is based mainly on the mature mineralogical assemblage of the sandstones (described in Chapter 6), and secondly, on the northerly-directed currents suggested by flute cast measurements (Section 2.2.6). 171 3.4.2 CHAOTIC FACIES ASSOCIATION OF THE SAN FERNANDO FORMATION Recall that this formation contains a heterolithic assemblage of both shallow- and deeper-water, calcareous and arenaceous foraminifera and numerous other fossil forms, and has been interpreted as shallow-water, shelf deposits, indicative of shallowing during the Late Eocene (Chapter 2, Section 2.3). The facies association for the San Fernando Formation comprises a heterolithic, chaotic assemblage with numerous disconformities, extreme variations in grain size, extensive reworking of older rocks and fauna, and inconsistent faunal abundances between planktonic and shallow-water foraminifera. It is best represented by facies association VI with its characteristic block slides, lenticular, massive sandstones and conglomerate horizons (Table 3.3). The association is comparable to facies "A", "E", "F" and "G" of Mutti and Ricci Lucchi (Table 3.4), which collectively define their slope facies association. Facies association VI of the San Fernando Formation is interpreted as a middle to upper slope canyon fill as suggested by this comparison. The discordant limestone blocks found on Soldado Rock, including the Paleocene Soldado Formation, are interpreted as variably-sized, internally coherent shallow-water blocks that form part of a slope canyon fill (Figure 3.4). These rocks were sourced along canyon walls that breached the coeval shelf and was dissected and later filled by the Late Eocene. The 17 m thick block-conglomerate of the Boca de Serpiente Formation (Kugler and Caudri, 1975; Section 2.3.4, Figures 2.15 and 2.17) is also interpreted to be part of the slope canyon fill that was sourced from rocks of Middle Eocene age and resedimented during the Late Eocene. An analogy is provided from undeformed slope sequences off of the Brazilian continental margin. Cainelli (1994) described blocky and angular shelf- edge Paleocene carbonate rocks that now comprise a significant portion of the fill of the East Sao Francisco Canyon; the canyon was dissected and filled during the Eocene and breached the Paleocene carbonates during its incision. The cobble conglomerate facies (e.g. Plaisance and Marabella conglomerates) is interpreted as the channelized lag deposits of inertia-driven grain flows within the confined canyons. Where similar conglomeratic facies occur in ancient slope 172 environments, they are commonly channelized, and occur in relatively proximal slope environments (Aalto and Dott, 1970; Winn and Dott, 1977; Bruhn and Walker, 1997; Beaubouef et al., 1999; Posamentier and Walker, 2006), although they can also be prominent part of channelized fills at the base of slope (Hein and Walker, 1982). The conglomerates at Mount Moriah are transitional into interbedded "massive" calcareous sandstones and shales (Figure 2.13), and together with the cohesive flows, are also interpreted to be a component of the slope canyon fill. The scattered references to "block conglomerates" (e.g. Kugler referenced in Van den Bold, 1960; Bon Accord Boulder bed of Kugler, 2001) may also be part of this fill although field examination is necessary to confirm this (these were not exposed at the time of this study). The turbidites of the lenticular sandstone facies are resedimented sandstones beyond the influence of shallow-water reworking, now forming a minor component of the canyon fill relative to more cohesive flows and deposition of fine-grained beds. The rocks described from the now-depleted Morne Roche quarry (Kugler, 1996, Enclosure 12) provided the only evidence for an upper slope to outer shelf transition during the Late Eocene. The allochthonous nature of that outcrop though, precludes confident assertions about the location of that transition; it was likely part of the shelf edge sequence that was later displaced as an olistolith into the slope canyon fill. The abundance of reefal limestones and shallow water fauna (e.g. Vaughan and Cole, 1941) indicate proximity to the palaeo-shelf only, as the facies associations described above strongly suggest that these deposits have been resedimented. Similar to the Chaudiere and Pointe-a-Pierre formations, disconformable surfaces overlap Eocene to Cretaceous rocks as described from Mount Moriah (Section 2.3.2). These indicate significant hiatuses that may be associated with slope canyon erosion. Away from the San Fernando area, a correlative conformity is reflected in more stable palaeoenvironments and the transition to bathyal silts of the Cipero Formation, as suggested by several workers and evidenced from subsurface wells (Section 2.3.2, Figure 2.14). The individual beds that have been interpreted in the literature to indicate rapid sea level transgressions and regressions should be considered as relatively instantaneous depositional events. The conglomerate beds (Figure 2.14) are not indicative of 173 significant hiatuses beyond local erosion that occurred during their emplacement. Instead, such a major surface should coincide with the base of the canyon fill represented by the base of the San Fernando Formation at its para-type locality at Mount Moriah. Instead of a major unconformity overlying the San Fernando Formation, the depositional model presented here supports a conformable gradation from a "mature" (Cainelli, 1994) slope canyon fill into the silts of the Cipero formation; this was best reflected in the transitional contacts away from the slope canyons. The 245 m of the San Fernando Formation drilled in well FW-214 (Kugler, 2001, p. 177) is a suggested thickness the San Fernando Formation although the thickness of the slope canyon fill is possibly less. The width of the canyon fill is difficult to estimate with the current dataset. This interpretation of palaeoenvironmental conditions during the Late Eocene finds support within earlier published literature and has perhaps been forgotten or overlooked. Liddle (1946) has long interpreted "considerable erosion" from blocky conglomerates at Soldado Rock within an otherwise conformable Late Eocene to Oligocene transition, and Kugler (2001, p. 206) states that the Mount Moriah Sandstone Member is the only autochthonous member of the formation; others being affected by "large scale slumping". More recently, Pindell and Kennan have mapped linear subsurface trends of the San Fernando facies across the Southern Basin (J. Pindell, pers. comm., 2008); such trends are typical of slope incisions which tend to be oriented parallel to the palaeoslope (Stanley and Unrug, 1972). 3.4.3 AGGRADATIONAL SUCCESSION OF THE ANGOSTURA SANDSTONE The benthic foraminfera assemblage from a shale sample in well Kairi-1 suggests a turbid "flysch-type" environment of possibly upper bathyal water depths (Table 3.1). These water depths are supported by the facies and facies association for the sandstone as no conclusive evidence was seen to suggest deposition within storm or fair-weather wave 174 base. The Angostura Sandstone is assigned to facies association III, comprised of amalgamated massive and gradational turbidites and cobble conglomerates (Table 3.3). Channeling is evident within the thick-bedded gradational sandstones by the common irregular bed contacts and fining-uwpard bedsets. These are comparable to the channel fills described by Mutti and Normark (1987) (Figure 3.2) and these bedsets are therefore interpreted as an amalgamated turbidite channel complex. Channels are of both the depositional and erosional types, the latter supported by the graded pebble and cobble conglomerates (cobble conglomerate facies) which are interpreted to be lag deposits from the passage of high-density grain and fluidized flows. Channelized facies was recognized in several cored intervals (wells Angostura 1, Kairi 1-ST2, Kairi-1, Canteen-1 and Canteen-2) and account for approximately 58% of the examined cores, which suggests that much of the sandstone comprise channelized fills. Disorganized, matrix-supported cobble conglomerates indicate a debris flow component to the channel fill. The planar bed contacts and less irregular scours within the thick, metre-scale beds of coarse massive sandstone (massive thick-bedded sandstone facies) may be associated with broader channels down current of the channelized deposits. This combined with their thick-bedded nature and aggradational Bouma Ta intervals are interpreted to be proximal lobe deposits (Figure 3.2 D). The interbedded sandstone and shale (bioturbated sandstone and siltstone facies assemblage) are most analogous to the overbank deposits of Mutti and Normark (1987) with common ripple lamination among silts and non-amalgamated centimetre-scale turbidite beds. This facies association best compares with the inner to middle fan associations of Mutti and Ricci Lucchi (1978) with correlative facies "A" and "B" being the dominant types present in the core. An aggradational sandstone succession at least 300 m thick overlying the shales of the Navet Formation, is characteristic of the Angostura Sandstone. The repetitive bedding of thin, low-density turbidites (Tc-Td) and interbedded shale (Te) facies typical of distal, outer fan environments (Mutti and Ricci Lucchi, 1978) was not evident in the cores examined, and based on the relatively uniform gamma ray log signature throughout the sandstone and sharp basal contact, it is likely that these environments are not represented throughout the 300 m-thick succession. Considering all the evidence, a sand- 175 rich lower slope to inner fan channel and proximal lobe complex is interpreted for the Angostura Sandstone. The aggradational stacking, sand-rich nature and immense thickness of the sandstones are distinctive when compared to other sandstone intervals, and at least three conceptual models can be inferred to explain these characteristics: (1) Aggradational stacking pattern are characteristic of sand-rich delta-fed slope ramp systems (Link and Welton, 1982; Heller and Dickinson, 1985; Reading and Richards, 1994; Steel etal, 2000). (2) Deposition within a structurally confined basin (e.g. Annot Sandstone model of Sinclair, 2000; Macingo Sandstone model of Cornamusini, 2004; Scotland Formation of Pudsey and Reading, 1982). (3) Single-sourced slope canyon fill (e.g. Annot Sandstone model of Stanley et al., 1978). Structural confinement was the overriding control on the single-sourced slope canyon fill model for the Annot Sandstone, and this will therefore be considered a subset of option (2) above (Stanley et al., 1978; Sinclair, 2000). Application of these models depends on distinctive palaeocurrent orientations, sandbody geometries and orientation, knowledge of feeder channels and the basin floor configuration, most of which are insufficiently known. There is evidence however, to suggest both a slope-ramp margin and structural confinement. The sedimentary processes and stacking patterns of the Angostura Sandstone can be compared to those of the Annot Sandstone, Scotland Formation and Macingo Sandstone (Stanley et al., 1978; Larue and Speed, 1983; Pudsey and Reading, 1982; Sinclair, 2000; Cornamusini, 2004). As will be discussed in Chapter 6, the relative maturity of these sandstones suggests that an uplifting Caribbean Mountain was already being eroded at that time and may have been a source of detritus to the Angostura Sandstone. It is possible that its uplift to the north of the Angostura Sandstone sequence may have created the structural confinement necessary to produce the aggradational stacking patterns. Regarding a delta-fed, slope-ramp type setting for the Angostura Sandstone, the abundant organic matter may suggest a direct link to a fluvial-deltaic source, and the 176 likelihood of quasi-steady flows was already discussed above (Section 2.4.2.5). The parallel-laminated facies is a small component of the Angostura Sandstone facies association (Table 3.3), and as will be discussed below for the Nariva Formation, where both the parallel laminated and organic-rich facies are better developed, their occurrence have been associated with hyperpycnal flows in other basins. The location of these sands along the base of slope to proximal inner fan, their sand-rich nature and upper bathyal palaeobathymetry suggested from the benthic foraminfera assemblage (Table 3.1), suggest that the aggradational geometries may be related to a slope-apron to ramp type margin with a direct supply from deltaic sources. In summary, the Angostura Sandstone demonstrates facies and stacking patterns characteristic of lower slope to proximal basin floor channel and lobe complexes (Figure 3.4). It was a coarse-grained, sand-rich system, deposited by a range of sediment gravity flows including debris flows, grain and bedload traction, fluidized and turbulent suspensions and possibly quasi-steady flows. In terms of sedimentary processes, the sandstone is comparable to both the Pointe-a-Pierre and Nariva formations. Relative to the Chaudiere/Pointe-a-Pierre succession, the aggradational stacking geometry may indicate relative basin confinement and/or a delta-fed sand-rich sediment supply. The former is preferred for reasons to be elaborated upon in subsequent chapters. 3.4.4 FINING-UPWARD SUCCESSION OF THE NARIVA FORMATION The Nariva formation is interbedded with the bathyal shales of the Cipero Formation and neritic shales of the Brasso Formation near the top (Stainforth, 1948; Kugler, 2001). One sample from the eastern Central Range (sample HV7024) contained Late Oligocene and younger benthic fauna and may be correlative with the Nariva Formation (Table 3.1). This agglutinated foraminifera assemblage was suggestive of an upper to middle bathyal palaeobathymetry and reworking of Paleocene sediments (M. Kaminski, pers. comm., 2008). A fining-upward succession at least 800 m thick is suggested for the Oligocene Nariva Formation as constrained by outcrops and subsurface well data (Figure 2.31). 177 These consist of amalgamated pebbly sandstone facies upwards into amalgamated massive, thick-bedded and coarse-grained sandstones, to parallel-laminated and tabular sandstone facies (facies associations I and IV, Table 3.3). A similar depositional environment is interpreted for the Nariva Formation and the Chaudiere/Pointe-a-Pierre succession based on the facies associations and stacking pattern common to both (Table 3.3, Figures 2.9 and 2.31). The pebbly to fine-grained parallel-laminated facies association (association IV, Table 3.3), is however, specific to the Nariva Formation. Channelized deposits are suggested by the numerous erosive surfaces and fining-upward characteristics of facies associations I and IV (e.g. Corbeaux Hill and Sandstone Trace outcrops) as described by Mutti and Normark (1987), and this is the preferred interpretation for these facies associations. The associations can also be compared to the slope, inner and outer fan facies associations of Mutti and Ricci Lucchi (1978) as it best equates to their facies "A", "B" and "F"; the occurrence of debris flows (facies "F") is more diagnostic of slope environments. The parallel-laminated and organic-rich facies is however, not differentiated by their facies classes. The parallel-laminated and organic-rich facies are distinctive. The organic-rich content indicates a change in environmental conditions or basin settings from earlier Paleogene sandstones. An abundance of plant fragments in turbidite beds have been previously cited as evidence of direct deltaic or fluvial source (Sailer et al., 2006) and deposition from hyperpycnal currents (Mulder et al, 2003; Plink-Bjorklund and Steel, 2004; Poursoltani et al., 2007). Similar facies to the parallel-laminated facies described here has not been cited as typical of hyperpycnites (Mulder et al., 2003), although this facies appears to be recurrent in such deposits. Dott and Bird (1979) described parallel- laminated sands in beds up to 1 m thick overlying massive sandstones, and in turn, overlain by hummocky cross-stratified sandstones in the Tyee Formation of southwest Oregon. The facies was also present in delta front to upper slope deposits in the Eocene Central Basin of Spitsbergen, where it is associated with massive sandstone and abundant organic matter, sometimes present as entire leaves (Steel et al., 2000; Plink-Bjorklund and Steel, 2004). Both of these deposits are characteristic of delta-fed submarine ramps (Heller and Dickinson, 1985; Plink-Bjorklund et al., 2001; Plink-Bjorklund and Steel, 2004). A similar association was also reported for turbidites of the Kashafrud Formation 178 in Iran where fine-grained, thin-bedded and "planar-laminated" sands are "rich" in plant fragments and disseminated organic matter (Poursoltani et al, 2007). Bruhn (1994) also suggested a hyperpycnal flow origin for thick accumulations of parallel-laminated, fine- to medium-grained sandstones associated with massive beds in syn-rift deposits off of the Brazilian continental margin. An analogy is drawn between these occurrences and the Nariva Formation. The parallel-laminated facies is interpreted to indicate sustained flow conditions with simultaneous traction and sediment fallout at upper plane bed flow velocities. These quasi-steady, high velocity flows with an abundance of organic matter may have been related to hyperpycnal flows linked to fluvial-deltaic environments on the shelf. Based on the facies associations and fining-upward stacking succession, a slope environment is interpreted for the sandstones of the Nariva formations. The coarsest sandstones are preserved near the base of the succession as amalgamated channels and this fines-upward into massive and planar-laminated beds, probably within an upper slope to outer shelf environment (still below wave base). The latter is suggested based on the apparent link to a deltaic source, which provided significant amounts of plant fragments now preserved as debris flows or scattered fragments among the channelized sandstones. The "slope" interpretation presented here for the Nariva Formation differs from the tectonically active slope interpretation of Kugler (1953; 2001) which was based on his "wild flysch" hypothesis that was not validated for this thesis. Instead, the sedimentary features described herein do not provide evidence for active tectonics during deposition of the formation. Similarly, "migrating foredeeps" during Nariva Formation time (Kugler, 1953; Suter, 1960) cannot be assumed from the facies presented here but this idea will be revisited when the basin configuration is considered in Chapter 7. The interpretation presented here agrees with those of previous workers as far as deeper-water sedimentation is invoked (e.g. below-wave base deposition of Algar (1993)) but does not support a nearshore environment of deposition (Stainforth, 1948). 179 3.4.5 COARSENING AND THICKENING UPWARD SUCCESSION OF THE HERRERA SANDSTONE A mixuture of calcareous and agglutinated species was common to samples derived from the Herrera Sandstone Member and correlative shales of the Cipero Formation (samples HV6005 and HV6012, Table 3.1) from which middle to lower bathyal paleodepths have been inferred (M. Kaminski, pers. comm., 2008). A coarsening-upward succession was demonstrated from the Herrera Sandstone Member in which fine-grained and thin-bedded rippled sandstones transition upward to graded and medium to coarse-grained sandstones (Figure 2.35). The succession is at least 240 m thick (based on the thickness in well BP-347) and comprise at least three repeated coarsening upward cycles with the largest up to 75 m thick. These sandstones are assigned to facies association V, which consists of coarsening and thickening-upward rippled to massive sandstones (Table 3.3). The facies association is interpreted to represent deep-sea channel and channel- related overbank and lobe deposits. The coarsening-upward cycles are distinctive and similar cycles have been associated with lobe progradation into distal fan environments. (Figure 3.5; Mutti, 1977, Mutti and Normark, 1987). Similarly, coarsening-upward trends have been shown to occur at channel margins associated with channel overbank "spills" (Grecula et al., 2003; Lien et al., 2003) although at a much smaller scale than observed in the Herrera Sandstone (4 m as opposed to 75 m). Most of the prograding cycles comprise the rippled sandstone and shale facies for which the thin-bedded and ripple-laminated character is analogous to the overbank and channel margin deposits described by several workers (e.g. Mutti, 1977, Mutti and Normark, 1987; Slatt et al., 2000; Grecula et al, 2003; Posamentier and Walker, 2006). The association with channels is further evidenced by the fining-upward, amalgamated, graded and thick-bedded sandstones and conglomerate facies (graded thick-bedded sandstone facies) that cap the succession, sedimentary features that are typical of channel fill deposits. The coarsening-upward trend is interpreted to indicate increasing proximity to the channel (Figure 3.2 C). 180 Fades MAP VIEW STRATIGRAPHY POINT OF CYCLE DEVELOPMENT , I NONCYCUC Bioturbated shale "5 m ^ WK BASIN PLAIN {Zoophycos ichnofiacles) 3 BASIN PLAIN • MINOR THICKENING UPWARD FAN FRINGE MAJOR Rippled sandstone THICKENING UPWARD LOBES and shale Graded and rippled sandstone TIME 4 Graded thick- bedded sandstone LOBES Figure 3.5. Schematic illustration to explain the coarsening-thickening upward stacking pattern of the Herrera Sandstone in wells BP-344 and BP-347. Distal basin floor lobes, unconfined overbank deposits are progressively overlain by more proximal and thick-bedded channel- related deposits. The channels occur towards the top of the succession. The "Zoophycos ichnofacies" shales are described in Chapter 5. Modified after Shanmugam and Moiola, 1988. The facies association is comparable to the outer fan-distal basin association of Mutti and Ricci Lucchi (1978) based on a correlation with their facies "C", "D" and "G", the latter correlated to the shale-prone intervals seen in the core and at the Tarouba outcrop locality (discussed in Chapter 5). The amalgamated turbidites towards the top of the succession is correlative to their facies "B", and represents the progradation of channelized inner and middle fan environments into the distal basin floor. Considering the association and succession of facies, the Herrera Sandstone is interpreted to represent the progradation of channelized submarine lobes whereby relatively unconfined, low density turbidites (channel-related deposits) are progressively overlain by inner to middle fan channel deposits (Figure 3.5). Pelagic and hemipelagic 181 sediments are represented by bioturbated and fossiliferous shales (Table 3.1), with common Zoophycos and Chondrites trace fossils (Chapter 5). The coarsening and thickening upward progradational cycles are progressively coarser or thicker-bedded. The Herrera Sandstone is confined to a narrow, fault-bounded northeasterly- trending zone to the south of the Central Range and displays good lateral continuity in this direction (Bitterli, 1958; Jones, 1968; Hosein, 1990). This may in part represent the continued structural modification and confinement of the basin that was initially inferred from the aggradational stacking of the Angostura Sandstone. The apparent offset of progressively younger sands towards the south, simultaneous shale-out in this direction and thickening along anticlinal flanks (Jones, 1968; Hosein, 1990; Kugler, 2001) may reflect a syn-tectonic nature of deposition and structural-controlled offsetting of the migrating lobes (towards the south). It must be noted though, that the present-day trend is also due in part to post-depositional deformation and translation related to Early Miocene thrusting. This relationship and the provenance of these sandstones will be further discussed in Chapter 6. This interpretation varies from other Paleocene to Early Miocene sandstones in that the channelized sequences occur toward the top of the succession and relatively unconfined flows have been invoked. Similarly, the Herrera Sandstone represents the most distal facies relative to earlier formations and this concurs with the previous interpretations of Poole (1968) and Hosein (1990) who both interpreted these as deep- water turbidites. The sandstones indicate that deep-water environments still persisted in the Trinidad area during Early Miocene time, although there was evidence for coeval shallow-water reworking in Oligocene sands (Plum Mitan locality discussed below). The significance of these two contrasting palaeoenvironments will be returned to when provenance and basin evolution is considered (Chapter 6 and 7). 3.4.6 CIPERO FORMATION (PLUM MITAN LOCALITY) The symmetrical rippled facies provided the only evidence of wave reworking within Oligocene sandstones. The symmetrical ripples indicate oscillatory currents 182 within fair-weather wave base. A shelf environment is interpreted with localized migration of dune scale bedforms. These beds represent shallow water deposits among what was largely a deep-basin as evidenced by the adjacent deep-water elastics. The shallow water reworking suggested at this time coincides with several limestone occurrences in the stratigraphy (Table 1.1) and may both be related to similar basinal controls. The shoreline was oriented approximately north-south based on the ripple-crest orientations at the outcrop. 3.5 SUMMARY Paleogene sandstones were deposited by sediment gravity flow processes ranging from block slides and cohesive flows to low-density turbidity currents in deep-marine environments. More specifically, facies associations and successions in the Chaudiere/ Pointe-a-Pierre, San Fernando and Nariva formations and the Angostura Sandstone Member of the Cipero Formation are indicative of slope to proximal submarine fan depositional environments. Diagnostic facies include discordant sandstone (and limestone), block and cobble conglomerates, lenticular sandstones, thick-bedded amalgamated pebbly sandstones, irregular bedding and matrix-supported conglomerates and pebbly mudstones, facies that collectively indicate sediment bypass, instability, confinement and erosion. Similar facies were described for the Chaudiere, Pointe-a- Pierre and Nariva formations and outcrop and subsurface data suggests that the relative superposition of facies may also be similar. Fining-upward succession were recognized on two scales: channel-fills with coarse to pebbly sandstone passing upwards into finer grained tabular and massive sandstones measured at outcrop scale (tens of metres) and fining-upward slope successions inferred from outcrop correlations and subsurface well data over 300 m thick. The later phase and transgression of the Pointe-a-Pierre/ Chaudiere slope succession is inferred from the depositional-type channels and tabular sandstones seen in outcrops at Mt. Harris and eventual transition of the Charuma Silt Member into the Navet Formation. The Nariva slope succession instead shows evidence for sustained gravity flows and proximity to fluvial or deltaic sources. 183 A similar slope depositional model is proposed for the San Fernando Formation from facies described from both outcrop and published literature. From the latter, it was obvious that there has always been keen interest in the formation, spurred by the heterogeneous character of its sediments. The facies described are consistent with slope settings, with a sedimentary fill of more chaotic character than the underlying Pointe-a- Pierre Formation. Proximal slope canyon environments are inferred which dissected outer shelf sandstones and limestones that now form a prominent part of the slope canyon fill. The San Fernando Formation fill largely represents a transgressive basin phase, in which the deepwater canyon fill was continuous into the bathyal shales of the Cipero Formation, as described from areas away from the canyon fills. The Angostura Sandstone represents a deeper-water facies to the San Fernando Formation, and lower slope to proximal basin floor environments are inferred. The most distal deep-water facies is represented in the sandstones of the Herrera Sandstone Member with its characteristic thickening-upward middle to outer submarine fan lobe succession. Apart from the symmetrical ripples at Plum Mitan (Cipero Formation), there is no evidence for shallow water processes as previously reported in the literature. The biohermal limestones within the Late Eocene San Fernando Formation are resedimented deposits, likely sourced from the shelf-edge or canyon wall limestones and sandstones. This model finds support from the facies associations described in published literature. Low- and high-density turbidites were deposited from unsteady, waning flows. Within Oligocene sandstones (Angostura and Nariva sandstones) alternating low- and high- density layers and amalgamated traction bedding may indicate flows of longer durations (quasi-steady state), with abundant organic matter supplied by a direct fluvial or deltaic source. Hyperpycnal flows are assumed for deposition of some of these sandstones. 184 Chapter 4 - Lithofacies Associations and Depositional Environments of Late Miocene and Pliocene Formations The deltaic character of Late Miocene to Pliocene sediments in Trinidad has been recognized since the 1940s (Stainforth, 1978), and because of their importance as hydrocarbon reservoirs, they have been the subject of numerous publications detailing their faunal content, thickness, subsurface extent, depositional environment and general deltaic habit (e.g. Kugler, 1953; Barr et al., 1958; Ablewhite and Higgins, 1968; Barr and Saunders, 1968; Saunders and Kennedy, 1968; Michelson, 1976; Jones, 1998; Wach et al., 2004). Several sedimentation "cycles" were recognized throughout these sediments with major cycles represented by established formations or members (Barr et al., 1958; Barr and Saunders, 1968; Carr-Brown and Frampton, 1979). These cycles were recognized from subsurface well log data and measured on the scale of hundreds of metres. Individual cycles are separated by unconformities and each begins within clay beds and increases upwards in both sand content and lateral extent (Barr et al., 1958; Suter, 1960; Barr and Saunders, 1968). At least three such cycles are known in the Cruse Formation, and two in the Morne L'Enfer Formation (Table 1.1; Kugler, 1956; 2001). Despite the considerable attention to the Neogene stratigraphy, there are surprisingly very few studies that have attempted to discern specific sedimentary processes associated with individual beds, bedsets or even the larger "cycles". The reasons for this are the same as that for Paleogene sediments: the emphasis on process sedimentology succeeded the major period of active exploration and investigation during the 1950-60s. Recent studies have addressed this shortcoming (e.g Babb, 1998; Wach et al, 2004; Winter, 2006; Osman, 2007). This chapter will describe the range of sedimentary characteristics and facies common to Late Miocene to Late Pliocene outcrops across the Southern Basin of Trinidad and provide a framework to examine the changing sedimentary processes relative to the earlier Cenozoic sandstones (Chapter 2 and 3). The choice of formations was dictated by the excellent exposures along the southern coastline and southern Gulf of Paria. A section of the Manzanilla Formation along the eastern coastline, of equivalent 185 age to the Cruse Formation (Table 1.1), was also examined, primarily for its trace fossil assemblage, and a synopsis of the related sedimentary processes is provided in Chapter 5. The outcrops of the Cruse and Morne L'Enfer formations were examined to varying levels of detail (Table 1.3). The Morne L'Enfer Formation in particular, was examined in sufficient detail to allow the recognition of flooding events and other sequence stratigraphic surfaces within the large-scale "cycles" described by previous workers. As a result, the sedimentary lithofacies and processes throughout the formation will be described within a sequence stratigraphic framework. This approach was not possible with the other formations described in this investigation. The method of study of these outcrops was the same as adopted for the earlier Cenozoic sediments and described in Section 1.4. 4.1 CRUSE FORMATION The Cruse Formation is an important hydrocarbon reservoir in the western Southern Basin and as a result, has been studied in relative detail (Barr et al., 1958; Kugler, 2001 and references therein; Winter, 2006). For this study, only a limited section of the formation was investigated in order to decipher the associated sedimentary processes and collect samples for mineralogical analysis. The descriptions that follow partially represent the estimated 1800 m thickness for the formation (Kugler, 2001), but the change in lithofacies associations is significant from a palaeoenvironmental perspective. The sediments off the Morne Diablo coastline, southern Trinidad (Figure 4.1) document a transition from unstable slope facies into shelf deposition, and represent the first input of deltaic and shallow marine sediments (Barr et al., 1958) in this part of the Southern Basin. The beds along the south coast in the vicinity of Morne Diablo dip at 64° towards the south and strike at 080° azimuth. This is parallel to the trend of the coastline and affords a strike-oriented view of a section of the Cruse Formation. Vertical facies changes can be reviewed at promontories on either side of the bay. The base of the section is west of the car park at the Morne Diablo fishing depot. In the following 186 Figure 4.1 Geological map showing Late Miocene to Pleistocene sediments across the Southern and Northern basins of Trinidad. The location of outcrops discussed in the text are shown. Outcrop locations differentiated by letters are from the Morne L'Enfer Formation and further details on these are given in figure 4.5. Geology modified after Kugler, (1959) and Saunders et al., (1998). 187 foint Paloma Legend Pleistocene Pliocene Late Miocene-Pliocenel Outcrop description and/or sample point • Continuous outcrop section Faults Syncline Anticline section, two lithofacies are described in detail as well as a summary of observations from other locations. 4.1.1 FACIES OF THE CRUSE FORMATION AT MORNE DIABLO 4.1.1.1 DISCORDANT SANDSTONE AND SHALE FACIES Description This lithofacies consists of several hundred metres (measured along strike) of detached sandstone blocks, some tens of metres wide by several metres thick (Figures 4.2 A and 4.3). The sandstone blocks are mostly fine-grained and range from structureless to well-stratified blocks displaying low-angle swaley or (rarely) hummocky cross-laminae. Most of the blocks contain remnant networks of Ophiomorpha nodosa, with burrow diameters measured up to 7 cm diameter (Figure 4.3 C). It is apparent that the structureless sands were due to intensive bioturbation. The sandstone blocks lie within a melange of contorted silt and clay beds displaying numerous slump folds, isolated silty pods and floating debris of varying composition. Discontinuous, lenticular bodies of chaotic, mud-supported sand, silt and organic matter are present from 15 cm to a few metres thick; some contain abundant clasts of mudstone, sandstone and clumps of organic matter within a silty matrix (Figure 4.4 A, D). Some of the clasts are laminated and were apparently sourced from the same beds as the sandstone blocks. Organic matter is particularly abundant on bedding planes among both the sand blocks and the contorted matrix. Interpretation The chaotic bedsets and detached sandstone blocks indicate instability and sediment mobilization. The large blocks were emplaced by block slides without internal deformation. The downslope movement of these blocks would have deformed the softer silts and shales in their path, resulting in the numerous slump folds and chaotic bedding. The blocks preserve structures that indicate sedimentary processes within shelf environments. These structures include low-angled cross laminae, swaley and 189 Metres **••» 20 I«HW*»M • it ar«w Interp Fades Fades retation «A» WJS>4 Massive thick- Ta-Tb-Tc bedded sandstone turbidites, 12"1 Discordant sandstone and Discordant shale sandstone and Turbidites, debris flows shale •J V & and block sides Legend Massive thick- bedded sandstone ® Sample location (l Fining-upward T Churned bed Planar cross- •sss^ stratincetion Low-angled cross •s^ -stratification «£» Parallel laminae >*•«! •: Organic matter M Muddast £? Sandstone clast Discordant Debris flows Contorted bed sandstone and %r and block sides Flame structures shale A XT Load structures •: ••Llgnlte-H w -^r Scour \J\J Dish structures Tracs fouls e£io OpNomorpha c<^o Thatassinoides 1 Gyrctilhes Om—' Figure 4.2 Facies of the Cruse Formation exposed west of Morne Diablo fishing depot. A) Chaotic interval of detached sandstone blocks and slumped beds with rafted wave-influenced shelf sandstones in deformed shales and siltstones. B) Massive thick-bedded sandstone facies with interbedded turbidites and debris flows overlying chaotic slumped beds and interbedded organic debris. 190 Figure 4.3 Deformed slope canyon fill facies west of Mome Diablo fishing depot. A) Large, allochthonous, metre-scale blocks of sandstone (two numbered) within slumped siltstone and sandstone beds. B) Slump fold within laminated silt, ruler = 25cm. C) Low-angled cross-lamination and Ophiomorpha nodosa burrows (arrowed) within an allochthonous sandstone block. Inset shows nodular exterior of the Ophiomorpha burrows. D) Interbedded boulder conglomerate. Ruler = 80cm. 191 hummocky cross-stratification. A similar environment is suggested by the abundance of Ophiomorpha nodosa burrows, which are found in situ higher in the stratigraphy (discussed below). Cohesive debris flows were also common among the silty sediments and involved the downslope movement of a considerable amount of organic matter. The abundance of the latter suggests a direct link to an organic source such as a river mouth or shelf accumulations. The depositional environment will be discussed in greater detail when the collective facies for the section are summarized below. 4.1.1.2 MASSIVE THICK-BEDDED SANDSTONE FACIES Description A dip-oriented section was described from the western promontory of the bay (Figure 4.2 B). The 18 m section begins with the chaotic assemblage of contorted sandstone and siltstone beds, with lenses consisting entirely of silty and lignitic material (tens of cm thick). The section becomes more organized upwards where the chaotic beds are interbedded with amalgamated beds of massive and ripple-laminated sandstones up to 120 cm thick. These beds are either massive throughout, or are gradational-upward into parallel and ripple-laminae. A uniform grain size (fine-grained) is common throughout most of these beds. Sedimentary structures include load and flame structures at the base of thicker beds and dish structures near their tops. Towards the top of the section, thin, planar cross-stratified beds appear for the first time. Only the upper 4 m contain in situ bioturbation, ranging from completely churned beds to rare burrow networks. Ophiomorpha annulata is the most common burrow, distinguished by a distinct but smooth lining. Gyrolithes is also present. Overall, there is a low diversity of trace fossils even among the churned beds as suggested by the distinctive ichnofabric imparted to the rock. Interpretation The chaotic assemblage of contorted sandstone and siltstone with organic-rich lens are interpreted as slumped horizons, several metres thick, while the lenticular, 192 organic-rich beds represent debris flows interbedded or incorporated with the slumps. The amalgamated bedsets of massive and ripple-laminated sandstones are low-density turbidites, which overlie and are partially interbedded with the chaotic beds and debris flows. The turbidites display typical transitions from massive Ta intervals (Bouma, 1962) into parallel (Tb) or ripple laminated (Tc) intervals. Dewatering and loading structures resulted from rapid deposition. The uniform grain size may be a reflection of the sediment source or due to the erosion of upper, finer grained intervals (Tc-Td) by successive turbidites. Only the highest turbidite beds in the section are bioturbated with a restricted, but in situ, assemblage. Palaeoenvironmental conditions were becoming increasingly favourable upward, supporting a restricted endo-benthic community. This may indicate a relative shallowing towards the (shelf) source of the detached sandstone blocks, which also contain large Ophiomorpha traces. Additional evidence for this transition from chaotic, deposits to outer shelf sediments is present on the eastern side of the bay. 4.1.2 LITHOFACIES ALONG THE EASTERN MORNE DIABLO COASTLINE The following observations were made between the Morne Diablo fishing depot and Siparia Point to the east, approximately 3 km from the previously described section (Figure 4.1). This part of the bay was not logged in detail but observations support the interpretations made along the western end. A change of lithofacies is obvious along a west to east traverse, estimated to represent between 100-150 m of stratigraphic section. The section ends at Siparia Point and includes, in stratigraphic superposition: 1. Amalgamated sandstones and interbedded shale similar to the thick-bedded massive sandstone facies. These beds are not bioturbated. They are interpreted as low-density turbidites just as the massive sandstones to the west. 2. Contorted grey shales are exposed on the wave-cut platform at low tide. The shale beds are intensely deformed with fold wavelengths measuring tens of metres. A sedimentary origin for the folds cannot be proven with the preliminary observations 193 made, but the abundance of soft-sediment deformation along the traverse makes it very likely. The magnitudes of these folds decrease in younger strata along the traverse where they occur between conformable strata (Figure 4.4 F). 3. Metre-scale beds of fine-grained, blocky and consolidated sandstones occur either in situ or form mounded rock debris along the wave-cut platform. No sedimentary structures are obvious (massive character). They may represent either an amalgamated turbidite channel fill or sandy debris flows (Shanmugam, 1996). The absence of traction-related sedimentary structures suggests that these were re- sedimented below the influence of waves and tides or not affected by bottom currents. 4. Interbedded rippled siltstone and contorted strata are common as one approaches Siparia Point. Both current and oscillatory ripples are common. The cyclic occurrence of extensively bioturbated beds (Planolites ichnofabric) within fine grained sand beds suggests that they are associated with recurrent depositional events (?storm beds). Sandstones also display low-angled cross-stratification, likely from reworking of oscillatory currents. The youngest beds contain Ophiomorpha nodosa networks, Subphyllochorda, and other unidentified traces. 4.1.3 SYNOPSIS OF SEDIMENTARY PROCESSES AT MORNE DIABLO The sediments observed along the Morne Diablo coast were deposited by a range of sedimentary processes. Sediment gravity flows and block slides account for most of the strata observed. Coherent block slides and slumps, along with cohesive, fluidized and turbulent flows are evident among the chaotic sequence described west of the fishing depot. Debris flows, slump folds and turbidites (Ta-Tb-Tc) are some of the related products. It was obvious that the allochthonous sandstone, preserved among the gravity flow deposits, was initially reworked by oscillatory currents and storm waves, prior to being resedimented. Where these are in-situ near the top of the section (Siparia Point) they provide evidence for a change in sedimentary processes from gravity-dominated to traction-bedload and the reworking of sediments within wave-base. The transition was 194 gradual over the estimated 100-150 m of section with evidence of sedimentary slumps even among the wave-reworked sands and silts. 4.1.4 DEPOSITIONAL ENVIRONMENT OF THE CRUSE FORMATION ALONG THE MORNE DIABLO COAST The sediments west of the Morne Diablo fishing depot are interpreted to be part of a slope canyon fill. The discordant sandstone and shale facies is comparable to facies "F" of Mutti and Ricci Lucci (1978) (Table 3.4) and together with the massive thick-bedded sandstones, are best correlated to their slope facies association. Similar facies have commonly been related to slope canyon fills in other basins (Lowe, 1972; Cook, 1979; Klein et al., 1979; Cainelli, 1994). The sandstone blocks and their in-situ equivalents at Siparia Point originated on the shelf within the influence of oscillatory currents and storm waves. The Morne Diablo-Siparia Point succession preserves the complete transition from unbioturbated and deformed slope deposits to bioturbated and wave-reworked shelf sandstones through the estimated 100-150 m of strata. The undeformed and muddy slope facies, away from the interpreted canyon fill, was described approximately 5 km to the west of the Morne Diablo fishing depot by Winter (2006). Winter described a transition from undeformed slope muds to channelized outer-shelf sandstones overlain by tidal- and fluvial-influenced lithofacies. Other outcrops within the Cruse Formation (or equivalent in age) also display well-defined coarsening-upwards cycles typical of shelf successions. They begin with extensively bioturbated silts and end in thick-bedded sandstones with abundant Ophiomorpha nodosa burrows (e.g. Point Radix, Figure 4.1). These beds likely formed part of the three cycles that characterize the Cruse Formation (Kugler, 2001). 195 Figure 4.4 Cruse Formation slope and (outer) shelf sediments, Morne Diablo coastline. A) Debris flow with clumps of black lignite within sandstone matrix; ruler = 20cm. B) Turbidite beds showing loading at base, followed by parallel (Tb) and ripple-laminae (Tc). Ruler = 15cm. C) Turbidite bed with massive fine-grained sandstone (Ta) overlain by parallel (Tb) and ripple (top 3cm) laminae (Tc). D) Thin (15cm) debris flow between turbidite beds comprises abundant organic matter (darker fragments) within a siltstone matrix. E) Wave-rippled sandstone near top of the section at Siparia Point. F) Beds become increasingly organized up-section as shown by the slumped mudstones overlain by conformable strata. The latter comprises wave-rippled siltstones and storm beds. 196 4.2 LLTHOFACIES OF THE MORNE L'ENFER FORMATION (LATE PLIOCENE) A Late Miocene to Early Pliocene age interpreted from fossil flora provided the earliest age constraints for the Morne L'Enfer Formation (Hollick, 1924; Berry, 1925; 1937). More recent references to the formation tend towards a Late Pliocene age based, on fossil foraminifera and pollen zonations (Batjes, 1968; Saunders and Bolli, 1985; Saunders et al, 1998; Carr-Brown, 1998; Jones, 1998; de Verteuil and Johnson, 2003). Vincent et al. (2007) reported a Late Pliocene age based on palynomorph assemblages found at the top of the Morne L'Enfer Formation. The Pliocene Morne L'Enfer Formation represents a late cycle of deltaic sedimentation within the Southern Basin of Trinidad (Sutton, 1955; Barr et al., 1958; Suter, 1960; Ablewhite and Higgins, 1968; Bower, 1968) and overlies other deltaic sediments of the Forest and Cruse formations (Table 1.1). Several outcrops occur along the coast of the southwest peninsula of Trinidad and extend to the west within the Erin and Siparia synclines (Figure 4.5). Based on map (Kugler, 1959) and field measurements, the formation is approximately 1600 m thick along Puerto Grande Bay and 1200 m thick along Cedros and Esperanza bays, the difference is likely caused by thinning across pre-existing highs or growth thickening across normal faults (Vincent et al, 2007). The majority of published references discuss the lithology, stratigraphy, thickness and regional extent of the formation in very general terms only (e.g. Waring, 1926; Liddle, 1946; Kugler 1953; Ablewhite and Higgins, 1968). The paucity of detailed studies is surprising given the excellent exposures along the coasts and its importance as a hydrocarbon reservoir. The earliest known attempt at discerning the sedimentary processes and depositional environments associated with individual bedsets was that of Saunders and Kennedy (1968). Other notable and recent investigations included Wach et al. (2004) and Osman (2007). 197 Approximately 1100 m of outcrop section for the Morne L'Enfer Formation were reviewed as part of this study. From these outcrops at least eight lithofacies assemblages are described that represent most of the formation; a complete treatment was hindered by the lack of exposures in the Base Upper Forest Clay and Lot 7 Silt members. In general, a wider range of sedimentary processes was active during deposition of the Morne L'Enfer Formation than suggested from previous studies. In addition, the large-scale cycles described for the formation can be subdivided into several parasequences and sequence boundaries not previously described. The lithofacies and sequences described here form the basic groups that will be used when Pliocene mineralogy and ichnofacies are considered below. Recognized trends and inferred sedimentary processes within each will ultimately be integrated to provide a clearer understanding of changing basin settings during the Pliocene. 4.2.1 OVERVIEW OF THE MORNE L'ENFER FORMATION The Morne L'Enfer Formation consists of five members (Saunders et al, 1998; Kugler, 2001) (Table 4.1). From the youngest, they are: the Upper Forest Clay, Morne L'Enfer Silt, Lower Morne L'Enfer Sandstone, Lot 7 Silt, and Upper Morne L'Enfer Sandstone members (Kugler, 1959; Saunders et al., 1998; Kugler, 2001). Informally, the Lot 7 Silt Member divides the Morne L'Enfer Formation into the 'lower' and 'upper' Morne L'Enfer. The type locality for the Morne L'Enfer Formation is located at Morne L'Enfer hill although the inaccessibility of this location led Kugler (2001) to recommend Puerto Grande Bay as a co-type section (Figure 4.5). Most of the Upper Morne L'Enfer Sandstone Member is preserved at Puerto Grande Bay, though only the uppermost part of the Lower Morne L'Enfer Sandstone Member is exposed at that locality. A more complete section of the lower Morne L'Enfer (Lower Morne L'Enfer Silt and Lower Morne L'Enfer Sandstone members) is exposed along Cedros Bay in the southern Gulf of Paria (Figure 4.5) and this is a more suitable co-type section for these members. The base of the Morne L'Enfer Formation (Upper Forest Clay Member) consists of grey, "well-bedded" clay grading upward to silts of the overlying Morne L'Enfer Silt 198 Outcrop Locations F: StoBmeyer oilsand quarry ^ Erin Formation Outcrop A: Fuiarton G: Well E257 locality Upper Morne L'Enfer Sandstone Mbr (continuous section) B: Cedtos Bay H: Seotts Road, Penal Lot 7 Silt Member C: Puerto Grande Bay «J^ Morne L'Enter Formation type locality I: Southern Mam Road, Penal Lower Morne L'Enfer Sandstone D: Forest Reserve J: Marchan trace & Morne L'Enfer Silt Members E: Guapo Bay Figure 4.5 Geologic map of southwest Trinidad showing distribution of the Morne L'Enfer Formation and the locations of logged exposures for this study. Geology after Kugler, (1959). Member (Kugler, 2001). The Morne L'Enfer Silt Member consists of cleaning-upward, thin-bedded siltstone to sandy bedsets. The member is estimated at 200 m thick based on a correlation of well FE-107 to outcrops at Cedros Bay (Figure 4.5). The overlying Lower Morne L'Enfer Sandstone Member is also gradational from grey silts to thick, amalgamated, sandy bedsets at least 100 m thick with abundant oscillatory wave ripples, swaley cross-stratified strata and local flaser-wavy bedding. These sands are known for their sheet-like geometry (Barr et al., 1958), which allowed for "excellent" well log correlation (Jones, 1968; Saunders and Kennedy, 1968, p. 124). One regional erosive horizon occurs near the top of this member overlain by sandy beds that display uni directional, dune-scale cross-stratification. Archie (2004) recognized incised valleys occurring within the Lower Morne L'Enfer Sandstone Member in the subsurface of the Soldado Field, Gulf of Paria, erosive into the underlying Forest Formation. The Lot 7 Silt Member overlies the Lower Morne L'Enfer Sandstone Member and forms a distinctive marker in subsurface wells across the western Southern Basin (Bower, 1968). Within the Upper Morne L'Enfer Sandstone Member, sandy bedsets are typically channelized with lenticular geometries measuring tens of metres in thickness with multiple erosive surfaces, mudclasts horizons and laterally accreting bedsets capped by lignite horizons. An unconformable relationship was proposed between the Upper Morne Depositions! environments from previous studies Saunders and Kennedy Bower This Study Member/ Formation Wach(2004) Vincent (2005) (1965) (1968) Erin Formation Fluvial Fluvial Fluvial Tidal flat-mangrove Upward Subtidal channels, intertidal "Upper swamp; distributary transition from flats; tidal-influenced Upper Morne L'Enfer Brackish Morne channels and mouth tidal- to fluvial- floodplain/ nearshore; delta- Sandstone Member water L'Enfer" bars; interdistributary dominated top lagoons; wave-modified bay; estuary processes delta; quiet-water bay-fills Lower shoreface to distal Lot 7 Silt Member offshore Prodelta; lower shoreface; Lower Morne L'Enfer Fluvial- "Lower middle and upper shoreface; Sandstone Member estuarine fill Morne fluvial-estuarine channel fills L'Enfer" Morn e L'Enfe r Formatio n Lower Morne L'Enfer Silt Distal prodelta Upper Forest Clay Table 4.1 Members of the Late Pliocene Morne L'Enfer Formation and interpreted depositional environments of various workers, including this study. 200 L'Enfer Sandstone Member and the overlying Erin Formation by several authors (Wilson, 1940; Barr et al., 1958; Bower, 1968; Kugler, 2001) while a conformable relationship is suggested in the stratigraphic column of Saunders et al. (1998). The contact between the two is defined by lithology and is mapped as the base of the 'porcellanite' beds outcropping at Puerto Grande Bay (Kugler, 1956; 1959). In addition, Kugler (2001) describes the base of the Erin Formation as a "fairly coarse-grained basal sandstone". This bed can be observed just west of Quoin cliff (Figure 4.5) as a basal channel lag with porcellanite pebbles. The occurrence of multiple lag horizons throughout the Upper Morne L'Enfer Sandstone Member suggests that the coarse-grained basal lag is not indicative of a major unconformity, but of local erosion at the base of migrating channels. A gradual, though distinctive change in physical sedimentary structures occurs within the uppermost Morne L'Enfer Sandstone Member, more analogous to beds of the Erin Formation, and this is more representative of the top of the Morne L'Enfer Formation rather than a specific horizon. The overlying Erin Formation consists of fluvial channels, 'porcellanites' and thick lignite-mud horizons. 4.2.2 FACIES OF THE MORNE L'ENFER FORMATION The Morne L'Enfer Silt Member comprises at least two lithofacies that collectively define a cleaning upward succession. It begins with laminated silts (LS) which are overlain by flaser and wavy sands (TUFW). These are described from Cedros Bay. 4.2.2.1 LAMINATED SILTS (LS) Description This lithofacies consists of approximately 50 m of interlaminated silts and grey mud with common fine sand laminae. Bedsets are locally disconformable with common low-angled slump scars, contorted beds and ball and pillow structures. Organic matter is present as either finely disseminated grains, drapes on current rippled silts and very fine sand, or rare wood fragments. Silty sands occur in isolated laminae or as starved current 201 ripples; these increase in thickness and abundance upward. Symmetrical wave ripples also become common up-section, coincident with an increase in biogenic sedimentary structures (also see Vincent and Wach, 2007 b). Interpretation A distal to proximal prodelta depositional environment for this lithofacies is favoured based on litho- and ichnofacies (Section 5.5.2.1) assemblages. Laminated clayey silt and sand beds suggest sedimentation from suspension settling from hypopycnal currents capable of carrying only the finest grain sizes into a muddy environment. Current-rippled sand and silt laminae were deposited by traction currents. The disconformable bedsets were likely the result of laterally shifting sediment source and avulsion on the delta front. A prodelta environment is also supported by the localized slump scars and ball and pillow structures, as evidence of gradient-induced sediment instability. The increase in symmetrical ripples upward records a gradual shallowing and increased influence of oscillatory currents as sediments were deposited within active wave base. The greater agitation associated with these currents introduced an environment more favourable to benthic organisms, as reflected in the increase of trace fossils towards the top. 4.2.2.2 THICKENING-UPWARD FLASER-WAVY SANDS (TUFW) Description Approximately 40 m of this lithofacies crop out at St. Marie Point, Cedros Bay, gradational from the laminated silts facies. It is differentiated from this underlying facies by the disappearance of symmetrical ripples with wavy and bifurcating shale and sand laminae becoming the dominant lithology (Figure 4.6 A). Yellow, poorly consolidated, very fine-grained sand beds attain a maximum thickness of 30 cm. They have a massive appearance due either to obscured internal stratification that resulted from weathering or destruction by bioturbation. Bioturbation is common to abundant with a diverse assemblage of traces. 202 The distinguishing criterion is the presence of flaser- wavy, and occasionally lenticular bedding, capping thickening-upward bedsets. Within other occurrences of this lithofacies in the Morne L'Enfer Formation (Puerto Grande and Cedros bays) planar, trough and sigmoidal crossbed sets are common, within higher bedsets, sometimes capped by rooted horizons (Figure 4.6 B). Where cross bedding is abundant, the lithofacies show many similarities to the "laterally accreted sands" facies (described below). Bi-directional ripples are very common while 'herring-bone' cross-stratification, symmetrical ripples and swaley cross-stratification form a minor component. Interpretation This lithofacies was deposited within water depths sufficiently shallow to be influenced by reversing currents, likely within a proximal deltaic environment. Flaser bedding suggests that sands were preferentially deposited during active tidal flows and capped by thin shale drapes during waning currents (Reineck and Singh, 1973). These drapes are partially eroded with a subsequent increase in current velocity and ripple migration. Such cyclical trends in current velocities were associated with tide reversals or passage of oscillatory waves (Reineck and Singh, 1973). Tidal processes may have played an important role during deposition and reworking of this lithofacies. Other evidence supportive of tidal origin includes the sigmoidal cross-stratified sands and herring bone cross-stratification. The sigmoidal and trough cross-stratified sands represent migrating dune-scale bedforms likely associated with subtidal channels near the top of the assemblage. This is evidenced by the overlying rooted horizons and similarities to the "laterally accreted sands" lithofacies. 203 Figure 4.6. Representative graphic logs of lithofacies within the Morne L'Enfer Formation. A) "Laminated silts" at base of section upward to "thickening-upward fiaser- wavy sands" facies. The section is capped by prodelta slumps associated with delta abandonment (see text for discussion). The trace fossils shown are representative of the entire section but increase in diversity and intensity upward. B) Cleaning-upward section through "transitional silts and shale" facies upward to "thickening upward fiaser- wavy sands", this time capped by cross-bed sets, lignite and a rooted horizon. "I" represents 'lenticular-wavy beds' and "II", 'parallel beds' of this facies. C) "Trough cross-stratified sands" of fluvial origin incised into "swaley cross-stratified", shoreface sands representing a basinward shift in facies and a sub-regional unconformity. Interpretations are shown in italics. A and C from Lower Morne L'Enfer Sandstone Member, B from Upper Morne L'Enfer Sandstone Member. See Figure 4.8 for key to symbols. 204 (p*fSUfUIOp MMt (pojeuiwop IB/Any-m^dpooe^fseoo) - pjQJf m/ap pegpotu swan i oosyaioiis) spues psgjeijs-sseuo y§naii spues poK^jjs-ssoio Xe)BMs D«*> %• =L m * f^T UJ jl iZ 1 (sossaoaid MM pu a spp :sjeuteP3JO»u! 'stm Aeq 8u|pnpu| 'snoue/\) (pnouiuiop»pn-B)iappMUfx&Jd<^fugi4mi»fif'l'K3) 9|8i|8 pue 8gp leuesisuejx (A1dnjJspUW^BM-i»9^pJB«dn-Buiu»3p)lU. H CO CQ = i! Jm 4- S B>4 o CO Ml ^ •o ,J1 3H I fauauno AHABJB pue Affsuep - aaegaiot/s } 206 207 The Lower Morne L'Enfer Sandstone Member is separated from the Morne L'Enfer Silt Member by slumped sands and silts of similar lithology to the thickening- upward flaser-wavy sand (TUFW). The deformed horizons include slump scars, intraformational boulders, and ball and pillow structures (Vincent and Wach, 2007b). These deformed sediments are interpreted to be delta-front slumps and they represent a deepening relative to the underlying flaser-wavy sands. The sequence stratigraphic significance of this flooding event will be readdressed below. The Lower Morne L'Enfer Sandstone Member comprises at least three lithofacies distinguished by abundance of sand, bioturbation and sedimentary structures. 4.2.2.3 GREY, BIOTURBATED SILTS (GBS) Description Along Cedros Bay, grey and bioturbated silts are interbedded with and continuous from slumped and contorted beds that overlie the flaser-wavy sands (TUFW). They are eventually replaced by thin-bedded silts with occasional fine-sand laminae. Throughout most of the section, primary bedding is obscured by a relatively high diversity and abundance of trace fossils, although parallel laminae among the silts appear most common (Figure 4.7 D). Flat, disc-shaped and fine-grained sand cobble and boulders are commonly found along the erosional remnants upon the wave-cut platform and rarely seen in situ among the bioturbated silts where they form interlaminated 'pods' that are also extensively bioturbated. Interpretation The slump scars, contorted beds and intraformational cobbles in the lower part of this facies indicate sediment instability initiated on the distal prodelta slope and front. The interbedded bioturbated and parallel laminated sands and silts represent fair- weather sediments, but do not show any indication of wave or tide reworking. Traction- related sedimentary structures are absent and the fine-grained beds may be the product of density-driven hypopycnal flows and suspension settling into quiet waters. The discontinuous sand 'discs' represent greater sand accumulation, although local (i.e. not laterally extensive). The disc-shape was likely derived from subsequent loading of the 208 silty substrate. The abundant bioturbation also suggests relatively slower sedimentation rates. Relative to the underlying tidally influenced sediments, this lithofacies represents a significant deepening of the basin that may be partly associated with deltaic avulsion. A lower shoreface or offshore transition (Reading and Collinson, 1996) environment of deposition is assumed. 4.2.2.4 SWALEY CROSS-STRATIFIED SANDS (SCSS) Description The distinguishing characteristics of this facies are the swaley cross-stratified sands, common symmetrical ripple-laminae and pervasive bioturbation. A 40 m representative section was measured at Cedros Bay. A sharp contact separates the grey, bioturbated silts below, marked by a 1.3 m thick interval of deformed and contorted fine sand with through-going flame structures and other sedimentary loading features, dewatering pipes, and low-angle, cross-stratified sandstones (a representative section is shown in Figure 5.15). Symmetrically rippled sandstones are interbedded with thin, wavy, grey shale laminae. Much of this facies comprises amalgamated swaley cross- stratified sands with common pebble-sized mudclasts. Hummocky cross-stratification is rarely present (Figure 4.7 F). The top of the representative section is marked by a 1.5 m thick bedset of medium-grained, trough cross-bedded sandstone. Away from the representative section, several additional characteristics become obvious. At the Scotts Road outcrop within the Siparia Syncline (Figure 4.5), two well defined thickening-upward intervals are present (Vincent et al., 2007); the thickest sand beds contain low-angled cross-laminae and swaley cross-stratification. At Puerto Grande Bay, the sands are less amalgamated, separated by continuous, thin shale beds; organic matter commonly occurs as either disseminated grains or concentrated to form laminae sets within silty beds. 209 Esperanza Bay Stollmeyer Quarry, Guapo • *~2~=r* 101 LEGEND -*v>r .Scour ^ wavyparaMM ===== •; Organic matter «* Unficular sands Telchlchnus * Bumjw(w*tof*ted) Sftouihos •St Ftaser tMddsd Ftanw«nx)|gro» schoubcyfindrichma; s 76 Contorted bedflamlnae Palwopfeycus ,A>V. Symmetrical ripple •H ThatoafrtoWes V load east Pritontchnus T Churned Qphtomorpha Currant rippit 3S56 Swatey cros4 staOftaMfen £ 'V CyfifH&khnus Artnloofetss *r fthfeoooraiKum ->- Trough crmbtd Ro»Sa o^ 4* U*T imprint .a^- Planar cross b«d& Bergaueria -Sfe Lew angled cross Gyrofitrw& stratification tamieuiaf A RootM horizon aaonwey •» ^ Wood fragment Figure 4.8 Representative graphic logs of lithofacies within the Morne L'Enfer Formation. A) Fining- upward section of laterally accreted sands lithofacies (LAS). Lower sands are partially schematic. The base of the section unconformably rests on laminated shale of a previous cycle (dashed line). B) Estuarine channel fill overlying fluvial sediments, the representative facies are labelled at left of the section. The succession is capped by low-angled cross-stratified sands with Ophiomorpha and Skolithos traces, suggesting the onset of more marine conditions. A) from Upper Morne L'Enfer Sandstone Member and B) from Lower Morne L'Enfer Sandstone Member. 210 Figure 4.9 Tidal and fluvial-estuarlne fades in the Morae L'Enfer Formation. A and B) Large, possibly in situ, fossilized tree trunks within nearshore-fiuvial facies. 'A' is in apparent growth position and 'B' lies above lignite bed. C) Sigmoidal cross-stratification of fluvial-estuarine origin. Dark colour is due to oil- staining D) Large floating sandstone boulder within deformed clays of the ASCS facies. E) Bedded and fining-upward mudstone conglomerate of possibly fluvial origin. F) Close-up view of mudstone conglomerates shown in (E). Dark specks are organic fragments. G) Mud rip-up clasts at the base of fluvial-estuarine channel. (A, B, D, and G) from Stollmeyer oil sand quarry, lower Morne L'Enfer; all others from Puerto Grande Bay, upper Morne L'Enfer. 211 Interpretation This lithofacies was strongly influenced by oscillatory wave processes along open shorelines or an abandoned delta front. Amalgamated swaley and hummocky cross- stratified intervals may extend towards middle to upper shoreface environments supported by its association with lower shoreface silts and sands (grey, bioturbated silts facies) and trough cross-bedded sands at the top (upper shoreface). 