Sedimentology, Diagenetic History and Reservoir Characterization of the Coronach Member, Herald Formation, Wiiliston Basin, SE Saskatchewan
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fullfillment of the Requirements for the Degree of Master of Science in Geology University of Regina
by Mark Anthony Urban Regina, Saskatchewan July 22,2010
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FACULTY OF GRADUATE STUDIES AND RESEARCH
SUPERVISORY AND EXAMINING COMMITTEE
Mark Anthony Urban, candidate for the degree of Master of Science in Geology, has presented a thesis titled, Sedimentoiogy, Diagenetic History and Reservoir Characterization of the Coronach Member, Herald Formation, Wiliiston Basin, SE Saskatchewan, in an oral examination held on May 5, 2010. The following committee members have found the thesis acceptable in form and content, and that the candidate demonstrated satisfactory knowledge of the subject material.
External Examiner: Dr. Malcolm Wilson, Office of Energy and Environment
Supervisor: Dr. Hairuo Qing, Department of Geology
Committee Member: Dr. Guoxiang Chi, Department of Geology
Committee Member: Dr. Donald Kent, Adjunct Professor, Department of Geology
Chair of Defense: Dr. Daoyong (Tony) Yang, Faculty of Engineering and Applied Science Abstract
The Coronach Member of the Herald Formation (late Maysvillian to early
Richmondian) in southeastern Saskatchewan was deposited on a gently-sloping, shallow- water ramp, which was part of a larger, vast epicontinental sea that covered most of
Laurentia in the Late Ordovician. Sabkha-type evaporites and intertidal stromatolitic boundstones characterize the upper ramp facies, whilst the lower ramp consists of subtidal skeletal wackestones to red algal-green algal-stromatoporid reef mounds or biostromes. The succession portrays a shallowing-up and brining-up carbonate-evaporite cycle similar to the modern Abu Dhabi Sabkha of the Persian Gulf.
The Coronach Member can be divided into five facies based on the depositional and diagenetic settings. In upwards succession they are: 1) an anoxic subtidal setting, 2) an oxygenated, shallow-water subtidal setting, 3) a penesaline intertidal setting, 4) a hypersaline supratidal (sabkha) setting, and 5) an exposed diagenetic caliche horizon.
Initial deposition of the Coronach Member began with a deepening event that resulted in deposition of basal, organic-rich rocks that are very similar to kukersites from the Yeoman Formation (Edenian to Maysvillian). These shallow-water, photosynthesizing alginites are succeeded by shallow to very shallow-water, dominantly algal-reef mounds and skeletal rudstones/grainstones. Reef mounds display a consistent vertical ecological zonation similar to modern reef systems. Rising salinity, due to increasing restriction or reduced energy, is indicated by a drop in skeletal diversity and abundance with deposition of Planolites-bunowed mudstones. These were deposited in a lagoonal environment. A tidal flat system containing tidal channels, beach ridges, levees, and variable forms of stromatolites prograded overtop of subtidal sediments.
i Stromatolites are composed of cyanobacteria, which trapped mainly storm-deposited peloidal sediment by the process of agglutination. Stromatolitic forms include a wide range from domal to smooth and flat. Salinity continued to rise with deposition of gypsum and anhydrite in a sabkha-type setting. Nodular anhydrite was emplaced in the capillary zone by highly-evaporated marine waters and refluxing brines. Locally, saline ponds led to rare bedded anhydrite. Reflux brines also led to complete dolomitization of the intertidal and supratidal sediments. As regression continued, either due to sediment infill of the basin or falling sea-level, supratidal rocks were subjected to prolonged exposure. Diagenetic alteration of these sediments led to formation of a caliche horizon.
Early dolomitization of intertidal stromatolites has led to a zone with the highest porosity. Reservoirs in this facies make for prolific producers on the United States side of the Williston Basin. Production on the Saskatchewan side however, has not been recorded in the Coronach Member, which is a function of 1) lower porosity and permeability, 2) slightly thinner reservoirs, 3) increased distance from thermally-mature source rocks, 4) hydrodynamic flushing of stratigraphic traps, 5) a shorter deep- exploration period, and 6) smaller structural traps.
The Coronach Member does have potentially large reserves in Saskatchewan, as observed from consistent oil-staining and porous rock in core. Exploration should focus on existing structural traps where Red River reservoirs are already producing, or other structures related to basement highs that can be found using two- and three-dimensional seismic. Existing Coronach reservoirs in north-eastern Montana occur mere kilometres from the Saskatchewan border, emphasizing the possible presence of hydrocarbon accumulations in the northern half of the Williston Basin.
ii Acknowledgments
I would like to thank Dr. Hairuo Qing for his supervision and direction of this thesis, the workers at the Geological Subsurface Laboratory in Regina and at the North Dakota Geological Survey lab in Grand Forks, and Talisman Energy for facilities and information support, especially the library staff. An NSERC Discovery Grant (155012) and the Ministry of Energy and Resources, under the Geoscience Research and Student Training Program, provided financial support for the research. The author is greatly indebted to John Lake (Lake Geological Services, Inc.), Dr. Jean-Yves Chatellier (Talisman Energy), Hugh Reid (Reid & Associates, Inc.) and Dr. Brian Pratt (University of Saskatchewan) for discussions on various topics. Also, the members of the 'Carbonate Liars Club' were a great resource for insights and suggestions. Lastly, I would like to thank my wife for her patience and support over the last few years.
iii Table of Contents Page
Abstract i Acknowledgements iii Table of Contents iv List of Figures vi List of Plates vii List of Tables viii List of Abbreviations ix
1.0 Introduction 1
2.0 Geological Setting 8 2.1 Structural Setting of the Williston Basin 8 2.2 Lower Paleozoic Stratigraphy 13 2.3 Palaeogeographical Setting 21 2.4 Red River Petroleum System 23 2.5 Williston Basin Hydrodynamics 24
3.0 Previous Work 28
4.0 Methods 31
5.0 Facies Descriptions and Interpretation 35 5.1 Lake Alma Anhydrite 38 5.1.1 Lake Alma Anhydrite Interpretation 41 5.2 Lake Alma Dolomudstones 44 5.2.1 Structures 44 5.2.2 Grains 49 5.2.3 Matrix 50 5.2.4 Diagenesis 51 5.2.5 Lake Alma Dolomudstone Summary and Interpretation 52 5.3 Facies 1 56 5.3.1 Structures 56 5.3.2 Grains 58 5.3.3 Matrix 58 5.3.4 Facies 1 Summary and Interpretation 58 5.4 Facies 2 62 5.4.1 Skeletal Grains 62 5.4.2 Non-skeletal Grains 79 5.4.3 Primary Structures 81 5.4.4 Matrix 83 5.4.5 Facies 2 Summary and Interpretation 84 5.5 Facies 2 Upper Contact 98 5.6 Facies 3 98 5.6.1 Primary Structures 101 5.6.2 Matrix and Grains 106 5.6.3 Facies 3 Summary and Interpretation 106 5.7 Facies 4 123 5.7.1 Primary Structures 123 5.7.2 Matrix 123 5.7.3 Facies 4 Summary and Interpretation 125 5.8 Facies 5 129 5.8.1 Matrix and Grains 130 5.8.2 Facies 5 Summary and Interpretation 130 5.9 Summary of Depositional Environment 136 5.9.1 Modern Depositional Analogues 148
iv 6.0 Diagenesis: Description, Geochemistry and Interpretation 155 6.1 Anhydrite 155 6.1.1 Anhydrite 1 Description and Interpretation 155 6.1.2 Anhydrite 2 Description and Interpretation 158 6.1.3 Anhydrite 3 Description and Interpretation 158 6.2 Dolomite 160 6.2.1 Dolomite 1 Description and Interpretation 165 6.2.2 Dolomite 2 Description and Interpretation 169 6.2.3 Dolomite 3 Description and Interpretation 171 6.2.4 Dolomite 4 Description and Interpretation 177 6.3 Silica 181 6.3.1 Silicas 1-5 Description 181 6.3.2 Sources of Silica 183 6.3.3 Timing of Silicas 1 -5 187 6.3.4 Silica 6 Description and Intepretation 188 6.4 Calcite Description and Interpretation 189 6.5 Hardgrounds 195 6.6 Dissolution 196 6.7 Compaction 196 6.8 Subaerial Exposure 199 6.9 Pyrite 200 6.10 Diagenetic Summary 200
7.0 Reservoir Characterization 204 7.1 Introduction 204 7.2 Reservoir Development 204 7.3 Trapping Mechanisms 207 7.4 Reservoir Characterization Summary 209 7.5 Comparison to U.S. Equivalents 211
8.0 Conclusions 213
9.0 References 220
Appendix A: Lithologs 241
Appendix B: Isotope Data 285
V List of Figures Page
Figure 1.1 Stratigraphic nomenclature of the Upper Ordovician Williston Basin 2 Figure 1.2 Location of Study Area 3 Figure 2.1 Tippecanoe Sequence of the Williston Basin 9 Figure 2.2 Mechanisms of formation for the Williston Basin 11 Figure 2.3 Paleogeography of Laurentia 14 Figure 2.4 Areal Extent of Red River anhydrites 16 Figure 2.5 Milankovitch Cycles 17 Figure 2.6 Late Ordovician Plate Re-construction 19 Figure 2.7 Correlation of Gondwana Glaciation with Key Secular Fluctuations through Late Ordovician 20 Figure 2.8 Palaeogeographic Position of Laurentia in Late Ordovician 22 Figure 2.9 Distribution of Red River oil pools 25 Figure 2.10 Hydrodynamic flow in the greater Williston Basin 26 Figure 5.1 Carbonate Rock Classification Scheme of Wright (1992) 36 Figure 5.2 Type Log of the Red River Formation 40 Figure 5.3 Kendall's depositional model for basin-central evaporites 43 Figure 5.4 Process of False-Reverse Micro-Faulting 48 Figure 5.5 Lake Alma anhydrite sturcture and exposure limits map 54 Figure 5.6 Interpretation of the Lake Alma depositional sequence 55 Figure 5.7 Lake Alma Anhydrite isopach map 61 Figure 5.8 Red Algae Sketch 68 Figure 5.9 Modern Skeletal Distributions 85 Figure 5.10 Distribution of calcareous algae through time 88 Figure 5.11 Reef Organisms through time 88 Figure 5.12 Sketch of Facies 2B 91 Figure 5.13 Four stages of reef growth 93 Figure 5.14 Conceptual Classification of Reefs and Mounds 94 Figure 5.15 Isopach of Facies 2 96 Figure 5.16 Laminate Layering 103 Figure 5.17 Computer sketches of stromatolite features in core 107 Figure 5.18 Levee and beach ridge models 111 Figure 5.19 Zonation of laminate morphology from the Abu Dhabi sabkha, UAE 117 Figure 5.20 Sketch of Facies 3 structures 118 Figure 5.21 Isopach map of Facies 3 121 Figure 5.22 Isopach map of Facies 4B 126 Figure 5.23 Litholog Cross Section North-South through the Study Area 134 Figure 5.24 Interpretation for top sequence of Coronach Member 135 Figure 5.25 Facies cross section 137 Figure 5.26 Aggrading versus prograding basin models 138 Figure 5.27 Depositional model of the Coronach Member 139 Figure 5.28 Temporal Changes in Sea Level, Climate, Granite Emplacement, and carbonate taxonomy 142 Figure 5.29 Relation of carbonate particles to water energy and CaC03 supply 147 Figure 5.30 Scale comparison between modern carbonate environments to Coronach Member 149 Figure 5.31 Comparison of modern tidal flat environments 150 Figure 5.32 Facies Distribution and Satellite Images of the Abu Dhabi sabkha 152 Figure 5.33 Ramp profile and section from the Abu Dhabi modern depositional environment 153 Figure 5.34 Lake MacLeod evaporite basin 154 Figure 6.1 Oxygen versus carbon isotopes for all samples 161 Figure 6.2 Oxygen versus carbon isotopes in Coronach dolostone samples 162 Figure 6.3 Strontium Isotopes 163 Figure 6.4 Seepage/reflux model 167 Figure6.5 Geopelal dolomitizalion 172,173 Figure 6.6 Schematic model for multi-stage reflux dolomitization 175 Figure 6.7 Schematic model for single-stage penesaline dolomitization 175 Figure 6.8 Representative burial history diagram for the Williston Basin 179 Figure 6.9 Summary of diagenetic environments 202 Figure 7.1 Core porosity and permeability 205 Figure 7.2 Northrock Bryant 15-8-5-7W2 litholog 208 Figure 7.3 Seismic profile of the Midale Field 210
vi List of Plates
Page
Plate 5.1 Lake Alma Anhydrite Structures 42 Plate 5.2 Upper Lake Alma (L.A.) Member 45 Plate 5.3 Exposure Features in the L.A. Dolomudstones 46 Plate 5.4 Thin section features from L.A. Dolomudstone 47 Plate 5.5 Laminated, organic-rich lime mudstones of Facies 1 57 Plate 5.6 Skeletals from Facies 1 59 Plate 5.7 Brachiopods and Crinoids 63 Plate 5.8 Bryozoans of Facies 2 66 Plate 5.9 Red Algae 67 Plate 5.10 Dimorphosiphon Green Algae 70 Plate 5.11 Ortonella 71 Plate 5.12 Molluscs 73 Plate 5.13 Stromatoporoids 75 Plate 5.14 Corals 76 Plate 5.15 Arthropods and Formaninifera 78 Plate 5.16 Peloids 80 Plate 5.17 Burrows 82 Plate 5.18 Biostrome examples 92 Plate 5.19 Facies 2/3 contact 99 Plate 5.20 Facies 3A laminations 100 Plate 5.21 Variations in structure of Facies 3B 102 Plate 5.22 Laminate features 104, 105 Plate 5.23 Facies 3 matrix 108 Plate 5.24 Facies 3 hydrocarbon indicators 122 Plate 5.25 Facies 4 anhydrite 124 Plate 5.26 Features from Facies 5 131,132 Plate 6.1 Anhydrite 159 Plate 6.2 Cathodoluminescence 164 Plate 6.3 Dolomite diagenesis 170 Plate 6.4 Silica diagenesis 182 Plate 6.5 Algal-related mottled textures 184 Plate 6.6 Diagenetic mottles and nodular textures 185 Plate 6.7 Calcite cement 190 Plate 6.8 Hardgrounds 191 Plate 6.9 Other calcite cements 194 Plate 6.10 Diagenetic breccia 197 Plate 6.11 Compaction diagenesis 198
vii List of Tables Page
Table 1.1 Cumulative Oil Production in North Dakota 5 Table 1.2 Oil production in North Dakota, 2005-2008 6 Table 5.1 Selected Skeletal Mineralogy of Coronach Member Taxa 37 Table 5.2 List of facies with primary lithology and diagnostic features 39 Table 5.3 Skeletal, grain, and ichnotaxa distribution and abundance in the Coronach Member 86 Table 5.4 Textural and structural components of laminites and stromatolites 114 Table 5.5 Forms of stromatolites from modern and ancient examples 115 Table 5.6 Facies Table with Interpretation of the Depositional Environment 144 Table 6.1 Diagenetic Paragenesis 156 Table 6.2 Burial temperatures for saddle dolomite samples 180 Table 6.3 Facies list of diagenetic environments 203 Table 7.1 Core analysis data for all facies 206
viii List of Abbreviations
API American Petroleum Institute gravity of oil (141,5/specific gravity -131.5) C Carbon Ca Calcium CL Cathodoluminescence cm centimeter E East Ga Billion years HI Hydrogen Index hz horizontal km kilometer m meter Ma Million years Mg Magnesium mm millimeter MRS Maximum Regressive Surface N North PI Production Index PPL Plane-polarized light ppm parts per million ppt parts per trillion R Range S South Si Silicon Sr Strontium SSD Soft-sediment deformation T Township TOC Total organic carbon UAE United Arab Emirates (im/um Micro-meters (1x106 meters) W West W2/W1 West of the second/first meridian line XPL Cross-polarized light
ix 1.0 INTRODUCTION
The objective of this study is to evaluate the potential for oil and gas production
from the Coronach Member, Herald Formation in Saskatchewan from the Williston
Basin. The Coronach Member is the middle of three carbonate-evaporite cycles of Late
Ordovician age (Figure 1.1) that extends across Manitoba, Saskatchewan, Montana,
North Dakota and South Dakota. In the study area (Figure 1.2), the Coronach Member
lies between 2000 to 3000 meters depth. Generally disregarded by the Oil & Gas Industry
in favour of shallower horizons such as Mississippian strata, the Red River Formation*
did not seem prospective until the Midale Field discovery in 1995 with Berkley et al. 4-2-
7-11W2. Since then, approximately 21 fields/pools of varying sizes have been discovered
(Kreis and Kent, 2000). Production however, has been limited to the lower-most cycle of
the Red River Formation (Haidl et al, 1996).
Information on the Coronach Member is relatively limited. Only twenty-six cores
from the Coronach Member exist within the study area. Although numerous deep wells
have been drilled in southeastern Saskatchewan, the Coronach Member is often
overlooked for those targeting the lower cycle (Yeoman Formation and Lake Alma
Member). Intuitively, the latter is a more suitable reservoir and trap because it has
thicker, porous carbonate intervals and an effective, thicker anhydrite cap rock. The
Coronach Member is essentially a thinner replica of the lower carbonate-evaporite cycle,
which reduces the former's potential for economic accumulations of hydrocarbons.
Most information on the Coronach Member comes from reservoir studies in the
U.S. (Ruzyla and Friedman, 1985; Montgomery, 1997; Kohm and Louden, 1988). This
* The 'Red River Formation' is terminology used in the United States and is entrenched in the Canadian literature even though it is no longer formally recognized in the latter. It is equivalent to the Herald and Yeoman Formations.
1 * < 2. z Saskatchewan Manitoba North Dakota
1 I stages (N.A.) Gamachian Formations Members r - Stony Gunton Stony I Gunton i Wl ] Stony Mountain Fm + : Richmondian Mountain __ 6unn ' Mountain I Gunn { M Fm "T Hartaven Fm Penitentiary 'A'Unit + ; Redvers | Herald Coronach: 'B'Sequence -4- Fm Fort Garry Lake Alma ~ — Maysvillian Selkirk , - •C' Sequence . « Yeoman Fm + Cat Head C BoTO a Dog Head ' Edenian
+ Producing horizons
Figure 1.1. Stratigraphic nomenclature of the Upper Ordovician from the Williston Basin. Coronach Member is equivalent to the 'B' sequence of North Dakota. Figure 2.1 shows Cambrian through Silurian sequences. Modified from Pratt and Haidl (2008).
2 Figure 1.2. Location of study area in southeastern Saskatchewan, showing structure contours on top of Coronach Member (C.I. = 100m) and location of cores described in this study. Inset map shows outline of the present-day Williston Basin, and the location of major lineaments and other structural features. Modified from Kreis and Kent (2000).
hvixi T15
399k ° *—V Cotora do-Wyoming Fault Lineament Zone
T10 HH* SMMFWu IM EdpalArttwanCmoM 3HM IAWU-.B-UO*- s ar-ri—" WnNaflftAmrinn Cwlrtli "| i- M |
0 CanHMkOMM 1 l{ •I ^
LWofdwtrtead-gm: 01.4-2-14-21W2 12.14-26-6-11W2 02.6-5-8-22W2 13.12-2-7-11W2 03.6-5-6-19W2 14.2-11-10-8W2 04.12-13-2-19W2 15. 3-6-6-6W2 05.11-20-2-18W2 16.15-8-5-7W2 06.13-23-1-17W2 17. 9-34-3-4W2 07.10-25-1-15W2 18.16-23-2-1W2 08.8-16-2-14W2 19. 2-34-1-32W1 09.15-9-2-14W2 20.15-28-12-2W2 10. 3-16-2-10W2 21.1-9-21-16W2 11.13-23-6-11W2 is due in part to the relatively early discovery in the Red River Formation. In 1951 discovery of significant commercial accumulations of oil along the Cedar Creek
Anticline in Montana led to the exploration and development of numerous Red River pools across Montana, North Dakota and South Dakota (Clement, 1987). In North Dakota the Coronach Member (Red River 'B' equivalent) accounts for nearly 6% of the states cumulative production through December 2008 (Table 1.1). From 2005 to 2008, the
Coronach Member contributed between 24 and 35% of annual production totals in North
Dakota (Table 1.2); however, in Saskatchewan the Coronach Member has not produced oil.
Production from the Coronach Member in the U.S. is mainly attributed to
'laminites'. This is a 2 to 10-foot thick dolomitized mudstone exhibiting a laminated, possibly stromatolitic fabric, occurring just below the Coronach Anhydrite (= 'B' anhydrite; Whiteman et ai, 1998). Major structural features such as the Nesson and
Cedar Creek anticlines have aided in creating large fields of oil-charged reservoirs
(Whiteman et ah, 1998). Red River production in Saskatchewan on the other hand is limited to reservoirs overlying small, basement structures (Kreis and Kent, 2000).
The Coronach Member may be a less significant reservoir relative to the Yeoman
Formation; however, it is an under-studied horizon with significant reserves in North
Dakota that warrants an investigation in southeastern Saskatchewan.
This study will evaluate the reservoir potential of the Coronach Member by making 1) a comprehensive reconstruction of the depositional and diagenetic environments through 'comparative sedimentology' (Ginsburg, 1974), analysis of cores and thin sections, and geochemical data; 2) a facies model to investigate trap type(s) and
4 Bakken 70306101 4.2237 1095 Bakken/Three Forks 721 0.0000 4 Birdbear 17440674 1.0478 170 Cambro/Ordovician 376678 0.0226 5 Dawson Bay 4011598 0.2410 14 Deadwood 953 0.0001 1 Devonian 98138387 5.8957 137 Duperow 49107164 2.9501 336 Gunton 233994 0.0141 10 Heath 65717418 3.9480 197 nterlake 8568 0.0005 1 Lodgepole 54843380 3.2947 46 Lodgepole/Bakken 5883 0.0004 1 Madison 895672156 53.8077 5457 Midale/Nesson 1577371 0.0948 40 Mission Canyon 16544 0.0010 1 Ordovician 31415947 1.8873 121 Ratcliffe 175570 0.0105 4 Red River 102564896 6.1616 689 Red River B 100934266 6.0636 524 Red River C 11829 0.0007 1 Rival 440312 0.0265 4 Sanish 12899045 0.7749 56 Silurian 62974968 3.7832 219 Souris River 58090 0.0035 2 Spearfish 608834 0.0366 25 Spearfish/Charies 48882470 2.9366 210 Spearfish/Madison 4418316 0.2654 93 Stonewall 14846795 0.8919 122 Stony Mountain 5668 0.0003 1 Three Forks 2003 0.0001 1 Tyler 14688188 0.8824 80 Tyler A 2911935 0.1749 7 Winnipeg 138542 0.0083 3 Winnipeg/Deadwood 31010 0.0019 6 Winnipegosis 9113665 0.5475 55
Table 1.1. Cumulative oil production in North Dakota, by formation, through Dec. 2009. Modified from North Dakota Oil and Gas Division (2009).
5 Bakken 985496 2.7902 226 2245411 5.6740 300 7382025 16.5139 457 27233329 43.6698 881 Birdbear 1305418 3.6960 96 1242060 3.1386 109 1153949 2.5814 111 908059 1.4561 117 Cambro/Ordovician 15214 0.0431 2 15754 0.0398 2 12489 0.0279 2 12549 0.0201 2 Dawson Bay 35759 0.1012 3 34061 0.0861 3 31178 0.0697 3 26233 0.0421 3 Devonian 1098339 3.1097 58 962058 2.4311 59 992888 2.2211 62 952526 1.5274 62 Dupe row 904296 2.5603 119 901638 2.2784 121 806651 1.8045 121 746653 1.1973 114 Gunton - - - 18822 0.0476 1 16729 0.0374 1 5029 0.0081 1 Heath 194320 0.5502 43 220369 0.5569 40 180224 0.4032 40 206673 0.3314 38 Lodgepole 2076906 5.8803 29 1596325 4.0338 29 1331618 2.9789 29 1160293 1.8606 28 Madison 11732155 33.2172 2069 11680192 29.5151 2107 11352593 25.3962 2123 11022447 17.6750 2133 Midale/Nesson 76068 0.2154 22 155200 0.3922 30 178634 0.3996 28 342726 0.5496 36 Mission Canyon 2879 0.0082 1 2213 0.0056 1 1967 0.0044 1 1576 0.0025 1 Ordovician 593650 1.6808 57 533782 1.3488 55 471503 1.0548 54 441636 0.7082 51 Ratcliffe 13555 0.0384 4 11876 0.0300 4 10512 0.0235 4 11052 0.0177 4 Red River 1911464 5.4119 200 1871889 4.7301 203 1891163 4.2306 209 1772346 2.8420 208 Red River B 11922208 33.7553 239 15706913 39.6903 269 16722579 37.4091 278 15467112 24.8022 304 Rival ------17291 0.0387 4 14483 0.0232 3 Sanish 65811 0.1863 13 67118 0.1696 13 61987 0.1387 13 99408 0.1594 16 Silurian 584537 1.6550 56 593657 1.5001 55 576815 1.2904 56 576630 0.9247 55 Spearfish 15766 0.0446 11 15465 0.0391 9 21612 0.0483 13 26233 0.0421 13 Spearfisti/Charles 439246 1.2436 105 416980 1.0537 106 374252 0.8372 109 325762 0.5224 106 Spearfish/Madison 48149 0.1363 36 63128 0.1595 36 53579 0.1199 36 51303 0.0823 38 Stonewall 512509 1.4511 49 463033 1.1701 51 417206 0.9333 50 375882 0.6027 50 Tyler 482040 1.3648 43 433896 1.0964 45 374096 0.8369 42 291897 0.4681 41 Tyler A 32881 0.0931 3 31035 0.0784 4 29680 0.0664 4 28729 0.0461 4 Winnipeg 40 0.0001 1 ------Winnipeg/Deadwood 1101 0.0031 2 1267 0.0032 2 1371 0.0031 3 1382 0.0022 2 Winnipegosis 269703 0.7636 16 289508 0.7316 16 237343 0.5309 19 259941 0.4168 20 PMilllllMIIII—W •M—1 —1BBWBBB •MHOS MWHHM HK^HSUflW
Table 1.2. Oil prcxjuction in North Dakota from 2005 to 2008, by formation, highlighting Red River B. Modified from North Dakota State Oil and Gas Division (2009). their locations; 3) a qualitative reservoir characterization; and 4) an integration of previous studies on petroleum geochemistry and hydrodynamics to address the potential for hydrocarbon entrapment, migration, and thermal maturity.
7 2.0 GEOLOGICAL SETTING
2.1 Structural Setting of the Williston Basin
The Williston Basin (Figure 1.2) originated as a craton-margin or indentation along the continental shelf. It later became an intracratonic basin during deformation of the Cordilleran Orogen and due to crustal additions to the western margin (Gerhard et al,
1990).
The precise timing of the Williston Basin formation is of debate. Lefever et al.
(1987) believe increased subsidence began to form no later than late Tremadocian time, or during deposition of the Deadwood Formation (Figure 2.1). Fowler and Nisbet (1985) also placed the timing of subsidence in Cambrian time. Others contend that initial subsidence occurred in the Middle Ordovician (Peterson and MacCary, 1987; Gerhard et al., 1982; Ahern and Mrkvicka, 1984) while Lochman-Balk and Wilson (1967) put subsidence as originating in earliest Ordovician. Despite the specific timing of subsidence, it is generally agreed that negative relief in the interior of the North America craton was established before carbonate sedimentation of the Red River Formation (Late
Ordovician).
The mechanism of subsidence is also unclear. Theories include thermal contraction (Ahern and Mrkvicka, 1984), diapirism of asthenosphere into lithosphere
(Crowley et al, 1985), structural depression related either to shear zones (Gerhard et al,
1982), lithospheric loading (Nisbet and Fowler, 1984), or crustal weakness (Kent, 1987).
The formation of the Williston Basin is undoubtedly related to the interaction of underlying crustal plates (Kent, 1987). The crust formed from the collision of
Precambrian palaeocontinents (Kent, 1987). Studies of the crust indicates Archean ages
8 MEADOW LAKE ESCARPMENT ? WILLISTON BASIN
OOWNIOHUW PMMXMN UPPER KTERLAKC
TONY MT FM. =, STONYHERALO MOUNT =3G£22E=
mCMMMCAUAH MAN(iOMIAN
Figure 2.1. Time stratigraphic diagram of the Tippecanoe sequence across the Williston Basin from NW to SE. Modified from Osadetz and Haidl (1989).
9 (>2.5Ga) for the Superior and Wyoming cratons while a younger (1.8 - 1.9Ga) island arc
(Trans-Hudson Orogen) was caught between the collision of these plates (Kreis and Kent,
2000). The boundary between the Superior and Trans-Hudson provinces of the Canadian
Shield coincides with the eastern hingeline of the basin (Gerhard et al., 1990), whereas the western edge of the Trans-Hudson province passes through the very center of the basin and is highlighted by the North American Central Plains (NACP) conductivity zone
(Figure 1.2). The latter is the focus of local basement block faulting and subsidiary linear faulting during various periods of Phanerozoic time (Kent, 1987) and likely influenced hydrocarbon accumulation, the character of structural elements, as well as basin hydrology and fluid flow in the area (Canter, 1998).
Brown and Brown (1987) add that the structural style of deformation displayed in the basin is associated with wrench fault tectonics. Two major left-lateral shear zones
(expressed in the sub-surface as the Brockton-Froid and Colorado-Wyoming Lineaments) are found bounding the Williston Basin block (Figures 1.2 & 2.2). Furthermore, the extension of these to the southwest is congruent with the southwest orientation of a
Paleozoic marine connection with the basin, which established open-circulation between the basin and the shelf (Figure 1.2).
Cambrian and Silurian shear faults, associated with the aforementioned fault zones, were aligned NE-SW and NW-SE with extensional fractures trending essentially north (Brown and Brown, 1987). This lineament system suggests a series of en echelon, northwest-tilting grabens. The tectonics displayed in the basin likely controlled depositional patterns (Osadetz and Haidl, 1989; Kreis and Kent, 2000) as well as dolomitization patterns within the Red River Formation (Kohm and Louden, 1978).
10 BROCKTON- FROID CENTRAL ROCKY MOUNTAINS SHEAR & WILLISTON BASIN BLOCK SYSTEM /
COLORADO-WYOMING SHEAR SYSTEM
AREA OF TENSION
Figure 2.2. Possible mechanics for formation of the Williston Basin. A) Left-lateral shear zones indicated by the Fromberg fault zone (Brockton-Froid lineament) and the Colorado Lineament (Colorado-Wyoming) creating an area of tension or pull-apart between the two zones. Location of lineaments in Figure 1.2. B) Strain ellipse indicating orientation of major shear faults (oriented NW-SE and NE-SW) with possible extension faulting oriented N-S. Re-drafted from Gerhard et al. (1990).
11 Studies in support of a post-tectonic depositional setting for the Red River
Formation include Pu et al. (2003), who showed that in the Midale Field (Townships 6-7;
Range 11W2) Red River strata are draped over pre-existing basement structures. Potter and St. Onge (1991) demonstrated a similar conclusion for the Minton Field (Township
3, Range 21W2). They surmise that because isopach variations were not observed in the
Red River, basement highs pre-existed 'Red River' time. These highs were later re activated in the Silurian, Upper Devonian and lower Mississippian. LeFever and Crashell
(1991) and LeFever et al. (1987) suggest episodic movement in Devonian- and
Mississippian-times for those structures within the United States. Clement (1985) adds a post-Silurian time, and episodically thereafter, for the Cedar Creek anticline of Montana, while Kohm and Louden (1988) indicate Silurian movement for North Dakota structures.
Kreis and Kent (2000), on the other hand, suggest syn-deposition of some structures due to Red River thinning and associated local fades' anomalies in the Yeoman Formation.
However, this thinning was not demonstrated as being due to drape over significant topographic highs.
Thus, it seems that regional tectonic activity across the basin was likely idle during deposition of the Coronach Member, though locally some structures might have been activated in Late Ordovician time. The only major orogenic event occurring at this time was the Taconic Orogeny along eastern Laurentia, thousands of kilometers away
(Osadetz and Haidl, 1989). This event was local, affecting only the northern part of the
Appalachians with the principle orogenic activity taking place before the Maysvillian stage (Berry and Boucot, 1973).
12 2.2 Lower Paleozoic Stratigraphy
The earliest strata of the Williston Basin (Sauk Sequence) are basal clastic rocks of the Mid-Cambrian to Early Ordovician Deadwood Formation (Figure 2.1; LeFever et al., 1987). They were deposited on the Precambrian crystalline basement during a transgression into an indentation in the Cordilleran shelf (Figure 2.3) on the site of the
Williston Basin (Gerhard et al., 1990).
By the end of the Sauk sequence the Williston Basin became a depressed structural unit for the first time (Gerhard et al, 1990). A major unconformity that cut into the Sauk Sequence signified widespread regression and erosion that affected much of the interior of North America throughout the Middle Ordovician (Peterson and MacCary,
1987). Subsequent transgression initiated deposition of the Tippecanoe Sequence (Middle
Ordovician to Lowest Devonian strata). The base of the Tippecanoe sequence is comprised of transgressive sandstones and shales of the Winnipeg Group (Mid-
Ordovician). As transgression continued a carbonate factory was established and the
Upper Ordovician Bighorn Group was deposited. The base of the Bighorn Group is comprised of Edenian to Richmondian carbonates of the Red River Formation. Red River sediments onlap the Winnipeg Group and the Precambrian basement (Osadetz and Haidl,
1989).
During 'Red River' time the Williston Basin periodically became increasingly restricted and hypersaline as evidenced by evaporite deposition (Kendall, 1976). Three upward, successively thinner carbonate-evaporite depositional sequences are recognized in the Red River Formation. In Canadian terminology, the earliest cycle is comprised of the Yeoman Formation, the Lake Alma Laminated Member and the Lake Alma Anhydite.
13 Paleo-Tethys
PmUhalassic
f-doe of m; - continent F - .. *
h V rordiMeran shelf| i •"u-ntjtion SubcJuctfon
•- j — * M * lapetus
Late Cambrian (500Ma)
Figure 2.3: Palaeogeography of Laurentia during Late Cambrian (left) and Late Ordovician (right) time. Brown shaded areas are land masses during maximum marine transgression. In Late Cambrian time, the Williston Basin probably had its beginnings as simply an indentation in the Cordilleran shelf. By Late Ordovician the basin had formed as a slight depression situated in a much larger epicontinental sea. The equator likely passed very near, or through the Williston Basin. Modified from Blakely (2007). The second of these cycles is the Coronach Member and Coronach Anhydrite
(Maysvillian to Richmondian). The Redvers Unit is the final carbonate/evaporite cycle.
Figure 1.1 shows the Canadian and American stratigraphic terminology of these units.
Each of the Red River cycles consists of thin, basal argillaceous dolomites, overlain by fossiliferous mudstones/wackestones, a transitional zone of laminated dolomites, and capping anhydrites (Kendall, 1976). The anhydrites of each successive cycle are less widespread than the previous (Figure 2.4).
Red River Formation thickness varies from 215m in the center of the basin to less than 150m at the margins where it is truncated by pre-Late Devonian and pre-Cretaceous erosion (Peterson and MacCary, 1987; Osadetz and Haidl, 1989). Tectonic margins include the transcontinental arch to the south where the Red River Formation thins due to onlap, the Sweetgrass Arch and Meadow Lake Escarpment to the northwest, the Cedar
Creek Anticline that separates the Williston from the Powder River basin to the southwest, and the Severn Arch to the northeast (Figure 1.2).
The three Red River cycles represent deposition during a period of about six million years (Longman and Haidl, 1996). The exact time scale of the Coronach Member, roughly late Maysvillian to early Richmondian (Sweet and Bergstrom, 1974), has never been conclusively established. Nowlan and Haidl (2001) used conodont biostratigraphy to suggest the Coronach Member was from the Late Maysvillian, although lack of specimens prohibited a more precise age.
Glacio-eustasy, as driven by Milankovitch cycles (Figure 2.5), is largely invoked to explain rapid transgressions (Tucker and Wright, 1990), which may be the process responsible for the cyclic deposition of the Red River Formation. Tectonism is unlikely
15 Saskatchewan Manitoba
Saskatoon
Reglna / • X "C" ANHYDRITE
M Miles Limit Of C" Laminated Anhydrite
Figure 2.4. General extent of Red River anhydrites. "C", "B", and "A" correspond to Lake Alma, Coronach and Redvers, respectively. Modified from Longman and Haidl (1996).
16 i 1 ECCENTRICITY 111 §wOW more i zs x<^ cwz 'essI PRECESSION < 5 UJ U) 24.00 [{j 23.50 OC 23.00 S 22.50 O BLIQUITY 200 100 THOUSANDS OF YEARS AGO
Figure 2.5. Milankovitch cycles over the last 250,000 years arid 100,000 years into the future. Cycles show the periodicity of orbital perturbations, including 1) eccentricity (100,000 years), 2) precession of equinoxes (23,000 to 19,000 years), and 3) obliquity (41,000 years). All influence global sea level changes over the same time range. Milankovitch cycles are orders of magnitude shorter in duration than tectono-eustacy; the latter could not have played a part in sea level during deposition of the Coronach because of the short time in which it was deposited. From Tucker and Wright (1990).
17 because sea level fluctuations, through changes in seafloor spreading rates, are on very long time scales and cannot lead to rapid sea-level rises (Embry, 2009).
In Late Ordovician time, glaciers covered much of Gondwanaland (Figure 2.6), which was situated about the south-pole (Berry and Boucot, 1973; Jaanusson, 1984;
Fortey, 1984; Stampfli et al., 2002). It is not clear what initiated glaciation (Gibbs et al.
1997) but it has been demonstrated as controlling oceanic circulation and upwelling
(Pope and StefFen, 2003), climate (Spjeldnaes, 1974; Lindstrom, 1984; Webby, 1984), and global sea level and subsequent cyclic sedimentation (Dennison, 1974; Sutcliffe et al.
2000). Saltzman and Young (2005) clearly illustrated the link between glacial deposits in
Late Ordovician time with related excursions in atmospheric CO2 concentrations, Carbon isotopes (513C), Strontium isotopes (87/86Sr), oceanic upwelling and sea level (Figure 2.7).
More specifically, Sutcliffe et al. (2000) identified and described two glacial advance- retreat successions that they related to eccentricity cycles (100,000 years).
Maximum glaciation is thought to have occurred in the Richmondian (Dennison,
1974). This implies that the Coronach Member was deposited during glacial build-up.
Though the growth of an icecap may take several million years, the cyclic changes in glacio-eustatic sea level may be on the order of just tens of thousands of years (Brenchley and Newall, 1984). Given the overwhelming evidence of glaciation controlling sedimentation over the greater part of the Ordovician (Dennison, 1974; Jaanusson 1984;
Brenchley and Newall, 1984; Sutcliffe et al, 2000), the Red River cycles, including the
Coronach Member, are also likely a function of this process.
18 Late Ordovician (-545 MA ago)
Figure 2.6. Late Ordovician plate reconstruction showing Gondwana (current-day Africa, South America and parts of Asia) covered by glaciers. South Pole situated over present-day Libya. Modified from Stampfli et al. (2002).
19 Mfdcont Frequency Sea level Sen,. Stay 4 8 12 18 low . high 443 Ma Garni I 1 Hrnan shetznri Gondwana c cKvetgens glaciation .2 C J grandts <•-» c II© .9 robustus " 2 cCO & (0 £CO I c o> si* veEcuspis a "o 5 © c < c "O — 'S l / C ZZ c o b a Figure 2.7. Correlation of Gondwana glaciation with key secular fluctuations through Late Ordovician. Timing and duration of glaciation coincides with specific conodont zonations, greenhouse/icehouse transitions, oceanic upwelling, carbon and strontium isotope excursions, atmospheric C02 fluctuations and sea level changes. From Saltzman and Young (2005). 20 2.3 Palaeogeographical Setting Palaeomagnetism data indicates that from Early to Late Ordovician time, Laurentia, the pre-cursor tectonic plate to North America, occupied equatorial latitudes and was rotated about 45° clockwise relative to today's position (Figure 2.3; Kent and Van Der Voo, 1990). Witzke (1990) used palaeoclimate data to further constrain the palaeolatitude position for Laurentia. He determined that the Laurentian plate was moving southward from the Cambrian through Early Devonian. In the Late Ordovician, the equator likely ran through or near the Williston Basin, based on a belt of arid-zone evaporites deposited throughout the central continent (Figure 2.8). Scotese (2007) corroborates this by adding that kaolinites are also present across Laurentia during this time. Palaeobiological indicators were also used to confirm an equatorial position for Laurentia. Shallow marine bathyurid trilobites and endemic molluscs and brachiopods indicate Laurentia was lying at a low-latitude, isolated position (1000's of km) at this time (Cocks and Fortey, 1990). Much of the North American craton was occupied by a warm shallow epeiric sea in the Ordovician (Kreis and Haidl, 2004; Peterson and MacCary, 1987). The Williston Basin area alone was well within the carbonate belt at this time (Witzke, 1990). The presence of primary anhydrites deposited throughout the Red River Formation not only suggests periodic restriction of the Upper Ordovician epeiric sea, but confirms a dry, semi-arid climate postulated by Witzke (1990). Trade winds were from the southeast (Figure 2.8; Scotese and Barrett, 1990) while offshore surface-water currents were directed south (Scotese, 2007). 21 revailin s = sulphate evaporites (anhydrite, gypsum) 0 = ooids p = phospharite or phosphatic sediments A Mountain terrains LATE ORDOY1CIAN--Ed«iUn-M«ysv111i»n Figure 2.8. Palaeogeographical position of Laurentia during Late Ordovician relative to equator. Shaded areas show distribution of land areas during maximum marine onlap. The trend of sulfate evaporites (s) delineates the palaeo-equator. Sulfates are abundant in an area occupied by the Willsiton Basin and indicate hot dry conditions. Modified from Witzke (1990). 22 2.4 Red River Petroleum System The Williston Basin has been used as a model for petroleum exploration around the world and there is a wealth of information available on this subject. Numerous oil horizons and a need to update Williston Basin petroleum systems has led to studies including: division of Williston Basin oils into families or groups (Dow, 1974; Williams, 1974; Osadetz et al., 1994; Leenheer and Zumberge, 1987); fingerprinting oils (Jarvie, 2001; Zumberge, 1983); determining oil to source correlations (Macauley et al., 1990); oil to oil correlations (Obermajer et al., 2000); measuring thermal maturities (Osadetz and Snowdon, 1995); and assessing hydrocarbon migration (Burrus et al., 1996; Li et al., 1998). These elements of petroleum geochemistry have been applied to the Red River system. Red River oils are distinguished from other oil families in that they exhibit little to no biodegradation, show an enrichment of normal paraffins from Cg+ gas chromatograms, have a low number of C20+ normal-alkanes, an odd-carbon preference of normal-alkanes between C14 and C20, and low concentrations of Pristane and Phytane biomarkers (Jarvie, 2001; Zumberge, 1983). The characteristics mentioned above are indicative of Type I kerogens, or an algal source rock (Hunt, 1995), which was at first thought to be from the Winnipeg Shale (Williams, 1974; Dow, 1974). Now however, through oil to source correlations, Red River oils are thought to be sourced from organic-rich 'kukersites' within the upper l/3rd of the Yeoman Formation (Osadetz and Snowdon, 1995). Kukersites are composed of an alginate maceral derived mainly from Gloeocapsomorpha prisca (G.Prisca) (Obermajer et al., 1998), which is consistent with a Type I kerogen. 23 A small number of maturity studies have been done on kukersites from the Yeoman Formation (Osadetz and Snowdon, 1995; Macauley et al., 1990). These studies indicate that kukersites are mature to marginally mature in southern Saskatchewan. In northern portions of the Williston Basin, several producing fields, are well outside of this maturity zone (Figure 2.9). However, Li et al. (1998) convincingly showed, using pyrrolic nitrogen compounds as "tracers", that long-distance lateral migration of oil has taken place in the Williston Basin. 2.5 Williston Basin Hydrodynamics Previous work on the hydrodynamics of the Red River was undertaken by Barson et al. (1998) and Khan et al. (2006). More regional basin flow modeling has been done by Downey et al. (1987), Toop and Toth (1995), Hannon (1987), and Bachu and Hitchon (1996). All studies conclude basin-wide flow is from the southwest to northeast. Recharge is supplied by high-potential freshwater intake in southern Montana and North Dakota and includes the Black Hills and the Bighorn Mountains (Figure 2.10). Outflow of fluids is in the low-potential area of central Manitoba and north-eastern North Dakota where the Red River Formation outcrops. Potentiometric maps of the Red River Formation indicate the same north-easterly flow direction across the Williston Basin. Fluid flow direction is fairly consistent and has probably deflected oil migration in the same north-easterly direction (Barson et al., 1998). Khan et al. (2006) add that petroleum migration occurred before hydrodynamic flow was established. Otherwise, hydrodynamic flow would have forced hydrocarbon migration trajectories away from southern Saskatchewan. A corollary of this is 24 ChBpleautaka rrobablo ntMit of 'matura 0. Prttcm dlsumkiatad organic "scrcxr faefta aourca araa tuning Cechux Ewuob- CljMaw »rwwiinn Weff HII jff Kirv jsfo'd Ba lublar JtVflts Matura zona tor 6. Prttcm mat 33 22 21 20 °ramte fori*! 4 ^!gVre ^ Distribution of Red River oil pools. Also shown is distribution of thermally-mature kukersites from the Yeoman Formation (grey lines). Kukersites have two mature zones based on the two types of G Prisca organic micro-facies. Extent of mature Yeoman Formation kukersites is township 9, yet several Red River pools exist north of this region ?n£5?Sxting significant migration of hydrocarbons. Modified from Qing et a! (2001a) and Fowler et al. (1998). 25 Canadian Shield Alberta ^ / \\ (•'//vjyV vprj*!* I v\ Basin t \\ Svjlfl / Williston / daWA Powder (3ZS WYOMING I NEBRASKA/^ \ \ Alliinca L«mX Nsin Mtnt \ | 0 100 200 km T COLORADO V SO 100 ml Freshwater flow direction l l Brines (>100.000 mg/L salinity) Brine flow direction jp* Interbasin flow from the Alberta basin B rwtMnc water | Aquiduda I Btkw* (»100,090 m®\ wirtty) MannvNa (Dakota) Aquifar System JoU Fou (SkuK Creek} Aqultard \ \ Viking (NewcaoUa) Aquiter sA \ I Cretaceou» AquUrd SystaTi Mtuouh Canadian Trench Manitoba ShieW Escarpment Permian-Jufattk Aqukwd System Pe*n«ytvanian * Mtaalwlpptan Aquitan) Devonian Aquifer System Mfwiaaipptan (Madison) Ptalrls Aqutclude Aquifer Sytfem N Winnipegosta Aquifer Silurian-Devonian Aquitard Basal Aquifar System Figure 2.10. Hydrodynamic flow in the greater Williston Basin. A) Map showing recharge areas on the southwest side of the basin, which include a belt of highs runnning from central Montana through Wyoming and South Dakota. Fluid flow is northeastward from these highs into Saskatchewan and Manitoba where fluids discharge via outcrop. B) Profile of the Williston Basin from S-SW to N-NE indicating flow directions as they relate to topography-driven flow. The Coronach Member is part of the slow-moving, briny Basal Aquifer System. Modified from Bachu and Hitchon (1996). 26 stratigraphically trapped hydrocarbons in Saskatchewan, under hydrostatic conditions, may have been flushed from the onset of hydrodynamic conditions. This severely limits the potential for stratigraphic traps to develop in the Coronach Member. Hydrodynamic flow from southwest to northeast has aided those reservoirs on the down-dip side of the Williston Basin (South Dakota, southeast North Dakota and eastern Montana). In south-eastern Saskatchewan, up-dip flow combined with up-dipping strata has limited the potential of hydrocarbon accumulations within the Coronach Member to those of structural-type traps. 27 3.0 PREVIOUS WORK Dowling (1900) was the first to describe Ordovician rocks along the outcrop belt in Manitoba. He noted three units, which Foerste (1928, 1929) grouped into the Red River Formation. Rader (1952) subdivided the Red River into an upper and lower unit based on studies on subsurface rocks. Porter and Fuller (1959) greatly added to the understanding of the Lower Paleozoic, including the Coronach Member and its equivalents, by correlating outcrops in Manitoba with subsurface formations in Saskatchewan and North Dakota. They also divided the Red River Formation into an upper and lower unit based on work by Rader (1952, 1953). In 1958 the Saskatchewan Geological Society attempted to standardize Lower Paleozoic nomenclature by using the two-fold unit subdivision of the Red River by naming the upper unit "Herald" and lower unit "Yeoman". Kent (1960) was the first to give member status to the Herald and Yeoman units. Kendall (1976) gave formation status to the Herald and divided it into three units; the middle of which, the Coronach, he gave member status to. There has been a wealth of studies discussing the Yeoman Formation and the lower unit of the Herald Formation, Lake Alma Member. However, previous work on the Coronach Member is sparse (Longman and Haidl, 1996; Montgomery, 1997; Whiteman et al., 1998) and those that do include the Coronach Member are usually combined with more detailed studies on the lower Red River cycle (Kohm and Louden, 1978; Longman etal., 1983; Canter, 1998). Previous studies on the Yeoman Formation and Lake Alma Member may still be useful in assessing the Coronach Member. The main reason is because the Coronach Member was deposited in the same paleogeograhical regime and exhibits similarities in cyclical deposition and general lithological characteristics. Interpretation of the depositional environment for the Red River Formation is varied. Kent (1960), Fuller (1960), Kendall (1976), and Kohm and Louden (1978) suggested an aggradational subtidal origin. Longman et al. (1983) added a "brining- upward" phase to the subtidal deposition for the Lake Alma Member. However, Asquith et al. (1978), Carroll (1978), Wittstrom and Chimney (1980), Ruzyla and Friedman (1985), and Derby and Kilpatrick (1985) interpret the Lake Alma deposits as shallowing- upwards, implying a progradational model. Both schools of thought are backed up by their own petrographic evidence. Fox (1993) concluded that both these hypotheses may be correct, depending on location of the study area. Thus, some combination of processes may have acted upon the Red River Formation. More recent studies have focused on specific topics such as dolomitization (Zenger, 1996a, b; Qing et al., 2004; Heinemann et ah, 2005; Kendall, 1984; Longman et al., 1984; Kissling, 1997, 2001), basement controls (Kreis and Kent, 2000), anhydrites (Nimegeers and Haidl, 2004), conodonts (Nowlan and Haidl, 2001; Haidl et al., 2003), isotopes (Qing et al., 2001a, b) and ichnology studies (Pak et al., 2001; Pak and Pemberton, 2003). Reservoir studies on the U.S. portion of the Red River Formation are numerous and usually include the Coronach Member (Ruzyla and Friedman, 1985, Clement, 1985, Derby and Kilpatrick, 1985; Montgomery, 1997; Kohm and Louden, 1978, 1983, 1988; Mayer, 1987; Fisher and Hendricks, 1995; Sippel, 1998; Bogle et al., 1998; Longman et al., 1983, 1992, 1998; Tanguay and Friedman, 2001a, b). Reservoir studies from Saskatchewan are rare and have not included the Coronach Member (Potter and St. Onge, 1991; Pue/ al., 2003). Other more general topics that include mention of the Red River Formation, among other Paleozoic strata, are those dealing with structural development of the Williston Basin; these studies were mentioned in section 2.1. Investigations pertaining to petroleum geochemistry and hydrodynamics of the Williston Basin have invariably included the Red River Formation and are summarized in section 2. A geological summary of the Red River Formation including the Coronach Member has been done by Kreis and Haidl (2004). There are currently no sedimentological or diagenetic studies involving solely the Coronach Member on the Saskatchewan side of the Williston Basin, other than Urban and Qing (2007). 30 4.0 METHODS Twenty-five cores from the Saskatchewan side of the Williston Basin were used for a detailed study of the Coronach Member and Anhydrite. The study area encompasses Ranges 30W1 to 22W2 and Townships 1-15 within southeast Saskatchewan (Figure 1.2). One core (1-9-21-16W2) was used as a control point north of the study area to document changes in sedimentary, diagenetic, and reservoir characteristics, as well as to delineate reservoir potential for the Coronach Member. The rock units of focus include the Coronach Member and Coronach Anhydrite of Kendall (1976) terminology or the equivalent "B" sequence of Kohm and Louden (1978); see Figure 1.1. Each core was cleaned and a few samples were slabbed to aid in logging. Cores are described as per the Wright (1992) classification for carbonate textures and Choquette and Pray (1970) for porosity. Mineralogy was determined in core from 10% HC1 + H2O mixture and confirmed through petrographical analysis. Hydrocarbon indicators were established qualitatively in core by visual and olfactory aids, in addition to a UV-light provided by the Saskatchewan Geological Subsurface Laboratory. Pentane was used as a solvent to liberate oil from core samples, while oil maturity was determined subjectively with a UV-light and compared to Hunt's (1995) maturity color index. All cores were photographed in detail using a Kodak 4.0 digital camera and a Myatt Microscopic camera for small-scale features. Sampling was random for the purpose of obtaining average skeletal and mineralogical percentages, but a few samples were taken from distinct sedimentary or diagenetic features of nearly every core logged. For closely spaced cores (more than one core within a single township) samples were only taken from one core. A total of 75 samples were sent to Vancouver Petrographies for cutting into thin sections. All thin sections, cut to 0.03mm thickness, were stained with Alizarin Red S to determine mineralogy and mineral percentages. Some samples were chosen for impregnation with blue epoxy to establish porosity types and concentrations. Thin sections were examined with a Nikon Eclipse LVIOOPOL microscope and Nikon DXM1200 camera. The white-light method outlined by Dravis and Yurewicz (1985) was employed to determine allochems from thin section in fine-grained samples. Over 2500 geophysical well logs were used to pick the tops and base of the Coronach Member and the anhydrite where present. Cross sections and structural and isopach maps were constructed from this database. Production information and core analysis data were obtained from Saskatchewan Industry and Resources and the North Dakota Geological Survey. Lithologs were drawn using Trivision PowerCore 9 (see Appendix A). Nearly all rock samples were drilled with a Mastercraft drill press, utilizing 1.59mm drill bits, for obtaining rock powder for isotopic analysis. Most dolomite samples analysed were 100% dolomite, except where otherwise indicated. Limestone samples had variable concentrations of dolomite and may not be composed of pure calcite (see Appendix B for percentages). Powder was placed into dry glass vials. Twenty-three powdered mineral samples were analyzed for Strontium (Sr) isotopic composition by mass spectrometry at the Department of Earth and Sciences, University of Alberta. Approximately 50mg of each 32 sample was dissolved in 0.75N HCI under clean-room conditions, and Sr chemically separated by conventional cation chromatography. Chemical processing blanks are < 200 picograms (trillionths of a gram) of Sr, and are insignificant relative to the amount of Sr analyzed for any water sample. Sr isotopic abundances are measured in static mode by multi-collector ICP Mass Spectrometry, and are normalized for variable mass fractionation to a value of 0.1194 for 86Sr/®8Sr using the exponential law. All analyses are presented relative to an 87Sr/ 86Sr value of 0.710245 for the NIST SRM987 International Sr isotope standard. Fifty-two carbonate samples were analyzed for carbon and oxygen isotopic composition by the Saskatchewan Isotope Laboratory at the University of Saskatchewan. Samples were roasted in a vacuum oven at 200°C for 1 hour to remove water and volatile organic contaminants that may confound stable isotope values of carbonates. Stable isotope values were obtained using a Finnigan Kiel-IV carbonate preparation device directly coupled to the dual inlet of a Finnigan MAT 253 isotope ratio mass spectrometer. 