4.2.2.5 TROUGH CROSS-STRATIFIED SAND (TCSS) Description This lithofacies is present in both the Lower and Upper Morne L'Enfer Sandstone members and has been partially described by Saunders and Kennedy (1968) from exposures at Guapo Bay. A representative section is described from Upper Morne L'Enfer Sandstone Member outcrops along Esperanza Bay (Figure 4.5) and this is supplemented by observations made at other localities. Within the Upper Morne L'Enfer Sandstone Member at Esperanza Bay, trough cross-stratified sands sharply overlie tidally influenced sands (laterally accreted sands described below). This facies is distinguished by the common trough cross-beds, in association with mudclasts horizons of varying thicknesses (<3 m) and lens-shaped sand bodies ranging from 2-10 m thickness. Trough cross-beds are unidirectional with occasional mud drapes on foresets. They may occur within individual beds up to 2 m thick, though are commonly less than 50 cm (Figure 4.7 G). Alternatively, these beds amalgamate into lens-shaped sand bodies, which are then draped by interbedded sand- silt-shale bedsets and organic matter. The mudclast horizons contain angular or rounded, cobble to pebble-sized mudclasts occurring at erosional surfaces either bounding lens- shaped sand bodies, or within them. Other common sedimentary structures within these sands include planar cross-stratification, flame structures, load casts and contorted shale laminae. Within the uppermost beds of the Upper Morne L'Enfer Sandstone Member at Esperanza Bay, lignite beds are commonly interbedded with organic-rich, grey muds, attaining cumulative thicknesses over 3 m; this is unlike lignite beds found associated 212 with other facies that rarely exceed a few tens of centimetres. Metre-scale fossilized wood fragments are a common component of these finer-grained beds. At Puerto Grande Bay, a distinction can be made within a lens-shaped sand body (up to 12 m thickness) with a sandy, axial facies and clayey marginal facies overlying erosive contacts (Figure 4.10 A-C). At this bay, clast-supported mudstone conglomerate and pebble beds are also significant, attaining thicknesses up to 5 m. The thickest bed observed displayed normal grading and decreasing amalgamation upwards into discrete mudstone conglomerate beds tens of centimetres thick (Figure 4.9 E, F). These contain intraformational rounded mud clasts within a fine to medium grained sandy matrix. A similar mudclasts facies from Guapo Bay (Figure 4.5) shows a channelized geometry to these mudclasts beds (Saunders and Kennedy, 1968, Figure 10). These beds are interbedded with silty intervals of flaser-wavy and lenticular bedding, the latter with common bi-directional current ripples (Figure 4.10 D, E). In the Lower Morne L'Enfer Sandstone Member, the trough cross-stratified sands facies is found in erosive contact with swaley cross-stratified sands (SCSS) at Cedros Bay, and at an outcrop adjacent to well E-257 at Guapo (Figures 4.6 C and 4.7 H). At the well site, at least 9 m of incision exist between the trough cross-stratified sands (TCSS) above and the swaley cross-stratified sands (SCSS) below. The facies can also be observed at the base of an oil sand quarry west of the wellsite (Stollmeyer oil sand quarry), where it is described in detail by Vincent and Wach (2007b). There, a 60 cm fossilized tree trunk was found in an upright position, encased within thin sand and silt beds (Figure 4.9 A). Interpretation The association of lens-shaped sand bodies, multiple erosive surfaces, trough cross-beds, mudstone conglomerates, lignite and in situ fossilized wood is interpreted to have formed within coastal to fluvial-floodplain depositional environments. Tidal influence is suggested by the mud drapes on trough foresets and common bi-directional ripple laminae found along Puerto Grande Bay. The lens-shaped sands with erosional base and common mud rip-up clasts are the associated channel-fill deposits with lateral and vertical transition to shale prone margins. The trough cross-beds were produced by 213 Figure 4.10 Lithofacies of the Mome L'Enfer Formation. A) and B) Photo and line drawing depicting the pinch-out of lens-shaped channels in the Upper MLE Sandstone Member. Note the shaly channel margin and capping organic-rich mud. The boxed area is shown in (C). C) Muddy channel margin fill unconformable over sands of an earlier channel. The erosion boundary is arrowed and back-pack at left for scale (50 cm). D) Wavy-lenticular sands are common throughout the formation. E) Bi-directional ripple laminae and slack-water shales provide evidence of short-term bi-directional currents, likely associated with tide reversals. F) Laterally accreted bedsets overlying parallel laminated shale beds of the "laterally accreted sands" facies. All photos from the Upper Morne L'Enfer Sandstone Member. 214 bedload movement of sands within these channels as migratory dune-scale bedforms. Unidirectional flow was the norm. The mudclasts may have been derived from either channel bed erosion (mud rip-up clasts) or derived from muddy intra-channel slumps along channel margins. The rounded mudclasts and graded bedsets is reflective of bedload transport and waning flow velocities. The overlying drape of fine sands, silts and organic matter represents a late stage of channel infill, or possibly channel abandonment. Lignite and mud-rich intervals are interpreted as coastal lagoons or interfluves. 4.2.2.6 AMALGAMATED SIGMOIDAL CROSS-STRATIFIED SANDS (ASCS) Description This lithofacies is found only within the Lower Morne L'Enfer Sandstone Member and has been previously described (Wach et al., 2004; Osman, 2006; Wach and Vincent, 2008). The best exposure occurs within the Stollmeyer oilsand quarry at Guapo where approximately 23 m of sigmoidal and trough cross-stratified sands overlie channel fills of the trough cross-stratified sands facies. The two are separated by a mudclasts conglomerate up to 3 m thick (Figure 4.9 G). This lithofacies forms an almost continuous set of amalgamated fine-grained sandstone beds. Individual bed thicknesses vary from 10 to 200 cm. Bedsets consist entirely of sigmoidal and trough cross-stratified sands with lunate crest geometries evident in plan view and unidirectional crossbed dips, mainly towards the southeast. Climbing ripples and discontinuous clay and silt drapes are present upon the lower foresets and toesets of the sigmoidal cross beds. Approximately 20 m (height) x 100 m (width) of these sands are exposed at the abandoned section of the oilsand quarry where large-scale cross- stratification (Bridge, 2006) oriented oblique to paleoflow are also exposed (Figure 4.11). There, the outcrops display a lower amalgamated bedset with dune-scale trough cross- stratification superimposed upon the larger cross-strata. More heterolithic bedsets are apparent near the top that may be related to an increase in shale content. The sigmoidal and large-scale cross-stratified sands are abruptly overlain by thin- bedded, fine-grained sands, laminated silts and clays with common slumped boulders and 215 contorted beds (Figures 4.8 and 4.9 D). This is overlain by bioturbated, low angle cross- stratified sands similar to the swaley cross-stratified sands described above. Interpretation The amalgamated sigmoidal cross-stratified sands are interpreted as fluvial-tidal in origin, deposited within a transgressive estuarine complex. The large-scale cross- stratification are laterally accreted beds that were associated with channelized point bars while the dune-scale trough cross-beds were likely smaller, dune-scale bedforms superimposed upon these larger features. Collectively they formed a sand-rich channel complex with a high degree of amalgamation. Clay drapes on cross laminae were likely deposited during waning currents associated with tidal slack-water periods prior to current reversals which subsequently eroded the tops of bar crests forming the convex topset to foreset laminae (e.g. Kreisa and Moiola, 1986). The mudclasts conglomerate beds represent basal channel lag associated with the amalgamated channel complex. The overlying silts and slumps are likely associated with a later stage of channel infill prior to abandonment of the fluvial-tidal channels. The overlying bioturbated, low-angled and cross-stratified sands suggest the onset of more marine conditions (flooding) near the top of this lithofacies which also finds support from changing palynofacies (Vincent et al., 2007).. 4.2.2.1 LATERALLY ACCRETED SANDS (LAS) Description This facies was observed only within the Upper Morne L'Enfer Sandstone Member and is best exposed along Esperanza Bay. The facies consists of sets of large- scale cross-strata each ranging between 12-25 m thick and capped by metre-scale intervals of bioturbated or organic rich shale (Figures 4.8 A and 4.10 F). At least six individual sets have been recognized along the bay where it is apparent that at least two are oriented perpendicular to the palaeoflow direction indicated by lunate bar crests exposed along the modern shoreface (i.e. northeast-directed). One set of large-scale cross-strata approximately 16 m thick (perpendicular to upper and lower contacts of the 216 Figure 4.11 Amalgamated sigmoidal cross-stratified facies. (A) and (B) Outcrop photo and line drawing of oil-stained, amalgamated channel sands with large-scale cross-stratification and minor scours. A change in bedding style is apparent towards the top (stippled pattern in B) that is attributed to increased shale content at the top of the channel. Palaeocurrent orientation is towards the viewer; the locations of (C-E) are shown. (C) Trough and sigmoidal cross-beds are superimposed on the large-scale cross-stratification. (D) Close-up view of the large-scale cross-stratification oriented oblique to palaeoflow. (E) The overlying beds comprise contorted horizons succeeded upward by low-angled cross-stratified sands; note birds for scale. inclined strata), begins with an extensively bioturbated silt bed overlying bioturbated, parallel-laminated shale of a previous set. Above the silt bed, the section consists of fine grained, wavy and flaser bedded sands up to 15 cm thick with common shale drapes, upwards into lenticular-bedded, rippled silts. This is followed by an abrupt transition to the parallel-laminated, bioturbated shale. A sharp contact (planar or irregular) is common to all occurrences of this lithofacies. The lower sand-prone beds may consist of dune-scale, amalgamated, low- angled cross-stratification with internal erosive surfaces overlain by contorted beds, common flame and sediment loading structures and locally abundant mudclasts. The beds within the package thin upwards to lenticular, flaser and wavy-bedded sandstones, also with common planar cross beds. The bioturbated shale beds are typically 10 m± thick, grey in colour, well-bedded, parallel-laminated or massive. Current-rippled sand and silt laminae (up to 3 cm) are common and organic matter occurs as concentrated laminae. Localized scours also occur. Only within the uppermost metre is lenticular and wavy bedding again recognizable before being overlain by laterally accreted bedding of another package. This upper shale interval may be replaced by beds of the swaley cross-stratified sand lithofacies or discontinuous, organic-rich mud with thin lignite beds. At Puerto Grande Bay, laterally accreted sands are interbedded with mudstone conglomerates, trough cross-beds and lens-shaped sand body geometries; characteristics very similar to the trough cross-stratified facies described above. Interpretation This lithofacies is differentiated by the large-scale cross-stratification associated with the lateral accretion of channelized sediments. These are interpreted as sub- to intertidal channels and intertidal flats based primarily on the succession of lithofacies within this assemblage. The laterally accreted beds overlie sharp, irregular bases and are subsequently capped by flaser-wavy and lenticular sands and silts, an assemblage usually associated with tidal environments (Reineck and Singh, 1973; Weimer et al., 1982). The thick mud beds that top the sequence (parallel laminated and massive muds) provide additional evidence for quiet-water sedimentation, interpreted as intertidal flats or quiet- 218 water bayfill sediments, farther supported by the common bioturbation. The lignite-mud beds that also cap the laterally accreted sands are interpreted as muddy channel fills adjacent to coastal-lagoon environments. The internal erosive surfaces, contorted laminae sets, cross-beds and rip-up clast horizons are part of the channelized fill, which also display evidence of tidal influence (flaser-wavy-lenticular bedsets). The fining- upward records the eventual abandonment or lateral migration of each channel. Where the swaley cross-stratified lithofacies occurs over the laterally accreted sand, wave reworking is inferred and provides additional evidence of coastline proximity for these channels. The laterally accreted bedsets are not easily distinguished from the trough cross-stratified facies at Puerto Grande Bay, and this may be attributed to the interplay of both fluvial and tidal sedimentary processes within an overall nearshore, coastal environment. 4.2.2.2 TRANSITIONAL SILTS AND SHALE (TSS) Description This facies incorporates intervals within the Morne L'Enfer Formation that do not fit within any of the groups described above. They are shale-prone intervals that often transition between other facies and can be as much as 50 m thick. The facies is most common to beds within the Upper Morne L'Enfer Sandstone Member and is best observed along Puerto Grande Bay. Two bedding styles are common to this facies; both occur as a minor component of other facies groups. The first is characterized by lenticular-wavy bedding (Figure 4.10 D). Intervals of lower sand content are dominated by lenticular bedding with bi directional cross-laminae. Flaser bedding occurs with increasing sand content although this forms a minor component of this lithofacies. The second bedding style is parallel bedded/ laminated silts and shale. Wave ripples and scours less than 1 m wide by a few centimetres height with cross-stratified fills, are common. A gradual transition may occur from one bedding style to the other, or the two may interdigitate. 219 Bioturbation among this lithofacies ranges from absent to abundant, and typically with a moderate diversity of trace fossils. Psilonichnus burrows dominate the trace assemblage. The lenticular and wavy bedding character is common to sediments deposited under the variable flow regimes of tidal environments. These intervals may represent intertidal flats or sheltered bays away from major sediment pathways. A similar environment is interpreted for the parallel-bedded silts and shales where shallow waves were active. 4.2.3 LITHOFACIES SUCCESSION AND SEDIMENTARY PROCESSES IN THE MORNE L'ENFER FORMATION: SUMMARY There is a much wider range of sedimentary processes throughout the Morne L'Enfer Formation than was evident from Paleogene sediments. These processes are summarized in Table 4.2. Sands of the lower Morne L'Enfer were deposited primarily from wave processes with subordinate tidal reworking. Density and gravity driven currents were common to silty intervals characterized by thin sands and overall low sediment input. The upper Morne L'Enfer was dominated by tidal processes with a transition to fluvial-dominated deltaic and floodplain deposits towards the top. Depositional environments within the Morne L'Enfer Silt Member included lower shoreface, distal prodelta and proximal prodelta. Silts and thin sands were deposited mainly by density driven currents and later reworked by epibenthic organisms. The prodelta silt beds gradually thickens upward into more proximal deltaic environments, accompanied by increasing bioturbation, wave and tidal reworking. Abandonment of the delta is suggested by the sudden deepening of environment above the proximal deposits evidenced by the distal prodelta slumps and slump scars, indicative of re-sedimented flows along the prodelta slope. The relative deepening continued with the bioturbated lower shoreface or distal prodelta silts. It will be shown in Chapter 5 that the trace fossil assemblage is typical of the Cruziana ichnofacies that characterizes distal offshore environments (Pemberton et al., 1992; MacEachern et al., 2007). 220 The lower shoreface silts are overlain conformably by the amalgamated shoreface sandstones of the Lower Morne L'Enfer Sandstone Member. Wave reworking of the fine-grained sands was the dominant process as indicated by the swaley cross-stratified sands, and resulted in tabular and laterally continuous sands as can be observed along the coast between Los Gallos Point and Fullarton (Figure 4.5) in the southwest peninsula of Trinidad. The uppermost sands in the Lower Morne L'Enfer Sandstone Member comprise channelized fluvial and fluvial-estuarine sands, the latter dominated by tidal processes and comprising amalgamated sandy bedsets. A significant change in sedimentary processes, depositional environments, sandstone geometries and sediment stacking occurred during the Upper Morne L'Enfer Sandstone Member time. Whereas the Lower Morne L'Enfer Sandstone Member was dominated by aggradational shoreface sandstones, the Upper Morne L'Enfer Sandstone Member was dominated by laterally accreted subtidal channels forming aggradational bedsets throughout most of its thickness. This is especially evident along Esperanza Bay where these channels are overlain by trough cross-bedded, fluvial sandstones and 10 m- thick organic-rich muddy horizons. The relationship is less evident along Puerto Grande Bay where these two facies (TCSS and LAS) are intercalated. The lithofacies association suggests a change from tide-dominated to fluvial-dominated processes in the uppermost Morne L'Enfer Formation. 4.2.3.1 PALAEOCURRENT ORIENTATION IN THE MORNE L'ENFER FORMATION Palaeocurrent orientations were derived from several outcrops north and south of the Los Bajos fault that dissects the southwest peninsula with at least 6 km of dextral strike slip displacement (Wilson, 1968). North of the fault, cross bedding indicates a southeast direction of sediment transport for the Morne L'Enfer formation (Figure 4.12). South of the fault, an east to northeast direction is indicated based on the orientation of ripple crests and cross-beds along Cedros bay. Apparent cross-bed dips along Puerto Grande Bay suggest a similar orientation. Palaeocurrent orientations are consistent with an easterly shale-out of the Morne L'Enfer Formation as mapped by Barr et al., (1958) (Figure 4.12). 221 Table 4.2 Summary of lithofacies, processes and sand dimensions of Pliocene sediments. The proposed system tracts are discussed in the text. APPROXIMATE FACIES AND ASSOCIATED DOMINANT SEDIMENTARY DEPOSITIONAL THICKNESS OF SAND BODY SAND BODY SYSTEMS LOCATION OR SEDIMENTARY STRUCTURES PROCESS ENVIRONMENT INDIVIDUAL CYCLE THICKNESS GEOMETRY TRACT EXAMPLE Mome Laminated silts Laminated silts & current- Density and gravity driven cleaning- HST1 St. Mary's L'Enfer (LS) rippled fine-sand laminae; currents and suspension upward, single Point, Cedros intra stratal slumps, slump settling; minor traction occurrence Bay scars; disconformabte bedsets; bedload; sediment instability; rare symmetrical ripples wave reworking near the top. Mome Thickening- Wavy-flaser-lenticular bedding; sensu Oscillatory and bi-directional Proximal delta Laterally cleaning- HST 1, 2 Cedros Bay MLE Silt, Lower and L'Enfer upward flaser- planar, trough, sigmoidal and Skolithos traction currents; wave and top/ lagoon persistent thin upward, single Puerto Grande Upper MLE wavy sands herring-bone cross-beds; bi- tide reworking beds occurrence Bay Sandstone (TUFW) directional ripples; Mome Grey bioturbated Laminated and contorted silts; Cruziana Density and gravity driven Distal prodelta Discontinuous HST1 Cedros Bay, Lower MLE L'Enfer silts (GBS) slump scars; thin deformed currents; hypopycynal plumes or lower thin beds Fullarton Sandstone sands and suspension settling shoreface Mome Swaley cross- Swaley, hummocky, low-angled Skolithos with Oscillatory currents; wave Middle to upper <40 Tabular, Aggradational HST1 Cedros Bay; Lower MLE L'Enfer stratified sands and rare trough cross- Cruziana reworking shoreface or laterally and multiple Puerto Grande Sandstone; restricted (SCSS) stratification; oscillatory ripples incursions wave-modifed continuous thickening- Bay; Scotts occurrence in Upper delta front upward cycles Road, Penal; MLE Sandstone Fullarton, Los GallosPt.; E- 257 Morne Trough cross- Unidirectional trough cross bed; Unidirectional traction Nearshore, tidal- 1.5-10 m Lens-shaped, Aggradational LST, HST Cedros Bay; Lower and Upper L'Enfer stratified sands multiple erosive surfaces; rip-up currents and bedload influenced channelized to back- 2 Puerto Grande MLE Sandstone (TCSS) mud-clasts and graded migration; fluvial transport fluvial floodplain stepping Bay; E-257 and mudclast conglomerates; lignite and lagoons Stollmeyer and wood fragments Quarry, Guapo Morne Amalgamated Sigmoidal and trough cross- Overlain by Mostly uni-directional traction Fluvial- 27 m Channelized Aggradational LST, TST Stollmeyer Lower MLE L'Enfer sigmoidal cross- stratification; rip-up mudclast Skolithos currents; evidence for bi- estuarine quarry, Guapo; Sandstone stratified sands horizons; climbing ripple; ichnofacies? directional tidal influence Cedros Bay; (ASCS) contorted strata, slump limited intraformational blocks exposure at Puerto Grande Bay Mome Laterally Large-scale inclined Psilonichnus, Bedload traction and bar form Sub-tidal to Ribbon, Aggradational HST 2 Esperanza Bay, Upper MLE L'Enfer accreted sands stratification; parallel laminated Skolithos migration; channelized flow intertidal channelized Puerto Grande Sandstone (LAS) shale; wavy-flaser-lenticular channels Bay bedding; planar and trough cross-beds; intrastratal scours Mome Transitional silts Lenticular and wavy bedded Psilonichnus, Varied tide and wave induced Bayfill, intertidal HST 1, Puerto Grande Upper MLE L'Enfer and shales (TSS) silts; swaley cross stratified and Skolithos currents; low energy flats HST 2 Say, Cedros Sandstone low-angled cross bedded silts suspension settling Bay Discordant Rotated and discordant n/a Sediment gravity flows; slide Slope canyon extreme Highly irregular chaotic TST? Mome Diablo Upper Cruse sandstone and sandstone blocks; slump folds; blocks and cohesive debris variation: beach shale (DSS) debris flows, disorganized flows 10s mto cobble conglomerates 10s cm Massive and Massive and normally graded Sediment gravity flows; low (upper) slope 12 m minimum 12 m Tabular, blocky Aggradational TST? Mome Diablo Upper Cruse gradational sandstones; Bouma Ta, Tb, Tc; density turbidites canyon beach sandstones debris flows and slumps (MGS) North Los Bajos Fault South Los Balos Fault Legend UMLE UMLE Palaeocurrent ^ measurements Sand/shale ratio to 0 4 Figure 4.12 Palaeocurrent orientions and isopach map throughout the Morne L'Enfer Formation. All measurements are within the Upper Morne L'Enfer (UMLE) and Lower Morne L'Enfer (LMLE) Sandstone members north (A, B) and south (C, D) of the Los Bajos fault. All measurements from cross beds except 'D' which are ripple crest orientations. (A) derived from Saunders and Kennedy (1968), Guapo Bay; (B) Stollmeyer oilsand quarry; (C) and (D), Cedros Bay. Sand/shale ratios map modified after Barr et al., 1958, Figure 9.) 4.3 SEQUENCE STRATIGRAPHY OF THE MORNE L'ENFER FORMATION A sequence stratigraphic model for the Morne L'Enfer Formation was presented in Vincent and Wach (2007b) and Vincent et al. (2007) arising largely from this study. The model is based on approximately 1100 m of measured section throughout the Morne L'Enfer. Outcrop facies was correlated to a subsurface gamma ray signature derived from published literature with the aid of an outcrop gamma tool run along a section of the outcrop. The results are presented in Figure 4.13. The facies changes provided the basis for interpreting major surfaces of flooding and erosion and the recognition of parasequences and parasequence sets (Van Wagoner et al., 1990; Posamentier and Allen, 1999). These formed the basis for interpreting at least two major highstand sequences represented by the lower and upper Morne L'Enfer with intervening lowstand and transgressive deposits. 4.3.1 RECOGNITION OF FLOODING SURFACES AND PARASEQUENCES Flooding surfaces were inferred where there was evidence for deeper-water strata conformably overlying shallower-water strata in keeping with the definition of Posamentier and Allen, (1999, p. 5). Three types of flooding surfaces were identified on this basis: 1. Marine shoreface (SCSS facies) or bayfill sands (TSS) overlying rooted horizons and lignites of proximal deltaic and/or coastal floodplain environments (TUFW facies) (e.g. Vincent et al., 2007, Figure 4 E). 2. Distal prodelta and lower shoreface silts overlying proximal delta top sands (e.g. Figure 4.6 A at 34 m) 3. Laterally accreted bedsets of subtidal channels overlying rooted horizons or intertidal/bayfill shales of a previous cycle (e.g. Figure 4.8 A at 20 cm and Figure 4.10 F). 224 OUTCROP SECTION (CEDROS BAY) Estuarine fill (ASCS) Distributary channels (TCSS) Wave modified delta front/ shoreface (SCSS) Proximal delta (TUFW) Wave modified delta front/ shoreface (SCSS) Distal pro-delta slumps/ lower shoreface' (GBS) Proximal delta (TUFW) Distal pro-delta silts (LS) Figure 4.13 Facies succession and depositional environments of the lower Morne L'Enfer correlated to subsurface gamma log signature with the aid of an outcrop gamma. A sequence stratigraphic interpretation is proposed based on flooding and erosion surfaces recognized along Cedros Bay and correlative exposures. 225 At least two flooding surfaces were recognized in the lower Morne L'Enfer that defined at least three regressive parasequences (Figure 4.13). Recognition of flooding surfaces in the upper Morne L'Enfer was more ambiguous largely resulting from fewer exposures during fieldwork and the change in depositional environment. Still, at least five flooding surfaces can be proposed on the criteria described above from outcrops at Puerto Grande and Esperanza bays. They define parasequences approximately 25 m thick that equate to the scale of individual channels. 4.3.2 RECOGNITION OF UNCONFORMITIES Unconformities were interpreted where there was evidence for significant erosion accompanied by a basinward shift in facies above the incision (Posamentier and Allen, 1999). One unconformity was identified within the Lower Morne L'Enfer Sandstone Member on this basis where marine shoreface sands (SCSS facies) are overlain by fluvial/ coastal fioodplain sands (TCSS facies) (Figures 4.6 C at 11 m and 4.7 H). Erosion was evident at Cedros Bay and E-257 wellsite, north and south of the Los Bajos Fault (Figure 4.5). Another unconformity at the base of the formation has been suggested by previous workers (Ban* et al., 1958; Kugler, 2001) while an unconformity at the top of the formation is questionable as discussed above (Section 4.2.1). 4.3.3 SEQUENCES AND SYSTEMS TRACTS The lower Morne L'Enfer highstand systems tract (HST) consists of at least three regressive, coarsening and thickening-upward parasequences (Figures 4.13 and 4.14). These are bounded by flooding surfaces identified by marine sands overlying coastal/ proximal deltaic facies or associated with delta abandonment and subsequent drowning. The uppermost parasequence is truncated by an incision that separates marine sands below from fluvial channels above, and this is interpreted as a lower Morne L'Enfer sequence boundary. The succeeding lowstand systems tract (LST) deposits are represented by approximately 30 m of fluvial sands (TCSS facies) overlain by the 226 transgressive fluvial-estuarine fill exposed in the Stollmeyer oil sand quarry (ASCS facies). This transgressive systems tract (TST) is capped by the Lot 7 Silt Member maximum flooding surface. This surface was not observed in outcrop but a marine incursion is suggested in the youngest observed beds of the Lower Morne L'Enfer Sandstone Member at Puerto Grande Bay and Stollmeyer oil sand quarry, characterized by the swaley cross-stratified sands facies. This is further supported by marine amorphous kerogen found in palynomorph samples (Vincent et al., 2007). At least six parasequences were identified for the upper Morne L'Enfer but further measurements are needed to establish their relative stacking pattern (regressive, aggradational or trangressive?). A regressive parasequence set is suggested by the overlying fluvial facies, which represents the progradation of more terrestrial environments within the upper Morne L'Enfer HST that continues into the Erin Formation. The base of the Erin Formation as mapped at Esperanza Bay (Kugler, 1959) is poorly constrained due to the poor exposure (Kugler, 2001) and was mapped higher in the stratigraphy than shown here (Figure 4.14). This position was chosen based on similar lithofacies to the base Erin Formation at Puerto Grande distinguished by amalgamated, trough cross-stratified, channelized sands, lignite-mud horizons up to 10 m thick (both features occur on a larger scale than typical for the upper Morne L'Enfer) and the occurrence of thin (tens of cm) "porcellanite" beds that are characteristic of the Erin Formation (Kugler, 1959). 4.4 SUMMARY OF LATE MIOCENE TO PLIOCENE SEDIMENTARY PROCESSES The Late Miocene to Pliocene formations documented important changes in the character of sedimentary deposits, which reflect the transition from slope to shelf environments and the onset of shallow water deposition, and reduced accomodation space in the basin (see "F" and "G" in Figure 3.4). Similar to the Plum Mitan locality (Section 2.6), there is abundant evidence for shallow-water reworking of the sandstones that is not 227 West CEDROS& East ESPERANZA BAYS -16 km- PUERTO GRANDE BAY 1600m Figure 4.14 Main sedimentary processes, thickness and sequence stratigraphy of the Morne L'Enfer Formation. 228 a feature of earlier Paleogene sandstones that were deposited under slope to basin floor conditions. Unlike the Plum Mitan locality, these deposits are widespread at this time and document the perpetuation of these environments, a change that continued into the Late Pliocene Morne L'Enfer Formation and fluvial deposits of the Erin Formation (Table 1.1, Kugler, 2001). The deltaic character of these formations has long been established (Michelson, 1976; Stainforth, 1978), but the diversity of sedimentary processes and depositional environments have not been extensively documented. The Morne L'Enfer is a diverse deltaic sedimentary environment with a wide variability of processes spanning wave, fluvial and tidal regimes. Similarly, the data presented above demonstrates the potential for study of finer-scale sequences (parasequences) than the large member-scale cycles commonly referred to in published literature (e.g. Barr et al., 1958; Michelson, 1976). From a basin-scale perspective, the palaeocurrent data derived from the Morne L'Enfer Formation provides important constraints on the direction of sediment dispersal into the basin (easterly), and as will be further demonstrated when mineralogy is considered, this likely represents a dominant transport direction for sediments into the basin. 229 Chapter 5 - Ichnofacies Analysis Applied to the Trinidadian Stratigraphy 5.1 ICHNOLOGY, ICHNOFACIES AND SEDIMENTOLOGY The disciplines of sedimentology and ichnology are complimentary. The palaeoecology of benthic and epibenthic communities were determined in part by sedimentological processes and depositional settings that eventually preserved behavioural aspects of those communities in the rock record. The modern study of this fossil record (ichnology) can reveal insights into environments that existed at the time of deposition. Frey and Seilacher (1980) defined ichnology as the study of organism- substrate relationship, involving the description, classification and interpretation of trace fossils (and their behaviour). Trace fossils are inorganic trails, burrows or borings produced by animals (vertebrate and invertebrate) and plants that are now preserved in the rock record in response to their environmental settings. They were created by some aspect of the organism's behaviour or lifestyle. The underlying principle behind trace fossil diagnosis and classification is the activity or ethology preserved by the trace, and this is emphasized in most fundamental publications on these topics (e.g. Frey, 1975; Pemberton et al., 1992; Miller, 2007). It is understood that one organism may routinely create a wide variety of traces dependent on changes in ethology (eg. feeding, locomotion or resting) and conversely, the same trace can be created by a variety of organisms that exhibit similar behavioural traits. Traces are classified mainly on taxonomic and ethological basis (Figure 5.1) although these, and other criteria, have been applied inconsistently. Some of the inconsistencies stem from insufficient descriptions of type specimens (some of which are not trace fossils see Olivero, 2007), absence of a systematic naming convention and the varied emphasis on morphological characteristics (e.g. Pemberton and Frey, 1982; Pickerill, 1994). Efforts have been made to provide taxonomic and nomenclature guidelines to standardize the identification and classification of trace fossils (Pemberton and Frey, 1982; Pickerill, 1994; Bertling, 2007). It is telling that the trace fossil 230 taxonomy was relegated to a miscellaneous supplement in the Treatise of Invertebrate Paleontology (Hantzschel, 1975). The following discussion will review the application of ichnology and ichnofacies concepts towards deciphering paleoenvironments and by extension, paleobathymetry. Some of the advantages and disadvantages of the discipline will be highlighted and finally, past applications of the discipline to the Trinidad Stratigraphy will be reviewed. 5.1.1 EVOLUTION OF THE ICHNOFACIES CONCEPT The value of ichnology to sedimentology stems from the empirical recognition of recurring assembages of traces that reflect a dominant mode of behaviour of a benthic community. This mode of behaviour is a direct response to several paleoenvironmental conditions such as substrate stability and composition, oxygen levels, water salinity, turbidity and sedimentation rate; factors also of concern to sedimentologists. These recurring assemblages are formally termed "ichnofacies" and their presence (or absence) in the rock record is a direct reflection of paleoenvironmental conditions (Pemberton et al., 1992; Ekdale, 1988). Adolf Seilacher is credited as the pioneer for the "Modern Era" of ichnological research (Pemberton et al., 2007 p. 15; MacEachern et al, 2007, Ekdale, 1988). He introduced the ichnofacies concept with seven trace fossil communities within shallow marine and continental sediments that showed a systematic association with sedimentary environments (Figure 5.2) and implied a bathymetric control (Seilacher, 1967). This implication along with the lateral succession of ichnofacies were appealing notions to sedimentologists and aided in the popularity of the ichnofacies concept. It was subsequently shown that many ichnofacies did not conform to a simple bathymetric succession as implied in the original model (Frey et. al., 1990; Ekdale, 1988). For example, the Skolithos ichnofacies was proposed for high-energy shallow marine environments (Seilacher, 1967; Frey and Seilacher, 1980) but similar ichnofacies characteristics were recognized in deep sea fans (e.g. Crimes, 1977; Crimes et al., 1981; 231 NOMENCLATURE (ichnogenus, ichnospecies) FORM (size, orientation, configuration, preservation) TAXONOMIC BRANCHING (unbranched, branched, degree of branching) BURROW FILL (active, passive) BURROW BOUNDARIES (lined, unlined, ornamented) ETHOLOGICAL REPICHNIA (crawling) ASSEMBLAGE, DIVERSITY, ABUNDANCE, SUBSTRATE 1. COPRINISPHAERA(subaerial, continental) 2. MERMIA (freshwater, continental) 3. SCOYENIA (low energy, continental) 4. PSILONICHNUS (stressed nearshore) 5. TEREDOLITES (woody substrate, coastal) ICHNOFACIES 6. TRYPANITES (bioerosion, lithified substrate) 7. GLOSSIFUNGITES (firm substrate, marine) 8. SKOLITHOS (high energy, marine) 9. CRUZIANA (variable energy, outer shelf) 10. ZOOPHYCOS (anoxic, quiet water) 11. NEREITES (turbidites, bathyal) Figure 5.1 Contrasting scales of observation and classification employed by ichnologists (taxonomical classification) and sedimentologists (ichnofacies classification) linked by an ethological framework. Taxonomic classification compiled from Pickerill, 1994; ethological classification modified after Pemberton et al., 1992b; Ichnofacies classification compiled from MacEachern et al., 2007). 232 Figure 5.2 The initial sequence of marine ichnofacies proposed by Adolf Seilacher which were spatially arranged according to bathymetry. Modified after Seilacher, 1967, Figure 2. Buatois and Lopez Angriman, 1992; Poursoltani et al., 2007) and continental slope (e.g. Hayward, 1976; Shultz and Hubbard, 2005) environments. There, prevailing energy, turbidity, substrate stability and other environmental conditions mimicked the shallow marine realm and encouraged similar behavioural patterns among organisms. It is now accepted that these and other factors (e.g. salinity, oxygen and pH levels, food supply, depositional rate) also control ichnofacies distribution and evolution, and bathymetric controls can only be inferred once these factors are considered (Ekdale, 1988). Still, according to Frey et al. (1990, p. 155), the idealized succession of ichnofacies as proposed by Seilacher (1967) works well in "most normal situations" and this is demonstrated by ichnofacies models developed for wave/storm-dominated shelf successions (Pemberton and Frey, 1984; Pemberton et al., 1992c). Since the initial "Seilacherian" model, at least sixteen additional ichnofacies have been defined from both continental and marine environments (Figure 5.1; Mcllroy, 2004, Table 2) that have received varied acceptance and are not all included in fundamental publications (e.g. MacEachern et al., 2007). To account for variations within the Seilacherian ichnofacies groups, established ichnofacies were subsequently divided into ichnosubfacies (e.g. Seilacher, 1974; Uchman, 2001). In addition, environmental delimiters have since been used to differentiate assemblages from the archetypal 233 Seilacherian model. For instance, "proximal" and "distal" may refer to mixed ichnofacies associations (e.g. Pemberton et al., 1992c). The role of taphonomy has also been considered in the recognition of ichnofacies, as exemplified by Bromley and Asgaard (1991). Explicit in an ichnofacies definition is the diversity and abundance of trace forms and these may be modified solely by taphonomic controls. For example, taphonomic controls dictate that vertical trace forms and deeper tier structures stand a higher chance of preservation than horizontal grazers in the Skolithos ichnofacies, especially considering the typical "high-energy" and "abrupt erosion" typical of this facies (Frey and Seilacher, 1980, Table 4). Considering this bias, the true diversity of the Skolithos ichnofacies will vary depending on the amount of erosion, or conversely, the amount of preserved specimens. Similar preservational biases exist for 'flysch' sequences. If not eroded by turbidites, the Nereites ichnofacies may be disguised by post-turbidite fossil suites formed by opportunistic colonizers with a higher chance of preservation. Taphonomic controls are commonly considered in the recognition and utility of ichnofacies (Bromley and Asgaard, 1991). Ichnofacies are not the only end-product of ichnological studies. Trace fossil "assemblages" that form the basis for Sielacherian ichnofacies models, are distinct from "ichnocoenoses". An "ichnocoenose" is a trace fossil community (Bromley, 1996; Mcllroy, 2004) and reflects to a greater degree the response of individual (traces) organisms to specific (palaeo) environmental parameters, such as competition. Communities are reflected in bedding scale "ichnofabrics" and fossil tiering relationships (e.g. De Gibert and Goldring, 2007) and potentially provide a greater degree of resolution of palaeo-environmental processes. 5.1.2 APPLICATION OF ICHNOLOGY AND THE ICHNOFACIES CONCEPTS The utility of trace fossils and ichnofacies to sedimentology and stratigraphy is summarized as folllows: 234 1. As sedimentary structures, ichnofacies show recognizable and recurring vertical and lateral changes, conforming to Walther's Law. It is therefore an additional technique in the elucidation of the succession of paleoenvironments, especially when combined with physical sedimentary structures (Pemberton et al., 1992a). 2. Trace fossils provide a more sensitive indicator of ecological and environmental conditions than do physical sedimentary structures as changes in any one of these conditions are often reflected in changes in trace fossil diversity and abundance, even where depositional processes are constant. 3. Trace fossil are ubiquitous in both outcrops and cores. They are usually autochtonous or it can be readily determined if not. The long temporal duration of most traces allows for comparison among a wide geological time frame (Frey and Seilacher, 1980). 4. Ichnofacies can be a useful tool to indicate relative bathymetry when other environmental factors have been considered. Although the idea of bathymetry as proposed by Seilacher (1967) has proven to be simplistic, many environmental controls display gradients with water depth and hence conclusions can be indirectly drawn on bathymetry (Pemberton et al., 1992a, c). 5.1.3 SHORTCOMINGS OF THE ICHNOFACIES CONCEPT 1. Goldring (1993) argues that the existing ichnofacies groups were insufficient to reflect the number and complexity of sedimentary depositional environments and facies and as a result, the ichnofacies concept cannot (on its own) provide the resolution required by modern standards. He encouraged the use of ichnology in concert with sedimentology. A similar viewpoint was earlier alluded to by Ekdale (1988, p. 466). 2. Individual ichnofacies are named after a representative ichnogenus although the facies groups (in the field) are not defined by the presence of that ichnogenus or other specific forms (Ekdale, 1988). The allocation of strata to particular ichnofacies is not straight forward and involves an interpretation of the dominant ethological attributes of the facies assemblage (MacEachern et al., 2007). This is compounded by the fact 235 that boundaries are not distinct between ichnofacies successions and many traces, for example Zoophycos, are "facies-crossing" (Goldring, 1993, p. 404). 3. The observed trace fossil assemblage may not be a true reflection of the original bio diversity as taphonomic factors may modify the initial assemblage (Bromley and Asgaard, 1990). 4. The implied bathymetric control is often erroneously applied using individual trace fossils without regard to the wider assemblage, fair-weather versus extraordinary events and the evolutionary progression of traces. Mcllroy (2004) is of the opinion that the future utility of ichnoiogy to sedimentology is not in the creation of additional ichnofacies, partly because of inconsistent facies criterion (this was earlier alluded to by Bromley and Asgaard, (1991)), the inconsistent recognition of proposed ichnofacies and the absence of defined boundaries to ichnofacies groups (reflected in common terminology such as "distal" and "proximal"). He suggested instead that the future of ichnoiogy was in developing detailed, basin-scale ichnological models that incorporate both trace fossil assemblages and trace fossil communities (ichnocoenoses). 5.1.4 ICHNOFACIES AND DEEP WATER DEPOSITIONAL ENVIRONMENTS Ekdale (1988) was of the opinion that there were insufficient ichnofacies groups relative to the number of depositional environments and this assertion was repeated by Goldring (1993). Indeed, there has been variable conformance of trace fossil assemblages to established ichnofacies. Within marine environments, wave-dominated shoreface models best conform to the Seilacherian ichnofacies succession where transitions from nearshore Skolithos to outer shelf Cruziana have been demonstrated repeatedly (Howard and Frey, 1984; Pemberton and Frey, 1984; Pemberton et al., 1992c). Within deltaic successions however, the ichnofacies assemblage of wave-dominated strata may be indistinguishable from shoreface successions (MacEachern et al., 2005). Other parts of 236 deltas are less conformable to simple ichnofacies transitions and show wide variations according to relative stresses induced by river and tidal processes (MacEachern et al., 2005). Deep sea turbidite environments also display a range trace fossil assemblages that demonstrate the overriding influence of local environmental stresses (Table 5.1). For these environments, the "Seilacherian" ichnofacies model predicts a complex of grazing and feeding trails and graphoglyptid burrows of the Nereites ichnofacies. Several studies of turbidite deposits illustrate much variance from this simple model. Cruziana and Skolithos ichnofacies elements have long been recognized within deep sea fan environments. Eocene deep sea fans systems of northern Spain (Crimes, 1977; Heard and Pickering, 2007) showed lower diversity and abundance of trace forms in proximal and axial regions where "post-depositional" (Ksiazkiewicz, 1970; Seilacher, 2007) traces dominated. An increase in diversity, abundance and pre-depositional traces occur toward more distal environments and lateral to proximal flow axes. There is also an increase in the number of graphoglyptid trails toward distal fan and off-axis channel margins. In contrast to this trend, the highest diversity within the Gurnigel and Schlieren submarine fans of Switzerland occur along lobe channels where "shallow water" trace fossils were likely "introduced" into the deeper water (Crimes et al., 1981, p. 984). So-called "shallow-water" traces (e.g. Diplocraterion, Arenicolites, Ophiomorpha, Skolithos) are ubiquitous and commonly found in deeper water environments, though tend to be absent from distal regions (e.g. Crimes et al., 1981). The same is not true of "deep-water" traces (graphoglyptids) as typical fossils of the Nereites ichnofacies are rarely reported in more proximal (upper slope to marginal marine) environments (Crimes et al., 1981, Table 1). Very few studies have investigated the ichnocoenosis of the intermediate slope environment, and often only as an extension of deep marine fans (e.g. Heard and Pickering, 2007). One notable exception is the description of Miocene slope sediments (outer neritic to lower bathyal) in New Zealand dominated by dwelling traces of crustaceans and filter feeding organisms (Thalassinidoides, Rhizocorallium, Skolithos) and common deposit feeding traces (Planolites, Scalarituba) (Hayward, 1976). In modern sediments of the Hueneme Slope Caynon off the California continental shelf, Scott and Birdsall (1978) documented a 237 varied intensity and diversity of trace fossils in water depths ranging from 82-343 m. Skolithos occurred at all water depths while Scolicia and possible Asterosoma were noted down to 250 m. They also demonstrated varying intensity within the slope canyon from highly bioturbated canyon margins to low intensity along the canyon axis. Their observations demonstrate the dominance of Skolithos within settings not expected in conventional ichnofacies groupings. Instead of the high-energy environments expected of low-diversity Skolithos assemblages, the main depositional process involves fine grained, low-density turbidites with rippled beds less than 10 cm thick (Scott and Birdsall, 1978). Trace fossil distribution from the Polish Carpathians show a lower trace diversity among coarse, thick-bedded turbidites and intervals of thick shales (Ksiazkiewicz, 1970; Roniewicz and Pienkowski, 1977), while the highest diversity occurs in intervals of alternating fine-grained sandstone and shale. A similar observation was made within the Cretaceous deep-sea sediments of the Kodiak Formation, Alaska (McCann and Pickerill, 1988) where the highest diversity and abundance of trace fossils occurred within interchannel areas with heterolithic sand and shale deposits. McCann and Pickerill (1988) suggested that taphonomic influences may be most favourable for preservation in these areas, as opposed to environments with more homogenous lithologies. Despite the differences in the spatial distribution of trace fossil assemblages from the idealized "Seilacherian" model, the assemblages have shown a remarkable correlation with local environmental variables and physical sedimentary processes (MacEachern et al.,2005; Heard and Pickering, 2007). Local proximality trends have been demonstrated in wave-dominated shoreface and deep-sea environments that correlate well with sedimentological data and these have prompted the further subdivision of established ichnofacies (e.g. Heard and Pickering, 2007). The underlying value in the ichnofacies concept stems from this information as it allows inferences to be made about processes and paleo-ecological conditions not constrained by water depth. Information on specific environments can be deduced when this information is integrated with sedimentological, biostratigraphic and other data. . This chapter is based on the premise that trace fossil assemblages in Cenozoic sandstones can provide insights into changes in basin settings 238 Table 5.1 Characteristic diversity, intensity and interpreted ethology of trace fossils in popular marine ichnofacies. Duration of Ichnofacies Subichnofacies Characteristic trace fossils Note Diversity and intensity trace Reference community Psilonichnus Psilonichnus, Aulichnites, Lockeia, Macanopsis, "J", "Y", or "U"-shaped dwelling burrows Locally high long-term MacEachern et al., Planolites, rhizoliths (2007), Frey et al., (1984) Skolithos Skolithos, Diplocraterion, Ophiomorpha, Conichnus, Predominantly vertical, cylindrical or "U"- General low diversity, long-term MacEachern et al., Schaubcylindrichnus, Palaeophycus, Arenicolites, shaped dwelling burrows; local sediment but locally abundant 2007 Gyrolithes saxonicus, Taenidium, Siphonichnus, instability; suspension feeders and burrows Macaronlchnus, Cylindrichnus, Rosselia passive carnivores, few deposit feeders Cruziana Taenidium, Siphonichnus, CyBndrichnus, Rosselia, Abundant crawling traces, mostly deposit High diversity, high long-term MacEachern et al., Teichichnus, Planolites, Rhizocorallium, Thalassinoides, feeders mixed with dwelling structures abundance 2007 Phoebichnus, Phycodes, Asterosoma, Chondrites, of suspension feeders and passive Zoophycos, Rusophycus, Cruziana, Lockeia, Gyrochorte, carnivores; mixed horizontal, inclined and Helminthopsis, Phycosiphon, Cosmorhaphe, vertical and other complex structures. Palaeophycus, Ophiomorpha, Diplocraterion, Arenicolites, Skolithos Zoophycos Zoophycos, Helminthopsis, Phycosiphion, Cosmorhaphe, Predominance of deposit feeding; Low diversity, individual long-term MacEachern et al., Planolites, Chondrites, Thalassinoides, Scolicia, abundant grazing structures; horizontal to traces may be 2007 Spirophyton gently inclined. Some complex structures, abundant; generally impoverished relative to Cruziana ichnofacies "Proximal" Nereites Ophiomorpha, Diplocraterion, Lorenzinia, Spiromaphe, Complex grazing traces and feeding/ long-term MacEachern et al., Spirophycus, Zoophycos, Scolicia dwelling structures; organized 2007 behaviour. Mainly deposit feeders, scavengers or microbe farmers. Nereites "Medial" Nereites Helminthorhaphe, Urohelminthoida, Cosmorhaphe High diversity, low long-term MacEachern etal., abundance 2007 "Distal" Nereites Nereites, Paleodictyon, Paleomeandron, Fustlglypus, long-term MacEachern etal., Zoophcos 2007 Ophiomorpha rudis Ophiomorpha Rudis Thick- and medium-bedded turbidites in short-term; Uchman 2001; 2007 channels and proximal lobes; occurs opportunist along with horizontal traces of other colonizers ichnofacies. Nereites Paleodictyon Casts of Paleodictyon and other graphoglyptid burrows Turbidites 10s of cm with erosive bases; ? Long term Seilacher, 1974 sandy environnent; proximal Nereites Nereites Infill of original burrow; Oldhamia, Chondrites, Nereites, Distal fan environments; mud prone; thin long-term Seilacher, 1974 Dictyodora, Phycosiphon, Zoophycos turbities Arenicolites Skolithos, Arenicolites, Polykladichnus Episodic deposition such as storm beds Low diversity short-term; Bromley and Asgaard, or turbidites; recurrring assemblages of opportunist (1991) vertical traces in relatively quiet colonizers environments; opportunistic suspension feeders. directly through an assessment of their relative diversity and indirectly by assessing the controls responsible for these changes. The chapter will attempt a resolve of the first order differences (or similarities) in diversity, intensity and ethology between selected sandstone intervals. It is assumed based on the previous discussions that controls are linked to changing paleo-ecology, sedimentary processes and paleo-environments. The trace fossil assemblages will be integrated with known lithofacies and physical sedimentary structures (Chapter 7) in order to recognize these first order changes in basin settings, directly reflected in changing depositional environments. After a brief review of the role played by trace fossils in the Trinidad stratigraphy, selected Cenozoic intervals will be examined in detail from the Eocene Pointe-a-Pierre Formation to the Pliocene Morne L'Enfer Formation. These were examined to different levels of details and this will be highlighted in the relevant sections that follow. A synopsis of trace fossil assemblages and ichnofacies relationships will follow where significant differences throughout the stratigraphy will be highlighted. 5.2 ICHNOFACIES APPLIED TO THE TRINIDAD STRATIGRAPHY This chapter will outline the trace fossil assemblages characteristic of individual members of Cenozoic formations, and provide interpretations to account for their relative differences. Emphasis was placed on trace fossil assemblages, and although individual traces are described, interpretations are based on the diversity and intensity of entire populations. The environmental significance of individual traces will be highlighted where appropriate. As much as possible, the descriptions will relate to the lithofacies groups described in Chapters 2-4, as these two approaches (physical and biogenic sedimentary structures) will eventually be integrated to discern changes in depositional settings. The results that follow provide a basis to assess the utility of established ichnofacies schemes to the Trinidadian stratigraphy, both as a stand-alone analysis and when integrated with sedimentology. This effort is the first such compilation known that details the trace fossils within such a wide time interval of the Trinidadian stratigraphy. 240 The integration and analysis of physical and biogenic sedimentary structures has played a minor role in the elucidation of palaeoenvironments within the Trinidadian stratigraphy. The first published record of trace fossils came from the Pointe-a-Pierre Formation (Bayer, 1955; Kugler and Saunders, 1967), although the specimens were described erroneously as body-fossil casts of a new pennatulid species (Anderson, 1979). These were later recognized as trace fossils {Pennatulites) that occurred with other fossils such as Helminthoidea and Paleodictyon (Kugler, 2001, p. 190). In addition, Zoophycos was recognized in the Cretaceous Naparima Hill Formation and Thalassinoides in the Pointe-a-Pierre Formation (Algar, 1993), while Punch (2004) assigned the latter to the "Cruziana facies". Kugler (2001, p. 190) compared trace fossils of the Pointe-a-Pierre and Scotland (Barbados) formations to 'flysch' facies in Venezuela and Europe. These references placed very little emphasis on trace fossil assemblages, which are better suited for palaeoenvironmental interpretations. For this study, trace fossils were documented from both outcrop and subsurface well cores (Table 5.2). Trace fossils were described from individual beds from cores or grouped into bedset assemblages (metres to tens of metres) at some outcrops. The relative diversity of species was recorded as high, moderate or low, with a 'high' diversity corresponding to a typical Cruziana ichnofacies (MacEachern et al., 2007). The intensity of bioturbation was noted as rare, common, abundant or churned and an approximation to bioturbation indices is shown in Figure 5.3; the relative abundance of individual ichnogenera was also noted. Identification was not always possible at the species level due to either poor preservation or insufficient numbers of individuals to facilitate identification. The assemblage, intensity, diversity and relative abundance of traces formed the basis for paleo-ecological interpretations. Ichnofacies were assigned guided by the assemblages of Pemberton et al. (1992a), Mcllroy (2004) and MacEachern et al. (2007), but mindful that not all assemblages and sedimentary depositional environments will be represented in current ichnofacies schemes (Ekdale, 1988; Goldring, 1993). When comparing trace fossil assemblages from core and outcrop, one must consider that the types of traces observed will depend on the degree of exposure (Pemberton et al., 1992c; Bromley, 1996). Outcrops afford good three-dimensional 241 exposures but are limited by bed weathering, which can obscure subtle features. Subsurface cores provide good vertical continuity on usually fresh exposures, but traces that depend on planar geometries for identification (e.g. graphoglyptids) will not be easily recognized. The sampling constraints inherent in cores must also be considered, (e.g. the likelihood of intersecting a vertical trace relative to a horizontal trace from a vertical core barrel). Furthermore, a three-dimensional extrapolation of trace geometries may be required in core (Pemberton et al., 1992c; Bromley, 1996). 5.3 TRACE FOSSILS OF THE PIERRE POINT SANDSTONE MEMBER (POINTE-A-PIERRE FORMATION) Trace fossils from the Pierre Point Sandstone Member of the Pointe-a-Pierre Formation were studied from the San Fabien Road locality in Gasparillo, and along the rocky banks and bed of the Chaudiere River in the eastern Central Range (see Figure 2.1 for location). These were the only two outcrop localities where trace fossils were seen. Table 5.2 Stratigraphic sections studied for biogenic sedimentary structures and discussed in this chapter. See Table 2.1 for relative length of sections for each unit. LOCATION LEVEL OF DETAIL AGE MEMBER/ FM OUTCROP CORE PRELIMINARY DETAILED Upper Morne L'Enfer Esperanza, Sandstone Member Puerto Grande */ bays and others Late Pliocene (Morne L'Enfer Fm.) Lower Morne L'Enfer Cedros Bay Sandstone and Silt and others A/ members (MLE Fm.) Late Miocene/Early Cruse and Manzanilla Point Radix, Pliocene formations Morne Diablo, v' Pt Paloma Herrera Sandstone Well BP-347 Late Middle Miocene Member, v' Cioero Formation Corbeaux Hill, ABM-44& Late Oligocene/Early Nariva Formation Miocene Kelly Hill, ABM-54 +/ Esmeralda Angostura Sandstone Wells Kairi-1 & Late Oligocene Canteen-2 +/ Member (Cipero Fm) Pierre Pointe San Fabien Late Eocene Sandstone Member, Road, s/ Pointe-a-Pierre Fm. Chaudiere River Cunapo Late Paleocene Chaudiere Formation Southern Road */ 242 Most of the specimens from the Chaudiere River were observed from displaced cobbles and boulders but the drainage along the traverse investigated is solely within sediments of the Pointe-a-Pierre Formation (Kugler, 1959; Saunders et al., 1998). The sandstones of the Pierre Point Sandstone Member are characterized by a moderate diversity of trace fossils of generally low intensity. Trace intensity increases within thin-bedded, fine-grained intervals and tends to be restricted in thicker, amalgamated bedsets. Horizontal grazing and feeding traces dominate, although dwelling structures are common. Specific details of these will now be given. Figure 5.3 Schematic diagram illustrating bioturbation intensity for different substrates; the numbers correspond to ichnofabric indices. The descriptions used for this study corresponded to "rare" ~ 2, "common ~ 3, abundant ~ 4 and churned ~ 5/6. (A) for thin bedded strata and (B) for fine-grained deep water sediments. Modified after Pemberton et al. (1992b). 243 5.3.1 DESCRIPTION OF TRACE FOSSILS Chondrites Chondrites is the most common trace fossil among the Pierre Point Member sediments. It is common among fine-grained turbidites and shale beds but not observed among the thick-bedded, coarse-grained turbidites. The tubes are recognized by conspicuous branching, small size (commonly less than 5 mm), and in shale beds, by differences in sediment colour (Figure 5.4 A-D). Some specimens were recognized by a similar orientation of tube segments that do not intersect (Figure 5.4 B). Chondrites is one of the few trace fossils found both in epi- and hypichnial preservation in these sediments. Chondrites is interpreted primarily as a deposit-feeding trace (Hantzschel, 1975; Seilacher 2007). Although the trace maker is unknown, it fed by probing through the substrate creating successive branching elements that do not intersect (Scott, 1957; Hantzschel, 1975; Seilacher, 2007). The main palaeoenvironmental significance of Chondrites lies in its association with black, carbonaceous sediments deposited in low- oxygenated waters, suggesting that the trace-maker has a relatively high tolerance for anoxic environments (Bromley and Ekdale, 1984). Paleodictyon At San Fabien Road, the base of a sandstone boulder, not far removed from its original depositional site (discerned by bed thickness, sedimentary structures and grain size), contained sets of regular perforations displaying an overall 'honeycomb' texture (Figure 5.4 E, F). The hypichnial preservation mode and honeycomb appearance are typical of the ichnogenus Paleodictyon (Seilacher, 1977; 2007). The traces are analogous to the systematic 'search-nets' of Paleodictyon nodosum although a definitive species diagnosis is hampered by the poor preservation. Paleodictyon traces are grouped with other graphoglyptid burrows, known for their systematic and complex morphology (Seilacher, 2007). Although the trace-makers are unknown, they are attributed to a specific style of feeding in which the organism trapped nutrients (bacteria, algae and other benthic organisms) via a network of open pits 244 on the sediment surface (Seilacher, 1977; 2007). Paleodictyon has long been considered a characteristic fossil of deep-sea environments and diagnostic of the Nereites ichnofacies (Frey and Seilacher, 1980). Fursich et al. (2007) extended the known range of the ichnogenus to prodelta-upper slope environments from Mesozoic sediments in Iran. There, they were associated with traces characteristic of the Cruziana ichnofacies {Rhizocorallium, Thalassinoides, Diplocraterion and Teichichnus). When associated with turbidites, they occur exclusively with "pre-turbidite" trace assemblages, attributed to extended periods of relative quiescence on the deep-sea floor (Seilacher, 2007). This agrees with observations from the Ainsa Basin of northern Spain where they increase in relative abundance in "proximal off-axis" and "distal fan regions" (Heard and Pickering, 2007). They are increasingly associated with Ophiomorpha in more proximal deep-sea fan environments. Ophiomorpha Two specimens of the ichnospecies Ophiomorpha nodosa are described from the San Fabien Road and the Chaudiere River locations. At the former, a miniature (1 cm diameter) cylindrical, tube with a knobby exterior is partially preserved in positive relief within a silty Tc-Td turbidite interval (Figure 5.5 C). This miniature size and knobby exterior also fits the description of Granularia Pomel, 1849 (Seilacher, 1967; 2007; Bromley, 1996). At Chaudiere River, an Ophiomorpha specimen was found in a cobble along the riverbed displaying the characteristic rugose external lining with an internal meniscate fill (Figure 5.6 C, D). The 3 cm diameter specimen is preserved within a 5 cm- thick, fine-grained sandstone. Other specimens of Ophiomorpha without the rugose exterior were recognized at both localities. At San Fabien Road, a few specimens of horizontal branching tubes up to 3 cm diameter are preserved in sandstone beds (Figures 5.5 D-F and 5.6 A). The branching habit showed inconsistent orientation and angle or comprised an irregular set of polygons (Figure 5.5 E). Expanded intersections are occasionally preserved (Figure 5.5 F). Specimens are preserved as both hypichnia and epichnia in beds up to 40 cm thick though commonly less than 5 cm. 245 The various ichnospecies of Ophiomorpha have been described in detail from nearshore depositional environments (e.g. Frey et al, 1978; Miller and Curran, 2001; Curran and Martin, 2003) and this may have fuelled its perception as a "shallow-water form" (Crimes et al., 1981). The ichnogenus commonly occurs among deep-sea turbidite sequences where they are often associated with relatively proximal deep-sea environments (Seilacher 1962; Crimes, 1977; Armentrout, 1980; Crimes et al., 1981; Bottjer et al., 1988; Buatois and Lopez Angriman, 1992; Bruhn and Walker, 1997; Tchoumatchenco and Uchman, 2001; Uchman, 2001; Heard and Pickering, 2007). Uchman (2001) proposed the Ophiomorpha rudis ichnosubfacies to represent the most proximal part of the Nereites ichnofacies, characterized by the occurrence of Ophiomorpha rudis. Granularia is considered the 'flysch' counterpart of the larger Ophimorpha nodosa (Bromley, 1996, p. 180) and the smaller size may be a necessary adaptation for the "deep-sea" environment (Seilacher, 2007). Despite this differentiation, the functional morphology of the two ichnogenera is the same and they are considered synonymous by some (Pemberton and Frey, 1982). Collectively, they form a class of dwelling structures comprising a network of tunnels and shafts. Ichnospecies all occur within sandy substrates and may occur exclusively among thick sandstone beds (e.g. Seilacher, 1967), suggesting an adaptation to extreme environmental conditions by opportunist trace-makers (Seilacher, 1962; Bromley, 1996; Uchman, 2001). cf Cylindrichnus Two specimens of cf. Cylindrichnus were found at San Fabien Road; one preserved within thin silt (Bouma Tc-Td) overlying a fine-grained turbidite (Ta) bed (Figure 5.5 C) and a second on the sole of a fine-grained turbidite bed (Figure 5.5 B). Both specimens display a curved, cylindrical geometry with funnel-shaped ends. The larger specimen (Figure 5.5 C) also displays a thick inner lining, although the distinctive laminae that define the ichnogenus (Howard and Frey, 1984) could not be discerned. As a result of the other morphological aspects defined above, the trace is tentatively identified as 'Cylindrichnus'. 246 Figure 5.4 Deposit-feeding and farming traces within the Pierre Point Sandstone Member. Chondrites (Ch) occur as branching (A and C) or sub-parallel (B) burrow casts on turbidite soles or preserved within shale (D). The linear trace in (A) may be Planolites (PI) or an unbranched section of Chondrites. (E) Several 'nets' of Paleodictyon (Pal) preserved in negative relief at the base of a fine-grained turbidite. Only one is highlighted for reference. The specimen to the farthest right is magnified in (F). Another unidentified trace (Un) is at the base of the photo, see also figure 4.5F). All traces from San Fabien Road except (D), fromChaudier e River. 