20-50 micrograms of carbonate was reacted at 70°C with 3 drops of anhydrous phosphoric acid for 420 seconds. The evolved CO2 was then cryogenically purified before being passed to the mass spectrometer for analysis. Isotope ratios were corrected for acid fractionation and 170 contribution using the Craig correction, and reported in per mil notation relative to the PDB scale. Data was directly calibrated against the international standard NBS-19 that is by definition 6 13C = 1.95%o VPDB and 5 180 = -2.2%o VPDB. Accuracy of data was monitored through routine analysis of NBS-19 and in-house check standards which have been stringently calibrated against NBS-19. Accuracy of 8 13C and 8180 are 0.05%o and 0.1 l%o, respectively (n = 25). Actual sample 33 errors may be greater than these due to heterogeneity, and more accurate data may be obtained for such through repetition. All isotope data is listed in Appendix B. i 34 5.0 FACIES DESCRIPTIONS AND INTERPRETATION Facies descriptions were made from observations of 21 cores and 75 thin sections within the study area. Rock types are described using the classification scheme of Wright (1992), which is a modification of classifications from Dunham (1962) and Embry and Klovan (1971) (Figure 5.1). Although not yet widely used, the Wright (1992) system is the only classification that fully describes the complexity of these rock types and effectively distinguishes between the major processes (depositional, biologic and diagenetic) that contribute to their formation. Textural fabrics of dolomites are defined using the classification of Sibley and Gregg (1987). Porosity is described using the classification of Choquette and Pray (1970). Crystal shapes are described using terminology of Folk (1965) for calcite and Gregg and Sibley (1984) for dolomite. Table 5.1, modified from Scholle (2002), was used as the main reference for skeletal mineralogies, otherwise other references are cited herein. This chapter is broken into sections representing each of the major facies as well as the underlying Lake Alma Anhydrite. All facies' sections include 1) an introduction with diagnostic characteristics; 2) a closing summary with thickness, porosity estimations, and hydrocarbon indications; and 3) an interpretation of the depositional environment. Each facies section also includes subsections on skeletal and non-skeletal grains, sedimentary structures, and matrix components. A summary of the depositional environment, including depositional models and modern analogues, conclude Chapter 5. Diagenetic features are described and interpreted in Chapter 6. DEPOSITIONAL BIOLOGICAL DIAGENETIC Matrix supported OMter- (eiay & Mtgnil*) Grain-supported Insltu organism* Norhebttteratfv* Mivs MP* yam* wttrMtix mnwrli Eftcrualna Oigantra Wn Mow grain Moot grain Gry*Wt>lO bMhg •cflnQ to bWlto <£$L componaniia cammm OOMMBIM awntow dominrt OMMBl mwmym mMMOKM QNttnM CMSmumoM WMtitm RMMIon* GnMsni BOiTOMM fummm Fmtwtorw tnrtnikni QMtalpiv Bp«r«ton» FtMMM* fto# ttot sss jgjgn Grata >2 mm ftOTmlDM Figure 5.1. Carbonate classification scheme of Wright (1992) used in this study. Wright's classification blends Dunham (1962) and Embry and Klovan (1971) classifications but also adds a diagenetic component. Wright's classification distinguishes between depositional, biological and diagnetic processes. 36 Both Aragonite Taxon Aragonite Calcite and Calcite HMg 0 5 10 15 20 35 30 35 T . ii p .1 i i Calcareous Algae Red • • Green X Foraminifera Benthonic R • •# Planktonic •—• Sponges R • • Stromatoporoids (A) X •—? Corals Rugose (A) Tabulate (A) •—? Bryozoans R R Brachiopods •HI Molluscs Pelecypods X X Gastropods X X Cephalopods X Arthropods Ostracodes • • Trilobites (A) • Echinoderms • • X Common R Rare (A) Not based on modern forms Table 5.1. Skeletal mineralogy of the taxa identified in the Coronach Member. Modified from Scholle (2002). 37 Detailed descriptions of lithofacies, along with observations from vertical and lateral lihofacies' changes were used in conjunction with the comparative sedimentology method (Ginsburg, 1974) to split into the Coronach Member into five facies (Table 5.2). Descriptions from thin section and core were used to construct lithologs (Appendix A). Lithologs, isopach maps and structural maps were then supplemented to the lithofacies' descriptions to make interpretations on the depositional setting. Core and thin section analysis indicate that the best reservoir quality, in terms of porosity, permeability and hydrocarbon shows, is in Facies 3. Facies 4 and 5 are very tight and act as effective "cap rocks". Facies 1 and 2, though generally non-porous, contain kukersites that may be a potential source rock for this member. 5.1 Lake Alma Anhydrite Underlying the Coronach Member is the Lake Alma Anhydrite which can be sub divided into 1) a lower unit of nodular bedded anhydrite, 2) a middle unit of laminated (to massive) cryptocrystalline dolostone and 3) an upper unit of thinly bedded anhydrite (Kendall, 1976). The formal base of the Coronach Member occurs at the top of the last occurrence of anhydrite from the Lake Alma Member (Kent, 1960). Though this appears concrete, the upper portion of the Lake Alma Member is described in detail here, as the transition from Lake Alma to Coronach is ambiguous. The Lake Alma Member is easily identified because of its high density and corresponding low porosity on logs (Figure 5.2). Some authors have grouped the anhydrites of the Lake Alma Member into a single unit (Montgomery, 1997), likely 38 Sub- Formal Name Facies Primary Lithology Diagnostic Features Facies Breccia's, mudcracks, mud rip-ups, oxidation, Facies 5 Dolomudstone/calcimudstone blackened arains: scour surfaces B Anhydrite Individual to coalesced nodules of anhydrite Facies 4 Randomly oriented lath-like crystals of A Cryptocrystalline Dolomudstone anhydrite B Dolomud stone Disrupted, wavy, domal or flat laminations Facies 3 A Calcitic to Dolomitic Mudstone Organic-rich; hz, planar laminations Coronach Member D Peloidal Calcitic/Dolomitic Mudstone/Wackestone Peloids, Planolites burrows, ostracodes C Skeletal Grainstone Rare micritic mud; rounded & abraded grains Facies 2 Algal-Stromatoporoid Reef Mounds (Strom. Boundstones; B Very high fossil abundance and diversity Dimomh. Bafflestones: Solen. Frame/Boundstones A Cherty Wackestone Chert nodules Laminations, kukersites, low skeletal diversity; Facies 1 - Calcimudstone Planolites & Palaeophycus traces B Dolomudstone to Anhydritic Dolomudstone Mudcracks, mud rips-ups, solution breccia Upper Lake Alma Anhydrite Lake Alma A Anhydrite Laminations and dissolution surfaces Member Lower Lake Alma Not described Anhydrite Table 5.2. List of facies with primary lithology and diagnostic features. Redvers Unit AT" Coronach Anhydrite Coronach Member Lake Alma Anhydrite Lake Alma Laminated Member Kev • Productive Intervals Gamma ray log Neutron porosity log Density porosity log Limestone • Dolomite • Anhydrite Figure 5.2. Type log of the Red River Formation. Illustrated is the stratigraphic nomenclature of Mid- to Late-Ordovician strata, from the Williston Basin of south eastern Saskatchewan. Highlighted in s grey is the Coronach Member. because of its ease of correlation on well logs. However, they have not recognized that the Lake Alma Anhydrite is more complex and has distinctly differing textures throughout. The lower portion of the Lake Alma Anhydrite is comprised of enterolithic, nodular or "chicken-wire" textures (Plate 5.1). Nodular textures grade, most often sharply, into an upper section of planar, interbedded anhydrites and dolomudstones with a moderate concentration of organics; the latter imparts a dark brown to black color upon these rocks. The Lake Alma Anhydrite is further complicated because the anhydrites are interbedded with decimetre to meter scale, rarely-laminated massive dolomudstones (Plate 5.1). The Lake Alma Anhydrite requires more study to identify the sub- environments that may exist. 5.1.1 Lake Alma Anhydrite Interpretation The Lake Alma Anhydrite is basin-centered (Figure 2.4), which has largely been cited as and evidence for subaqueous deposition in a shallow-water/shallow-basin salina environment (Kendall, 1992; Figure 5.3). The Lake Alma Anhydrite was thus the result of an aggradational, brining upward sequence (Kent and Kissling, 1998) related to "progressive shallowing and evaporitic drawdown in the central basin region" (Nimegeers and Haidl, 2004). The interpretation is consistent with most of the Upper Ordovician strata, which were deposited in a warm, shallow epeiric sea that covered most of interior North America (Macauley, 1964). 41 Plate 5.1. Lake Alma Anhydrite structures. Anhydrite grades from nodular, enterolithic forms up to bedded and laminated, organic-rich anhydrite. The latter is interbedded with massive to laminated dolomudstones. Numerous sharp and gradational contacts are marked by coloured pins and lines. Core from well 15-9- 2-14W2; depth 3043.75 - 3048.15m. 42 Evaporite Fades Associated Facies Brine-pan &evaporftSc flat my Muonat aaa Perennial shallow-subaqueous Sandflat Oispladve (in mudftat environments) MBft Deep-water (Lamlnltes) Prograding supratidal sediments ^ Brine level Shallow Water > * ft ft A ft A, A A > Shallow water & Shallow Basin subaerial sediments Model Figure 5.3. Kendall's depositional model for basin-central evaporites. Lake Alma Anhydrite was deposited in a shallow-water/shallow basin model. Prograding supratidal sediments are mudflats which may contain dispiacive anhydrite. Modified from Kendall (1992). 43 However, dissolution surfaces and displacive anhydrite nodules in southern Montana may be indications of a supratidal setting (Ruzyla and Friedman, 1985). A similar setting is proposed for the top of the Lake Alma Member in southern Saskatchewan based on the same observations in the overlying Lake Alma Dolomudstone. 5.2 Lake Alma Dolomudstones Beds and laminations of anhydrite and organic-rich dolomudstones of the upper most Lake Alma Member typically grade into a 5 to 30 cm thick transition interval, before grading into normal marine lime mudstones of the Coronach Member. The transition interval is a massive to irregularly-laminated light grey to light brown dolomudstone (L.A. Dolomudstone). It is characterized by a wide range of textures and structures owing to multiple sedimentary and diagenetic processes (Plates 5.2 to 5.4 & Figure 5.4). The overlying contact of L.A. Dolomudstone is recognized by a gradual to abrupt loss in anhydrite. This change appears conformable in some cores, but unconformable in others. Examples of unconformable surfaces include irregular contacts from dissolution of the underlying anhydrite and erosional or exposure surfaces, as identified by mud rip- up clasts and mudcracks (Plates 5.2 - 5.4). 5.2.1 Structures The most common structures in the L.A. Dolomudstone are exposure-related features, including mudcracks, sheet cracks, detached beds and breccias (Plates 5.2 & 44 Plate 5.2. Upper Lake Alma (L.A.) Member. A) Sharp, irregular dissolution surface (DS) on top L.A. Anhydrite. Faintly laminated dolomudstones overlie the contact. Soft-sediment deformation (SSD) textures are evident in the overlying dolomudstones. From 6-5-6-19W2, 2715m. B) L.A. Dolomudstones grading into basal Coronach Member; the former shows soft-sediment deformation textures (SSD), a zone of clasts, and an irregular surface. These grade sharply into overlying, organic-rich limestones of the Coronach Member. From 8-16-2-14W2, 3024.6m. Scale at bottom in em's. C) Lower Coronach Member contact showing sharp dissolution surface (DS) on top of L.A. Anhydrite. Overlying the contact are dolomudstones, with an organic lens, exhibiting flame structures and a large pseudo-brecciated zone that continues upwards on photo 'D'. Mudcracks also present. From 4-2-14-21W2, depth from base 'C' to top 'D' is 2110-2109.6m. Cores in 'A', 'C' and 'D' are 9cm wide. 45 t Top 1 mm C — Plate 5.3. Exposure features in the L.A. dolomudstones. A) A zone of rip-up (Ru) mud clasts near the top of the L.A. Also shown is a detached bed; dashed arrow shows where it's connected. This may be a teepee structure. Core photo from 14- 26-6-11W2; depth 2561.9m. Core is 9cm wide. B) Mudcracks (mc) and sheetcracks (sc) in L.A. Dolomudstone. A clast-zone overlies these exposure features, which in thin section are micritized bioclasts. Also shown at bottom of photo is a ptygmatically folded mudcrack. From 15-8-5-7W2, depth 2656.2m. Core photo is 6cm across. C) Mudcrack in thin section partially filled by anhydrite. 2-34-1-32W1, 2317.25m. 46 Plate 5.4. Thin section features from L.A. Dolomudstone. A) Unknown rounded clast with a thin carbonaceous coating; 13-23-6-11W2, 2588.5m. B) Laminations of angular to sub-angular clasts, usually found as thin beds. Most exhibit high alteration in a dolomicrospar matrix; 15-8-5-7W2, 2656.4m. C) Fenestral patches filled by dolo-microspar overlying a marine hardground; 2-34-1-32W1, 2317.25 m. 47 * * A K. i F 1^-' s * * '-K,»ftn(uuy8 i 15 degree bed dip of unlithified Soft-sediment slumping offsets laminae which is taken up by mudstones compaction of successive laminations - Creep Creep _C^_ M- Continued creep produces Creep of laminae down- a false reverse orientation of dip rotates the offset laminae offset lamine until the laminae are cemented in place Figure 5.4. A) Offset laminae producing a false reverse-fault orientation. Fractures do not extend more than 4cm through the core and are more likely the result of slumping followed by creep; see figure B. From 3-16-2-10W2, depth 3016.4 m. 48 5.3). Mudcracks were observed in four cores and are generally about l-2cm's long, vertical to sub-vertical or even folded in rare cases (Plate 5.3B). Sheet cracks were observed in two cores and average 2 to 4 cm long. Detached beds show separations of up to 1.5 cm (Plate 5.3A). Mudcracks, sheet cracks and interstices between detached beds are in-filled with mud from overlying deposits, based on identical lithology and color. In core, detachment structures are accompanied with pebble lag deposits suggesting that erosional and subaerial exposure processes were concomitant. In one core there is a 25cm-thick interval of "crackle breccia" consisting of 1cm2 nodules of light brown dolomudstone surrounded by darker brown to grey dolomudstone (Plate 5.2C, D). The latter lithology resembles the dolomudstone-anhydrite interbeds from the underlying Lake Alma Anhydrite. The nodules are not transported rip-up clasts because they show no grading and can be fit back together without rotation. Therefore, they formed in-situ, either from extensive mudcracking or more likely from dissolution of anhydrite. This is a pseudo-breccia, a term given to breccias that have not been transported (Demicco and Hardie, 1994). 5.2.2 Grains Lithoclasts are the most prominent grain type found in the Lake Alma dolomudstone. They are composed of ripped-up lime- or dolomudstone and in concentrated numbers make up pebble-lag deposits. The best examples are sub-rounded to sub-angular, mm- to cm-sized clasts of dolomuds (Plate 5.3). These appear to be rip- ups of previously lithified mud from earlier-deposited beds based on like lithology and color. In thin section, a second type of clast was identified. They range in size from 0.1mm to 0.4mm, are subangular to subrounded, and often have a micritic envelope (Plate 5.4). They are either arranged in random order or in discrete lmm-thick intervals. They are also found interbedded with mudstone containing rare ostracodes. Some of these may be bioclasts. Bioclasts that are dispersed randomly in the matrix have brown to dark grey colours in PPL and show no extinction in XPL. These grains are often micritized. The origin of these grains is unclear, but they may be bioclasts extensively micritized by fungi, bacteria or microbes. Only one skeletal grain was observed in thin section. They are not well-preserved, having undergone partial to complete replacement as well as compaction producing an elliptical shape. They mostly resemble ostracodes. They are described in more detail in Facies 1, as they become more prominent. 5.2.3 Matrix The L.A. dolomudstone consists mainly of dolomicrite with rare dolospar. Bladed and equant calcite spar may contribute up to 1% where it cements the inside of ostracode shells. The matrix composes -90% of the facies; the rest is made up of clasts 7%, cements 2%, and ostracodes 1%. 50 5.2.4 Diagenesis Dolomite is the most prominent diagenetic mineral, comprising up to 100% of the matrix. Dolomite is almost entirely micrite-sized to cryptocrystalline. Generally, small dolomite crystal size indicates early diagenetic dolomitization, as opposed to late burial dolomitization (Ruzyla and Friedman, 1985). Several diagenetic structures, recognized in core and thin section, were described above. Other products of diagenesis include marine hardgrounds. Plate 5.4C shows a very sharp irregular surface consisting of dolomicrite overlain by an originally fenestral porous carbonate cemented with dolospar. A slight discoloration at the top of the hardground surface can also be seen. Fractures are very common throughout most cores. In the L.A. Dolomudstone, several unique fractures consist of finite, reverse-type micro-faults that have offset mud laminae (Figure 5.4). Reverse faults are typically indication of tectonic processes; however, the minute size and discontinuous nature of these fractures suggests another origin. It is proposed that soft-sediment slumping, followed by creep, could have rotated originally normal fractures to a reverse orientation (see Figure 5.4 for details). In thin section irregular fenestrae were identified. These are horizontal void spaces with no apparent support in the matrix (Demicco and Hardie, 1994). The fenestrae are filled by secondary dolospar cement, but because of their irregular shape, their true origin is unclear. 51 5.2.5 Lake Alma Dolomudstone Summary and Interpretation Fine-grained dolomudstones, exhibiting erosion, subaerial exposure, or a hiatus in deposition include structures such as 1) pseudo-breccia, 2) solution breccia 3) mudcracks and sheetcracks, 4) crinkled laminations, and 5) mud rip-ups are common diagenetic criteria for exposure (Shinn, 1983; Esteban and Klappa, 1983); mudcracks in particular, are the most useful structures for identifying exposed tidal flats (Demicco and Hardie, 1994). Pseudo-breccias and solution breccias are not the result of deep-marine slope and toe-slope environments where debris-flows might occur. The brecciation observed in this unit is due to exposure; beds can be fit back together and thus, are not the result of sediment or gravity transport. Ruzyla and Friedman (1985) identified solution breccia and wavy laminations in southern Montana, which they attributed to removal of anhydrite and gypsum in a supratidal environment. They also identified dessication cracks, truncation surfaces, and in situ dislocation of supratidal sediements. Porter and Fuller (1959) add that a number of mudcracks exist in the upper Red River Formation, which resulted from "intermittent subaerial exposure". Kendall (1976) proposed an erosional contact between the Lake Alma and the Coronach Members, based partly on the recognition of quartz grains. Some mud rip-ups probably represent "transgressive lags" where rip-up of older rock occurs during sea level rise of the next sedimentary cycle (Demicco and Hardie, 1994). Evidence for this includes 1) rip-ups found in nearly all cores and thus representing a regional event - not likely the result of localized hardgrounds, and 2) rip- ups are immediately overlain by sediments that represent deepening. 52 A reduction in exposure features to the southwest was evident, accompanied by a northeast increase in exposure "intensity", as judged by depth of diagenetic alteration and number of exposure-type features (Figure 5.5). This is an apparent indication that the southern study area may have remained inundated with hypersaline water, while the northern area was subaerially exposed for some length of time. Ruzyla and Friedman (1985) have described very similar features on the opposite of the Williston Basin in southern Montana; there may have been a peripheral belt of exposure encircling the basin center. The aforementioned features indicate these dolomudstones were probably deposited in a stressed mudflat environment before being exposed. Therefore, the dolomudstones represent maximum sea level drawdown, as overlying deposits from the Coronach Member signify deepening. For this reason, these dolomudstones are placed in the Lake Alma depositional sequence, as they may represent the updip, basin-periphery, time-correlative of the Lake Alma Anhydrite. A potential depositional model is depicted in Figure 5.6, which is similar to the model of Figure 5.3. The Lake Alma/Coronach contact is placed above these exposure features or, where absent, at the base of organic- rich calcimudstones of Facies 1 (discussed below). In summary, the Lake Alma dolomudstones were deposited in an evaporitic mud flat environment, which were then exposed during continued regression of the Lake Alma sequence. Exposure may have resulted in physical and diagenetic removal of some anhydrite. 53 IMVW-JL JiSfLIlS -560 Increasing exposure intensity" '860 % '863 Lake Alma 2 Limits 1 Un-exposed Lake Alma based on exposure indkEln SreC(pinS^)Udy '** ^ ^ diVid8d int° tW°re9lons bythe exposure limit line, Max Sea Level Fall High-tide line Hypersaline: Sub-tidal or Standing water Dolomudstone Basal Coronach Disconformity Basal Coronach Correlative Contact Alberta Saskatchewan Manitoba WilNston Basin WY 300 km 200 Ml Figure 5.6. Interpretation of the Lake Alma depositional sequence. Subaqueously- deposited anhydrites grade into supratidal mud flats with strong indications of exposure. Exposure indicates maximum sea level fall at this time. Therefore, the contact between dolomudstones and the overlying Coronach deposits is a disconformity surface. This surface becomes conformable deeper in the basin where the Coronach sediments sit atop the Lake Alma anhydrite. Inset shows location of profile. 55 5.3 Fades 1 The base of the Coronach Member is a variably laminated to bedded, argillaceous black calcimudstone or dolomudstone (Plate 5.5). It is 5-20cm thick and porosity is nil throughout. There are no hydrocarbon indicators in this facies. The change in lithology from the Lake Alma Member to Facies 1 of the Coronach Member is either gradational or sharp. 5.3.1 Structures Organic-rich laminites are common sedimentary structures in Facies 1. They most often occur directly overlying the lower Coronach Member contact and are very similar to "kukersites" identified in the upper 173rd of the Yeoman Formation by Osadetz and Snowdon (1995) and Haidl (1990). Kukersites are laminated bituminous lime mudstone composed of marine Gloeocapsomorpha prisca (G. prisca) alginite (Macauley et al. 1990). They may occur as laminae less than 1 mm thick or as distinct beds up to a few em's thick (Longman and Haidl, 1996). Planolites' burrows are common, having produced a number of small, 0.3-0.5cm diameter horizontal structures. They usually stand out clearly against the black color of this facies (Plate 5.5). Palaeophycus are lined burrows and are a minor trace-maker in Facies 1. Soft-sediment deformation features such as boudinage are also present (Plate 5.5B). 56 Plate 5.5. Laminated, organic-rich lime mudstones of Fades 1. A) Laminites are gradational from anhydrites below, but end abruptly before being overlain by normal marine rocks of Fades 3; 6-5-8-22W2, 2510.05m. Core is 9cm wide. B) Fades 1 includes sedimentary boudinage (sb). Below that is a zone of intense deformation related to advanced boudinage or possibly cryptalgal features; 14-26- 6-11W2, 2561.6 m. Core is 9cm wide. C) Thin, organic-rich laminae similar to kukersites of the Yeoman Formation; 6-5-8-22W2, 2508.4m. D) Planolites' burrows in an organic-rich bed, possibly a kukersite. Some burrows have linings, which is indicative of Palaeophycus burrows; 9-34-3-4W2, 2615.95m. 57 5.3.2 Grains Skeletal carbonate grains in Facies 1 are limited to bivalves (Class Pelecypoda, Subphylum Diasoma, Phylum Mollusca) and ostracodes (Superclass Crustacea, Phylum Arthropoda). Bivalves are articulate, have an elliptical shape, and show equal-sized valves. Internal structure is not preserved due to destruction by prismatic calcite. Some bivalves are completely leached; identification is only possible through recognition of the remnant elliptical-shape of the remaining internal cement (Plate 5.6B). Ostracodes are slightly less elliptical, but are distinguished from bivalves by having overlapping valves (Plate 5.6D). The internal structure was also not preserved in these skeletals. 5.3.3 Matrix Micrite and microspar dominate the matrix, while dolomicrite and dolomicropsar are the main subordinate components. The fine-grained matrix has very little porosity ( 5.3.4 Facies 1 Summary and Interpretation Facies 1 sharply overlies Lake Alma dolomudstones, or anhydrites if the former is not present. Minor concentrations of taxa including euryhaline ostracodes and possibly cryptalgal features suggest a stressed environment - either due to high salinities or low oxygen levels. However, there must have been enough circulation of bottom waters to allow for Planolites' burrowers to flourish. 58 200um 500um 200um Plate 5.6. Skeletals from Fades 1. A) An articulate bivalve on the left shows equal-valve size and an elliptical shape. The valves are replaced by bladed calcite cement, while calcite spar has filled the inside of the grain (all stained red). The bivalve on the right however, has dolomite rhombs within it (un-stained). This bivalve has been dolomitized because its shell has been breached. Dolomitization likely occurred after the void-filling calcite cement. The matrix is dominantly dolo-microspar with minor lime micrite to microspar; 13-23-6-11W2, 2589 m, XPL. B) This bivalve, from the same sample, has it's shell completely dissolved leaving only dolospar. Since the bivalve has retained it's shape, it implies dissolution occurred after or syngenetic with dolomite replacement. In both A and B, dolomitization mimics the precursor crystal size; Ibid., PPL. C) A bivalve replaced by dolo-microspar and in-filled with anhydrite cement; 8-16-2- 14W2, 3024.8 m, XPL. D) The internal cement of this ostracode is sparry calcite cement (stained with alizarin red-S) and dolo-spar, while the matrix is dolomicrite; 12-13-2-19W2, 2993.4 m, XPL. 59 Stasiuk and Osadetz (1989) indicate that kukersites from the Yeoman Formation are relegated to a deeper sub-basin during 'Yeoman' time (Figure 5.7). The sub-basin can also be identified by a Lake Alma Anhydrite thick (Figure 5.7). Kukersites were recognized at the base of the Coronach Member in ten cores. Their distribution is very nearly the same as the sub-basin postulated by Stasiuk and Osadetz (1989), indicating that this part of the proto-Williston Basin was an area of negative topography that extended into 'Coronach' time. G. prisca were probably photosynthetic and formed kukersites in anoxic yet photic subtidal settings (Stasiuk et al, 1991). Within the sub-basin, these planktonic algal blooms condensed and lithified into kukersites. Beyond the sub-basin, where shallower conditions prevailed, they were either not deposited or destroyed via bioturbation. Kukersites are important to note as they are potential hydrocarbon-generating source rocks. Facies 1 is interpreted as a time of deepening in the Williston Basin. Flooding may have caused rip-up clasts, which are found above the Lake Alma Anhydrite (Longman and Haidl, 1996; this study). The deposit marks the transition from the regressive Yeoman Formation and Lake Alma Member to initial transgression of the Coronach Member. The marine environment may have been stagnant at various stages resulting in highly-organic rich un-dolomitized deposition of calcimudstone. The low skeletal diversity indicates moderately stressed subtidal conditions. The presence of kukersites may also indicate shallow water conditions because they are composed of the photosynthesizing algae G. prisca (Stasiuk and Osadetz, 1989). e Coronach core Kukersites in Coronach core Q ( ^ Yeoman Sub- basin & -LLLLj_y L.l'i- (1989) and In the southwestern part of the study area Facies 1 oversteps Lake Alma dolomudstones and sits conformably on the Lake Alma Anhydrite. The boundary between the Lake Alma Anhydrite and the Coronach Member is considered a sequence boundary. 5.4 Facies 2 Facies 1 grades sharply into Facies 2: a thick, organic-rich, peloidal lime wackestone, with local packstones, grainstones, floatstones and rudstones. It grades upwards into bafflestones, boundstones and framestones. Facies 2 is always partially dolomitized at its top. A diverse faunal assemblage characterizes this facies. Red algae, green algae, brachiopods, crinoids, and stromatoporoids dominate the facies, but in addition are Ortonella, ostracodes, bivalves, tabulate colonial corals, bryozoans, cephalopods, benthic foraminifera, trilobites, and solitary corals. The vertical changes in faunal distribution create an ecological zonation that allows for a four-fold subdivision of this facies, which is developed further in section 5.4.5. The high percentage of silica cement is also a distinguishing feature of this facies. 5.4.1 Skeletal Grains In thin section Brachiopods (Phylum Brachiopoda; Plate 5.7A-C) are calcareous and have not undergone alteration other than rarely developed micritic crusts. They are usually found as fragments of valves with substantial lateral variations in thickness and with an internal fibrous structure that's oblique to an impunctate inner shell wall. Outer 62 Plate 5.7. Brachiopods & Crinoids. A) Fractured brachiopod fragment showing well- developed internal structure (inner shell wall (/) has oblique-oriented fibers and outer shell (o) has parallel-oriented fibers). Fracture cutting grain has been enlarged due to dissolution; 13-23-1-17W2, 3043.2m. B) Transverse cut through the brachial valve showing elliptical openings interpreted to be the "sockets" of an articulate brachiopod; 10-25-1-15W2, 3118.05 m. C) Valve with substantial crenulations and lateral thickness changes. Note fibrous internal structure oriented parallel to outer shell wall; 4-2-14-21W2 at 2109.6m. D) Crinoid grain showing "honeycomb" texture, which is only evident due to in-filling of micro-pores by micrite; 12-2-7-11W2, 2549.2m. E) Crinoidal grainstone with numerous circular, semi-circular and blocky ossicles, some exhibiting fragmentation; 2- 11-10-9W2, 2289.75m. F) Core sample of crinoid fragments; 2-11-10-9W2, depth 2289.75m. Scale bar in mm's. 63 shell walls, where preserved, have an internal fibrous structure that parallels the shell wall. Marked crenulations, due to development of exterior ribs, are also a common morphological trait in these valves (Plate 5.7C). One transverse cut through the brachial valve of a brachiopod, shows the sockets of the skeletal (Plate 5.7B); teeth and sockets are found only in articulate brachiopods (Clarkson, 1979). An excellent example of the morphology of these skeletals was found in a core sample where a bed of in situ brachiopods display an oval-shape with well-defined ribs and growth lines. Their morphology, calcareous mineralogy, teeth and socket articulation, and internal structure are common features of brachiopods in the Order Orthida, Class Rhynchonellata (Clarkson, 1979). Tate (2007) and Scholle and Ulmer-Scholle (2006) identified very similar-looking brachiopods as Platystrophia cypha species. Intact valves range in size from 3mm to 15mm in diameter. Fragments vary anywhere from 0.5mm to 12mm. They are common throughout the facies and make up on average 5-10% of the rock volume in thin section. Generally, brachiopod size increases upwards in core. Crinoids (Class Crinoidea, Phylum Echinodermata) are found as 0.5mm to 2mm disarticulated plates or ossicles (Plate 5.7D-F). Crinoids have an internal micro-structure of regularly arranged micro-pores. When these micropores are filled with cement or organic material, it gives the grains a "dusty" appearance in PPL. They are distinguished from other invertebrates mainly by their unit extinction, since each crinoid component acts like a single-crystal of calcite (Scholle and Ulmer-Scholle, 2006). Crinoids are composed of high-Mg calcite which makes them susceptible to alteration. They commonly exhibit diagenetic calcite alteration and partial replacement by silica. Many 64 crinoids also have syntaxial calcite cement overgrowths. Crinoids, like brachiopods, occur throughout Facies 2, and average about 5-10% in thin section. Bryozoans (Order Cryptostomida, Class Stenolaemata, Phylum Bryozoa), were identified in thin section and closely resemble Stictopora fenestrata (Scholle and Ulmer- Scholle, 2006). Bryozoans are colonial organisms whose morphologies vary; however, only branching forms were identified in Facies 2. Plate 5.8 shows the types of bryozoans with their common morphology and internal structure (see also Plate 5.15B for possible Cyclostome Bryozoan). Preservation of these skeletals is generally very high; however, branching bryozoans are fragile and break down easily. Most were recognized as fragments of the larger organism. One possible in situ branching bryozoan was observed in core attached to a hardground. Rapid sedimentation likely preserved this specimen. Coralline Red Algae (Family Solenoporaceae, Phylum Rhodophyta) were found mainly in the upper l/3ri of the facies as relatively complete encrusting or nodular masses (Plate 5.9 & Figure 5.8). They average 5cm across in thin section but can easily reach the maximum width of most cores (9cm). They occasionally dominate Facies 2, contributing up to 95% of some thin sections and core samples, but they typically average about 5- 30% in the upper 1/3"1 of Facies 2. Red algae are found encrusting hardgrounds, other skeletals, or even other red algae. The Solenoporaceae Family lack conceptacles and have elongate, divergent, radiating cellular fabrics that reveal polygonal geometries in transverse section (Riding, 1991). These specimens are likely Solenopra sp. as they also lack strongly-developed, horizontal partitions which are more common to Parachaetetes sp. (Johnson, 1961). The reticulate to elongate tubular internal structure is most commonly calcified. The tubular cavities however, are cemented by microspar, which in 65 Plate 5.8. Bryozoans of Fades 2. A) Caldfied bryozoan with characteristic "shreddies" morphology. From 13-23-1-17W2; 3043.1m. B) Bryozoan showing bilateral symmetry common to Stictopora fenestrata-, 10-25-1-15W2, 3119.6m. C) Well-preserved in situ organism with thick, dendritic branches that resembles a bryozoan. Grain is 2mm wide and attached to a marine hardground. Scale bar on left is in mm. From 3-6-6-6W2, depth 2559.3 m. 66 Plate 5.9. Red Algae. A) Nodular Solenopora sp. showing elongate, divergent, radiating cellular or tubular fabrics. The tubules have been filled by calcite microspar (stained red), while the walls are calcified. This calcareous algae has been partially replaced by the siliceous cement chalcedony (Si); from 12-13-2- 19W2, 2993.4m, PPL. B) Red algae showing both polygonal geometries in transverse section (lower half) and elongate tubules in longitudinal section (upper half). A dissolution seam separates the two structure types. Tubules are filled with microspar and walls composed of micrite; 10-25-1-15W2, 3118.05m, PPL. C) Bedding-parallel, encrusting Solenopora, with characteristic elongate tubules and partial replacement on outer edges by silica (Si) and pyrite (Py); 12-13-2-19W2; 2993.4m. D) Nodular, silicified red algae enhanced in core with an outline (in black). Evident even in core is the radiating tubular structure 13-23-1-17W2, 3043.2m. 67 Figure 5.8. Red Algae sketch. A) Core photo of oil-stained Solenopora Red Algae, with its corresponding trace on the right (B). In black is calcareous algae, which make up about 30% of this core sample. Grey circles are identified crinoid grains. White is mud matrix with un-differentiated skeletal fragments. Core is 7cm across; from 10-25-1-15W2, 3118.4m. C) Another core photo of calcareous algae with its tracing on the right (D). Algae make up about 35% of this core sample and varies from nodular to tabular encrusting forms. White is a wackestone to packstone lithology. From 6-5-6-19W2, 2711m. 68 turn may be partially replaced by chalcedony or dolomite. Original mineralogy of red algae is very high-Mg calcite (Scholle and Ulmer-Scholle, 2006), thus their preservation is likely due to early transformation to low-Mg calcite. Solenopora have created numerous "mottled" textures in core and is expanded upon in later section. Green Algae (Family Codiacea, Phylum Chlorophyta) are another dominant taxonomy in Facies 2 (Plate 5.10). They consist of poorly-preserved oval grains or plates that closely resemble Dimorphosiphon talbotorum, described by Boyd (2007) in Red River equivalent outcrops from Wyoming. Derby and Kilpatrick (1985) also identified these Codiacean algae exclusively in the Red River 'B', but nowhere else in the Red River. They perceive Dimorphosiphon as an "index fossil" for the Coronach Member. In Facies 2 Dimorphosiphon contribute up to 35% of the rock. They are composed of aragonite (Boyd, 2007) and therefore are rarely preserved. They have commonly been replaced by microspar or siliceous cement, whereas the tubes are filled with peloidal dolomicrite, dolo-microspar, microspar or siliceous cement (Plate 5.10). The cementation of tubes usually preserves the general morphology. The main keys to recognition include 1) oval to circular shapes when transversely cut, owing to a club-shaped thallus; 2) relatively large (100-300^im) circular, densely packed tubes within the medulla; and 3) radial tubes that penetrate and are perpendicular to the cortex (Boyd, 2007). A third type of "algae" identified in Facies 2 is Ortonella (Plate 5.11). This is a problematic taxa that has been assigned to microbial and green algal groups, but may be a diagenetic taxa (B. Pratt, pers. comm.). There is a strong relationship between presence of Ortonella and sparry calcite cement; the latter has probably cemented the rock before Ortonella break down. This has three major implications: 1) some parts of the Coronach 69 Plate 5.10. Dimorphosiphon green algae. A) Two examples of transverse cuts of Dimorph. The grain on the far left is replaced by microspar with the tubes filled or cemented by peloidal dolomite (Do). The skeletal on the right shows the same microspar (Mc) grain replacement, however the internal sediment within the tubes, as well as parts of the hard skeletal, have been replaced by chalcedony and mega-quartz (Si). From 12-13-2-19W2, 2993.4 m, PPL. B) Dimorph. from same sample as previous, showing partial or complete cementation of tubes by peloidal dolomicrite (unstained) and microspar (Mc). Microspar also replaces the skeletal; PPL. C) Two transverse, and one longitudinal, sections of Dimorph. (outlined in white dashed lines) in a peloidal-algal grainstone. Tubules are faintly present in transverse cuts, but more apparent in longitudinal section. D) Core sample showing a bed of upright Dimorph., some attached to a surface and thus in situ. From 16-23-2-1W2, 2525m. Scale in mm. 70 Plate 5.11. Ortoriella. A) In center of photo is a elliptical grain with densely packed thin, straight to slightly curved "tubes". Between tubules is micritic material. Size, shape and internal features are similar to Ortonella, a Codiacean Green algae. The surrounding matrix is comprised of marine calcite spar, likely due to exceptionally high rates of marine cementation. From 6-5-6-19W2, depth 2714 m. B) Nodular, radiating growth form of Ortonella; 6-5-6-19W2, 2714 m. C) Ortonella showing fine tubules. Between them the grain is composed of dark micrite and peloids. Preservation is again attested to rapid calcite spar cementation. This sample has high vuggy porosity (0), as indicated by the white patches of balsam and air bubbles. From 6-5-8-22W2, 2504.6m. D) Out-lined in white are two possible Ortonella specimens. The upper one has an encrusting habit. No tubules are preserved, showing the full spectrum of poorly-preserved Ortonella to well- developed ('B'). From 6-5-6-19W2, 2714m. 71 Member had exceptionally high rates of marine cementation; 2) Ortonella in sufficiently high numbers may have created boundstones, possibly also with framework structures; and 3) Ortonella may have been ubiquitous in Facies 2, but were not preserved unless calcite cement precipitated early. Ortonella are distinguished from Dimorphosiphon and Solenopora by having more slender, straight to slightly undulating tubes (Johnson, 1961) with consistent diameters of 50-100|im. The "identifiable" specimens were found in the lower half of Facies 2 and average 2mm in size. They typically form nodular masses or small rounded nodules (Johnson, 1961). In core they appear to take on encrusting forms. In thin section they may comprise up to 45% of the rock. Two classes of Molluscs are present in cores and thin sections. Bivalves (Class Pelecypoda, Subphylum Diasoma, Phylum Mollusca) lack crenulations and have thinner and smoother valves relative to brachiopods (Plate 5.12A). They are usually found as single shells or fragments, but articulate specimens have an elliptical shape and equal- valve size that aids in their identification. The valves are composed of neomorphic calcite cement (almost always microspar) with rare preservation of primary structure; likely because the original mineralogy is aragonite. One sample though, shows a prismatic internal structure oriented perpendicular to the shell wall. In thin section there are many unknown thin fossil fragments (range 5-50%; average 15% of the rock) that are likely a combination of Mollusc and bryozoan fragments. Bivalve fragments range in size from 0.5 to 2.5mm and whole specimens are 0.75 to 4mm. They average less than 5% of samples, and are found randomly throughout Facies 2. 72 Plate 5.12. Molluscs. A) Bivalve with characteristic thin-shell walls showing rarely preserved internal structure with fibrous crystals oriented perpendicular to the valve walls. From 10-25-1-15W2, 3119.6m. B) Cephalopod showing individual chambers. The skeletal has been replaced by microspar. From 13-23-1-17W2, 3043.1m. C) Example of a Nautiloid (Class Cephalopoda) in core showing individual body whorls filled by anhydrite; 13-23-6-11W2, 2586.4m. Core is 9cm across. 73 Other molluscs include Cephalopods (Class Cepholopoda, Subphylum Cyrtosoma). These were identified only in the uppermost part of the facies (Plate 5.12B). Preservation is rare and usually only occurs through replacement of the originally aragonitic grains. No internal structures are preserved, so identification is based solely on shape. One Nautiloid (Subclass Nautiloidea, Class Cepholopoda) was recognized in core (Plate 5.12C). Anhydrite has filled its "body whorls". Although generally minor contributors to Facies 2 (~1%), one thin section did have up to 5% cephalopods; abundance may have been much higher but poor preservation reduces the ability to establish true concentrations. Cephalopods range in size from 0.25 mm up to 7 cm. A few macro-fossils were also recognized in core samples. Tabulate to semi- hemispherical stromatoporoids (Class Stromatoporoida, Phylum Porifera) are the most prevalent (Plate 5.13). They have encrusting habits and are well preserved because of a stable, calcite mineralogy. They are predominantly found in the lower half of Facies 2, range from 6-10cm long, average 1cm thick, and constitute up to 20% of the lower portion of Facies 2. Tabulate colonial corals (Order Tabulata, Subclass Zoantharia, Class Anthozoa, Phylum Cnidaria), average 4cm x 5cm and are limited to three or four specimens in the upper part of the facies (Plate 5.14). They are well preserved due to a low Mg-calcite mineralogy. The corallites are either void (moldic porosity) or cemented by micritic mud or white calcite. One type of tabulate coral has distinct tabulae that extend across the corallum, while the corallites are packed closely together (Plate 5.14A). However, no transverse cuts reveal the geometric shape of the corallites. Thus, the colonial form of 74 Mamelons A Plate 5.13. Stromatoporoids. Both photographs show stromatoporoids with tabulate to semi-hemispheroidal morphology, sometimes with significant relief as in lower 'B'. In 'A' on the lower right, and in the middle of 'B', are multiple generations of encrusting stromatoporoids. Horizontal laminae and mamelons (circled) are apparent from the stromatoporoid in the middle of 'A'. Cores from 8- 16-2-14W2, 3020.5 m (A) and 13-23-1-17W2, 3044.7m (B). Scales in em's. 75 500um Plate 5.14. Corals. (A) arid (B) show tabulate colonial corals with well-developed horizontal partitions that extend across the coralline, indicating they are cerioid Favosites; from 13-23-1-17W2, 3043.1m and 10-25-1-15W2, 3118 m, respectively. Scale bar in em's. C) A transverse cut through a tabulate coral showing elliptical corallites joined end to end identifying this specimen as a cateniform Halysites; 3-16-2-10W2, 3010.9 m. Scale bar in em's. D) Transverse cut through a Rugose coral (Rg). Partially preserved are the radially-symmetric septa; 4-2-14-21W2, 6921.5ft. 76 these tabulate corals is somewhat speculative, but the features described above are common to cerioid forms of Favosites (Suborder Favositina; Clarkson, 1979). A second type of tabulate coral was recognized in core (5.14C). A transverse cut shows its' corallites are elliptical and join end to end, a feature associated with cateniform colonials. This morphology is indicative of Halysites' corals (Suborder Halysitina). Just two solitary Rugose corals (Order Rugosa, Subclass Zoantharia, Class Anthozoa, Phylum Cnidaria) were identified from core and thin section in the lower half of the facies (Plate 5.14D). Other, more minor constituents identified from thin section include Arthropods and benthic Foraminifera (Plate 5.15). The Arthropods (Phylum Arthropoda) include Ostracodes (Class Ostracoda, Superclass Crustacea), which have thick-walled overlapping valves (Plate 5.15A, B) and Trilobites (Superclass Trilobitomorpha), which were identified as having characteristic "hook" shapes (Plate 5.15C) or by sweeping extinction of the thoracic segments (sclerites) under XPL. Very few specimens of Trilobites were positively identified, but those that were are located in the middle of Facies 2. They range in size from 2mm to 6mm. Ostracodes have a higher abundance (average 3%, maximum 15%) and were found dominantly at the top of Facies 2. Both arthropod classes usually do not have a preserved internal structure, but one Trilobite does shows very fine microcrystalline fibers. Ostracodes are ovoid in shape with paired, smooth valves. They are very small, ranging from 0.3mm to 1mm. Intact ostracodes are usually filled with sparry calcite cement. Some specimens have bladed cement growing on the interior of the valves. 77 Plate 5.15. Arthropods and Foraminifera. A) An ostracode with characteristic overlapping valves. Grain is filled by single calcite spar in middle of photo; 13-23- 6-11W2, 2586.75 m. B) Several oval-shaped ostracodes just below a bryozoan fragment. Bryozoan has thin internal wall structure that has been cemented with calcite. The zooecia have blocky shapes and thin walls (but cemented with calcite overgrowths), which suggests it may be a Cyclostome\ 13-23-1-17W2 3043.2m. C) Characteristic hook-shape of a trilobite grain; 13-23-6-11W2, 2586.75 m. D) benthic Foraminifera showing multiiocular test morphology, possibly planispiral. The grain has thick micritic walls; 16-23-2-1W2, 2524.6 m. 78 Benthic Foraminifera (Order Foraminiferida, Phylum Sarcomastigophora, Kingdom Protista) are unicellular protozoans (Jones, 1996) that exhibit a multilocular (multiple-chambered) test morphology (Plate 5.15D). However, the lack of specimens prohibits further subdivision based on the arrangement of chambers. Internal wall structure also was not identified. Forams were only found in a well-cemented bed, possibly hardground, near the top of the facies. They average 0.25mm in size. 5.4.2 Non-Skeletal Grains Peloids are the only non-skeletal grain in Facies 2 and are locally abundant (Plate 5.16). Peloid is a "term of ignorance" describing any grain lacking internal structure (Scholle and Ulmer-Scholle, 2006). Specifically, they are polygenetic allochems composed of 1) cryptocrystalline or microcrystalline carbonate, or 2) precipitated calcium carbonate (Scholle and Ulmer-Scholle, 2006). The former may be derived from faecal pellets, calcareous algae, micritized allochems or reworked mud clasts (Tucker and Wright, 1990). Recognition and distinction between peloidal types is often very difficult to establish (Maclntyre, 1985). In Facies 2, some peloids are more circular and appear to be clotted, or structure grumeleuse of Bathurst (1971). They commonly line the interior of skeletal cavities or are associated with sparry calcite cement (Plate 5.16A, B). This type of peloid, though rare in Facies 2, is believed to be cement and is described in more detail in Chapter 6 on diagenesis. Other samples show packstones and grainstones of elliptical-shaped peloids (Plate 5.16C, D). These constitute up to 50% of some samples, yet only average 8% of the 79 . :t Calcite . Spar 1 *#? / Clotted Ortone a Peloids oOOum 375pm Burrow Skeletals/ Peloids Burrow 375pm n 375um Plate 5.16. Peloids. (A) & (B) show examples of cement-type peloids and (C) & (D) are allochem peloids. In (A) peloids occur with sparry calcite lining inside of brachiopod valves. The peloids are of consistent size, circular in shape and mainly restricted to the inside of the shells. Taken together these features suggest they are a precipitate, otherwise they would preferentially accumulate only on the gravitational side of the brachiopod (Maclntyre, 1985). From 13-23-6-11W2, 2586.75 m. B) A group of clotted peloids in sparry calcite cementstone. The clotted geometries and association with calcite spar suggests these peloids may be a cementation product. No micritic mud was observed in this sample. From 6- 5-6-19W2, 2714m. C) Oval- to elliptical-peloids in this photo have been pushed aside, or excavated, by the action of burrowers; no peloids are found within the burrows. These are actual "grains", either micritized skeletal fragments or pellets. Peloids of this type are the majority in Fades 2. From 12-2-7-11W2, 2550m. D) Oval- to elliptical-shaped peloids make up 70% of the matrix. From same sample as previous. 80 matrix in Facies 2. Given the high number of organisms present in Facies 2, it is likely that most matrix peloids are faecal in origin. In bioturbated samples they are concentrated between burrows, possibly due to excavation during the burrowing process (Plate 5.16C). Thus, these peloids were not cemented, but rather lying loosely on or below the sediment floor prior to being excavated. Furthermore, allochthonous peloidal grainstones are found on the tidal flats of the overlying facies. These peloids must have been transported onto tidal flats by waves or tides. Transportation of peloidal cement on the other hand is not possible. 5.4.3 Primary Structures Planolites' burrows were identified in core and thin section based on similar observations by Pak and Pemberton (2003) for the Yeoman Formation. Kendall (1976, 1977) described ubiquitous Thalassinoides burrows throughout the Yeoman Formation; however, none were recognized here suggesting a unique environmental control for the Coronach Member. A hard substrate, including hardgrounds and numerous skeletal- dominated rocks may have inhibited these burrowers from establishing themselves. Diagenesis has complicated identification, as burrows and matrix may be dolomitized, destroying key fabrics such as the nature of burrow-fill and burrow-lining. Therefore, the following descriptions based chiefly on morphology. Planolites' traces dominate certain sections of Facies 2, particularly the top (Plate 5.17). In two dimensions they range in size from 3.5mm by 2mm to 10mm by 3mm. They are usually selectively dolomitized and surrounded by un-dolomitized matrix. They are circular to ovoid in cross section and are elongate in profile up to 1cm. The main 81 1 Top mm scale B Dolomitized burrows Un-dolomitized Burrows Peloids Dolomitized Anhydrite-lined burrows fracture Plate 5.17. Burrows. A) Planolites' burrows in light tan set against a slightly darker tan-coloured dolostone, showing circular cross sections and horizontal to sub- vertical, elongate transverse sections. Entire rock is dolomitized. From 15-28-12- 2W2, 1911.6m. B) Rare, Y-branched Planolites. However, without a three- dimensional view, they may be interpenetrating burrows; 11-20-2-18W2, 2993.9m. C) A scanned thin section showing selective dolomitization of the centers of burrows but in some cases not their edges. This may indicate multiple-burrow stages, whereby dolomitization has been mediated by the 2nd-generation burrow. Un-dolomitized burrows are composed of very clean micritic mud except for larger allochems such as crinoids. The matrix consists of excavated peloidal grainstones. From 12-2-7-11W2, 2550m. 82 distinguishing qualities of this ichnogenera is an unlined burrow with structure-less fill that is different from that of the host rock (Pemberton et al., 1998). They have a very specific distribution, occurring at the extreme basal and top parts of this facies. Both of these sections are muddier and more organic-rich than the rest of Facies 2. Planolites are always dolomitized, markedly contrasting the usually dark-coloured lime matrix (Plate 5.17C). However, at the top of the facies where dolomitization of the matrix is more common, identification of the burrows is more difficult (Plate 5.17A). Other, less abundant, primary sedimentary structures include geopetals. Geopetals are produced by shelled skeletals partially-filled by mud followed by cementation of the remaining void space. Though uncommon, they make for good orientation indicators, in the absence of bedding. Normal, graded-bedding generally is not preserved in core, but can be assumed based on orientation of skeletal beds and geopetals. 5.4.4 Matrix The matrix is fine-grained and consists on average: 80% micrite (or microcrystalline calcite), 8% peloids, and 12% microspar. Relative to all constituents (matrix, grains, cement, porosity), micrite (and dolomcicrite) account for an average of 28%, 18% and 41% of the lower, middle and upper portion of Facies 2, respectively. Cements are relatively rare. Although most samples are mud-supported, grainstones, packstones, and biologically-produced rudstones, framestones and rare bafflestones also exist in significant number. The high skeletal diversity suggests the majority of the matrix is primarily from skeletal breakdown, as opposed to direct precipitation from seawater. 83 Some of the matrix is composed of organic-rich material. Samples that have not been significantly altered by diagenesis are dark grey to black or rich brownish-grey in color. They often give off a petroliferous odour upon sanding of the core samples. The presence of diagenetic dolomite is concurrent with an absence of organics (possibly due to chemical dissolution of the latter). A dolomite-dominated matrix gives the rock a light to medium brown color. 5.4.5 Fades 2 Summary and Interpretation Facies 2 consist of 1) a lime matrix formed in situ from carbonate mud, probably derived from the breakdown of organisms, and 2) skeletals and algae that increase upward in diversity, concentration and sometimes size. As important as structures and textures are to the interpretation of Facies 1, taxonomic stratigraphy is to Facies 2. Fourteen biota (whole or fragments) were identified, as well as one ichnotaxa. The abundance, form, and diversity of autochthonous skeletal types can give clues to the water depth, salinity, turbidity, water clarity and firmness of the substrate at the time of sedimentation (Heckel, 1972; Figure 5.9). The dominant or distinguishing skeletal distribution(s) were also used to subdivide the facies into four sub-facies. Table 5.3 shows the diversity, distribution, and relative abundance of taxonomies identified through all facies examined in this study. The lower 173rd of the facies is primarily cherty calcitic wackestones (Sub-Facies 2A). Sub-facies 2A contains mainly the skeletals brachiopods and crinoids. The characterizing feature however, is the presence of beige and dark brown chert nodules. Chert is a siliceous rock that is likely biogenically sourced (discussed in Chapter 6). B rmkm Tnmibonal i HypenOni FRESH WATER „20 R«#icl»dMam 30 40 Marm SO 60 SUPRATIDAL INTERTIDAL Red Algae SUBTIDAL Green Algae Cyanobacteria Radiolarians Coccollths Diatoms 60 FT Calc. Foram. Agglutinated Foram. Demosponges Corals Calc. Worm Tubes BOO FT Bryozoans Brachiopods Echinoderms Cephalopods Pelecypods Gastropods Ostra codes Substrate | Soft | Mobile Clear Water | Increasing Turbidity Rapid Deposition Mode of Life Cemented Rooted Reclining Buried & Burrowing^ Suspension Feeders •4 Crawling Dominant Deposit Feeders - Feeding Type Carnivores. Scavengeis Red Algae Green Algae Red Algae Cyanobacteria Green Algae Foraminifera Cyanobacteria Sponges Foraminifera Solitary Corals Sponges Colonial Corals Corals Calc. Worm Tubes Calc. Worm Tubes Bryozoans Bryozoans Brachiopods Brachiopods Echinoderms Echinodeims Pelecypods Pelecypods Gastropods Gastropods Ostracodes Ostracodes Barnacles Bamades Other crustaceans Other crustaceans Figure 5.9. Modern skeletal distributions and their relationship to depth (A), salinity (B), substrate stability (C) and sedimentation rate (D). Modified from Heckel (1972). SkBtotal* as an Mtknatad * of total rock voluma | >10% 5-10% Facies I <5% Rare 4-5 T •T*!