247 Figure 5.5 Feeding and dwelling trace fossils of the Pierre Point Sandstone Member, San Fabien Road locality. A) Horizontal grazing trace of Planolites beverleyensis. B) Cylindrichnus (Cyl) at turbidite sole embedded among flute casts. C) Cylindrichnus, Ophiomorpha nodosa (Op) and Chondrites traces. D) Branching Ophiomorpha within thin, coarse-grained bed. The bed thickness can be seen just below the scale bar. E and F) Irregular branching tunnels of Ophiomorpha within coarse-grained sandstone. The traces are highlighted in the insets. Junctures are occasionally swollen (F) providing evidence for a dwelling function to the trace. All traces preserved as positive epichnia except B, which is positive hypichnia. 248 Figure 5.6 Dwelling and deposit-feeding trace fossils within the Pierre Point Sandstone Member. A) Hypichnial, positive relief, branching Ophiomorpha burrow. B) Sub vertical, unlined Psilonichnus dwelling burrow. C) Section of Ophiomorpha nodosa burrow showing rugose lining and meniscate fill. A section of the burrow is magnified in (D). E) Gyrochorte, found on cobble on river bed; positive relief, ?epichnial. F) Unidentified fossil found in positive, hypichnial preservation adjacent to Paleodictyon (see Figure 4.4 E); both association and form of preservation suggest an agrichnia function. A, B, F from San Fabien Road, all others fromChaudier e River. 249 The functional significance of the fossil is still uncertain (Goldring et al., 2002; Gibert et al, 2006) though MacEachern et al., (2007) list Cylindrichnus as a deposit- feeding structure typical of the Skolithos and Cruziana ichnofacies. The trace was likely created by an opportunist organism as it occurs in association with Ophiomorpha nodosa at the San Fabien Road locatioa Planolites At the San Fabien Road exposure, specimens of P. beverleyensis are simple, horizontal traces most frequently observed within silty bed tops (Figure 5.5 A). One specimen of P. annularis with characteristic transverse annulations (Pemberton and Frey, 1982) was also observed (Figure 5.7 C). Planolites burrows are interpreted as deposit-feeding structures created by vagile organisms that ingested and actively backfilled the burrow. They have been found in virtually all environments (Pemberton and Frey, 1982). Psilonichnus One specimen was found preserved in full relief within a fine-grained turbidite bed (Ta) at San Fabien Road (Figure 5.6 B). It is a large, sub-vertical and unlined burrow, enhanced at its margins by bed weathering. It is up to 4 cm diameter and the burrow tapers downwards before thickening again at a bulbous termination. The size and form of the burrow is similar to Psilonichnus upsilon, a crustacean dwelling burrow known in nearshore-tidal and shallow marine environments (Frey et al., 1984; Gingras, 1999). The size and morphology of the specimen illustrated here is similar to fiddler crab burrows within Pleistocene sediments in the Bahamas (Curran and Martin, 2003, Figure 8). Poursoltani et al. (2007) reported occurrences of the trace fossil in "thick-bedded" "high-density" turbidites deposited within a slope to basin floor environment of the Kashafrud Formation in Iran. 250 Gyrochorte comosa One specimen was found in positive relief on a rock fragment along the Chaudiere River; the original orientation of the bed is unknown (Figure 5.6 E). The trace shows remarkable preservation of detail and the species is tentatively assigned on account of the descriptions given by Ksiazkiewicz (1970), Hallam (1970) and Hantzschel (1975). The 1.5 cm wide ridge contains a medial furrow symmetrically flanked by chevron- patterned 'plaits'. The description of Hallam (1970) suggests that the 'plaits' occur only in epirelief preservation although Bromley (1996) notes that they also occur rarely in hyporelief. Hallam discounted Gyrochorte as the trace of a grazing organism, and instead favoured an organism burrowing through the sediment. He identified the fossil within shallow marine sediments while Crimes et al. (1981) recorded its occurrence within deep-sea fan sediments. Arenituba verso Chamberlain ("Micatuba") Specimens occur as a radial set of burrows extending from a central lobe (Figure 5.7 E-H). Individual burrows are up to 2 cm diameter, straight or meandering, occasionally branched and collectively, may be asymmetrically arranged around the lobe. They occur in positive relief, oriented horizontally along the top-bedding plane within a thin silt bed (Tc-d) overlying coarse sandstones (Ta). Individual lobes may be joined by one common 'arm'. These characteristics are similar to Arenituba verso (formerly Micatuba verso Chamberlain, see Stanley and Pickerill, 1995). Chamberlain (1971) interpreted the structure as the permanent dwelling trace of a deposit feeder, accessing nutrients in the sediment by an extended probe in a chondritid-like fashion; the search radius was limited to the bedding plane. The trace was initially described from shallow marine sandstones of the upper Atoka Formation (Oklahoma), with common "broad" cross-stratification, oscillatory and current ripples, where it was allocated to the Cruziana ichnofacies (Chamberlain 1971b, Table 1, Figure 6). Lockley et al. (1987) found rare specimens of the trace within marginal-marine sediments of the Carboniferous Minturn Formation of Colorado and allocated it to their "Curvolithus" ichnofacies, which was characterized by relatively high sedimentation rates. Heard and Pickering (2007) found the specimen within the Guaso fan, the shallowest of a series of deep marine fans in the 251 Ainsa Basin of Spain. The fan was deposited in approximately 500 m water depths (upper bathyal) and is overlain by a prodeltaic clastic shelf (Pickering and Corregidor, 2005). Saportia Linear, branching traces preserved in positive relief (Figure 5.7 B, D-F) are found in the same bedding plane with specimens ofArenituba verso at San Fabien Road. The branching appears random over much of the bed, though one particular trace displays unidirectional set of branches extending from a central, linear axis (Figure 5.7 D, E). All the branches extend from the central axis at a similar (acute) angle, suggesting a more systematic arrangement than immediately apparent. This dendritic form is similar to the trace fossil Saportia, interpreted as a vagile deposit-feeding trace (Hantzschel, 1975). The dendritic arrangement of branches and preservation style support deposit-feeding activity similar to Arenituba verso. Instead of a radial foraging pattern, the organism probed laterally from the central axis, maintaining a horizontal orientation along the bedding plane. Scalarituba missouriensis These traces are preserved in positive relief within the thin silt beds overlying thicker, coarse-grained turbidites (Figure 5.7 B). They occur as horizontally oriented linear ridges with a distinct meniscate fill forming transverse ridges along the trace length, typical of this ichnospecies (Conkin and Conkin, 1968). Scalarituba missouriensis was interpreted as a deposit-feeding trace, (Conkin and Conkin, 1968; Hay ward, 1976) in which the organism ingested the sediment during grazing and actively back-filled the burrow behind it. It is found in a range of depositional environments ranging from tidal-flats (Conkin and Conkin, 1968), submarine canyons (Hayward, 1976) and outer submarine fans (Crimes, 1977). Unidentified trace fossil This trace fossil cannot be identified because of incomplete preservation. An ethological interpretation can be attempted based on its association with Chondrites and Paleodictyon specimens, its orientation and morphological character. It consists of a 252 Figure 5.7 Deposit-feeding trace fossils of the Pierre Point Sandstone Member, San Fabien Road locality. A) Bioturbation is often limited to a thin, silty drape (Tc-Td) along the tops of turbidites as shown here. B) Scalarituba missouriensis (Sc) and Saportia (Sap). C) Planolites annularis. D) Dendritic, horizontal probing trace of a deposit feeder, assigned to Saportia. See top right of (E). E) Common systematic feeding traces along the top of a turbidite bed. The traces are highlighted in (F) and consist of radial, linear and dendritic forms including Arenituba and Saportia (see D and G). G) Radial feeding trace of Arenituba verso. Trace highlighted in (H) where 'A' marks central lobe. Same trace is shown at lower right of (E). All traces preserved in epichnia as positive relief. 253 branching, hypichnial ridge in a fine-grained turbidite at San Fabien Road (Figures 5.4 E and 5.6 F). The preservation suggests that the original burrow consisted of a branching network of open tunnels along a muddy substrate, typical of graphoglyptids C?Dendrotichnium). Like Paleodictyon, the burrow may represent feeding traces (agrichnia) within relatively quiet water conditions. 5.3.2 SUMMARY OF TRACE FOSSIL ASSEMBLAGES FOR THE PIERRE POINT SANDSTONE MEMBER Ethology The assemblage of trace fossils described from San Fabien Road and along the Chaudiere River can be summarized in order of relative abundance: -•* 1. Common vertical to oblique deposit-feeding traces typified by Chondrites. This trace occurs at both localities along the tops and bases of turbidite beds and within sand and shale substrates. Cylindrichnus is also included here. 2. Common horizontal traces made by either sedentary (e.g. Arenituba) or vagile (e.g. Planolites, Scalarituba, Saportia, Gyrochorte) deposit feeders. These are preserved within thin silt beds (Bouma Tc-d) overlying coarse-grained turbidites (Ta). 3. Common dwelling structures typically associated with crustaceans. These are represented by Ophiomorpha (including Granularia) and Psilonichnus. 4. Rare agrichnia traces characterized by Paleodictyon and possibly IDendrotichnium. Note that the preservation style of these traces may have inhibited their recognition as lower bedding planes were rarely exposed. The ethological classification of trace fossils, in order of abundance (1= highest abundance) is: 1. Pascichnia {Scalarituba, Saportia, Planolites, Gyrochorte) 2. Fodinichnia (Chondrites, Arenituba, Cylindrichnus) 3. Domichnia (Ophiomorpha, Psilonichnus, Cylindrichnus) 254 4. Agrichnia (Paleodictyori) Overall, the diversity of trace fossils is relatively low with deposit feeders being most common. The most abundant form is horizontal Pascichnia and Fodinichnia deposit-feeding traces. Most of the dwelling structures are also horizontal and limited to individual turbidite beds. With the exception of Chondrites and Paleodicyton, these traces are interpreted to represent a post-depositional assemblage comprised of opportunistic colonizers. This is based on (1) the confinement of traces to either individual beds or silty laminae along the tops of turbidites; (2) emphasis on deposit- feeding, with dwelling being a secondary function; and (3) lower diversity of trace fossils often reflecting a smaller "colonization window" and environmental conditions that favour pioneers and opportunists (Bromley, 1996). These are often associated with event beds such as tempestites or turbidites with the latter being preferred based on the associated lithofacies. Distribution of individual traces The significance of individual trace forms is now considered. Although several trace fossils that are commonly found in high-energy, shallow-water environments are also common to deep-water environments, the reverse is not true for specimens associated with quiet deep-water environments. For example, agrichnia traces are still largely restricted to undisturbed bathyal environments (Crimes, 1977, Table 1). Paleodictyori and Chondrites are interpreted to represent the "pre-turbidite' assemblage. The feeding patterns of Paleodictyon suggest relatively quiescent, undisturbed distal delta front to bathyal environments (Crimes, 1977; Seilacher, 1977; Fursich et al., 2007). Hence, despite their apparent rarity, the agrichnia traces limit the Pierre Point Sandstone Member to at least distal offshore regions. A deeper-marine bathyal environment of deposition is preferred over a distal delta front when the associated benthic fauna and lithofacies are considered (Sections 2.2.4 and 3.1). The domichnia traces identified are typical of high energy environments with shifting substrates in shallow water regimes, though vertical burrow components are overall, relatively rare. Ophiomorpha has a widespread occurrence, though as stated 255 above, is common within more proximal sediments of deep marine depositional environments. It is interpreted as an opportunistic trace associated with the episodic deposition of turbidites into quiet waters inhabited by the Paleodictyon-Chondrites trace assemblage. Integration with lithofacies The greatest diversity of traces is found within the "distal" or "off-axis" tabular sandstone (TS) facies, while only grazers (pascichnia) were found at the margins and tops of the massive thick-bedded sandstone (MTBS) (Figure 5.8). Similar lithofacies-trace fossil trends have been observed in other deep-water sediments where the diversity tends to increase towards channel margins (e.g. Crimes, 1977; Heard and Pickering, 2007); this is likely related to taphonomic factors (Bromley and Asgaard, 1991). 5.3.3 ICHNOFACIES OF THE PIERRE POINT SANDSTONE MEMBER Collectively the trace assemblage and diversity is not typical of the established ichnofacies groups (Pemberton et al., 1992c; Pemberton et al., 1992a; Mcllroy, 2004; MacEachern et al., 2007). The diversity of traces is much less than the archetypal Cruziana ichnofacies while traces that characterize the Skolithos ichnofacies (Table 5.1) are rare. The complex feeding traces of the Nereites ichnofacies are similarly rare. The assemblage finds the greatest similarity to the Ophiomorpha rudis subichnofacies of the Nereites ichnofacies, characterized by common Ophiomorpha burrows found in "proximal, off-axis" channels and lobes in the Ainsa Basin of northern Spain (Uchman, 2001; Heard and Pickering, 2007). It is also tentatively compared to the Paleodictyon subichnofacies (Seilacher, 1974) of the Nereites ichnofacies based on the occurrence of Paleodictyon within a sandy turbidite succession. Seilacher (1974) suggested that this occurs as a proximal turbidite ichnofacies relative to the Nereites subichnofacies. 256 Figure 5.8 Stratigraphic log from a section of the Pierre Point Sandstone Member at San Fabien Road showing the location of trace fossils. The highest diversity occurs in the tabular sandstone facies while bioturbation is restricted to the silty top of sandstone beds in the massive thick-bedded sandstone facies. Inset sketch illustrates the mode of preservation relative to bedding, for the different traces. Pl- Planolites; Pa- Paleophycus; Ps- Psilonichnus; Cy- Cylindrichnus; Sap-Saportia. 257 5.4 TRACE FOSSILS OF THE ANGOSTURA SANDSTONE The following ichnofacies description was derived from a review of 131 m (393 ft) of full-hole core within well Kairi-1 and Canteen-1 in the Angostura oilfield. The analysis must be considered preliminary due to the time constraints when examining the core. When comparing trace fossil assemblages with outcrop exposures, the preservation bias discussed earlier must be considered (types of traces observed are dependent on exposure). In general, the Angostura Sandstone has a relatively low diversity and abundance of trace forms, although individual beds may be commonly bioturbated. In the discussion of the traces that follows, reference can be made to descriptions in earlier sections for specific details; these are provided for newly, described forms. 5.4.1 DESCRIPTION OF TRACE FOSSILS Planolites Commonly occurs in shaly beds as endichnial, circular burrows with sand and silt fills (Figure 5.9). The burrows are often associated with Paleophycus, cf. Teichichnus and cryptobioturbated horizons. Planolites is interpreted as the trace of deposit-feeding organism(s). Palaeophycus Differentiated from Planolites by the presence of a wall lining and passive fill (Figure 5.9 C) (Pemberton and Frey, 1982; Keighley and Pickerill, 1995). It commonly occurs in finer-grained intervals where it is associated with Planolites and cf. Teichichnus. Palaeophycus is interpreted as domichnia, possibly of a predaceous vermiform organism, and is recognized from a wide variety of environments including deep-sea turbidites (e.g. Buatois and Lopez Angriman, 1992; Poursoltani et al., 2007). 258 Figure 5.9 Trace fossils of the Angostura Sandstone from well Kairi-1. A) Endichnial Planolites (PI) and Thalassinoides (Th). B) Vertical Ophiomorpha within coarse-grained sandstone. C) Various fodinichnia and domichnia traces: Paleophycus (Pa), Planolites and Ophiomorpha (Op) and several unidentified traces (Un) parallel to bedding. D) Local, commonly bioturbated sediment where sand beds are almost completely deformed by deposit-feeders, Planolites and cf. Teichichnus. E) Horizontal grazing and deposit-feeding traces, Planolites and Scolicia. F) Vague outline of vertical trace with bulbous form, highlighted in (G). The form of the trace is typical of the domichnia, cf. Rosselia. Scale at lower right = 1cm. 259 cf. Teichichnus rectus This trace fossil occurs within interbedded sand and shale intervals where sand beds are almost entirely bioturbated. The uncertainty of classification arises from the rare occurrence of the spreiten that characterizes this ichnogenus, although the curvilinear geometry of deformed sand lens may be transverse sections of the fossil (Figure 5.9 D). Teichichnus is interpreted as the dwelling burrow of a deposit-feeding organism (Pemberton et al., 1992c) although the trace fossil may be transitional to Thalassinoides, in which case the dwelling function will take priority. It is absent (Ksiazkiewicz, 1970; Crimes, 1977; Kern, 1980; Crimes et al., 1981; McCann and Pickerill, 1988) or uncommon (Heard and Pickering, 2007) in deep-sea turbidite deposits. cf. Rosselia One specimen is tentatively assigned to this ichnogenus (Figure 5.9 F, G). Only the outer shape of the specimen is discernible, and the absence of the inner linings that characterize this ichnogenera precludes a confident diagnosis, which was made on the basis of the bulbous opening that tapered downward into a narrow tube. Cylindrichnus is another possibility. The trace is preserved as endichnia in silty sediments. Rosselia is a vertically preserved form within a group of dwelling burrows characterized by radial backfills that also includes Asterosoma (Seilacher, 2007). The structure was inhabited by a deposit-feeding organism (Pemberton et al., 1992c; Nara, 1997; Seilacher, 2007). Rosselia is normally associated with shoreface sediments (Chamberlain, 1971; Howard and Frey, 1984) and is a common fossil within the Cruziana ichnofacies (MacEachern et al., 2007). It is notably absent in descriptions of deep-sea turbidite sediments (Ksiazkiewicz, 1970; Chamberlain, 1971; Crimes, 1977; Kern, 1980; Crimes et al., 1981; McCann and Pickerill, 1988; Heard and Pickering, 2007), although the related fossil Asterosoma occurs within upper bathyal sediments of Ainsa-Jaca basin of northern Spain (Heard and Pickering, 2007). Scolicia Scolicia occurs as a sub-circular trace up to 3 cm diameter preserved along the upper bedding plane of a sandstone bed (Figure 5.9 E). It is apparent that the organism 260 was foraging at the sandstone-shale interface as the latter was displaced upward. Scolicia is interpreted as a feeding trace of a deposit-feeding organism. It is discussed in more detail with the Herrera Sandstone Member (Section 5.5.1) where it occurs in greater abundance. Ophiomorphids These occur rarely within coarse-grained and silty substrates. Ophiomorpha specimens are preserved within sandstones where they are recognized by a rugose mud lining. The vertical orientation of one specimen is well preserved in the core (Figure 5.9 B). Specimens of Thalassinoides occur as horizontal traces within interbedded sandstone and siltstone. The ichnogenus is here differentiated from Planolites by a larger burrow diameter (7-8 mm) and an interpreted passive fill (fill similar to host substrate), and differentiated from Palaeophycus by the absence of a wall lining (Figure 5.9 A). Like Ophiomorpha; Thalassinoides represent dwelling structures of probable crustaceans (Howard and Frey, 1984; Seilacher, 2007). It represents a variable mode of preservation within shaly and silty substrates where there is less need for the organism to reinforce the burrow wall. The two traces may be gradational. Unidentified trace fossils There are several unidentified trace forms and cryptobiourbated horizons. All of the unidentified traces occur along bedding planes and may represent the grazing, farming or deposit-feeding burrows of benthic organisms (Figure 5.9 C). 5.4.2 SUMMARY OF TRACE FOSSIL ASSEMBLAGES FOR THE ANGOSTURA SANDSTONE Ethology The assemblage of trace fossils described from the Angostura Sandstone in well Kairi-lcan be summarized in order of relative abundance: 261 1. Horizontal deposit-feeding traces (Planolites, Scolicia, cryptobioturbated horizons). 2. Variably oriented, dwelling/feeding structures {Ophiomorpha, Thalassinoides, cf. Teichichnus, cf. Rosselia). The ethological classification of trace fossils, in order of abundance (1= highest abundance) is: 5. Pascichnia {Planolites, Scolicia) 6. Domichnia and fodinichnia {Ophiomorpha, Thalassinoides, cf. Teichichnus, cf. Rosselia) Traces are common (trace intensity ~ 4) and comprise a low diversity. They are limited to the finer-grained strata in the "bioturbated sand and silt" lithofacies. The ethology is similar to that of the Pierre Point Sandstone Member as it is dominated by the grazing traces of deposit-feeders. Dwelling structures such as Thalassinoides and Ophiomorpha are similarly present, although the latter had a distinct vertical component not observed in the Pierre Point Sandstone Member. Tiering relationships are simple on account of the low diversity. This diversity and intensity of traces combined with the simple tier structure suggest a very short colonization window in which only a restricted range of organisms flourished. These factors are interpreted to represent mainly opportunistic or pioneering colonies. An assessment cannot be made on the presence or absence of graphoglyptid traces as these depend on plan-view geometries for accurate determination. As a result, a comparison is difficult with the Pierre Point Sandstone Member. Significance of Individual Traces None of the trace fossils encountered is particularly distinctive of a specific depositional setting. Like the Pierre Point Sandstone Member, Ophiomorpha is interpreted to represent the dwelling structure of a post-turbidite, opportunistic colonizer because of its association with the coarse-grained turbidites. Its association with proximal deep-sea environments was discussed above, although it spans a wide range of 262 marine and coastal environments. Rosselia is most common to shoreface environments and in particular, to outer shelf silty substrates of the Cruziana ichnofacies (Table 5.1). Its association with turbidites suggests outer shelf environments to proximal deep marine (slope environment). Teichichnus is also uncommon to deep-sea deposits. The pre-turbidite assemblage is interpreted for the finer-grained beds of the "bioturbated sandstone and siltstone" lithofacies and is dominated by deposit grazers and feeders (fodinichnia, pascichnia), similar to the Pierre Point Sandstone Member. The diversity of trace fossils is less than in the Pierre Point Sandstone Member and this may reflect either taphonomic controls or a more stressed environment for benthic communities. The association with the proximal lobe and channel deposits suggests high rates of amalgamation in sediments laid down by confined flows, which proved unfavourable either for benthic communities or the eventual preservation of their traces. 5.4.3 ICHNOFACIES OF THE ANGOSTURA SANDSTONE The trace fossil assemblage does not conform to conventional ichnofacies groups. The tentative identification of both Teichichnus and Rosselia suggests a Cruziana association but the relative diversity of traces is not characteristic. A proximal deep-sea environment is interpreted based on the Ophiomorpha-tuvbidite association, together with the numerous horizontal grazing trails (See Ophiomorpha rudis, Table 5.1). 5.5 TRACE FOSSILS OF THE HERRERA SANDSTONE MEMBER (CIPERO FORMATION) Trace fossils for the Herrera Sandstone Member are described from subsurface core in the Barrackpore oilfield where approximately 220 m (660 ft) of core was described from the well BP-347. Trace fossils were found in all lithofacies discussed in Chapter 2 except the "graded thick-bedded sandstone and conglomerate" facies. A low diversity of traces is common, although individual trace forms may be locally abundant 263 and impart a distinctive ichnofabric to the sediment. Separate assemblages were deduced for shale and interbedded sand/shale intervals. An assemblage is also described from an outcrop of the Cipero Formation on account of the similarity with traces seen in the core. The outcrop locality lies within the Cipero Formation where approximately 15-20 m of green calcareous shales were exposed at an excavation site for a sporting stadium in Tarouba, north of the town of San Fernando (see Figure 2.18 for location). Sands were entirely absent at the site with the coarsest sediment comprising thin, tan-coloured, silt beds, which stood out against the green shales. The correlation with the cored section stems from the restricted trace fossil assemblage common to both, comprised entirely of Zoophycos and Chondrites with subordinate Planolites and Thalassinoides. 5.5.1 DESCRIPTION OF TRACE FOSSILS Chondrites Chondrites was recognized by its branching form and silty fill which stood out against the green calcareous shales at Tarouba. They occur within beds (endichnial) although the branching protrusions are seen along bedding plane surfaces. They consist of very thin (4 mm diameter), branching cylindrical tubes (Figure 5.10 A) or branching networks (Figure 5.11 B). The ethology and palaeoenvironment of Chondrites is discussed above (Section 5.3.1). Zoophycos The delicately arranged spreite of Zoophycos can be observed in both longitudinal and plan view at Tarouba (Figure 5.11 D, E) where it commonly occurs. Within the core, it can be found primarily among shales (Figure 5.10 B), with some indication that it may also exist among the fine-grained turbidite beds (Figure 5.12 A). The Zoophycos trace and its creator has been an enigma since it was first proposed in 1855 (Olivero, 2007), although it is inferred as resulting from deposit- feeding (e.g. Oliver and Gaillard, 2007) and microbial gardening, with spreite created by active backfilling of the sediment (Bromley and Hanken, 2003). 264 Similarly, the Zoophycos ichnofacies is among the least understood, and according to MacEachern et al. (2007), the most debated. The ichnofacies is associated with quiet-water, oxygen-deficient environments rich in organic matter, with a tendency for low benthic diversity (Frey and Seilacher, 1980), although the trace fossil itself is not restricted to these conditions (MacEachern et al., 2007). Skolithos verticalis Rare specimens of sub vertical cylindrical tubes no more than 2 mm thick are preserved as endichnia within silty substrate (Figure 5.10 E). The lining of the tubes is highlighted by differential weathering. Skolithos is commonly associated with high-energy environments in both shelf and deep-sea sediments (Hayward, 1976; Crimes, 1977; Frey and Seilacher, 1980; Howard and Frey, 1984), although it can be found in virtually any environment (Scott and Birdsall, 1978; Pemberton et al., 1992c). Within shelfal environments, it is diagnostic of the Skolithos ichnofacies where it occurs with other vertically oriented domichnia and equilibrichnia. It is interpreted as domichnia, probably of a vermiform, suspension-feeding organism (Howard and Frey, 1984; Pemberton et al., 1992c). Thalassinoides These occur as endichnial, sand-filled burrows within shale; branching is apparent. Burrows are up to 1 cm diameter, though typically thinner. Both vertical shafts and horizontal tunnels occur (Figure 5.10 G). The functional significance of the trace was discussed with the Pierre Pointe Sandstone Member. Ophiomorpha One specimen occurs as a thinly lined endichnia within a sandy substrate. The burrow is 1 cm in diameter and displays a single retrusive spreite, interpreted to represent vertical adjustment of the burrow by the trace maker (Figure 5.10 C). 265 Figure 5.10 Trace fossils within the Herrera sandstone from BP-347 core. A) Plan view of Chondrites showing linear branching. (B) Zoophycos spreite in grey calcareous shale. C) Ophiomorpha and other unidentified traces. D) Unidentified, lined dwelling trace within massive sandstone bed. E) Skolithos verticalis within silty substrate. F) Escape trace. G) Thalassinoides, Palaeophycus (Pal) and synaeresis cracks (Syn). 266 Figure 5.11 Trace fossils in Cipero Formation shales at Tarouba. The same trace assemblage and lithology occur in the BP-347 core. A) A section of the excavation site showing approximately 25 m of green, calcareous shale (inset, hammer for scale) overlain by a recent soil cover. B) Branching Chondrites burrows in silty shale; endichnia. C) Branching 'arms' of Thalassinoides burrows in green calcareous shale; endichnia. The fill comprises silt from an overlying bed. D) Transverse and plan view (E) of spreite structure typical of Zoophycos. Arrows indicate the direction the organism migrated through the sediment. 267 [Bl 9 FI «•*" 268 Palaeophycus heberti These are predominantly horizontal or inclined cylindrical burrows distinguished from Planolites by its distinct lining and fill similar to its substrate (Pemberton and Frey, 1982; Keighley and Pickerill, 1995). The species is recognized by its thick wall lining relative to the burrow fill (Figures 5.8 G and 5.10 A). They are interpreted as domichnia, probably of a predaceous vermiform organism (Howard and Frey, 1984) or a suspension feeder (Pemberton et al., 1992c). Scolicial Subphyllochorda The Scolicia and Subphyllochorda ichnogenera refer to different preservation styles of a trace attributable to burrowing echinoids. The diagnosis of a specific ichnogenus depends entirely on outcrop preservation (Smith and Crimes, 1983) and a separation cannot be made from cores, which shows only a vertical representation of the burrow. For this section only, the burrow form will be referred to the more widely used term, Scolicia (e.g. Pemberton, 1992c). Within BP-347 core, these burrows occur within the "rippled sandstone and shale" and "rippled and graded sandstone" lithofacies (Section 2.7.1). The burrows are recognized by their meniscate backfill that results in pseudo-stratification when abundant (Figure 5.12 D). The burrows always occur at the top of sandstone beds or along a sand- shale interface (Figure 5.12 B, E-G). It is the most common trace form found throughout the cored interval. Scolicia traces are attributed to the mining and deposit-feeding of echinoderms (Bromley and Asgaard, 1975; Smith and Crimes, 1983). It is one of the few traces in which body fossils have been found at the ends of traces (e.g. Bromley and Asgaard, 1975). They burrow to various depths in the substrate depending on substrate type, species, oxygenation and other factors (Bromley and Asgaard, 1975). It is apparent that Scolicia frequents relatively deep-sea environments. Pemberton et al. (1992a) and MacEachern et al. (2007) assigned the trace fossil to relatively distal environments of the Zoophycos and proximal Nereites ichnofacies, while Uchman (2001) noted its common occurrence along the tops of thick, "channel-margin", turbidite beds where it occurs exclusively with Ophiomorpha. In this sense, it is similar to the. 269 Figure 5.12 Trace fossils within the BP347 core. A) Palaeophycus (Pa), Thalassinoides (Th) and possible Zoophycos (Zo). A synaeresis crack is also shown (Syn). B) Unidentified vertical dwelling structure and Scolicia (Sco). C) Vertical trace with funnel-shaped aperture similar to Arenicolites. D) Pseudo cross-stratification in fine-grained sandstone resulting from the common traces of Scolicia. E, F) Transverse view of Scolicia at top and within sandstone beds. G) Oblique view of Scolicia. 270 opportunistic trace fossils described for the Pierre Point Sandstone Member above (e.g. Saportia, Arenituba, and Scalarituba). Scolicia has previously been associated with episodic depositional events where the trace is the dominant or only fossil in completely reworked sediments. There are examples where such an ichnofabric alternates with unbioturbated beds or other ichnofabrics in both shallow (Bromley and Asgaard, 1975) and deep (Colella and D'Alessandro, 1988; De Gibert and Goldring, 2007) marine sediments. To explain these occurrences, De Gibert and Goldring (2007) and Colella and D'Alessandro (1988) interpreted Scolicia as an opportunistic trace, adapting to short lived, stressful environments uninhabitable to other tracemakers. Scolicia being the most common trace fossil seen in the core may be a response to similar palaeoenvironmental conditions. The ethological significance of the burrow lies in its deposit-feeding, grazing habit (Pascichnia). These ideas will be further developed below. Miscellaneous Other trace fossils in the Herrera Sandstone include cf. Arenicolites, cf. Thalassinoides and escape structures. The partially preserved cf. Arenicolites is interpreted based on its vertical orientation and collapse of sediment at the funnel-shaped aperture of the burrow (Figure 5.12 C); the geometry is reminiscent of the feeding pattern of the lugworm Arenicola marina, where the collapsed sediment is due to the ingesting of sediment below one opening and excretion to the sea floor through a second (see Figure 3.12 of Bromley, 1996). A funnel-shaped aperture is also typical of Monocraterion although both fossils represent a domichnia function. Arenicolites is normally associated with marine sequences and the Cruziana ichnofacies but they are also common among deep-sea turbidites. Bromley and Asgaard (1991) and Bromley (1996) described the Arenicolites ichnofacies, where the trace fossil was associated with specimens of Skolithos as opportunistic colonizers associated with event beds. The fossil was also present with other opportunistic domichnia in proximal fan deposits of the Whisky Bay Formation off Antarctica (Buatois and Lopez Angriman, 1992). Large, apparently branching trace forms occur in conjunction with Chondrites trace fossils within the Cipero shales at the Tarouba site (Figure 5.11 C). They are 271 preserved as endichnia within the monotonous shale beds. They are tentatively assigned to Thalassinoides based on their size (5-7 mm) and are comparable to specimens seen in the core (Figure 5.10 G). The radial branching form is distinctive and the trace may also be a large variety of Chondrites. An escape structure (fugichnia) is preserved as vertical chevron patterns within a sandstone bed (Figure 5.10 F). It records the sudden upward migration of an organism in response to an influx of sand. Subaqueous synaeresis or shrinkage cracks, although not a trace fossil, occur throughout the cored interval (Figure 5.10 G). The origin of these physical sedimentary structures has attracted keen interest and discussion (see reviews by Donovan and Foster, 1972; Plummer and Gostin, 1981), from which several mechanisms have been proposed. The cracks are formed by tensile forces either at the sediment-water interface, or within the shallow subsurface (Donovan and Foster, 1972; Plummer and Gostin, 1981; Kidder, 1990; Pratt, 1998). The proposed causative mechanisms for these forces include seismic- induced dewatering (Pratt, 1998), sedimentary loading (Plummer and Gostin, 1981; Kidder, 1990), clay deflocculation induced by salinity changes, compaction, freezing, tectonic stresses and others (Donovan and Foster, 1972; Plummer and Gostin, 1981). Their occurrence in the Herrera sandstone is likely associated with sedimentary loading, although there are too many rheological unknowns to be conclusive. 5.5.2 SUMMARY OF TRACE FOSSIL ASSEMBLAGES FOR THE HERRERA SANDSTONE MEMBER The assemblage of trace fossils in the Herrera Sandstone Member include: 1. Fodinichnia (deposit-feeding/ dwelling) represented by Chondrites and Zoophycos, agrichnia (gardening) represented by Zoophycos, and pascichnia (feeding/grazing) represented by Planolites. These occur within shaly intervals. 2. In order of relative abundance, Pascichnia (Scolicia, Planolites), domichnia (Skolithos, Ophiomorpha, Thalassinoides, Terebellina, Palaeophycus and cf. Arenicolites), 272 fugichnia (escape) and fodinichnia (cf. Zoophycos) within interbedded sands and shale beds. Within the Herrera Sandstone Member, there is a higher diversity of trace fossils within the rippled sandstone and shale (RSS) and rippled and graded sandstone facies (RGS); the graded thick-bedded sandstone (GTBS) is barren. The overall diversity is however relatively restricted. Shaly intervals in the core are dominated by deposit feeders. Seilacher (2007) still sees value in the trace fossil Zoophycos as a relative depth indicator, as it has shown an affinity for "impure and structureless sands and muds corresponding to quiet-water palaeoenvironments" (Seilacher, 2007, p. 108). This is more likely when the fossil occurs to the exclusion of other trace forms, except perhaps Chondrites. Both these traces show a greater tolerance for increasing levels of anoxia in sediments while other trace forms become relatively depleted (Bromley, 1996, p. 221; Savrda and Bottjer, 1986). According to Pemberton et al. (1992a), Zoophycos is also abundant in similar anoxic sediments in lacustrine environments. 5.5.3 ICHNOFACIES OF THE HERRERA SANDSTONE MEMBER The association of Zoophycos, Chondrites, Thalassinoides and Scolicia is interpreted to represent the Zoophycos ichnofacies (Table 5.1). The monotonous shales at Tarouba show a low diversity of traces characterized by the anoxia-tolerant ichnogenera (all excluding Scolicia). The sandstones of the Herrera Sandstone Member are superimposed upon the Zoophycos ichnofacies and are characterized by a more diverse suite of traces including an opportunistic Scolicia. The opportunistic tendency of Scolicia was noted above, where it occurred either exclusively or with Ophiomorpha within and along the tops of deep-sea turbidites (Colella and D'Alessandro, 1988; Uchman, 2001; De Gibert and Goldring, 2007). The assemblage of traces within the sandstones demonstrates similarities with the Skolithos ichnofacies, with vertical, semi permanent and permanent dwelling burrows, possibly of suspension-feeding organisms. Both the abundance and diversity of trace forms are however relatively low when compared to nearshore Skolithos ichnofacies assemblages. 273 5.6 TRACE FOSSILS OF THE LATE MIOCENE AND PLIOCENE FORMATIONS Trace fossils and their lithofacies associations were investigated in Late Miocene to Pliocene outcrops across the Southern Basin to further refine the sedimentology derived from physical sedimentary structures, and to compare with earlier Cenozoic formations. Only a preliminary assessment was completed for Late Miocene-Early Pliocene formations at Point Paloma, Point Radix and Morne Diablo, while a more detailed assessment was completed for the Morne L'Enfer Formation (see Figure 4.1 for location). The following discussion will demonstrate a more diverse range of trace fossils within Late Miocene and Pliocene formations than found throughout the Early Cenozoic, a change that parallels the onset of shelf and deltaic sedimentation indicated by physical sedimentary structures. Trace fossil assemblages conform more readily to established archetypal ichnofacies (Seilacher, 1967) than do the earlier Cenozoic formations. 5.6.1 TRACE FOSSILS OF THE MANZANILLA AND CRUSE FORMATIONS Sediments of the Manzanilla and Cruse formations were examined near Point Paloma and Point Radix, on the east coast of Trinidad. The Cruse Formation was also examined at Morne Diablo along the southern coastline (see Figure 4.1 for location). Within the Manzanilla Formation sedimentary facies were not evaluated in detail and only a synopsis is provided. The interval is shale-prone, with thin sandstone beds ranging from fine- to coarse-grained and occasional pebbly intervals. Soft-sediment deformation exists in the form of sand dykes, load ripples, load casts and contorted laminae, likely deformed in response to sediment influx. Both oscillatory and current ripples were common along with dune-scale trough cross-bedded intervals, and at least two rooted horizons were observed. The interval reflects relatively shallow-water sedimentation compared to the sediment gravity flow-dominated environments of earlier 274 formations. The deformation features may be a response to high shelf-sediment input into an otherwise shale-prone, quiet-water environment. Within these beds, the trace fossil assemblage includes Gyrolithes, Arenicolites, Asterosoma, Diplocraterion, Thalassinoides, Ophiomorpha, Skolithos, cf. Teichichnus and a rooted horizon. Trace intensity ranges from common to rare. Cruse Formation sediments at Point Radix display at least one thickening and cleaning upward succession. Again, sedimentary facies were not examined in detail for this investigation. The lower shale-prone portion of the succession contained Thalassinoides, Rosselia, Zoophycos, Scolicia, Ophiomorpha and other grazing and locomotion traces. The higher beds in the succession are dominated by large vertical networks of Ophiomorpha nodosa within amalgamated sandy bedsets. The trace fossil assemblage at Morne Diablo has already been discussed together with the sedimentary facies (Section 4.1). To recap, a restricted assemblage occurs within the massive and ripple-cross-laminated sand lithofacies (turbidites) dominated by Ophiomorpha annulata, Gyrolithes and thin beds with churned ichnofabrics. The youngest rocks at the Morne Diablo section (Siparia Point) contain Terebellina, Planolites, Ophiomorpha nodosa, Subphyllochorda, cf. Asterosoma and other unidentified traces. 5.6.2 DESCRIPTION OF TRACE FOSSILS Ophiomorpha annulata Distinguished by its thick wall lining but smooth exterior, the pellet lining typical of the ichnogenera is not developed (Howard and Frey, 1984). The trace occurs primarily as a horizontal network within turbidite beds. Like other forms of Ophiomorpha, it is considered a dwelling burrow created by crustaceans. The poorly developed pellet lining is characteristic of more distal facies including turbidite deposits (Howard and Frey, 1984,p.205;Uchman,2001). 275 Gyrolithes This trace fossil occurs as endichnia within sandy substrates and was recognized by its corkscrew form. It may be transitional to other trace fossils such as Ophiomorpha and Thalassinoides (Hester and Pryor, 1972; Frey et al., 1978; Bromley, 1996; Seilacher, 2007) as observed at the Morne Diablo section, where it occurs with Ophiomorpha annulata. The association suggests a domichnia function to the trace fossil, likely created by a crustacean (Goldring et al., 2007). The fossil is found in a variety of environments including brackish water (Pemberton et al, 1992c, figure 12), intertidal, and shallow subtidal (e.g. Curran and Frey, 1977). It is not recognized within deep-sea turbidites (Ksiazkiewicz, 1970; Crimes, 1977; Kern, 1980; Crimes et al., 1981; McCann and Pickerill, 1988; Heard and Pickering, 2007). The trace fossil is associated with the Skolithos ichnofacies (MacEachern et al, 2007). Arenicolites This trace fossil is preserved as endichnia within sandy substrates. It is interpreted as the stationary domichnia of polycheate organisms (e.g. lugworms in tidal flat environments) (Bromley, 1996). It is found in a diverse range of environments. It has been described from shallow water sediments such as tidal flats (e.g. Bromley, 1996), upper shoreface sediments (e.g. Howard and Frey, 1984; Pemberton et al., 1992c) and episodic depositional layers such as turbidites or storm beds (Bromley and Asgaard, 1991; Pemberton et al., 1992c; Bromley, 1996). It has also been described from deep-sea fans where it is associated with other "shallow-water" forms (Crimes, 1977; Buatois and Lopez Angriman, 1992; Heard and Pickering, 2007). Bromley (1996) and Bromley and Asgaard (1991) suggest that its occurrence in deeper water may be related to an opportunistic organism. Their Arenicolites ichnofacies is different from the Skolithos ichnofacies as it represents short-term, high-energy deposition (event beds) within otherwise quiet water settings, which allows for preservation of both shallow and deeper tier traces, unlike the Skolithos ichnofacies. It is also a typical trace form in the Skolithos ichnofacies (Frey and Seilacher, 1980; MacEachern et al, 2007) and may be common in the Cruziana ichnofacies (MacEachern et al., 2007). 276 Asterosoma The trace fossil is preserved as epichnia within sandstone. Seilacher (2007) classified this trace form under asterosomids, representing a particular burrowing technique that includes radial backfills. Asterosoma represents a horizontal preservation of this technique and largely fulfils a fodinichnia function. The trace fossil is known from lower shoreface (e.g. Pemberton et al., 1992c; MacEachern et al., 2005), distal delta front (e.g. MacEachern et al., 2005) and upper bathyal slope fan (e.g. Heard and Pickering, 2007) environments. It has not been recognized in distal deep-sea fan deposits (e.g. Ksiazkiewicz, 1970; Chamberlain, 1971; Crimes, 1977; Kern, 1980; McCann and Pickerill, 1988). It is a characteristic trace fossil of the Cruziana ichnofacies (MacEachern et al., 2007) although Chamberlain (1971) included the fossil within his Zoophycos ichnofacies. Diplocraterion This trace fossil was recognized by its 'dumbbell' shape on the top surface of a sandstone bed. It is interpreted as a permanent dwelling structure (domichnia) of a suspension-feeding organism (Pemberton et al., 1992c; Seilacher, 2007). MacEachern et al. (2005) recognized the trace in a variety of environments including proximal lower shoreface, distal prodelta and tempestites; it may also form a significant (Crimes, 1977) or rare (Buatois and Lopez Angriman, 1992) component among post-depositional assemblages in turbidite successions. According to Hantzschel (1975), its trace maker was adapted to unstable environments with several stages of erosion and deposition. Diplocraterion is typically associated with the Skolithos ichnofacies although it may be locally abundant in the Cruziana ichnofacies (Frey and Seilacher, 1980; Pemberton et al., 1992a; MacEachern et al., 2007). Skolithos These are simple vertical to sub-vertical tubes within sandy substrates. They are interpreted as the permanent domicile of a suspension feeding or carnivorous organism that is well adapted to high sediment rates and unstable environments. A wide variety of potential trace makers have been identified (Pemberton et al., 1992c; Bromley, 1996), 277 and as a result, the trace has been found in a wide variety of depositional environments ranging from shallow marine, slope (Hayward, 1976, Scott and Birdsall, 1978) to deep marine (Crimes, 1977; Buatois and Lopez Angriman, 1992). Bromley and Asgaard, (1991) described the trace as belonging to an opportunistic colonizer when occurring together with Arenicolites in deep-water. These authors considered this trace assemblage typical of their Arenicolites ichnofacies. It is a typical specimen of the archetypal Skolithos ichnofacies where it is usually associated with Ophiomorpha, Arenicolites, Diplocraterion and other domichnia traces (Frey and Seilacher, 1980; MacEachern et al., 2007). Planolites This trace fossil occurs within the Cruse Formation at Morne Diablo coast where it forms a recurrent ichonofabric within rippled silts and fine sand. The trace is diagnosed primarily on the absence of a distinct lining, which is characteristic of similar trace forms, Palaeophycus and Macaronichnus (Clifton and Thompson, 1978; Keighley and Pickerill, 1995; Bromley, 1996). The fossil is not branched and preserves the gregarious habit of the trace maker. The recurrent Planolites ichnofabric occurs within interbedded silts and ripple cross-laminated fine-grained sandstone. The ichnofabric increases in thickness and abundance in younger beds, parallel with an increase in the sandstone/shale ratio. The recurrent trend was obviously in response to depositional conditions related to the input of sand within otherwise quiet-water sedimentation (shales). The occurrence of oscillatory ripples among the Planolites-ichnofabric may be related to tempestite deposition in a distal shelf environment, below normal wave-base. Schaubcylindrichnus/Terebellina Both traces were recognized by their distinct lining on vertical to oblique cylindrical tubes (Howard and Frey, 1984; Frey and Pemberton, 1991; Pemberton et al., 1992c; Miller, 1995). Their distinction follows that of Frey and Pemberton (1991) who reserve Terebellina to isolated tubes while Schaubcylindrichnus occurs in groups (Miller (1995) suggested they both be referred to the latter). They occur rarely within laminated silty shale of the Cruse Formation along the Morne Diablo coast 278 Frey and Pemberton (1991) suggested that the bundled tubes of Schaubcylindrichnus are environmentally distinctive, restricted to argillaceous, distal offshore environments and always part of the stable ichnocoenose. It has also been reported from prodelta and distal delta front sediments (MacEachern et al., 2005). It is interpreted as the dwelling tube(s) of a suspension feeder (Frey and Pemberton, 1991; Pemberton et al., 1992c). 5.6.3 TRACE FOSSIL ASSEMBLAGES 5.6.3.1 CRUSE FORMATION ALONG THE MORNE DIABLO COAST The ichnofacies assemblage of Late Miocene to Early Pliocene sandstones at the Morne Diablo coast can be summarized as follows: 1. Post-depositional, opportunistic traces represented by crustacean domichnia {Ophiomorpha annulata) and thin beds with churned fabrics within upper slope turbidites. An analogy is drawn between this assemblage and that of the earlier- described Pierre Point and Angostura sandstone members based on the low diversity, Ophiomorpha-tmbidite association. The recurrent Planolites ichnofabric is also included here. It occurs within younger beds than the crustacean burrows and may be related to tempestite deposition within the upper slope to distal offshore environments. 2. Terebellina is a background dwelling trace of a suspension feeder that is typical of stable distal offshore or delta front environments; it is characteristic of a mixed Cruziana-Skolithos ichnofacies (Frey and Pemberton, 1991). 3. A more diverse range of traces in the youngest beds examined including domichnia (Ophiomorpha nodosa), pascichnia (Subphyllochorda, Planolites) and fodinichnia (cf. Aster osoma). 5.6.3.2 CRUSE FORMATION AT POINT RADIX The ichnofacies assemblage of Late Miocene to Early Pliocene sandstones at Point Radix can be summarized as a combination of domichnia (Thalassinoides, 279 Ophiomorpha), pascichnia (Scolicia) and fodinichnia (Zoophycos, Rosselia) within silt beds. Domichnia dominates the upper sand-prone beds. The decrease in diversity upward may indicate a transition from Cruziana to Skolithos ichnofacies, the latter dominated by Ophiomorpha nodosa. 5.6.3.3 MANZANILLA FORMATION NEAR POINT PALOMA The ichnofacies assemblage of Late Miocene to Early Pliocene sandstones in the vicinity of Point Paloma is dominated by domichnia (Gyrolithes, Ophiomorpha, Skolithos, Thalassinoides, Arenicolites, Diplocraterion, cf. Teichichnus) with secondary fodinichnia (Asterosoma). The common domichnia and equilibrichnia (e.g. Diplocraterion, Skolithos, Ophiomorpha, cf. Teichichnus) suggest unstable substrates, relatively higher energy environments and sedimentation rates and unstable substrates that are typical of a nearshore environment. When these are considered together with the physical sedimentary structures and rooted horizons (Section 5.4.1 above), they suggest environmental conditions akin to the Skolithos ichnofacies. 5.6.4 SUMMARY OF TRACE FOSSIL ASSEMBLAGES FOR THE CRUSE AND MANZANILLA FORMATIONS The low diversity assemblage described west of Morne Diablo fishing depot is similar to that described for earlier sandstones with their low diversity Ophiomorpha- turbidite assemblage. The higher diversity in the Manzanilla Formation represents a departure from this trend with its Skolithos ichnofacies assemblage. The collective diversity of these Early Pliocene rocks, with common vertical domichnia and equilibrichnia trace fossils, is more typical of archetypal Seilacher ichnofacies models when compared to the Early Cenozoic sandstones (Pierre Point, Angostura and Herrera sandstone members), but the diversity associated with Cruziana ichnofacies was not observed. Further work on the stratigraphic order of traces at Point Paloma and the 280 identification of further species at all localities would be useful to further validate these conclusions. 5.7 ICHNOFACIES OF THE MORNE L'ENFER FORMATION The lithofacies and trace fossil assemblages were reviewed in the Morne L'Enfer Formation in relative detail. The descriptions that follow relate the trace fossil assemblages to the eight lithofacies identified in the Morne L'Enfer Formation. Details of individual traces follow. 5.7.1 DESCRIPTION OF TRACES Psilonichnus upsilon The identification of this trace fossil throughout the Morne L'Enfer Formation was guided by Gingras (1999). It was recognized by the characteristic vertical 'J' and 'Y' shaped burrows that can attain lengths greater than 1 m. More commonly, it was recognized by the concave meniscate laminae that resulted from passive fill of the burrow. This differentiates the trace in vertical section from Thalassinoides, which was reserved for unstructured fills in vertical section (although Thalassinoides may also display a meniscate fill). The trace is interpreted as domichnia, created by a variety of crustaceans (Gingras, 1999), and has mostly been described from ancient tidal nearshore and backshore environments (Frey et al., 1984; Gingras, 1999) or modern intertidal flats (Curran and Martin, 2003). Psilonichnus is one of the most recurrent trace fossils found throughout the Morne L'Enfer Formation. It is most abundant within the wavy and lenticular-bedded silts of the thickening-upward wavy-flaser sands facies (TUFW) and the intertidal deposits of the laterally accreted sands facies (LAS). Both facies occur in the Upper Morne L'Enfer Sandstone Member where these traces are most commonly found. They occur rarely within the distal prodelta silts (laminated silts facies), shoreface sands (swaley cross- stratified sands facies), distal prodelta/lower shoreface (grey bioturbated silts), and is 281 entirely absent within the fluvial and estuarine sediments (trough and sigmoidal cross- stratified sands, respectively). Ophiomorpha nodosa Ophiomorpha within the Morne L'Enfer Formation is dominated by the ichnospecies Ophiomorpha nodosa with well-developed pelletoid exteriors. Relative to Early Cenozoic sandstones, branching networks are well developed (consider the outcrop Figure 5.13 Outcrop examples of Psilonichnus upsilon (A and B) and schematic interpretation of the burrow (C). Psilonichnus is one of the more commonly occurring trace fossils in the Upper Morne L'Enfer Sandstone Member. After Gingras, 1999, Figure 3.6. 282 bias though) and tunnels and shafts may attain diameters up to 6 cm. The ethological classification is as described previously. Ophiomorpha nodosa is particularly distinctive of the swaley cross-stratified sands facies (shoreface sands) where it may occur in high intensity with a low diversity of other traces (mainly Skolithos). It is also common to the flaser-bedded sands within the TUFW facies (proximal delta) where a smooth-walled variety was also observed among the trough cross-beds. Terebellina/Schaubcylindrichnus coronus The distinction between these traces and their interpreted palaeoecology is discussed above. They have a restricted occurrence, found only among the argillaceous silts of the grey bioturbated silts facies and laminated silts facies (prodelta, distal prodelta/lower shoreface) where they may be locally common with individual tubes less than 1 cm wide. They are restricted to argillaceous, distal offshore or delta front environments and are always part of the stable ichnocoenose; they are characteristic of a mixed Cruziana- Skolithos ichnofacies (Frey and Pemberton, 1991). Skolithos linearis These burrows are widespread throughout the formation and recognized by their vertical form, sometimes up to 1 m in length, lined or unlined within various substrates. Their preservation ranges from single, unlined vertical tubes within silty substrates up to 1 m long to abundant, lined vertical tubes within sandy substrates. The highest burrow intensity occurs within localized beds of the swaley cross-stratified sands facies where they occur with Gyrolithes, Ophiomorpha and other vertical traces. The lowest intensity is within the laminated silts facies (prodelta) where they occur with Schaubcylindrichnus and rare Psilonichnus. Skolithos represents a domichnia of a suspension-feeding organism. Their occurrence and functional ecology is discussed above. 283 Thalassinoides This trace has a widespread occurrence throughout the formation where it is associated with all facies (except sigmoidal and trough-cross bedded sands). It is differentiated from Psilonichnus by its structureless fill, often coarser than the substrate. It is particularly common among the grey bioturbated silts and extensively bioturbated, argillaceous horizons in the Upper Morne L'Enfer Sandstone Member. Thalassinoides fulfils a domichnia function. The ecological significance was discussed above. Rosselia Well-preserved specimens of Rosselia up to 10 cm long with distinctive inner lining and vertical habit were common to two facies. They are common to the grey bioturbated silts facies where they are best recognized in epichnial preservation by their cylindrical lining. They were also found within organic-rich silty beds that capped the thickening-upward flaser- wavy sand facies where they are preserved in endichnia, sometimes below rooted horizons. The functional significance of the trace was discussed previously; it is essentially the trace of a deposit feeding organism (Pemberton et al, 1992c; Nara, 1997; Seilacher, 2007) and a distinctive form in the Cruziana ichnofacies. They have been reported from proximal to prodelta deltaic environments associated with the Cruziana and Skolithos ichnofacies (MacEachern et al., 2005). Conichnus/Bergaueria/ The differentiation between these trace fossils and their respective ichnospecies was hindered by the two-dimensional exposures, the identification was guided by Pemberton et al., (1988). Bergaueria was reserved for concave burrows relative to the top of sandstone beds (negative epirelief preservation) with a rounded, semi-circular cross-sectional geometry while Conichnus was assigned to similar trace fossils with a conical cross-sectional geometry. Gradations between these two were also observed in specimens up to about 15 cm wide. Specimens occurred either singly, or in groups. Generally an assignment to either ichnogenus was made only when found in association with other trace fossils to avoid misidentification with non-biogenic sedimentary 284 structures. Generally, these traces occur within the thickening-upward wavy-flaser sands facies and the swaley cross-stratified sands of the Morne L'Enfer Formation. Both Bergaueria and Conichnus are interpreted to represent actinian dwelling and/or resting traces (Pemberton et al., 1988; Seilacher, 2007). Crimes (1977, Table 4) restricted its occurrence to intertidal to shoreface environments, although it is apparently more common to the latter (MacEachern et al., 2005, Tables 1 and 2). Poursoltani et al. (2007) recorded the occurrence of Conichnus in deepwater "thick-bedded" high-density turbidites. It is characteristic of the Skolithos ichnofacies (MacEachern et al., 2007). Teichichnus Teichichnus was recognized by its concave, crescent-shaped spreite structure within longitudinal sections commonly over 5 cm and transverse sections of similar height, always in full relief preservation. Burrows were not lined. Forms were sometimes difficult to distinguish from longitudinal sections of Psilonichnus but an assignment to this ichnogenus was made only where vertical reworking of the sediment could be inferred as opposed to the passive fill of Psilonichnus. Recognized ichnospecies included T. rectus (in longitudinal sections) and T. zigzag (in transverse sections) as illustrated by Seilacher (2007). Teichichnus was most common to the silty beds of the swaley cross-stratified sand facies and the wavy and lenticular-bedded sands of the laterally accreted sands facies (shoreface and tidal influenced sands respectively). Teichichnus is interpreted as the dwelling burrow of a deposit-feeding organism (Pemberton et al., 1992c). It commonly occurs across a variety of associated deltaic environments in fluvial, wave, tide and storm-dominated settings (MacEachern et al., 2005). Heard and Pickering (2007) reported its occurrence in deep-sea turbidites while Ekdale (1977) reported it from abyssal plain sediments. It is associated with the Cruziana ichnofacies (MacEachern et al., 2007). Rhizocorallium Identification of the fossil was guided by Hantzschel, (1975), Pemberton et al., (1992c), Bromley (1996) and Seilacher (2007). It was easiest recognized in epirelief preservation upon bedding planes by its 'U'-shape and protrusive spreite and large (1 cm) 285 burrow diameter that distinguishes this ichnogenus from Zoophycos, where the enclosing burrow is not observed. Rhizocorallium was always found in silty substrates in the grey bioturbated silts, swaley cross-stratified sands and the laterally accreted sands facies. Rhizocorallium is interpreted as the dwelling trace of a deposit-feeding organism (Hantzschel, 1975, Pemberton et al., 1992c) that fed by lateral 'strip-mining' of the substrate (Bromley, 1996). The burrow also indicates some readjustment to substrate conditions (Seilacher, 2007). It appears common to delta front and brackish lagoonal environments (Pemberton et al., 1992c; MacEachern et al., 2007) but also occurs on deep-marine fans in association with Ophiomorpha, Diplocraterion and Paleodictyon (Crimes, 1977). It is associated with a distal Cruziana ichnofacies (Pemberton et al., 1992c; Bromley, 1996; MacEachern et al., 2007). Scolicia/ Subphyllochorda These ichnogenera usually attributed to migratory echinoderms, were discussed in detail above (see Herrera Sandstone Member). They occur commonly in the swaley cross-stratified and grey bioturbated silt facies associated with a diversity of other traces. They do not dominate the assemblage, unlike that described for the Herrera Sandstone Member. Miscellaneous trace fossils Other ichnogenera identified throughout the Morne L'Enfer included Planolites, Palaeophycus, Lockeia, Cylindrichnus, and Asterosoma. 5.7.2 SUMMARY OF TRACE FOSSIL ASSEMBLAGES BY DEPOSITIONAL ENVIRONMENT Particular ichnogenera occur commonly in association with particular facies throughout the formation. This was alluded to in the descriptions above, but the explicit distinctions based on depositional environment are useful from a palaeoenvironmental perspective. 286 5.7.2.1 LAMINATED SILTS (PRODELTA FACIES) Trace fossils are rare to absent in the lowest exposed silts. The trace fossil assemblage within the upper beds, coincident with the occurrence of symmetrical ripples, includes Psilonichnus, Planolites, Terebellina and Skolithos. The lithofacies is characterized by a low intensity and diversity of trace fossils. A restricted assemblage is characteristic, composed of rare dwelling and grazing traces. This may be in response to several environmental stresses such as substrate instability, turbulence or anoxia. The greater agitation associated with oscillatory currents introduced an environment more favourable to benthic organisms, as reflected in the increase of trace fossils toward the top. 5.7.2.2 THICKENING-UPWARD WAVY-FLASER SANDS (PROXIMAL DELTA FRONT) Bioturbation is common to abundant with a diverse assemblage of traces including Skolithos, Teichichnus, Planolites, Palaeophycus, Psilonichnus, Lockeia, Thalassinoides, Cylindrichnus, Conichnus, Rosselia and Ophiomorpha nodosa. The assemblage is dominated by domichnia (Skolithos, Teichichnus, Palaeophycus, Psilonichnus, Thalassinoides, Ophiomorpha, Conichnus) and also includes fodinichnia (Rosselia), pascichnia (Planolites) and cubichnia (Lockeia). 5.7.2.3 GREY, BIOTURBATED SILTS (DISTAL PRODELTA/ LOWER SHOREFACE) Primary bedding is often obscured by the relatively high diversity and intensity of trace fossils. The assemblage includes Thalassinoides, Palaeophycus, Terebellina/Schaubcylindrichnus, Planolites, Psilonichnus, Teichichnus, Ophiomorpha nodosa, Asterosoma, Rosselia, Scolicia, Rhizocorallium and other unidentified grazing traces. This lithofacies character is supported by the predominance of horizontal domichnia and pascichnia, as opposed to vertical domiciles usually associated with 287 suspension feeders in agitated waters (Pemberton, 1992b). The intense bioturbation also suggests relatively slower sedimentation rates. 5.7.2.4 SWALEY CROSS-STRATIFIED SANDS (WAVE MODIFIED DELTA/ MIDDLE TO UPPER SHOREFACE) Throughout the Morne L'Enfer Formation, the trace fossil intensity and diversity within this lithofacies ranged from churned rock fabric to rare Planolites traces on bedding planes. At Cedros Bay and Scotts Road (see Figure 4.5 for location), traces within the thick sand beds are dominated by Ophiomorpha nodosa and Skolithos, with Psilonichnus less common. A mottled rock fabric at Puerto Grande Bay includes Ophiomorpha nodosa, Skolithos, Psilonichnus, Gyrolithes, Cylindrichnus, Teichichnus, Thalassinoides, Diplocraterion and Bergaueria. Shale- and silt- prone intervals are dominated by a low intensity of Thalassinoides, Psilonichnus, Arenicolites, Scolicia and Rhizocorallium. Churned beds indicate relatively lower sedimentation rates that allowed extensive reworking of the sediment. These may have occurred within confined bays away from direct sediment input, or within more distal occurrences of this facies where it is transitional with the grey bioturbated silts facies. 5.7.2.5 TROUGH CROSS-STRATIFIED SANDS (COASTAL PLAIN DISTRIBUTARY CHANNELS) Bioturbation is rare to common within organic-rich, grey muds, though not observed throughout most of this lithofacies. One 30 cm long vertical shaft suggestive of escape activity was noted in sand beds of the Upper Morne L'Enfer Sandstone Member at Esperanza Bay. Saunders and Kennedy (1968) described a similar feature in the Upper Morne L'Enfer Sandstone Member at Guapo Bay. The relative absence of trace fossils indicates a stressed environment, possibly due to unconsolidated sediment substrates and excessive turbidity associated with the distributary channels. The mudstone conglomerates, with cobble-sized clasts and associated erosion surfaces, indicate relatively high velocity flows. The absence of traces may in part be due to taphonomic influences, as the preservation potential adjacent to the 288 shifting and eroding channels is low. This is supported by the rare occurrence of equilibrichnia traces. A low diversity and intensity of traces appear typical of river- dominated deltaic sediments (MacEachern et al., 2005). 5.7.2.6 AMALGAMATED SIGMOIDAL CROSS-STRATIFIED SANDS (ESTUARINE/ MARINE INCURSION) These amalgamated sandstones are devoid of bioturbation. A fossilized wood fragment with Teredolites borings (G. Wach pers. comm.) and rare Ophiomorpha nodosa and Skolithos linearis were observed among silts that overlie the sigmoidal cross- stratified sands, and are attributed to the marine incursion within the overlying transgressive sediments. As with the distributary channels/coastal floodplain environments, the scarcity of trace fossils is attributed to a combination of stressed conditions and taphonomic influences likely induced by the confined flows, high sediment rates and turbidity. The rare Ophiomorpha and Skolithos burrows and low-angled cross-stratified sands towards the top of this assemblage suggest the onset of more marine conditions (flooding) overlying this lithofacies. 5.7.2.7 LATERALLY ACCRETED SANDS (SUB AND INTERTIDAL CHANNELS/ TIDAL FLATS) This lithofacies is commonly bioturbated throughout with a low diversity of traces. The trace fossil assemblage is dominated by horizontal to oblique traces and includes Thalassinoides, Teichichnus, Skolithos, Psilonichnus, Ophiomorpha and Diplocraterion. Silty beds with abundant organic matter also contain Rhizocorallium, Planolites and Thalassinoides. This diversity decreases within the shale beds to include only Skolithos and 'Y'-shaped Psilonichnus with less common Thalassinoides. Burrow traces reach lengths up to 1 m and some display an oxidized rim around the burrow wall. The trace fossil assemblage within the shale beds suggests that some adjustment within an aggrading substrate was necessary, though within generally quiet waters. This 289 is indicated by the long vertical traces created by persistence of the burrow over time. The oxidized rim around the burrow wall may be attributable to periodic exposure during falling water levels as may have occurred within the inter-tidal zone. The abundance of Psilonichnus represents more proximal intertidal to supratidal environments dominated by crustaceans. 5.7.3 SUMMARY AND ICHNOFACIES INTERPRETATION FOR THE MORNE L'ENFER FORMATION The variety of depositional environments and processes within the Morne L'Enfer Formation is coincident with a wide range of trace fossils and trace fossil assemblages. Collectively, the assemblage of traces represents the benthic response to environmental controls such as shifting substrates, erosive currents, salinities and turbidity. There was no indication of agrichnia (farming) in any of the exposures, while fodinichnia (deposit- feeding/dwelling) is secondary to domichnia (dwelling) traces. These are not post- depositional assemblages as seen in the Paleocene to Miocene sandstones but represent established communities with developed trace fossil tiers. The diversity and intensity of trace fossils show a dependence on the facies associations and interpreted depositional environments and this is summarized in Figure 5.14 Trends varied from intensely bioturbated silts with a high diversity of trace forms (e.g. grey bioturbated silts) to non- bioturbated amalgamated and trough cross-bedded sands that may have been associated with strong currents and shifting substrates precluding either a diverse benthic community, or the eventual preservation of their traces. The different assemblages are representative to varying degrees, of the archetypal ichnofacies associations known from shallow marine and nearshore environments (Table 5.1). Examples include: (1) The transition from Cruziana to Skolithos ichnofacies within the Lower Morne L'Enfer Sandstone member exposed at Cedros Bay and Fullarton, where distal prodelta or lower shoreface silts are replaced upwards by middle to upper shoreface sands (Figure 5.15). The Cruziana ichnofacies is represented by the grey bioturbated silts facies with a high bioturbation intensity and numerous trace forms. Distinctive 290 traces include Asterosoma, Rosselia, Cylindrichnus, Teichichnus, Thalassinoides, Schaubcylindrichnus, Arenicolites among others. The Skolithos ichnofacies is represented by large Ophiomorpha nodosa and Skolithos burrows, occurring almost to the exclusion of other trace forms, suggesting relatively higher-energy and shifting substrates associated with relative shallowing. (2) Aspects of the Psilonichnus ichnofacies can be demonstrated in parts of the Upper Morne L'Enfer Sandstone Member where tidal processes assumed greater importance than wave processes. Psilonichnus is the most widespread trace fossil throughout this member and its association with rooted horizons is characteristic in part, with the Psilonichnus ichnofacies (Table 5.1). The association is interpreted to represent more proximal intertidal to supratidal environments that were inhabited by burrowing crustaceans. Oxidized rims on some burrow walls suggest falling water levels and periodic exposure. These are most common to the laterally accreted sands, and to a lesser extent, the thickening-upward wavy-flaser sands facies. The overall poor diversity of traces within sandy bedsets may again be attributable to unstable substrates, salinity or turbidity stresses associated with tidal channels, and in this respect, is akin to the Skolithos ichnofacies. Both represent relatively nearshore environments. 5.8 DISCUSSION At least two major trace fossil groups can be distinguished from the Trinidad Cenozoic as discerned from this study (Table 5.3): (1) a low-diversity Early Cenozoic turbidite association (Pierre Point, Angostura and Herrera sandstone members) that is distinct from (2) a diverse shallow-water, Pliocene assemblage (Manzanilla-Cruse and Morne L'Enfer formations). The low-diversity trace fossil assemblage of the Early Cenozoic sandstones consists primarily of deposit feeding and dwelling traces, while evidence for suspension feeding patterns is rare (Table 5.3 A). In contrast, suspension feeding may have been common to the Pliocene assemblage based on a Skolithos, Diplocraterion, Terebellina, 291 Ophiomorpha and Thalassinoides assemblage within wave- and tide- modified substrates, collectively suggesting relatively shallow, agitated waters. The Early Cenozoic assemblage is dominated by horizontal grazers (mainly deposit feeders), which suggest relatively quiet-water environments with a rich food supply near the sediment-water interface. In contrast, horizontal grazing traces of deposit feeders were not observed in the youngest sandstones investigated (Late Pliocene Upper Morne L'Enfer Sandstone Member), and the assemblage is instead dominated by vertical and variably inclined domichnia and escape traces (compare "b", "c" and "d" in Table 5.3 B). Evidence for agrichnia feeding patterns was limited to a Paleodictyon specimen in sandstones of the Pierre Point Sandstone Member, which suggests relatively deep, quiet-water palaeo- environmental conditions ("a" in Table 5.3 A). Bromley and Hanken (2003) also associated Zoophycos with this feeding pattern, which extends the range of agrichnia to the Angostura and Herrera sandstone members. These traces were rarely observed among the diverse assemblage of Pliocene sands (limited to one specimen in Cruse siltstones at Point Radix) suggesting a relatively shallow-water, high-energy aspect. The two groups can also be distinguished by the relative abundance of Chondrites which is ubiquitous in shales and siltstones of the Pierre Point and Herrera sandstone members but was not observed in the Pliocene assemblage. These trends are interpreted to indicate two contrasting stages of basin fill and associated ichnofacies. An "underfilled" stage is represented by the low-diversity, Early Cenozoic sediments in which quiet, possibly deeper-water environments favoured deposit feeders and horizontal grazers within silty substrates and post-depositional opportunistic traces within sandy intervals. The second stage of basin fill is represented by the Late Pliocene Morne L'Enfer Formation, Manzanilla sediments at Point Paloma and less by the Cruse Formation along the Morne Diablo coastal section, and is characterized by feeding and dwelling habits indicative of shifting substrates, energy stresses and active competition for nutrients. This stage of basin fill is associated with reduced and fluctuating accommodation space within relatively shallow-water shelf to nearshore environments. The transition between these two stages is reflected in the Cruse Formation trace fossil assemblage with a change from post-depositional, opportunistic trace fossils (first from slope turbidites below storm wave base, and secondly, from 292 tempestites within outer shelf to slope environments) into a more diverse trace fossil assemblage of fodinichnia, domichnia, pascichnia and equilibrichnia, which conform more readily to archetypal ichnofacies models (Seilacher, 1967). These stages of basin fill are also reflected in the ichnofacies associations. 5.8.1 ICHNOFACIES INTERPRETATIONS The Seilacherian ichnofacies model (Seilacher, 1967; Frey and Seilacher, 1980; Pemberton et al, 1992a; MacEachern et al., 2007) largely reflects the longer-term response to palaeoenvironmental conditions with defined groups of traces. Other ichnofacies, such as the Arenicolites ichnofacies (Bromley and Asgaard, 1991) and Ophiomorpha rudis subichnofacies (Uchman, 2001), reflect organism response to short term stimulants such as nutrient supply, turbidity and erosion. Ichnofacies interpretations were put forward in foregoing sections based on the trace fossil assemblages for each formation. The interpretations included: « Trace fossils of the Pierre Point Sandstone Member were compared to the Ophiomorpha rudis and Paleodictyon subichonfacies of the Nereites ichnofacies. • Trace fossils of the Angostura Sandstone Member were compared to the Ophiomorpha rudis subichnofacies and aspects of the Cruziana ichnofacies. • An opportunistic Scolicia-Skolithos assemblage was interpreted to be superimposed upon a Zoophycos ichnofacies assemblage in the Herrera Sandstone Member. • The Cruse Formation contained similar ichnofacies elements as earlier formations (Ophiomorpha-twbidite association) along with ichnofabrics interpreted to be related to tempestite deposition within upper slope to distal offshore environments (recurrent Planolites ichnofabric). Aspects of the Cruziana and Skolithos ichnofacies were recognized in sandstones at Siparia Point. The Skolithos ichnofacies was interpreted for sandstones of the Manzanilla Formation at Point Paloma with Gyrolithes, Ophiomorpha, Skolithos, Thalassinoides, Arenicolites and Diplocraterion t « Transitions from the Cruziana to Skolithos ichnofacies in sands and silts of the Lower Morne L'Enfer Sandstone Member, while aspects of the Psilonichnus ichnofacies 293 IDEPOSITIONAL LITHOFACIES TRACE FOSSILS ENVIRONMENT CHARACTERISTIC TRACES 7. LATERALLY Sub-intertidal ACCRETED SANDS channels and tidal flats u ArenfcoHtes 6. AMALGAMATED Estuarine/ channel ^g) Astarosoma SIGMOIDAL CROSS abandonment- Confchmis/Borguerta STRATIFIED SANDS V marine incursion JT Cyllnddchnus 5. TROUGH CROSS Distributary Diplocraterion STRATIFIED SANDS w channels/ coastal Gyrolithes plain I d± Ophiomorpha 4.SWALEYCROSS Progradational o Palaeophycus STRATIFIED SANDS shoreface (middle- m Planolltes upper) 4^ % Psitonlchnus 3. GREY Distal prodelta or ^7*£*> <%>^ Rhizocoralttum BIOTURBATED SILTS lower shoreface Figure 5.14 Trace fossil summary chart for seven lithofacies in the Morne L'Enfer Formation. The fossil assemblage for the eighth lithofacies, transitional silts, is dependent on the bounding facies and so not included. Variations in trace diversity, intensity and trace identity can serve as a useful discriminator between lithofacies and depositional environments. ^^ . LITHOFACIES FOSSILS tOphbmorpha nodosa tThalasslnoides •Stofflhos tPtonolltos SWALEY *Dtetocraterian GROSS- *Other STRATIFIED unidentified SAND Lsggnd CO Scour UJ Wavy parallel laminae Parallel laminated Organic matter tThalasslnoldes Lenticular sands eStaffihos I Load cast *Planolites z 3Z «Tefch/chnus I Baser bedded tAmnicolites a Flame structures •CyflnaVfcftnus Contorted bed/laminae *Rosse#a in GREY *Asterosoma Symmetrical ripple BIOTURBATED tPsilonlchnus SILT Baft and pillow tPaleophycus Churned *Tembelllna tBengaueria s Current ripple *ef. Swaley crose-stratMcetion RNzocorallium Hummocky •fit s 'Ni, cnMtt-sUeUficstton DiDtocraterion MudrJast •Other Trough crass bad b>HTrough cross bed Dewaterlng pipes Figure 5.15 Composite stratigraphic section from Cedros Bay and Fullarton within the Lower Mome L'Enfer Sandstone Member, illustrating transition from archetypal Cruziona to Skolithos ichnofacies. Underlined trace fossils were found in equivalent lithofacies at Puerto Grande Bay. 295 Table 5.3 Summary of trace fossils found throughout the CenozoicTertiary stratigraphy of Trinidad. A) Trace fossils arranged according to dominant ethology. B) Trace fossil arranged according to most common orientation. Dwelling Feeding D.Fd 1 I i FORMATION OR MEMBER O CD SL CO fit Upper Mome CEnfer Sandstone Mbr Lower Mome L"Enfar Sandstone Mb* Cruse & Msnzanlta fwwm • • Herrera Sandstone Mbr DD DD D Nartva Formation Angostura Sandstone D D Pierre Potate Sandstone • Mbr Chaudlere Formation Acronyms (primary function listed first): H D- dwelling; F- feeding;E - escape; d- deposit feeding; s- suspension feeding; a- agrichnia. (a) NereMuNIke environments SKol/fnos-Uk* environment: Low sedimentation rale endlong <- _Vertically aggrading and/or eolonlzelton wlndew or rich nutrient thmng substrate*; agKeted supply at surface waters Various Vertical B m FORMATION OR \ ri^ l"5t !»3* liP i«* L MEMBER N. 'Upper' Mome UEnfer s. • •• • tower' Mome (."Enter Cruse & Manzanlfta • •••• Herrera Sandstone Mbij • a Native Formation • nan Angostura Sandstone D D • l(o) Pierre Pointe Sandstone! D" V Chaudlere Formation J Common to abundant; several specimens identified, M H Rare; one specimen Identified 1. Ichnogenus tentatively Identified based on ovenil • morphology; diagnostic criterion not preserved or obvious. 2. Specimen not ftisrtu. [Slsnaly Intervals only 296 occur in sands of the Upper Morne L'Enfer Sandstone Member. The Ophiomorpha rudis subichnofacies and Scolicia-Skolithos association represent short colonization windows in which opportunistic traces responded to local environmental factors such as episodic nutrient-supply and sedimentation. These groups contain low trace diversity and poorly developed fossil tiers and trace fossils are now preserved as epichnia or endichnia among turbidite beds. Within the Pierre Point Sandstone Member, they are represented by either Ophiomorpha, preserved within coarse-grained, thin-bedded turbidites, or by deposit feeders within silty drapes along the top of massive turbidites (e.g. Arenituba verso) (Figure 5.8). Ophiomorpha is a known opportunistic trace of thick-bedded turbidites, sometimes to the exclusion of other trace fossils (Uchman, 2001). Ophiomorpha also occurs in the Angostura Sandstone. The Paleodictyon subichnofacies suggests relatively longer colonization windows between episodic events, which allowed the development of more delicate and complex grazing habits (Seilacher, 2007) that were subsequently cast by the turbidites. This group is represented in the Pierre Point Sandstone Member by the ubiquitous Chondrites traces and the individual specimen of Paleodictyon. Both traces can be found among thin- bedded, fine-grained turbidites and interbedded shales which suggests a relatively stable and off-axis environment relative to the massive thick-bedded sands with horizontal grazing traces (opportunists) restricted to their top (Figure 5.8). Similar palaeo- ecological conditions may be represented in the Angostura Sandstone by forms such as Teichichnus and Rosselia that were tentatively identified among shaly or silty intervals indicating relatively slower sedimentation rates. In the Herrera Sandstone Member, an opportunistic colonizer is represented mainly by Scolicia, although other forms such as Arenicolites may form part of this group. Scolicia was the most common trace seen in the core and is another trace known to inhabit environments not amenable to others (Bromley and Asgaard, 1975; Colella and D'Alessandro, 1988; De Gibert and Goldring, 2007). The opportunistic trace fossil suite of the Herrera Sandstone was superimposed onto a Zoophycos ichnofacies habitat. The Zoophycos-Chondrites association is interpreted to represent "circalittoral" to bathyal quiet water, relatively anoxic conditions (Bromley and Ekdale, 1984; MacEachern et al., 2007) away from active turbidite deposition. This is supported in the Herrera Sandstone 297 Member by the recovery of abundant planktonic foraminifera in shale samples taken from Tarouba, far in excess of benthic forms (Chloe Younger, pers. comm.). The Skolithos- Scolicia trace assemblage is common to the Herrera Sandstones and is similar to the modern slope assemblage off of California where both trace fossils were recorded to water depths down to 250 m (Scott and Birdsall, 1978). Typical shallow-water ichnofacies (Cruziana, Skolithos and Psilonichnus) are better represented in the shallow-water, Pliocene assemblage (Manzanilla-Cruse and Morne L'Enfer formations) that represents the late stage of basin-fill. These trace fossil groups reflect a longer-term response to palaeo-environment conditions reflected in their higher diversity and established tiering relationships. 5.8.2 ICHNOFACIES AND DEPOSITIONAL MODELS The ichnofacies model initially proposed by Seilacher (1967) suggested a bathymetric dependence to trace fossil communities, a relationship later shown to be invalid if other variables are not considered (Frey et al., 1990, Ekdale, 1988). The current dataset has showed varied conformance to these established ichnofacies. There is good conformance to the shallow marine ichnofacies within the diverse shallow-water Pliocene assemblage (Figure 5.15). In particular, sediments of the Lower Morne L'Enfer Sandstone Member show good conformance to the Cruziana and Skolithos ichnofacies and good agreement with physical sedimentary structures as demonstrated by Pemberton et al. (1992c). More detailed studies may reveal similar results for the Manzanilla Formation at Point Paloma. The trace fossil assemblage of the Upper Morne L'Enfer Sandstone Member shows greater trace variety. These sediments were deposited within a variable delta setting with the interplay of wave, fluvial and tide processes, the last being dominant (Section 4.2). Some elements of the Skolithos, Cruziana and Psilonichnus ichnofacies can still be recognized as demonstrated by MacEachem et al., (2005) for deltaic deposits. Generally, the trace fossil assemblage, diversity and intensity within the Morne L'Enfer Formation successfully discriminate between the different environments (Figure 5.14) and support the shallow-water interpretation suggested by the physical sedimentary structures. 298 The Zoophycos ichnofacies was the only recognized archetypal ichnofacies among the low-diversity Early Cenozoic turbidite association. This ichnofacies was proposed for slope environments. Lithofacies and their associations also support a deep water palaeo-environment, but instead, suggest channel-lobe progradation within deeper, basin-floor settings (Section 3.4.5). It is proposed that the Zoophycos ichnofacies here reflects restricted, anoxic basin conditions and not only palaeobathymetry per se, and so was determined by localised environmental conditions. The lithofacies associations and successions of the Pointe-a-Pierre Formation suggest a slope origin; archetypal ichnofacies would therefore predict Zoophycos to proximal Nerites ichnofacies association (see Figure 5.2). The trace fossil assemblage instead, was similar to the modified subichnofacies classes (Seilacher, 1974; Uchman, 2001) that commonly occurred among proximal turbidite and slope successions with numerous dwelling and variably inclined forms (e.g. Hay ward, 1976; Crimes, 1977; Crimes et al., 1981; Buatois and Lopez Angriman, 1992; Shultz and Hubbard, 2005; Poursoltani et al., 2007). The Early Cenozoic trace fossil assemblages reflect localized environmental conditions as exemplified in the pre- and post-turbidite assemblages of these formations. 299 Chapter 6 - Provenance of Cretaceous to Pliocene Sandstones This chapter is divided into two parts. The first describes the rationale behind the classification used for this study and outlines the methodology employed for petrographic and heavy mineral analyses. This section ends with descriptive petrography and heavy mineral assemblages of the selected Cenozoic sandstones. The second part uses these mineral descriptions to provide interpretations of sandstone provenance with a review of potential sources. The summary discussion places the findings in a regional context and highlights the changing sedimentary sources, influence of tectonism on sedimentation and overall implications for the basin setting. 6.1 PART 1 - DESCRIPTIVE PETROGRAPHY OF CENOZOIC SANDSTONES 6.1.1 INTRODUCTION Quantitative modal analysis9 of sandstones using petrographic techniques provides a basis for classification and reveals provenance and sedimentological relationships that are not immediately obvious in outcrop-scale investigations. Classifications are derived from the recognition of similar mineralogical and textural attributes and serve as an additional basis for the subdivision and comparison of sandstones. This descriptive value is not only fundamental to any study, but also provides the foundation upon which genetic associations are made, and this is the focus of this chapter. 9 The "mode" is the "composition of rock expressed in terms of the relative amounts of minerals actually present" (Chayes, 1956, p. 1). A "modal analysis" refers to any procedure that estimates the mode, such as geochemical analysis or thin section point counts. 300 The use of mineralogy for this study stemmed from the need to distinguish between the various Cenozoic sandstones as their relative compositional and textural attributes and character of lithic grains serve as a guide to sandstone provenance. This information is intended to complement sedimentary processes and lithofacies (Section 2.3.4) and provides constraints the on relative sediment sources and transport directions. 6.1.2 RATIONALE FOR CLASSIFICATION SCHEME The sandstone classification used for this thesis was based on Pettijohn et al., (1972), the reasons for which are now given. The choice of a classification scheme for sandstones is not trivial as numerous have been proposed with significant differences in their defining criteria, class boundaries, mineralogical (or textural) end members and the role of the detrital matrix component (Klein, 1963). Classifications and nomenclature for sedimentary rocks are based on both mineralogical and textural attributes. Mineralogical attributes are the first-order controls because the relative amounts of Si02 and CaC03 serve to distinguish between the two major sedimentary rock types, carbonates and siliciclastics. Texture is concerned with grain size, shape, orientation, packing, sorting and percent of detrital clay fraction (Pettijohn, 1949; Griffiths, 1952; Folk, 1954; Bokman, 1955; Dunham, 1962). The mineralogical criterion considers the relative proportions of the major detrital framework grains, quartz, feldspar and lithic rock fragments and generally coincides with the "arenites", "arkoses" and "greywackes"10 respectively (Pettijohn, 1949). Other constituents such as heavy minerals are rarely considered (Okada, 1971). Some authors have argued for an explicit distinction between textural and mineralogical characteristics and instead encourage the use of descriptive modifiers or secondary diagrams for textural attributes (Folk, 1954; 1956; van Andel, 1958; Klein, "Wacke" or "greywacke" is a controversial term resulting from the placement of quantitative mineralogical boundaries on a textural-based term originally used for field descriptions. The controversy has been reviewed in detail by Dott, 1964 and in part by Klein, 1963, Dickinson, 1970 and texts such as Pettijohn et al., 1972, and Blatt et al., 1980. 301 1963; Pettijohn et al., 1972). The descriptive terms "coarse-grained quartz arenite" and "poorly-sorted, calcareous lithic wacke" serve as examples. An alternative opinion is that these are interdependent variables and should be represented equally on any classification scheme (e.g. Pettijohn, 1949, p. 227; Bokman, 1955). Proponents of the latter recognize that quartz-rich sandstones tend to show increasing textural maturity and vice versa, while opponents recognize the numerous exceptions to this general trend resulting largely from the greater influence of depositional environments (i.e. degree of sediment reworking) on texture than on mineralogical composition (Folk, 1954; 1956); the latter is more a function of sediment source and chemical weathering (Van Andel, 1958; Harrell and Blatt, 1978). The disagreement partly surrounds the role of detrital clay as an indicator of the relative "maturity" of sandstones. Those who prefer the distinction betweent textural and mineralogical attributes neglect detrital clay as a primary consideration on the basis that its occurrence depends as much on the initial mineralogy (source characteristics) as on secondary modifications specific to individual depositional environments (Folk, 1954; 1956; Van Andel, 1958). This is compounded by difficulties in confidently differentiating between detrital and authigenic matrix in thin sections (Dickinson, 1970). Opposing views include clay as an end-member to classification schemes on the basis that it was a significant mineralogical component at deposition ("fluidity index" of Pettijohn, 1954) and according to Bokman (1955), its relative stability in "undisturbed" environments. The choice of a classification scheme for this study was influenced by the considerations outlined above and by the objective to discern provenance relationships. While the descriptive aspect was needed to differentiate between the Cenozoic sandstones, the aim was to deduce mineralogical differences that may point either to specific source areas or relative changes in sources. Textural maturity was a secondary objective only because it is dependent on many other variables. After reviewing several classification schemes (Folk, 1954; Bokman, 1955; McBride; 1963; Klein, 1963; Dott, 1964; Okada, 1971; Folk, 1974) it was decided to follow that of Pettijohn et al. (1972), modified after Dott (1964) (Figure 6.1). Their classification firstly emphasizes the mineralogical composition of detrital grains and secondly, the textural maturity of the 302 sandstone. The mineralogical-based classification depends on the modal composition of the three major sandstone constituents: quartz, feldspar and lithic grains while the textural Figure 6.1. The sandstone classification scheme of Pettijohn et al. (1972) forms the basic nomenclature followed throughout this thesis. Further details are given in text. After Figure 5-3, Pettijohn etal. (1972). maturity depends on the relative amount of detrital matrix within the sample. Pettijohn et al. (1972) divide sandstones into the following groups based on their modal composition (Figure 6.1): Arenites - sands with less than 15% matrix. Quartz arenite - less than 5% matrix and no more than 5% feldspar or rock particles. Arkosic arenite - sands with less than 5% matrix and more than 25% feldspar; feldspar exceeds rock fragments. Lithic arenite (or litharenite) - less than 5% matrix and more than 25% rock fragments; rock fragments exceed feldspar. 303 Subarkose - less than 5% matrix and between 5-25% feldspar; feldspar exceeds rock fragments. Sublitharenite - less than 5% matrix and between 2-25% rock fragments; rock fragments exceeds feldspar. Their classification further differentiates between the "arenites" and "wackes" on a secondary plot, based on the percentage of detrital matrix, for which a division at 15% was proposed. Sandstones with less than 15% detrital matrix are classified as "arenites" while those with 15% or more are classified as "wackes". The "wackes" are divided into quartzwacke, feldspathic wacke and lithic wacke, based on their collective matrix percentage and modal detrital mineralogy. The classification of Pettijohn et al. (1972) is preferred for the following reasons: 1. The inclusion of chert grains together with lithic rock fragments varies from other widely used classifications (e.g. Folk, 1954). This was useful, as a confident distinction could not always be made between chert and other polycrystalline quartz fragments of metamorphic origin (phyllite and schist), as experienced by previous workers (Dickinson, 1970; Folk, 1974; Dickinson, 1985). It was therefore preferred that these rock fragments be grouped. Such a grouping is reasonable when the genetic implications are considered. Chert fragments within sandstone are as much an indicator of sedimentary sources as phyllites are of metamorphic rocks and this provenance distinction is lost when it is counted together with quartz. In addition, the separation of chert from the "stable" quartz pole on ternary diagrams can be justified as chert has been shown to be an unstable mineral relative to monocrystalline quartz apparently due to its lesser resistance to chemical weathering (Klein, 1963; Okada, 1971; Folk 1974; Harrell and Blatt, 1978). A similar separation of chert from the quartz pole was adopted by van Andel (1958), Folk (1974) and Fuchtbauer (1974). 2. The chosen tripartite mineralogical end-members are consistent with commonly used methods for provenance determination (e.g. Dickinson and Suczek, 1979; Dickinson, 1985), and also facilitate comparisons with van Andel's (1958) study across northern South America that is relevant to this thesis. Both are discussed in greater detail below. 304 3. The secondary distinction between arenites and wackes provides an additional discriminator between the Cenozoic sandstones (Figure 6.1). Some inferences can be made about likely causes for changing proportions of interstitial clay within the sandstones, as the lithofacies associations and depositional processes are very similar throughout most of the study interval, with minimal post-depositional winnowing of fines. The assumption is made that the detrital clay fraction in these samples reflects the lithology at source (including intra-basinal sources). 6.1.3 MODAL DETRITAL FRAMEWORK AND PROVENANCE RELATIONSHIPS One of the principal objectives of this investigation was to discern the genetic relationships between the Cenozoic sandstones and their sources. One method to accomplish this was the use of the modal detrital framework of sandstones as a guide to their initial tectonic setting. The method is based on the principle that regional-scale tectonics is a primary control on sandstone composition. The method arose from actualistic models during the 1970-80's (Crook, 1974; Ingersoll and Suczek, 1979; Dickinson and Suczek, 1979; Dickinson et al., 1979; Dickinson, 1985) in which ternary plots were used to represent combinations of detrital minerals, which were subsequently grouped. Three principal sediment sources were distinguished by these models: (1) stable and uplifted continental blocks, (2) magmatic arcs and (3) recycled orogens. These sources were discriminated initially using mean values of framework detrital constituents from 88 sand and sandstone suites from known tectonic settings (Dickinson and Suczek, 1979). Data from similar basin settings formed clusters on the ternary plot and provided the basis for the subdivisions into the respective source areas (Figure 6.2). Based on actualistic studies from both modern and ancient sandstones, the relative proportions of the framework minerals show an apparent consistency depending on second-order provenance controls dictated by plate tectonics (Crook, 1974; Dickinson and Suczek, 1979; Ingersoll, 1990; Dickinson, 1985). Feldspar-rich sandstones (arkoses) are derived from areas where plutonic and gneissic basement rocks were exposed and eroded, such as is typical of stable and uplifted cratonic areas ("basement uplift" and 305 "transitional continental" of Figure 6.2). This can be transitional to quartz arenites in which less stable feldspar is gradually eliminated from the sedimentary cycle. In Provenance categories Recycled orogen Craton Magmatic arc interior Craton Continental block interior Quartzose recycled Transitional continental Transitional recycled Basement uplift Lithic recycled PROVENANCETYPE TECTONIC SETTING DERIVATIVE SAND COMPOSITION 1. Continental block Continental Interior or Quartzose sand (Qt-rich) with high Qm/Qp and K/P ratios (Stable craton Interior) passive margin 2. Continental block Rift shoulder or transform QuartzofeMspathic (Qm-F) sands low in Lt with Qm/F and K/P (Basement uplift) rupture ratios similar to bedrock 3. Magmatic arc Island arc or continental Feldspatholilic (F-L) volcaniclastic sands with high P/K and Lv/Ls arc ratios grading to quartzofeldspathic (Qm-F) batholith-derived sands 4. Recylced orogen Subduction complex or Quartzolithic (Qt-Lt) sands low in F and Lv with variable Qm/Qp fold-thrust belt and Qp/Ls ratios Figure 6.2 Provenance domains discerned from modal detrital frameworkanalysi s of sandstones. The two ternary diagrams emphasize (A) compositional maturity and (B) types of source rock. The dashed lines in (B) encircle the position of initial data points (modal averages) upon which the provenance domains were based ('a', continental block; 'b', magmatic arc and 'c', recycled orogen). The table summarizes the characteristic sandstone compositions and tectonic setting for each domain. Qt = total quartz, Qm = monocrystalline quartz, Qp = polycrystalline quartz, F = feldspar, L = lithics, Lt = total lithics (includes polycrystalline quartz), Lv = volcanic lithics, Ls = sedimentary and metasedimentary lithics. All modified after Dickinson, 1985, Figures 1,2 and Table 2. 306 addition, quartz arenites may be derived directly from sources enriched in quartz either from weathering (e.g. Johnsson et al., 1988) of labile minerals following transport to an alluvial plain, or as a result of sediment recycling, typical of stable "craton interior" domains flanked by passive continental margins (Crook, 1974). Lithic arenites or wackes derived from magmatic arc settings are typically rich in volcanic detritus ("undissected arc") with variable amounts of plutonic lithic fragments from erosion of deep-seated plutons ("dissected arc"); these are typically poor in quartz. Recycled orogenic sources are the most variable as the source composition is dependent on the rocks being deformed. They tend however to be consistently poor in feldspar (e.g. van Andel, 1958), and their lithic proportion varies from quartz-rich sublitharenites to lithic wackes. Valloni (1985) showed that the relative ratios of lithic fragments may be an even better discriminator of these relative provenance domains. There are several variations to these idealized mineralogical associations and limitations to the inferences that can be drawn. Although it is argued that source mineralogy is an overriding control on the eventual mineralogy of sedimentary basins (e.g. van Andel, 1958), secondary modifications such as weathering, abrasion, sediment recycling and mixing that occur between the erosion at source and the eventual deposition, can drastically affect the composition of sandstones and lead to misleading plots on provenance diagrams. For example, extensive wave reworking of shoreface sandstones can lead to quartz enrichment relative to labile fragments, which will result in samples plotting within the craton interior field of Dickinson and Suczek (1979), regardless of the initial provenance (Mack, 1984). The same is true for post-depositional diagenetic dissolution and compaction in which feldspars, carbonates and argillaceous fragments are particularly vulnerable (McBride, 1985). Similarly, extensive stable cratons may incorporate river systems that traverse numerous rock types and drainage basins promoting compositional mixing and a dilution of original compositional signatures (Dickinson and Valloni, 1980). Mack (1984) drew attention to plate tectonic settings that were unrecognized within the compositional diagrams of Dickinson and Suczek (1979), including transitional episodes. He cited examples of Palaeozoic sandstones in Alabama and Quebec sourced from arc-continent collision tectonic settings that were not correctly represented by the provenance fields. Similarly, citing sediments 307 form the Barbados Accretionary prism, Velbel (1985) drew attention to complex depositional and post-depositional sediment transfers from initial source domains tectonically unrelated to their site of deposition and in which the genetic tectonic- sedimentary link is lost. Another limitation to the provenance plots is inherent in their derivation where carbonate fragments are not considered. These may form a significant percentage of the lithic component (e.g. Critelli et al., 2007; Stefani et al, 2007) and their exclusion will lead to erroneous representation on the plots (Mack, 1984), although this has been partly addressed by modified ternary plots that consider both intra- and extra- basinal carbonate lithic fragments (Zuffa, 1985; 1987). Ternary plots are still widely used for provenance analysis with other geochemical and mineralogical methods (Arribas et al, 2007 and references therein), and the provenance fields of Dickinson and Suczek (1979) are largely unchanged (e.g. Ochoa et al., 2007; James et al., 2007). Their usage was endorsed even after multivariate statistical testing incorporating additional data points, although it was recommended that future studies include all compositional variables (Qm, Qp, F, P, K, Lt, Lv, Ls) to discriminate between fields as opposed to the three variables imposed by the usage of ternary plots (Weltje, 2006). 6.1.4 HEAVY MINERAL COMPOSITION AND PROVENANCE RELATIONSHIPS "Heavy minerals" as used in sedimentary petrology refers to detrital mineral grains found in modern and ancient sands and sandstones with specific gravities greater than those of the major framework constituents (Morton, 1985). Mange and Wright (2007) define these as mineral densities above 2.8 g/cm3. Approximately 50 translucent minerals are commonly encountered in routine heavy mineral analyses (Mange and Maurer, 1992; Garzanti and Ando, 2007a). Most of these are initially formed in igneous and metamorphic 'parent' rocks where they may have been part of the rock-forming framework, then subsequently eroded, transported and incorporated into the sedimentary cycle. They may have been abundant in their initial environment but usually approximate to 1% in detrital elastics (Morton, 1985; Mange and Maurer, 1992). 308 The utility of heavy minerals for sedimentary provenance lies in the diagnostic properties of individual minerals or mineral associations that can be traced directly to specific igneous and metamorphic sources or basin-scale tectonic domains. Rare and diagnostic mineral species found within the heavy mineral fraction can potentially provide the only remaining link to the sediment source. The method has been widely applied to the study of sedimentary provenance and sediment transport pathways (e.g. Valloni et al, 1991; Garzanti and Ando, 2007a; 2007b) including sediments to the north of Venezuela and along the coastal margins of Trinidad and Guyana (van Andel and Postma, 1954; Nota, 1958; Morton and Johnsson, 1993). The method has also found utility in the correlation of subsurface sandstones, assessing the effects of erosion and deposition along modern shorelines, and locating economic placer deposits (e.g. Morton and Hurst, 1995; Frihy, 2007). The analysis of heavy minerals for sedimentary provenance is based on the assumption that individual minerals and mineral associations are a reflection of the mineral composition of their source rocks and, as with the major framework constituents (quartz and feldspar), these can be determined by regional tectonic controls (Nechaev and Isphording, 1993; Garzanti and Ando, 2007a; 2007b). Their advantage over the lighter detrital fraction is the greater diversity of mineral species, some of which are diagnostic of a limited range of source rocks. Yet, this basic assumption is limited by several factors that can alter, disguise or even invalidate this genetic relationship. These involve the loss of mineralogical species as a result of chemical weathering, mechanical abrasion, hydraulic sorting or burial diagenesis, all of which affect mineral species at varying rates and ultimately determine their concentration in the sediment (Table 6.1). Dissolution will alter the diversity of a heavy mineral suite at the final site of deposition and can potentially destroy any provenance information (e.g. Valloni et al, 1991; Van Loon and Mange, 2007). It is a function of mineral chemistry, soil acidity, sediment permeability, temperature and time (Pettijohn, 1941; Nickel, 1973) and is controlled by both climate and relief (Picard and McBride, 2007; Johnsson, 1990). The relative susceptibility of heavy minerals to chemical dissolution and alteration during exposure and burial diagenesis was determined by laboratory analysis (Nickel, 1973), and subsurface and field investigations (e.g. Morton, 1979; 1985; Lang, 2000; Walderhaug 309 Table 6.1 Idealized sedimentary cycle showing different mechanisms that can alter the ratio of mineral species from the parent rock to the daughter sediments (Bateman and Catt, 2007). PHASES MODIFYING ELEMENTS A. Pre-erosional phase 1. Pedochemical weathering, at source 2. Hydraulic sorting B. In-transit phase 3. Mechanical weathering 4. Pedochemical weathering, at sink C. Post-depositional, pre-burial phase 5. Authigenic growth 6. Geochemical weathering D. Post-burial phase 7. Authigenic growth 8. Pedochemical weathering, at (re)exposure E. Exhumation phase 9. Authigenic growth 10. Anthropogenic addition and Porten, 2007). The importance in accounting for possible dissolution effects is reinforced by the trend of reduced diversity and lower proportions of heavy minerals in older sandstones (Pettijohn, 1941; Hubert, 1962; Morton and Hallsworth, 1994; Garzanti and Ando, 2007a). The relative stability of minerals to dissolution is shown in Table 6.2. Hydraulic sorting of heavy minerals is a function of depositional environment, grain size, grain density, relative settling velocity and grain-entrainment potential (Rubey, 1933; Reid et al., 1985; Komar, 2007). Komar (2007) provided a review of past studies and summarized the current knowledge and theory behind hydraulic mineral sorting. In general, there is a tendency for minerals of lower density and larger grain size (e.g. quartz, augite, epidote, hornblende) to be preferentially removed by waves and currents because of the greater effectiveness of lift forces to entrain them. As a result, these are also preferentially moved to offshore environments. The effectiveness of this process is known from studies of modern nearshore sands (see references in Reid et al., 1985; Frihy 2007). Hydraulic sorting results in a complex distribution of minerals that shows a strong dependence on quartz grain size (Rubey, 1933). Unlike chemical weathering, it may not alter the diversity of minerals within a population, although mineral species can be missed if this effect is not considered while sampling. Studies involving modern sediments have demonstrated the local variations that can occur among 310 mineral species and are attributed to hydraulic sorting (van Andel and Postma, 1954; Frihy, 2007; Garzanti and Ando, 2007a). Mechanical abrasion does not appear to cause significant variations in heavy mineral abundance relative to that of chemical dissolution and hydraulic sorting (Morton, 1985; Morton and Hallsworth, 1999; Bateman and Cart, 2007), as was once believed (Rubey, 1933). 6.1.5 MODERN APPROACH TO HEAVY MINERAL ANALYSIS The common theme in fundamental texts and publications on the use of heavy minerals to discern sandstone provenance is the potential effect of hydraulic sorting and chemical dissolution on grain concentrations (Morton, 1985; Morton and Hallsworth, 1994; 1999; Mange and Wright, 2007). The recognition of these effects was one of the reasons for a decline in the popularity of the method during the middle of the 20th century (Mange and Wright, 2007). The continued use and resurrection of the method was encouraged by a better understanding of these limitations, coupled with more comprehensive analysis and measures to limit the inherent shortcomings. A popular approach is the use of various mineral indices to better gauge the effect of dissolution and sediment sorting on a sample (e.g. Hubert, 1962; Morton and Hallsworth, 1994; 1999; Garzanti and Ando, 2007a; 2007b). They are based on the assumption that dissolution and sorting can be discerned by comparing minerals of similar chemical stability and density respectively. These minerals are expected to be similarly affected by those processes and their varying proportions are likely to be provenance-related. The zircon-tourmaline-rutile (ZTR) (Hubert, 1962), heavy mineral concentration (HMC), and modified low-grade and high-grade metamorphic (LgM-HgM) (Garzanti and Ando, 2007a; 2007b) indices will be used for this thesis. The ZTR index is the percentage of zircon, tourmaline and rutile among the transparent, non-micaceous heavy minerals. It gives an idea of the relative concentration of ultrastable heavy minerals, which indicates mineral recycling, and maturity of composition. The HMC index is the abundance of all heavy minerals within the fine- to very fine-grained sand portion and 311 Table 6.2 Relative stability of non-opaque heavy minerals in weathering profiles. Stability decreases downward from the top of the table. After Morton and Hallsworth 1999, Table 1 Gneiss, Dolerite, Tertiary kaolinitic Calcareous Amphibolite Crystalline schist Granite sand Bavarian molasse sandstones Aeolian coversands Northern USA Northern USA Germany Germany Germany Germany England Dryden and Dryden Weyl and Werner Goldich (1938) (1946) Piller (1951) (1951) Grimm (1973) Lemke et al. (1953) Bateman and Catt (1985) Zircon, Rutile, Zircon, Rutile, Tourmaline, Tourmaline, Andalusite, Kyanite, Staurolite, Zircon Zircon Zircon, Rutile Staurolite Titanite Tourmaline, Tourmaline Andalusite, Kyanite Sillimanite Monazite Kyanite Kyanite Kyanite, Epidote Calcic amphibole Calcic amphibole Staurolite Staurolite Staurolite Epidote Epidote Apatite Garnet Garnet Garnet Garnet Garnet, Apatite Garnet Garnet Calcic amphibole Calcic amphibole Calcic amphibole Epidote Clinopyroxene Clinopyroxene Clinopyroxene Clinopyroxene Olivine Orthopyroxene Calcic amphibole Apatite Apatite Olivine weighted average densities of total framework and total dense grains, expressed as a ratio. The underlying principle is that different sources can be associated with low and high heavy mineral concentrations (e.g. chert or limestone versus ultramafic sources). The LgM and HgM indices differentiate between these potential sources and are based on the grouping of diagnostic minerals. The modifications to this index are described below. A second mechanism to counteract the effects of dissolution and mineral sorting is the varietal approach to heavy mineral analysis where provenance is discerned from the physical and chemical variations of individual species (Morton, 1991; Lihou and Mange- Rajetzky, 1996; Morton and Hallsworth, 1999; Mange and Morton, 2007). This approach eliminates the constraints imposed by dissolution and sorting as only one mineral species is involved. 6.1.6 SAMPLE COLLECTION AND PREPARATION A total of 222 rock samples were collected from outcrops and cores both within the primary study interval (Paleocene to Pliocene) and adjacent epochs (Cretaceous) and correlative sandstones (Scotland Formation of Barbados). Of the total samples, 159 were sands and sandstones, 40 mudstones and silts, 8 calcareous mudstones and biohermal limestones, 8 conglomerate clasts, 5 metamorphosed slates and mica-schists, one lignitic and one was a volcanic sample. Of the sandstone samples, 55 were from core plugs intended for apatite fission track analysis. The metamorphic and volcanic samples were intended to examine potential source terrains. A total of 94 thin sections were prepared for optical analysis within the Department of Earth Sciences, Dalhousie University at a standard thickness of 30 um. Most of the samples were stained with a blue dye incorporated within the epoxy in order to enhance pore spaces. The thin section cover slip was then glued using Canada balsam. Quantitative mineralogical data were obtained from point counts using Leitz polarizing microscope with lOx oculars and up to 50x objectives. A total of 350-450 (mostly 400) counts were made on each thin section using a Frantz mechanical stage counter attached to the microscope. An assignment to pre-defined categories was made 313 based on what lies below the cross hairs of the microscope with each increment of the stage counter. The Gazzi-Dickinson method of grain counts (Dickinson, 1970; Ingersoll et al., 1984) was employed for these samples. This involved the assignment of sand-sized grains (> 63 um) to their mineral species (e.g. quartz, feldspar, muscovite) as opposed to a lithic category (e.g. metamorphic rock fragment). Aggregates less than 63 um were assigned to its lithic category, when discernible. This method is best suited for comparing samples of different grain sizes based on the assumption that larger grains and mineral aggregates are eventually reduced to smaller grain sizes and individual mineral components during sediment transport and abrasion. For example, sands removed from a granitic source will eventually be represented by individual quartz and feldspar minerals, with little or no plutonic fragments to represent the original source. A grain count of both a coarse, lithic-rich fraction and a fine-grained fraction of that sandstone using the Gazzi- Dickinson method should theoretically produce very similar statistical results. Yet the loss of direct information from the lithic fraction is a major disadvantage of this method. Within all samples counted, the lithic fraction was represented although an underestimation was unavoidable. This information was also captured by qualitative thin section descriptions. The different categories that were chosen for point counts were guided by both the recommendations of previous workers (Dickinson, 1970) and constraints placed on differentiating between different grain categories. The categories are listed in Appendix 9. 6.1.7 HEAVY MINERAL SEPARATES Twenty-five heavy mineral separates were made from the sample set described above. Four of the samples are from the Eocene Scotland Formation in Barbados11 while the remainder was derived from Paleocene to Pliocene sands and sandstones in Trinidad. For 24 of those separates, 120 g of the sample were disaggregated using a ceramic mortar Samples from Barbados were also reviewed because of correlations to Trinidad sandstones and the likelihood for similar provenance. 314 and pestle. No chemical treatment was applied during this process. Samples were then wet-sieved in distilled water into four grain size categories: (1) >1 mm, very coarse sand, (2) 0.25-1 mm, coarse to medium sand, (3) 0.0625 mm-0.25 mm, fine to very fine sand (4)<0.0625 mm, silt and clay. Only a small percentage of the silt and clay-sized fraction was retained from a few samples to allow mineralogical comparison to coarser fractions. Each separate was then oven dried with low heat (60°C) for 12-16 hours and the weight of each dried fraction obtained to the nearest milligram. Differences from the initial sample weight were assigned to loss of the silt and clay-size fraction. The grain size distribution of the heavy mineral samples is shown in relative weight percent in Appendix 10. The 0.0625 mm - 0.25 mm sand fraction (fine to very fine) was chosen for gravity separation as this falls within the recommended range likely to contain a greater percentage and diversity of heavy minerals (Y. Kettanah, pers. comm.; Morton, 1985). The mineral separation procedure was guided by Mange and Maurer (1992). Magnetic grains were first removed from the samples (these were very sparse overall) prior to gravity separation using sodium polytungstate at 2.89 g/cm3 (Callahan, 1987; Mange and Maurer, 1992). The washed and oven-dried samples were then weighed, inclusive of any magnetite minerals previously removed. Optical thin sections were made from separated grains mounted in Canada balsam and a few were selected for polished thin sections for microprobe analysis. One of the samples was originally intended for apatite fission track analysis and underwent a different separation procedure (sample BD-2 from the Scotland Formation). Disaggregation using a jawcrusher and disc-mill was followed by Wilfley table density separation, sieving to 0.25 mm and liquid fractionation as described above. The sample was then magnetically separated and these portions were rejoined to produce the thin section grain mount in Canada balsam. The grain counting was guided by Mange and Maurer (1992). At least 300 grain counts per sample were carried out using an optical microscope and mechanical point- counter using the line counting method. Muscovite and biotite were not included in the counts as their platy habit results in loss of grains during separation. Chlorite is also excluded from grain counts in general practice, but was included here as their sudden appearance and abundance was significant for provenance determinations; it is likely that 315 the counts will underestimate their abundance. The entire slide was examined for minerals that may have been missed during the counts and these were classified as "accessories". The identification of minerals was guided by standard texts (Kerr and Rogers, 1977; MacKenzie and Guilford, 1980; Mange and Maurer, 1992; Nesse, 2004; Perkins and Henke, 2004) and the assistance of Dr. Y. Kettanah, adjunct professor of the Department of Earth Sciences at Dalhousie and an experienced mineralogist. 6.1.8 SAMPLING CONSTRAINTS Efforts were made to collect geographically spaced samples representative of different grain sizes and lithofacies within each formation. This was accomplished with varying success. The sandstones of the Chaudiere Formation are restricted to the vicinity of Mt. Harris in the eastern Central Range. Sandstones display relatively homogenous grain size and bedding characteristics and were all attributed to one lithofacies (Section 2.2.3.1). Based on this homogeneity, the samples described herein are considered representative. Samples from the Eocene Pointe-a-Pierre Formation are geographically spaced and representative of all grain sizes and lithofacies. Samples were also derived from both friable and consolidated outcrops. In contrast, exposures within the San Fernando Formation are few and disjointed with a wide range of rock types and lithofacies. Only a few samples were collected from both in-situ and dislodged rocks derived from type locations. Additional sampling may be warranted in the future. Samples from the Angostura Sandstone were all derived from subsurface core depths ranging from 4667 ft to 5432 ft and limited to the coarse and medium grain size. This was the most common grain size of the rocks examined. Samples from the Oligocene Nariva Formation were derived from both outcrop and subsurface core at geographically dispersed localities. They represent all grain sizes, the range of lithofacies and rocks at various stages of weathering. Herrera sandstones were similarly derived from both outcrop and subsurface core (9700-10350 ft) and represent the range of grain sizes. All samples were well consolidated but showed varying stages of oxidation. 316 Late Miocene to Pliocene samples were collected from variably consolidated outcrops along coastal sections, and ranged from granule-sized to mainly fine-grained. The additional samples collected from Cretaceous rocks were intentionally limited, as these were outside the main scope of the project and provided data to constrain earlier compositional trends. Overall, the samples are regarded as adequate when considering the regional objectives and the constraints imposed by time and outcrop accessibility. As will be shown below, they indicate first- and second-order compositional and textural variations that can serve as a guideline for additional sampling in the future. 6.1.9 PREVIOUS PETROGRAPHIC AND HEAVY MINERAL STUDIES IN THE SOUTHEASTERN CARIBBEAN There are few published studies on the modal detrital framework and heavy mineral composition on the Cenozoic sandstones of Trinidad, although it is apparent that a larger collection exists within the archives of oil companies (e.g. Patterson, 1991). Much of the earlier contributions were by J.E. Griffiths and although most of his work on the Cenozoic stratigraphy remained unpublished, it is commonly referenced by others. For framework detrital grains, Griffith's work demonstrated the immature, "sub- grey wacke" character of much of the sands and sandstones, and a tendency for decreasing compositional maturity in younger stratigraphic intervals (Griffiths, 1950 referenced in Suter, 1960, p. 47). Similar maturity and trends were recognized by later workers (Algar, 1998; Punch, 2004). Dickinson plots have previously been applied to discern provenance although workers questioned the validity of results produced by the method (harry, 1992; Punch, 2004). Punch (2004) noted the inability of that method to adequately discern between cratonic and recycled orogenic sources for her study of Eocene sandstones, for which she suggested a cratonic source along continental South America. Harry (a992) deduced both a "high quartzose" and "moderate to quartz-rich, orogenic source" for Pliocene sands of the Moruga Formation but also noted "anomalously" plotting points on his Dickinson plots. A similar continental source for Mesozoic and Cenozoic sediments was proposed by Patterson (1991) and common recycling of sediments was suggested. 317 Algar (1993) also proposed a similar source for Mesozoic Northern Range sediments although quantitative petrography was not used. Van Andel's (1958) comprehensive work on Cretaceous to Eocene sandstones of western Venezuela involved over 2000 samples from which he recognized arkoses, mature quartz arenites, sublitharenites and "sub-greywackes". He demonstrated an apparently systematic change in the occurrence and distribution of these various suites involving decreasing feldspar content and increasing to decreasing compositional maturity throughout the Cretaceous to Eocene. The demonstrated trends are very similar to trends that will be described below. Eocene to Oligocene (Senn, 1940; Speed, 1985), mature to sub-mature quartz wackes and arenites with very little feldspar are also known from Barbados, and inferred to originate from metamorphic rocks within the South American craton (Matley, 1932; Senn, 1940; Pudsey, 1985; Speed, 1985; Velbel, 1980; Pudsey and Reading, 1982; Punch, 2004). This differs from the Late Eocene arc-derived deepwater sandstones of the Tufton Hall Formation of Grenada to the west of Barbados, where volcanic rock fragments dominate the lithic component (Saunders et al., 1985). A few studies on modern sands are worth mentioning. The tectonic and climatic control on sediment composition was investigated in modern rivers along the northern Andes and adjacent foreland basins (Barinas-Apure drainage basins), where the increasing maturity of sediments away from the mountain front was demonstrated, and the various reasons for this discussed (Johnsson et al., 1988; Stallard et al., 1990). Potter (1994) included the Orinoco River drainage basin and northern South American margin as part of his continental study of modern sands. His, and the other studies referenced, highlight the strong imprint of Andean tectonics on sediment composition and the subsequent partial removal of this imprint by chemical weathering. One of the early uses of heavy minerals in Trinidadian sandstones was for the differentiation of units with identical lithofacies attributes that complicated correlations. The best example is the distinction between sandstones of the Eocene Pointe-a-Pierre and Oligocene Nariva formations, the latter with a more diverse heavy mineral assemblage (Illing, 1928). The first known attempt at a stratigraphic correlation of Trinidad sandstones using heavy minerals was that of J. E. Griffiths (Appendix 11). In general, 318 relatively stable minerals dominate the Cretaceous to Eocene rocks of the Northern and Central Ranges (zircon, illmenite, rutile, tourmaline) while a more diverse assemblage (hornblende, staurolite, garnets, glaucophane, kyanite and others) occurs in the younger sandstones (Illing, 1928; Griffiths, referenced in Suter, 1960). Suter (1960, pg. 274) surmised, based on heavy minerals, both a "local" and "granitic" source for Oligocene and older sandstones, and a metamorphic source for the younger sandstones, with mineral reworking being common12. Kugler (2001, p. 60) cited Griffiths who inferred a reworked heavy mineral source and an additional glaucophane-garnet-staurolite source for "Miocene" sandstones. Harry (1992) noted the moderate compositional maturity of heavy minerals and also concluded mixed igneous and low- to medium-grade metamorphic sources for Pliocene sediments. He noted the occurrence of garnet, staurolite, zircon, chloritoid and rutile among other minerals in those sands. A comprehensive investigation of both the heavy and light mineral fractions was carried out in the modern sediments of the Gulf of Paria and its surrounding lowlands (van Andel and Postma, 1954). The modern sediments in the Gulf of Paria were derived from multiple sources including the first and second cycle "orthoquartzites" (Q<85,F<8,L<5 + chert, glauconite and micaceous clays) from the Orinoco Delta, to "greywackes" (Q6o- 2o,F<5,L 12 The metamorphic source is stated for "Trinidad sands" in "general" but discussed under "Pliocene". The actual timing of relative sediment contribution is unclear. 319 Heavy mineral and modal detrital framework analyses have been applied with varying success to the Trinidad stratigraphy. On the positive side, the work of van Andel and Postma (1954) convincingly demonstrated the utility of heavy minerals for discerning modern provenance domains in the Trinidad area, while the published references to J.C. Griffith's work and the notes of Illing (1928) also suggest a similar utility for ancient sediments. The heavy mineral results of J. C. Griffiths still remain largely inaccessible, which inhibits its utility for provenance studies; although his listing of minerals by stratigraphic ages (Suter, 1960) is invaluable, ages and formation units have since been modified and it is not obvious which individual sandstones are being referred to13. References to ancient strata by Illing (1928) and van Andel and Postma (1954) are subject to the same limitation. Regarding quantitative detrital framework, important trends were apparent from the results of different workers that suggested significant changes in the provenance of ancient sandstones. Somewhat disadvantageous however, the value of actualistic models such as Dickinson plots have been questioned as an effective method for discerning provenance domains. Heavy mineral studies were included in this study to resolve the mineralogical character of individual sandstones that were not obvious from past investigations. This study also reviews sandstones not known to previous workers (e.g. Angostura Sandstone) and provides a critical review of the effects of chemical dissolution on mineral assemblages, as demanded by modern investigations (Mange and Wright, 2007). Dickinson plots are still widely used for provenance studies; an assessment of a wider stratigraphic interval may help to resolve the anomalies associated with previous applications and serve as an independent assessment of the method. Importantly, these petrological methods (heavy minerals and modal detrital framework) complemented the wider approach adopted for this study and provided an independent assessment of overall basin settings, likely sediment transport pathways and textural and compositional sediment changes that could later be integrated with the sedimentary processes, facies and facies successions derived from outcrop sections. 13 Griffiths (1951) included Upper Morne L'Enfer to Lengua sediments (Late Miocene to Late Pliocene) as "Miocene", and Nariva and Herrera sediments (Late Oligocene to Middle Miocene) as "Oligocene"; it is uncertain whether the table referred to used a similar stratigraphy. 320 The following sections describe the mineralogy of Trinidad Cenozoic sediments. The descriptions are intended to highlight compositional variety and proportions as a guide to classifications and sedimentary provenance as described above. These are accompanied by a qualitative description of textural attributes such as grain sorting, shape and roundness, general descriptions of the quartz extinction patterns, and finally, a general description of diagenetic properties as a constraint on the pre-weathered sediment composition. A collective description will be put forward for each formation in turn, where it was felt that the compositional and textural attributes were sufficiently homogeneous (e.g. Pointe-a-Pierre Formation). For these, further details for individual sections can be reviewed in Appendix 12. Individual thin sections are described for heterogeneous formations or where there were few samples. A summary of the compositional and textural variations between sandstones is provided at the end of this section and this will in part form the basis for the provenance determinations that follow. Cenozoic sandstones include quartz arenites, sublitharenites and lithic arenites. If the matrix-cement component is considered, these can be further divided into quartz and lithic wackes. A wider range of sandstones that includes quartz arenites, sublitharenites, arkosic arenites and subarkoses are known from the Cretaceous (Figures 6.3 and 6.4). 6.1.10 CHAUDIERE FORMATION Number of samples: 5 Sample locations: All samples are from "Growing Rock", along Cunapo Southern Road where a roadside boulder (-3-4 m) forms an excellent marker (see Figure 2.1 for location). Number of thin sections: 2 (samples HV5043 and HV5044) Thin section locations: Both samples were taken from thick-bedded sandstones 100 and 150 m west of large (~18 m) outcrop face located east from the roadway (i.e. uphill). HV3043 was derived from the crest of the hill in that location. General outcrop description: see Section 2.2.3. 