+' -CL 1. t I CD O CD 0 V) gj O 73 CO O u 3. 5 "O <" CD Q> c CO 0 3 5- CD 3 3 Q. O "D cr CQ 3 «-* 0) o O 3" 3 © O- 3 3 sr o O N zr c o 0) o 2* > CQ < CO 3 0 CD Qu O ICD CD cd Jtt o 1 CO o' CL CD CD 0) CO CO fi) 1 0) o o CD 3 T3 03 s- <0 CD o Q. CO IF 3 qT •o CO O CD CO o o *o CD Table 5.3, Skeletal, grain and ichnotaxa distribution and abundance in the Coronach Member. Percentages based on thin section and core observations. Sponges are common sources of biogenic silica (Clarkson, 1979) and were important reef-builders during the Ordovician (Rigby, 1971). These rocks grade upwards into Algal-Stromatoporoid biostromes (Sub-facies 2B), which exhibit a distinct vertical ecological zonation. They can be sub-divided into 1) lower Stromatoporoid rudstones to boundstones, 2) middle calcitic green algal (Dimorphosiphon) floatstones and rare bafflestones, and 3) upper dolomitic red algal (iSolertopora) framestones and boundstones. Hemi-spherical to tabular stromatoporoids are found in well-oxygenated, clear waters, but energy levels are not as easy to gauge; they can be found in a variety of energy level settings from fore-reef to inter-reef to back-reef settings (Scholle and Ulmer- Scholle, 2006). In Ordovician to Devonian they were important reef builders (Clarkson, 1979). Dimorphosiphon green algae are a relative of the modem Halimeda (Riding, 1991). Growth of delicate branching taxonomies such as these implies the substrate was firm, while energy remained relatively low (see Figure 5.9). Riding (1991) adds that Recent examples of green algae occupy shallow, tropical to subtropical waters with low to moderate energy and must have remained in the photic zone. In addition, green algae are likely a major contributor to carbonate production upon death (Neumann and Land, 1975). Red Algae became abundant in the Ordovician (Figure 5.10) where they were capable of reef-building (Pitcher, 1964; Wray, 1971). Their encrusting habits are typical of moderate to high energy waters with firm to hard substrates (see Figure 5.9). Red 87 CHLOROPHYTA RHOOOPHYTA |f«i al|it rri «l|>a CENOZOIC cirlllmai CRETACEOUS JURASSIC TRIASSIC PERMIAN CARBONIFEROUS DEVONIAN SILURIAN ORDOVICIAN CAMBRIAN Figure 5.10. Distribution of calcareous algae through time. Highlighted is Late Ordovician showing relative abundance of Solenopores (Red Algae), green algae and blue-green algae (now termed cyanobacteria). From Wray (1971). CYCLE II CYCLE I :maeocyathans Figure 5.11. Reef organisms through time. Late Ordovician reefs are characterized by calcareous algae, sponges, bryozoans, corals and stromatoporoids. Only sponges were not identified in the Coronach Member. From James (1983). 88 Algae tend to flourish in very shallow water, typically less than 25m (Wilson, 1975), where waters are warm and clear (Johnson, 1961). Sub-facies 2B is found in nearly every core (80% of all logged) and always shows the aforementioned vertical ecological zonation. Stromatoporoids and calcareous algae were all common reef-builders in the Mid-Ordovician through Devonian (Figure 5.11; James, 1983; James and Maclntyre, 1985; St. Jean, 1971). Calcareous red algae, in particular, were the principal contributors to Ordovician reefs (Wray, 1971). It is apparent from core and thin section study that these reef-building organisms were present in significant number in the 'Coronach' sea, and had been constructing build-ups elsewhere at least since the Mid-Ordovician. Stromatoporoid-Red Algal assemblages have been described in Mid-Ordovician reefs from outcrops at Isle LaMotte in Vermont (Pitcher, 1964; 1971). Furthermore, in the Williston Basin a stromatoporoidal biostrome was identified by Pratt et al. (1996) from the Yeoman Formation. The build-ups of the Coronach Member started with basal Stromatoporoids that probably acted as both binders and framers, helping to stabilize the seafloor. It is not clear how they established themselves, but frequent marine hardgrounds and other skeletals may have provided the hard substrate or material for encrustation. Stabilization of the sea floor helped the colonization of numerous erect, branching green algae (Dimorphosiphon). They likely acted as baffles trapping micritic mud, which constitutes the majority of the matrix of the entire facies. Diversification increased with the appearance of minor taxa, including in-situ tabulate colonial corals such as Favosites. They acted as frame-builders providing some rigidity to the overall build-up. Encrusting forms of Solenopora dominate the crests of build-ups and acted to bind and cement mud 89 and biotic debris together; a similar process in many modern forms of reefs (Wray, 1971). The zonation from stromatoporoids to encrusting red algae is evidence for shallowing-up under conditions of static or falling sea level (Pratt, 1995). Allochthonous crinoids, ostracodes, bryozoans are the major contributors to off- reef, open shelf areas and were washed into interstices of the build-ups. Upon death, they likely aided in the encrustation by Solenopora. Brachiopods and trilobites on the other hand may have lived within the interstices of the build-up. Figure 5.12 is a sketch of the vertical zonation and major contributors that constitute these micro-environments. Plate 5.18 shows core examples of reef mound-type facies (see also Plates 6.5,6.8, and 6.10). The vertical ecological zonation described above is a succession commonly observed in the construction of modern reefs and mounds (James and Maclntyre, 1985). Figure 5.13 shows the four stages of reef growth of which Sub-facies 2B shows elements of all. Classifying these constructs beyond the general term build-up is difficult. They may not have a modern counterpart since today's reefs are subjected to high-energies of the open ocean, while many ancient reefs are formed in relatively quiet intracratonic basins (Heckel, 1972). Secondly, current classifications (James and Bourque, 1992; James and Maclntyre, 1985; Wright and Burchette, 1996) are conceptual and do not take into account specific assemblages or concentrations. Figure 5.14 is one such classification and shows the subjectivity of defining Sub-facies 2B. The terms 'reef or 'reef mound' are only applied if two general conditions are met: 1) they are biologically produced and 2) they possess some topographic relief (Tucker and Wright, 1990). These constructs are clearly biological in origin, but the latter 90 Biostrome Crinoidal/Bryz Flanking ^ Packstones Dimoi phosiphun Solenopo Figure 5.12. Sketch of Fades 2B showing ecological vertical zonation of major and minor constituents. Basal reef mounds begin with seafloor-stabalizing Stromatoporoids, which grade upwards into Dimophosiphon bafflestones, before being dominated by Solenopra framestones. Crinoids and Brachiopods provide flanking or capping packstones and grainstones. Corals added rigidity to the overall build-up and Ortonella may have also contributed boundstones to the overall build-up. Packstone/ Skeletal and pc(oidal(?) Floatstone Grainstono #r Packstone/ Ofmorphosiphvn Rtidstone Floatstone StromatoporoW t3oundstons'* Plate 5.18. Biostrome examples. A) Grainstones, rudstones and boundstones from 11-20-2-18W2, 2996.85m. B) Red Algae (Solenopora boundstones) inter-bedded with packstones and floatstones; Ibid., 2994.4m. Photos (C) & (D) are two examples of unknown mottling that does not appear to be burrow related, based on the large, highly irregular shapes. These are morphologically similar to Solenopora, however other possibilities might include i nfi 11ed-cavities or microbial encrustations. (C)from 3-6-2-10W2; 3007.25m. (D)from 10-25-1-15W2, 3119.4m. All scale bars in em's. 92 Facies 2B STRUCTURE STAGE LIMESTONE DIVERSITY SHAPE Representative Domination Bindstone Low Laminate Solenopora Framestone Encrusting Boundstones REEF Climax < Domal Massive ^ Framestone Diversification High Lamellar X . Bindstone Branching Encrusting Corals + Dimorphoslpon Bafflestone Branching Colonization Low Bafflestones Floatstone Lamellar MOUND Pioneer Stromatoporoid Grainstone Stabilization Low Skeletal Framestones/ Debris Rudstone Rudstones Figure 5.13. Sketch of the four stages of core facies generated by ecological succession of reef builders. Build-ups from the Coronach display elements of all four stages (listed on right), though somewhat less of the Diversification stage. Modified from James and Bourque (1992). 93 Skeletal Metazoan Reefs Reef Mounds Microbial Mud Buildups Mounds Calcified Small Algae Skeletal Laminated Thrombolite Mud Sponge Stromatolite Figure 5.14. Conceptual classification of reefs and mounds. Classification is divided by skeletal, mud or microbial dominant constituents. Hypothetical example shows possible evolutional path taken by Fades 2B. Basal Fades 2B begins in the mud dominated triangle (Point X) but evolves to calcified algal reef mounds (Point Y). A dominance by wave-resistant Red Algae implies rigidity and an in-situ framework - both criteria of reefs (Point Z). Dynamics of reefs tends to blur the lines between reefs and reef mounds. Individual build-ups may take several different paths and end in various positions in the classification depending on ever-fuctuating mud, skeletal and algal percentages. Modified from James and Maclntyre (1985). 94 is more difficult to prove. An isopach of Facies 2 (Figure 5.15) does not reveal isolated thicks. Possible reasons are 1) they are very low-relief structures due to biological or hydrodynamic constraints, or 2) accommodation space restricted the height at which reef mounds could aggrade. Based on the observations in core and from mapping, topographic-relief should not be a necessary component for classification of reef-like build-ups if it can be shown that accommodation space was a limiting factor. Bedded carbonate build-ups without relief are termed 'biostromes' (Wilson, 1975) and is probably the best classification for Sub-facies 2B. The upper !4 of Facies 2 consists of alternating crinoidal grainstones (Sub-facies 2C) and peloidal, calcitic to dolomitized mudstones and wackestones (Sub-facies 2D). Sub-facies 2C was recognized in 25% of all cores logged and averages 5cm in thickness. It may be found sharply overlying Sub-facies 2B or 2D and occasionally in Facies 3. These grainstones may have been deposited on the flanks or tops of biostromes where accommodation space was low and wave energy was at its highest. When they are found associated with Facies 3, they probably represent storm deposits. The paucity of Sub-facies 2C suggests high-energy conditions were not the norm during 'Coronach' time. Sub-facies 2D was identified in 75% of logged cores. It is skeletal-deficient and has a high concentration of peloids and Planolites' traces relative to the rest of Facies 2. Skeletals are limited to mainly ostracodes and molluscs. A low diversity may suggest salinity was slightly higher (penesaline) relative to the rest of Facies 2. This allowed preservation of organic-matter while limiting skeletals to those such as euryhaline ostracodes. inw;» o>to Increased salinity is likely a function of restriction. Extreme shallowing may have provided barriers to current and wave circulation. Peloids are common in modem reduced-energy settings such as lagoons in Turks and Caicos, British West Indies (Wanless and Dravis, 2008). Organic content of Facies 2 is moderate to high, which lends the rock a rich dark brown color; accompanying this is a light petroliferous odour upon sanding. Porosity is generally low due to cementation by silica, anhydrite, calcite and sometimes dolomite, but several samples that were dolomitized or leached have patchily-developed intercrystalline, vuggy or moldic porosity up to a maximum of 8%, based on petrographic estimates. The best developed porosity is directly related to dolomitization; however, permeability is usually very low at less than ImD based on core analysis. Porosity may also be very low because of dewatering of the mud-dominated matrices (Harris et al., 1985). Trace fossils are common throughout Facies 2 but none were recognized in Sub- facies 2B. The sediment in the latter may have been too firm for burrowing activity. Other possible reasons for lack of burrowing are the inferred high sedimentation rates (discussed below) and the high competition for space in the substrate from skeletal organisms. It is reasonable to assume that these same factors have adversely affected Thallassinoides, which are ubiquitous in the Yeoman Formation (Kendall, 1977), yet absent in the Coronach Member. Figure 5.9 also shows that the skeletals of Facies 2 represent deposition in 1) shallow to very shallow water; 2) good clarity, particularly for corals and Solenopora; 3) relatively normal salinity (30 - 40 ppt) with slightly higher values in Sub-facies D; 4) a 97 firm to hard substrate that allowed for branching Bryozoans and Dimorphosiphon and encrusting Solenopora to flourish, while inhibiting trace-makers such as Thalassinoides; and 5) low to moderate turbulence, supported by absence of ooids and marine cement but high percentages of micritic mud and peloids. Minor exceptions to these overall generalizations include a softer substrate for Sub-facies D, which allowed for burrowing. 5.5 Facies 2 Upper Contact The contact between Facies 2 and 3 may be disconformable or conformable (Plate 5.19). Possible indications of a disconformity include irregular and sharp contacts, changes in bed-angle dip, and brecciation. Evidence for a conformable contact include: 1) facies' transitions without alteration of the underlying rock, and 2) rare gradational transitions between Facies. 5.6 Facies 3 This facies has two distinct rock types, but is characterized by laminations throughout. The lower l/3rd of the facies (Sub-facies 3A) is a black-coloured, organic- rich calcimudstone with variable percentages of dolomite from 25 to 95% (Plate 5.20). Laminae are fine, planar and usually horizontal, though 15° dips are present (Plate 5.19). It ranges in thickness from 10cm to lm, averages 82cm, and is missing in 23% of the studied cores. The upper 2/3rds of the facies (Sub-facies 3B) sharply overlies Sub-facies 3A. The former is characterized by sub-horizontal laminites of probable stromatolitic origins. This sub-facies is always dolomitized and laminar, although laminae grade upwards from 1) 98 t Base Top Facies 3 Mottles Top Facies 2 i J ' S Top Facies 2 A Plate 5.19. Facies 2/3 contact. A) Contact between facies marked by an upward change in color, from dark brown to light brown; mineralogy, from limestone to dolomite; and structure, from massive to laminated and bedded. An in situ brecciated zone with tabular, inclined clasts denotes slumping. From 3-6-2-10W2, 3006.25m. Core is 9cm across. B) Top of Facies 2 marked by sharp, irregular contact. Below contact in Facies 2 are small laminar labechiid stromatoporoids ('S'; Brian Pratt, pers. comm.) and mottled texture - likely algal in origin - although smaller circular mottles could be Planolites burrows. Contact is overlain by cross- laminated mudstone. From 8-16-2-14W2, 3019 m. Scale bar in em's. C) Sharp, irregular contact (white arrow) at top Facies 2. From 6-5-6-19W2, 2709.8 m. Core is 9cm across. 99 Plate 5.20. Fades 3A laminations. A) Characteristic laminations from Facies 3A showing planar to sub-planar laminations. Facies is dark grey to black and organic-rich. Some laminations are lens-shaped and interpreted as starved- ripples (outlined in white). From 13-23-1-17W2, top of core at 3042.1m, scale in em's. B) Lenticular bedding of Facies 3A showing points of pinchout (white arrows). These are interpreted as starved ripples. From 12-13-2-19W2, 2993.05m. 100 disrupted, possibly brecciated, to 2) crinkled, wispy and domal, to 3) smooth, sub- horizontal. It ranges in thickness from 45cm to 2.6m and averages 1.36m. Laminations are absent in three of the most northern studied cores. No skeletals or burrows were identified in Facies 3. Peloids are the dominant grain in Sub-facies 3B but none were observed in Sub-facies 3A. 9 5.6.1 Primary Structures Sub-facies 3A is characterized by alternating very fine (0.1mm) and thick (0.5- 2mm) laminations. Most laminations are horizontal and planar; although in a few cores rare beds are discontinuous and lens-shaped. These are interpreted as starved-ripples (Plate 5.20). Starved ripples are few in number and generally thin ( 20° cross-bedding at the base of the facies (Plate 5.19B). Sub-facies 3B has three different textures based on the structure of the laminae. In order from base to top they are: 1) discontinuous or disrupted laminations; 2) irregular or "wispy", sub-horizontal to sub-vertical laminations, laterally continuous, and in some cases domal in nature; and 3) smooth continuous, horizontal to sub-horizontal laminations (Plate 5.21). This succession was fully developed in 6 of 15 cores. Laminations of Sub-facies 3B consist of couplets of very thin argillaceous dolomite and peloidal sediment of variable thickness (Figure 5.16). Fine laminations are usually contorted and yet intervening peloidal sediment has not slumped or filled pits or localized lows. Rather, sediments appear to taper-off on the downslopes of dipping laminae, indicating agglutination of detrital sediment onto a mat (Plate 5.22). Some 101 Top 4 0.5cm A Plate 5.21. Variations in structure of Fades 3B. A) Basal, discontinuous or disrupted laminations grade up to B) irregular or "wispy" laminations (B), which in turn grade up to C) sub-horizontal, more continuous laminations. All samples from 8-16-2-14W2 at depths of 3018m, 3016.6m, and 3016.2m, respectively. D) Laminite fades showing large mudcrack, or prism crack, on right side of sample. Labelled are detached fragments of the original bedding that have fallen down into the opening. Sample from 14-26-6-11W2, 2555 m. 102 Peloidal sand layer mk • > Possible Algal (cyanobacterial) Mat 0.63mm thick 1• J Peloidal sand layer Figure 5.16. Laminate layering. A) Thin section photograph showing dark, thin micritic layer with no definable texture sandwiched between two layers of peloidal sand. B) Diagram of alternating thin algal (=cyanobacterial) mats and peloidal sand, from Hardie and Shinn (1986). 103 Plate 5.22. Laminite features from Sub-facie 3B. A) Core sample showing rare plan-view of a small domal stromatolite that may be laterally-linked to one or two other domal stromatolites (arrowed). From 12-2-7-11W2, 2549.9m. Core is 9cm wide. B) Very high relief stromatolite in lower left comer that grades upwards to sub-horizontal at top. Laminations do not change in thickness despite angle of repose clearly exceeded. Indication of either intense disruption of beds after lithification by some agent not present in core, or more likely, the sediment has been bound by cyanobacteria. From 3-6-6-6W2, 2552.8m. On following page: C) "Jelly roll" structure, outlined in black, whereby laminations/ beds have been overturned; similar structures are produced in stromatolites from Shark Bay, Australia where subaerial exposure dries the mat leading to a decrease in weight prior to inundation by flood tides. From 15-8-5-7W2, 2648.9m. D) Sample from the same core depicting 1) convoluted or tufted stromatolites in centre of core and 2) a larger stromatolite at top whose laminations taper down the sides indicating binding of sediment at the crest. From 15-8-5-7W2, 2649.4- 2649.5m. 104 CM Plate 5.22 (continued). 105 laminations exhibit uniform thickness even though they are oriented near-vertical. Other lamination-sets exhibit low-relief domal constructions (Figure 5.17 and Plate 5.22). Some laminations may also be overfolded creating "jelly roll" structures (Plate 5.22C). One core sample indicates they have circular to elliptical outlines in plan view (Plate 5.22A). Other primary structures include mudcracks or larger prism cracks (Plate 5.2ID). 5.6.2 Matrix and Grains Sub-facies 3A consists dominantly of a micrite matrix with variable concentrations of dolo-microspar (Plate 5.23A); nearly every core studied was only partially dolomitized. Dolomite ranges from xenotopic, to planar-s to planar-e textures. Higher dolomitization (>80%) usually results in development of the former crystal texture. Dolomitization also increases upwards in the facies and appears to be selective of certain laminae. No grains or other cements are present in this sub-facies. Six thin sections from Sub-facies 3B reveal it does not have a matrix, but is composed entirely of dolomite and dolomitized peloids (Plate 5.23B, C). Peloids constitute 70-90% of the facies and some are rimmed by dolomite microspar (~4p.m). Peloids range in size from 100-350nm. In thin section, peloidal laminations alternate with laminations of dark, amorphous material (Plate 5.23C). The former ranges from 0.5mm to 6mm in thickness, while the latter ranges from 0.1mm to 1.25mm in thickness. 5.6.3 Facies 3 Summary and Interpretation Sub-facies 3A is mud-dominated, variably dolomitized, organic-rich but very thin with low porosity. This could be a local source rock for the Coronach Member. 106 Figure 5.17. Computer sketches of stromatolite features in core. Sample 'A' shows domal laminites with a shared, near-flat bottom but high-relief tops that distinguish these as two separate and divergent laterally-linked stromatolites. In 'B* are three generations of small, low-relief domal laminites with thick laminae on their crests that taper down the sides; an indication of sediment-binding. Core sample from 10-25-1-15W2, 3115.7m. 107 Plate 5.23. Facies 3 matrix. A) Finely laminated dolomitic calcimudstone from Facies 3A showing partially replaced micritic matrix (stained red) by dolo- microspar. Two horizontal styolites are also present. From 12-13-2-19W2, 2992.7m, PPL. B) Matrix of Facies 3B showing 90% dolomitized peloids, the remainder is dolo-microspar and intercrystalline porosity. From 10-25-1-15W2, 3118.8m. C) Amorphous organic material from Facies 3B sandwiched between two peloid laminations. From same sample as 'B\ D) Anhydrite pseudomorphs of gypsum (black) showing small lath-like crystals in "chopstick" form oriented randomly throughout a dolo-microspar to dolo-micrite matrix. From 10-25-1- 15W2, 3115.8m. E) Sample with high vuggy porosity shown in black; 4-2-14- 21W2, 6902ft. 108 The high degree of organics and planar laminites in Sub-facies 3A can be a product of widely variable depositional settings including deep water, shallow but anoxic water, and levee deposits with cyanobacterial mats. Deep-water can probably be ruled out because of the intracratonic setting. Shallow, anoxic waters would allow for preservation of the organic-rich material. It would also explain why this facies is devoid of skeletals. Laminations observed in core may be condensed algal blooms similar to kukersites at the base of the Coronach Member. Sedimentation must have slowed markedly, as there is strong evidence for starved ripples. The contact between Facies 2 and Sub-facies 3A is very sharp implying a quick change from near-normal marine conditions. It is not clear what might have caused this change; physical restriction of the basin from the rest of the epeiric sea or subsidence leading to oxygen stratification are two possible explanations. Several cores showed inclined bedding and pseudo-breccia at the base of Sub-facies 3A, which can not be explained by this depositional setting. The very fine laminations and starved ripples are also identical to those features described in levee and beach-ridge deposits from Andros Island, Bahamas by Hardie and Ginsburg (1977) and Hardie and Garrett (1977). The former authors state that deposition in the intertidal environment is from storms, not tides. These storms, carrying mud and peloids, deposit their load during ebb flow over tidal flats. Levees and beach ridges however, are rapidly-drained topographic highs that only allow thin mud laminae to accumulate, regardless of the magnitude of the storm. No peloids are deposited. Algal (cyanobacterial) mats then trap only the finer material in continuous, uniformly thin layers. Starved ripples are created when deposition of mud fills local, small depressions on the levee crests. These descriptions fit remarkably well with the observations in core 109 for Sub-facies 3A. Figure 5.18 shows the characteristics of levee and beach ridge sediments. Other similarities with the levee model include the variability of dolomitization. Since levees are subaerially exposed, they are not subjected to a continual supply of hypersaline (dolomitizing) fluids relative to the larger tidal flat complex. Examples from Andros Island show very little dolomite on levee crests while dolomite accounts for up to 50% on levee backslopes (Figure 5.18A, B). Dolomite is usually less than 50% in the Coronach Member. The contact between beach ridges and subtidal deposits can be extremely sharp and is a characteristic feature in the Coronach Member. The few cores that showed cross- bedding dips of about 15° (Plate 5.19B) could represent the front of beach ridges or the backslopes of levees and beach ridges. The levee-beach ridge model consists of localized settings that do not fit with the blanket-like nature of Sub-facies 3A. Although a prograding tidal flat with an advancing beach ridge and laterally migrating tidal channels could conceivably produce widespread facies. No tidal channels were positively identified in core. However, Davies (1970) described similar sediments at the base of tidal channels from Shark Bay, Australia. The levee model is also best documented from the humid environment of Andros Island, but the Coronach Member was deposited under arid conditions, as described in later sections. Peloids are not present in Sub-facies 3A although they dominate the overlying facies. This can be explained in several ways. The first is lack of dolomite, which allows soft pellets to be compacted, destroying them or creating a clotted texture (Hardie and Ginsburg, 1977). Other explanations depend on the depositional setting. If an anoxic 110 300" *- A 10% Dolomite 25-50% Dolomite Crust rj Normal Highm Burrowed Intertidal Sediment "7 . ' • • • Channel -i-ri-!'.y -V- Normal .'c * • , Low Tide •?? ;?.\ J flat pebble Imbrk« Beach Ridge High Algal, Marsh .Cemented Crust Levee Crest Figure 5.18. Levee and beach ridge models. A) Profile of a levee and channel illustrating the flat lamination of levee crest sediments, as well as the percentage of dolomite from levee crest to levee backslope. B) Profile of a beach ridge, essentially identical to levee crests with flat lamination and deposition above mean high tide (MHT) level. Front of beach ridge (left side) is subject to under-cutting creating brecciation or high-angle cross-bedding. C) Plan view of a tidal channel setting showing relationship between sub-environments. Figures re-drafted from Hardie and Garrett (1977) and Hardie and Shinn (1986). m shallow-water setting is presumed then the peloids may never have been produced since no organisms seem to have existed at this time. If a levee model is presumed then peloids by-passed these topographic highs, as outlined above. The structures and matrix of this facies does not allow one to pinpoint a specific environment. Adjacent facies need to be used to infer a depositional model with sedimentation occurring either due to aggradation or progradation. Perhaps the most important indicators are thin grainstone beds that inter-finger Sub-facies 3A and 3B. The source of these skeletals is most likely Facies 2, which would not be possible in an aggradational model because Facies 2 would be buried at the time of Facies 3 deposition. The structural features from Sub-facies 3B including evidence of sediment agglutination are indication of the construction of stromatolites (Davies, 1970; Ginsburg et al., 1971; Demicco and Hardie, 1994). Stromatolites are laminated organo-sedimentary structures built by sediment- trapping, sediment-binding, or carbonate precipitating activity of microbial communities (Kennard and James 1986). The latter type are in situ stromatolites formed as a result of precipitation of sea-floor-encrusting isopachous calcite or dolomite (Pope et al., 2000); most types however, are formed by the binding and trapping action of cyanobacteria, formerly called blue-green algae (Scholle and Ulmer-Scholle, 2006). In thin section, very thin bituminous layers may be composed of remnant cyanobacterial mats. However, dolomitization has destroyed any remnant filaments or cellular textures making unequivocal interpretation difficult. Bitumen layers are typically sandwiched in between peloidal sands; the latter is deposited either from diurnal to semi diurnal tides (Ginsburg et al., 1971) or from storms (Hardie and Ginsburg, 1977). 112 Hofmann (1969) provides an excellent working summary of stromatolite attributes that seems to have been lost in the literature (Table 5.4). It can be applied to the stromatolites of Sub-facies 3B, which exhibit 1) even, wavy or crinkled curvatures; 2) flat to convex profiles; and 3) linked, or partly linked, low-relief, horizontal to stratiform morphology. Core makes it hard to determine if cyanobacteria constructed stromatolites into large columns or club-shaped build-ups (Plate 5.22B). However, stromatolite curvatures are probably enough to indicate that most are stratiform or flat-lying sheets. Notable exceptions include small domal types that may represent larger sets of laterally- linked hemispheroids, similar to those described by Logan et al. (1964) (Plate 5.22A, D). Based on aforementioned morphologies, stromatolites of the Coronach Member most resemble the un-branching varieties Stratifera or Paniscollenia (Table 5.5), though three- dimensional outcrop is necessary for a more precise interpretation. Stromatolites are found in a variety of ancient and modern environments including subtidal (Frost, 1974; Horodyski, 1977; Dravis, 1983), intertidal (Davies, 1970; Pratt, 1979), lacustrine (Sanz-Montero et al., 2008), and deep water (Hoffman, 1974). That stromatolites of Sub-facies 3B are associated with peloids, micritic mud, dessication features, and lenticular to wavy bedding, however, suggests a peritidal setting (Demicco and Hardie, 1994). Stratiform types are found in intertidal settings such as Shark Bay, Australia (Davies 1970) and the Abu Dhabi Sabkha, United Arab Emirates (Kendall and Skipworth, 1968). Johnson and Lescinksy (1986) also described stromatolites from the Williston Basin within Interlake Formation (Silurian) outcrops. Classification of stromatolites based on variations of laminae structures in tidal flat settings is given by Logan et al. (1964), and expanded upon by Kendall and 113 Laminae Stromatolites COMPONENTS Grow* todtr 1 |MN ji• {I cjwfn. M »-(M .. # * (uHHnete ^ tafewt .jfc. MKhilor — ttrcHform 0 tpfierettel pemlwwW VoritMRy | uniform M emtoti | CftftSffkfH • ifutty I | ttyQti | Vender /w\ 2«dm nnrv ^1S AHihi* I straw | and / hdfaM — horixonW AAA 3«*n f curved (ftewmbe* /decumbent ^ Mm * • cenlrifvfef s 1 Branching ityte yi fufcoit ^ wnlMAMt A l A ] A 1 1^ tffiteie ^ fentfrofd ° 1 O I ^ codeteenl ^ awtttmHwd 11j rWMM'~ CVMffi-•._ *-- NpHM|-•« •* * IWV* ^ wioetti O ^ owMk SURFACE tatorculale 80= , OftNAMDfTATKW ^ fimbriate & ! CP s ^ nipte o Mh»»Mi axiol rate A/V> MM rtfct (plan view) LINKA9C Hr*t MM MTONAL FEATURES 10-' Aeetfe (P»0) octm or Mcmua Table 5.4. Textural and structural components of laminites and stromatolites. From Hofmann (1969). 114 CONVEX LAMINAE ENCAPSULATING LAMMAE CONICAL LAMINAE STRATIFORM gas mmStrotifvra ^Wttdka GongyNna &&Irrtjulorio NODULAR NuclMila Coll«n.«llo Otogio BULBOUS Crypfozoon UNBRANCHMO Aliilllfonfecoittnki Cotanttlo mConophyton FURCATE ill JUL Ijfi lit AND UMBELLATE f ttlt jffiBKEk ffitt * T*nupoiut*lia vwPtotilla CoHcnia JocutophytonHI HHHtllMlMAfchatozoen Gyrono»oJ«n Mtajcrlo Kotovia oc DIGITATE DENDROID 0*Kotuikottio 5ttPoiudia IfflLtntllo St]Boicolio ;*r*Turuchoflka Tun^ussio ANASTOMOSE! rPormitct a Table 5.5. Forms of stromatolites from modern and ancient examples. From Hofmann (1969). 115 Skipworth (1968) and Davies (1970). Figure 5.19 shows an example from the Abu Dhabi sabkha in the Persian Gulf. Seaward-prograding tidal flats consist of, from top to bottom, 1) a flat zone of smooth mats, 2) a crinkle zone, 3) a polygonal zone and 4) a cinder zone. These forms are specific to sub-environments of the intertidal zone, as controlled by 1) length of exposure, 2) sedimentation rates, and 3) elevation relative to tide level and drainage (Logan et al., 1974). They are very similar, morphologically, to lamination types described in the Coronach Member (Figure 5.20). Also shown on Figure 5.20 are the Andros Island and Shark Bay examples. All the modern tidal flat analogues have many similarities with the Coronach Member, which are described below. Kendall and Skipworth's (1968) cinder, polygonal and crinkle zones of the lower intertidal zone are similar to discontinuous and wispy laminations described in the lower 2/3rds of Sub-facies 3B. Disrupted laminations are due to 1) gas pockets, 2) gypsum/anhydrite growth in the unlithified sediment, 3) dessication during exposure, or 4) cycles of drying and wetting (Davies, 1970). The upper l/3rd of Sub-facies 3B is the same as Kendall and Skipworth's (1968) upper intertidal flat zone. Davies' (1970) descriptions of tidal flats from Shark Bay, Australia employ different terms but are fundamentally the same. Andros Island has many differences, mainly due to the presence of fresh water in the form of ponds/marshes. This has led to bioturbation of the low-lying sediments, thus stromatolitic mats are usually not preserved. Similarities to the Coronach Member include a crinkled zone and possibly also the levee-beach ridge facies as compared to Sub-facies 3A. 116 CRINKLE ZONE POLYGONAL ZONE>NE / FLAT ZONE CINDER ZONE INTERTIDAL SABKHA SAND CRUST BEACH IDGES i 7-HW M- —- ^ cMJlMbiil MENT ALGAL PEAT -2Km NORTH SOUTH Figure 5.19. Zonation of laminate morphology from the Abu Dahabi sabkha, UAE. Laminations progress landward from cinder zone, to polygonal zone to crinkle zone to flat zone and are essentially the same as those described by Davies (1970) from Shark Bay, Australia. Vertical successions show landward zones overlying seaward zones indicating progradation. From Kendall and Skipworth (1968). 117 Modem Laminae Morphological Types (Sub-environment) Coronach Lamination Tvoe Core Sketch Coronach Davies Kendall & Hardie & (Interpreted Fades (1970) Skioworth (1968) others (1977) Sub-environ.) Massive dolomicrite & gypsum; Basal ram laminations Facies 4 gradational Bioturbated peloidal mud, Planar to sub-planar, Smooth Zone Flat Zone prism cracks tan laminations; (Upper Intertidal) (Upper Intertidal) (fresh water ponds peloids & gypsum X's and channels) gradational Crinkled, fenestral Wispy, crinkled Facies 3B laminae; to domal Tuned & Cinder, Crinkle 4 tufa zones.lithified laminations; Convoluted Zones Polygonal Zones «*»* P®lo'dal™ds peloidal; gypsum X's (Lower Intertidal) (Lower Intertidal) 98 marS gradational Disrupted laminae, Discontinuous, mudcracks, intraclasts irregular (Backslopes) laminations; peloidal Smooth, flat discont. laminations; Smooth Zone Smooth flat (Base of Sand Flats starved ripples laminations; Fades 3A Tidal Channels) (Levee & starved ripples Beach Ridge) 9cm core Figure 5.20. Sketch of Facies 3 laminae structures. Laminations from Coronach Member compared to modern, stromatolitic (cyanobacterial) and mechanically- deposited laminites shows a very similar affinity. Modern arid to semi-arid tidal flat examples include Shark Bay, Australia and the Persian Gulf by Davies (1970) and Kendall and Skipworth (1968), respectively. The modern humid setting example is from Andros Island, Carribean studied mainly by Hardie and Ginsburg (1977). All sub-environments are listed in parenthesis. The latter study have subdivided the tidal channel belt into more sub-environments than could be recognized in the Coronach Member; the listing above is as faithful a summary of their descriptions as possible. 118 The presence of stromatolites (many of them disrupted), anhydrite pseudomorphs of gypsum, evidence of dessication, dominance of peloids, and lack of skeletals is very similar to many modern-day hypersaline intertidal settings. Hypersalinity allowed for preservation of cyanobacterial mats from being fed upon by grazing organisms. Sediment is dominated by mud and peloidal sediment; the latter decreases landward. Peloids are known to feed the major tidal-flat complex at Andros Island (Wanless and Dravis, 2008). Further evidence of increased salinities is lath-like crystals of anhydrite evident in thin section and core (Plate 5.23D; see also Plate 5.25). They are randomly oriented in the sediment, suggesting they grew within pore fluids as opposed to settling out of a water column. This cement was likely originally gypsum, which naturally converts to anhydrite upon dehydration (Kerr, 1977). Both gypsum and anhydrite are found today in upper intertidal flat settings from Shark Bay, Australia and the sabkha at Abu Dhabi, UAE (Hardie and Shinn, 1986). Other diagnostic criteria of tidal flats that are rare or missing in the Coronach Member include mudcracks, fenestral porosity, and quartz grains. Taken together, the lack of the features may not support a tidal flat origin. However, numerous examples show that many of these "diagnostic" characteristics are not present in modern nor in ancient tidal flats and therefore, should not be considered violation against subaerial origins (Wanless, 1975; Hardie and Ginsburg, 1977; Davis, Jr., 1975). Furthermore, mudcracks may not be rare but ubiquitous if the discontinuous-type stromatolites are due to exposure. In addition, one prism crack was identified in core, indicating at least intermittent exposure (Demicco and Hardie, 1994). 119 Domal stromatolites (laterally-linked hemispheroids of Logan et al., 1964 terminology) were formed in intermittently water-covered flats of the lower intertidal setting. The more discontinuous laminations probably represent indurated crust (or pavement) formed from exposure. Either landward, or in progressively shallower water, these subaerially exposed stromatolites are succeeded by more smooth, wavy laminations common in modern upper intertidal zones. This gross intertidal setting lies sharply on the subtidal setting of Facies 2 and displays evidence of progradation, as compared to modern tidal flats. However, an isopach map of Facies 3 shows thickening towards the basin center, which could be evidence of aggradation (Figure 5.21). Sub-facies 3B has the best reservoir quality in the Coronach Member; porosity and permeability are both the highest, as determined from core analysis. Porosity increases downwards from nil to values of 12% as indicated by core analysis. This increase is likely related to the systematic change in 1) laminae structure type and 2) dolomite and peloid grain size. Porosity types are intercrystalline and vuggy. Where porosity is highest, oil staining is most prevalent. Under UV light, samples commonly showed bright yellow fluorescence (Plate 5.24), with milky-white cuts upon liberation of hydrocarbons from the core by pentane. Sub-facies 3A has a very strong petroliferous odour upon sanding and light hydrocarbon staining in thin section. Porosity types include intercrystalline for dolostones and microcrystalline in calcimudstones, but overall porosity is very low (< 3%). 120 ... ! jpiLjCtS^ L R25 R20! W ijlTANjft IIORl n D/KOIA Figure 5.21. Isopach map of Facies 3, showing very gradual thickening from North to South. Zero-line contour may not represent depositional edge, as diagenesis has masked lamination needed for proper identification. Extent of potential source rock (Facies 3A) is approximately at zero-edge. t t Top Top A B Plate 5.24. Fades 3 hydryocarbon indicators. A) Strong yellow fluorescence, under UV-light, from the disrupted textures of Fades 3B. From 2-11-10-9W2; 2288.2m. B) Sharp change in fluorescence from the top of Fades 3, which is bright yellow, to Fades 4, which does not fluoresce except in the lower 3cm. Same location as (A); yellow pin at 2287.7m. Both core samples are 9cm across. 122 5.7 Fades 4 The contact between Facies 3 and Facies 4 is either gradational or sharp. Facies 4 consists of a massive cryptocrystalline dolomudstone (Sub-facies 4A) and an upper evaporite (Sub-facies 4B). Overall, Facies 4 is characterized by 1) an upwards increase in anhydrite concentration and 2) an absence of structures, grains, skeletals and burrows (Plate 5.25). The evaporite facies is equivalent to the Coronach Anhydrite. This evaporite consists of 70-100% anhydrite while any remaining rock is composed of stringers of cryptocrystalline dolomudstone sandwiched between nodules. 5.7.1 Primary Structures Facies 4 is predominantly massive (Plate 5.25C), though some minor structures exist. Laminations were found in just two cores; they are planar and horizontal to sub- horizontal. Anhydrite is prevalent in this facies and appears to be the result of in-situ growth. Nodular or "chicken-wire" structures of anhydrite (Plate 5.25A, D) appear to displace rare laminations. These very early diagenetic features are expanded upon in Chapter 6. Only a single core exhibited bedded or laminated textures of anhydrite and this zone was just 10cm thick (Plate 5.25B). 5.7.2 Matrix Facies 4 is composed of cryptocrystalline dolomite and lath-shaped or nodular anhydrite. No other cements, grains, or original matrix are present. Anhydrite occurs in 123 Disrupted lamination / 1,5mm I.Smm Plate 5.25. Fades 4 anhydrite. A) White, nodular anhydrite of Fades 4B with dark brown stringers of dolomite between nodules. Nodules are highly variable in shape and size. Core is 9cm wide; from 10-25-1-15W2, 3113m. B) Core sample showing rare laminated anhydrite; 15-8-5-7W2, 2646.75m. C) Core sample from Fades 4A with tiny lath-shaped crystals of anhydrite - likely a pseudomorph of gypsum - in a massive dolomudstone; 5-8-5-7W2, 2647.8m. D) A thin section showing variably- sized anhydrite nodules composed of small laths. Nodules also displace one rare lamination, suggesting growth of anhydrite in a soft substrate; from 10-25-1-15W2, 3113.4m. E) Thin section with 100% anhydrite cut by dissolution seams; Ibid., 3114m. 124 two forms. The first is small ( Large, nodular anhydrite takes over as the dominant form in the upper half of Sub-facies 4B. Nodules are grey in color, have a large range in size from 0.20cm to 5cm in diameter, and are composed of an amalgamation of lath-like crystals of anhydrite (Plate 5.25D). They account for up to 95% of the rock. The rest of the rock is composed of individual anhydrite laths and cryptocrystalline dolomite. 5.7.3 Facies 4 Summary and Interpretation This facies usually has extremely low porosity (<1%) mainly due to a cryptocrystalline matrix and pore-plugging anhydrite. Vugs may develop to a minimal extent, but the lack of permeability precludes reservoir development. The facies is rarely missing although it was not cored in six of the studied cores. Sub-facies 4A ranges in thickness from 0.76 m to 2.2 m. Sub-facies 4B is equivalent to the Coronach Anhydrite and is the only facies that can be mapped on logs. Its maximum thickness in the study area is 4.5m and it pinches out to the north and east (Figure 5.22). Basin-wide maps show that it has a roughly N-S trend (Figure 2.4). 125 Figure 5.22. Isopach map of Facies 4B, the Coronach Anhydrite. Facies 4 shows evidence of increasing salinity. Anhydrite and dolomite are the only two minerals present and the rock is completely devoid of skeletals. The percentage and texture type of anhydrite allows for a two-fold sub-division of this facies. Sub-facies 4A has randomly oriented lath-like crystals of anhydrite, which may be pseudomorphs of gypsum, indicating growth within the substrate from supersaturated pore waters (Moore, 2001). Only one sample from the basal part of Facies 4 has anhydrite with a horizontal orientation, which was just 10cm thick. This deposit probably formed due to direct precipitation from hypersaline water and subsequent settling of the crystals to the bottom of the sediment floor. Localized hypersaline ponds, or salinas, such as those found along the southern coast of Australia (Warren and Kendall, 1985), may have acted as the precipitating medium. The Coronach Anhydrite (Sub-facies 4B) has individual nodules of anhydrite coalesced together forming nodular or chicken-wire textures. Anhydrite nodules may develop from dehydration of gypsum (CaS04 • 2H2O) crystals to construct plastic masses of small crystal laths that are easily deformed into nodules (Spencer and Lowenstein, 1990). However, subaqueous anhydrite, upon burial, may also form nodular anhydrite (Kendall, 1992). Therefore, identifying the depositional setting for ancient evaporites can be very difficult and this is inherent in the Red River Formation (Nimegeers and Haidl, 2004). Kendall (1976, 1992) and Nimegeers and Haidl (2004) suggested Red River evaporites are subaqueous in origin mainly because of their basin-centered distributions (Figure 2.4). An isopach of the Coronach Anhydrite does show it thickening towards the basin center (Figure 5.22). However, notwithstanding the Lake Alma or Redvers 127 Anhydrites, the Coronach Anhydrite could be interpreted as sabkha-type deposition because of rarely-preserved laminae that are displaced by growth of anhydrite nodules in the substrate. The lack of evidence for subaqueously-deposited gypsum is perhaps more telling for sabkha-type deposition. In situ bottom-grown gypsum crystals tends to have its textures preserved in ancient deposits (Spencer and Lowenstein, 1990). They develop as vertically-oriented prisms, or chevrons in the case of halite, that grow from a common, laterally continuous substrate. Flooding may provide drapes of mud over the top of these crystals, which is then used as a new substrate for gypsum growth. The result is a bedded to laminated evaporite rock with laminations of impurities (Warren and Kendall, 1985). Gypsum that precipitates out of the water column and settles to the bottom may produce a similar end-product. Burial diagenesis may recrystallize a great deal of the original evaporite, but much of the gross bedding textures would be preserved upon deep burial. Laminated anhydrites from the upper Lake Alma Member are present within the same cores as nodular anhydrite from the Coronach Member. Laminated textures are most likely the result of subaqueous origins (Warren and Kendall, 1985). By argument then, the Coronach Anhydrite should have a different origin. The same burial processes should be acting on both evaporites because they are separated by just 10-12m depth. Thus, the contrasting textures are more likely the result of different primary-controlled depositional settings. The origins of the Coronach Anhydrite is discussed further as a diagenetic precipitate in Chapter 6 (Anhydrite 1). 128 The center of the basin was not included in this study and further work may show more direct petrographic evidence of subaqueous origins. This should be identified by bedded or laminated anhydrite among other petrographic criteria including vertical, elongated nodules and intra-nodular impurities (Warren and Kendall, 1985). Warren and Kendall (1985) state that salinas and sabkhas may not be mutually exclusive, rather many sabkhas held localized salinas or large-scale salinas were fringed by sabkhas. Further studies of Red River anhydrites may show that such a relationship existed. Modern examples include the Abu Dhabi Sabkha in the Arabian Gulf and the MacLeod Evaporite Basin along the west coast of Australia. In the former, a gypsum mush is precipitating on tidal flats above an algal-laminated zone and the gypsum mush grades laterally landward into nodular anhydrite (Shinn, 1983). The MacLeod basin is a barred graben with aggradational carbonates and evaporites (Logan, 1987); evaporites precipitate at or just below the surface as the sedimentation surface is only periodically covered by brines. These modern analogues have different depositional settings yet both produce similar stratigraphic records and petrophysical characteristics. Either setting could be applicable to the Coronach Member. 5.8 Facies 5 Facies 5 is a thin (<0.5m) dolomudstone or calcimudstone overlying the Coronach Anhydrite. When Sub-facies 4B is absent Facies 5 is more intensely developed. It has grey, orange, or greenish-white colours. Characteristic features of this facies include 129 rapid colour changes and exposure features such as mudcracks, oxidation and in situ brecciation (Plate 5.26). 5.8.1 Matrix and Grains Facies 5 consists primarily of cryptocrystalline dolomudstone. Clasts also appear to be composed solely of dolomudstone, while others are aggregates of skeletal(?) clasts (or lumps) of unknown origin. Some clasts are "blackened grains" (Plate 5.26G), while others display evidence of micro-boring. 5.8.2 Facies 5 Summary and Interpretation This thin, 10 - 90 cm horizon has undergone significant exposure and is generally non-porous. Mudcracks, mud chips, sheetcracks, breccias, teepee structures, blackened grains, micro-bored grains and scour/erosional surfaces all indicate this facies, or at least the upper portion of the facies, is the product of subaerial conditions. Some of these features are present at the top of the Lake Alma Member as well; however, they are much more pronounced and extensive here. Facies 5 reduces in thickness towards the basin- center and is the only facies to do so. Facies 5 is the product of diagenetic alteration of previously deposited facies due to exposure and erosion. Kreis and Kent (2000) and Nimegeers and Haidl (2004) also recognized subaerial exposure at this interval. The latter suggested that the anhydrite zero edge may reflect erosion (both regressive and transgressive) along the basin margins. This facies is not present in the southern part of the study area (closer to the central basin) and increases in thickness towards the basin periphery from just a few 130 Plate 5.26. Features from Fades 5. A) Core shows a progression from a green- grey colored mudstone cut by a scour surface and filled by mud-chips (derived locally), to a mudcracked interval followed by a thin zone of mud rip-ups clasts. From 15-28-12-2W2,1910.45m - 1910.65m, scale at top in em's. B) Prism crack at the center of a teepee structure. From 4-2-14-21W2, 2103.9m, core is 7.5cm wide. On following page: C) Mudcracks, sediment-filled sheet cracks, and mud- chips overlying a zone of mud rip-up clasts at the top of the facies. Several vertical solution pipes are filled by anhydrite and are late-stage, as the styolite does not cut through them. Zone of exposure (above green line), as identified by oxidized muds, reaches down into the interval of mud clasts. From 12-2-7-11W2, 2543.45m; core is 6cm wide. D) Flat and elongate clasts of same origin to the host rock, forming a pseudobreccia; little to no transport of clasts suggesting exposure-related; 10-25-1-15W2, 3110.5m; core is 9cm wide. E) Mudcracked zone where vertical and horizontal openings are filled by mud. From 14-26-6- 11W2, 2550.2m. F) Exposure surface in thin section, with dark cryptocrystalline dolomite below and dolo-micrite above. From 4-2-14-21W2, 2103.6m. G) Thin section photo of a blackened grain. From 1-9-21-16W2,1764.4m. 131 •• •H 100jjm Plate 5.26 (continued). 132 centimetres to 20 cm (Figure 5.23). Thickness is related to depth of diagenetic alteration, which in turn is probably a function of duration of exposure and its intensity, climate, and position of the water table (Esteban and Klappa, 1983). Figure 5.24 shows the change in the upper Coronach Member contact with palaeogeographic position along the basin periphery in both aggradational and progradational models. The present-day expression of the upper Coronach surface is represented by three core sketch examples. In location '3' evaporite sediments are kept moist due to a relatively high water-table (Progradational Model) or they are covered in brines (Aggradational Model). Flooding of the next depositional sequence (Redvers Unit) preserves the contact and underlying anhydrite. However, further inland at location '2', evaporite is removed, which creates a dissolution or exposure surface at the top of the Coronach Anhydrite in either model. Limited subaerial exposure time preserves much of the anhydrite. Yet further inland, at location '1', prolonged exposure removes all anhdyrite (Progradational model), or anhydrite was not deposited (Aggradational Model). The resulting rock is the same in both - a caliche horizon (Facies 5). The top of the Coronach Member can be considered a sequence boundary, and is the same type of surface as that bounding the base of the Coronach Member. Both surfaces are maximum regressive surfaces (MRS) (Embry, 2008 terminology) and the sediments below are diagenetically altered due to exposure, though the top of the Coronach is far better developed. 133 N Diaaenetic Overprinting 4-2-14-21W2 -Exposure 12-13-2-19W2 - Anhydrite removal ? 71.4km Index Map Figure 5.23. Litholog cross section North-South through the study area showing correlation of all major fades across long distances. Fades 5, exposed caliche horizon, is the only fades that thickens landward, and is likely a function of exposure time. Litholog legend is in Appendix A. Tod Coronach Member: Agaradatlonal Model Marine Deposits Top Cpronwh Member; Progradrtlpnai Mp Water Table Intertidal Deposits Base \ Redvers Base Mud-rip ups Red vers Exposure Surface Dissolution Nodular Caliche surface Nodular Floatlnfl Anhydrite Anhydrite breccia Horizon o Figure 5.24. Interpretation for top sequence of Coronach Member for two opposing depositional models. See text for details. 135 5.9 Summary of Depositional Environment All facies except Facies 5 and Sub-facies 4A were documented across the study area. Correlation of these facies for many kilometres (Figure 5.25) show these are wide facies' belts - a diagnostic feature of ramp-type settings, as opposed to platforms (Wilson, 1975). Also, isopach maps (Figures 5.15; 5.21; 5.22) show constant thickening to the southwest with no apparent break in slope. This is another feature evident of ramps (Wilson, 1975) and is consistent with deposition in an epicontinental sea. The Coronach Member can be interpreted as either having been deposited as an aggradational system or as a prograding tidal flat complex (Figure 5.26). This is due to the ambiguous nature of the rocks. Both models have their pros and cons. Evidence in support of the aggradational model includes 1) blanket-like facies across the study area, and 2) thickening of most facies towards the basin center. Evidence for the progradational model includes 1) petrographic evidence of intertidal stromatolites and sabkha-anhydrites that are very similar to modern analogues, and 2) that peloids found in the intertidal setting must be fed by an adjacent, co-existing carbonate factory in the subtidal setting. Figure 5.27 shows a detailed progradational model that may reflect the means of deposition for the Coronach Member. Subtidal deposits of moderate to shallow depths (Facies 1 & Sub-facies 2A), grade into shallow-water biostromes (Sub-facies 2B) creating a shallow-water barrier behind which skeletal grainstones (Sub-facies 2C) and partially restricted lagoonal mudstones (Sub-facies 2D) were deposited. Sub-facies 2C may also occur as thin beach deposits or tidal channel fills. The shallowness of these sub- environments also helped protect and establish intertidal and supratidal mud flats (Facies 136 w 11-20-2-18W2 16-23-2-1W2 I i Figure 5.25. Fades cross sectio PROGRADATION supratidal intertidal subtidal sea level •ggggient transport «. ^ * "factory" Progradfng Tidal Flat Wedge sea level (ponds) supratidal -intertidal" subtida| AGGRADATION Simultaneously Aggrading Sheet Figure 5.26. Aggrading versus prograding basin models. The prograding tidal flat wedge is gnerated by sediment transport onto the tidal flats from the offshore environ. A simultaneous aggrading sheet accretes sediment vertically and the whole platform becomes intertidal and then supratidal. From Pratt et al. (1990). 138 CARBONATE RAMP BACK RAMP »*•¥*«« h? 'o/. mounds/ Ptlcli raofe f L ^ Figure 5.27. Possible prograding depositional model of the Coronach Member. Facies are widespread with no apparent break in slope, and have remarkably similar components to those of ramp-type settings (inset). Inset adapted from Moore (2001). 