321 Hand specimen description: Granule-sized to fine-grained poorly sorted sandstone within a fine sandy or silty matrix. Coarser grain sizes are dominant. Generally friable with common sub-angular grains although larger grains tend to be sub-rounded; cream, white or yellow in colour with red oxidized spots due to surface weathering; non- calcareous. Classification: QUARTZ ARENITE 6.1.10.1 PETROGRAPHIC DESCRIPTION The following descriptions are a summary of the thin sections listed above. These poorly sorted samples consist of quartz grains between 3.5 - 0.2 mm (granule-sized to fine sand), the latter comprising the sandstone matrix. Quartz comprises at least 98% of framework detrital components (QFL)14 and at least 93% of total15 detrital grains (Figures 6.4 and 6.5A). Other minerals include accessory muscovite (0.5%), lithic fragments (siltstone, sandstone, cherts, phyllites and metamorphic rock fragments, 1%) and opaque grains (1%). Heavy minerals comprise 2% of the framework grains with mostly zircon and tourmaline; zircon grains were commonly broken. Samples are cemented primarily by oxide and silica cements and secondly with sparse sericite and kaolinite (Figure 6.5 B, C); collectively cements accounted for 6% of total counts. Primary porosity is up to 28% and this may be increased by pervasive, intra-grain fractures within quartz. Quartz grain outlines can be obscured by silica overgrowths but some qualitative assessment of grain shape was still possible. The coarser grains tend towards rounded outlines while angular outlines are more common to the finer quartz matrix. Some grains are embayed. Monocrystalline grains are dominant (97%) and most display undulose extinction. Grains are clear, although pale green to colourless, acicular inclusions are common (muscovite?). Cloudy vacuoles define the margins of quartz overgrowths, which are sometimes abraded, suggesting that at least some were derived from a previous Framework detrital components include quartz, feldspar and lithic grains only. Quartz includes mono- and polycrystalline varieties, excluding chert, which is considered under the lithic category. 15 Total detrital component includes QFL and all grains other than matrix and cement. 322 A LEGEND D A Upper Nfincepe to Pttocene D A Moruga Formation Q • Moras L'Etfer Formation QUARTZ • Springvale Formation 5% ARENITE 5% jL "arenites" + Cruse Formation \ Quartz / • Manzamlla %k <15% ^\ A» / * \ Pskoceae to Lower Miocc&c / / \\ ^Hi \ At /f»°t $ ^ Herrera Sandstone Member * •y • Plum Milan (Cipero Fm) Q / lx v Ml X Nariva Formation "wackes" / \ \ 7 n r X V O Angostura Sandstone >15% / * S»i Fernando Formation \/ e.t*\ / \* "ft" +°\ \ A ^ ** "A A Potate-a-Pierre Formation # A "t \ r^^\ • Chaudiere Formation ?» \ Upper Cretaceous / O Galera Formation O Naparima Hill Formation ^ y^ O F -j£- -^ ' V r\ D Gautier Formation 0 *<* \Q!0,U, Lower fTrdaceous a Cuche Formation • Toco Formation ARKOSIC UTHIC \ 1/ "- o-" \-~~s\ / ARENITE ARENITE U50, l-so A Feldspar LitMcs U50, ("50 U50J L50 (including chert) Figure 6.3. Classification of Trinidad sandstones. (A) Quartz-feldspar-lithics ternary plot of sandstones from various stratigraphic intervals in Trinidad and Soldado Rock classified according to Pettijohn et al. (1972). Sandstones range from Cretaceous arkosic and subarkosic arenites to Cenozoic (shaded interval) quartz arenites, sublitharenites and lithic arenites. (B) Cenozoic sandstones divided into "arenites" and "wackes" based on amount of clay matrix. The Chaudiere, Pointe-a-Pierre and Angostura sandstones comprise mainly quartz arenites while quartz- and lithic wackes are common among other sandstones. Only the upper half of (A) is shown in (B) and Gautier and Naparima Hill data points in (A) were derived from Patterson (1991). See figure 6.4 for plots of individual formations. Cretaceous Chaudiere and Pointe-a-Pierre San Fernando formations Formation Q arente\J( 5 HV60O3 1IV7041 •\HV7016b I1V70J4 HV60^Subaikose SuMttiarenileV / Ariiosic \ / Ulhic \ / arenite \ / aretnle \ "50, rffl "M» l-so Hen-era Sandstone Nariva Formation & Angostura Sandstone Member (Cipero Formation) Cipero Formation (Plum Mitan) Cruse and Manzanilla Morne L'Enfer, Springvale, formations Moruga formations Figure 6.4 Ternary classification diagrams of individual Mesozoic and Cenozoic sandstones by formation, member or unit. Plots are arranged in stratigraphic superposition from top left to lower right. Numbers adjacent to plots represent sample numbers and these can be referenced in subsequent sections and Appendix 13. Only the upper half (Q=50) of the ternary diagram is represented for all diagrams as labelled in the "Cretaceous" plot only. See Figure 6.4 for key to symbols. 324 diagenetic cycle. 6.1.11 POINTE-A-PIERRE FORMATION Number of samples: 14 Sample locations: Fabien Road, Allen Road, Caratal Road, Tabaquite Sawmill, Chaudiere River (Mt. Harris and Los Armadillos), Tormos Brake Factory (see Figure 2.1 and Appendix 15) Number of thin sections: 10 Thin section locations: Fabien Road, Allen Road, Caratal Road, Tabaquite Sawmill, Chaudiere River (Mt. Harris and Los Armadillos), Tormos Brake Factory General outcrop description: Outcrops range from tabular fine-grained sandstone to thick-bedded, coarse grained sandstones of similar aspect to beds of the Chaudiere Formation. See Section 2.2.4.1. Table 6.3 Abbreviations commonly used in this chapter. Abbreviation Meaning Abbreviation Meaning Alg Red algae Lep Lepidocyclina Be Bioclast Li Lithic fragment (unidentified) Bio Lithic bioclast Lt Total lithics (including chert and polycrystalline quartz) Ca Calcite Mc Lithic mudclast Cbn Carbonate lithic Mol Mollusc Ch Chert Mrf Metamorphic rock fragment Chi Chlorite Num Nummulites Dis Discocyclina Op Opaque mineral Dol Dolomite Q Quartz (on ternary plots, this indicates the sum of mono-and polycrystalline quartz) F Feldspar Qm Monocrystalline quartz Fm Feldspar, microcline Qp Polycrystalline quartz For Foraminifera Sch Mica-schist rock fragment Fp Feldspar, plagioclase Ser Sericite Gl Glauconite Sit Siltstone Ka Kaolinite Sst Sandstone lithic L Lithics Zr Zircon 325 Figure 6.5. Photomicrographs showing features of quartz arenites of the Chaudiere Formation. (A) Mature mineralogical assemblage comprising only sub-rounded, very coarse to granule-sized quartz grains. (B) Kaolinite cement between the coarse quartz grains. (C) Platy texture of kaolinite crystals under high magnification (x500), sample HV5044. (D) Polycrystalline quartz accounts for approximately 3% of quartz grains, HV5043. All samples from "Growing Rock" locality, pp = plane polorized light, xp = cross polarized light. See table 6.3 for meanings to abbreviations. This format will be followed for subsequent figures in this section. 326 Figure 6.6 Quartz arenites of the Pointe-a-Pierre Formation. (A) Mature quartz-dominated mineralogy of a poorly sorted sandstone. The largest grain exhibits typical undulose extinction. HV5006, Caratal Road. (B) Angular, coarse-grained quartz with an opaque pore-filling ferruginous cement. HV5047, Fabien Road. (C) Silica-cemented fine-grainedarenite . Ferruginous clay occurs as secondary cement, filling open pore spaces and fractures (arrowed in pp). Rare chert grains are also in view. HV5011, Tabaquite. (D) Same as 'C but also includes at least three zircon grains recognised by high relief and birefringence colours. Zircon is the dominant accessory mineral in these samples. HV6029, Chaudiere River, Mount Harris. 327 328 Hand specimen description: There is a wider variation in grain sizes relative to the Chaudiere sandstones, though sandstones of the Pointe-a-Pierre Formation are still relatively uniform in lithological character. Grain size ranges from fine to granule-sized with occasional pebbles; grains are variably subangular, with distinctive planar faces in larger quartz crystals, or sub-rounded. Grain sorting improves with decreasing grain size to very well sorted fine-grained sandstones. Medium and coarser grains occur within a silty-sand matrix. Sandstones are white or cream on freshly exposed surfaces, but generally weathered to brown or yellow. Around the Mt. Harris area, finer grained, indurated specimens are grey in colour. Sandstones tend to be well indurated, though weathering may be locally severe, producing friable rock specimens. All samples tested were non- calcareous. Opaque grains and micas are easily observed with the hand lens. Classification: QUARTZ ARENITE and QUARTZ WACKE 6.1.11.1 PETROGRAPHIC DESCRIPTION Samples range from poorly sorted with granule-sized quartz grains (up to 3 mm) to well-sorted and fine-grained (Figure 6.6). Framework detrital grains comprise an average of 97% quartz (ranges between 91-100%) with accessory lithics (chert, metamorphic rock fragments and sandstone, maximum 2%) and opaque minerals (maximum 3%). Glauconite, muscovite and feldspars collectively account for less than 1% of total grains. Zircon, tourmaline and rutile are the main heavy minerals and collectively average 1.5% of total detrital grains. Cement/matrix accounts for up to 35% of counts and consist primarily of silica overgrowths with lesser ferruginous, kaolinite and sericitic clays and chert. Silica overgrowths may be abraded suggesting that some are detrital. Porosity averages 10% among the 10 thin sections (maximum 26%) and is highly variable due to the localized nature of the silica cement. Pervasive, intra-grain fractures on quartz grains serve to increase porosity as some fractures are through-going and lined with oxide cement. Chert cement also displays intragranular porosity. Larger quartz grains are dominantly sub-rounded and sometimes embayed; finer grains are dominantly sub-angular. Polycrystalline quartz grains rarely exceed 4% of 329 total quartz and display a granular habit or rarely, elongated and aligned crystals typical of metamorphic rock fragments. Most monocrystalline quartz crystals display undulose extinction. Inclusions in quartz include muscovite, linear vacuoles (sometimes pervasive and gives a cloudy appearance to grains), zircon, tourmaline and other opaque minerals. 6.1.12 SAN FERNANDO FORMATION Number of samples: 10 Sample locations: Hubert Ranee Street, San Fernando (HV5035, HV5037); San Fernando Terminal (HV5034); Bon Accord, Pointe-a-Pierre (HV5001); Bonne Aventure, Gasparillo (HV7042A, HV7042B); Soldado Rock (HV7039, HV7040, HV7041, HV7045). Number of thin sections: 7 Thin section locations: as above. General outcrop and hand specimen description: The lack of exposure of the San Fernando Formation was one of the major obstacles to its study. It was unavoidable that some rock samples be taken from allochthonous boulders within the respective type localities, details of which are provided below. The wide variation in lithology alluded to in previous discussions (Section 2.3) is similarly reflected in the lithological variety of samples. In order to adequately address this uncertainty and variety, the outcrop localities will be discussed together with the hand specimen description. Two samples of silty calcareous mudstone were derived from an excavation on the grounds of Southern Medical Clinic at Hubert Ranee Street in San Fernando. One was derived from thinly bedded to laminated, cream-coloured beds exposed just below the current roadway (sample HV05037), from which nannofossil specimens were derived (Section 2.3.2). A thin section was made from the second sample, differentiated from the first by its reddish colour and generally thicker bedding (Sample HV5035), and this is described below. 330 One sample (HV5034) was taken from a roadside boulder (>2 m diameter) within the mapped extent of the formation (Appendix 3). There was no indication of exposed bedding in the vicinity of the boulder, which undermines this sample's utility for sedimentological study. Mineralogical and textural attributes are however very similar to other sandstones from the San Fernando Formation, and its inclusion is warranted on that basis. The boulder comprised a rust-brown, indurated and calcareous, very fine-grained sandstone with no indication of bedding or other obvious sedimentary structures. A sample from the Plaisance Conglomerate Member of the San Fernando Formation was similarly derived from its type locality. In-situ bedding was inaccessible but the location comprised several scattered boulders of pebble and cobble conglomerates. Two samples were derived from the now-depleted Morne Roche quarry, Bonne Aventure, Gasparillo (HV7042A, HV7042B). All that remains are scattered boulders of coarse-grained quartzose and calcareous sandstone and it is from these remnants that the samples were obtained. Other samples from the formation were derived from Soldado Rock. Three samples were taken from the massive sandstone beds described in Section 2.3.4 (HV7039, HV7041, HV7045) and one sample from bed '10' of Kugler and Caudri (1975) consisting of foraminiferal limestone (HV7040). Figures 2.15 and 2.16 show the position of these samples on Soldado Rock. Classification: CALCAREOUS AND BIOCLASTIC QUARTZ ARENITES, SUBLITHARENITES, SILTY CALCILUTITES. 6.1.12.1 PETROGRAPHIC DESCRIPTIONS Sandstone sample from San Fernando This sublitharenite (HV5034, Figure 6.4) comprises very well sorted, fine-grained quartz. Quartz accounts for 92% of framework detrital grains and up to 90% of the total detrital component. Grains are typically angular and this represents a marked change from the older sandstones of the Chaudiere and Pointe-a-Pierre formations. Chert is the only lithic fragment and comprises 6% of the framework detrital component while 331 feldspar (plagioclase and microcline) is only 3%. Accessory minerals include opaques and glauconite that collectively account for no more than 1% of detrital grains. Samples are cemented by authigenic calcite, dolomite and ferruginous clays that are up to 47% of total counts, and almost completely occlude pore spaces (porosity of 4%) (Figure 6.7 E). Abraded silica overgrowths on quartz grains are very common. Quartz grains display both uniform and undulose extinction with the latter being dominant, while polycrystalline quartz grains are generally rare (<5%). Inclusions in quartz include linear vacuoles and unidentified acicular crystals, green to colourless in plane polarized light. Plaisance Conglomerate (located at Bon Accord, Pointe-a-Pierre) This sample (HV5001), derived from a boulder in Bon Accord, Pointe-a-Pierre, comprises up to granule-sized quartz grains as the matrix of a much coarser grained conglomerate bed (Figure 6.7 A, B). It is poorly sorted with a range of rounded to sub- angular grains. Compositionally, quartz accounts for almost all of the framework detrital component (99%) and up to 97% of total detrital grains. The remaining minerals include opaques (1%), zircons (1%), lithic chert and sandstone fragments (<1%) and muscovite (Figure 6.7A). Samples are cemented by authigenic kaolinite and chlorite that fills both pore spaces and grain fractures, similar to samples from the Chaudiere and Pointe-a- Pierre formations (Figure 6.7B). The prominent crimson coloured clasts that are typical over the outcrop are opaque in thin section. Monocrystalline quartz comprises over 99% of quartz grains and mostly display undulose extinction; inclusions are mainly in the form of linear vacuoles. Morne Roche Quarry Of the two samples taken from remnant boulders at the quarry site, quantitative mineralogical information was obtained from only one (HV7042B) and a qualitative description was done on the other (HV7042A). They are identical in lithology, differing only in the relative amount of bioclastic fragments. Sample HV7042B contains the lesser 332 amount with up to 3% of bioclastic fragments and the remainder being moderate to poorly sorted quartz (95%), accessory glauconite (1%) and heavy minerals (<1%). Up to 13% of the sample comprises calcite cement. The bioclastic fragments include several species of foraminifera (e.g. nummulitids, discocyclinids, globogerinids, quinqueloculines and other forms) and fragments of molluscs, coral and corraline red algae (Appendix 4). Quartz grains are rounded to angular, dominantly monocrystalline and typically display undulose extinction. Open grain fractures are also common. Silty calcilutite, Southern Medical Clinic This sample (HV5035) comprises a calcareous clay framework with silt-sized to very fine quartz grains typically between 50-100 um. The quartz accounts for less than 10% of the thin section (approximated only) and occur either scattered throughout the clay-sized matrix or as concentrated laminae (Figure 6.7 C). Quartz grain shape ranges from rounded to angular and displays mostly undulose extinction. Feldspar (microcline and plagioclase), lithics (chert, phyllites, mica-schist), glauconite and zircon are also recognized among the silt-sized component. The calcareous clay is the major framework component, which may in part comprise pale-green chlorite (further analysis is needed to confirm this). Calcareous nannoplankton was derived from an adjacent sample at this locality. Sandstone samples from Soldado Rock In the three samples from this locality, quartz grain size typically ranges from very fine to medium (0.08-0.3 mm) with a few grains up to granule size (3.6 mm maximum). All samples are well sorted or bimodal (Figures 6.8 C, D and E). Quartz accounts for 78-92% of framework detrital grains and up to 88% of the total detrital component. As with the sample from the San Fernando terminal (HV5034), grains are typically angular. Feldspar ranges between 3-9% of framework detrital grains. It comprises plagioclase, microcline and possibly orthoclase. Lithics range between 4-13% of framework detrital grains and consist mainly of chert followed by metamorphic rock 333 Figure 6.7 Photomicrographs of marls, sandstones and conglomerates of the San Fernando Formation. (A) Poorly sorted granule-sized sandstone matrix of the Plaisance Conglomerate Member. Field of view contains a large quartz arenite lithic grain (centre), sub-rounded quartz and cement (arrowed). HV5001, Bon Accord, Pointe-a-Pierre. (B) Magnification of kaolinite and chlorite cement filling pore spaces. Kaolinite shows platy texture in PP and chlorite is recognized by its anomalous blue-grey interference colours in XP. HV5001. (C) Silt-sized to very fine-grainedquart z laminae within a calcareous mudstone. HV5035A, Hubert Ranee St., San Fernando city. (D) Angular nature of quartz grains cemented by calcite. HV5034, San Fernando Terminal (E) Euhedral dolomite rhombs are a late stage diagenetic feature of these sandstones. HV5034. 334 •J, ** i'v •' , •*, ' ".' i ' ! 'rO"y , "~fc <• : . t > V <-'-<> • "'it* I I'- ., *• , 335 fragments. Accessory minerals include, in order of decreasing abundance, opaques, muscovite, zircon, garnet and tourmaline (from thin section only). These collectively account for an average of 4% of the total detrital component. Samples are variably cemented by sericitic clays, chert, kaolinite and chlorite (Figure 6.8 E) although x-ray diffraction is needed to confirm the true identity of the latter two. It is uncertain what portions of these minerals represent an authigenic or detrital assemblage. Abraded silica overgrowths are very common on quartz grains, derived from a previous diagenetic cycle (Figure 6.8C). The cement/matrix component accounts for an average of 16% of total counts (excluding open pore spaces). Up to 12% of samples contained open pore spaces. Most quartz grains display undulose extinction. Polycrystalline quartz grains are generally rare (<4%) and inclusions in quartz include muscovite, tourmaline, linear vacuoles and unidentified acicular crystals, green to colourless in plane polarized light. The latter is also common to all older sandstones. 6.1.13 ANGOSTURA SANDSTONE (CIPERO GROUP) Number of samples: 7 Sample locations: Wells Kairi-1, Canteen-1, Canteen-2 Number of thin sections: 7 Thin section locations: Wells Kairi-1, Canteen-1, Canteen-2 (see Figures 2.18 and 2.20) General outcrop description: All samples were derived from subsurface core. Hand specimen description: The following descriptions were derived from core plugs over the interval 5399- 5432 ft in well Kairi-1. Grain size ranges from fine to granular with improved grain sorting in the finer grained fraction. Coarser grains are within a fine sandy matrix and sub-angular grains are common. Sandstones may be well consolidated or friable. Friable intervals are non-calcareous while consolidated intervals were always reactive to 10% HC1 acid, suggesting that calcite is the main cementing agent. Wispy organic particles and pebble-sized mud rip-up and limonitic clasts are common. 336 Figure 6.8 Photomicrographs of sandstones from the San Fernando Formation. (A) The entire view of this bioclastic sandstone consists of quartz and bioclastic fragments including coralline algae, nummulitids and other foraminifera. HV7042B, Morne Roche. (B) Same as (A) with a higher percentage of quartz grains, many of which are angular. HV7042B, Morne Roche. (C) Abraded silica overgrowths (arrowed) are very common in most samples from this formation. HV7041, Soldado Rock. (D) Sample from massive sandstone bed showing bi-modal grain size, abundant quartz and minor feldspar and chert. HV7041, Soldado Rock. (E) Angular quartz with chert and muscovite in a massive sandstone bed. A chloritic matrix is assumed based on the pale-green colour. HV7045, Soldado Rock. 337 338 Classification: QUARTZ ARENITE AND SUBLITHARENITE 6.1.13.1 PETROGRAPHIC DESCRIPTION All samples were of medium-grained sand or larger (0.1-4 mm range). Quartz ranges between 87-99% of framework detrital grains but may be as low as 82% of the total detrital component. Matrix/cement is typically less than 11% in samples with a maximum of 48% in a quartz wacke sample. Accessory minerals include glauconite, opaques and feldspar (microcline and plagioclase) with rare muscovite (Figure 6.9). Glauconite may be completely deformed between quartz grains, altered to limonite and almost indistinguishable from the matrix component. Unlike older sandstones, the percentage of metamorphic rock fragments (mica-schists, phyllites) equates to siliciclastic rock fragments (chert, sandstone and siltstone). Others include intraformational mudclasts, bioclasts (foraminifera) and carbonate fragments (Figure 6.9). Lithic fragments do not exceed 8% of framework detrital grains. Heavy minerals are less than 1% of total detrital grains and comprise mainly zircon, tourmaline, rutile (from thin section), epidote and garnet (from separates, discussed below). Samples are variably cemented by calcite, sericite and ferruginous clays. Porosity is as much as 23% in well sorted sandstones to total occlusion in calcite-cemented samples (Figure 6.9 B). Similar to the other sandstones described previously, abraded silica overgrowths on quartz are fairly common. Polycrystalline quartz grains are generally rare (<3%) except in one sample (AS3.50) where this component reaches up to 13%. Most quartz grains preferentially display undulose extinction and are variably subrounded or angular/sub-angular. Inclusions include muscovite, linear vacuoles, zircon and epidote. 339 Figure 6.9 Calcareous arenites and sublitharenites of the Angostura Sandstone. (A) Deformed detrital clay laminae among cross-grained quartz and chert. The deformed mudclast grades into the sericitic matrix recognized by the speckled, red-brown colour in cross-polars. (B) Calcite-cemented, well sorted cross-grained quartz arenite with bioclastic fragments and glauconite. (C) Sandstone lithic fragment (D) Sandstone lithic fragment alongside a potassium feldspar (microcline) crystal. 340 341 6.1.14 NARIVA FORMATION Number of samples: 22 Sample locations: Esmeralda Junction, Kelly Hill, Well ABM-44, Corbeaux Hill (see Figure 2.18 for locations). Number of thin sections: 12 Thin section locations: Esmeralda Junction, Kelly Hill, ABM-44, Corbeaux Hill General outcrop description: Outcrops display a heterogeneous sandstone character with both distinctive "Nariva" beds and others that are remarkably similar to beds of the Pointe-a-Pierre Formation. Petrography and heavy mineral assemblages were useful in distinguishing the latter. Beds range from thin tabular and wavy fine-grained sandstones to thick-bedded, massive and gradational pebbly sandstones. Distinctive "Nariva" beds contain abundant organic matter and mica. Hand specimen description: All samples were grey or reddish-cream in colour with the latter imparted by a silty matrix in medium- and coarse-grained varieties. Fine- to medium-grained samples ranged from very well to moderately well sorted. The quartzitic sanstones contain abundant micas, opaques and organic-rich laminae. Leaf imprints are also common at some localities (Kelly Hill, Esmeralda Junction), randomly oriented throughout the rock fabric. All the sandstones tested were non-calcareous. Classification: QUARTZ ARENITE AND SUBLITHARENITE 6.1.14.1 PETROGRAPHIC DESCRIPTION Samples are moderate to well sorted, even among the coarser grain sizes (Figure 6.10). Quartz accounts for 80-98% of framework detrital grains (65-97% of total detrital grains). Lithic grains comprise up to 18% of the detrital framework and consist of phyllites, mica-schist, chert, siltstone and rare bioclastic fragments (Figure 6.10 C, D). Feldpars are rare and often altered, accounting for only up to 4% of framework detrital grains (Figure 6.10 E). Other detrital grains include opaques (<3%), muscovite up to 5%, 342 and glauconite up to 1%. Heavy minerals account for less than 3% of detrital grains except at the Esmeralda locality where they are unusually abundant. Zircon and tourmaline are the main heavy minerals seen in thin section with rare chlorite. Matrix/cement accounts for an average of 16% of the total thin section, with sericitic and ferruginous clays together with calcite being the primary cementing agents. It appears that silica overgrowths were derived from a previous diagenetic phase based on the abraded appearance and rare occurrence on some grains (Figure 6.10 F); otherwise, it may be a minor cementing agent relative to the sericitic clays. The overgrowths are defined by cloudy margins and euhedral outlines on quartz grains. Quartz grains are predominantly angular to sub-angular, monocrystalline and commonly exhibit undulose extinction. Polycrystalline quartz accounts for less than 11% of total quartz grains. Inclusions in quartz include muscovite, linear vacuoles, hematite and other opaque minerals. Porosity is highly variable, ranging between 5-28% in well- sorted, fine-grained sandstones alone (e.g. samples HV5008 and HV6023). 6.1.15 PLUM MIT AN OUTCROP (CIPERO FORMATION) Number of samples: 1 Sample locations: Citrus estate, Plum Mitan (see Figure 2.1 for location) Number of thin sections: 1 Thin section locations: Citrus estate, Plum Mitan General outcrop description: See symmetrical rippled sandstone facies (see Section 2.6) Hand specimen description: Very well sorted fine-grained sandstone; yellowish-brown in colour with abundant mica and opaque minerals that give a speckled appearance to the rock. Classification: SUBLITHARENITE 343 Figure 6.10. Photomicrographs of Nariva Formation sublitharenites. (A) Poorly sorted, coarse and medium-grained quartz cemented by calcite, the latter displaying typical high birefringence colours in XP. GWHV19, Corbeaux Hill. (B) Well-sorted, fine-grained sandstone with numerous lithic (chert) fragments and monocrystalline quartz grains. Good porosity (= 17% for slide, highlighted by blue colour) attributed to sparse sericitic cement. HV6035, Kelly Hill. (C) Medium-grained quartz with feldspar, lithic fragments(cher t and mica-schists) and sparse sericitic cement. HV5009, Kelly Hill. (D) Mica-schist rock fragment; quartz with embedded, aligned mica crystals (high birefringence in XP). HV5009. (E) Secondary porosity created by altered crystal assumed to be feldspar. Twin planes are sometimes discernible in altered crystals. HV5009. (F) Abraded silica overgrowths on quartz grain (arrowed) were derived from a previous diagenetic cycle. Sericite is the main matrix component in this sample. HV6033, Kelly Hill. 344 345 6.1.15.1 PETROGRAPHIC DESCRIPTION The sample is well sorted with dominantly fine quartz grains and a few up to medium size (0.4 mm) (Figure 6.11). Quartz comprises up to 92% of framework detrital grains (83% of total detrital grains) while the lithic component accounts for 8% and includes metamorphic rock fragments, siltstone and chert (Figure 6.11 B). Feldspar is less than 5% of framework constituents and was almost always partially dissolved (Figure 6.11 A). Accessory minerals include opaques, muscovite (each accounts for approximately 1% of sample counts) and glauconite. Zircon was rare (1:400 counts). Sericitic and ferruginous clays appear to be the main cementing agent though they are relatively sparse, accounting for only 6% of sample counts. The absence of cement or matrix resulted in a relatively high porosity (24%) for the sample. The sericitic cement 346 may have been derived from the breakdown of the fine-grained metamorphic rock fragments that are rich in phyllosilicates. Abraded silica overgrowths are common on quartz crystals, similar to the older sandstones. Quartz grains range from rounded to sub angular and comprise predominantly monocrystalline crystals that exhibit undulose extinction. Polycrystalline quartz accounts for less than 6% of total quartz grains, and a few grains contain c-axis parallel crystals (metamorphic rock fragments). Inclusions in quartz are in the form of linear or cross-hatched vacuoles, sufficiently abundant to give a cloudy appearance to individual crystals. Figure 6.11. Photomicrographs of sublitharenties of the Cipero Formation (citrus estate, Plum Mitan). (A) The thin section typically comprises rounded to sub-angular quartz grains with very little matrix or cement shown by amount of pore spaces (blue staining). Feldspar is also commonly altered and chert lithics are common. (B) Schist fragment is differentiated from coarser chert varieties only by the presence of mica fragments. One is circled in the cross polarized light (xp) image. 347 6.1.16 HERRERA SANDSTONE MEMBER (CIPERO FORMATION) Number of samples: 5 Sample locations: Wells MD-34, BP-342 and BP-347. Outcrops in the Rock River area and along Moreau Road, Moruga (see Figure 2.18 for location). Number of thin sections: 6 Thin section locations: (as above) General outcrop description: Outcrop samples were derived along riverbanks and poorly exposed beds in densely vegetated areas. No descriptions were possible other than from the immediate bed vicinity. Sample GWHV21 was derived from well BP347 within the rippled and graded sandstone lithofacies (Section 2.7.1.3). Sample HV6011, derived from the Rock River area, was obtained from thin-bedded sandstones similar to the rippled sandstone and shale facies. (Section 2.7.1.1) Hand specimen description: The examination was limited to well-sorted fine- and medium-grained specimens. Sandstones are generally grey in colour with a rust-brown hue imparted by outcrop weathering. All samples were well consolidated and reacted with 10% HC1 acid. Dark and opaque grains are common which give a speckled appearance to the rock. Classification: SUBLITHARENITE, LITHARENITE AND LITHIC WACKE 6.1.16.1 PETROGRAPHIC DESCRIPTION Thin section samples included both fine- and coarse-grained sandstones (<0.6 mm) all of which displayed well to moderate sorting (Figure 6.12). These are compositionally immature sandstones with lithic fragments comprising up to 30% of framework detrital grains. Quartz grains average 77% of the framework constituent and do not exceed 82%. Lithic grains comprise mica-schists, phyllites, bioclasts, carbonates, chert, sandstone, mudstone and siltstone (Figure 6.12). Feldspars comprise plagioclase and microcline varieties and are generally less than 6% (often altered). Accessory minerals include opaques (<5%), glauconite (<4%) and muscovite (<1%). Zircon and 348 Figure 6.12. Photomicrographs of Herrera Sandstone Member sublitharenites and lithic arenites. (A) Immature mineralogical assemblage comprised of numerous lithic fragments (chert, mud clasts and carbonate), glauconite and quartz within a sericitic matrix that sometimes cannot be differentiated from deformed lithics. GWHV20, BP-342, 10333'. (B) Numerous lithics within a coarse-grained lithic wacke. GWHV21, BP-347, 9807'. (C) Typical lithic fragments found in all samples: 1. siltstone, 2. carbonate, 3. chert and mud clast, 4. bioclast. (D) Feldspar is commonly altered, here plagioclase shown being replaced by chlorite. GWHV20. 349 350 tourmaline are the main heavy minerals seen in thin section and occur together with chlorite, apatite and epidote. Samples are cemented by calcite, sericite, silica and ferruginous clays (in no particular order). Porosity is consistently below 3% in all samples, attributed to the high matrix and cement content of samples. Quartz grains are predominantly angular/sub-angular between both the coarse and fine-grained sand fractions, while in one sample (HV6011) uniform extinction was most common, representing a departure from all older sandstone samples. Polycrystalline quartz accounts for up to 13% of quartz grains, and inclusions include muscovite, linear vacuoles and opaque minerals. 6.1.17 LATE MIOCENE - EARLY PLIOCENE SANDSTONES (CRUSE AND MANZANILLA FORMATIONS) 6.1.17.1 CRUSE FORMATION Number of samples: 4 Sample locations: Moreau Road, Marac (2) and Morne Diablo coast (2) (See Figure 4.1 for location). Number of thin sections: 4 Thin section locations: (as above) General outcrop description: Moreau Road samples were derived along its southern end within the Marac area of Moruga. They were taken from well-consolidated, massive blocks of sandstone that are commonly scattered over the area. These rocks also crop out towards the south along the Moruga coast. The Morne Diablo samples were taken along the Morne Diablo coastline. Sample HV7005 is shown in Figure 4.2 and described therein, while sample HV7006 was taken from a bioturbated and cross-stratified sandstone bed in the vicinity of Siparia Point (see Figure 4.1 for location). 351 Hand specimen description: All samples are up to fine-grained, very well sorted, calcareous and well consolidated. Colour ranges from grey to greyish-green. Micas and opaque grains are common. Classification: CALCAREOUS SUBLITHARENITES AND LITHARENITES Petrographic description The thin sections examined ranged from moderate to well sorted, fine- to very fine-grained sandstones, although coarser grains up to 0.8 mm were present. Quartz ranged between 68-81% of framework detrital constituents while lithic fragments (chert and mica-schists) averaged 16% (Figure 6.13 A, B). Feldspars comprised plagioclase, perthite, albite, orthoclase and microcline varieties and are up to 7% of framework detrital constituents. They showed no signs of alteration in three out of four samples (Figure 6.13 C). Muscovite accounted for less than 2% of total detrital constituents while glauconite and epidote each accounted for less than 1%. Chlorite and biotite are also accessory minerals. Calcite is the primary cementing agent and made up 47% of one sample (e.g HV7005) providing the main supporting mechanism for the rock. Pore spaces are almost completely occluded as a result of the abundant calcite cement (porosity less than 8% in all samples). Quartz grains are predominantly angular to sub-angular, monocrystalline (>90%) and exhibit undulose extinction. There are relatively few inclusions, consisting mostly of vacuoles. 6.1.17.2 MANZANILLA FORMATION Number of samples: 1 Sample locations: Point Paloma (Figure 4.1) Number of thin sections: 1 352 Figure 6.13. Photomicrographs of calcareous sublitharenites in the Cruse Formation. (A) Fine-grained quartz and chert completely encased within calcite cement. Many grains are angular which is characteristic of these samples. (B) Polycrystalline quartz, chert and mica-schist lithic fragments encased within calcite cement. (C) Unaltered feldspars are relatively common in these samples as exemplified by this microcline grain. Calcite cement shows typical high birefringence. All from sample HV5032, Moreau Road. 353 Thin section location: Point Paloma General outcrop description: See Section 5.6.1. Hand specimen description: Very poorly sorted granule-sized sandstone; porous, non-calcareous and friable. Classification: LITHIC WACKE Petrographic description The thin section comprised poorly sorted, rounded to angular, coarse to granule- sized quartz and lithic grains. Quartz accounted for 91% of framework detrital grains while the remainder comprised mostly lithic fragments of mica-schist, chert and possibly siltstone (in order of decreasing abundance). Other minerals include feldspar, glauconite, muscovite and opaques that collectively account for less than 2% of the total detrital grain population. An opaque ferruginous clay is the main cementing agent and accounts for up to 29% of the total count. An olive-green, sometimes micaceous clay (sericite altered to chlorite?) sometimes encloses quartz fragments, their localized occurrence and often-elliptical shape suggests that these are deformed argillaceous detrital fragments. There is a complete range of shapes for quartz and lithic grains from rounded, fractured and polycrystalline to fine, angular and monocrystalline. It is apparent that the latter was derived from the breakdown of the coarser component. The sample contains abundant open pores among the coarse grains (16% porosity) as there is no fine-grained matrix. Collectively, these features suggest either extensive winnowing and abrasion of the sediment or close proximity to the source. In such a coarse-grained sample, the Gazzi-Dickinson counting method apportions most of the lithic fragments to the mineral species and not the lithic category. As a result, the 7% lithic fraction (of framework detrital grains) represents a gross underestimation. Similarly, the 7% attributed to polycrystalline quartz grains (of total quartz) must also be considered a conservative value. Both grain types are abundant (Figure 6.14), many with minute mica crystals embedded along grain boundaries. Polycrystalline habit varied from granular, to elongated and aligned crystals with well- defined schistose cleavage (Figure 6.14 C). In addition, polycrystalline grain boundaries 354 are occasionally sutured. These mica-schist lithics and possibly, the polycrystalline quartz fragments (without mica), suggest a metamorphic source for these elastics. As is typical for these Cenozoic sandstones, most of the quartz crystals exhibit undulose extinction. 6.1.18 LATE PLIOCENE SANDSTONES (MORNE L'ENFER, SPRINGVALE AND MORUGA FORMATIONS) Number of samples: 4 Sample locations: Point Paloma coastline (Springvale Formation), Mayaro coastline (Moruga Formation), Cedros and Erin bays (Morne L'Enfer Formation). (Figure 4.1) Number of thin sections: 4 Thin section locations: as above General outcrop description: The sample from the Point Paloma coastline originated in the Springvale Formation (HV6037) where it was taken from the first channelized sands just below the prominent 'porcellanite' beds. The channelized sands are approximately 13 m thick and are recognized by its sharp base overlying shales and the fine-grained to pebbly sandy fill that exhibits deformed and contorted bedding in places. The channel sands are associated with wavy and lenticular bedding and lignite, interpreted as a nearshore, tide-influenced environment. The sample from the Mayaro coastline (HV7003) was derived from a hummocky cross-stratified bed in the Moruga Formation interpreted to have a wave- modified shoreface origin. The two samples from Cedros (HV6039) and Erin bays (HV6018) were derived from the Morne L'Enfer Formation. The Cedros Bay sample originated within the Upper Morne L'Enfer Sandstone Member and was taken from bioturbated and parallel-laminated sands that are among the first visible beds north of McDonald Trace (see Figure 4.5 for location). They equate to the laterally accreted sand lithofacies (Section 4.2.2.7) interpreted as sub-tidal in origin. The sample from Erin Bay was taken from trough cross-bedded sands underlying lenticular-wavy bedding that forms the uppermost beds of the Lower Morne L'Enfer Sandstone Member, interpreted as 355 ^fe.3 : 'J$&\ *-««, -.; % Figure 6.14 Representative photomicrographs of a lithic wacke from the Manzanilla Formation. (A) Polycrystalline mica-schist rock fragments with (B) distinct quartz grain alignment. (C) Mica-schist rock fragments showing well-defined schistose cleavage (grain at left). Opaque clay cement surrounds the grains to the right of the slide (arrowed). 356 fluvial-estuarine in origin (Section 4.2.2.6; Vincent and Wach, 2007b; Wach and Vincent, 2007). Hand specimen description: All samples showed uniform properties in hand specimen. They were fine grained, micaceous and friable. Sample HV6018 was non-calcareous (the other samples were not tested). Classification: SUBLITHARENITES, LITHIC ARENITES 6.1.18.1 PETROGRAPHIC DESCRIPTION These were all well sorted, fine- to very fine-grained sands (maximum grain size 0.4 mm (sample HV6018), though most quartz grains were between 0.1-0.25 mm) (Figure 6.15). Quartz ranged between 67-76% of framework detrital constituents while lithic fragments (chert, mica-schist and argillaceous metamorphic rock fragments) averaged 23% among the samples (Figure 6.15 B, C). Within a few slides it was difficult to differentiate the argillaceous metamorphic rock fragments from a sericitic matrix, and as a result, the lithic component may be underestimated. Feldspars comprised plagioclase, perthite and microcline varieties and are up to 9% of framework detrital constituents. They displayed variable stages of alteration (to sericite) and dissolution. Muscovite (up to 7% of total detrital grains) and biotite were also common with the latter more so in the Moruga Formation (sample HV7003). Detrital heavy minerals consisted of epidote, zoisite-clinozoisite, zircon and tourmaline. They accounted for a maximum of 4% of total detrital grain counts (sample HV7003). The cementing agent is uncertain as cements were rarely observed, and most of these samples were impregnated with resin to assist in grain bonding. Many of the quartz grains are rimmed by a sericitic clay, either derived from the metamorphic rock fragments or the breakdown of feldspars, and this may have been the cementing agent. Similarly, opaque rims occur around some grains, suggestive of ferruginous cement (Figure 6.15 D). Ultimately, the friable nature of these sands suggests that cements are sparse or provide a very weak bond. Quartz grains are predominantly angular to sub-angular, monocrystalline (92-96% of quartz grains) and exhibit both undulose and uniform extinction. Many of the grains 357 Figure 6.15 Photomicrographs of sublitharenites of the Springvale, Mome L'Enfer and Moruga formations. (A) Typical well-sorted, fine-grainedcharacte r of these sands composed mainly of quartz (white and grey in XPL), numerous lithic fragments (cloudy in PPL, speckled in XPL) and lesser amounts of feldspar (twinned grain in centre of view); HV6018, Erin Bay. (B) Higher magnification view of same slide showing quartz, chert and argillaceous metamorphic rock fragments. HV6018. (C) Abraded mica-schist rock fragment. HV6018. (D) Sparse opaque ferruginous cement binding several quartz grains. The 'opaque' cement at the base of the photo exhibits high order interference colours that may be produced by sericite within the clay matrix. HV7003, Mayaro Coast. 358 359 contain natural open fractures (especially true for sample HV6037). Most of the inclusions in quartz comprise muscovite fragments. 6.1.19 SUMMARY OF PETROGRAPHIC PROPERTIES OF CENOZOIC SANDSTONES A few general statements can be made regarding Cenozoic sandstones based on the preceding descriptions. The range of sandstones is limited to quartz arenites, sublitharenites and lithic arenites, with additional silty calcilutites and bioclastic sandstones occurring in the Late Eocene and Middle Oligocene (San Fernando Formation and Angostura Sandstone respectively). In addition, all sandstones are characteristically low in detrital feldspars; arkosic sandstones appear limited to Cretaceous strata (Figure 6.3 A). When changes in sandstone types and composition are considered, trends are evident that suggest the existence of systematic controls on their relative compositions. Similar assertions can also be made for textural attributes, although with less certainty. The following discussion will highlight some of these trends arising from the preceding descriptions and it will be shown that these are related to regional-scale controls on sediment supply with direct implications for provenance. The discussion will review the relative changes in compositional and textural maturity, diagenesis and abundance of rock fragments, which are all somewhat related. 6.1.19.1 CHANGES IN COMPOSITIONAL MATURITY Generally, compositional maturity decreases throughout the Cenozoic from mature quartz arenites in Paleogene strata to immature lithic arenites and wackes in Pliocene strata. The average framework detrital composition of arenites in the Paleocene-Eocene Chaudiere and Pointe-a-Pierre formations is Q9gF 16 Figures represent average values of three framework detrital components expressed as a percentage, summed from all the thin sections counted for that formation. 'Q' = average mono plus poly crystalline quartz, 'F'= average feldspar and 'L'= average lithic fraction. 360 all Cenozoic sandstones. Their unique compositional maturity in combination with similarity of sedimentary processes (Section 2.2.7) suggest that these sandstones are genetically related in both time and space, adding credence to their supposed conformable succession (Kugler, 2001) and doubt to significant differences in their ages and suggestions of a faulted relationship between them (Algar, 1993; 1998). They comprise mostly quartz arenites and subordinate quartz wackes (Figures 6.3 and 6.4) with a detrital component almost entirely of monocrystalline quartz. Chert and sandstone lithics are rare. Their mature detrital framework is also consistent with the abundance of the ultrastable heavy minerals (zircon) observed in thin section and confirmed from heavy mineral separates (discussed below). The Oligocene Angostura Sandstone is also dominated by compositionally mature quartz arenites (Figures 6.3 and 6.4) with an average framework composition Q96F2L2. A similar mature heavy mineral assemblage comprising ultrastable grains was seen in thin section and confirmed by mineral separates. Compositionally mature quartz arenites also occur in the Late Oligocene Nariva Formation (average framework Q90F2L8), although most of the samples are better classified as sublitharenites on account of their greater lithic content (Figures 6.3 and 6.4). The trend of decreasing maturity continues into the Late Miocene Herrera Sandstone Member (Q83F3L14)17 and Pliocene sands (Q75F6L19), for which all samples are classified as sublitharenites or lithic arenites. 6.1.19.2 CHANGES IN TEXTURAL MATURITY Several authors equate the presence of clay matrix with textural immaturity in sandstones (Folk, 1954; Dott, 1964; Pettijohn et al., 1972). Similar to changes in compositional maturity, a trend is apparent in the relative amounts of clay matrix (authigenic plus detrital) between samples (Figure 6.16). The Paleocene-Eocene sandstones of the Pointe-a-Pierre and Chaudiere formations contained on average the lowest clay matrix percentage. The average clay content often samples These figures do not include intrabasinal lithic fragments. If these are considered, the framework averages will be (Q77F3L20). 361 % clay content (authigenic and detrital) arenites ! wackes EARLY PLIOCENE A Cruse/Manzanilla• A tm A Herrera ! A m A Legend Nariva AAA >• Ai A A A Sample point f Average value Angostura A AA A • A San Fernando AA A ! m A MAA AA* A A A PALEOCENE Pointe-a-Pierre/ Chaudiere A r- 10.0 15.0 20.0 30.0 40.0 50.0 B very coarse - granule AA • A A coarse-grained - & A&4&CI A A AA A medium-coarse grained A AAA • A fine-grained - M A A AA •AA A AA A very fine A A grained • 10.00 20.00 30.00 40.00 50.00 Amount of samples per sandstone unit Pointe-a-Pierre/ San . . ... „ Cruse/ Grain Size Chaudiere Fernando Angoslura Nanva Herrera Manzanilla > coarse 5 2 4 5 1 1 medium-coarse 1 1 1 2 0 0 fine 6 2 0 3 2 2 very fine 0 1 0 0 0 1 Figure 6.16 Changes in textural maturity based on clay matrix content for successively younger Cenozoic sandstones. (A) Percent of detrital and authigenic clay matrix for samples arranged by decreasing age. Note tendency for decreasing maturity in successively younger sandstones, except for those derived from the San Fernando Formation. Dashed line separates the "arenites" from the "wackes" based on a 15% cut-off. (B) Clay matrix content arranged by sample grain size suggesting some dependency between the variables. (C) The distribution of grain sizes among samples based on the Wentworth size classes (Folk, 1974); all sandstone units are represented in the coarse and fine fraction except the Angostura Sandstone, which is not represented in the finer grain sizes, n = 40. 362 investigated was 11% with only three containing more than 15%. This is an overestimation of the relative maturity of these formations, as the clay matrix content contains mostly diagenetic ferruginous cement and kaolinite, and not detrital clay. The average clay content in successively younger sandstones was 19.5% (San Fernando), 15.6% (Angostura), 16.4% (Nariva), 27.4% (Herrera) and 38% (Cruse/Manzanilla). These changes are likely due to sediment source as there is very little difference in depositional environment; samples were all derived from turbidite beds deposited below wave base where post depositional reworking was minimal to absent. Only the Cruse/Manzanilla samples were derived from both turbidites and shelf sediments. There is a dependence between clay matrix content and grain size (Figure 6.16 B). The figures quoted are representative of all grain sizes, except for the Angostura Sandstone where all samples were medium- to very coarse-grained. Later Pliocene samples (Morne L'Enfer and Springvale formations) were not considered because of their friable nature and wide variety of nearshore depositional environments. Based on qualitative observations of grain shape and roundness, there is an apparent decrease in grain roundness in younger strata. The compositionally mature sandstones of the Chaudiere-Pointe-a-Pierre formations do not exhibit the abundance of angular quartz fragments in both the coarse and fine-grain size fraction relative to the stratigraphically younger sublitharenites of the Nariva Formation. Harry (1992) also noted the predominantly angular shape of quartz grains within Pliocene sands of the Moruga Formation. More work is needed though, to prove this textural relationship between the sandstones. 6.1.19.3 DIAGENESIS The types and abundance of particular cements are sufficiently varied to differentiate between the sandstones. Silica cement is common to Eocene sandstones of the Pointe-a-Pierre Formation and, together with secondary ferruginous clays and kaolinite, comprises the major cementing agents. Silica cement was sufficiently 1R Not all thin sections were included for the clay matrix analysis. Sections with calcite cement were excluded along with samples for which grain sizes were not quantified. 363 pervasive to completely occlude pore spaces, while ferruginous clays often occured within secondary pores and fractures (e.g. Figure 6.6 C). This is in contrast to younger sandstones (Late Eocene and younger) where silica overgrowths occurred sporadically and most were abraded, suggesting derivation from a previous diagenetic cycle. Instead, sericitic and ferruginous clays were present in younger sandstones, including all of the samples from the Nariva Formation, where they are a common cement. Calcite cement was not observed in any of the 13 samples from the Chaudiere and Pointe-a-Pierre formations but is locally important within all other sandstones except the Late Pliocene sands. It is particularly important in San Fernando, Angostura, and Herrera sandstones, which are all associated with abundant calcareous fossils (biohermal reefs, bioclasts, coquinas) (Figure 6.19). From these observations, there is an apparent relationship between the abundance of particular cements and detrital constituents. Calcite cement is common in sandstones with higher bioclastic content or with known associations to a calcareous source (e.g. biohermal reefs of the San Fernando Formation); sericitic clay increases in abundance to the Nariva Formation, which has the highest relative abundance of phyllosilicates (muscovite) derived from mica-schists and phyllite rock fragments; silica dominates in the presence of clean quartzose sandstones without a significant calcareous or phyllosilicate component. It is apparent that the dominant cement was directly influenced by the initial sandstone composition and availability of silica, calcium or iron precipitates. This is a common occurrence in the diagenesis of sandstones (Blatt, 1979). 6.1.19.4 ROCK FRAGMENTS The most systematic and arguably, significant change in the framework constituents of these Cenozoic sandstones occur in the lithic component. This change was alluded to in previous paragraphs but it is sufficiently distinctive to warrant a separate discussion. The lithic component (including chert) ranges from less than 4% average for the Chaudiere-Pointe-a-Pierre sandstones to 28% average for Late Pliocene sands (Figures 6.17 and 6.18). Individual samples ranged from 0.4% in the Chaudiere- Pointe-a-Pierre sandstones to 37% and 33% in the Middle Miocene (Herrera) and 364 Pliocene sandstones respectively. The increase appears systematic when both average and maximum percentages of lithic fragments are considered and intrabasinal rip-up clasts are excluded. The increase in lithic fragments is attributable to increasing amounts of metamorphic rock fragments for each successive formation. There is an incipient but progressive change throughout the Paleogene, with an apparent increase in the rate of input of metamorphic rock fragments in the Late Oligocene, coincident with sandstones of the Nariva Formation. The increasing lithic fraction is interpreted to be related to changing sediment sources, with the most significant change occurring during deposition of the Nariva Formation. It will be shown below that this change coincides with other changes in the heavy mineral fraction. The significance will be readdressed when potential sediment sources and changes in basin settings are considered in subsequent sections. 6.1.19.5 QUARTZ INCLUSIONS, SILICA OVERGROWTHS AND EXTINCTION PATTERNS These attributes were not quantified but some qualitative assertions can be made. Quartz inclusions comprised mainly linear vacuoles common to grains in all sandstones. They were particularly common from Paleocene to Miocene sandstones and sparse in sandstones of Pliocene Cruse Formation. Other inclusions included minerals such as zircon, tourmaline, muscovite and rare albite. Muscovite was particularly common in later sandstones, coincident with the increase in metamorphic rock fragments in the lithic fraction. Similarly, abraded silica overgrowths on quartz are common throughout the entire Cenozoic and sometimes locally abundant as in samples from the San Fernando Formation (Figure 6.8 C). Undulose extinction was the norm for the majority of quartz grains of all stratigraphic intervals. One anomaly came from a sample within the Herrera Sandstone Member (HV6011) in which quartz grains demonstrated mostly uniform extinction. This was coincident with a general increase in the amount of similar grains in other samples, although undulose extinction was always dominant. The constant inclusions and extinction patterns throughout Paleogene strata may be related to a constant sediment source or sedimentary recycling of quartz grains, as 365 Percentage lithic fraction (including chert and polycrystalline quartz) 10 15 20 25 30 35 40 45 50 Formation/ Member 1 1 1 1 1 1 i • • Mome L'Enfer, Sprinavale. Moruaa Cruse/Manzanilla 10 Herrera Sandstone Nariva 20 (Q £ 30 CO ® / #<$> <§> / San Fernando 40 ^^•i ^ •/ Pointe-a-Pierre 50 & • O / Chaudiere 60 Thin section sample point <> Average value performation o r member # Figure 6.17 Increasing lithic fragments throughout Cenozoic strata. The change is obvious in both the maximum (arrow at right) and average (left) lithic percentage per sandstone. The latter suggests there was a change in the rate of input of lithic clasts around 20 Ma. The change is primarily due to increases in metamorphic rock fragments (also see Figure 6.18). Figure 6.18 Detrital lithic fractiono f Cenozoic and Mesozoic sandstones. Sample numbers refer to thin sections and a modified stratigraphic column (after Saunders et al., 1998) is shown for reference. Note the increasing lithic component from around the Early Miocene (Nariva Formation) and increase both in percent and occurrence of metamorphic rock fragments (dark shading) fromth e Oligocene. Volcanic lithic fragments fall under "other" category described from Patterson (1991) where reference was made to "volcanic" lithics in the Gautier Formation but not explicitly numbered; the category represents a possible maximum of volcanics in that formation only. The percentage of carbonate lithcs is relative to all other lithic fragments. The provenance implications of these trends are discussed in the text. 367 % TOTAL LITHIC %METAMORPHIC, SEDIMENTARY % CARBONATE UTHICS FRAGMENTS AND VOLCANIC LITHIC FRAGMENTS (Including BIOCLASTS) 0 20 40 «0 10 100 0 20 40 00 «0 100 0 20 40 tO M sample Formations CIOIMFI /HV7003 'HWSOW HV6039 \HV8037 HV7016bl 368 further suggested by the common abraded quartz overgrowths. The anomalies in inclusions and extinction patterns however all occur post-Paleogene and may be related to changing sediment source. Although more precise data on these optical properties may provide more conclusive results, they coincide with other changes in compositional percentages and further suggest post-Paleogene changes in sediment source. 6.1.20 HEAVY MINERAL ANALYSIS The results of 25 heavy mineral separates, including four from correlative Eocene sandstones of the Scotland Formation in Barbados, are presented below. The characteristic heavy minerals of Cenozoic sandstones are listed in Table 6.4 and graphically portrayed in Figure 6.19. In general, zircon is the dominant mineral in all sandstones along with abundant tourmaline and lesser rutile. Muscovite was common to all samples although it was not included in grain counts. At least three mineral assemblages are recognized among the Cenozoic sandstones: (1) The first is dominated by the ultrastable minerals (zircon, tourmaline and rutile >90% of translucent minerals) and all others are rare; (2) Several 'common' minerals collectively occur in significant proportions (>20%) although the ultrastable minerals still dominate. The common minerals include chloritoid, staurolite, apatite, chlorite and garnet; (3) Samples in which ultrastable minerals are less than 50% and other minerals assume greater numerical significance (detrital chlorite19, epidote and apatite). The abundance of ultrastable minerals in assemblage "1" may have been inherited from the sediment source, or resulted from the selective removal of less-stable minerals by either multiple reworking (multiple-cycle sediments), or mineral dissolution (Hubert 1962). Both factors are assumed to contribute to the observed assemblage and the relative merits of each will be discussed when provenance is considered below. The rare aluminosilicates, andalusite and sillimanite, together with staurolite in assemblage "1" (Table 6.4), originated from an area of medium- to high-grade metamorphism of Al-rich 19 Detrital chlorite is not generally included in grain counts (Mange and Maurer, 1992) but is included here because of their limited abundance in younger sandstones, which has implications for provenance. It is not considered in ZTR index calculations. 369 FORMATION/UNIT SAMPLE # HV6017(3P§3 Morne L'enfer Formation HV6039 HV6040 (3} HE Cruse Formation HV5032 H—HI Y////////////////, Herrera HV5026 (2 Sandstone HV5029 (2)| HV5007 (2) Nariva HV5009 (2; Formation HV5022 (2, HV5023 (2 Cipero Formation HV5018(r Zircon (Plum Mitan) Rutile Angostura AS1.9(1 Sandstone mm Tourmaline San Fernando HV5001 (1 • Andal/Sillim/Kyan Formation HV7039 (2 E3 Staurolite Hi Chloritoid HVS006 (1) HVS012(1] • Epidote group Pointe-a-Pierre Formation HV5013(1; BH Garnet HV5046 (1; 31 • Aclinoiite HV6029(1) CZ] Apatite ggg Chlorite Chaudiere HV5044(1» Formation HV5049(1J| mmm S Brookite BD1 (1 Scotland HV6007(2; Formation (Barbados) HV6O08 (2) HV6009 (2] 200 250 400 450 Quantity Figure 6.19 Composite bar chart showing actual counts of translucent heavy minerals and their relative contribution to the total fraction. The lower counts in the Herrera Sandstone Member was due to the abundance of opaque minerals (see Figure 6.20). Numbers in parenthesis adjacent to sample denotes the heavy mineral assemblages discussed in the text. See Appendix 18 for actual mineral counts. 370 pelites (Winkler, 1974; Nockolds et al., 1978). Samples from the Chaudiere and Pointe- a-Pierre formations, Angostura Sandstone, Plaisance Conglomerate (San Fernando Formation) and Cipero Formation (Plum Mitan), fall into this category. The common garnet and staurolite (29% of translucent minerals, assemblage "2") within Late Eocene sandstones of the San Fernando Formation (Figure 6.19, sample HV7039) also indicate a similar metamorphic source, although garnet is not restricted to those rocks (Winkler, 1974; Nesse, 2004). Significant minerals within assemblage "2" include chloritoid, detrital chlorite, garnet and apatite. Chloritoid is common in metamorphic rocks up to greenschist facies and the presence of chlorite and epidote is also diagnostic. These minerals attain significant numbers in the sandstones of the Late Oligocene to Early Miocene Nariva Formation (e.g. chloritoid averages 16% of translucent minerals) and persist into the Pliocene sands. Assemblage "3" is characterized by abundant epidote (average 60% of translucent minerals) and chlorite (up to 41%), and a variety of other minerals including actinolite, sillimanite, kyanite, andalusite, hornblende, apatite, staurolite, chloritoid and biotite. These occur in addition to the ultrastable minerals. They collectively represent a diverse mineral assemblage that may have been derived from numerous sources, including high- grade metamorphic (sillimanite-kyanite-andalusite-staurolite-hornblende), low-grade metamorphic (chloritoid-chlorite-actinolite) and igneous (hornblende) rocks (Winkler, 1974; Nesse, 2004). This mineral assemblage is common to Pliocene sandstones of the Cruse and Morne L'Enfer formations. Samples from the Scotland Formation (Chalky Mount Member) are assigned to both assemblages "1" and "2" based on the abundance of ultrastable minerals as well as the collective significance of garnet, chloritoid, chlorite, andalusite, kyanite and sillimanite. The mineral assemblages indicate a mix of high- and low-grade metamorphic and ultrastable sources. The heavy minerals described here are similar to those described by previous authors (Illing, 1928; van Andel and Postma, 1954; Griffiths, referenced in Suter, 1960; Harry, 1992), although some of the rarer minerals described by them (e.g. glaucophane), were not encountered. A larger number of samples may have allowed for recognition of 20 'Epidote' refers to the epidote group, which also includes zoisite and clinozoisite. 371 these minerals in this study. A comparative listing of heavy minerals found by various workers is shown in Appendix 11. 6.1.21 SCOTLAND FORMATION HEAVY MINERALS (BARBADOS) Lithological and chronological correlations have been made between the Scotland Formation of Barbados and the Eocene Pointe-a-Pierre Formation, although they are known to possess a different diversity of heavy minerals (Senn, 1940; Kugler, 2001). Similar to the Pointe-a-Pierre Formation, the samples from the Scotland Formation contain zircon, tourmaline and rutile (ultrastable minerals) and medium- to high-grade metamorphic minerals such as andalusite, sillimanite, staurolite and garnet. The ultrastable assemblage is similarly dominant. Unlike the Pointe-a-Pierre Formation, these metamorphic minerals appear more common and also include kyanite. However, they still occur in relatively insignificant numbers (compare the collective average 0.2% in the Pointe-a-Pierre Formation [n=5] with 2% in the Scotland Formation [n=4]; this average includes a 'flood' of garnet in sample HV6007 with up to 10% garnet. More significant is the occurrence of chloritoid (average 5% of translucent minerals [n=4]). The mineralogy of the Scotland Formation shares a greater similarity with sandstones from the Nariva Formation. Chloritoid is a common product of low-grade metamorphism of Al and Fe-rich rocks. The collective occurrence of chloritoid, chlorite (average 5%) and kyanite is significant as regards provenance, as these can be linked to a particular tectonic setting. Further details will be provided when provenance is considered in the second section to this Chapter. The heavy mineral yield as indicated by the HMC index (Section 6.1.5) for the Scotland Formation is relatively low and similar to those of the Trinidad sandstones (Figure 6.20). The compositional maturity indicated by the ZTR index is also similar to sandstones of the Nariva Formation. 372 6.1.22 SUMMARY OF DESCRIPTIVE PETROGRAPHY 1. Cenozoic sandstones range from quartz arenites to lithic arenites and decrease in maturity with decreasing age. The most significant change occured in the Late Oligocene to Early Miocene Nariva Formation. Arkosic arenites are limited to the Cretaceous. 2. Increasing lithic proportions are attributed to increasing metamorphic rock fragments. Igneous rock fragments are absent in Cenozoic sandstones. 3. Compositional maturity of framework detrital grains parallels the compositional maturity of heavy mineral assemblages. Decreasing textural maturity is also apparent throughout the Cenozoic. 4. The dominant sandstone cement appears to be dependent on the initial (depositional) composition of the sandstone. 5. At least three heavy mineral assemblages can be distinguished by the relative proportion of ultrastable minerals. Assemblage "1" dominated by ultrastable minerals includes most of the Paleocene and Eocene samples while Assemblage "3" with the least amount of ultrastable minerals occur in the Pliocene samples. 6. The heavy mineral assemblage also contains metamorphic minerals of low (assemblages "2" and "3") to high (assemblage "1") grade. The former appears significant from the Nariva Formation and also in the Scotland Formation of Barbados. 6.2 PART 2 - PROVENANCE OF CENOZOIC SANDSTONES 6.2.1 INTRODUCTION The first-order control on sandstone composition is the mineralogy of the parent rock(s), while the regional tectonic setting is considered a secondary determinant (Ingersoll, 1990). Climatic effects can completely alter or disguise any genetic link 373 between these two domains (parent rock and daughter sediment). Topographic relief at the sediment source has an indirect control as it largely determines the transport pathways and the duration of exposure of a grain to chemical attack, with steeper slopes increasing their chance of survival (e.g. Morton and Johnsson, 1993; Picard and McBride, 2007). Before a genetic link can be established between any sediment and its source, the modifying effects of climate and relief must be considered (Basu, 1985). Plate tectonic reconstructions suggest that the northern margin of South America and Trinidad retained its equatorial Latitude throughout the Late Cretaceous and Cenozoic (Pindell, 1994; 2007); humid tropical climates therefore provided conditions ideal for weathering and mineral chemical dissolution throughout this time. In the special case of feldspar, this can lead to erroneous conclusions from compositional ternary plots (Helmold, 1985; McBride, 1985), and lesser stable heavy minerals such as apatite will be selectively removed from the sedimentary cycle. The potential effect of dissolution on Cenozoic sediments will be evaluated in light of these two commonly occurring but readily altered minerals (feldspar and apatite). 