3 & 4). The hydrologic system was probably divided by salinoclines, which in Shark Bay, Australia are a function mainly of sills (Logan and Cebulski, 1970). Biostromes may have acted as such a sill, because deposits landward of Sub-facies 2B have significantly reduced taxa. Subtidal deposits are sharply overlain by laminites from the beach ridge and levee sub-environments (Sub-facies 3A); these are part of a larger tidal channel belt. They grade into intertidal-supratidal deposits including stromatolites (Sub-facies 3B) and sabkha-type dolomites and anhydrites (Sub-facies 4A & B, respectively). In a landward direction, sediments were subjected to exposure and erosion, removing or diagenetically altering parts of the upper sequence, particularly Facies 4, and creating a caliche horizon (Facies 5). Diagenetic removal of anhydrite from infiltration by fresh water may have also played some part in this, although to what extent is unknown. The aggradational model (Figure 5.26) starts off much the same, with shallow- water deposition of Facies 1 and 2. Then increasing salinity shut down the carbonate factory across the basin. It is not clear what caused this increase in the aggradational model, but it may have been due to concentration of seawater due to 1) restriction by a physical barrier, 2) sea level fall, 3) sediment accretion, or 4) some combination of the three. However, shallowing is believed to have created an intertidal- and supratidal-like setting resulting in deposition of stromatolites (Facies 3) and dolomudstones and anhydrites (Facies 4). Salinities continue to increase, likely due to concentration of seawater through evaporation. Tides are probably not responsible for the lamination features of these deposits because tides could not operate at such large horizontal distances; instead alternate flooding (by storms) and exposure may create them in the 140 aggradationl model (Pratt et al., 1990). Facies 3 & 4 were exposed and altered to caliche (Facies 5) in parts of the basin that did not remain inundated with brines. In either basin model, the climate at the time of deposition was arid (Witzke, 1990), and is affirmed by the presence of dessicated stromatolites, mudcracks in Facies 5, and anhydrite. Humid climates tend to remove anhydrite during the wet season (Shinn, 1983). Climate was largely controlled by paleogeography. The position of the study area in Late Ordovician was likely within 0-10° latitude south of the equator (Ross Jr., 1974), creating a hot climate (Scotese and McKerrow, 1990). This is also outside the trade wind belt (10-23° N and S) implying relatively low to moderate wave energy. Evidence to support this includes high mud- and peloidal-content, as well as lack of marine cements and absence of ooids. The Taconic Orogeny along the Appalachian side of Laurentia may have also obstructed south-easterly trade winds from carrying moisture from the Iapetus Ocean into the interior of Laurentia. The extensiveness and shallowness of the basin in either depositional model may have also reduced the kinetic energy of waves by drag effect along the bottom of the seafloor (Wilson, 1975). The abundance of aragonitic Dimorphosiphon green algae suggests either 1) algae have biological control over what calcium carbonate polymorph they precipitate (Ries, 2006), or 2) sea water chemistry at this time was more conducive to aragonite-secreting organisms (Boyd, 2007); the latter however, is contrary to the common belief that 'calcite seas' characterized the Ordovician (Figure 5.28; Hardie, 1996; Stanley and Hardie, 1998). The presence of green and red algae also suggests that the study area of the basin was well within the photic zone; it is believed that even the center of the basin was in a like position (Longman and Haidl, 1996). 141 ^'ARAGONITC THRESHOLD* M P Pm Tr BS Hlgh44g catito and, lw abundinly, aragonie •1 Catena, Mq contort ganafaly iowar, IncreaainQ naar HvMhokT PC | CAM. I QRD. ISlLj DEV. I CARB.I PM. |TR-| JUR. | CRET- I CBN. | ICEHOUSEi GREENHOUSE T~QREEMHOUSE |ICE| - CUMAnC EPISODES - FBCHB»(I«!) S SEA LEVEL CURVES 11 • •• * 11' i1'"i" •' i"" i" " i" " i •'. • 590 S00 450 400 360 300 250 200 150 100 GO 0 Ma C1WM Figure 5.28. Temporal changes in A) sea level, climate, granite emplacement and B) carbonate mineralogy and taxa due to secular changes in the mid-oceanic ridge hydrothermal brine flux, which in turn has been derived II • by oscillations in sea-floor production rates. In (B), the distribution of taxa in roles of major reef builders and 33=1 cQ sediment producers (Stanley and Hardie, 1998) njgoMeaals ccfcracMnten corals coincides with distributions of non-skeletal carbonates > .1 GTMcaooa (Sandberg.1983) and of secular variation in Mg/Ca ratio Q |dtmoaponga* and Ca concentration in seawater (Hardie, 1996). Blue • haam Iwtazoan conk line shows the boundary between nucleation fields of • low Mg-calcite and aragonite + high-Mg calcite (Mg/Ca ntopo = 2). Coronach Member deposition is Late Ordovician, < I ptiyMddgM Y/S/ysSlTcmtotlaxmSinta which indicates predisposition of low-Mg calcite I calcte • wagon** m mineralogy at that time. Modified from Stanley and T777X foTubtptytn B Q Mo-cak*» Q toianapares Hardie (1998) and Scholle and Ulmer-Scholle (2006). Water depth was likely shallow and is affirmed by studies on conodonts in the Coronach Member (Nowlan and Haidl, 2001; Haidl et al. 2003), which indicate an upward progression from shallow to extremely shallow. Pratt and Haidl (2008) suggest 20-30 meters for much of the upper Yeoman Formation and Lake Alma Member based partly on presence of patch reefs. The Coronach Member was probably slightly shallower at less than 20m because it is thinner and less areally widespread. Dominance of encrusting-type red algae at the top of the subtidal facies indicates water depths likely fell to less than 4m. Overall, the Coronach Member displays a shoaling-upward and a brining-upward sequence along a homoclinal ramp in a hot, arid climate. It remains unclear if sediments accreted laterally (progradation model) or accreted vertically (aggradation model). Table 5.6 shows the facies described along with the aforementioned depositional interpretation. Micrite mud dominates the matrix of all facies. Given the very high fossil abundance and diversity, it is likely that most of the mud was derived from skeletal breakdown, possibly bioerosion, as opposed to direct precipitation from seawater. Algae alone could account for a high-degree of production in sediment (Neumann and Land, 1975) and is probably a major source for many ancient carbonates (Stockman et al., 1967). The recognition of Dimorphosiphon and Ortonella is important, as they break down into lime mud that is typically not recognizable as organic in origin (Ginsburg et al., 1971). Both appear numerous and may have grown rapidly. Green algae in particular are major suppliers of sediment in Recent carbonates (Stockman et al., 1967), partly due to high growth rates and partly because they can become so numerous (Ginsburg et al., 1971). Though Dimorphosiphon is a Codiacean-type algae, which tend to break down 143 Sub- ••positional Environment Depositional Environment Abu Dhabi Sabkha Formal Nam* Facies Primary Lithotogy Diagnostic Features Facias (Programing Model) (Aggrading Model) Analogue Facias Breccia's, mudcracks, mud rip-ups, Facies 5 - DokVCalamudstone Caliche Caliche Not described oxidation, black, drains: scour surfaces B Anhydrite Individual to coalesced nodules of anhydrite Sabkha Salina or Supratidal Facies 4 Sabkha Evaporites and Mud Cryptocrysiaibne Randomly oriented lath-Ike crystals of Supratidal Mud Flats & A Salina or Supratidal Dokxnudstone anhydrite Hvoersalne Ponds B Dokxnudstone Disrupted, wavy, domal or flat laminations Intertidal 'IntertkJal" (Restricted Salina) Facies 3 Cyanobacterial Mats Calcific to Dolomitic A Organic-rich; hz, planar laminations Levee and Beach Ridge 'IntertidaT (Restricted Salina) Mudstone Petoida! Calcific Coronach Member D Peloids, Planotttes burrows, ostracodes Lagoon and Tidal Channels Restricted Subtidal Pellets and Mud Wackestone Rare micritk: mud; rounded S abraded C Skeletal Grainstone Reef Flat or Beach Shalow Subtidal Pellets and Skeletal Sands Facies 2 arains Algal-Stromatoporoid Organic Reefs and skeletal B Very high fossil abundance and diversity Shalow Subtidal Shalow Subtidal Biostromes sands Shallow to Moderate Depth Shalow to Moderate Depth A Cherty Wackestone Chert nodules Skeletal Sands Subtidal Subtidal Laminations, kukersites, tow skeletal Facies 1 - Calcimudstone Euxinic Subtidal Euxinic Subtidal Not described diversity; Planolites & Palaeophycus traces Dolomudstone to Upper Lake B Mudcracks, mud rips-ups, solution breccia Evaporftic Mud Flats Anhydritic Dokxnudstone Alma Lake Alma Member Anhydrite A Anhydrite Laminations and dissolution surfaces Salina LowerLaxe Alma Not described Table 5.6. Expansion of Table 5.2 showing list of facies, with interpreted depositional environment, and comparison to Abu Dhabi facies. into sand-sized particles, experiments show that they may also house aragonite in their interuticular spaces (Stanley et al., 2010). This aragonite is related directly to the ambient concentrations in seawater, which during Late Ordovician time was supersaturated with respect to calcium and likely promoted precipitation of both aragonite and calcite (Stanley et al., 2010). The major implication of algal production in an intracratonic setting is that 100% of mud produced is deposited at the site of production. In contrast, most modern environments lose a large portion of sediment to transport off-bank (Neumann and Land, 1975). This leads to 1) a significant amount of mud being washed onto tidal flats allowing for relatively fast progradation of that system, or 2) a basin that is apt to aggradational infilling, overcoming effects of subsidence, erosion, and solution. It is likely that energy levels were never very high in Coronach time given 1) the high amount of micritic mud; 2) the scarcity of marine cements; 3) rarity of well-sorted grainstones; and 4) the conspicuous absence of ooids. Encrusting forms of Solenopora may indicate high-energy conditions but they were probably growing in the fair-weather wave zone (<4m), which does not necessarily imply a high-energy environment. Ooids are coated grains of carbonate found in a number of modern and ancient carbonate environments (Flugel, 1982), but none were identified in the Coronach Member. Ooids require high-energy conditions to form and a "backstop", or topographic high, for accumulation (Dravis and Wanless, 2008). It is possible that neither existed in southeastern Saskatchewan at this time. Wave energy is linked to winds, and in modern carbonate environments such as those in the Caribbean, ooids are forming mainly because of high-wave energy associated 145 with the trade wind belt (Wanless and Dravis, 2008). The 'Coronach basin' may have been just outside the trade wind belt (Figure 2.8), which ranges from 10-23° South and North of the equator (Dravis and Wanless, 2008). Therefore, these sediments were never subjected to the daily assault of waves, which can reach depths of 4m on a daily basis. Furthermore, most paleogeographic studies place the proto-Williston Basin very close to the equator (Scotese and McKerrow, 1990; Kent and Van Der Voo, 1990; Witzke, 1990). The absence of ooids may be evidence for a 0-10° equatorial position of the Williston Basin during Late Ordovician time (Ross Jr., 1974). The second requirement for ooids is a backstop for accumulation. The orientation of paleoshoreline was nearly N-S in the Ordovician, with land to the east. Therefore, the easterly trade winds would have been blowing waves offshore, as opposed to against or along the shoreline. Thus, a backstop for oolitic shoals may never have been established. Wave energy is also linked to water depth (Flugel, 1982). That shallow conditions prevailed in Facies 2 over vast distances might suggest that waves lost their kinetic energy as they dragged along the sea floor. It is probable that the shallowness of the basin at this time, in combination with low wind energy, combined to produce a quiet-water setting. Figure 5.29 shows the relationship between carbonate particles with water energy and carbonate precipitation. Lime mud is the dominant matrix constituent of most samples from the Coronach Member, followed by peloids. The chart suggests that low to moderate energy is the setting type based on the dominance of these components. Oolitic shoals have been identified at the base of the Lake Alma Member in southeastern Saskatchewan (Kendall, 1976; Kreis and Kent, 2000). What was the difference between this setting and those of the Coronach Member? Kendall (1976) 146 MICRITIC INTRACLASTS, STROMATOLITES SUPERFICIAL OOiDS OOIDS LIME MUD AND SILT SKELETAL GRAINS AND TERRIGENOUS MATERIAL OUlET WATER QUIET WATER OPEN LAGOONS LAGOONS Increase in Water Energy Figure 5.29. Relation of carbonate particles to water energy and CaC03 supply. Only particles that are controlled by water energy are included. Fades 2 consists predominantly of lime mud and peloids, which can be used to determine that low to moderate energy conditions prevailed. From Flugel (1982). 147 suggested relatively deep water in southeastern Saskatchewan relative to Manitoba and south-central Saskatchewan. The deep water may have allowed waves to reach their full kinetic potential. This higher-energy regime produced ooids that were then deposited onto localized shallows related to basement highs (Kreis and Kent, 2000). 5.9.1 Modern Depositional Analogues Modern examples of epicontinental seas are rare, as only about six exist today (Heckel, 1972), and most of these do not have near-flat seafloors (Jaanusson, 1984) and/or they are subjected to at least some siliciclastic influx. Many modern analogues of prograding systems can be compared to the Coronach Member. Unfortunately, Lake MacLeod of Western Australia is the only aggradational depositional system from the Holocene. Figure 5.30 compares the scale of some aforementioned environments to that of the study area and the maximum extent of the epicontinental sea covering Laurentia during the Late Ordovician. The Coronach Member has distinct characteristics that are similar to these modern environments, which are described below. Portions of the ramp setting for the Coronach Member are similar to shallow- water deposition in parts of the isolated carbonate platforms in the Caribbean, and to intertidal and supratidal deposits of tidal flats at Shark Bay, Australia (Figure 5.31). But perhaps the best progradational model is from the southern coast of the Arabian Gulf, the Abu Dhabi. It can be considered a modern analogue for a carbonate ramp because the sea floor inclines gently from the shoreline down to the center of the basin at just 80-100m depth (Harris, 1994). Other characteristics that are similar to the Abu Dhabi model 148 Figure 5.30. Comparison of scale between modern carbonate environments including Lake MacLeod and Shark Bay, Australia and Abu Dhabi, UAE to the study area. Modern analogues are a close approximation to scale of study area, but dwarfed relative to the maximum extent of the epicontinental sea during Late Ordovician. Satellite images on right modified from Harris (1994); on left modified from Logan (1987); center image from Blakely (2007). REGIONAL COMPARISON OF / RELATIVE DISTRIBUTION OF STRUCTURES, SEDIMENTARY FEATURES / GRAINS AND MINERALS / f/f/f/ / / // / / J ffy C?/«W/ ^ }/4?/ */ */ $/ £/ «?/ Ar /«^0°^ Figure 5.31. Comparison of modern tidal flat environments. Shown are the sedimentary features between two Persian Gulf examples, Andros Island, and western Australia. Not shown is the Turks & Caicos Islands, which is very close to the Andros Island example (Hardie and Shinn,1986). Circle 'A' denotes the Quatar-type tidal flats, which lack well-developed algal mats or anhydrite. Circle 'B' shows soil clasts, current-deposited intraclasts, minor algal heads and domes, mud polygons, and mudcracks from Andros Island. Circle 'C' depicts the Trucial Coast (Abu Dhabi sabkha) and Western Australia with nodular anhydrite. Circles 'D' and 'E' distinguish the two where the former may have coral reefs and the latter has large club-shaped algal structures and rippled cross-bedded sands. Adapted from Shinn (1983). 150 include: 1) a hot and arid climate; 2) evaporite minerals including dolomite, gypsum and anhydrite; and 3) significant progradation of the tidal flats over lagoonal muds (Harris, 1994). Figures 5.32 and 5.33 depict the facies from the Abu Dhabi Sabkha in plan view and profile, respectively, as well as the diagnostic sedimentary structures of each environment. The sabkha is roughly 80 miles long and 5-15 miles wide. Landward of the sabkha are older exposed rocks. Seaward, the sabkha grades into 1) cyanobacterial mats, 2) pellets and skeletal sands, 3) pellets and mud, 4) organic reefs, 5) oolites and 6) skeletal sands. All of these facies, other than oolites, are present in the Coronach Member (see Table 5.6 for comparison). Lake MacLeod is the only known modern example of an aggradational system. Figure 5.34 shows that is completely enclosed by the continental interior to the east and north and a barrier that bars it from the open ocean to the west and south. Today it is an evaporite basin partially filled by an ephemeral brine sheet, with deposits of gypsum and halite at or below the sediment surface (Logan, 1987). Underlying these evaporites are accretionary limestones, among other lithologies, deposited during transgressive marine- basin phases (Logan, 1987). This simple carbonate-evaporite sequence is represented in the middle sketch of Figure 5.34C and is similar to the Coronach Member. Another similarity of this analogue includes the basin-centered nature of the evaporites. 151 Figure 5.32A. Interpreted fades distribution around Abu Dhabi City, UAE. The Abu Dhabi sabkha provides an exceptionally good modern analogue to the ramp setting of the Coronach Member. Similar climate, hydrology, water depth and wave energy has created similar fades. The 10 fathom contour equals ~18m. High-lighted box shows location of satellite photo below. Re-drafted from Kendall and Skipworth (1969). Figure 5.32B. Annotated satellite image from the Abu Dhabi sabkha showing complexity of shoreline and associated fades. Sabkha is area of active halite, gypsum and anhydrite formation, as well as cyanobacteria mats in the intertidal setting. Adapted from Kendall et al. (2009). 152 anhydrit* Diagnostic Sedimentary Structures quarti ••Han aand with rsat mark*. Unconformity. | (chlckan wlr* Inlan). [O Gradatlonal cantact. Highly srganlc algal lamlnatlMi* with blrdaaya volda and madcracka. Lamlnatlwia laaa algal downward grading into tarrwid llm* mad ar dslomlta. Gray faurrowad and pallatal lima mud. A. Barad gralnatsn* cruat v may or may not b« praaant. (A)Craaabaddad earbmata gralaatana [tidal bar or baach). May bo oolitic or alllclclaatk aand poaalbly uadarlaln by coral or othar opan watar faciaa. (j) Lagoonal faciaa. Cray burrow-mottled lima mad (may ba dolomltlc). Figure 5.33. Profile (A) and section (B) from the Abu Dhabi modern depositional model. In (A) the vast supratidal flats contain anhydrite. This grades into a gypsum mush zone, followed by an intertidal zone of algal (cyanobacterial) laminated mats and burrowed lime muds. Deepening leads to a subtidal lagoon, which is protected by an outer barrier island. The section in (B) shows this profile down to the subtidal lagoonal fades. The gradation from subtidal up to supratidal indicates an off-lapping sedimentary prism. Listed on the right are key characteristics of each zone. There is an extremely close similarity between the features of this depositional setting, as well as the prograding nature, with those characteristics described in the Coronach Member. Taken from Shinn (1983) and Hardie and Shinn (1986). 153 Australia BARRIFR GRABEN HINTERLAND MACLEOD LVAPORITC THEALLA DEPUCH rMTN BIBflA LIMLSfONC DUOBBA SANDS 0 to Ifim I IT f LE CHICK FUTN Of. IREALLA /CAmOABIA DAMPICR FMTN IIMC-STONE. / WESTPHAl CLAY K OHO JON FORMATION GIRAIIA CALC ARENtTE / TRFAILA TQlPALtA C-ARDABIA OMOUP 1CAP0A15JA KOROJON fMTM KOROJON FMTN Figure 5.34. Lake MacLeod evaporite basin. This basin, from western Australia, is barred from the open ocean by a limestone and sand dune barrier to the west, as depicted on the satellite image (B). A cross section (C) from barrier through the basin to the hinterland shows a thick carbonate (Trealla Limestone) overlain by a basin-centered evaporite deposit, which is actively precipitating halite and gypsum. Other lithologies are also present in the basin, such as clays, but the accretionary style of carbonate to evaporite could represent the only Recent aggradational analogue to the Coronach Member. Modified from Logan (1987). 154 6.0 DIAGENESIS: DESCRIPTION, GEOCHEMISTRY and INTERPRETATION Twenty-six diagenetic events have been recognized in the Coronach Member. These were placed in order of timing relative to each other, or diagenetic paragenesis, based on petrographic observations (Table 6.1). Most events have acted to degrade reservoir quality in the Coronach Member. Following is a description of all diagenetic features from each facies followed by hypotheses on their origins. 6.1 Anhydrite Three occurrences of anhydrite (CaS04) were recognized in core and thin section. 6.1.1 Anhydrite 1 Description and Interpretation Anhydrite 1 consists of nodules of anhydrite, which in turn are composed of small lath-like crystals. It is found mainly in Facies 4, thus it seems to be related to depositional environment. A lack of primary features such as bedding, slump folding, mudcracks, and flat-pebble conglomerates in Facies 4 suggests pervasive diagenetic destruction due to recrystallization, replacement or deformation (Spencer and Lowenstein, 1990). "Chicken-wire" textures characterize Anhydrite 1, which may be found as syngenetic deposits in modern sabkha settings (Schneider, 1975). These textures, however, are not restricted to such settings, as discussed in section 5.7.3. Though nodules may not give unambiguous information about their environment of formation (Spencer and Lowenstein, 1990), there is evidence in the Coronach Anhydrite for disruption by intra-sediment anhydrite/gypsum growth. Rare, single 155 Diagenetlc Paragenesis Impact on Reservoir DiaoeneticEvant ^Ujcatjon Eooeneoc Anhydrite 1 (nodular anhydrite) Factes 4 degrade Anhydrite 2 (anhydrite pseudomorphs) Factes 3-4 degrade Dolomite 1 (CryptocrystaMine to microcrystaBine Fades 3-4) Faaes 3-4 degrade & enhance Cafcffe 1 (Fibrous to balded marine crusts) Factes 2 degrade Calcite 3 (Sparry cemerrtstone of algal reef mounds) Faaes 2 degrade Calcite 5 (Pendant arid menicus-type) Faaes 2 degrade Calcite 6 (Kdcritization of skeletals) Fades 2 degrade Calcite 7 (Peioktal cement) Faaes 2 degrade CalichUication (Fades 5) Fades 5 Dissolution ofaragonitic skeletals Faaes 2 enhance Silica 3 (Chaiecdony infill of Soienopora) Factes 2 degrade Calcite 4 (Sparry cement inM of dissolved grains) Factes 2 degrade Silica 4 (MegaQtz cement of Dimoph & mimic Ca-replace) Fades 2 degrade Dolomite 2 (fabric-seldctive dofo of burrows) Factes 2 enhance Dolomite 3 (Non-fabric selective doto of matrix; downward How) Faaes 2 enhance Silica 5 (Mottle structures) Factes 2 degrade Compaction (Non-deforming) Fades 1-5 degrade Pyrite Factes 1-2 noeffed SHica 1 (white nodular chert) Factes 2 degrade Silica 2 (brown bedded to nodular chert) Factes 2 degrade Mechanical Deformation (Fracturing) Factes 1-5 enhance Chemical Solution (StyoHtization) Factes 1-5 degrade Calcite 2 (Neomorphic spar) Factes 2 no effect Dolomite 4 (HTD or Burial Dolomite) Factes 2 degrade Silica 6 (Bed at top Coronach Member disconfbrmity) Fades 5 degrade Anhydrite 3 (Biaded & PoikMotopc anhydrite) Faaes 2 degrade I Near-Surface 8h—owsuto-etfto < 600m | 600-1000m > 1000m I Table 6.1. Diagenetic Paragenesis. Twenty-six diagenetic products were recognized, mainly secondary cementation and replacement, occuring through near-surface to deep burial realms. Depth divisions based on Machel (2004). Eogenetic includes near-surface marine phreatic, mixing zone, freshwater phreatic and freshwater vadose zones. Mesogenetic is moderate to deep burial processes. Telogenetic refers to exhumed rocks into zone of subaerial exposure or erosion, which may include calichification of Facies 5. Grey areas denote possible extension of events into other diagenetic realms. laminations or sediment appear to be "moved" by nodular growth. Also, nodules grade downwards into randomly oriented gypsum pseudomorphs (Anhydrite 2), which is another criteria for intra-sediment growth (Spencer and Lowenstein, 1990). Therefore, Anhydrite 1 may be a diagenetic precipitate as opposed to a primary subaqueous precipitate. Anhydrite 1 is probably the product of eogenetic transformation from gypsum, which itself was syngenetically (primary to very early diagenetic) emplaced within a supratidal environment, whether in a basin-centered aggradational model or a prograding sabkha model. What is not clear is if the present-day Coronach Anhydrite was deposited as anhydrite, or altered from gypsum upon burial diagenesis. Subsequently, it is also not clear if such alteration took place soon after burial or in the deep burial environment. Sabkha-type anhydrites precipitate in the capillary zone, occurring between the water table and the sediment surface (Kendall and Skipworth, 1969). The precipitation of anhydrite in the capillary zone continues until capillary evaporation is shut off. This zone is usually no more than lm in recent and ancient examples (Moore, 2001). However, the capillary zone fluctuates with seasons, grain size, or a rise and fall in sea level (Moore, 2001). By reasoning, a capillary zone of lm could expand vertically due to active sedimentation, progradation of the supratidal flats, changes in the hydrological regime, and minor fluctuations in sea level to produce a thicker anhydrite. Re-hydration of anhydrite could also allow fluids to reach greater depths and precipitate diagenetically in the sediment (Moore, 2001). Thus, capillary zones are dynamic and could, over time, produce a 4m thick anhydrite zone. 157 6.1.2 Anhydrite 2 Description and Interpretation Anhydrite 2 is found only in Sub-facies 3B and 4A. It occurs as small laths ranging from 0.5 to 1mm in length (see Plate 5.23D), which is very similar to those that coalesce into nodules (Anhydrite 1). The former however, are found as individual crystals to twin-sets dispersed randomly through the matrix. These are probably pseudomorphs of gypsum because gypsum typically takes this form (Kerr, 1977). Concentration of anhydrite ranges from 0-20% and increases upward into Facies 4. That Facies 3 and 4 were subjected to hypersaline water suggests gypsum growth occurred diagenetically very early. No other diagenetic events are present to indicate a more precise paragenesis. In modern settings gypsum is found in the upper lm of sabkha sequences (Moore, 2001), but is also found in modern intertidal zones (Kendall and Skipworth, 1969). Given Anhydrite 2's close juxtaposition to Anhydrite 1, the two are likely related. 6.1.3 Anhydrite 3 Description and Interpretation Anhydrite 3 occurs as 1) large, l-3cm long bladed crystals (Plate 6.1A-D) and 2) poikilotopic cement (Plate 6.IE); both are restricted to the subtidal facies (Facies 2) and are grouped together for this reason. It averages 3% in all samples taken from this facies, but is most common in the lower 1/3"1. Bladed crystals may take "rosette-like" structures but probably do not form within soft sediment because they are commonly associated with, and may line, fractures (Plate 6.1A-D). They also cut through all other diagenetic minerals, such as chert or 158 Plate 6.1. Anhydrite 1. A) Bladed anhydrite cutting through dolomitized section. Dolo rhombs are partially-replacing anhydrite; both are probably burial products. From 4-2-14-21W2, 2109.6m, XPL. B) Rosette-shaped anhydrite blades growing within, and radiating outward, from a fracture. From 3-16-2-10W2, 3013.25m, XPL. C) Rosettes of bladed anhydrite in core. From 9-34-3-4W2, 2615.4m. D) Numerous anhydrite blades up to 2cm long in core, associated with a fracture on right side of the core. From 14-26-6-11W2, 2549.7m. E) Poikilitic anhydrite filling pore space around dolomite crystals. From 15-28-12-2W2,1918.5m, XPL. 159 dolomite, and are not cut by styolites, thus its timing is considered very late diagenetic (deep-burial). It is probably unrelated to Anhydrites 1 and 2; however, due to differences in timing, its source is not evident. A deep-burial origin may suggest that basinal fluids infiltrated the Coronach Member via faults and fractures; bladed crystals were mainly associated with fractures in the core. Large crystals of poikilotopic anhydrite were found in just one sample. Poikilitic anhydrite is commonly cited as forming in the burial diagenetic environment (Harris et al., 1985; Choquette and James, 1990). One sample contains poikilitic anhydrite engulfing dolomite rhombs. Therefore, this anhydrite is post-dolomitization, but a more specific timing is not known. 6.2 Dolomite Four types of dolomite (CaMg(CC>3)2) were recognized in thin section. Figure 6.1 is a plot of oxygen versus carbon isotopes for all carbonate samples, which will be drawn upon for the following interpretations on dolomite and calcite. Figure 6.2 is the same plot but for dolostone types. Figure 6.3 shows strontium isotopes from samples of the Coronach Member, which will also be used for interpretation of calcite and dolomite. Cathodoluminescence (CL) petrography is a method used to shed light on depositional facies, diagenetic fabrics and porosity relationships (Dravis and Yurewicz, 1985). Particularly, CL has been used to recognize differences in manganese (Mn) and iron (Fe) contents (Reeder and Prosky, 1986; Savard et al., 1995). All dolomites were placed under a CL microscope (Plate 6.2) and those observations are also mentioned below. 160 5.00 • • • ... .'••• ' • . • 4.00 • Limestone • 3.00 • Dolomite 2.00 " * • . #• , 1.00 . 0.00 -1.00 ... . • • '^"'i -2.00 wSpr -3.00 . "" ' -4.00 , • i—< . <• •• •• ..I- • " * -5.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00 8180 PDB Figure 6.1. Oxygen versus carbon isotope plot for fifty samples from the Coronach Member. Limestone samples have at least 90% calcite. Dolomites have 30-90% dolomite. Percentages are listed in Appendix B. 161 3.00 2.00 1.00 • 'A* 0.00 ^ it -1.00 • Facies 2 (Dolomites 1-4) i»*r -2.00 • Facies 3 (Dolomite 1) t' ' A Facies 4 (Dolomite 1) -3.00 • Facies 5 (Dolomite 1) -4.00 -a.oo -7.oo -a.oo -5.00 -4.00 -3.00 -2.00 5 0 PDB Figure 6.2. Oxygen versus carbon isotopes in Coronach dolostone samples. Data is divided into facies: Facies 1 has no dolomite; Facies 2 has undifferentiated Dolomites 1-4; Facies 3-5 all contain only Dolomite 1. Average isotopic values of all samples: ,80/160 = -5.7%o and 13C/12C = -0.09%. 