6.2.1.1 DISSOLUTION EFFECTS ON FELDSPAR As demonstrated in Part 1 of this chapter, feldspars are characteristically rare in all Cenozoic sandstones and in particular Paleocene and Eocene sandstones of the Chaudiere and Pointe-a-Pierre formations. The low percentage is due in part to grain dissolution, as altered feldspars and oversized pores attributed to feldspar dissolution were seen in thin section (Figures 6.10 E, 6.11 A and 6.12 D), and recognized in previous studies (Punch, 2004). The effect of feldspar dissolution on provenance interpretations of ternary plots will be to shift the sample points towards the lithic pole and into the "mixed provenance" or "recycled orogen" provenance fields of Dickinson and Suczek (1979) and Dickinson, (1985); Figure 6.2. There is however several lines of evidence suggesting that the low feldspar composition did not result from chemical dissolution or alteration at the depositional site, but instead was a characteristic feature acquired from the source basin. Firstly, feldspar is very common within Early and Late Cretaceous sandstones of the Gautier and Toco formations respectively (Figures 6.3 A and 6.4), and although 374 sericitization is obvious in the latter (determined from sample HV6001), many feldspar grains still remain. These rocks are older than the arenites of the Chaudiere and Pointe-a- Pierre formations and it can be reasonably assumed that they were affected by similar weathering processes over a much longer time duration. Their greater abundance in Cretaceous sandstones was derived from the sediment source and dissolution did not erase their relative abundance. Secondly, modern sands around Trinidad sourced from local highs and the Orinoco delta are also poor in feldspars, constituting no more than 8% of detrital grains (van Andel and Postma, 1954). It is assumed that this reflects the original source composition, as chemical-weathering effects will be absent or minimal. The content of feldspars in modern sands is similar to the maximum found in Pliocene to Eocene sandstones (9%). Thirdly, low feldspar content is a characteristic feature of Early Cenozoic and some Cretaceous sandstones along the northern margin of South America from western Venezuela to Barbados (van Andel, 1958; Velbel, 1980; Punch, 2004). In the Maracaibo region of western Venezuela, feldspar-rich arkoses are intercalated with feldspar-poor quartz arenites and this was attributed to changes in sediment source (van Andel, 1958). In contrast to the low feldspar content in these basins, feldspar is abundant in Late Eocene sandstones of the Tufton Hall Formation in Grenada, where it remains a significant detrital component despite being commonly altered (Saunders et al., 1985). The difference is related to sediment source, as the Tufton Hall sandstones also contain abundant volcanic rock fragments and pyroxenes. These sandstones are within the same climatic belt as the sandstones in Trinidad and Barbados. Considering these factors, it is assumed that the relative abundance of feldspars is primarily related to changes in sediment source, despite evidence of some dissolution and alteration. 6.2.1.2 DISSOLUTION EFFECTS ON HEAVY MINERALS Heavy minerals are susceptible to chemical dissolution and effects vary with mineral species, stage of sedimentary cycle, relief, age of the rock, burial depth and 375 sediment permeability (Pettijohn, 1941; Nickel, 1973; Morton, 1979; Morton, 1985; Morton and Johnsson, 1993; Picard and McBride, 2007; Garzanti and Ando, 2007a). The effects of dissolution on mineral species must be accounted for in any heavy mineral study (Morton and Hallsworth, 1994). Some assumptions can be made for this investigation based on two indices and the occurrence of apatite. The ZTR index (Hubert, 1962) is a measure of the maturity of a heavy mineral assemblage; mature assemblages, indicated by higher ZTR values, are more likely to reflect dissolution of less-stable mineral species. The heavy mineral concentration (HMC) (Garzanti and Ando, 2007a) is a measure of the relative heavy mineral yields from sands and sandstones. Low concentrations are likely to reflect dissolution. Together they provide a measure for the effect of dissolution on a grain population (Garzanti and Ando, 2007a). The zircon-tourmaline-rutile (ZTR) index is higher within mineral assemblages "1" and "2" (94-100% and 58-91% respectively) and decreases within the younger sandstones of assemblage "3" (19-46%) to a minimum in the Pliocene Mome L'Enfer Formation (Figure 6.20). This trend of decreasing compositional maturity in younger sandstones may be attributed to either dissolution of mineral species in stratigraphically older sandstones, or the addition of newer mineral species in the younger, related to provenance. The latter is the preferred explanation and the reasons are given below. The rationale behind the heavy mineral concentration index (HMC) is discussed by Garzanti and Ando (2007a) from where the following synopsis is derived. An index value >10 is typical for high heavy mineral yields such as from modern, first cycle sediments derived from active orogenic belts that supply mid-crustal, basic igneous amphibolite or eclogite facies metamorphic detritus to drainage basins. It is also typical of detritus from undissected volcanic arcs. In contrast, HMC <0.8 indicates relatively depleted assemblages as a result of chemical dissolution, sediment recycling or detritus from sources initially poor in heavy minerals, such as ancient platform cover, chert or limestone-dominated lithologies. Extreme HMC index (>90) is typical of mineral concentrations such as in placer deposits. A declining HMC with increasing age of samples is a good indication of grain dissolution assuming that they have a common source. 376 B 100.0 HV6017 \i^ [= Mome L'Enfer Fm Hv«03» HVCCMO Cruse Fm HV5W2 V Mome L'Enfer -&, 80.0 Herrera Sandstone + Cruse \x O 7 Member OHerrera HVS007 V xf' HV5009 xNariva Nariva Formation HVS022 60.0 * HVSB3 m • Plum Mitan Cipero Formation HV5018 •a (Plum wan) •Chaud o Angostura Sst ASI.9 '1- ^ APointe-a-Pierre 40.0 SanFemandoFm {"J" *San Fdo HVW06 O Angostura S p / HWM12 Pointe-4-Pieiie Fm HV5013 • Scotland Fm MvSM6 HV6029 (Barbados) 20.0 Chaudtere Fm HV5W9! BD1 0.0 HV6007 Scotland Fm HVSQOS 0.1 1 10 100 HV600S Heavy Mineral Concentration (HMC) Figure 6.20 Yield quantity and composition of heavy minerals from Cenozoic sandstones in Trinidad and Barbados. (A) Heavy mineral yield (HMC) plotted against zircon-tourmaline-rutile (ZTR) index. There is no apparent change in heavy mineral yield with changing mineralogical maturity. Dashed polygons encircle Pliocene (P), Oligocene (O) and Eocene/Paleocene (E) Trinidad samples. (B) Percentage of opaque versus translucent heavy mineral yields. The ZTR index per sample is superimposed to show decrease in ultrastable minerals in younger sandstones (Herrera to Morne L'Enfer). The HMC index for Cenozoic sandstone ranges from 0.2 - 4.0 and is indicative of relatively low heavy mineral yields (Figure 6.20). There is no difference in the range of values with increasing age, which would be expected if dissolution were the main determinant on heavy mineral abundance (e.g. Garzanti and Ando, 2007a). Similarly, when considered against the ZTR index (Figure 6.20 A), there is no difference in yields with increasing compositional maturity, i.e. the same quantity of heavy minerals per unit rock volume were derived from both stable and unstable assemblages. The constant values can be attributed to either (1) constant supply of heavy minerals from low-yielding source rocks without appreciable loss of minerals either by dissolution (in older sandstones) or sediment reworking (in younger sandstones), (2) initial high input of ultrastable minerals within older sandstones, which minimized any dissolution effect or (3) an additional source of heavy minerals in the later Cenozoic. Options (2) and (3) are preferred. These indices do not suggest that grain dissolution was detrimental to heavy mineral grain population for the following reasons: 1. Very similar yields were derived from all samples, regardless of age. Some of the best yields were derived from older samples (e.g. Herrera Sandstone Member and Pointe- a-Pierre Formation), whereas the opposite would be expected if grain dissolution were a determinant factor. 2. The occurrence of 'new' mineral species coincides with significant changes in lithic fraction and other textural and optical grain properties, as outlined in Part 1 of this Chapter. This suggests that there were other controls on the diversity of grains in younger sands. 3. Heavy mineral yields do not decrease with compositional maturity, i.e. the relative abundance of a diverse mineral assemblage resembles that of a stable mineral assemblage with only a few mineral species. The stable minerals of assemblage "1" (Table 6.4; Figure 6.20) may be largely representative of the depositional 'diversity'. Dissolution was not detrimental in changing the grain population within the basin and the heavy mineral population is representative of sediment sources. It is likely that the stable heavy mineral assemblage of Paleogene sandstones characterized by zircon, tourmaline and rutile, is representative of the original 'depositional' assemblage, with 378 minor dissolution effects. This is in parallel with the compositional maturity indicated by the light grain fraction where stable, monocrystalline quartz was the dominant framework mineral. In addition, the local preservation of minerals susceptible to weathering such as apatite (e.g. sample HV7039, Figure 6.19) in older rocks supports this assertion. Apatite is a sensitive indicator of chemical dissolution as it is a very unstable mineral in acidic weathering environments (Morton, 1985). It is also a very common detrital mineral in sandstones, and chemical weathering was very likely where it is absent (e.g. Morton and Johnsson, 1993) Its occurrence is inconsistent among Cenozoic sandstones. It was entirely absent from samples of the Chaudiere, Pointe-a-Pierre, Nariva formations and Angostura Sandstone Member21, very common within one sample from the Late Eocene San Fernando Formation and common in samples from Middle Miocene and younger sediments. Its occurrence in Late Eocene sandstones precludes any assumption of increased dissolution with time. There are obviously other controls to its distribution and sediment source is likely to be one of them. It is proposed therefore, that the heavy mineral assemblage "1" was a function of the sediment source or transit into the depositional basin, while the diversity of assemblages "2" and "3" are related to new sediment sources. It is assumed that the effect of dissolution within the depositional basin was not sufficient to completely mask the mineralogy imparted from the sediment source. This is exemplified for both feldspars and heavy minerals. This assumption is strengthened when mineralogical changes in the light fraction are also considered, together with the input of metamorphic detritus. Separates were made specifically for apatite in these sandstones using up to 2kg of sample in some cases. They all proved barren of apatite. 379 6.2.2 POTENTIAL SEDIMENT SOURCES 6.2.2.1 THE GUYANA SHIELD The Guyana Shield comprises approximately 35,000 square kilometres of exposed Archean, Precambrian and Palaeozoic crystalline continental basement rock in the northern South American continent (Figure 6.21; Lopez et al., 1942). It encompasses portions of eastern Venezuela, Guyana, Suriname, French Guyana and northern Brazil, and together with the Brazilian Shield, account for approximately 39% of the surface area across South America (Potter, 1994). It is located between the Orinoco River drainage basin to the north and west and the Amazon trough to the south; to the west and north it continues into the basement complex below the Andean foreland fill (Edmond et al., 1995). The Shields have been an emergent feature since the Middle Precambrian with limited accumulation of continental beds in the Triassic (Harrington, 1962). The oldest rocks are 3.1-3.7 billion year old granulites found in the Imataca Complex in the northeast of the Shield (Figure 6.21; Almeida, 1978; Santos et al., 2000). The Guyana Shield consists of numerous intrusive and extrusive igneous rocks of both continental and oceanic origin variably metamorphosed in successive deformation events. These are intercalated with continental sandstones and quartzites (Almeida, 1978; Santos et al., 2000) and in places covered by thick and extensive soil horizons below forest cover, some as old as the Cretaceous (Potter, 1994). The first intense phase of metamorphism and deformation dates back to the Trans-Amazonian Orogeny 2-2.25 Ga (Santos et al., 2000) and this was followed by numerous other thermal episodes (e.g. Bosma et al., 1983). The lithological variety across the Guyana Shield is tabulated in Figure 6.21. Santos et al. (2000) provided a collection of geochronological data across the area. The Shield is often cited as a primary sediment source for Mesozoic and Cenozoic sediments off northeastern South America. It is a convenient hypothesis, as the Shield comprises over 2400 m of basement strata (Lopez et al., 1942), currently drained by large rivers (Amazon, Orinoco, Essiquibo, Demerara) that debouch to the northeast of the continent. Palynological and faunal evidence suggests that precursors to the Orinoco and Amazon rivers also drained areas of the Shield to northwest Venezuela and Colombia, 380 Figure 6.21. Northern South America showing provinces of the Guyana Shield and the extension of the Caribbean Mountain belt to Trinidad. These are two potential sediment sources. A third potential source occurs in the low relief, transport-limited areas between these two domains that comprise the Llanos and Orinoco river drainage basins (TL). Another potential source is the volcanic island arc (Lesser Antilles) towards the north. The lithology of the Caribbean Mountains and various provinces in the Guyana Shield are tabulated (the latter with their protolith ages). Zircon and apatite fission track (ZFT and AFT) and argon (Ar/Ar) ages are shown from the Merida Andes (MA) to the Northern Range of Trinidad and Cerro Bolivar in the Guyana Shield. These constrain the timing of uplift around the northern continental margin relative to the stable Shield. The dashed outline represents the current extent of the Orinoco River drainage basin. Gr = Grenada Compiled from Maresch, 1974; Kohn et al., 1984a, Kohn et al., 1984b; Speed et al., 1991; Cerveny and Snoke, 1991; Edmond et al., 1995; Grist and Zentilli, 1997; Algar et al., 1998; Santos et al., 2000; Weber et al., 2001b; Meade et al., 2002. 381 382 prior to the Neogene uplift of the northern Andes that eventually diverted their courses to the east (Hoorn et al., 1995; de Gamero, 1996). These drainage patterns together with the range of rock types present across the Shield, combine for a highly probable sediment source, and this is reflected in the numerous references supported by radiometric dates, mineral attributes, paleocurrents, sandstone isopachs, and proximity among others (e.g. van Andel and Postma, 1954; Nota, 1958; van Andel, 1958; Jones, 1968; Baldwin, 1986; Algar, 1993; 1998; Barr et al., 1958; Patterson, 1991; Goldstein et al, 1997; Punch, 2004; Pindell et al., 2005). The Shield is characterized by relatively slow erosion and transport rates and weathering in alluvial storage areas is a dominant control on the calibre and composition of sediments delivered to the continental edge (Johnsson et al., 1988; Stallard et al., 1990). 6.2.2.2 LATE CRETACEOUS TO EARLY CENOZOIC SEDIMENT SOURCES Depending on the post-Cretaceous palaeo-reconstructions adopted,mpact inferences on sediment sources and dispersal patterns along the northeastern continental margin will be varied. At least two basic models are commonly inferred, following from the Late Jurassic to Early Cretaceous rifting. The 'passive' margin model represents a continuation of this basin setting into the Early Cenozoic with quiescent, fine-grained and transgressive deposition of organic-rich shales, chert and limestones along a north facing slope (e.g. Algar, 1993; Ostos et al., 2005). These sediments can later be redeposited into Cenozoic sandstones as relativel mature elastics, with chert and carbonate lithic fragments. Other authors propose an 'active' continental margin with subaerial or submarine uplifts and intervening foredeeps or depocentres in response to regional tectonics (e.g. Senn, 1940; Hedberg, 1950; Kugler and Saunders, 1967; Tyson and Ali, 1990; Pindell et al., 2005). Lithic-rich arenites with more proximal sediment sources are to be expected in this case. There is evidence for both arc-continent collisions during the Late Cretaceous and Early Cenozoic uplift of oceanic basement in western Venezuela (Maresch, 1974). Multiple sediment sources and dispersal paths can be inferred in this case and detritus rich in volcanic fragments is to be expected (Dickinson and Suczek, 1979). 383 6.2.2.3 CENOZOIC UPLIFTS Major Cenozoic uplifts are confined along the northern margin of South America (Figure 6.21). These northern uplifts belong to the Caribbean Mountain belt, the easterly extension of the Andean Mountain belt that traverses western South America. The Caribbean Mountains consist of several east-west trending, fault-bounded tectonic units that are named from south to north, (1) Piemontina nappe, (2) Villa de Cura nappe, (3) Loma de Hierro nappe, (4) Caucagua-El Tinaco nappe, (5) Cordillera de la Costa nappe and (6) Margarita coastal ophiolite nappe (Bellizzia and Dengo, 1990). The range lies east of the Merida Andes mountain belt of western Venezuela and it continues to the east as the Northern Range of Trinidad and the Main Ridge of Tobago (Kugler, 1953; Dengo, 1953; Gonzales de Juana et al., 1968; Frost and Snoke, 1989). These are metamorphic belts of varying grade, generally increasing in a northerly direction in Venezuela and decreasing towards the east of Trinidad (Maresch, 1974; Smith et al., 1999; Frey et al., 1988; Weber et al., 2001). Most of the rocks are of greenschist facies grade, but zeolite- prehnite-pumpellyite, blueschist and amphibolite grades also occur (Dengo, 1953; Maresch, 1974; Smith et al., 1999). The Villa de Cura nappe varies from the others in that it contains both metavolcanics of oceanic crust affinity and blueschist-facies metamorphic rocks formed during Late Cretaceous subduction-related deformation (e.g. Maresch, 1974; Smith etal., 1999). The western extent of the Caribbean Mountains overlies granitic gneiss of the Sebastopol Group22 (Dengo, 1953) while the basement in Trinidad is inferred to be oceanic crust associated with Caribbean Plate underthrusting (Pindell and Kennan, 2007). Internally, rock types are highly variable. Within the Cordillera de la Costa alone (including the Northern Range of Trinidad), they comprise slates and chloritic phyllites, sericite-epidote and quartz-mica schists, blueschists, amphibolites, eclogites, serpentinites, limestone, marble, feldspathic gneiss, conglomerates and gypsum beds (Dengo, 1953; Gonzales de Juana et al., 1968; Potter, 1968; Algar, 1993). A list of associated minerals is given in Table 6.5. Comprises abundant feldspars (orthoclase and microcline), quartz, muscovite, biotite, epidote, magnetite and apatite (Dengo, 1953). 384 The current position of the Caribbean Mountain System is attributed to southward displacement of individual belts onto continental crust along deep-rooted thrust faults (Maresch, 1974; Bellizia and Dengo, 1990; Smith et al, 1999). At least two phases of metamorphism have been recognized. The first occurred during the Late Mesozoic represented by the blueschist facies rocks of the Villa de Cura nappe prior to its current emplacement. The second was associated with uplift and emplacement of all other nappes during the Cenozoic (Maresch, 1974; Beets et al., 1984; Smith et al., 1999). The timing of uplift of the Caribbean Mountains and the Venezuelan Andes to the west ranges from Late Eocene to Miocene based on thermochronologic and radiometric data (Maresch, 1974; Beets et al, 1984; Kohn et al., 1984a, Kohn et al., 1984b; Speed et al., 1991; Speed et al., 1993; Cerveny and Snoke, 1993; Smith et al., 1999; Weber et al., 2001). In the western extent of the mountain range, reset zircon fission track ages of 60- 61 Ma (Late Cretaceous) within the Merida Andes and 42-49Ma (Eocene) within the Caucagua-El Tinaco nappe suggest that uplift was ongoing at those times (Kohn et al., 1984a; Kohn et al., 1984b). In the Northern Range to the east, 40Ar/39Ar ages of 25-30 Ma for metamorphic white mica and reset zircon and apatite ages of 11 Ma and 12Ma, respectively, collectively suggest that uplift began later in the east (Speed et al., 1991; Speed et al., 1993; Algar et al., 1998; Weber et al, 2001). A diachronous uplift trend from east to west along the northern South American margin was suggested by Speed et al. (1991) and this finds support in the west to east decrease in metamorphic grade across the Northern Range (Frey et al., 1988; Weber et al., 2001). 6.2.2.4 IGNEOUS SOURCES Cretaceous volcanic (Tobago Volcanic Group), metamorphic (North Coast Schists) and plutonic rocks crop out over the island of Tobago, which Cerveny and Snoke 1993) suggested occupied upper crustal levels since the mid-Cretaceous, based on (fission track ages. The volcanic rocks comprise mafic volcaniclastic breccias and lavas while the plutonic suite includes ultramafic rocks, gabbro-diorite and biotite-hornblende tonalite (Snoke et al., 2001). The North Coast Schist comprises metamorphosed rocks up 385 Table 6.4 Metamorphic facies and mineral assemblages of representative terrains in the Caribbean Mountains of northern Venezuela and Trinidad. Minerals in bold font are the most commonly occurring. Nappe Metamorphic zone Modal constituents Reference Pumpellyite-actinolite pumpellyite, chlorite, quartz, albite, actinolite, titanite, calcite, white mica Glaucophane-lawsonite amphibole (glaucophane and actinolite), lawsonite, chlorite, quartz, albite, white mica, titanite Villa de Cura Smith etal., 1999 Glaucophane-epidote glaucophane, epidote, quartz, albite, chlorite, titanite, white mica, relict clinopyroxene Barroisite epidote, chlorite, quartz, albite, barroisite, white mica, titanite, clinopyroxene Amphibolite facies quartz, muscovite, garnet, glaucophane, epidote, chlorite, sphene, apatite, actinolite, graphite, feldspar Cordillera de la Costa Greenschist facies feldspar, biotite, epidote, garnet, muscovite, Dengo, 1953 apatite, clinozoisite, chlorite, tremolite, graphite, antigorite, magnetite, pyrite, pyroxene Greenschist facies quartz, muscovite, chlorite, pyrophyllite, dolomite, chloritoid, rutile, titanite, Freyetal., 1988 stilpnomelane Northern Range Greenschist facies albite, chlorite, actinolite, epidote, calcite, Gonzales de Juana, biotite, chloritoid 1968, Vierbuchen, 1984. to greenschist facies that includes metatuffs, graphitic and siliceous schists and argillite (Snoke et al., 2001). The geological history of the island has shared a closer affinity to the Caribbean Plate to the north than sediments south of the Northern Range (Pindell and Kennan, 2007). When the rock types, their age and timing of uplift is considered, Tobago represents a potential souce of igneous detritus into the basin. 6.2.2.5 OTHER POTENTIAL SEDIMENT SOURCES Several studies on modern sands across northern South America have highlighted the role of lowland plains as depocentres and modifiers of sediment composition through relatively long term sediment residence. Chemical weathering is enhanced by a combination of slow erosion and transport, thick soil horizons and a warm-wet climate, and is arguably the most important determinant in the composition of sands delivered to the coasts from craton and foreland regions (Franzinelli and Potter, 1983; Johnsson et al., 1988; Stallard et al, 1990; Johnsson et al., 1990; Johnsson, 1990). These depocentres act as a sediment 'filter' producing increasingly mature, first-cycle sediments that are ultimately delivered to river mouths and continental shelves (e.g. van Andel and Postma, 1954). For example the abundance of feldspar from granites, amphibolites and sandstones in Guyana Shield basement rocks that lie within the Orinoco drainage basin is not reflected in the feldspar content of modern sands delivered to the river mouth (see "light" fraction in Figure 6.22), as much may have been chemically dissolved within the drainage basin. This disguises or destroys any compositional link to specific source rocks within the Shield (or from the Cenozoic uplifts). These lowland, transport-limited areas are sufficiently large to be recognized as an individual petrologic province. Other Cenozoic uplifts have been speculated about in geological reconstructions or inferred to explain perceived anomalies. The compositional characteristics discussed in this chapter provide a criterion for validating their existence through their erosional products. 387 Figure 6.22. Compilation of modal framework and heavy mineral percentages from modern sands and ancient sandstones in north-eastern South America. Heavy mineral associations are from this investigation and are discussed further in text. Heavy mineral percentages are fromth e Gulf of Paria and mouth of the Orinoco River except where otherwise labelled. Note the separation of zircon from the main graph as depicted in the legend. Arrows indicate sediment transport direction. Data compiled from: Gulf of Paria - van Andel and Postma (1954), Tables 3 and Dl; "Guyana Shelf, coastal plain" - Nota, (1958), Table 3 and Wong et al., 1998; "Barinas Apure" - Morton and Johnsson, 1993, Table 1, "Caribbean Mountains" sourced only; Imataca - Kalliokoski, 1965, Tables 1, 3,4. 388 CM1 ASSOCIATION Mineral Abbreviations Act Actinolite And Andalusite Ap Apatite Bio Biotite Chid Chloritoid Ep Epidote Fd Feldspar Glaup Glaucophane Gn Garnet Hn Hornblende Ky Kyanite Law CM2 ASSOCIATIOI Lawsonite Mon Monazite Op Opaques 00 Pyr Pyroxene Qu Quartz Ru Rutile Sil Sillimanite Sph Sphene Spin Spinel Stau Staurolite To Tourmaline Top Topaz Zr Zircon Source Heavy minerals % ail other minerals Caribbean Mountain Associacton CM1 Epidote+ChtoritokJ+Homtotende CM2 Epidote+CWcritoid+Hornotende+Glaucoohane/lawsoritte CM3 Eprdote+Pyroxene Orinoco Association 01 Zircon 02 Epidote+Rutile+Hornbtende Guyana Shield Association GS SHKmanite+Epidote+HornWende+Staurolite (List = "other minerals) 6.2.3 DISTINGUISHING BETWEEN POTENTIAL SOURCES Distinguishing using modal detrital framework Actualistic studies using modern sands provide one basis for discriminating between these various sources. The utility of compositional plots (Dickinson and Suczek, 1979) was discussed above. Studies involving modern sands across the South American continent have shown that the fill of many basins (e.g. Barinas-Apure, Llanos, and Eastern Venezuelan) is strongly reflective of the local basin setting, and a clear differentiation can be made between sediments derived from the craton and areas of Cenozoic uplift (Franzinelli and Potter, 1983; Johnsson et al., 1988; DeCelles and Hertel, 1989; Stallard et al., 1990; Potter 1994). Litharenites are generally associated with the uplifts, and mature, coarse-grained quartzose sediments with the Guyana Shield, although transitions may blur this distinction. Assuming uniformity in geological processes through time, including chemical weathering, this distinction should also be traceable through the geological record. The 'maturing' effect of lowland areas on sediment composition is explicitly accounted for in the "craton interiors" and "intracratonic basins" (of the Dickinson model, 1985), but the compositional signatures of "recycled orogens" are potentially eliminated. Provenance determinations are however still possible (DeCelles and Hertel, 1989; see also discussion by Johnsson et al., 1990), as compositional characteristics remain in the sediment for some distance away from the mountain front (>300 km in the Apure River basin of Venezuela, Stallard et al., 1990). Consequently, changes in provenance attributed to rising orogens should be identifiable in areas adjacent to the Caribbean Mountains (i.e. Northern Range and Southern Basin of Trinidad). The dataset of Potter (1994) provides an example of how these various sediment sources can be distinguished. He identified five mineral associations across South America based on modal detrital framework of modern sands, character of drainage basin and climate. These are (1) Pacific association (Q21F15R64)23, Fmax44, Rmax96 (2) 23 Values denote average ratio of quartz (Q), feldspar (F) and rock fragments (R) and maximum feldspar (Fmax) and rock fragment (Rmax) by traditional point count; values 390 Argentine association (Q26F18R56), Fmax44, Rmaxg6, (3) Transitional association (Q61F7R32), Fmax26, Rmaxgo, (4) Caribbean association (Q57F13R30), Fmax48, Rmaxgs and the (5) Brazilian association (Q86F7R7), Fmax2o, Rmax2o. The latter three associations are of interest to this study. The Caribbean association includes sands sourced from the Caribbean Mountains. The Transitional association extends west from the Gulf of Paria and includes the Llanos basin and other lowlands of the Andean foreland, and represents mixed provenance sources (see Figure 6.21 for location). The Brazilian association includes sediments sourced from the Guyana Shield, inclusive of the Orinoco River drainage basin. Potter's spatial compositional associations reflect different sources and basin settings. Compositional analogies can be drawn between his dataset and ancient strata from this investigation on the assumption that these associations also persisted in the past and they provide an additional means to differentiate the different sediment sources. A more direct distinction can also be made from the lithic fragments. Mica schists and phyllites are characteristic of uplifting metamorphic terrains such as the Caribbean Mountains with its abundant mica-schist in the Caracas Group (Dengo, 1953), and lesser quantities in the Northern Range of Trinidad, where phyllites are most common (van Andel and Postma, 1954; Algar, 1993). The modal composition of sediments from the Imataca Complex in the northern Guyana Shield is shown in Figure 6.22. The granites, amphibolites and arkosic sandstones provide a ready source of feldspar that may be reflected in ancient sediment, especially given the close proximity to the northern continental shelf. These modal percentages should be represented in sediments that were supplied directly from the Shield, or at least, from the basement rocks of the Imataca Complex. Distinction using heavy minerals The criteria for distinction proposed below are based on the modal composition of both modern and ancient sands from published literature. General trends can be seen in as given by Potter (1994). "R" equates to "L" (lithic rock fragments) previously used in this thesis. Traditional point counts will always give a higher lithic percentage than the Gazzi-Dickinson method. 391 heavy mineral distribution that can be extrapolated to ancient sandstones, albeit with inherent uncertainty. The contribution of metamorphic sources in the samples investigated for this thesis far outweighs that of igneous sources, which only become apparent in the youngest sands. This relative absence was also noted by previous workers (see mineral listing in Appendix 11) and appears to be related to available sources as opposed to dissolution effects, as they are also rare in modern sands (Figure 6.22). Therefore the differentiation between provenance terrains depended primarily on the distinction between metamorphic and ultrastable heavy mineral suites, the latter being dominant throughout most of the Cenozoic. At least three petrologic domains were established among these mineral assemblages: 1. Transport-limited, ultrastable domain (e.g. Llanos Basin, Guyana Shield lowlands) Mature mineral assemblages are being generated from first cycle sands in transport-limited (Stallard et al., 1990) terrains such as lowlands of the Apure and Llanos drainage basins and foothills of the Guyana Shield. This environment produces mineral species resistant to chemical weathering such as zircons, tourmaline, rutile and monocrystalline quartz. Minerals such as apatite, feldspar and epidote, with a low tolerance for acidic weathering conditions, are unlikely to be present in significant numbers (e.g. Morton and Johnsson, 1993). The dissolution of feldspar from the Imataca province of the Guyana Shield was referred to previously and less resistant heavy minerals are likely to be similarly affected. This suite is represented in modern sands produced at the mouth of the Orinoco River by the "Orinoco Association" that is dominated by zircon and abundant quartz in the "light" sand fraction (Figure 6.22). Hornblende and epidote are common accessories. Van Andel and Postma (1954) interpreted these to originate from the Llanos Basin, with the hornblende and epidote suggesting other Guyana Shield sources. The abundant zircon in most modern sands may also reflect contributions from this source. This domain is comparable with, and includes the "Brazilian Association" of mature sandstones (Potter, 1994) derived from the Guyana Shield and lowland areas prone to chemical weathering. 392 2. High and Low Pressure/ Low Temperature metamorphic domain (Caribbean Mountains) This domain is a modification of the HgM - LgM (high-grade and low-grade metamorphism, respectively) index used by Garzanti and Ando (2007a) to differentiate between these sources based on the relative abundance of index minerals. The Caribbean Mountains contain low pressure, low temperature (LP/LT) metamorphosed rocks with characteristic minerals of low-grade metamorphism (e.g. chlorite, epidote, chloritoid, actinolite) (Table 6.5). The zones of high pressure/low temperature (HP/LT) metamorphism are the blueschists of the Villa de Cura and Cordillera de la Costa and they are characterized by the additional presence of glaucophane and lawsonite. Kyanite is the stable aluminosilicate (Maresch, 1974), with sillimanite and andalusite being rare to absent. This is also reflected in modern sands (Figure 6.22). Along the southern flanks of the Northern Range and Cordillera de la Costa are there are sands rich in epidote and chloritoid that were derived directly from the mountain belt (CM1 Association), while locally abundant contributions of epidote were also derived from the San Souci metabasalts further east (CM3 Association). Epidote is also locally abundant further west along the Caribbean Mountain belt where Morton and Johnsson (1993) sampled sands from rivers that drained the Caribbean Mountains; epidote together with zircon, chloritoid and hornblende were among the most abundant minerals (CM2 Association of Figure 6.22). Other local sources of epidote exist within the greenschist facies rocks such as the Tacagua Formation of the Caracas Group (Dengo, 1953). The sodic amphiboles, glaucophane and lawsonite, are also diagnostic of high pressure metamorphism and form part of the Caribbean Mountain Association of heavy minerals, even when occurring in small quantities (CM2 Association, Figure 6.22). 3. Low pressure/ High temperature petrologic domain (Guyana Shield, Merida Andes) Sillimanite is the stable aluminosilicate under conditions of high temperature metamorphism. Singh (1968) recorded the abundance of sillimanite in regionally metamorphosed granites of the Kanuku Group in southern Guyana, and Kalliokoski (1965) noted their abundance in granite gneiss of the Imataca Province of the Guyana Shield. Investigations using modern sands have shown its common occurrence in 393 sediments along the Guyana and Suriname shelf and coasts, likely derived from rivers that drain the Guyana Shield (GS Association of Figure 6.22; Nota, 1958; Wong et al., 1998). Morton and Johnsson (1993) used sillimanite to differentiate river sediments derived from the high-grade gneisses of the Merida Andes from Caribbean Mountain sources. Hence the presence of sillimanite in Cenozoic sediments more likely indicates derivation from Shield and other high-grade metamorphic sources relative to the Caribbean Mountains. The likelihood is increased when found in association with other high grade metamorphic minerals such as andalusite, garnet and staurolite (GS Association of Figure 6.22). Hornblende is ubiquitous in modern sands around the northeastern margin of South America and was likely derived from multiple sources. The mineral is common in Orinoco-derived sands, which may have originated from Imataca Province (Guyana Shield) amphibolites or similar rocks (Figure 6.22). The mineral was also present in river sands that drain the Northern Range of Trinidad (van Andel and Postma, 1954) where volcanic beds in the Maracas Formation are a potential source (see Jackson et al., 1991). Yet the supply from these beds is likely to be volumetrically inferior to Orinoco-derived hornblende judging from the widespread occurrence of the mineral in Orinoco-derived sands. Pyroxenes are limited in number in both modern and ancient sands (Appendix 11, Figure 6.22). In modern sands, some contribution comes from the Guyana Shield (GS Association) and metabasalts in the Caribbean Mountains (San Souci Formation of Figure 6.22). 6.2.4 SEDIMENT PROVENANCE INTERPRETATIONS (TRINIDAD BASINS) The index minerals described above have already been used to distinguish the provenance of South American sands. Hoorn (1993) used the change in Miocene heavy mineral assemblages from a lower, ultrastable-dominated to an upper, diverse suite (with chloritoid, epidote and garnet), to indicate a change in provenance from Guyana Shield to 394 Andean uplifts in the Solimoes Basin of northwest Brazil. The inference was supported by palynology and other indicators. The use of sillimanite by Morton and Johnsson (1993) was previously mentioned. They also used glaucophane, lawsonite, hornblende, actinolite, epidote, chloritoid and ultrastable minerals to differentiate between sands derived in the Caribbean Mountains from the Merida Andes, the latter with minerals characteristic of higher temperature metamorphism. Mineral assemblages derived from this investigation were plotted using three indices in order to discriminate between the three potential source groups (Figure 6.23). The "transport limited" index emphasizes the role of environments with a mature heavy mineral assemblage, almost to the exclusion of all other minerals (i.e. high ZTR index) produced by either deep weathering in stable lowland plains or reworking from mature sandstones. These sediments may be derived from intracratonic basin, craton lowlands or 'stable' foreland basins such as within the Guyana Shield or Llanos Basin. Additionally these may be supplied from uplift and erosion of mature sedimentary rocks. Other criteria will be required to differentiate between these two basin settings (e.g. textural immaturity). This index is determined by: ^{zircon, tourmaline, rutile ) x ZTR where ZTR refers to the stability index of Hubert (1962), expressed as a decimal. Based on the ZTR weighting, samples with higher ultrastable suites will plot closer to the "transport-limited/reworked sedimentary" pole, while those with other statistically significant minerals will be drawn away. The direction away from this pole is determined by the relative amounts of the other two indices. The second index emphasizes the importance of low temperature-high pressure/ low pressure (LT/HP-LP) metamorphic sources such as the Caribbean Mountains, and is the sum counts of index minerals for low-grade, greenschist facies metamorphism. Minerals include those characteristic of Caribbean Mountain lithology and detritus. They compare to the "Caribbean Association" of heavy minerals in Figure 6.22. Detrital chlorite is also considered because of its relative abundance in some samples and utility as an index mineral of low-grade metamorphism (Winkler, 1974). The third index emphasizes the role of high temperature metamorphic minerals and is also the sum 395 counts of index minerals. Sources for these will lie in the Guyana Shield or the Merida Andes to the west of Venezuela and they compare best with the "GS association" for modern sands (Figure 6.22). The various indices were normalized to 100% and represented in a "TL-HG-LG" (transport limited- high grade- low grade) ternary plot (Figure 6.23) from which three groups can be recognized. Samples from the Paleocene-Eocene of Trinidad cluster around the "transport-limited pole" while Pliocene samples cluster at the low-grade metamorphic pole. Samples from the Late Oligocene/Early Miocene Nariva sandstones and the Eocene-Oligocene Scotland Formation of Barbados tend away from the "transport-limited" pole toward the low-grade metamorphic sources. These general trends will be discussed in relative detail below, incorporating the modal detrital framework of sandstones. LT/HP-LP LEGEND metamorphic Pliocene (Caribbean Mountains) Mineral assemblages • Morne L'Enfer Formation Transport- High grade LWHP/LP + Cruse Formation Brntted metamorphte Lower fro Midfl(e Miocene metemorphrs ^ Herrera Sandstone Member zircon sillimanits Oliflocene - Lower Miocene tourmaline stauroHte cWoritoid • Cipero Fm (Plum Mitan) ruttle garnet chlorite X Nariva Formation x2tr¥t@© andalusite actinoftte 0 Angostura Sandstone Paleoccne-Eocene (other Index) A San Fernando Formation glaucophane A Pointe-a-Pierre Formation lawsontte • Chaudi&rc Formation kyantte Scotland Fm (Eocene of Barbados) High grade Transport-limited metamorphic Reworked sedimentary (craton, Merida (craton, stable foreland) Andes) Figure 6.23 Ternary plot of the relative abundance of minerals ascribed to the "Transport-limited", "High- grade metamorphic" and "Caribbean Mountains" provenance groups in individual samples from Trinidad and Barbados. The minerals used to discern these groups are shown in the table; "other index" minerals can also be diagnostic but were not sampled or occurred in insignificant numbers (e.g. kyanite). 396 6.2.4.1 CRETACEOUS The only arkosic arenite was derived from the Toco Formation of Aptian (Early Cretaceous) age (Figures 6.4 and 6.5). This feldspathic sandstone contained rare plutonic rock fragments. Barr (1962) also noted the arkosic character of these sandstones together with the occurrence of granitic pebbles; he noted the same in the "Balandra Grits" also of Early Cretaceous age. The Albian Gautier and Santonian-Campanian Naparima Hill formations also contain feldspathic sandstones (Figure 6.4; Patterson, 1991) though these are compositionally more mature than that of the Toco Formation. These Cretaceous samples collectively plot within the "transitional continental" to "craton interior" provenance fields of Dickinson and Suczek (1979) (Figure 6.24), interpreted to originate from feldspar-rich basement complexes. They were likely sourced directly from granites, amphibolites and other exposures known in the Imataca Complex and greater Guyana Shield, or reworked from arkosic sandstones (Figure 6.22). The low lithic and high feldspar fractions (Q72F76LL1) are similar to the arkosic "Brazilian sub-Association" of Potter (1994) sourced from basement uplifts and highland areas within the Shield. Maastrichtian sandstones of the Galera Formation comprise mature quartz arenites with rare chert lithics (Figures 6.4 and 6.5). This is consistent with the observations of Punch (2004) from the same formation. These arenites are one end- member of an apparent transition to increasing compositional maturity (arkoses to arenites) throughout the Cretaceous (Figure 6.24). Guided by the interpretations of Dickinson and Suczek (1979), the transition reflects changing sediment sources from cratonic highlands and uplifted basement blocks (e.g. Toco Formation), to stable intracratonic basins and lowland plains during the Cenomanian-Maastrichtian. It is proposed that the loss of feldspar occurred by chemical dissolution, enhanced by the longer residence times within increasingly stable basin settings, as currently occurs within lowland areas of the Guyana Shield (Stallard et al., 1990). The same can occur within 'stable' foreland basins as is happening in the Llanos Basin, outboard of the Guyana Shield (Johnsson et al., 1988; Stallard et al., 1990). The sample was derived from a coastal exposure at L'Anse Noir along the north coast of Trinidad. 397 The South American continental craton south of the present study area is the most likely source for Cretaceous sediments. Early Cretaceous arkosic and quartzose sediments were eroded from uplifted plutonic, gneissic and sedimentary basement rocks as currently exposed within the Imataca complex of the Guyana Shield and delivered to the continental edge by north-flowing precursors to the Orinoco and Amazon (Hoorn, 1993). The quartz sublitharenite also known from the Early Cretaceous Cuche Formation with very low feldspar and metamorphic lithic fragments (Figures 6.14 and 6.18) indicate that other sediment sources were also active at that time. 6.2.4.2 PALEOCENE-EOCENE Similar to the Upper Cretaceous sandstones, the average composition of Paleocene to Middle Eocene quartz arenites of the Chaudiere and Pointe-a-Pierre formations plot within the "craton interior" field on QmFLt provenance diagrams (Figure 6.24), but also converge towards a transitional area that represents a "compositional bridge" between major provenance domains (Dickinson and Suczek, 1979, p. 2173). Three scenarios are considered regarding their origin. First, their mature mineralogical composition can be a direct correlation to a compositionally mature source rock; second, the composition is due to pre-depositional weathering and/or abrasion within the source basin as described above; and third, the composition is as a result of post-depositional reworking and diagenetic alteration. The second scenario is preferred as the Paleocene-Eocene arenites represent the minimum of an apparently systematic decline in feldspar content with decreasing age since the Cretaceous (Figure 6.24). Post- depositional diagenetic dissolution would show the opposite trend (i.e. increasing feldspar quantities with decreasing age). The low feldspar content also appears characteristic of the sediment source as discussed above (Section 6.2.1). Quartz enrichment due to post-depositional reworking within energetic depositional environments (e.g. Mack, 1984) is unlikely, as these turbidite beds have not been reworked in their deep-water environment (Chapters 2 and 3). The preferred interpretation is that the relative enrichment of quartz occurred prior to deposition in the 398 Figure 6.24. Provenance of selected Trinidad sandstones from QmFLt Dickinson plots. (A) QmFLt plot of Trinidad Cenozoic and Mesozoic sandstones showing a continental block and recycled orogenic provenance. (B) The same plot with only average detrital composition of selected Cenozoic and Mesozoic sandstones (individual samples in Galera and Toco formations) showing the transition in provenance from continental sources (Cretaceous) to a gradually increasing recycled orogenic phase throughout the Cenozoic. Late Eocene to Early Oligocene sandstones were deposited during a transitional phase (t, see text). The reasons for the 'out-of-sequence' Late Eocene sandstones are discussed in text. Note that polycrystalline quartz was not differentiated in Gautier and Naparima Hill averages as required for these plots (from Patterson, 1991, see Figure 6.3) and the attached arrow shows the expected shift in data if this were done. 95% confidence polygons are shown around the Early Cenozoic sandstones only. In (B), Chaudiere sandstone is included in the Pointe-a-Pierre sandstone average. 399 LEGEND Upper Pliocene $ all U. Pliocene A Moruga Formation • Mome L'Eafer Formation • Springvate Formation Upper Miocene to Lower Miocene j£ all II. Miocene to L. Pliocene B + Cruse Formation Qm\ Late Cretaceous • Manzanilla Formation Paleocene/Mid Eocene n = 13 Paleoeene lo Lower Miocene GaleraFm =1 O Herrera Sandstone Member " < _^- "out-of- sequence' • Plum Milan (Cipero Fm) \Mid Oligocene n=7 X Nariva Formation O Angostura Sandstone >> Late Eocene n=6 *• San Fernando Formation Late Cretaceous A Pointe-a-Pierre Formation Gautier (14) & Late Oligocene n=13 • Chaudiere Formation iHJH(1) Upper Cretaceous © Ga lcra Formation • Gautier & Naparima Hill Fm Mid Miocene n=7 Lower Cretaceow # Toco Formation Early Pliocene n=5 Early Cretaceous \ n=1 Late Pliocene n=4 Lt F^ Qm^, LtjeQlllsa receiving basin. The initial quartzose composition of the sands finds further support in the abundant silica cement that shows an affinity for quartz-rich sandstones (Blatt, 1979; also see Section 6.1.19.1). The northern South America passive margin was the most likely source for the Paleocene-Eocene arenites. Quartz enrichment occurred along the foothills of the Guyana Shield or other intracratonic basins before incorporation into the sedimentary cycle and delivery as deep-water turbidites north of the continental margin. In parallel with the low quantity of feldspars, the relative absence of lithic fragments (Figures 6.17 and 6.18) also suggests prolonged chemical weathering and, less likely, long transport distances (Harrell and Blatt, 1978; Picard and McBride, 2007). The dominant siliciclastic detritus and subordinate schists and phyllites suggest that eroded sedimentary and metamorphic cover may have been the primary contributing source rocks. Some inferences as to the original source rock can also be made from the associated heavy minerals. Paleocene to Eocene arenites are characterized by heavy mineral assemblage "1", dominated by ultrastable minerals, and plot at the "transport- limited" pole on the TL-HG-LG ternary plot (Figure 6.23). Similar to the framework components, the enrichment of ultrastable minerals occurred within the source basin. The same abundance and diversity of heavy mineral species in both well-cemented (impervious) and friable samples support this assumption, as post-depositional dissolution would have resulted in greater depletion in permeable horizons (Morton, 1985; Morton and Hallsworth, 1994). The enrichment in ultrastable heavy minerals provides additional evidence of prolonged residence time of sediments within source catchments. The rare occurrence of high-grade metamorphic minerals gives the only indication of at least one parent rock (Figure 6.25); these minerals are most common to the 'GS association' for modern day sands derived from the Guyana Shield (Figure 6.22). The mature composition of these sandstones (average Q98F1L1) is best equated with the "Brazilian Association" of Potter (1994), currently derived from tropical rivers such as the Orinoco, with watersheds in crystalline basement rocks and extensive foreland plains. The low relief of their drainage basins facilitates the chemical dissolution of mineral species and maturation of the sands until almost pure quartz and 401 zircon are delivered to their river mouths (e.g. Orinoco River: van Andel and Postma, 1954). The previous inferences of an Early Cenozoic northern orogenic source (see Sections 2.2.1 and 2.2.2), are not supported by these findings. Mature quartz arenites are not a product of proximal orogenic uplifts. These are associated with sublitharenites and litharenites with common sandstone, metamorphic or igneous lithic fragments depending on the deformed protolith (Crook, 1974; Dickinson et al., 1985; Stallard et al., 1990; Garzanti et al, 2007). A southern source for Paleocene-Eocene arenites is preferred, derived from platform covers or intracontinental basins on a stable South American craton. The mineralogical data is in agreement with northerly-directed paleocurrents for turbidites in the Pointe-a-Pierre Formation (Figure 2.10, Section 2.2.6). 6.2.4.3 LATE EOCENE THROUGH MIDDLE OLIGOCENE The arenites and sublitharenites of the San Fernando Formation and Angostura Sandstone (Cipero Formation) characterize this interval (Figures 6.4 and 6.5). Their average compositions plot within a transitional area between the "craton interior" and "recycled orogen" provenance fields on QmFLt diagrams (Figure 6.24), and hence a clear distinction cannot be made between these two provenance domains. Similarly, their total average lithic percentage is intermediate between sandstones from the "craton interior" and "recycled orogen" provenance domain (i.e. Pointe-a-Pierre and Nariva formations respectively in Figures 6.17 and 6.18), but is still relatively low. Average feldspar content remains low (2.6%), but is still greater than the Pointe-a-Pierre Formation. The low feldspar and lithic abundances are attributed to the same source constraints as with the Eocene samples from the Pointe-a-Pierre Formation. The quantity of feldspar is marginally greater and this reflects a reversal from the Cretaceous to Eocene trend of decreasing feldspar. This increase occurred in parallel with a marginal increase in lithic fragments, and may collectively reflect the onset of changing sediment sources relative to earlier sandstones. This is more evident in samples from the 402 % Sample no. 0 20 40 60 80 100 Aae (approx.) Formation/unit 8 assemblage (3)HV6017 i i LATE Morne L'Enfer Fm (3) HV6033 PLIOCENE (3)HV6040 EARLY Cruse Fm (3)HV5032 PLIOCENE EARLY Herrera Sst Mbr (2) HV6026 MIOCENE (2) HV5029 (2) HV5007 LATE (2) HV5009 Nariva Formation OLIGOCENE (2) HV5022 (2) HV5023 (1)HV5018 * OLIGOCENE Angostura Sst Mbr (1)AS1.9 * (1)HV5001 * LATE San Fernando Fm EOCENE (2) HV7039 (1) HV5006 * (1) HV5012 * Pointe-a-Pierre Fm (1)HVS013 * (1)Hv5046 EOCENE- (1) HV6029 * PALEOCENE (1)HV5044 * Chaudiere Fm (1)HV5049 * (1)BD1 EOCENE Scotland Fm (2) HV6007 (Barbados) (2)MV6Q08 :::,:;;;i;::i;,;;il (2)HV6009 ::'X;:-:-i':-:-:- :;;•:;:•:•:•;-:•:•:•:•:• :•:•;•:•:-;• !-i'!-!-!'^H i 1 HGM LGM I •:->:::•;,•! Figure 6.25 Relative proportion of low grade (LGM) versus high-grade (HGM) metamorphic- derived heavy minerals within Cenozoic samples from Trinidad and Barbados. LGM includes chlorite, chloritoid, epidote and actinolite and HGM includes garnet, andalusite, sillimanite and staurolite. Samples with asterisks (*) comprise ultrastable minerals, all from heavy mineral assemblage '1'. See text for rationale behind the choice of minerals. Numbers in parenthesis denote the heavy mineral assemblage group discussed in text. 403 Angostura Sandstone where the proportions of metamorphic and sedimentary rock fragments are approximately equal, unlike earlier arenites that were dominated by sedimentary rock fragments (Figure 6.18). Derivation from older sedimentary rocks is still suggested by the sandstone, siltstone and chert fragments in the Angostura Sandstone and abraded silica overgrowths in the San Fernando arenites. Lithic fragments are fewer within the younger Angostura Sandstone relative to the older San Fernando Formation, and this represents a departure from the trend with decreasing age between all other Cenozoic sandstones ("out of sequence" in Figure 6.24). This reversal may be a reflection of differences in sediment sources and depositional environments, particularly within the San Fernando Formation. Alternatively, this may be an artifact arising from the sampling constraints with the San Fernando Formation (Sections 2.3.1 and 6.2.1.2). The large confidence interval around the San Fernando data point (Figure 6.24) attests to this uncertainty. Another difference with the Eocene sandstones is the common bioclastic and carbonate rock fragments. The mode of occurrence and types of bioclastic fragments (Figures 6.8 B and 6.9 B and) suggest that many of these are intrabasinal. They will be further considered during the discussion of basin settings and palaeogeography in Chapter 7. Similar to Eocene sandstones, ultrastable heavy minerals dominate the heavy mineral suite in both the San Fernando Formation and Angostura Sandstone. Samples plot at the transport-limited pole of the TL-HG-LG plot (Figure 6.23) indicative of a similar sediment source as the Chaudiere/Pointe-a-Pierre sandstones. Common garnet and staurolite within one sample from the San Fernando Formation (see sample HV7039 in Figures 6.19 and 6.25) caused a departure from the transport-limited pole toward the high-grade metamorphic pole and is suggestive of an additional contribution from this source, also similar to the Chaudiere/Pointe-a-Pierre sandstones. Those minerals are correlatable with the "GS association" of heavy minerals within modern sands that were derived from the Guyana Shield (Figures 6.22). A similar source is interpreted for heavy minerals in the San Fernando sample. The composition of these sandstones (average Q96F2L2 and Q91F3L6 for Angostura and San Fernando respectively) is also analogous to the "Brazilian Association" of Potter 404 (1994), which suggests similar derivation as the Chaudiere/Pointe-a-Pierre sandstones (Shield-sourced). During the Late Eocene to Middle Oligocene, compositionally mature sediments were still being derived from the South American craton, with a contribution from both recycled sedimentary and high- to medium-grade metamorphic rocks. There is no significant change in the heavy mineral diversity from earlier sandstones. An increase in the feldspar and metamorphic rock fragments relative to earlier sandstones may however reflect changes in basin settings and the onset of "recycled orogen" provenance. This becomes more obvious in younger sandstones of the Nariva Formation. 6.2.4.4 LATE OLIGOCENE TO EARLY MIOCENE The sandstones of the Nariva Formation characterize this interval (Figures 6.4 and 6.5). Their average composition plots within the "recycled orogen" provenance field on the QmFLt diagram (Figure 6.24), which suggests a change in basin settings from earlier formations. Lithic fragments are more abundant on average than older Cenozoic sandstones due to an increase in mica-schists and phyllitic rock fragments indicative of a metamorphic source (Figures 6.17 and 6.18). There is no significant change in feldspar abundance relative to the San Fernando Formation and Angostura Sandstone. The "recycled orogen" provenance is characteristic of numerous tectonic settings but is generally indicative of deformation, uplift and erosion. The increasing input of metamorphic lithic fragments, very low feldspar content and numerous abraded silica overgrowths (indicative of sediment recycling) (e.g. Figure 6.10 F) within these sandstones, are all characteristic of this tectonic basin setting (Dickinson and Suczek, 1979; Dickinson, 1985). The changing heavy mineral compositions lend additional support for changing sediment dispersal patterns at this time. The change to heavy mineral assemblage "2" with significant quantities of chloritoid and chlorite is a departure from earlier sandstones. These minerals cause samples from the Nariva Formation to plot away from the "transport-limited" pole and towards the "Caribbean Mountain" pole in the TL-HG- LG ternary plot (Figure 6.23). The heavy mineral assemblage is analogous to "Caribbean 405 Mountain Association" for modern sands ("CM1" in Figure 6.22). All these factors suggest a low grade, up to greenschist facies, metamorphic source and a significant input of sediments from the Caribbean Mountains. The ultrastable heavy minerals are still dominant and indicate the perpetuation of earlier sediment sources (South American craton), erosion and sediment recycling of earlier formations. The composition of these sandstones (average Q90F2L8) is similar to the "Brazilian Association" of Potter (1994), suggesting accumulation within low relief basins in cratonic areas during some time of the sedimentary cycle, prior to final deposition. The collective petrological evidence suggests that an uplifting metamorphic orogen, up to greenschist facies, was then supplying significant amounts of detritus to the Nariva Formation sandstones. The age of these rocks coincides with dates of uplift for the Caribbean Mountain System (49-12 Ma, zircon fission track; 25 Ma, Ar/Ar, see Figure 6.21) and this is proposed as the partial source for these sediments. Most of these coarse elastics were still being derived from the South American craton. 6.2.4.5 EARLY TO MIDDLE MIOCENE This interval is represented by the Herrera Sandstone Member of the Cipero Formation. The average framework composition of these sandstones plots within the "recycled orogen" field on QmFLt plots where they conform to the trend of increasing lithic fragments in successively younger Cenozoic sandstones (Figures 6.17, 6.18 and 6.24). This increasingly immature composition may indicate closer proximity to the orogenic source as demonstrated in modern sands along the Andean front of northern South America (Stallard et al., 1990). Unlike samples from the Nariva Formation, sedimentary rock fragments are the most abundant lithic fraction (Figure 6.18) but the presence of mud rip-up laminae, fossiliferous siltstone, mudstone lithics and bioclastic fragments suggests that many were derived from proximal or intrabasinal sources. These will be further integrated when sandstone lithofacies and mineralogy are collectively considered (Chapter 7). Ultrastable minerals still dominate the heavy mineral assemblage (assemblage "2") and the samples plot very near the "transport-limited" pole in the discriminatory 406 ternary diagram (Figures 6.19 and 6.23). This suggests a supply primarily of mature sands from lowland areas on the continental platform and/or sedimentary recycling of older formations, the latter is supported by the numerous sedimentary lithics. The heavy mineral composition indicates continued supply of low-grade metamorphic detritus with common chloritoid and chlorite, very similar to the "Caribbean Mountain Association for modern sands ("CM1" in Figure 6.22). Input from the low grade metamorphic rocks of the Caribbean Mountains was the most likely source, further supported by the presence of kyanite, the primary aluminosilicate associated with the mountain belt (Maresch, 1974). The composition of the sandstones (average Q83F3L14) compares best with the Brazilian "sublithic" Association of Potter (1994) and, similar to the older Cenozoic sandstones is suggestive of a Guyana Shield source. In summary, these sandstones originated from multiple sources: (1) proximal, reworked sedimentary rocks; (2) Caribbea Mountain; and (3) lowlands on the South American craton. 6.2.4.6 PLIOCENE The sublitharenites and lithic arenites (Figure 6.4) of the Cruse, Manzanilla and Morne L'Enfer formations characterize this interval. The average composition of these sands and sandstones plots within the "recycled orogen" field on the QmFLt plot, and this suggests an origin associated with uplift and erosion (Figure 6.24). They contain the highest lithic percentage of all sandstones investigated and are interpreted to indicate the closest proximity to the orogenic front (Stallard et al., 1990; Potter 1994). Metamorphic detritus is abundant, present as coarse, schistose and strained, polycrystalline quartz lithic fragments in the Manzanilla Formation, and finer grained mica-schists in Cruse and Morne L'Enfer sediments (Figures 6.14 and 6.15). Heavy mineral assemblage "3" predominates with abundant epidote25, chlorite and chloritoid within a diverse suite relative to older sandstones. Pliocene samples plot Epidote is a common mineral in the basic igneous rocks of the San Souci Formation that crop out to the northeast of Trinidad. Although not described herein, a thin section 407 closest to the "Caribbean Mountains" pole on the discriminatory ternary diagram (Figure 6.23) suggesting that for the first time, this was the dominant source of sediments into the basin. The heavy mineral suite can be directly correlated to the "CM1" association for modern sands both in terms of relative abundance of index minerals and mineral diversity (epidote +chlorite +chloritoid + hornblende +actinolite +kyanite). Minerals indicative of higher grades are also present but in the minority (Figures 6.19, 6.22 and 6.235). The composition of the Pliocene sands (average Q76F5L19) approximates to the "transitional association" of Potter (1994; average Q61F7R32) or the "sublithic Brazilian Association" (lithics <20%). Within the continent they are found either in the lowlands immediately east of the Andes (e.g. Llanos Basin), or within rivers that drain the mountain front. Their composition can range from immature lithic arenites sourced directly from the Andean mountains to mature quartzose sands in distal river reaches. This correlation with modern sands suggests that, of all the sands investigated, Pliocene sands show the strongest "Andean petrographic signal" (Potter, 1994, p. 221), and derivation from the Caribbean Mountains was most likely. The Caribbean Mountains is interpreted to be a primary contributor of sediments into the basin at this time. The lithofacies attributes of Pliocene environments indicate relatively neritic environments proximal to the Northern Range of Trinidad (Manzanilla Formation) were coeval with relatively deeper-water slope to outer shelf environments towards the south (Cruse Formation; Sections 4.1 and 5.4.4), although the effect of an uplifting Central Range (Babb and Mann, 1999) on their lateral continuity is uncertain. West to east paleocurrents occur in the Morne L'Enfer Formation (Figure 4.12;) indicating longitudinal sediment transport, parallel to the strike of the mountain belt. The continental sources that supplied mature sands throughout most of the Cenozoic are now suppressed as reflected in the low ZTR index values and relative immaturity of sands. Its contribution may still be reflected however in the stable (zircons) and high-grade metamorphic minerals (andalusite, sillimanite, garnet). Zircon- rich sands are currently abundant at the mouth of the Orinoco River and Gulf of Paria, as this source has continued throughout the Cenozoic (Figure 6.22; van Andel and Postma, from this formation was examined. Also see modal analysis of van Andel and Postma (1954) illustrated in Figure 6.22. 408 1954), and compositionally mature sediments are known to exist within the Apure-Llanos Basin (Johnsson et al., 1988). During the Pliocene, there was also considerable potential for southerly derived sediments from the large rivers that empty south along the Brazilian and Guyana shelf (Amazon, Essiquibo), as these currently supply sediment volumes to northern areas that equal or exceed that supplied by the Orinoco river (van Andel, 1967; Eisma et al., 1978; Warne et al., 2000; Asian et al., 2003). 6.2.5 SEDIMENT PROVENANCE INTERPRETATIONS (SCOTLAND FORMATION) Sandstones of the Scotland Formation (Barbados) are mature quartz arenites of similar composition to Paleogene sandstones of Trinidad (average Q96F>iL<4). This composition compares best with the "Brazilian Association" of Potter (1994) of Guyana Shield derivation. The average position of samples from the Eocene Scotland Formation sandstones lie within the "transitional" area between "craton interior" and "recycled orogen" provenance fields on QmFLt plots, hence a clear distinction cannot be made between the "craton interior" and "recycled orogen" provenance domain of Dickinson (1985). Of the four samples analyzed, one falls into heavy mineral assemblage "1" while three are characteristic of assemblage "2" (Figure 6.18). When compared to modern sands (Figure 6.22), the mineral assemblage contains elements of the Guyana Shield (GS), Caribbean Mountain (CM) and Orinoco (O) associations, which suggest derivation from multiple sources. Ultrastable minerals are statistically dominant but other minerals such as garnet, kyanite, chloritoid, andalusite and chlorite are also common. This is reflected in the TL-HG-LG ternary plot where there is a scatter among samples ranging from the transport-limited pole towards the low grade metamorphic pole, though all samples reflect the dominant ultrastable assemblage (Figure 6.23). The sources interpreted from this trend are lowland plains within stable continental or foreland basins, 26 This is not illustrated although the sandstones were also analyzed and counted along with others from Trinidad. 409 and/or reworked sedimentary domains. There may have been a minor input from low- grade metamorphic rocks and even less from high-grade metamorphic rocks. 6.2.6 SUMMARY OF SEDIMENT PROVENANCE Sandstone detrital framework and heavy mineral separates provided several insights into sediment provenance and dispersal patterns throughout the Trinidad Cenozoic. Evidence suggests that the South American continental margin to the south was overwhelmingly the primary supplier of sediment since the Early Cretaceous, from which time some of the early trends in basin evolution can be detected from the changing sandstone compositions. Only during the latest Cenozoic was the petrologic imprint from the continent suppressed and replaced by that of the Caribbean Mountains, indicating a major change in basin settings. Sandstones from the Scotland Formation of Barbados have always been correlated with those of the Eocene Pointe-a-Pierre Formation on lithological grounds, but their petrologic character is more akin to the Oligocene sandstones of Trinidad. Early Cretaceous arkosic sandstones, represented by the Toco Formation, were supplied into deep-water environments to the north directly from uplifted basement blocks and highlands in the Guyana Shield. The numerous feldspar-rich amphibolites, granites, gneiss, arkosic sandstones and other rocks in the Shield were all potential sediment sources for these feldspathic sandstones. By the Maastrichtian, arkoses were replaced by increasingly mature quartz arenites. Actualistic models based on modern sandstone compositions suggest that these changes were related to increasing tectonic stability of the continental craton, accompanied by simultaneous decrease in erosion and transportation rates from low-relief platforms and intracratonic basins. These areas effectively acted as a 'filter' whereby much of the labile minerals and fragments from primary source rocks were selectively removed by chemical weathering, creating instead quartzose and zircon-rich sands that were later transferred to the continental shelf and deepwater basins to the north. The petrologic imprint of such a source is strongest in the Maastritchtian to Eocene Galera to Pointe-a-Pierre formations, which comprise some of the most mature sandstones in the Trinidad stratigraphy. This source persisted 410 throughout the Cenozoic, and today is associated with the "stable" lowlands of both the Andean foreland basin and the Guyana Shield. The Cenozoic sandstones evolved from mature Paleocene-Eocene quartz arenites sourced from continental lowlands, into immature litharenites sourced primarily from the uplifted Caribbean Mountains. The transition in sediment sources was evident from Oligocene sandstones and in particular those of the Nariva Formation, for which there is overwhelming evidence from both the modal detrital framework and heavy mineral fractions. These sandstones show a clear "recycled orogen" signature on Dickinson compositional plots, and there is a significant increase in lithic fragments contributed mainly by metamorphic detritus; the latter represented a distinct change from the siliciclastic-dominated rock fragments of earlier sandstones. The evidence is strengthened by the associated heavy minerals with an abundance of chlorite, chloritoid and epidote, all attributed to low grade metamorphic sources. Sediment dispersal patterns gradually became south and east directed during the later Cenozoic. By the Pliocene it is apparent that most of the detritus supplied to the basin were derived from the uplifted mountain front to the west and north of the continental craton. For the first time since the Cretaceous, the South American craton was not the dominant contributor of sediments into northeastern basins. The changes in sedimentary provenance did not occur in isolation but can be correlated with similar changes in sandstone composition across northern South America, all associated with Neogene uplift of the Andean Mountain front. The temporal compositional changes observed in Trinidad show similar trends to spatial compositional variations in modern sands across the continent. Arkosic sediments occur around uplifted Shield highlands of the Gran Sabana and Serra do Mar, while increasingly quartzose sediments occur in associated lowland basins, resulting from chemical dissolution of labile constituents (Franzinelli and Potter, 1983; Johnsson et al., 1988; Stallard et al., 1990; Johnsson, 1990; Potter, 1994). Large rivers, such as the Orinoco, deliver quartzose sands to their mouths (van Andel and Postma, 1954) from quartz-rich, low-relief drainage basins characterized by long periods of sediment retention. These contrast with the lithic-rich sediments derived from Andean uplifts, with the abundance of lithic fragments directly correlatable to distance from the mountain front (Potter, 1994; Stallard et al., 1990). Potter describes this relationship with 411 sand "associations" sourced from the Andean highlands or Shield areas, whereby increasingly immature sediments occur towards the Andean foothills. Elements of his Shield-sourced "Brazilian association" and mixed-sourced "Transitional association" are today found in the northeastern margin of South America. This spatial relationship was also recognized in ancient sandstones where mature Shield-derived sands are replaced upward by "transitional" Andean-derived (Caribbean Mountains) sands. The spatial distribution of heavy minerals sourced from these various tectonic domains was also traced to ancient sandstones, and provided additional constraints on the incoming "Andean" influence around the Late Oligocene to Early Miocene. There is a good correlation between the two mineral fractions used (light and heavy), and these petrological changes provide very good constraints on sedimentary provenance. These changes have been recognized previously in ancient sediments around northern South America, but not explicitly so in the Trinidad area. Hoorn (1993) recognized the Miocene change in heavy mineral assemblages in the Solimoes basin of northwest Brazil, resulting from the Andean uplift. The comprehensive study by van Andel (1958) in northwest Venezuela documented mineralogical changes that were attributed to changing sediment sources, van Andel documented: 1. Pre-Aptian igneous and metamorphic-sourced arkosic sandstones of the Rio-Negro Formation co-existing with minor Guyana Shield-sourced quartzose sandstones (>95% quartz). 2. Aptian-Coniacian Guyana Shield-sourced quartzose sandstones. 3. Senonian quartzose and arkosic sandstones of the Colon Formation; feldspar content is lower than Pre-Aptian sandstones. Restricted belt of immature "greywackes" to the west of the basin with "very little" feldspar and "abundant" chert and sandstone rock fragments. 4. Paleocene "greywacke" province, sourced from the west and quartzose sandstone province in the east; both types of sandstone were equally common. 5. Middle Eocene "greywacke" and "subgreywacke" sandstones dominate. The encroaching "greywackes" over what was formerly arkosic and then dominantly quartzose sandstones are similar to changes documented in this investigation. 412 Van Andel similarly attributed the changes to uplift of the Colombian Andes and dispersal of its sediment into western Venezuela. The effects of the northern uplifts were recognized earlier in the western Venezuela stratigraphy than in the Trinidad area (i.e. Paleocene versus Late Oligocene). The results from this study do not support inferences for a northern source of elastics during the Paleocene-Eocene as proffered by several workers. Similarly, the results also suggest that a southern Guyana Shield was not the dominant source for Pliocene sands, which differs from that suggested by previous workers (Barr et al., 1958; Michelson, 1976; Stainforth, 1978; Henry, 1992). The results partially agree with that of Michelson (1976), who deduced a change in source direction to the Guyana Shield for sands younger than the Cruse Formation. The evidence presented here instead suggest a perpetuation of a northwest source to the late Pliocene. There was also no conclusive indication of potential igneous sources for the sandstones investigated as suggested by other workers (Suter, 1960; Harry, 1992). Although a significant source of igneous detritus persisted throughout the Cenozoic in the Guyana Shield to the south, it is apparent that this source rock signature was lost by chemical weathering prior to deposition within the Trinidad area. The results of this study, however, concur with previous assumptions of South American sourced sediments throughout much of the Cenozoic history, though it must be emphasised that the lithological variety in the Guyana Shield itself was not the main determinant of sediment composition in Trinidad basins to the north. Most of the petrological signatures from the Shield are destroyed by chemical weathering within the adjacent lowland plains, which eventually resulted in the delivery of compositionally mature sediments to Trinidad basins. The timing and relative contribution of the Caribbean Mountain belt has also been underestimated, and this is more so for the Pliocene sands that were often attributed to Guyana Shield sources. These conclusions regarding sediment dispersal patterns will be integrated with lithofacies and trace fossil associations in the following chapter. 413 Chapter 7 - Conclusions Changes in lithofacies, ichnofacies and mineralogy in Trinidad Cenozoic sandstones document a transition from coarse-grained, deep-water sediments sourced from a passive continental margin to fine-grainedshallow-wate r sediments sourced from an uplifted mountain belt. The two contrasting sources are the South American craton towards the south and the Caribbean Mountains towards the north. Paleogene sediments consisted of mature quartz arenites and sublitharenites derived from lowland areas on the South American craton and delivered to a northern passive continental margin. By the Pliocene, immature, syn-orogenic lithic arenites were being delivered from west and northerly sources associated with uplift of the Caribbean Mountains, north of the continental margin. There is no evidence from changes in sandstone composition, sedimentary processes, depositional environments and provenance to suggest that this change in basin settings occurred during the Paleogene, and it must be concluded that passive margin conditions continued during that time. Sandstone composition however documents the increasing influence of a secondary sediment source throughout the Cenozoic period, and it is likely that sediments were being introduced into Trinidad basins from the west. It was not until the Late Oligocene to Early Miocene that significant changes in sandstone composition and sedimentary stacking provided evidence for active deposition from the Caribbean Mountains, with syn-orogenic sediments actively delivered to the Trinidad area. This sediment source continued into the Pliocene when it became dominant. Cenozoic sediment dispersal patterns in Trinidad were investigated through the integration of lithofacies, ichnofacies and sandstone petrology. The foregoing chapters outlined the rationale and results arising from these approaches. This chapter integrates these results to address the objectives of the thesis and substantiate the conclusions presented above. This chapter will (1) review the depositional characteristics of sandstones within individual formations that provide insights into the overall basin settings; (2) review the palaeogeographic evolution of the basin throughout the Cenozoic with respect to changes in facies, processes, sandstone composition, palaeocurrents; and (3) discuss the implications for the formal stratigraphic column of Trinidad. A synopsis 414 of the results arising from this thesis and interpretations regarding the evolution of Trinidad basins is shown in Figure 7.1. Benthic foraminifera in the Maastrichtian to Paleocene Guayaguayare and Lizard Springs formations indicated bathyal to abyssal palaeodepths (Table 3.1; Kaminski et al., 1988). This deep-water setting provides a convenient starting point to review the changing depositional settings from the beginning of the Cenozoic. Facies and facies associations for Paleocene to Early Miocene coarse elastics were examined in Chapters 2 and 3, and it was interpreted that sediment gravity flows were the primary delivery mechanism for sediments from the Chaudiere Formation to the Herrera Sandstone Member; similar processes are also recognized in the Cruse Formation. Distinctive facies, processes and mineralogy will now be summarized. 7.1 CHANGING SANDSTONE ATTRIBUTES THROUGHOUT THE CENOZOIC 7.1.1 SANDSTONES OF THE CHAUDIERE AND POINTE-A-PIERRE FORMATIONS Late Paleocene to Eocene sandstones of the Chaudiere and Pointe-a-Pierre formations are similar in terms of compositional and textural maturity, sedimentary processes, and interpreted depositional setting; these factors are supported by the gradational outcrop contacts (Kugler, 2001). Chaudiere Formation sandstones consist of amalgamated beds of pebbly sandstones deposited within confined, lower slope settings. These are upward transitional into the massive, coarse- to fine-grained sandstones of the Pointe-a-Pierre Formation, and eventually into the shale-prone tabular and lenticular sandstone facies, which field relationships suggest are the youngest exposed sandstones. Collectively they were deposited within middle to upper slope settings as traction and suspension-related grain, liquefied and turbulent flows (steady and unsteady), cohesive flows and block slides. Trace fossils within the Pierre Point Member of the Pointe-a- Pierre Formation can be compared to the Ophiomorpha rudis and Paleodicyton subichno- 415 Figure 7.1 Summation of lithofacies associations, depositional environments, sandstone mineral characteristics and trace fossil assemblages described throughout the thesis. These have been collectively interpreted to demonstrate the timing and importance of syn-orogenic sedimentation in the Trinidad region of the northern South American related to the uplift of the Caribbean Mountains from a formerly passive margin setting. 416 L\V f i i l i l l l l l i I i i l l i i t ! t i l t l l l t i i l l l l l l l i i i l t i I l i i i l t i i i i i i i f r i « r-1 PALEOCENE EOCENE OLIGOCENE MIOCENE |PUOCENE| g|| m I S I i- mE D facies of the Nereites ichnofacies (Seilacher, 1974; Uchman, 2001), both of which have been found in relatively proximal channels and lobes of deep sea turbidite systems. This further supports the depositional environment inferred from facies associations. A coarse agglutinated benthic foraminifera assemblage within shales of the Pointe-a-Pierre Formation suggests outer neritic to bathyal palaeodepths of deposition, and also substantiates the environmental interpretations. These sandstones are the most compositionally, and (apparently) texturally mature of all Cenozoic sandstones investigated, comprising approximately 1% lithic grains and over 98% of ultrastable heavy minerals (zircon, tourmaline and rutile). Siliciclastic rocks dominate the lithic fraction relative to metamorphic rock fragments while volcanic rock fragments are absent (they were not observed in any of the Cenozoic sandstones investigated). These sediments were sourced almost entirely from lowland areas on the South American craton similar to the present-day Llanos Basin. Some may have also been derived from lowland plains within the Guyana Shield as suggested by the rare occurrence of high grade metamorphic minerals such as staurolite and andalusite. The mineralogical assemblage of these sandstones is the main basis for these conclusions, supported by palaeocurrent measurements from flute casts, which suggests northerly-directed palaeoflow for the Pointe-a-Pierre Formation sandstones. 7.1.2 SANDSTONES OF THE SAN FERNANDO FORMATION The Late Eocene San Fernando Formation represents a chaotic canyon fill comprised of block and breccia conglomerates (of shallow-water, carbonate origin), quartzitic sandstones and conglomerates, allochthonous biohermal reefs, debris flows and silry marls. Coarse-grained turbidites are interbedded with these sediments. Sedimentary processes are similar to those of the Chaudiere/Pointe-a-Pierre succession and were dominated by coherent block slides, inertia-driven grain flows, cohesive, liquefied and turbulent flows. Turbidites appear relatively insignificant to debris flows and block slides when compared to the underlying Chaudiere/Pointe-a-Pierre succession; this is a recognized characteristic of upper (Stanley and Unrug, 1972; Cook, 1979) and lower (e.g. Cainelli, 1994) slope canyon fills. The San Fernando Formation contains abundant 418 shallow water fauna, which has been resedimented downslope from adjacent shelf areas. The abundant "evidence" for shelf sedimentation in the Trinidad area (e.g. Morne Roche Quarry, Soldado Formation, "bed 10", (section 2.3) is all resedimented blocks as part of the San Fernando canyon fill ("morros" of Kugler, 1953). Trace fossils were not observed among these sediments and no attempt was made to recover benthic foraminifera. The heterogeneous lithology of San Fernando sediments is similarly reflected in compositional maturity ranging from the mature quartzose sandstones of the Plaisance Conglomerate (1% lithic fraction, ZTR index of approximately 98%) to the relatively immature sandstones found on Soldado Rock (13% lithic fraction, ZTR index of 60%). The lithic fraction is dominated by sedimentary rock fragments, as with the older sandstones of the Chaudiere and Pointe-a-Pierre formations. Quartz grains were also notably angular in a few samples. Overall, these are still mature sandstones when compared to the younger Paleogene and Neogene sediments. The mature composition of these sediments was a direct derivation from transport-limited, low-lying sources on the South American craton (including the Guyana Shield), similar to the earlier Chaudiere and Pointe-a-Pierre formations. A contribution from high to medium grade metamorphic source rocks, likely from Guyana Shield "protoliths", was also interpreted from the common staurolite and garnet in the heavy mineral fraction (Section 6.2.4.3). No significant changes in tectonic setting are interpreted for the San Fernando Formation relative to the underlying Pointe-a-Pierre Formation; the two may even share gradational or erosive contacts (Lehner, 1935; Kuger, 1996, enclosure 12, Kugler, 2001). 7.1.3 SANDSTONES OF THE ANGOSTURA SANDSTONE MEMBER (CIPERO FORMATION) The Oligocene Angostura Sandstone Member is an amalgamated succession of massive and gradational, coarse to granule-sized pebbly sandstones, interpreted as lower slope to proximal basin floor channels and lobes. Sedimentary processes are similar to the underlying San Fernando and Chaudiere/Pointe-a-Pierre successions and include a 419 combination of traction and suspension-related grain, liquefied and turbulent flows (steady and unsteady) and cohesive flows. Cobble conglomerates are also a significant facies. The Angostura Sandstone is characterized by a low-diversity trace fossil assemblage interpreted to represent opportunistic colonizers; the assemblage has been correlated to the Ophiomorpha rudis subichnofacies found in the proximal parts of submarine fans. An agglutinated benthic foraminifera assemblage derived from an interbedded shale was considered "flysch-type" and indicative of "proximal" channels or fans at upper bathyal palaeodepths (Table 3.1). This further supports the environmental interpretations derived from physical and biogenic sedimentary structures. Similar to the Chaudiere/Pointe-a-Pierre succession, these sandstones are also compositionally and texturally mature (Section 6.1.19) although with a marginally higher average lithic fraction and feldspar content. The heavy mineral sample showed a mature assemblage, dominated by ultrastable heavy minerals (Section 6.1.20). A similar sediment source as the elastics of the San Fernando, Pointe-a-Pierre and Chaudiere formations was interpreted for sandstones of the Angostura Sandstone Member. The difference with the Angostura Sandstone is the increased proportion of metamorphic lithic fragments relative to sedimentary lithics (~ 50/50), which suggests an incipient metamorphic source. The immense thickness and aggradational stacking pattern of the Angostura Sandstone is also distinctive relative to other sandstone units. An analogy was drawn between this stacking pattern and those of structurally confined sedimentary basins (Sinclair, 2000; Cornamusini, 2004; Pudsey and Reading, 1982) and sand-rich delta-fed slope ramp systems (Link and Welton, 1982; Heller and Dickinson, 1985; Reading and Richards, 1994; Steel et al., 2000). Evidence for the latter is seen in the organic-rich, parallel-laminated sandstones cited as evidence for hyperpycnal flows related to deltaic extension on the shelf (Section 3.4.4). The structurally confined basin model implies syn-tectonic deposition was associated with these sandstones. This model has already been proposed for the Scotland Formation of Barbados (Pudsey and Reading, 1982) which originated from the same sediment source and is very similar in age and composition to the Angostura Sandstones. Larue and Speed (1983) noted the difficulty in comparing the stacked, thick-bedded and amalgamated sandstones of the Scotland Formation (their facies Tc3) to popular models of deep-sea sediments; the stacking 420 pattern is very similar to that observed for the Angostura Sandstone (Appendix 6). When stacking patterns are considered together with the changing lithic fraction, they provide the first indication of changing basin settings and modification of the passive continental margin in the Trinidad region. 7.1.4 SANDSTONES OF THE NARIVA FORMATION Similar facies successions and stacking patterns are inferred for the Nariva Formation and the Chaudiere/Pointe-a-Pierre succession based on grain-size changes demonstrated and described from outcrop and core, and displayed in gamma ray log signatures from a continuous section through the formation. The Late Oligocene to Early Miocene Nariva Formation consists of amalgamated beds of pebbly sandstones, massive and amalgamated thick-bedded sandstones, parallel-laminated fine-grained sandstone and abundant organic matter. A slope depositional environment is inferred based on the facies association and inferred fining-upward stacking patterns. Sedimentary processes were for the most part, similar to those described for earlier formations and included traction and suspension-related grain, liquefied and turbulent flows and minor cohesive flows. The main difference with the Nariva Formation is the common amalgamated beds of parallel-laminated sandstones associated with the abundant organic matter, which suggest that sustained flows were more common to these sandstones. Delta-related hyperpycnal flows were interpreted, similar to the stratigraphically older Angostura Sandstone. Analogies can be drawn between the organic-rich and/or parallel-laminated facies of the formation and interpreted hyperpycnal flow deposits from other basins (Dott and Bird, 1979; Bruhn, 1994; Steel et al., 2000; Mulder et al., 2003; Plink-Bjorklund and Steel, 2004; Sailer et al., 2006; Poursoltani et al., 2007). No identification and assignment of trace fossil associations were possible for the Nariva Formation as only one specimen of Subphyllocorda was seen in outcrop. An assemblage of benthic foraminifera derived from a sample in the Eastern Central Range (Tamana Road junction) from an undetermined formation of Late Oligocene age or younger (suggested by the benthic assemblage) suggests upper to middle bathyal palaeodepths (Table 3.1). This age 421 correlates to that of the Nariva Formation and suggests deep-water palaeoenvironments at the time of deposition. There are significant changes in the composition of Nariva Formation sandstones in both the light and heavy mineral fractions, which suggest changes in sediment sources to the basin. On average, sandstones are compositionally immature relative to those of the older formations. There was a simultaneous increase in both the lithic fraction and contribution of metamorphic rock fragments relative to the older sandstones. The dominant sediment source was still the South American craton as suggested by the relative proportions of index heavy minerals (section 6.2.4), but there was now a significant contribution of chloritoid and chlorite that was likely derived from the Caribbean Mountains to the north of the South American continental margin. The additional sediment sources were also reflected in the lower ZTR indices for the Nariva Sandstones that was likely due to a dilution effect but the ultrastable minerals were still the most abundant in the heavy mineral fraction. The changing sediment sources alluded to in the Angostura Sandstone Member are now obvious in the sandstones of the Nariva Formation and these changes were interpreted to represent the uplifting of the Caribbean Mountains in closer proximity to Trinidad basins. The Nariva Formation sandstones represent a significant input of syn- orogenic sediments into the basin. This conclusion is supported from actualistic models (Dickinson plots) as the samples from the Nariva Sandstone demonstrate a clear "recycled orogen" source, which was not the case with the older sandstones. 7.1.5 SANDSTONES OF THE HERRERA SANDSTONE MEMBER The Early to Middle Miocene Herrera Sandstone Member consists of thin-bedded, rippled and graded sandstones within well-defined, coarsening upward cycles. The succession is interpreted as progradational lobe and channel-related overbank sediments deposited within the deep-sea distal basin floor. The channel sands occur at the top of the succession and consist of amalgamated, fining-upward bedsets of fine to pebbly sandstones. The succession is capped by a chaotic shale-prone package (pebbly 422 mudstones, debris flows, thin turbidites) that is interpreted to represent the abandonment of the channel-lobe complex. Similar depositional processes to the older sandstones are inferred. Sediments were deposited primarily from traction-related turbidity currents reflected in the numerous rippled thin-bedded turbidites. Grain, liquefied and cohesive flows are also evident among the massive and coarser sand fraction. A Zoophycos ichnofacies was interpreted for shale-prone intervals based on a Zoophycos-Chondrites- Thalassinoides trace assemblage, and supports the deep-sea environment inferred for these sandstones. Superimposed upon the resident Zoophycos ichnofacies is a more diverse suite of opportunistic trace fossils associated with episodic deposition and shorter colonization windows; Scolicia is the most common trace fossil in this group. This episodic deposition is associated with turbidite event beds. The inferred depositional environment is further supported by a calcareous and agglutinated benthic foraminifera assemblage, which suggests middle to lower bathyal or deeper palaeoenvironments associated with the Zoophycos ichnofacies shales. Zoophycos ichnofacies is usually associated with slope environments (Seilacher, 1967); the deeper, basin floor occurrence is likely due to basin setting and configuration at that time. Zoophycos ichnofacies is indicative of dysaerobic bottom-water conditions that may be due to restricted circulation within a confined basin setting. These sandstones were derived from at least three sources: (1) a syn-orogenic sedimentary source, (2) a mature craton source and (3) a metamorphic source. The compositional immaturity is due to the abundance of intra-basinal lithic fragments (siltstones, mudstones and bioclasts). If these intra-basinal lithic fragments are ignored, then the Herrera Sandstone conforms to the trend of increasing lithic fragments within progressively younger Cenozoic sandstones and a continuation of an apparently systematic change in sediment source that began in the Eocene (Figure 6.17). The difference with these sandstones is the abundant chert, siltstone, sandstone and carbonate rock fragments that suggest reworked sedimentary derivation. This is also interpreted from the relatively high amount of opaque heavy minerals (Figure 6.20). In general, the heavy mineral assemblage suggests similar sources to the earlier sandstones: an ultrastable heavy mineral source that was the South American craton and a chlorite- chloritoid-epidote source that was the uplifting Caribbean Mountains. 423 In summary, the Herrera Sandstone Member indicates multiple-sourced sedimentary supply into a relatively deep and confined basin setting, probably rimmed by carbonate reefs; abundant sedimentary lithics were likely due to erosion of proximal emerging high lands. 7.1.6 SANDSTONES OF THE CRUSE AND MANZANILLA FORMATIONS The Late Miocene to Early Pliocene Cruse Formation is significant from a palaeoenvironmental perspective as it records the transition from deep-marine facies, which is characteristic of the Pre-Cruse sandstones, to shallow-water shelf and nearshore environments. The formation consists of deep-sea facies analogous to the older sandstones (massive and gradational, thick-bedded sandstone and discordant sandstone and shale) that changes upwards into wave-reworked sandstones, tidal and fluvial sediments. The sedimentary processes changed from block slides, cohesive flows and liquefied and turbulent flows upwards into beds modified by oscillatory traction currents that recorded a transition from upper slope and slope canyon fill to outer shelf environments. This transition is also reflected in the trace fossil assemblage along coastal outcrops at Morne Diablo where the succession transitions upwards from a non- bioturbated slope canyon fill27 to a monospecific assemblage comprising Ophiomorpha annulata and Gyrolithes, and then a greater trace diversity among the wave-reworked sands. Depositional environments and trace fossil assemblages of the Manzanilla Formation are more proximal relative to the coeval Cruse Formation. Relatively shallow- water environments were interpreted from physical sedimentary structures (Chapter 4) supported by a Skolithos trace fossil assemblage. The basin shallowed during deposition of the Cruse and Manzanilla formations such that a more diverse range of sedimentary processes was active. The sublitharenites of the Cruse and Manzanilla formations were among the most compositionally and texturally immature examined, with angular fine- and coarse-grained 27 The trace fossils seen in this interval are not in situ. 424 quartz, and lithic percentage averaging 16% of framework constituents. Lithic fragments comprise chert, mica-schists and phyllites. The abundance of coarse mica-schists lithic fragments in a sample from the Manzanilla Formation point directly to a proximal metamorphic source for these sediments. Chlorite is the most abundant heavy mineral in a mineral separate from the Cruse Formation sublitharenites and suggests a Caribbean Mountain source for these sediments. Based on the relative amounts of heavy mineral constituents (Figure 6.24), the South American craton, including the Guyana Shield, was not the dominant source for Trinidad elastics for the first time in the evolution of the basin. 7.1.7 SANDS OF THE MORNE L'ENFER FORMATION The shallowing trend observed in the Cruse and Manzanilla formations continued into the Late Pliocene with the Morne L'Enfer Formation. Depositional environments ranged from distal offshore/lower shoreface to coastal plain, lagoon and distributary channels. Sedimentary processes varied from wave and tide-dominated in the Lower Morne L'Enfer Sandstone Member, to tide and fluvial-dominated in the Upper Morne L'Enfer Sandstone Member. Accomodation space is now limited in the basin and changes are reflected in progradational and aggradational cycles, flooding events and unconformities. Trace fossil assemblages are now diverse and varied in abundance, appearing specific to depositional environments. The shallow-marine ichnofacies of Cruziana and Skolithos can be readily recognized while elements of the Psilonichnus ichnofacies appear among the tide-influenced sands. The sands of the Morne L'Enfer Formation are predominantly fine-grained and of lithic arenite composition. Schist and phyllite rock fragments comprise the main lithic constituents, which suggest continued sediment supply from the Caribbean Mountains. This is supported by the abundant chloritoid and epidote in the heavy mineral fraction, which were both derived from the Caribbean Mountains. The craton source signature of zircon and other ultrastable heavy minerals is now suppressed and is now a subordinate supplier of sediments into Trinidad basins (Figure 6.24) although the increased amounts 425 of high-grade metamorphic minerals within Pliocene sands (Figure 6.25) are indicative of the "Guyana Shield Association"; at least some of the Pliocene detritus may have been derived from rivers draining the northeastern coast of South America as these rivers (e.g. Amazon) currently supply significant volumes of sediment to Caribbean basins (Section 6.2.4.6). Palaeocurrent orientations in sediments of the Morne L'Enfer Formation are mainly west to east and it is likely that this was the dominant sediment transport direction associated with the Caribbean Mountain sediments. 7.2 LATE CRETACEOUS TO PLIOCENE BASIN EVOLUTION This section presents an evolutionary synopsis and palaeogeographic model for Trinidad basins during the Cenozoic. It describes the continuation of passive margin sedimentation throughout most of the Paleogene and the influence of tectonism on later sediment dispersal patterns. The pre-Cenozoic phase of basin evolution is represented by the Cretaceous transition from arkosic to quartzitic arenites (Section 6.2.4.1). Arkosic sandstones were deposited across much of northern South America during the Early Cretaceous (van Andel, 1958; Barr, 1962; this thesis) sourced from uplifted basement blocks. Acutalistic sandstone models (Dickinson and Suczek, 1979; Dickinson, 1985) suggest that the increasing maturity of Late Cretaceous to Paleocene sandstones noted across the continental margin (van Andel, 1958; this thesis) were due to increasingly stable basin settings on the continent, which was the main sediment source for elastics into deeper water basins to the north, at that time. Schematic illustrations depicting the basin evolution and palaeogeography of sandstone units are shown in Figures 7.2 and 7.3. Late Cretaceous A north facing passive margin is the main basin setting. Deep-marine siliciclastic shales and argillite of the Naparima Hill Formation were deposited. Inferred clastic submarine fans related to a Maastrichtian sea level fall (e.g. Galera Formation) were also deposited ("1" in Figure 7.2 A). The coeval shelf is towards the south and out of the study area. Granitic sediment sources that persisted throughout the Early Cretaceous 426 (e.g. Toco Formation) are now insignificant as only mature, quartz arenites are being delivered into the basin. Middle Paleocene (Soldado Formation, Lizard Springs Formation) The region comprises a north-facing passive margin (Figure 7.2 B). Lower Paleocene bathyal to abyssal shales are conformable over the Late Cretaceous deposits, although the absence of the planktonic biozone Globorotalia psuedobulloides of earliest Paleocene (Saunders and Bolli, 1985) may be related to an unconformity. Calcareous and non-calcareous, bathyal shales of the Lizard Springs Formation are being incised on the slope due to possible falling sea level ("a" in Figure 7.2 B). Reefal limstones and coquinas on the coeval shelf are the precursor to the Soldado Formation, although these are not represented in the immediate study area. Sediment bypass is inferred through the slope incisions to basin floor environments leading to deposition of the "Chaudiere fan" (inferred) towards the north. A mature sediment source is inferred from the compositional maturity of both the Galera Formation sandstones and the succeeding "Chaudiere" slope channel fill (discussed below). Early to Middle Eocene (Chaudiere and Pointe-a-Pierre formations) A north-facing passive margin still persists in the Trinidad region (Figures 7.2C and 7.3 A). The slope incisions created by an earlier fall in sea level and associated with deposition of the "Chaudiere fan", are now being filled with Late Paleocene to Middle Eocene transgressive deposits. Off-axis bathyal shales of the Lizard Springs Formation and axial amalgamated pebbly sandstone of the Chaudiere Formation comprise part of the transgressive slope fill. These are replaced in the middle to upper slope by facies of the Pointe-a-Pierre Formation ("c" in Figure 7.2 C). A mature sediment source is assumed, supplying quartz arenites and ultra stable heavy minerals into the basin (Orinoco Association of Figure 7.3 A). The coeval shelf does not lie in the study area. 427 Late Cretaceous Middle Paleocene Study area-Trinidad ^/^ South American vT^ craton Future Northern Range Galerafan Inner fan? Distal fan. SHELF Slope (upper, middle)Lowe r slope/ Middle to outer fan sm _Chaud£refan South North Qt&amtai* A Early to Middle Eocene V>^ Middle to Late Eocene 1 Mt. Harris, Future Northern ' i Fatten Road Range ** J. .'—!-t'.Tt4""^^ga—>,__ "l" T" f T7Y T n k=s-^~ ^^^^•^^^^^^ ChaudWro fan D Figure 7.2 Schematic illustration depicting the changing sediment sources and basin settings during the Paleocene to Middle Miocene based on the collective changes in lithofacies, and sandstone composition. Late Eocene to Early Oligocene Middle Oligocene vy^ i > SoMadoRock .^^. San Fernando Fm <§> i r i i i i i i •? IH^SB-—^f——. - ^•^.T E V foredeep Future Northern Northern Late Oligocene Early to Middle Centra! 'Galera ^^- Sediment source/ major Chaudtere/ P-a-P 1 * Sediment source/ minor @ Sediment input (ram the west/ minor San Fernando 9 (•) Sediment input tram the west/ major Angostura -"2--» Slumps Nariva <£& Cobble conglomerates Herrera ^s^ Thrust faults Relative sea level fiaS limestone beds \jn (H^gh. L-tow) D) Early fa Middle Mjgqene Legend -«=C3? Deep-water sediments (g| Terrestrial environments [~~~~"j Shelf environments Caribbean Delta Mountain Association • 49Ma Uplift age <2^a Limestone beds (ZFT) Zircon fission track AT High (AFT) Apatite fission track Association! (Ar/Ar)Argon/argon (S»«Hn»Ep5 j Low (narrow basin or seaway) PaBntepastic restored coastline *v Measured palaeocurrent Modem coastline ^ Inferred palaeocurrent SASS Vegetation \ (line thickness denotes ":":v.:-*" Conglomerates relative significance) E) Middle Pliocene Figure 7.3 Palaeogeographic reconstruction for Cenozoic sediments. The reconstruction depicts a passive to active margin succession and asymmetric foreland basin fill and is based on lithofacies associations, ichnofacies, sandstone mineralogy and palaeocurrent measurements. Details are provided in the text. Palaeo-restoration of Trinidad and northern Venezuela after Pindell and Kennan (2007) and Rohr (1991). Formations in italics are correlative units from Venezuela (e.g. Vidono), for which the palaeoenvironments and shoreline positions are less constrained. 430 Middle to Late Eocene (Pointe-a-Pierre and Navet Formations) A north-facing passive margin still persists (Figure 7.2 D and 7.3 A). Middle to Late Eocene calcareous shales of the Navet Formation dominates slope sedimentation with rare, coarse elastics (Charuma Silt Member of the Pointe-a-Pierre Formation). The Navet Formation represents transgressive deposits on a mature slope profile; a surface of maximum flooding (MFS) and equivalent condensed section is inferred upon the slope and basin floor respectively (between fans "2" and "3" in Figure 7.2 D). The coeval shelf does not lie in the study area but contains shelf-edge limestone equivalents to the "Boca de Serpiente Formation" (Figure 7.3 A). A westerly metamorphic source is already supplying low-grade metamorphic detritus into northwestern deepwater basins represented primarily by the sandstones of the Scotland Formation which lie much further west at this time (Figure 7.3 A). Prior to the Late Eocene, a fall in relative sea level is inferred that leads to further slope canyon incision that heads in the outer shelf. Incision was down to Cretaceous sediments, and slope sediment bypass led to the deposition of the "San Fernando fan" (inferred, Figure 7.2 D) in distal lower slope to basin floor regions. Sediment source was similar to that for the earlier fan deposition (i.e. South American craton). Paleocene to Middle Eocene limestones on the coeval shelf will later form a component of the slope canyon fill (e.g. Soldado and Boca de Serpiente formations). Late Eocene to Early Oligocene (San Fernando to Lower Cipero formations) A north-facing passive margin still persists in the Trinidad region (Figures 7.2 E and 7.3 B). Slight increases in metamorphic rock fragments seen in Trinidad sandstones are likely associated with incipient active margin tectonics and uplift further to the west and towards the north. Sediments of the San Fernando Formation are now part of the slope canyon fill ("d" in Figure 7.2 E) including Paleocene and Eocene carbonates that were resedimented from the shelf edge. The fill comprises chaotic discordant limestone, cobble and breccia conglomerates with rare glauconitic turbidites (Soldado and Boca de Serpiente formations, Plaisance and Marabella Conglomerates), as well as slide blocks of Late Eocene orbitoid limestones. Away from, and overlying the canyon-fill, shales rich 431 in planktonic foraminifera are transitional into the basal shales and siltstones of the Cipero Formation (Figure 7.3 B). The sediment source has shifted relative to earlier deposits of deep-marine elastics reflected in the higher feldspar content and common staurolite and apatite. The mature heavy mineral composition and high-grade metamorphic minerals of the San Fernando Formation, still suggest a South American sediment source (Orinoco and Guyana Shield associations). Further west along the continental margin (western Venezuela), immature sandstones have almost completely replaced mature quartz arenites suggesting that another sediment source was already active (van Andel, 1958; Section 6.2.6). Low-grade metamorphic minerals of the Caribbean Mountain Association are evident in the Scotland Formation (Figure 7.3 B). Deepwater, passive margin sedimentation still persists in the Trinidad region; any incipient uplift or deformation (Figure 7.2 E) is likely subaqueous, and does not significantly influence the composition of the sandstones. Middle Oligocene (Angostura Sandstone) A north-facing passive margin still persists (Figures 7.2 F). During Early to Middle Oligocene, a basinward shift in sedimentation and slope incision occurs (likely related to a relative drop in sea level) that leads to large amounts of coarse elastics being deposited within the base-of-slope Angostura channel-fan complex ("4" in Figure 7.2 F). The timing for the initiation of incision and deposition of the channel-fan complex is not known. The unconformable contact with Upper Eocene shales may represent either the depth of erosion or Late Eocene deposition (Figure 7.2 F). Hence synchronicity with the canyon systems of the San Fernando Formation is possible and these may have acted as sediment conduits for more distal facies of the Angostura Sandstone Member. The mature sediment source that supplied earlier deep-water systems is still active and is the main sediment supplier to the Angostura Sandstone complex (i.e. Orinoco association from the South American craton). An uplifted metamorphic source (Caribbean Mountains) is supplying an increasing amount of detritus to these sandstones relative to older elastics though this is still relatively insignificant in sediment volume. Subaqueous uplift in the Trinidad area (an easterly extension of the Caribbean Mountain uplift further west) may have created a restricted basin and confinement responsible for 432 the aggradational stacking patterns that are characteristic of these sandstones (Figure 7.3 C). The increasing amounts of organic matter also suggest relative proximity to deltaic sources while bioclastic fragments were sourced from shelf carbonates. Late Oligocene to Early Miocene Increasingly confined basin settings now exist, bounded by the "passive" margin to the south with a broad alluvial plain and shelf, and the orogenic high (Caribbean Mountain) to the west and north with a narrow shelf profile (Figures 7.2 G and 7.3 C). Much of the region remains in deep water represented by the bathyal shales of the Cipero Formation but outcrops such as Plum Mitan (symmetrical rippled sandstone facies, Section 2.6) provide evidence for localized highs within wave-base; ripple crest orientations suggest east-west palaeoflow directions. Conglomerate fan deltas occur south of the northern uplift (e.g. Guaico Conglomerates, see Appendix 5) that grade southwards into neritic shales (Brasso Formation) and slope turbidites of the Nariva Formation ("5" in Figure 7.2 G). Sediments are being fed directly into deeper water slope environments by alluvial and fluvial channels and small deltas, with large amounts of organic matter. Common chlorite and chloritoid combined with texturally immature sublitharenites with approximately 20% metamorphic rock fragments indicate an active low-grade metamorphic source (Caribbean Mountains) and significant input of syn- orogenic sediments. A mature sediment source is still dominant as indicated from ultrastable heavy minerals, although some may have been derived from sediment recycling. Early to Middle Miocene The Trinidad region is now an asymmetric foreland basin with deeper water environments to the east (Figures 7.2 H and 7.3 D). An active continental margin is now established as the passive margin has been deformed by southeast-verging thrust faults and probably right lateral strike-slip faults. A deep-marine trough occurs south of the active deformation front characterised by Zoophycos ichnofacies suggestive of 433 dysaerobic basin conditions. The basin-floor facies association of the Herrera Sandstone Member ("6" in Figure 7.2 H) represents the most distal environment of all Cenozoic sandstones and may have been deposited within a very deep-marine basin setting, induced by foredeep subsidence southeast of the orogenic high. The Herrera sandstones are interpreted as the earliest foredeep, syn-orogenic sediments into the basin. Sublitharenites with up to 35% lithic fragments are typical, comprised of metamorphic rock fragments, chert, sandstone and siltstone lithic fragments. Abundant intrabasinal lithic fragments (mudstone, bioclasts and limestone) also occur. The lithic fragments suggest that both sedimentary reworking and a metamorphic source introduced sediments into the deep-water basin. Ultrastable heavy minerals still dominate the Herrera sandstones and suggest that the mature South American source that acted throughout the Cenozoic, is still supplying sediment into the basin at this time. Late Miocene to Pliocene The asymmetric foreland basin has progressed to an overfilled stage from the deeper water environments that existed during the Early Miocene (Figure 7.3 E). The asymmetric basin was gradually filled throughout the Miocene and the transition from deep-water turbidites to shelf sedimentation was recorded in the Cruse Formation. The coeval and relatively proximal Manzanilla Formation which outcrops to the north of the Cruse, suggests deposition from north to south. The overlying Morne L'Enfer Formation was deposited with decreased accommodation space in the basin coupled with sediment progradation from the west. This direction is inferred to have been the predominant direction of sediment transport (parallel to the basin axis) associated with the asymmetric "Caribbean Mountain" foredeep. The Caribbean Mountains were the main sediment source for Pliocene elastics. 7.3 IMPLICATIONS FOR THE STRATIGRAPHIC TABLE The present-day structural configuration coupled with the poor exposure has complicated the stratigraphic superposition of rock units. Paleogene rock units are particularly susceptible to this. These have been resolved to some degree by high 434 resolution biostratigraphic data from numerous subsurface wells and outcrops (e.g. Renz, 1942; Bolli, 1957 abc; Eames et al., 1965, Stainforth, 1968; Kugler, 2001) that have led to the stratigraphic column as currently known (Table 1.1 A). There are still however, intervals, entire rock units and stratigraphic relationships that are subject to controversy. 7.3.1 SOLDADO AND BOCA DE SERPIENTE FORMATIONS The status of the Soldado (Paleocene) and Boca de Serpiente formations was questioned (Kugler and Caudri, 1975) because of their occurrence among Eocene rocks and complicated stratigraphic contacts. The Soldado Formation consists of a 22m thick limestone in unconformable contact with Late Eocene strata while the Boca de Serpiente Formation comprises a 17 metre-thick block conglomerate of "Middle Eocene" rocks, similarly juxtaposed among Late Eocene rocks (Kugler and Caudri, 1975). Both or these "Formations" occur on Soldado Rock where they have been described in detail. A "slumpmass" character to the Boca de Serpiente Formation has been recognized but descriptions of the Soldado Formation suggest that it is in place relative to Eocene strata (Kugler and Caudri, 1975; Caudri, 1975). The true stratigraphic superposition of both the Boca de Serpiente and Soldado formations is unknown in the Trinidad area as there is no in situ outcrop . When related sedimentary processes and depositional environments are considered, both the Boca de Serpiente and Soldado formations are Paleocene to Middle Eocene rocks emplaced within Late Eocene strata as block slides, debris flows and inertia-driven grain flows. The only difference between these and other exotic clasts found within the Late Eocene strata (identified only as lithological units) is their size and age; most others appear to be pebble to boulder-sized as opposed to the 22 m thick Soldado Formation and 17 m thick Boca de Serpiente Formation (section 2.3.4, Figure 2.15). These "formations" were recurring depositional events analogous to the allochthonous slide blocks within the canyon fill deposits described for the Pliocene Cruse Formation (Figure 4.2). Correlative limestone units several 10s of meters thick are known in their correct stratigraphic position in parts The "Soldado Formation" outcrop along Moreau Road, Moruga, is also disconformable within Oligo-Miocene shales (see Figure 2.18 for location). 435 of Venezuela and as far west as Colombia where they are described by different stratigraphic nomenclature (e.g. Guasare Formation, Liddle, 1946) It is recommended that these rock units be considered as reworked lithological units within Late Eocene strata instead of "formations". They comprise part of the diverse lithology known to exist in the slope deposits of the San Fernando Formation. According to the International Stratigraphic Guide (Salvador, 1994), there is no restriction on the thickness of "formations" or "members" but the stratigraphic relationships should be unambiguous. The true nature of the Soldado Formation as discerned from Kugler and Caudri (1975) consists of several Paleocene limestone blocks, boulders and pebbles scattered throughout Late Eocene silts and marls of the San Fernando Formation and also found in the "Middle Eocene" Boca de Serpiente Formation (Kugler and Caudri, 1975). The Boca de Serpiente Formation conforms more readily to stratigraphic definition as it refers to a distinct boulder bed. However, the associated sedimentary processes and bed contacts indicates that it occurs within the greater San Fernando Formation. Considering their subordinate stratigraphic status to the San Fernando Formation, these formations should at least be relegated to "member" status, although it is preferred to consider these recurrent depositional events simply as lithological units. 7.3.2 CONGLOMERATE MEMBERS It is apparent from publications on the San Fernando Formation that the Plaisance Conglomerate and Marabella Conglomerate members also represent recurrent depositional events. Cobble conglomerates is a common facies to deep-water environments (e.g. Aalto and Dott, 1970; Lowe, 1972; Cook, 1979; Morris and Busby- Spera, 1988, Bruhn and Walker, 1997) and individual beds are not necessarily associated with changing basin settings or regional unconformities. Based on the descriptions from numerous authors (section 2.3.3.1, Figure 2.14), conglomerates appear to be a recurrent facies throughout the Eocene that likely extended into Oligocene sediments. These are not syn-orogenic conglomerates as suggested by the mature mineralogical composition of a sample from the Plaisance Conglomerate Member of the San Fernando Formation 436 (Section 6.1.12) and so there is little justification in them being represented as a continuous succession as is typical for Oligocene-Miocene conglomerates (e.g. Cunapo Formation in Table 1.1 B). Correlations between individual conglomerate beds and "members" remain tentative at best. Future work may reveal that these "members" are not restricted to the San Fernando Formation as it is currently defined. Similar "members" may exist for the Pointe-a-Pierre (Middle Eocene) and Cipero (Oligocene) formations as already described by Liddle (1946) for the former. 7.3.3 RECOMMENDED CHANGES TO THE STRATIGRAPHIC COLUMN Slope canyons are localized features that may erode several hundred metres into pre-existing strata representing significant periods of time (e.g. Cainelli, 1994). Away from slope canyons, the deposition of fine-grained sediment may continue uninterrupted. This trend is apparent in the Chaudiere/ Pointe-a-Pierre and San Fernando formations. The Paleocene to Eocene Chaudiere/ Pointe-a-Pierre succession disconformably overlies Lower to Upper Cretaceous strata across the Central Range while a conformable succession is known towards the south (Figure 2.1; Bolli, 1957a). The San Fernando Formation also overlies Paleocene to Cretaceous rocks while a conformable succession is known away from the Mount Moriah (Figures 2.13, 2.14). This relationship is not represented on published stratigraphic columns. Kugler (2001) alluded to the status of Chaudiere Formation which can be considered a facies of the Lizard Springs Formation. Biostratigraphic data has demonstrated that the Chaudiere Formation is an arenaceous equivalent of the more calcareous and laterally extensive Lizard Springs Formation (Bolli, 1957a) and this is supported by the sedimentological interpretation presented in this thesis. The sandstones of the Chaudiere Formation were areas of confined, coarse clastic accumulation within a shale-prone slope depositional environment. It may be more appropriately considered a coarse-grained "member" of the larger Lizard Springs Formation. Similar can be said for the Pointe-a-Pierre Formation relative to the Upper Lizard Springs and Navet formations. 437 The following changes are recommended: (1) Representation of the "Angostura Sandstone Member" of the Cipero Formation, based on foraminifera and nannofossil control (Section 2.4). (2) Referral to olistostromes such as the "Boca de Serpiente" and "Soldado" formations as lithological units within the San Fernando Formation as their stratigraphic status is ambiguous. (3) Representation of erosional gaps associated with the San Fernando, Pointe-a-Pierre and Chaudiere formations to reflect their depositional setting; conformable successions occur away from the coarser elastics associated with these formations. These recommendations are shown in Figure. 7 3. 7.4 DISCUSSION This thesis presented the changing character of sedimentary processes, sandstone mineralogy and ichnofacies throughout the Cenozoic of Trinidad in order to assess the utility of these methods and resolve Cenozioic stratigraphic issues. Collectively, the methods demonstrated that: (1) The Trinidad region was a deep-water region throughout the greater part of its Cenozoic history with evidence for limited shallow water sedimentation only in the Late Oligocene. Shallow-water sedimentary processes and ichnofacies became established only during the Later Miocene to Early Pliocene. (2) Sediments have been derived from the South American craton towards the south for most of the Cenozoic. This source dominated sediment input into the basin at least until the Early Pliocene; thereafter a syn-orogenic source became dominant. Cenozoic changes in mineral composition document the deformation of the northern South American margin by a low-grade metamorphic belt that gradually supplied detritus to Trinidad basins. The mineral changes demonstrated in this thesis are similar to changes documented both spatially and temporally across northern South America by other workers. As discussed in Chapter 6, van Andel (1958) documented temporal changes in the maturity of sandstones in western Venezuela, though at an earlier time than recognized in Trinidad basins. Similarly, Hoorn (1993) documented changing 438 CIPERO FORIIATIOR 24- CIPERO FORMATION 26- L zLU — 111 28- o u 30- _ol __ o E 32- 'A Marabella conglomerate Ltthotoglcal units In the ,.,,,:.,,,,:^ San Fernando Formation 34- 1. Plaisance conglomerate <)m FESMAMOO F» j 2. MarabeBa conglomerate 5. Mome Roche limestone L 6. Bon Accord boulder bed 36- (A h 3. Boca de Serpfente limestone 4. Sofdado Hmestorw 38- 40- 42- NAVEIFH M 111 44- z — ouu 46- o 111 Boca de Serpient*t-e Fml 48- 50- vm*tom?™$$ 52- "E 54- '//////// 56- — L CHAUDltRE FN, )LOWER LIZARD >T \ SPRINGS FM 58- Ul Uzl 60- M ISOIPADO*" 4FM | 8UJ 62- QL E 64- 66- ^feUAVASUAYllMTi ~~ I CO 3 £ Figure 7.4 Recommended modifications to the Trinidad Paleogene stratigraphy based on the nature of sedimentary contacts. The stratigraphic table of Saunders et al., (1998) is shown for reference (A) and the recommended changes are illustrated in (B). The changes recommended are based on the nature of sedimentary contacts and relationship between coarser-clastic and fine-grainedintervals , reflective of their depositional setting. The table also reflects the variety of observations of previous workers. The "Angostura Sandstone Member" of the Cipero Formation is also included as this unit was not previously represented. 439 heavy mineral diversity that recorded a dilution of the ubiquitous Guyana Shield sediments in northwest Brazil during the Miocene. These changes have also been documented in modern sands spatially from the Andean Mountain Belt (including the Caribbean Mountains) to the mature sediments of the Guyana Shield (Stallard et al., 1990; Potter, 1994). It is apparent that the changes in mineralogy described in this thesis are consistent with the gradual deformation of Northern South America from the west. This is also supported by the relatively young reset ages of apatite fission track across the northern margin (Kohn et al., 1984a, Kohn et al., 1984b, Weber et al., 2001b). The elucidation of these changes using heavy minerals and modal detrital framework demonstrated the utility of these methods to resolving sedimentary provenance. The utility of trace fossils to the Trinidadian stratigraphy has also been demonstrated. Instances of archetypal ichnofacies occur within the younger Pliocene sands while correlations can be made with deep-water assemblages for Early Cenozoic sediments. More specifically, the trace fossil character can be used to discriminate between palaeoenvironments as demonstrated in the Morne L'Enfer Formation. It is best applied however, along with physical sedimentary structures. Process sedimentology provides the mechanism for understanding the mode of sediment delivery into the basin. Deep water sedimentary processes and environments were the major mechanisms during most of the Cenozoic. Without considering the sedimentary processes, the significance of resedimentation would be underestimated as is apparent from past interpretations of the Soldado and San Fernando formations. The resolution of sedimentary processes in accordance with biostratigraphy can provide explanations for ambiguous relationships between rock units as exemplified in the Trinidad Paleogene. Integration of the various results yielded by the different methods enhances their utility in basin analysis. This is especially important in structurally complex regions with poor exposures as is characteristic of Trinidad sediments. An example can be cited from the Pliocene sediments, which have traditionally been regarded as sourced from the Guyana Shield (Barr et al, 1958; Michelson, 1976; Stainforth, 1978; Harry, 1992). The conclusions derived from sandstone petrology are supported by numerous outcrop palaeocurrent measurements. Similarly, environmental interpretations are supported by 440 sedimentary processes, trace fossil assemblages and palaeontological data. There is also merit in the review of wider stratigraphic intervals as the relative sedimentological changes provide invaluable information that cannot otherwise be confidently assessed. There remain several areas for future research that can further validate or test the conclusions presented in this thesis. The structural history across the Central Range is still poorly understood and further resolution is needed to increase the utility of palaeocurrent measurements or refine lithofacies correlations across the area. Palaeomagnetic studies can be useful in this regard. Previous attempts to resolve the uplift history across the Central Range using fission track ages have been hindered by the paucity of apatite (Algar, 1993; this study). Still, there is potential for thermochronological studies in Miocene and younger sandstones where apatite is found in greater abundance (Herrera Sandstone and Cruse Formation29). Apatite is also common to sandstones of the San Fernando Formation on Soldado Rock although in situ exposures of this formation are rare. The stratigraphic relationships proposed for Paleogene Formations highlight the need to understand sedimentary processes along with biostratigraphy. Many of the key developments in the Trinidad stratigraphy and elucidation of depositional environments were made prior to the 1970s (reflected in the many key papers at that time) when the understanding of sedimentological principles were still being developed. This is particularly true of deep-water sedimentary environments and processes which have been extensively studied over the past 20 years or so, coincident with active hydrocarbon exploration in increasingly deeper waters. Our current understanding of Trinidad stratigraphic relationships can only benefit by applying advanced knowledge in deep- water sedimentary processes because of the proliferation of deep-water sediments throughout the Cenozoic. The history of sedimentation in Trinidad was intimately associated with that of northern South America and Eastern Venezuela in particular. Several lithological and structural correlations have been made between the two regions (e.g. Liddle, 1946; Hedberg, 1950; Kugler, 1953; Stanley, 1960; Gonzales de Juana, 1968; Salvador and One sample was counted from the Cruse Formation where apatite was found in sufficient quantities. The results are not presented in this thesis. 441 Stainforth, 1968; Jones, 1968; Algar, Erikson and Pindell, 1998; Pindell et al., 1998). Throughout the thesis, general references were made to parts of Venezuela and northern South America. The palaeogeographic maps depicted in Figure 7.3 also display the larger region though the best constraints are from the Trinidad sandstones. The maps can only benefit from a more detailed treatment of correlative Venezuelan sedimentary processes and depositional environments throughout the Cenozoic which was out of the scope of this study. The maps were not presented in isolation however, as similar deep- water and coeval shelf sediments were recognized for Paleogene sediments in Venezuela (e.g. Stanley, 1960; Erikson and Pindell, 1998). Hedberg (1950) recognized an asymmetry to the Cenozoic fill of Eastern Venezuela with coeval deeper-water sediments commonly occurring to the east along with the disappearance of unconformities in this direction. He also interpreted a Late Oligocene change in provenance to western and northern sources very similar to that presented in Figure 7.3. Similarly, the stratigraphic equivalents of resedimented limestones and conglomerates may be found from a more detailed assessment of northern South American geology (e.g. Liddle, (1946) correlated the "Soldado Formation" of Trinidad to in situ Paleocene limestone beds across northern South America, such as the Guasare Formation). These are just a few examples of how a more detailed and modern treatment of sedimentary units across northern South America can further constrain the interpretations presented in Figure 7.3. This thesis also demonstrated the potential to subdivide Pliocene sediments to metre-scale sequences as opposed to the large, member-scale sequences that are popularly described. Sequence stratigraphic principles have only been locally applied to younger sediments (e.g. Wood, 2000; Vincent et al., 2007). This is a potential area for future research encouraged by the extensive outcrop exposures along the coasts and numerous subsurface wells. 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Harris Geological map showing location of detailed outcrop sections and lithological summary in the Mount Harris area, eastern Central Range (see map at right which also shows outcrops of the Pointe-a-Pierre Formation across the Central Range). The map shows two river traverses, Chaudiere River to the north and Mitan River to the south. See Appendix 2 for details of the Chaudiere River traverse. Geology after Saunders et al., 1998. Probable contact Unconformable contact Fault * Elevation estimated from Trinidad map, 1989, Government of Trinidad and Tobago, Lands and Surveys Division 484 Appendix 2 Chaudiere River Traverse, Mt. Harris The traverse was mapped by bearing and distance measurements and GPS data points. The maps show the locations of sections shown below (structural measurements are shown on the lower map only). Facies mapped include amalgamated pebbly sandstone at the base (Section 1) and lenticular and tabular sandstone for most of traverse. See Appendix 1 for location. 485 •Sectiorr tocationsr A to*** Bearing-distance and GPS measurements combined at this point. A. Traverse olstanw estimated, nol measured. 4= Difference between GPS position B. Inaccessible outcrops and position Horn bearing-distance C. Thick bedded, coaise grained sandstones on river bed. Similar to section 17. D.PooHon of section 1 estimated. RIVBT bends 4Mo deo. Azimuth. • E. Brecdated dastt in shale Measured sections in stratigraphfe continuity F.Bnwdatedlantfnatetfshate.Beds dfrtowards the south, '0' Indhriduei measured sacScns X 0)pMraie of beddfng plane V Faaftptane IDCAJlOft Ormtf—ffiw, ffl&wf. jBWikt. , . .JllMiijJ _aiffl»i _SlffljM Jiik ...JISMMSJ _ 4^ 0\ Lenficuler sandstone Tabular sandstone fades. •-1 Base of section (near roadway) AMALGAMATED PEBBLY SANDSTONE ®i 3H JfiilWs Appendix 3 San Fernando Formation Lithology A) Boulder of Plaisance conglomerate from Pointe-a-Pierre from which sample HV5001 was derived. Inset shows cobble-sized clasts from another locality. B) Location of outcrop at Pointe-a-Pierre. C) Geological map of San Fernando area showing para-type locality of the San Fernando Formation. Note the unconformable nature of the basal contact and conformable upper contact with the Cipero Formation. D) Aerial photography of the San Fernando area showing location of two samples (position of sample shown in (C). E) Outcrop section of sample HV5037. 487 -J' , jJSim. \ '.&wim i.-<>*>11• imil' ..;*J1 Kugler (1996) Enclosure 7, 488 Q Sample number HV5034, just north of bus terminal compound jfek Sample number HVS037, Hubert Ranee Steet, Southern Medical Clinic. Type section of San Fernando Fm, also see Figure X, C. 180 175 cm calcareous mudstone (marl), white to 48W| cream, thinly bedded (cm- scale) to laminated. Planar bed contacts. Thin (8cm) bed with pebbles up to 2- 3cm within a green-grey mudstone matrix. Matrix- supported. Pebble bed overlies a mudstone bed of variable thickness (arrowed) with wavy bed contacts. Uppermost bed of reddish calcareous mudstone. 489 Appendix 4 Reefal and Shallow-Water Fossils in the San Fernando Formation A-D FROM BED "10", SOLADO ROCK AND E-H FROM MORNE ROCHE QUARRY, BON AVENTURE. A) and B) Discocyclinids (Dis) and nummulitids (Num) within a dolomitic matrix. C) Coral algal fragments (Alg) and nummulitids. D) Close-up view of dolomite rhombs which make up the matrix of bed "10". According to Kugler and Caudri, (1975), there is no quartz in the matrix component suggesting reefal, carbonate development. E) Mollusc (Mol), coral (Cor) and nummulitid fragments with quartz grains. F) Red algae fragment, a common component of coral reefs. G) Abundant nummulitids and quartz, suggesting reworked reefal fragments. H) Bi-serial foraminifera. 490 491 Appendix 5 Oligocene Guaico Conglomerates at Four Roads, Tamana The Guaico conglomerates are currently exposed in a quarry south of Four Roads junction, Tamana where the largest clasts (to boulder size) consist of coarse-grained quartzitic sandstones (Chaudiere Formation, Pierre Point and Angostura sandstones?). Similar to the Marabella Conglomerate, the most abundant clast composition are grey pebbles of chert, likely derived from the Late Cretaceous Naparima Hill Formation. These conglomerates form fan-shaped sediment bodies that thin in a southward direction from the Northern Range and are inferred to be derived from same (Babb, 1998; Babb and Mann, 1999). A) Outcrop face comprised only of structurless cobble conglomerates. Note person (circled) for scale. B) Close up of clast-supported conglomerate with rounded cobbles and (C) boulders. The boulders comprise quartzitic sandstones. Scale in (B) is 0.25m and lm in (C). D) Estimated clast composition of the conglomerates from a random survey of clasts at the outcrop. 492 Appendix 6 Facies of the Eocene-Oligocene Chalky Mount Member of the Scotland Formation, Barbados The Eocene - Oligocene Scotland Formation of Barbados has been correlated to the Pointe-a-Pierre Formation on lithological and faunal grounds (Illing, 1928, Kugler, 1936, Senn, 1940, Liddle, 1946). Similar lithofacies to the Chaudiere, Pointe-a-Pierre and Nariva formations and the Angostura Sandstone were described among approximately 270 m of section within the Chalky Mount Member. Similar deep-water sedimentary processes and depositional environments were interpreted. Sandy and conglomeratic debris flow deposits are a common component of the Chalky Mount succession, often interbedded with laterally continuous to lenticular-shaped amalgamated pebbly sandstones and graded turbidites. The association of amalgamated pebbly sandstone, massive and gradational sandstone, rippled sandstone and conglomeratic debris flows is interpreted to occur within base of slope to proximal basin floor environments. This is supported by the few trace fossils observed which included Ophiomorpha and Phycosiphon, both commonly associated with flysch deposits (Uchman, 2001). The high sandstone to shale ratio and aggradational stacking observed among the outcrops at Chalky Mount were very similar to the stacking pattern exhibited by the Angostura Sandstone Member of Trinidad. A few representative sections are shown below. 493 •"BUg- r *8U5~ Contorted strata -^r- Scour >* Scour / Fining-upward == Parallel-laminated Correlative Eocene-Oligocene deep water facies from Barbados. A) Section from Chalky Mount Village displaying interbedded amalgamated pebbly sandstone and sandy debris flows (darker shading); B) Slumped, sand-rich debris flows encased in shale (below hammer). This slumped mass is arrowed in C. C) Sandy debris flow thins from approximately four metres (foreground) to one metre between thick bedded turbidites. Another sandy debris flow overlies these deposits (arrowed). D) Thick, amalgamated succession of lower slope to basin floor pebbly turbidite beds of the Chalky Mount Member. E) Phycosiphon trace fossil at the base of a turbidite bed F) Ophiomorpha trace within turbidite bed. G) (next page) Logged section demonstrating facies of the Chalky Mount Member along the Coast Road outcrops. 494 G COAST ROAD SECTION. BARBADOS LOCATION: (below 'Sleeping Giant. Chalky Mounl) LOGGED BY: Wach, Vincent, Chaderton Depth (m) FACIES Interpretation 98.50cm pebble conglomerate: dominantly granule sized grains w/ abundant pebbles. Erosive base: clast supported matrix. 97. Pebbly to granular. Very poorly sorted. Massive. Internal debris How pinches out In both east and west. Upper beds granular with common pebbles. Flattened mud dasts at base (up to 40 cm). Sst tills relief on top debris flow. . LL 96. Sequence of beds: 1.4m interbedded vf sand and silty shale 4cm x 2 vf sand w/ erosive bases; current ripp. 30cm grey laminated shale w/ sst lens 12cm pinch and swell vc to granular sst. 10 cm vf silt sst w/ coarse qtz grains; abundant organic matter. 8 cm vc to eg sst; wavy contact 5cm f sst overlain by 5cm laminated silt. 95. Wavy divergent laminae. Coarse grained lenses at top. 94.25cm vf sand. Top 3cm wavy divergent silt 93. Summary of field notes: 250 cm of interbedded silty vf sand, and laminated shale. Sand with wavy divergent laminae. Some pinch and swell; current rippled. Occasional coarse and medium grained beds (3cm). Organic fragments. 92. Shale with contorted laminae. 91. Laminated silty shale overlain by I very fine sand and silly shale (wavy laminae). 90. Summary of field notes: Coarse to medium grained sandstone beds; occasionally very coarse. Beds commonly Dm upward from irregular bases. Common mud rollers. 89.40 cm, 'slurry-like'. Contact indistinct. Dewateringattop. 88.150 cm coarse to medium grain sandstone in a very fine sand matrix. Rare mud dasts. END at 6:20 pm. Section above logged by Vincent and Chaderton on Sun 5th March 06. CO 87.10 cm grey sandy silty clay overlain by ujiu coarse to medium grained sandstone beds, °-9 with Irregular, scoured contacts. Off 86.80cm Discrete flow. 'Slurry-like'. Irregular surface. Overlain by 190 cm, of same (medium few to coarse sendstone). SO 85.70cm coarse to medium moderately sorted. 84. Sharp planar contact with medium to 2< coarse grained sandstone (140cm). Concretion, ball and pillow. 83.120cm interlaminated silty fine sand and fine sand. Both wavy divergent and wavy parallel laminae. No trace fossils. 82.40 cm sandy silt, parallel laminated. 495 Appendix 7 Nannofossil Analysis This appendix is divided into three parts; the preliminary analyses was performed by Ms. Sarah Mason (4th year Honors Student, Department of Earth Sciences) while the detailed analyses was done by Dr. Gunilla Gard and Dr. Jason Crux of Biostratigraphic Associates Canada. 496 Part 1. Analysis done by Ms. Sarah Mason, 4th year honors student, Department of Earth Sciences, Dalhousie University. 05-HV003: BARREN 05-HV010: BARREN 05-HV011: BARREN 05-HV104: BARREN GWHV-14: BARREN 05-HV015: BARREN 05-HV106: BARREN GWHV-17: BARREN GWHV-22: BARREN 05-HV036: BARREN 05-HV037': HELICOSPHAERA, GEPHYROCAPSA, COCCOLITHUS PELAGICUS, RETICULOFENESTRA SP. 05-HV038: GEPHYROCAPSA, RETICULOFENESTRA, CALCIDISCUS? GWHV-24: BARREN Part 2 Paleontologist: Gunilla Gard. Biostratigraphic Associates (Canada) Time Scale: Hardenbol et al. 1998 Calcareous Nannofossils Tertiary Nannofossil zonation Martini 1971 Species lists with estimate of abundance P=present R=rare F=Few C=common A= abundant VA=very abundant 05019(A) Plum Mitan shale (Plum Mitan orange estate) Indeterminate coccolith R 06005(A) Torouba stadium excavation, Torouba Late Oligocene, NP 25 Zone Cyclicargolithus abisectus P Zygrhablithus bijugatus P LAD circa top NP 25 Reticulofenestra bisecta P LAD circa top NP 25 Discoaster calculosus P Triquetrorhabdulus carinatus C acme NP 25 Sphenolithus ciperoensis R FAD base NP 24-LAD NP 25 Reticulofenestra daviesii/gartnerii F Discoaster deflandrei R Helicosphaera euphratis 497 Clausicoccus fenestrates P Cyclicargolithus floridanus A Helicosphaera intermedia F Reticulofenestra minuta/producta VA Sphenolithus moriformis F Pontosphaera multipora R Coronocyclus nitescens R Coccolithus pelagicus F Helicosphaera perch-nielseniae P Helicosphaera recta R LAD circa top NP 25 Hughesius tasmaniae R Helicosphaera truempyi P NP 25 - NN 1 Pontosphaera spp. F 06012 (A) Rock River, Moruga latest early - middle Miocene NN 4 - NN 5 Watznaueria barnesae P (reworked) Sphenolithus cf. belemnos? P Discoaster brouweri R Triquetrorhabdulus carinatus? P Helicosphaera carteri F Discoaster deflandrei F Helicosphaera intermedia F Umbilicosphaera jafari P Reticulofenestra minuta/producta A Sphenolithus moriformis F Pontosphaera multipora P Discoaster pansus F Coccolithus pelagicus F Discoaster sanmiguelensis P 06012 (B) additional species Rock River, Moruga Discoaster barbadiensis P Coccolithus miopelagicus P Discoaster petaliformis P NN4 - NN5 Reticulofenestra pseudoumbilica P Helicosphaera vedderi P Micrantholithus vesper P Helicosphaera walbersdorfensis P Discoaster spp. P 06014(A) Lizard Springs Formation, San Fernando Indeterminate coccolith R 06027(A) (Pointe-a-Pierre Formation, Chaudiere River, Mt. Harris) Indeterminate coccolith R 06030(A) Pointe a Pierre Formation, Chaudiere River, Mt. Harris Barren 06031(A) Retrench Formation marls, Retrench village excavation early - earliest middle Miocene latest NN3 - NN 4 Helicosphaera ampliaperta F NN3 - NN4 Triquetrorhabdulus carinatus? P NN 2 or older? Helicosphaera carteri C Reticulofenestra daviesii/gartnerti P NN4 or older Discoaster deflandrei F Cyclicargolithus floridanus A Sphenolithus heteromorphus F latest NN3- NN4 Helicosphaera intermedia P Umbilicosphaerajafari P Triquetrorhabdulus milowi P Reticulofenestra minuta/producta VA Sphenolithus moriformis F Pontosphaera multipora P Coronocyclus nitescens P Discoaster pansus P Coccolithus pelagicus F Calcidiscus premacintyrei P Reticulofenestra pseudoumbilica P Scyposphaera spp. P 06036(A) Naparima Hill Formation, San Fernando Hill late Campanian - earliest Maastrichtian Helicolithus anceps P Watznaueria barnease C Cretarhabdus conicus R Cribrosphaerella ehrenbergii P Zeugrhabdotus embergerii R Reinhardtites levis R late Campanian - Maastrichtian Broinsonia parca parca R Campanian - earliest Maastrichtian Cylindralithues serratus R Micula staurophora F Uniplanarius trifidus R late Campanian - earliest Maastrichtian Retecapsa spp. P 499 PART 3 Paleontologist: Jason Crux, Biostratigraphic Associates (Canada) Time Scale: Hardenbol et al., 1997 Calcareous Nannofossils Tertiary Nannofossil zonation: Martini 1971 S - single, R - rare, F - few, C - Common, A - abundant, VA - very abundant Well Mt. Harris-1 2988' Chaudiere Formation Barren Well Canteen-1 (5076.4') Angostura Sandstone Member shale Middle Eocene - early? Miocene Reticulofenestra hampdensis group indicates a middle Eocene to early? Miocene age. This is supported by the tentatively identified Dictyococcites bisectus, which if correctly identified indicates a middle Eocene - Oligocene (NP 16 -NP 25) age. The presence of tentatively identified Watznaueria barnesae indicates the presence of reworked Cretaceous fossils. Dictyococcites bisectus! R Reticulofenestra hampdensis group R Rericulofenestra minuta R Watznaueria barnesae"? S Well Canteen-2 (4658.7') Angostura Sandstone Member shale Middle - late Eocene (NP 16 - NP 20) The presence of Cribrocentrum reticulatum indicates a middle - late Eocene (late NP 16 - NP 20) age. This is confirmed by the co-occurrence of Dictyococcites bisectus and Discoaster barbadiensis. Several reworked Cretaceous species are present in the sample, they include, Micula staurophora, Arkhangelskiella cymbiformis, Cribrosphaera ehrenbergii, and Watznaueria barnesae. Arkhangelskiella cymbiformis S Clausicoccus fenestratus R Coccolithus pelagicus F Cribrocentrum reticulatum R Cribrosphaera ehrenbergii R Cyclicargolithus floridanus C Cyclococcolithus formosus R Dictyococcites bisectus R Dictyococcites scrippsae R Discoaster barbadiensis S Discoaster cf. D. deflandrei S Heliocosphaera euphratis! R 500 Helicosphaera gartneri R Micula staurophora R Prediscosphaera cretacea S Reticulofenestra spp. A Reticulofenestra hampdensis group R Reticulofenestra minuta F Reticulofenestra minutula R Reticulofenestra samodurovii S Sphenolithus moriformis F Sphenolithus predistentus S Watznaueria barnesae R Zeugrhabdotus diplogrammus S Zygrhablithus bijugatus R Well Kairi-1 (5395.2') Angostura Sandstone Member shale The co-occurrence of Dictyococcites bisectus with Reticulofenestra samodurouvii indicates a middle - early Oligocene (NP 16 -NP 22) age. The presence of tentatively identified Helicosphaera lophota possible further restricts this age to middle - late Eocene (NP 16 - NP 18). Rare reworked Cretaceous species are present such as Cretahabdus conicus and Eprolithus floralis. Calcidiscus protoannulus R Coccolithus pelagicus F Cretarhabdus conicus R Cyclicargolithus floridanus R ! Dictyococcites bisectus R Discoaster deflandreil S Helicosphaera gartneri R Helicosphaera lophota? R Helicosphaera wilcoxonii R Eprolithus floralis S Reticulofenestra spp. C-A Reticulofenestra daviesii group R Reticulofenestra hampdensis group C Reticulofenestra minuta C Reticulofenestra minutula R Reticulofenestra samodurovii F Reticulofenestra umbilicus R Sphenolithus moriformis F 05 - HV010 Nariva Formation, Esmeralda Junction Barren 05 - HV036 Naparima Hill Formation, San Fernando Hill Barren 501 05-HV037 San Fernando Formation, Quenca St., San Fernando (San Fernando Medical clinic) The co-occurrence of Cribrocentrum reticulatum and Chiasmolithus grandis indicates a middle Eocene (late NP 16 - NP17) age. This age assignment may be further refined by the presence of Campylosphaera dela, whose extinction point lies close to the NP 16 - NP 17 boundary, but there is no agreement between authors as to the exact level. Blackites spinosus R Calcidiscus protoannulus R Campylosphaera dela R Chiasmolithus consuetus R Chiasmolithus grandis R Coccolithus pelagicus A Cribrocentrum reticulatum R Cyclicargolithus floridanus A Cyclococcolithus formosus C Dictyococcites bisectus R Dictyococcites scrippsae R Discoaster acerosl R Discoaster barbadiensis R Discoaster binodosus R Discoaster deflandrei R Discoaster saipanensis R Helicosphaera euphratis R Helicosphaera gartneri R Helicosphaera heezenii R Helicosphaera lophota R Helicosphaera seminulum S Pontosphaera multipora R Sphenolithus moriformis R Sphenolithus obtusus R Sphenolithus predistentus R Reticulofenestra dictyoda C Reticulofenestra hampdensis group C Reticulofenestra minuta VA Reticulofenestra minutula R Reticulofenestra samodurovii R Reticulofenestra umbilicus R Transversopontis spp. R Zygrhablithus bijugatus R 05 - HV038 Naparima Hill Formation, Circular Road car wash, San Fernando The presence of Uniplanarius trifidus, U. sissinghii and Broinsonia parca parca indicates an earliest Maastrichtian - late Campanian age. Arkhangelskiella cymbiformis R Broinsonia parca parca R 502 Cretarhabdus conicus R Cribrosphaera ehrenbergii R Cylindralithus spp. R Eiffellithus turriseiffelii R Micula staurophora F Prediscosphaera cretacea R Retecapsa spp. R Uniplanarius sissinghii R Uniplanarius trifidus S Watznaueria barnesae A GW-HV-14 Pointe-a-Pierre Formation, Fabien Road quarry, Gasparillo Barren 503 Appendix 8 Point Count Categories 1. Monocrystalline Individual quartz crystal greater than 63 um; undulose or straight extinction; quartz fractured or wholesome grains. 2. Polycrystalline Several quartz crystals either cemented or sutured together displaying variable quartz extinction patterns. Individual crystal sizes smaller than 63 microns. This category was sometimes indistinguishable from lithic chert and metamorphic rock fragments. 3.Lithicrock Metamorphic, volcanic, siltstone, chert; carbonate, bioclasts fragments 4. Lithic Mono or poly-crystalline quartz with muscovite inclusions large enough to be (metamorphic rock identified confidently under x500 magnification. Includes finely crystalline fragments) varieties (slates or phyllites) to coarser aggregates with aligned micas (mica- schists). 5. Lithic (granitoid Quartz-feldspar aggregates; volcanic rock fragments, with aligned feldspar laths rock fragments) within an aphanitic groundmass was not seen in these samples. 6. Lithic (siltstone, Euhedral to subhedral silt-sized quartz and clay aggregates. These are present in mudstone) forms gradational from quartz-rich siltstone to silty mudstone. They were differentiated by their rounded form and sometimes contained "exotic" bioclasts and minerals (e.g. glauconite) that were not otherwise part of the slide. Mudstone chips can be elongated. Grains larger than 63 um are counted as their mineral component (quartz, glauconite, matrix, etc.) under the Gazzi-Dickinson method and so "sandstone" will not be represented in the lithic fraction. 7. Lithic Variously-shaped, but distinct calcite clasts. Their identification is challenged (carbonates) when calcite is the primary cement, although the shape, orientation and general relationship with other grains and cements allowed an easy diagnosis. Others includes bioclastic fragments (e.g. foraminifera, algae, gastropod fragments) 8. Feldspar Twin planes and interference figures facilitated their recognition and differentiation from quartz. Often partially to completely dissolved with twin planes variably preserved. Sometimes altered to sericite. Where a confident diagnosis could not be discerned (e.g. "cloudy" quartz versus orthoclase), these were recorded as "unknown". Thin sections were not stained to aid in the recognition of feldspars and as a result, they may be under-represented, although their percentages are very low overall. 9. Cement/ Matrix Cement was distinguished by its usual pore-filling, sediment support or grain binding habits. Matrix did not normally show the latter. In reality, it was difficult to differentiate the two especially when both occurred as a sericitic clay fraction; they were grouped in the counts. There may have also been some overlap with deformed, argillaceous lithic fragments. The two were easily differentiated where calcite was the main cementing agent. 10. Heavy minerals Usually an order of magnitude smaller than quartz (hydraulic equivalence). The amount of a specific mineral was not noted as this was quantitatively treated elsewhere. To account for their smaller sizes relative to other grains, grains were counted once they entirely appeared within the field of view at x500 magnification, despite what was under the cross hairs. If more than one occurred at one time, the count was incremented by one only. Otherwise, this category would not be represented in most of the counts. Grains included zircons, tourmaline, epidote, rutile and garnet. 11. Other Other categories included glauconite, opaques, muscovite and detrital chlorites. Accessory minerals 12. Porosity Open pore spaces; aided by blue staining of slide. 504 Sample no./fraction Sample weight weight weight Weight D weight lost Weight Weight Weight Weight % of fines weight (am) fraction A fraction B fraction C %(A) %(B) %(C) %(losf) saved 5001 80.1 3.341 32.559 33.642 6.288 10.558 4.2 40.6 42.0 13.2 59.6 5006 87.94 16.41 43.3 19.68 3.21 8.55 18.7 49.2 22.4 9.7 37.5 5007 87.91 0 0.46 47.89 25.83 39.56 0.0 0.5 54.5 45.0 65.3 A: > 1 mm 5009 87.86 0 0.05 63.72 7.07 24.09 0.0 0.1 72.5 27.4 29.3 B: 0.25-11 5012 87.83 2.47 62.39 16.92 2.53 6.05 2.8 71.0 19.3 6.9 41.8 C: 0.0626 • 5013 80.56 20.377 39.967 15.596 2.462 4.62 25.3 49.6 19.4 5.7 53.3 D: < 0.062 5018 87.6 0 0.86 76.32 4.39 10.42 0.0 1.0 87.1 11.9 42.1 5019 88.35 0 0 0 0 88.35 0.0 0.0 0.0 100.0 0.0 Grain sizes 5022 87.99 0 2.38 67.88 5.77 17.73 0.0 2.7 77.1 20.2 32.5 5023 87.89 34.743 31.545 15.378 2.193 6.224 39.5 35.9 17.5 7.1 35.2 5025 88.65 0 0 0 0 88.65 0.0 0.0 0.0 100.0 0.0 5026 78.91 0 0 0 0 78.91 0.0 0.0 0.0 100.0 0.0 5029 86.96 16.04 6.501 38.085 3.869 26.334 18.4 7.5 43.8 30.3 14.7 5044 88.5 17.59 54.74 10.723 2.22 5.447 19.9 61.9 12.1 6.2 40.8 5046 87.72 1.82 57.19 18.91 4.63 9.8 2.1 65.2 21.6 11.2 47.2 5049 88.781 58.05 23.46 3.51 0 3.761 65.4 26.4 4.0 4.2 0.0 5052 87.31 0 0.03 38.71 21.5 48.57 0.0 0.0 44.3 55.6 44.3 6004 87.94 0.4 76.74 8.83 0 1.97 0.5 87.3 10.0 2.2 0.0 6007 87.94 44.87 21.13 12.42 3.54 9.52 51.0 24.0 14.1 10.8 37.2 6008 88.15 0 8.43 54.55 1.87 25.17 0.0 9.6 61.9 28.6 7.4 6009 87.82 0 0 0 0 87.82 0.0 0.0 0.0 100.0 0.0 6015 87.95 0 0 0 0 87.95 0.0 0.0 0.0 100.0 0.0 6015 87.59 0 0 0 0 87.59 0.0 0.0 0.0 100.0 0.0 6016 86.69 0.08 10.83 72.6 0.22 3.18 0.1 12.5 83.7 3.7 6.9 6017 88.3 0.03 0.18 67.5 6.73 20.59 0.0 0.2 76.4 23.3 32.7 6018 87.3 0.014 0.02 65.08 9.65 22.186 0.0 0.0 74.5 25.4 43.5 6028 73.91 0 0 0 0 73.91 0.0 0.0 0.0 100.0 0.0 AS1.9(Kairi1) 87.66 4.64 34.28 38.15 3.54 10.59 5.3 39.1 43.5 12.1 33.4 AS2.41 (Canteen 1) 87.38 6.84 37.12 35.98 2.34 7.44 7.8 42.5 41.2 8.5 31.5 Bonasse A 87.66 0 0 0 0 87.66 0.0 0.0 0.0 100.0 0.0 Bonasse B 87.76 0 0.52 50.66 4.69 36.58 0.0 0.6 57.7 41.7 12.8 Bonasse E 87.31 0 0 55.6 21.14 31.71 0.0 0.0 63.7 36.3 66.7 Fullerton Beach sand 88.73 0.13 4.34 81.05 0.577 3.21 0.1 4.9 91.3 3.6 18.0 Pt Paloma 88.07 0 65.04 21.81 0 1.22 0.0 73.9 24.8 1.4 0.0 A:> 1mm, phi>0, > very coarse sand B: 0.25 - 1mm, phi 2-0, mediumto coarse sand C; 0.0526 - 0.25mm,.phi.4-2, very fine Lo Fine sand D:< 0.0625 mm, < phi4, coarsesiltto clay Grain sizes basedon Wentworth 1922, after Folk (1980) Appendix 10 Some Results of Heavy Mineral Studies in Trinidad and Barbados Ullrastable Meiamorphic origin Others £ to S (0 & i8 •8 1 I "S. ! Glaucophan e (0 1 ! I _«L. i I I I l Ul I I 1 1 1 v> 1I I I Recent (Gulf of Paria) o • o o o • o o Pleistocene O o • o o Pliocene O o • o o o Miocene o o o • • o • o Oligocene • o • o o Eocene o • o o o o Soldado o • • • o va n Ande l an d Postma , 195 4 Cretaceous o • • o o o o Pliocene • • • • • # • o • • • • • • * ft it • "Miocene" • • • • • # • • o o "Oligocene" • W • • • • • • • • • ^ w €1 • Eocene • 0 • O w €1 • • • • • Griffiths , 194 4 Paleocene 4&0 « • • • • • o • • • O • • Cretaceous N. Range 0 • • • • o o • © • • Pliocene: Morne (.'Enter Fm. o O • o o o • • Cruse Fm. o o • • o • o o Early Miocene Herrera Sst Mbr. o • o o • o Oligocene: Cicero (Plum Milan) • o o o Oligocene: NarivaFm o • o • o o o 1 Oligocene Angostura Sst. o o o o o Eocene: I San Fernando Fm • o • • o • • Eocene Pointe-a-Pierre Fm o • o o o o Paleocene: Chaudlere Fm o o o o Eocene: Scotland Fm. • o • • o o o o o o • • o • • • o • o • • • o a Eocene: Scotland Fm. « • « m • • © © a « ® 9 b © ffl uS a> s I 3 | a 2 •B 1 % 1 s T3 (0 ! 1 ! Hornblend e IS) 5 i I ! R * s c5 i ! 1 i I i 1 1 1 a: Senn, 1940 b: Matley, 1932 # Abundant (Vincent, van Andel and Postma: x>30%l) c: chloriloid data given as a fraction of "others". # Common (Vincent, van Andel and Postma: 5< x <30%) ' Griffllhs(1944)denvedfromSuter(1960).Notethat Griffiths (1951) includes Upper Morna L'Enfer lo # Occasionally occurs (Griffiths only) Lengua as "Miocene" and Nariva and Cipero (Herrera) as "Oligocene"; his table above may use a O Rare (Vincent, van Andel and Postma: x<5%; Senn: occurrence < 63/113 slides) similar stratigraphy This varies from current stratigraphic dating. # Occurs (Matley only, no quantitative data) Griffiths, J.C., 1951, Size versus sorting in some Caribbean Sediments. Journal of Geology, V. 69,3, p. 211- 506 "QrairT ize (mm) Quartz —Ag e Location Stratigraphic unit Max Typical Grain size classification Grain sorting Grain roundness m on ocry stallin eery staHine/ Grain extinction Inclusion* number (Wentworth-Udden Scale) PolvcrYstaHina 1 Late Plocene HV7003 Mayara coast Moruga Formation 0.2 0.05-0.1 Vf sand 0.0625-0.125 very wel angular to sub angular, occ mostyt monocrystaline Many undujose, many rounded uniform > 1 Late Plocene HV6039 Cedros Bay Mome L'Enfer 0.35 0.1-0.2 Fine sand a 125-0.25 welsorted angular to sub-angular dominantly monocrystafline Many undulose, many mainly micas Formation uniform t> 0> •d 1 Late Pliocene HV6018 Erin Bay Mome L'Enfer 0.4 0.25 Medium sand 0.25 - 0.50 very wel angular • subangular domHnary monocrystaline most show undulose linear vacuoles, muscovite Formation tf A 1 Late Plocene HVB037 PtPaloma Springvale Formation 0.25 0.1-0.2 Fine sand 0.125-0.25 very wel angular to sub-rounded dominanlly monocrystalline mainly micas 3 p. 2 Early Pliocene HV5032 Moreau Road Cruse Formation 0.5 0.2 Fine sand 0.125-0.25 moderate mostly angular, few submd to Dominantly monocrystaline mostly undulose, many rare show uniform IT 2 Early Plocene HV70O5 Mome Diablo Cruse Formation 0.3 0.1 Fme sand 0.125-0.25 wel sorted angular Most monocrystaline Many undulose, many rare, mostly vacuoles to M uniform 2 Early Plocene HV70O6 Mome Diablo Cruse Formation 0.12 0.08 Vf sand 0.0625-0.125 very wel Ang-subang Most monocrystaRine Most show urKMase, Rare, Tzircon, vacuoles uniform common 2 Early Plocene HV5031 Moreau Road Cruse Formation 0.8 0.12 Fine sand 0.125-0.25 very well Ang-subang Most monocrystaline mast show undulose vacuoles, 2 Early Plocene GW6O01 Point Paloma Manzanida Formation 3 1.2 Granule 1 - 4 poorfy angular - subangular polycrystaline most show undulose vacuole trains a 3 Early Miocene HV5026 Rock River, Herrera Sandstone 0.5 0.55 Coarse sand 0.50 -1 very wel ang-subang dominantly monocrystalline mostly undulose muscovite, linear vacuoles Moruga Member 3 Early Miocene HV5029 Moreau Road Herrera Sandstone 0.4 0.016 Fine sand 0.125-0.25 very well Ang-subang Most monocrystaline gently undiiose muscovite, opaques, vacuoles Member to 3 Early Miocene HV5057 Wei MD-34 Herrera Sandstone 0.6 Coarse sand 0.50 -1 v»l sorted subang-submd.md (al ranges) domin monocrystaffine domin undulose. though muscovite Member many with uniform o 3 Early Miocene HV6011 Rock River, Herrera Sandstone 0.3 Fine sand 0.125 -0.25 very wel angular- subang occ sbmd dominantly monocrystaline dominantly uniform, linear vacuoles Moruga Member common undulose a 3 Early Miocene GWHV20 Wed BP-342 Herrera Sandstone 0.35 0.01 Fine sand 0.125 -0.25 moderately wel ang. sub ang, sub md Most Most undulose, many rare rt Member monocrystaflinecrystalrine uniform •1 Early Miocene GWHV21 WeP BP-347 Herrera Sandstone 1 0.28 Coarse sand 0.50-1 moderately wel subrnd-subang o Member OTQ o » -3 4 Late Otigocene HV5018 Plum Mitan Cipero Formation 0.4 0.2 Fine sand 0.125 -0.25 wel sorted dom submd-subang, occ md domin monocrystaline. very abundant vacuoles sometimes cross common poly hatched; cloudy qtz 4 Late Oligocene HV5007 Esmeralda Nariva Formation 0.2 Fine sand 0.125-0.25 very wel ang-subang Domin monocrystaline common undulose muscovite Junction 4 Late Otigocene HV50O8 Esmeralda Nariva Formation Fine sand 0.125-0.25 GO Junction r* "Lat e Oligocene HV50D9 KelyKiR Nariva Formation 0.55 Medium sand 0.25 • 0.50 very wel ang-subang domin monocrystaline domin uniform c Late Oligocene KV5058 WeRASM-44 Nariva Formation 0.6 Coarse sand 0.50 -1 moderately wel ang-subang domin monocrystaline domin undulose common linear vacuoles, muscovite, " (3015") bright red Thematite, opaques •»a• 4 .ate Oligocene HV6021 Corbeaux Hil Nariva Formation 0.6 0.4 Coarse sand 0.50 -1 ",„»»> ang-subang. occ submd dominanlty monocrystalline, common undulose muscovite A 4 Late Oligocene HV6022 Corbeaux Hil Nariva Formation 0.S3 0.28 Medium sand 0.25 - 0.50 wel sorted ang-subang, submd. occ md dominanRy monocrystalline, most show undulose vacuole trains, muscovite (0 few poly O Late Oligocene HV6023 Corbeaux Hil Nariva Formation 0.52 .08-.16 Fine sand 0.125 -0.25 ang-subang dominanlty monocrystaline, most show undulose linear vacuoles, muscovite " """' few poly a 4 .ate Oligocene HV6024 Corbeaux HHI Nariva Formation 0.23 Medium sand 0.25-0.50 moderately wel ang-subang. occ submd dominantly monocrystalline most show undulose, fair linear vacuoles, muscovite bit w&h uniform relative to i—i other slides s* _ate Otigocene HV6033 Kelly Hil Nariva Formation 3.6 0.15 Granule 2-4 moderately wel ang-subang, occ submd dominanlty monocrystalline, vacuole trains, muscovite " few poly a 4 jte Oligocene HV6Q35 KelyHil Nariva Formation 0.9 0.5 Coarse sand 0.50-1 """*" ang-subang, submd. occ md monocrystaline undulose and uniform common muscovite 4 Late Otigocene GWHV12 Sandstone Nariva Formation 4 Granule 2*4 poorly rounded to submd numerous poly most show undulose s Middle Oligocene AS 1.1 Kairi Angostura sandstone 0.44 0.28 Medium sand 0.25 - 0.50 very wel ang-subang, few submd monocrystaline dominant, rare most show undulose Tmuscovite, Tzircon, ?epidote. abundant poly vacuoles 5 Middle Oligocene AS 1.20 Kairi Angostura sandstone 1.3 0.415 Vc sand 1 - 2 P"""* ang-subang esp among smaler monocrystaline dominant, rare most show undulose grains, some sub md, rare md poly Middle Oligocene AS 2.41 Well Canteen 1 Angostura sandstone 3 0.1-0.5 Granule 2- 4 Poorly (bt-modal) md to angular monocrystaline dominant most show undiiose vacuoles Middle Oligocene AS 2.34 Kairi Angostura sandstone ,s 0.2 Vc sand 1 - 2 moderate md to submd. rare subang monocrystaline dominant, rare most show undulose vacuoles, muscovite ' pory Quart Age Sample Location Stratigraphic unit Fractures Overgrowths Other Framework minerals Accessory minerals Cement Classification Comment number 1 Late Pliocene HV7003 Mayaro coast Moruga Formation Feldspar, lithics {chert, MRF), biotite epidote, zircon, tourmaline 1 Late Pliocene HV6039 Cedros Bay Morne L'Enfer Feldspars (plag, microcline, perthite) sometimes biotite, epidote, clinozoisite, zircon, chlorite FeO and sericite cement Thin section made from poorly consolidated sand Formation altered to sericite, lithics (MRF, chert), muscovite (epidote-quartz aggregate seen); 'altered sample. Slide was impregnated with resin. glauconites to limonite 1 Late Pliocene HV6Q18 Erin Bay vlome L'Enfer Abraded sitica .rthics (aligned micaceous, chert), feldspar muscovite sub arkosic lithicarenite sutured polycrystalline grain boundaries Formation [albite, microcline), MRF (qtz rimmed w/ mica 1 Late Pliocene HV6037 Pt Paloma Springvale Formation many grains fractured and abraded silica Variably altered feldspar, lithics (chert, mica- muscovite Difficult to discern some MRF from matrix. angular schist MRF) a Early Pliocene HV5032 Moreau Road Cruse Formation Lithics (chert, MRF), feldspar (plag, microcline!) muscovite, chlorite, tourmaline calcite Several altered grains, possibilities indude altered chert, glauconite or feldspar; one MFR aggregate of Plag Feldspar, quartz and mica. 2 Early Pliocene HV7005 Morne Diablo Cruse Formation ME fractures are pervasive Feldspar (plag), lithics (chert, MRF) glauconite, biotite, muscovite calcite 2 Early Pliocene HV7006 Morne Diablo Cruse Formation All fractures are pervasive Feldspar (plag, microcline, ?orthoctase), lithics glauconite, epidote, clinozoisite, chlorite calcite, FeO, sericite (chert, MRF) 2 Early Pliocene HV5031 Moreau Road Cruse Formation Abraded silica Lithic (MRF, chert) feldspars (fresh-perthite, glauconite calcite Feldspathic sub litharenite microcline, orthoclase, albite), muscovite 2 Early Pliocene GW6001 Point Paloma Manzanilla Formation throughgoing fractures lithics (chert, silt stone, phyHite glauconite (altered), muscovite, feldspar Fe, ?chlorite Litharenite (phyllitic) C-axis alignment in polycrystalline quartz. quartz filled Abundant mica-schist lithic fragments 3 Early Miocene HV5026 Rock River, Herrera Sandstone calcite filled Feldspar (albite, microcline), lithics (MRF, Glauconite, sericrrJzed grains. Calcite, FeO, (oxidi2ed rims) sub litharenite (feldspathic) Moruga Member bioclasts, chert, ?carbonates, opaques (some bright red)) 3 Early Miocene HV5029 Moreau Road Herrera Sandstone Abraded silica glauconite (unaltered), fossils (forams), lithics untwinned feldspar, albite, perthite calcite, chert, ferruginous clay arkosic sublitharenite sericitic matrix; chatcedonic quartz in one chert Member (chert, mudstone, carbonates) tthic. 3 Early Miocene HVSD57 Well MD-34 Herrera Sandstone open Abraded silica lithics (MRF, carbonate, sandstone, silt stone, Glauconite (some deformed into pore Calcite, kaolinite and ferruginous Heteralithic - Wacke Lithic component may be understimated due to Member chert, bioclasts (forams) spaces), oxides, altered feldspar clays. Possibly sericite. abundance of anhedral mudctasts. Silt lithics with sericite matrix. Opaque rims on calcite lithics. Partial silica overgrowths; sutured grain boundaries 3 Early Miocene HV6011 Rock River, Herrera Sandstone open Lithic fragments (chert, MRF, feldspar (albite, Muscovite (partially altered to chlorite), Calcite dominantated, with minor Both relatively fresh feldspars and a few altering to Moruga Member microcline), opaques. glauconite, clinozoisite, chlorite ferruginous and sericitic clays sericite. ?Chert 3 Early Miocene GWHV20 Well BP-342 Herrera Sandstone Abraded silica Glauconite, feldspar (plag and microcline), lithics zircon, 'epidote, tourmaline Silica, argillaceous Chalcedonic chert lithics. Member {chert, calcite, MRF (phy Bites)) 3 Early Miocene GWHV21 Well BP-347 Herrera Sandstone glauconite, lithics (sandstone, mudstone, feldspar (microcline), tourmaline Calcite Siltstone lithics with micas, glauconite, feldspars Member siltstone, chert, calcite, bioclasts). & carbonate intraclasts & sericitic cement (?Nariva sst). Glauconite with silt-sized quartz inclusions; micritic carbonante clasts analagous to Cuche limestones; Chalcedonic chert lithics. 4 Late Oligocene HV5018 Plum Mitan Cipero Formation common abraded Lithics (MRF - rimmed grains), siltstone, chert feldspar, very altered (microcline, some opaque, sericitic and micaceous Litharenite derived silica overgrowths; rare C-axis alignment silica untwinned), deformed muscovite, altered cements. in polycrystalline quartz glauconite 4 Late Oligocene HV50O7 Esmeralda Nariva Formation Abraded silica lithic (MRF), clay matrix (opaque), sericite, chert deformed muscovite, glauconite or silica overgrowth, oxide, sublitharenite to qtz wacke Junction muscovite, altered feldspars kaolinite, sericitic clays 4 Late Oligocene HVS008 Esmeralda Nariva Formation Abraded silica Lithic fragments (chert, MRF) muscovite, 2ircon, rut lie, tourmaline, epidote. Ferruginous and sericitic clays. Abundant MRFs, grossly understimated using the Junction Gazzi-Dickinson counts. Abundant silt-sized heavy minerals. 4 Late Oligocene HV5009 Kelly Hill Nariva Formation Abraded silica Lithics comprise MRF (polyxBine qtz rimmed with deformed muscovite, feldspar ghosts, sericitic, ferruginous, possibly Common dissolution of feldspars. sericite), sandstone, siltstone, chert. ?glaucontie kaolinite 4 Late Oligocene HV5058 Well ABM-44 Nariva Formation Abraded silica lithics (MRF, chert, siltstone, bioclasts) Feldspars (variably altered microcline & ?sericite, oxides. This grain was Feldspathic sub litharenite Sample impregnated for strength; porosity (3015') albite), muscovite, garnet, epidote reinforced with resin unreliable 4 Late Oligocene HV6Q21 Corbeaux Hill Nariva Formation Muscovite, lithic fragments (chert, siltstone & glauconite Ferruginous and sericitic day MRF {finely xlline quartz with muscovite)) 4 Late Oligocene HV6022 Corbeaux Hit Nariva Formation Abraded silica Lithic (chert, MRF), muscovite (common) sericitic clay and kaolinite 4 Late Oligocene HV6023 Corbeaux Hi Nariva Formation Lithics (MRF-phylites, chert), altered feldspar muscovite, epidote sub arkosic lithicarenite sutured polycrystalline grain boundaries (perthite, microcline), 4 Late Oligocene HV6024 Corbeaux Hit Nariva Formation Lithic (MRF, siltstone, chert) muscovite, feldspars (varing stages of sericitic clay sub litharenite alteration), glauconite 4 Late Oligocene HV6033 Kelly Hill Nariva Formation Lithics (chert, rare MRF) Muscovite Ferruginous and sericitic day, sub litharenite Polycrystalline quartz with granular habit ?silica 4 Late Oligocene HV6035 Kelly Hill Nariva Formation Abraded silica muscovite, lithic chert and stretched Plagioclase feldspar (almost complete sericitic clay cement and chlorite Lithics may be underestimated due to difficulty in metamorphic quartz (with micas, i.e. MRF) dissolution) differentiation from matrix. 4 Late Oligocene GWHV12 Sandstone Nariva Formation few Lithics (chert, argilaceous MRF, mica shcist, tourmaline, zircon, chlorite (from alteration of sericite lithic component wifl be underestimated in counts siltstone), feldspar (plag, microcline), muscovite muscovite) due to coarse grain size; sutured grain boundaries in polycrystalline qtz. 5 Middle Oligocene AS 1.1 Kairi Angostura sandstone Abraded silica Glauconite (sometimes altered, where it is pore opaques, microcline and Carlsbad twinned days from alteration of glauconite Gtaouconitic fossiferous Siltstone lithic with several bioclasts in dark matrix rilling); lithics (mudstone dast, chert, bioclasts, feldspar, zircon (chlorite?), ferruginous clays (foraminifera, gastropods). Mudstone lithic with carbonate, MRF, siltstone) glauconite and quartz; both ikely intra-basinal. 5 MiddJe Oligocene AS 1.20 Kam Angostura sandstone Lithic fossil fragments, glauconite opaques, plag feldspars (partially altered to catata Glauconitic fossiferous chlorite), quartz arerute (tending towards bioclast) 5 Middle Oligocene AS 2.41 Well Canteen 1 Angostura sandstone Abundant Abraded silica Lithics (siltstone, chert, bioclast-foraminifera), arcora Calcite and ferruginous day feldspar (microcline) 5 Middle Oligocene AS 2.34 Kairi Angostura sandstone both opened and calcite lithics (bioclasts, carbonate, sandstone with microcline, opaques (in fine sand range) calcite? Glauconitic fossiliferous sutured polycrystalline grain boundaries. Ignore rilled opaque cement, MRF, chert), glauconite porosity counts on this slide. I i i 1 Grain size (mm) Quartz QuarU Age Sample Location Stratlgraphlc unit Max Typical Grain size classification Grain sorting Grain roundness monocrystalti necrystaH in ef Grain extinction Inclusions Fractures Overgrowths number (Wentworth-Udden Scale) Potvcrvstaline 5 Middle Oligocene AS 3.59 Well Canteen 2 Angostura sandstone 1.3 VcBand1-2 moderate md to subrnd monocrystaltine dominant most show undulose 5 Middle Oligocene AS 1.9 Well Kairi 1 Angostura sandstone 1.2 0.2-0.5 Vc sand 1 - 2 Poorly (bi-modal) md to angular Dominanlyt mono; most show undulose Jnear vacuoles Abraded silica polycrystaline with sutured grain boundary Middle Oligocene AS3.50 Canteen Angostura sandstone 0.45 Medium sand 0.25 • 0.50 >oorty rounded, subrnd and sug ang abundant polyxHine, displays most show undulose Good fracture porosity ' H_3908 granular habit Late Eocene D5HV001 Pointe a Pierre San Fernando Fm 2.8 Granule 2 - 4 soorly arger grains md-submd, many dominanlty monocrystaBine, dominantly undulose linear vacuoles cement fined, oxide lined (Plaisance Cortgl) sub-ang few poly 6 Late Eocene HV5034 Wharf, San San Fernando 0.23 0.1-0.2 Fine sand 0.125-0.25 very well angular dominantly monocrystalline Many undulose linear to cloudy vacuoles, green acicular Very common abraded Fernando crystals (?muscovite) silica Late Eocene HV7045 Soldado Rock San Fernando 0.08 .08-.05 Very fine sand very weH angular to sub-angular dom inanity monocrystalline Most show undulose numerous rimmed with mica 6 Late Eocene HV7D42A Morne Roche San Fernando 2.2 1.2-1.4 Vc to granular sandstone moderate to poor rounded to subrnd dominantly monocrystalline Mostly undulose typically with open fractures 6 Late Eocene HV5035A Hubert Ranee, San Fernando 0.25 .05-.1 Very fine sand very weH angular to sub-angular dominantly monocrystalline mostly undulose muscovite San Fernando 6 Late Eocene HV7041 Soldado Rock San Fernando 3.6 0.2-0.3 Bi-modal, medium grained sand moderate rounded to subrnd to sub ang dominantly monocrystaBine most show undulose Tourmaline, muscovite, vacuoles Very common abraded 6 Late Eocene HV7039 Soldado Rock San Fernando 0.3 0.2 Fine sand 0.125 -0.25 very weB angular to sub-angular Dominanlty monocrystalline Many display undulose acicular inclusions Very common abraded Formation 7 Middle Eocene HV5002 Fablen Road Pointe-a-Pierre 0.36 Medium sand 0.25 - 0.5O very well submd-subang dominanhy monocrystaBine domin undulose vacuoles giving cloudy appearance to qtz, Formation opaques, muscovite 7 Middle Eocene HV5006 Caratal road Pointe-a-Pierre 3 Granule 2-4 poorly arger grainB submd-subang, Most larger grains most larger grains linear vacuoles random, some open, some Formation sometimes pitted monocrystalline, rare poly. undulose oxide lined 7 Middle Eocene HV5Q11 Tabaquite Pointe-a-Pierre 0.6 0.2 Medium sand 0.25 - 0.50 very well interlocking xls dominantly monocrystalline Most undulose zircon Sawn iH Formation ?Middl e Eocene HV5D12 Tabaquite Pointe-a-Pierre 1.6 0.2 Fine sand 0.125-0.25 moderate larger grains eubmd, smaller domin monocrystalline domin undulose Linear vacuoles, abundant in some grains Many grains with open; occ Sawmill Formation subrnd-subang to give cloudy look; micas rilled with cement. Rare throughgoing. 7 Middle Eocene HV5013 Allen Road Pointe-a-Pierre Z4 0.45 Granule 2-4 moderate Dominantly Most undulose fractured grains Formation m onocrystali necrystalli ne, common poly 7 Middle Eocene HV5046 Fabien Road Pointe-a-Pierre 2.2 0.24 Coarse sand 0.50-1 moderate dom subrnd-md occ subang dominantly monocrystaSine, most show undulose muscovite many with open fractues One grain; possibly Formation common poly derived Middle Eocene HV5047 Fabien Road Pointe-a-Pierre 1 0.28 Coarse sand 0.50 -1 moderately well subang-ang, common submd monocrystatline dominant, undulose and uniform common, euhedral zircon, vacuole trains, grain factures are common Formation some poly bluish-green needle like, muscovite (also with opaque inclusions), 7 Middle Eocene HV6026 Chaudiere River Pointe-a-Pierre 0.88 0.44 Medium sand 0.2S - 0.50 moderate obscured by silica overgrowths monocrystalline dominant most show undulose vacuoles (some form lineationstn qtz), silica Formation muscovite, albite 7 Middle Eocene HV6D23 Chaudiere River Pointe-a-Pierre 0.2 0.17 Fine sand 0.125-0.25 very weH obscured by silica overgrowths monocrystalline dominant most show undulose vacuoles (some give a cloudy silica abundant, Formation appearance to qtz) sometimes abraded 7 Middle Eocene HV6029 Chaudiere River Pointe-a-Pierre 1.52 0.2 Fine sand 0.125-0.25 well sorted obscured by silica overgrowths dominantly monocrystalline dominanlty undulose vacuole trains, muscovite, albite silica Formation 7 Middle Eocene HV7011 Fabien Road Pointe-a-Pierre 1.6 0.24 Fine sand 0.125-0.25 weH sorted Rnd to submd m onocrystallinecrystalline dominantly undulose most clear, colourless; mica, tourmaline Rare, abraded silica Formation 7 Middle Eocene HV7015a Plum River Pointe-a-Pierre 0.3 0.22 Fine sand 0.125-0.25 very wel sub rnd-sub ang, dom sub ang dominantly monocrystalline, Many display undulose muscovite silica Formation common poly 7 Middle Eocene HV5D11B Tabaqutte Pointe-a-Pierre 0.7 0.21 Fine sand 0.125-0.25 very weH interlocking >ds Dominantly monocrystalline common undulose rare »p,n common Sawmill Formation 7 Middle Eocene GWHV10 Tormos Brake Pointe-a-Pierre Z6 0.6 Granule 2-4 poorly submd-subang (occ) Most monocrystaBine dominantly undulose, muscovite, linear vacuoles, zircon Abraded silica fact Formation largest show uniform 8 Late Paleocene HV5Q43 Growing rock Chaudiere Formation 1.6 0.2 Vc sand 1 - 2 poorly subrnd-subang; embayed Dominantly monocrystalline mostly undulose abraded silica 8 Late Paleocene HVS044 Growing rock Chaudiere Formation 3.5 Granule 2-4 moderately well subrnd common poly undulose linear vacuoles, tourmaline, zircon fracture posority 9 Late Cretaceous HV6002 Galera Galera 2.6 0.2 Granule 2-4 moderate dominanlty poly vacuoles, some X patterned. Some giving seriate filled (Maastritchian) rock a cloudy look, muscovite 10 Early Cretaceous HV6DQ3 Babndra Rio Seco Formation 2.6 0.1 Granule 2-4 poorly Larger sbmd to sbang, smaller dominanlty poly weak to strong undulose vacuoles, muscovite (Albian) "matrix" aubanfl 10 Early Cretaceous HV60Q1 Lanse Noir Toco Formation 2.6 0.2 Granule 2-4 poorly larger grains subrnd-md, smaller dominantly monocrystaBine, linear vacuoles, platy muscovite (Aptian) ang-subang common poly 15 Middle Eocene Hveooa Coast road Scotland Formation 1.8 Vc sand 1 - 2 poorly ang-subang, submd Most monocrystaBine Most uniform, though muscovite Many Barbados many with weak sweeping 15 Middle Eocene HV6015 Lidar RJdge, Scotland Formation 3 Granule 2-4 poorly Larger md-submd; finer fraction dominantly monocrystaBine most show undulose ?Biotite, muscovite, linear vacuoles, Very common, open Bbdos a ng-subang-subrnd vermicular inclusions (dirty appearance) fractures Quartz Age Sample Location Stratlgraphic unit Fractures Overgrowths Other Framework minerals Accessory minerals Cement Classification Comment number 5 Middle Oligocene AS 3.59 WeH Canteen 2 Angostura sandstone Lithics (sandstone with opaque cement, Glauconite with silt sized quartz inclusions, sparse, unidentified clay Sandstone lithic fragments very common. This will argillaceous with zircorvglauconite-quartz, MRF, variably dissolved feldspar (microdine). not be represented in the G-D point count method bioclasts, chert and catcite) and not reflected in trw modal tables. 5 Middle Oligocene AS 1.9 Well Kairi 1 Angostura sandstone Abraded silica Lithics (sandstone, carbonate, MRF, chert, Glauconite, opaques, zircon ferruginous days :eldspar variably dissolved; common 'ghost' biodast-foram inifera), feldspar {microcline, remains plagiodase). 5 Middle Oligocene AS3.50 Canteen Angostura sandstone Good fracture porosity feldspar (microcline and plag), lithics (chert, mud Calcite, muscovite mainly sericite, plus chert, Varied matrix, 1. dk brown to opaque mud, H_39D8 laminae, bioclasts, MRF), glauconite kaolinite & ferruginous clays aminated, or as isolated fragments. 2. Reddish, sericitic days. 2. Calcite, from deformed bioclasts. Late Eocene 05HV001 Pointe a Pierre San Fernando Fm cement filled, oxide lined Muscovite, zircon, opaques, sandstone lithic Kaolinite, chlorite quartz arenite Similar cement as Pointe-a-Pierre and Chaudiere (Plaisance Congl) (silica and oxide cemented- extrabasinal) :m (see Tormos Brake Factory) 6 Late Eocene HV5034 Wharf, San San Fernando Very common abraded Feldspar (plag, microcline), lithics (chert), Calcite and ferruginous clay Relatively immature suite with angular grains and Fernando silica opaques carbonate clasts. Similar to Cruse samples, but without MRFs 6 Late Eocene HV7045 Soldado Rock San Fernando Feldspar (plag), muscovite, lithics (chert, MRF), zircon, tourmaline same as HV7Q39, chlorite or This sample has a higher mica content and MRF kaolinite? than others from Soldado Rock. Many qtz rimmed bvmica. 6 Late Eocene HV7042A Morns Roche San Fernando typically with open fractures glauconite ok*. 6 Late Eocene HV5035A Hubert Ranee, San Fernando Feldspar (plag, microcline), lithics (chert and glauconite, zircon calcareous day and ?chlonte calduthite Sample consists of laminae of silt to fine grained San Fernando MRF) quartz within a calcareous day-size matrix. 6 Late Eocene HV7041 Soldado Rock San Fernando Very common abraded Variably sericrtized feldspar (microcline, plag, Zircon, garnet, muscovite. chlorite, chert, sparse sericite Note abraded silica. ?orthoclase), lithics (chert. MRF). 6 Late Eocene HV7039 Soldado Rock San Fernando Very common abraded Feldspar (plag, microcl, perthite, orthoclase), opaques, zircon Silica occurs locally, chlorite subarkosic arenite Abundant lithics Formation silica lithics (chert, MRF) and/or kaolinite? 7 Middle Eocene HV5002 Fabien Road Pointe-a-Pierre lithic (chert) silica, oxide?, ?sericite Formation 7 Middle Eocene HV5006 Ca ratal road Pointe-a-Pierre random, some open, some lithic (sandstone? Or MRF) oxide, silica (or chlorite) formation oxide lined 7 Middle Eocene HV5011 Tabaquite Pointe-a-Pierre chert, opaques, muscovite rutite, tourmaline (green), zircon silica and red ferruginous day 5011B Sawmill Formation 7 Middle Eocene HV5012 Tabaquite Pointe-a-Pierre Many grains with open; occ opaques, muscovite (or glauconite?) silica Sawmill Formation filled with cement. Rare throughgoing. 7 Middle Eocene HV5013 Allen Road Pointe-a-Pierre fractured grains muscovite, zircon, tourmaline kaolinite similar to 5044; larger finer-grained component Formation 7 Middle Eocene HV5046 Fabien Road Pointe-a-Pierre many with open fraetues One grain; possibly sericitic clay quartz arenite Formation derived 7 Middle Eocene HV5047 Fabien Road Pointe-a-Pierre grain factures are common Lithics (chert dominant, stretched quartz, muscovite, zircon Ferrugionous clay and ?chlorite Abundant day matrix or cement. Formation ?sandstone), glauconite (variably altered) 7 Middle Eocene HV6026 Chaudiere River Pointe-a-Pierre Lithic (potyxiine qt2, MRF), glauconite in various stages of alteration silica, chert, FeO euhedral outlines; 'dirty' quartz common Formation •*" 7 Middle Eocene HV6028 Chaudiere River Pointe-a-Pierre silica abundant, lithics (chert), muscovite glauconite (one shows pinkish IC). Some silica, chert quartz arenite Abundant heavy minerals; Feldspar dissolution Formation sometimes abraded altered to ?chlorite may have created oversized pores. 7 Middle Eocene HV6029 Chaudiere River Pointe-a-Pierre silica lithics (chert) Mainly silica; some chert with quartz arenite Formation intra granular porosity 7 Middle Eocene HV7011 Fabien Road Pointe-a-Pierre Rare, abraded silica Lithics (sandstone, chert), muscovite (one Ferruginous day around grains, Oversized pore space Formation partially altered to chlorite), tourmaline, kaolinite in pores; silica also ? Middle Eocene HV7015a Hum River Pointe-a-Pierre silica Muscovite, sericite, MRF, chert, feldspar, Silica, kaolinite, ferruginous Most amount of lithics of Pointe-a-Pierre samples. Formation zircon, tourmaline Abundant mica schists and chert 7 Middle Eocene HV5011B Tabaquite Pointe-a-Pierre open common phyllite, chert, zircon, tourmaline silica, oxide, 'Kaolinite quartz arenite sutured polycrystalline grain boundaries Sawmill Formation 7 Middle Eocene GWHV10 Tormos Brake Pointe-a-Pierre Abraded silica lithics (chert, stretched quartz (MRFs)) glauconite, muscovite, zirccon, tourmaline kaolinite, oxide, sericite bi modal; increased amonts of kaolinite and fact Formation sericitic cements 8 Late Paleocene HV5043 Growing rock Chaudiere Formation abraded silica Lithics (siltstone, chert, rare MRF), opaques. Tourmaline, zircon, muscovite, chlorite Mainly FeO. Also silica, ?sericite Looks like sample at end of Milan River Traverse & kaolinite 8 Late Paleocene HV5044 Growing rock Chaudiere Formation fracture posority Lithics (metasediments, sandstones), kaolinite Broken zircon crystals; no matrix on thin section muscovite 9 Late Cretaceous HV6002 Galera Gaksra sen cite filled poly and microxtline qtz, muscovite FeO sericite-muscovite matrix metam orphic or Polycrystaline quartz with sutured grain boundary (Maastritchian) sedimentary? 10 Early Cretaceous HV6003 Balandra Rio Seco Formation Muscovite as indivi grains and sericite matrix. opaques sericite met amorphic or sutured polycrystalline grain boundaries (AJbian) Lithics (MRF, Microxline qtz). sedimentary? 10 Early Cretaceous HV6001 Lanse Moir Toco Formation feldspar (variably altered to seriate, calcite and lithics (chert) Silica overgrowths on rounded subarkosic arenite At least 7 plutonic rock fragments were seen (Aptian) rimmed with iron oxide - microcline and albrte) quartz, some abraded. Others during counts (>63um). Micrographic quartz may include sericite and texture; sutured polycrystalline grain boundaries opaques. 15 Middle Eocene HV6008 Coast road Scotland Formation Many lithics (chert, MRF - microxlline quiz), muscovite feldspar (albite) Sericite, chlorite, FeO (localized) Barbados 15 Middle Eocene HV6015 Lida Ridge, Scotland Formation Very common, open Lithics (chert, MRF) muscovite, altered feldspar? Ferruginous and sericitic day. Bbdos fractures ?chert Appendix 12 All Counts on Samples Thin section point count numbers on all samples discussed throughout this thesis. The methodology was discussed in the text (Chapter 6). The raw data represented on the various ternary plots is also tabulated. 511 COUNTS Total Heavy Lfthie Glauconit Carbona Muscovtt Chlorit Unknow Matrix! Porosity Total SAMPLE* FORMATION Date Common name Quartz Opaque K. Feldsp Feldspar Feldspar minerals grains e te e e n Porosity cement count 1 1 HV7003 Mayaro Late Pliocene Mayaro coast 216 11 8 18 26 17 41 0 0 31 0 46 77 35 15 500 1 2 HV6018 Morne L'Enfer Late Riocene Erin Bay 172 8 1 9 10 6 52 1 0 6 0 20 105 21 26 401 1 3 HV6039 Morne L'Enfer Late Pliocene Cedros Bay 162 24 3 10 13 64 1 0 10 0 14 61 73 14 432 1 4 HV6037 Springvale Late Pliocene Paloma coast 191 6 2 10 1 45 1 0 8 0 11 98 60 23 431 2 5 HV5031 Cruse Early Pliocene Moreau Road, Marac 159 6 3 12 0 51 0 0 4 0 0 33 135 8 400 2 6 HV5032 Cruse Early Pliocene Moreau Road, Marac 146 5 0 10 0 25 1 0 3 1 5 6 99 2 301 2 7 HV70D5 Cruse Early Riocene Morne Diablo 188 5 0 18 2 42 1 0 4 0 3 7 230 1 500 2 8 HV70O6 Cruse Early Riocene Siparia Point 212 7 0 20 10 45 1 0 6 0 17 2 200 0 520 2 9 06GW001 Manzanilla Earty Riocene Paloma coast 214 0 0 4 0 17 0 0 0 0 5 63 97 16 400 3 10 GWHV20 Herrera Early Miocene BP342 10333' 156 7 2 9 4 34 3 0 0 0 2 0 80 0 300 3 11 GWHV21 Herrera Early Miocene BP347 9807' 184 1 2 2 2 78 8 0 0 0 0 2 73 1 350 3 12 HV5026 Herrera Early Miocene Rock River Road 195 0 0 7 2 55 5 0 0 0 4 8 124 2 400 3 13 HV5029 Herrera Early Miocene Moreau Road 1 150 0 0 0 0 43 4 0 0 0 3 3 116 1 319 3 14 HV5057 Herrera Early Miocene MD34 8594-8595' 50 0 0 2 1 27 3 0 0 0 0 0 17 0 100 3 15 HV6011 Herrera Early Miocene Rock River area 166 13 0 13 10 30 0 0 1 1 10 3 153 1 400 3 10b GWHV20 B Herrera B Early Miocene BP342 10333' 156 7 2 9 A 34 8 0 0 0 2 0 80 0 300 3 11b GWHV21 B Herrera B Early Miocene BP347 9807' 184 1 2 2 2 78 8 0 0 0 0 2 73 1 350 3 12b HV5026 B Herrera B Early Miocene Rock River Road 195 0 0 7 2 55 5 0 0 0 4 8 124 2 400 3 13b HV5029 B Herrera B Early Miocene Moreau Road 1 150 0 0 0 0 43 4 0 0 0 3 3 116 1 319 3 14b HV5057 B Herrera B Early Miocene MD34 8594-8595' 50 0 0 2 1 27 3 0 0 0 0 0 17 0 100 3 15b HV6011 B Herrera B Early Miocene Rock River area 166 13 0 13 10 30 0 0 1 1 10 3 153 1 400 4 16 HV5018 Miocene Miocene Plum Mitan 238 4 0 12 1 22 0 0 4 0 6 95 18 24 400 4 17 GWHV08 Nariva Oligocene Corbeaux Hil 245 5 5 7 3 15 0 0 6 0 2 31 36 9 350 4 18 GWHV12 Nariva Oligocene Sandstone Tr 247 0 3 3 3 4 0 0 3 0 1 60 29 17 350 4 19 GWHV15 Nariva Oligocene Corbeaux Hifl 222 3 0 1 3 3 0 0 0 0 1 21 46 7 300 4 20 HV5007 Nariva Oligocene Esmeralda Jet 220 3 0 7 18 16 1 0 5 0 0 30 100 8 400 4 21 HV5008 Nariva Oligocene Esmeralda Jet 151 0 0 4 40 34 Q 0 2 0 3 15 76 5 325 4 22 HV50O9 Nariva Oligocene Kelly HiH 239 7 0 5 9 31 0 0 2 0 9 61 37 15 400 4 ?3 HV5058 Nariva Oligocene ABM 44 3015* 220 7 4 10 6 21 0 0 1 0 1 10 24 3 300 4 24 HV6021 Nariva Oligocene Corbeaux Hill 205 0 0 0 4 22 0 0 3 0 0 41 75 12 350 4 25 HV6022 Nariva Oligocene Corbeaux Hill 291 9 0 0 1 14 0 0 1 0 3 102 29 23 450 4 26 HV6023 Nariva Oligocene Corbeaux HiH 187 2 0 6 3 32 0 0 12 0 4 122 62 28 430 4 27 HV6033 Nariva Oligocene Corbeaux HiH 246 3 0 0 0 4 0 0 1 0 1 63 32 18 350 4 28 HV6035 Nariva Oligocene Kelly Hill 195 6 0 8 4 11 0 0 5 0 5 59 57 17 350 5 29 AS 1.9 Angostura Middle Oligocene Kairi 1 5264.3 251 5 0 4 2 6 4 0 0 0 15 66 22 18 375 5 30 AS 2.34 Angostura Middle Oligocene Canteen 1 5097.3' 250 0 0 2 0 15 1 0 0 0 7 42 33 12 350 5 31 AS 2.41 Angostura Middle Oligocene Canteen 1 5101.4' 276 0 2 4 2 9 4 0 0 0 9 83 13 21 400 5 32 AS 3.50 Angostura Middle Oliqocene Canteen 2 4671.1' 150 0 0 10 0 19 2 0 0 0 6 45 169 11 401 5 33 AS 3.59 Angostura Middle Oligocene Canteen 2 4679.6' 255 5 0 6 1 15 1 0 0 0 0 48 27 13 358 5 34 AS1.1 Angostura Middle Oligocene Kairi 1 5257.15' 259 16 2 3 1 4 3 2 0 0 15 91 7 23 401 5 35 AS1.20 Angostura Middle Oligocene Kairi 1 5403.75' 223 3 0 0 0 1 3 8 0 0 1 0 161 0 400 6 36 HV5001 San Fernando Late Eocene Plaisance Congl 265 3 0 0 3 1 0 0 0 0 0 46 32 13 350 6 37 HV5034 San Fernando Late Eocene Kings Wharf 183 2 2 5 0 12 1 0 0 0 1 16 180 4 400 6 38 HV7039 San Fernando Late Eocene Soldado Rock 10 225 3 5 '0 15 1 35 0 0 0 0 6 48 67 12 400 6 39 HV7041 San Fernando Late Eocene Soidado Rock 9 370 16 15 2 17 0 0 0 0 1 61 43 12 525 6 40 HV7042B San Fernando Late Eocene Mome Roche 2 253 0 0 o 0 1 8 3 0 0 0 2 43 40 12 350 6 41 HV7045 San Fernando Late Eocene Soldado Rock 7 215 8 7 16 23 7 36 0 0 10 0 4 28 69 7 400 7 42 GWHV10 Pointe-a-Pierre Middle Eocene Tormos Brake Factory 298 2 0 0 8 2 1 0 0 0 3 9 28 3 351 7 43 GWHV16 Pointe-a-Pierre Middle Eocene Allen Trace 300 0 0 0 9 1 0 0 0 0 0 27 13 8 350 7 44 HV5011B Pointe-a-Pierre Middle Eocene Tabaquite 303 5 0 0 16 7 0 0 3 0 2 35 29 9 400 7 45 HV5012 Pointe-a-Pierre Middle Eocene Tabaquite 220 0 0 0 0 0 0 0 0 0 0 78 2 26 300 7 46 HV5013 Pointe-a-Pierre Middle Eocene Allen Trace 273 3 0 0 4 0 0 0 0 0 0 58 12 17 350 7 47 HV5047 Pointe-a-Pierre Middle Eocene Fabien Road 253 0 0 0 2 1 0 0 0 0 0 12 76 3 344 7 48 HV6026 Pointe-a-Pierre Middle Eocene Chaudiere River 344 11 0 0 0 1 1 0 1 0 5 26 11 7 400 7 49 HV6028 Pointe-a-Pierre Middle Eocene Chaudiere River 325 1 0 0 7 9 0 0 1 0 0 20 36 5 401 7 50 HV6029 Pointe-a-Pierre Middle Eocene Chaudiere River 327 6 0 0 3 0 0 0 0 0 5 53 6 13 400 7 51 HV7011 Pointe-a-Pierre Middle Eocene Fabien Road 236 1 0 0 4 4 0 0 3 0 0 21 131 5 400 10 56 HV7015a Pointe-a-Pierre Early Cretaceous Mitan river 221 2 0 9 0 17 0 0 1 0 0 13 87 4 350 7 52 HV5Q43 Chaudiere Late Paieocene Growing Rock 274 7 0 0 7 6 0 0 2 0 0 122 12 28 430 7 53 HV5044 Chaudiere Late Paieocene Growinq Rock 253 0 0 0 4 0 0 0 1 0 4 64 24 18 350 8 54 HV6Q03 Galera Late Cretaceous Toco 283 2 0 1 21 2 0 0 6 0 10 7 68 2 400 g 55 HV6001 Toco Early Cretaceous Lanse Noir 225 0 0 82 1 6 0 0 0 0 18 2 66 1 400 10 57 HV7016b Cuche Early Cretaceous Mitan river 226 1 1 5 5 20 0 0 2 0 1 0 90 0 350 is 58 HV6007 Scotland Middle Eocene Barbados, Coast Rd 298 0 0 o 0 0 2 1 1 0 0 2 8 88 2 400 15 59 HV6008 Scotland Middle Eocene Barbados, Coast Rd 165 9 0 1 0 1 1 0 8 0 3 167 60 40 415 15 60 HV6010 Scotland Middle Eocene Barbados. Chalky Mt 220 4 0 0 11 11 0 0 1 0 3 81 69 20 400 15 61 HV6015 Scotland Middle Eocene Barbados, Chalky Mt 257 1 0 0 2 4 0 0 0 0 6 100 30 25 400 16 62 HV6016 Columbus Recent Columbus Bay 340 9 0 7 3 37 0 0 0 0 4 0 0 0 400 16 63 HV7031 Cunapo Conql Oligocene Four Roads 222 6 0 0 6 16 0 0 1 0 1 31 23 10 306 16 64 HV7034 Cunapo Congi Oligocene Four Roads 246 9 0 0 5 9 0 0 0 0 0 14 17 5 300 16 65 HV7036 Cunapo Congl Oligocene Four Roads 208 5 0 0 4 44 0 0 0 0 3 14 74 4 352 QUARTZ LITHICS TOTAL LITHICS fa Cf E cr E 5 is E I > u 0 s 0 13 < z o a. s 1 o z a a 35 I a a 3 •a £ _1 1 u E £ o c c to E a E _ a 0 a a r - a: > s 2 -j - CD CN a "J; CD co a T ^r s o 1 en 5 K UJ - CM I o 3 2 s R . P- 8 S § K o V - X 1 5! o 1 1 o XJ CO - £ •* £ 6 S IN to CO ID a) 01 m - •V X > to to a! Q. * 1§ t 1-^ ' 0> » •* CN 8 s c s a O V E CM X 1 « Ul •c .o 2 • Morne L'Enfer Pliocene HV6017 Erin Bay 607 Amphibole, fir blotite, apatite, limonite, staurolite w Morne L'Enfer Pliocene HV6039 Cedros Bay 205 8 34 12 10 19 0 0 6 173 2 0 0 2 4 475 266 Morne L'Enfer Pliocene HV6040 Cedros Bay 453 30 31 7 13 21 3 23 201 2 6 6 796 hornblende 337 X Cruse Late Miocene HV5032 Moreau Road 253 33 43 5 11 23 111 6 39 16 540 staurolite 271 Middle Miocene HV5025 Rock River roa 913 1107 Biotite (from Patterson 1991 Middle Miocene HV5029 Moreau Road 954 1158 Kyanite, I epidote, ?sphene »«• Nariva Eariy Miocene HV5007 Esmeralda Jet 607 97 33 28 965 351 P Nariva Early Miocene HV5009 Kelly Hill 441 85 52 74 758 311 Cipero Early Miocene HV5018 Plum Mitan 539 84 181 32 5 ?sphene (2), sillimanite, i—• ?pumpeytlite Nariva Early Miocene HV5022 Corbeaux Hill 220 154 93 61 3 65 1 608 387 o Nariva Eariy Miocene HV5023 Sandstone Tr 223 161 36 54 33 67 10 594 ?sillmanite 361 Angostura Sst Oligocene Well Kairi 1 52' 725 17 979 o San Fernando Middle Eocene HV5001 Plaisance Con< 279 1 588 sillimanite, d epidote- clinozoisite 0 San Fernando Late Eocene Soldado Rock 536 8 854 ft- Pointe-a-Pierre Middle Eocene HV5006 Caratal Road 466 805 staurolite, andalusite, chlorite Pointe-a-Pierre Middle Eocene HV5012 Tabaquite 247 253 37 22 566 313 Pointe-a-Pierre Middle Eocene HV5013 Allen Road 123 237 57 32 449 326 Pointe-a-Pierre Middle Eocene HV5046 Fabien Rd 379 242 53 16 700 321 Pointe-a-Pierre Middle Eocene HV6029 Chaudiere Rivi 382 160 91 63 701 clinozoisite- 318 zoisite Chaudiere Paleocene HV5044 Growing Rock 277 264 591 sillimnite, ?garnet Chaudiere Paleocene HV5049 Growing Rock 208 259 5 525 Scotland Middle Eocene BD1 Chalky Mount 398 264 65 25 4 0 20 3 806 403 Scotland Middle Eocene HV6007 Chalky Mount 368 130 51 24 36 33 51 714 kyanite, 340 limonite, ?apatite Scotland Middle Eocene HV6008 Chalky Mount 447 127 106 44 6 30 0 4 786 ?anatase 331 Scotland Middle Eocene HV6009 Chalky Mount 483 200 69 28 12 6 1 6 824 339 Appendix 14 Sample Outcrop Descriptions The following sections are examples of outcrop descriptions for a few localities discussed in the thesis. Sections such as these were done for all the outcrops mentioned. 515 LOCATION: Tormos brake factory, Mayo LOGGED BY: H. VINCENT, K. GANGA DATE: 11th July 2005 Oopth (m) GR (10 cm resolution) miik i Photos/ Diagrams 9. > 2metres coarse to granular sandstone. Bedding planes not discernible. Thickness possibly up to 8m. Uncertain because of poor exposure. B. Silly mudstone 7. Dominantly very coarse-grained sandstone, with up to granule sized grains. Mud dast horizon in matrix of medium to coarse sandstone; longest ctast 25 cm diameter. Overlain by 'pinch and swell' fine grained sandstone. 6. Fining upward/gradational beds. One bed with] planar laminations at top. Internal erosive surfaces characteristic. Minor faulting. 5. Very coarse grained sandstone. Ibp surface exposed to reveal undulating relief - "ridge and furrows". Possibly remnants of erosive top. 4. As below. Graded planar cross beds at top. 3.80 on. As below with mud dasts at base (2 seen); mud ctasts lenticular with long end parallel to bedding plane. Size 6 cm max. 1. Granule sized to very coarse-grained sandstone. Clast supported, dominantly sub angular, some sub rounded. Very poorly sorted. Note 1 'Cliff face 2' from notes Iflfllik 676975 E, 1143253 UTM Zone 20, WGS 84 Pagel of 4 516 LOCATION: PLUM MITAN ORANGE ESTATE LOGGED BY: H. VINCENT, K. GANGA DATE: 12th July 2005 Interpretation Page 1 of 1 517 Location: San Fabian Road quarry. Section #9 near entrance (Potnte-e-Pterre Formation) Photos/ Diagrams 10 11. Section of folded fine-grained s referred to in note 8. JtO. Massive block of very coarse-grained •sandstone (230 cm). B. Laminated fine-grained sandstone. S3 Bub parallel laminations. Abundant Burrows. 8. Overturned folded sandstone bed encased in shale. Scour casts at base [confirm way-up. Shale thickness •maximum 145 cm. Deformed beds of fine Igraln size (total 66 cm). 17. Interbedded sand/shale. Fine silty Isand with linear burrow. Worm-like Localized sediment folding horizontal burrows at bed base. resulting from slumping and sliding of large sediment blocks. Shale acts as effective gHde plane. 6. Fine- to medium-grained sandstone beds. Lowest bed massive. Middle bed 3-H with planar laminations at top. Overlain by fine grained massive sandstone bed. 5. Laminated shale with thin sandstone ieds (3cm max). Sandstone beds pinch ind swell; lenticular. Wavy bases. No jurrows. Ta-Tb-Ta 2 — 4. Rippled sandstone bed; wavy contacts at base and top. (Climbing ripple cross lamination) Tc-Te 3. Very fine grained grey sandstone. 3 cycles recognized. First, 13 cm massive sst capped by thin laminated sandstone Tc 2nd and third cycles same (11,6cm resp.) Ripples?. Overlain by laminated shale. Ta-Tbr E. 86 cm laminated shale with very thin sandstone laminae. Background sedimenlabon (check for mtcroiossU content) h. Laminated very fine silty sandstone. 6 si I" mm ms 518 LOCATION: 'Upper'Mome L'Enfer Fm, Puerto Grande Bay LOGGED BY: H. VINCENT DATE: 18th July 2005 (revisit Aug 1st 05) DoptH (m) HIII/M 1 Photos/ Diagrams 20 51.10m dark gray wavy laminated shale. 18~—~j Abundant organic fragments; lenticular sands. 15cm intervals of (laser bedding. Dominant current ripple dip towards the east. Mottled horizons. i6™™i 50.40 cm lignite bed. Muddy at base. Sulphur stained. 49. Very fine-grained current rippled sandstone. Burrowed; mottled/ churned at top 40 cm. Intense btoturbatian; high abundance. high diversity. Prominent root traces. Bed top orange-rust stained from lignite above. 48. Dark grey massive shale; abundant organic fragments. Laminae largely preserved where present Common Skotfthos burrows. Sharp contact with shale below; change in colour. 47. Brown silly shale with contorted laminae; 1ST1 lenticular sands; common burrows. Low diversity, common abundance. 46. Very fine sand with constant thickness along exposure (30-40m). Large pits into shale below common (8cm diameter). Very fine sandstone; trough cross beds. Burrows, some oblique, some vertical trends. Scattered 10-1 organic fragments, though sometimes concentrated. Burrow intensity increases towards the top below shale. Low diversity, common abundance •45. Laminated grey shale, organic fragments land wisps; burrowed. M4. Very fine sttry sand. Dklsturbed beding lsfmflar lades as below. Large burrows (tunnels), mottled. Common to abundant burrows. 43.1.9m Dominant^ very fine sandstone with tow angle laminations and cm thick shale drapes. Current rippled and cross bedded. Sst beds up to 15 cm thick. Common burorws; shale Bned In sand. Large pits at top - remnants of large burrows (tunnels 4cm diameter x 10-15 cm long. Forms hard crust at top. 42.40 cm dominanHy lenticular bedding; rare burrows at top, oblique to bedding. 41.4m very firm sandstone, transitional from below. Sanstone beds increase in thickness upward; bed maximum 25 cm, separated by wavy grey shale. Increase in bioturbation in upper 2m. Dorfsnantly Skotithas, though many oblique to bedding, CyU'ndrichnus, Optocrarerion, internal scours. Traces common to abundant mo* Pagel ofX 519 ^€># / 4> / Angostura Sandstone L- . / rv co o Ul vm//7^//////7^^, '.y/' Recommended changes B