162 0.71050 1 0.71000 "I'mmi I'" • Limestone • Dolomite .2 0.70950 1 k. CO 0.70800 0.70750 i —i 1 i r 1111 i 6 8 10 12 14 16 18 Number of Samples '3r/"Sr MILLIONS OF YEARS Figure 6.3. Strontium Isotopes. A) Plot of "Sr/^Sr ratios of twenty-three samples from the Coronach Member. B) The Strontium isotopic range for seawater (in blue) plotted versus geological time; re-drafted from Veizer et al. (1999). Blue area is a best fit over data that includes over 4000 samples of brachiopods, belemnites, conodonts and micritic matrix. More than 90% of the samples from the Coronach Member fall within the range 0.70794 to 0.70895 (gray-shaded rectangle). Dolomites (purple double arrow) plot higher than the range for Late Ordovician seawater, but limestone (green double arrow) is a close fit. 163 B D E F Plate 6.2. A) Thin section showing rhombs of dolomite. B) CL photo of 'A' showing dull-red luminescing dolomite. From 3-16-2-10W2, 3013.25m. C) Mixture of calcite and dolomite, but accompanying photo (D) in CI shows remant tabular grains (center of photo) and possibly shells (top of photo). From 11-20-2-18W2, 2996.85m. E) Calcific wackestone that under CL (F) shows faint luminescent dolomite rimming unknown shell. Same sample as previous. All CL photos were enhanced by 20% brightness. 164 6.2.1 Dolomite 1 Description and Interpretation Dolomite 1 is a cryptocrystalline to microcrystalline dolomite constituting the complete replacement of Facies 3 and 4. It averages 40% and 90% of Sub-facies 3A and 3B, respectively. In Sub-facies 3A it increases in concentration upwards. Dolomitization may destroy laminated textures and in such cases the presence of the facies is inferred based on loss of skeletals and stratigraphic position. The small crystal size has commonly been used to infer fast rates of crystal growth (Ruzyla and Friedman, 1985). Cryptocrystalline textures are commonly associated with a syndepositional sabkha origin (Bathurst and Land, 1985). Therefore, dolomitization may have been occurred early when sediments were still permeable. Other evidence for early dolomitization is the preservation of peloids (originally soft pellets) from compaction. It is clear that Facies 3 and 4 were deposited in a hypersaline environment, as supported from the absence of skeletals and high concentration of anhydrite. Once gypsum and anhydrite precipitates out of a hypersaline fluid, the pore fluids dramatically increase in Mg/Ca ratio from 5:1 to over 35:1, which is conducive for the formation of dolomite (Moore, 2001). The replacement of aragonite and calcite by dolomitization is given by the equation: 2+ 2+ 2CaC03 + Mg -• CaMg(C03)2 + Ca (6.1) In supratidal settings carbonate is supplied in the form of bicarbonate due to a sabkhas slightly acidic diagenetic setting (Equation 6.2; Morrow, 1990). 2+ + 2+ CaC03 + Mg + HC03 -• CaMg(C03)2 + H +Ca (6.2) 165 A continual supply of marine water and intense evaporation leads to a circulation of fluids - referred to as the seepage-reflux model (Figure 6.4; Adams and Rhodes, 1960). This is a process that requires low-lying tidal flats and high evaporation rates in hot, preferably arid environments. Both requirements were present during deposition of the Coronach Member. In an aggradational model the process is probably much the same: the basin-wide intertidal\supratidal flats are recharged by seawater, but rather than being sourced from a laterally juxtaposed subtidal setting, seawater is derived from off-platform areas via major storms or minor sea level fluctuations. The seepage-reflux model suggests dolomite is very early diagenetic and precipitated soon after gypsum/anhydrite. The process that forms Anhydrites 1 and 2 and Dolomite 1 may even be penecontemporaneous with deposition, such as some sabkha dolomites in the Persian Gulf (Illing et al., 1965); however, most modern tidal flats typically only have 20-40% dolomite (Hardie and Ginsburg, 1977) implying that continued reflux is needed for complete dolomitization. The preservation of pellets is another indication of very early dolomitization. Otherwise these would have been compacted into a massive clotted micrite (Hardie and Ginsburg, 1977). Microcrystalline textures such as those observed in Dolomite 1 are commonly associated with sabkha dolomites and rarely reported for other dolomitizing environments (Allan and Wiggins, 1993). Dolomite 1 changes in crystal size from cryptocrystalline to microcrystalline downwards and might suggest the source of dolomitizing fluids was from above. Cryptocrystalline dolomite usually has no porosity but microcrystalline dolomite has fair to good intercrystalline and vuggy porosity. Vuggy porosity may be the result of 1) 166 A. RECHARGE Marine Recharge Lagoon Coast Sabkha B. EVAPORATION Marine + Mixed* Continental Lagoon Coast Sabkha — Water Table Figure 6.4. Seepage/reflux model. Re-drafted from McKenzie etal. (1980). In (A) winter seasons promote storms that recharge tidal flats. In (B) during summer seasons, evaporation exceeds recharge, promoting anhydrite/gypsum precipita tion in the capillary zone as well as dolomitization of underlying sediment as fluids percolate downwards. 167 flushing by meteoric water (Moore, 2001), as identified in Red River Fields such as Cabin Creek, Montana; 2) cannibalization of skeletals by Ca-undersaturated fluids (Kent, pers. comm.); or 3) the dolomitization process itself. Machel (2004) suggests that when Mg is used up, or if dolomite-calcite-water approach equilibrium, under-saturation with respect to calcite is maintained, thereby dissolving the host sediment. Dolomite 1 is depleted in 180 by 3.5%o relative to the expected range of -3.5%o to - 1.5%o for dolomites precipitated from Late Ordovician seawater (Figure 6.2; Major et al., 1992; Qing et al., 2001a). This assumes a mean fractionation of 2.5%o between dolomite |o and calcite. Figure 6.1 shows that dolomites, relative to limestones, are enriched in O, suggesting either fractionation or that the former precipitated from evaporated seawater, which is consistent with the reflux dolomite model. Figure 6.2 shows that Facies 3 dolomites are depleted in ,3C relative to Facies 4 and 5 dolomites. This depletion in carbon-13 may be indication of microbially-mediated dolomite, the source of which could be the cyanobacterial mats present throughout Facies 3. Dolomite 1, along with all other carbonate samples, may have had their isotopic signature reset during burial diagenesis through the process of recrystallization. Strontium isotopes (Figure 6.3) for Coronach dolostones are higher than expected values for Late Ordovician seawater. The values are more in line with Silurian seawater and might be indication that these, or other late diagenetic fluids, reset rocks from the Coronach Member. CL of Dolomite 1 shows a dull red luminescence similar to all forms of dolomite. The fine crystal sizes prohibit a more detailed examination of luminescence. 6.2.2 Dolomite 2 Description and Interpretation Dolomite 2 is the fabric-selective dolomitization of Planolites' burrow-fills (Plate 6.3C, see also Plate 5.17C). Dolomite crystals are euhedral and may be found throughout Facies 2, but particularly in Sub-facies 2D where burrows are most prevalent. Dolomite 2 ranges in size from microcrystalline (l-4|im) to microspar and pseudospar (5-50p.m). It is generally believed that the action of burrowing has created high-permeable pathways that have been exploited by dolomitizing fluids (Kendall, 1977; Gingras et al., 2001, 2004). Preferentially-dolomitized Thalassinoides burrows occur in the Yeoman Formation. They were first described by Kendall (1976) and have been ascribed to a number of possible physical and compositional controls (Kendall, 1977; Gingras et al., 2001; Pemberton and Gingras, 2005). The one given the greatest consideration is the focus of Mg-saturated fluids by the burrows, which have acted as high-permeable conduits in a relatively tighter matrix (Kendall, 1977). By analogy, the same process may have influenced burrows within the Coronach Member. One major difference however, is Planolites' burrows do not form a large, continuous network as Thalassinoides, partly because of their minute size. Other burrows show incomplete dolomitization creating a halo of un-dolomitized micrite around the dolomite crystals. It is not clear what causes this feature, but smaller causative burrows may be one hypothesis (Pak and Pemberton, 2003). Oxygen isotopes from Dolomite 2 (Facies 2) are similar to values for Dolomite 1, showing an enrichment of 180 relative to limestone samples. This might also be an indication of the formation of dolomite from slightly modified seawater or it may simply 169 Plate 6.3. Dolomite diagenesis. A) Dolo- psar (up to 100|jm) showing characteristic ..v •*» : rhombohedron morphology. From 6-5-8- 22W2, 2508.75m, PPL. B) Dissolved - :- 170 be due to fractionation. CL also showed the same dull red luminescence as in Dolomite 1. The larger crystals of Dolomite 2, however, did not show compositional zoning. Timing of Dolomite 2 is uncertain, although it does pre-date compaction- or seismic-induced fractures as well as Anhydrite 3. Dolomite 2 has enhanced reservoir quality in cases where planar-e textures are well-developed. Unfortunately, Planolites are too small volumetrically to be of any significance to economic hydrocarbon accumulations. Dolomite 2 is a replacement mineral, as shown by equation 6.1. 6.2.3 Dolomite J Description and Interpretation Dolomite 3 is the non-fabric-selective replacement of matrix and skeletals in Facies 2. Crystal sizes range from microcrystalline (l-4|am) to very fine crystals (80|im) with characteristic rhombohedral morphology (Plate 6.3A, C; see also Plate 5.15A, C). Planar-5 textures are dominant over subordinate planar-e textures and both types may occur together. One thin section is composed of 90% dolospar with crystals 20-80p.m in size (Plate 6.3A). Dolomite preferentially replaces matrix first. As the percentage of matrix-replacive dolomite increases, the skeletal grains appear increasingly susceptible to alteration as well (Plate 6.3E). Dolomite 3 shows two geopetal fabrics: 1) dolomite decreases in percentage downwards, and 2) brachiopod fragments act in an "umbrella-like" fashion protecting parts of the underlying matrix (Figure 6.5). A thin (< 3cm) zone of dissolved micrite and skeletals accompanies the geopetal features. It is found between the base of dolomitization and the top of unaltered limestone and has resulted in high vuggy and 171 -T- • , t Top 500um > r Brachiopod Conduit 0.5cm A Figure 6.5A. Geopetal dolomitization. On right is a hand sample used for a thin section, showing light brown areas of dolomite set against a dark brown calci- wackestone. Dolomitization geometry indicates downward orientation related to gravity flow of fluids (blue arrows denote likely flow orientations in two dimensions). Fluids flow around hard substrates and allochems such as brachiopods, while utilizing conduits, which are possibly fractures, to work their way through sediment. On left is a thin section photograph from the hand sample showing dolomitization abutting a brachiopod shell, clearly indicating a geopetal structure. The Brachiopod in this case acted as a barrier to fluid flow that was responsible for dolomitization of the micritic matrix. From 13-23-1-17W2, 9984.5ft, thin section in PPL. 172 Figure 6.5B. At top is a core sample showing complex diagenetic mottles created by dolomite (light-grey) and calcite (light to dark brown). The mottling takes on semi-circular patterns due to the presence of numerous brachiopods that are exerting a control on where micrite is dolomitized. Below are two close-up photographs of the core sample. Note the high-relief dolomite mottles, which appear to be "held", in some cases, by clusters of brachiopod fragments. The geopetal structure is not as evident because the mottles were churned post- lithification, indicating dolomitization was relatively early. Close-up photographs are about 1cm across. From 3-6-6-6W2, 2555m. 173 moldic porosity. This indicates carbonate dissolution and dolomitization were concomitant (Machel, 2004). These dolomites have little porosity (maximum 2% in thin section), and typically dolomite extends downwards from the top of Facies 2 from 0cm to 3m. The fact that most sediment immediately above Facies 2 is dolomitized (Dolomite 1), suggests that these stratigraphically adjacent dolomites may be related to the refluxing brines associated with the formation of Dolomites 1 and 2. Gravity and/or density-driven induced fluids could have entered these sediments (including Sub-facies 2D down to Sub- facies 2B) and replaced matrix and partially replaced skeletals before the hydrological system was shut down or the supply of Mg was used up. Incomplete replacement is a function of the percentage of matrix, proximity to source of dolomitizing brines, grain size, and permeability (Machel, 2004). However, one major oddity is the variably dolomitic to un-dolomitic Sub-facies 3A. If fluids percolated downwards to dolomitize the top of Facies 2 then Sub-facies 3A should show more complete dolomitization, but this is not the case. Two variations of the seepage-reflux model help shed light on this problem. The first, envisioned by Morrow (2001) and Sailer and Henderson (2001), involves multi stage dolomitization whereby early fluids dolomitize tidal flats and underlying lagoonal sediments (Figure 6.6). Continued flow, or a separate second-stage, adds dolomite to previously dolomitized areas, while becoming under-saturated with respect to calcite and aragaonite, creating a "front" of aggressive carbonate dissolution. Lateral flow is the major flow vector in this model. 174 Stage 1. Replacement Dolomitization by Normal Seawater & Mesohaline Brines of Shelf Interior Macrodissolution is minor in stage 1 because fluids are in bulk equilibrium with calcium carbonate Stage 2. Dolomite Cementation of Shelf Interior - Macrodissolution and Dolomitization of Downdip Limestones by Brines from Shelf Interior Brines evaporate in equilibrium with dolomite only in stage 2, yielding brines that can aggressively dissolve downdip limestones and dolomitize them Figure 6.6. Schematic model for multi-stage reflux dolomitization. Original dolo- mitizing fluids are succeded by second stage dolomitization which leads to carbonate dissolution in downdip subtidal limestones. Modified from Morrow (2001). SABKHA RESTRICTED PLATFORM OPEN MARINE SALINE -199 b* —PENESAUNE >72 &- -VITASAUNE Storm recharge Evaporation Free inflow High frequency sea-level changes drive reflux fluids into platform Sabkha Dolomite Penesa Ine Dolomite Marine Dolomite Figure 6.7. Schematic model for single-stage, simultaneous dolomitization of sabkha and platform carbonates by saline and penesaline fluids, respectively. Penesaline fluids driven into platform by high-frequency sea-level changes. Adapted from Qing etal. (2001c). 175 The second model (Qing et al., 2001c; Harvey et al., 2004) includes saline dolomitization of tidal flats in the sabkha environment, but instead of these brines continuing to percolate down to other zones, simultaneous dolomitization by penesaline fluids occurs in restricted platform settings (Figure 6.7). These fluids are driven through the sediment by reflux, which in turn is a function of high-frequency sea level changes. This model does not need to be modified for the aggradational depositional system. The first model, using multi-stage events, should produce dolomite crystals with compositional zoning owing to slightly different fluids from each successive 'pulse'. Zoning was not observed from CL petrography (Plate 6.2A, B). Neither is it reasonable that fluids could have percolated long-distances along the ramp profile in a progradational model; the hydraulic head required would be insufficient to push fluids such distances (100's of meters) without significant topographic relief. Therefore, a multi-stage dolomite model can probably be ruled out. The second model explains the lack of dolomite in Sub-facies 3A; fluids are not needed to circumvent this facies to reach Facies 2. Penesaline fluids of a partially restricted lagoon (Progradational model) or from a partially restricted basin (Aggradational model) dolomitized the upper potions of Facies 2. Examples of the restricted lagoon hypothesis are Hamelin and Freycinet Basins from Shark Bay, Australia which have salinity zonations from normal salinity through hypersalinity (Hagan and Logan, 1974; Logan and Cebulski, 1970). Carbon and oxygen isotopes show similar ranges as those observed in Dolomite 2. Dolomites may have formed from slightly modified seawater, though fractionation can also create the observed 180 value differences between dolomites and limestones. 176 Based on the above possible models, timing of Dolomite 3 is very early. Furthermore, the matrix would need to be permeable for dolomitizing fluids to create the geopetal structures observed in core (Figure 6.5). There was no direct evidence in thin section for a more concrete paragenesis. 6.2.4 Dolomite 4 Description and Interpretation Dolomite 4 is "saddle" dolomite, which is a term referring to its curved crystal faces that is commonly observed in thin section as undulose extinction (Allan and Wiggins, 1993). Saddle dolomite was present in two samples, showing characteristic curved crystal faces (Plate 6.3B, D). Saddle dolomite, a product of high-temperature (>80°) crystallization, occurs in Facies 2 as void-filling cement in vugs or molds. It ranges in size from 200|j.m to 700(im. It is a very minor constituent (< 1%) and is restricted to the lower half of Facies 2. Saddle dolomite is thought to have formed from recrystallization at high temperatures or by hydrothermal fluids (HTD; Davies and Smith, 2006). Dolomite cementation is most simplistically shown by Equation 6.3. 2+ 2+ 2 Ca + Mg + 2C03 "—> CaMg(C03)2 (6.3) HTD is usually considered a late diagenetic product because of its association with hydrocarbons, base-metal mineralization and sulfate-reducing processes (Radke and Mathis, 1980). Smith and Davies (2006) and Smith (2006) showed that HTD in the Black River fields of New York State was sourced from seismically-active faults that acted as conduits for fluid-flow originating from deeper formations. Relationships between faults and HTD have been established by Pierce et al. (2004), Packard in Packard and Workum 177 (2004), Davies and Wendt (2005), and Davies (2004). Without a delivery system such as this, hydrothermal fluids would equilibrate with the normal geothermal gradient and dolomite might not overcome thermodynamic factors necessary for precipitation. Notwithstanding hydrothermal origins for saddle dolomite, the latter can also form at elevated burial temperatures (Choquette and James, 1990). Saddle dolomites generally indicate temperatures of at least 80°C (Machel, 2004). Therefore, one can deduce the origins of saddle dolomite by investigation of the burial history. Burial history curves from southern Saskatchewan show that Late Ordovician rocks reached maximum depths of ~750m greater than present depths (Figure 6.8; Osadetz et al., 1998). At a normal geothermal gradient of 25°C per 1km in sedimentary basins (Choquette and James, 1990), that equates to temperatures of 96.7°C and 94.8°C for each of the two Coronach Member samples containing saddle dolomite (Table 6.2). That is clearly sufficient to have created saddle dolomite without the need for hydrothermal fluids. Furthermore, Osadetz et al. (1989) suggests a geothermal gradient of 40°C/km along the western side of the Nesson Anticline in the Williston Basin. This high heat gradient is believed to be related to a thermal anomaly, called the North American Central Plains Conductivity Anomaly (NACPCA) that runs N-S through the centre of the present-day Williston Basin (Figure 1.2; Majorowicz et al., 1988). This feature in turn is related to compositional changes in the Precambrian crust (Osadetz et al., 2000). The two samples are within this high heat zone; thus, the anomalous geothermal gradient would place maximum temperatures over 150°C. Lack of fracturing in the two cores with saddle dolomite suggests these are probably burial dolomites. Faults were probably not active until Silurian time or later and 178 K (Pi E i0| M til 2000 — Present Bunal Depth 2000m Max Burial Depth 2750m 3000 Ceepee Baildon 2-11-15-26W2 1 , , j-'f'-r i i |'"t •T"T" T" f"T"r r t -j-'t—r-r-t 1 i > t t r...r-r-,-r-r-r r r-r j i t "f r -j—r 550 500 300 200 100 Age (my) Figure 6.8. Representative burial history diagram for the Williston Basin. Location is the Ceepee Baildon well at 2-11-15-26W2, one range west of the study area. Herald Formation (Coronach Member + Lake Alma Member) is highlighted in red, showing it's maximum burial was at 2750m in the Eocene, or roughly 750m deeper than present day depths (2000m). Modified from Osadetz etal. (1998). 179 Saddle Dolomite Samples Maximum 'Max Burial "Anomalous Max Location Depth Burial Depth Temp CC) Burial Temp (°C) 10-25-1-15W2 3118m 3868 96.7 154.7 13-23-1-17W2 3043m 3793 94.8 151.7 Table 6,2. Burial temperatures for saddle dolomite samples. Two geothermal gradients are given, one for normal intracratonic basins, one for an anomalous gradient that runs through the study area. Maximum depths calculated from burial history diagram (Figure 8.5). * Normal geothermal gradient is 25°C ** Anomalous geothermal gradient is 40°C 180 burial history diagrams indicate Late Ordovician rocks didn't reach sufficient depths until the end of the Cretaceous (Figure 6.8). Unfortunately, there is not enough saddle dolomite to be analyzed for isotopes that would shed light on the temperature of formation. Under CL, Dolomite 4 has a dull red luminescence but a brighter red luminescence along fractured surfaces of the dolomite crystals. Timing is assumed to be late diagenetic because of the burial depths needed to reach sufficient recrystallization temperatures. 6.3 Silica Six types of siliceous cement have been identified based mainly on form and color in core and thin section. The first five types are all found in Facies 2, implying 1) a common origin for these types and 2) a relation to the subtidal depositional origin. Silica 6 is found in Facies 5. 6.3.1 Silicas 1-5 Description Diagenetic silica occurs in Facies 2 as chert, chalcedony, or microquartz and megaquartz (Plate 6.4; see also Plates 5.9A, C; 5.10A, B). Silica averages 12% in the lower l/3rd but just 1% in the upper 2/3rds of the facies. Silica 1 is a white to beige-colored nodular replacement chert, 2-4cm2 in size, and is found in the lower 2m of Facies 2 at a maximum of 5% of core. Rarely, it forms 3-5cm thick beds (Plate 6.4D). Silica 2 is a similar nodular replacement chert, but dark brown in color and more massive. It is associated with dissolution of the primary rock (Plate 6.4A), is limited to the lower half of Facies 2 and constitutes a maximum of 2% of Facies 2. 181 * i 'Mi D • I D D 1mm 250|jm Plate 6.4. Silica diagenesis. A) Dimorphosiphon (D) grairistone with chert nodule (black). Chert has replaced matrix (amorphous material) and several skeletal grains (megaquartz). Associated with chert emplacement is dissolution of matrix and green algal plates. From 2-34-1-32W1, 2317.3m. B) A massive encrusting Solenopora with siliceous cementation (light-colored) around its edges. Pyrite is also present (black grains). From 12-13-2-19W2, 2993.4m. C) Chert replacement of micrite matrix and meqaquartz replacement of ostracode(?) skeletal as well as the cementation of its interior. Megaquartz may have mimically replaced calcite, which has identical forms and crystal sizes in Fades 2. Skeletal was likely originally replaced by calcite spar while its interior space was cemented with calcite. From 1-9-21-16W2, 1767.8m. D) Core sample showing a nodular bed of brown-coloured chert. Scale on left in em's. From 14-26-6-11W2, 2557.8 m. 182 Silica 3 was recognized only in thin section as a spherulitic chalcedony cement-infill of mainly Solenopora tubules or complete to partial replacement of Solenopora (Plates 6.4B and 6.5). Spherulitic chalcedony exclusively forms as a void-filling cement, not as a replacement (Hesse, 1990a). Silica 4 is a microquartz (5-20^m) to megaquartz (20- 2000|im) cementation of pore spaces (Plate 6.4C), which may be created by dissolution of skeletals, particularly unstable Dimorphosiphon. Silica 5 is a white-mottled chert similar to Silica 1 but is found in just three cores in the uppermost l-2m of Facies 2 (Plate 6.6). They occur as patches or nodules resulting from differences in mineralogy and/or grain size. Several examples show dolomite and nodular calcimudstone are "cored" by chert. Contacts between chert and dolomite appear to be very gradational. This relationship implies some sort of genetic association. These mottles do not appear to be related to diagenetic replacement of calcareous red algae (Plate 6.5), nor are they produced by the fabric-selective dolomitization of burrows. 6.3.2 Sources of Silica Sources of silica include volcanic ash, hydrothermal fluids, or lacustrine, pedogenic and biogenic sources (Hesse, 1989; 1990a, b). Lacustrine sources can likely be ruled out because the Coronach Member was deposited in the marine environment. That silica is low in concentration generally rules out volcanic and lacustrine sources, which typically occur on the scale of beds, members and entire formations (Hesse, 1989). Furthermore, bentonites, volcanic ash deposits containing colloidal silica (Bates and Jackson, 1987), are not known from Ordovician rocks of the Williston Basin. However, they are frequent in carbonates as late as Maysvillian from the Appalachian 183 Plate 6.5. Algal-related mottled textures, as determined from companion thin sections. A) Partially silicified red algae; 11-20-2-18W2, 2994.9m. B) Encrusting red algae 12-2-7-11W2; 2549.7m. C) Massive red algae, cemented tight (light grey color), and partially replaced along their edges by silica (light brown) and anhydrite (darker colour) that produces a digitate fabric. From 14-26-6-11W2, 2555.3m. Scale bar in em's. 184 Plate 6.6. Diagenetic mottles and nodular textures. A) Nodular limestone (NL) surrounded by a "diagenetic bed" of lighter-colored dolomite (D). Dolomite also has been penetrated by white-colored chert (Ch). Dark patches of anhydrite (An) occur in all mineral types. From 2-34-1-32W1, 2316.9m. B) Mottles of light brown dolomite in a dark-brown limestone matrix. The dolo-mottles are "cored" by beige- colored chert. From 15-9-2-14W2, 9980.5 ft. 185 Basin (Baird and Brett, 2002). Bentonites were laid down by volcanism processes in relation to the Taconic Orogeny. Wind-blown ash from Taconic volcanism may have transported and deposited silica across Laurentia - not enough to create and subsequently preserve distinct beds - but enough to be diagenetically altered into chert nodules. Siliceous sponges on the other hand create minor amounts of siliceous cement in carbonate rocks (Hesse, 1989). All forms in the Coronach Member are considered minor in terms of volume and thus, if based solely on this point, are biogenic in origin. Sponge spicules have been widely quoted as a source of silica (Geeslin and Chafetz, 1982; Reid et al., 2008). Sponges are common in Ordovician shelves in other parts of the world (James, 1983); for example the carbonate build-ups in the mid-Ordovician Chazyan Formation (Pitcher, 1964; 1971) and Red River-equivalent strata in southwestern New Mexico (Geeslin and Chafetz, 1982). Furthermore, Paleozoic oceans probably had higher silica concentrations versus present-day oceans because diatoms had not yet evolved (Reid et al., 2008). Sponges, particularly Demosponges, have spicules composed of biogenic opal (Martin and Sayles, 2005). Opal dissolves quite readily in the shallow subsurface (Reid et al., 2008). The dissolved silica can lead to pore fluids super-saturated with respect to silica. Experiments indicate this fluid can have its pH lowered from ~7 to values of 5.7 to 6.2 if in contact with CO2 (Hesse, 1989). An acidic solution such as this would most likely dissolve the surrounding matrix. CO2 may be sourced from meteoric waters (or decreasing salinity), decay of organic matter, or by biological activity (Knauth, 1979; Chilingar et al., 1967). It is believed that a combination of carbonate dissolution and silica precipitation created some of the complex diagenetic features in the Coronach 186 Member including dolomite mottles cored by chert. A source of silica is likely of biogenic origins, as most Paleozoic examples are (Hesse, 1989; 1990b). 6.3.3 Timing of Silicas 1 -5 Silicas 1 and 2 involve replacement of matrix as well as mimetic replacement of calcite microspar, itself a replacement and/or cementation of skeletals. Timing is therefore post-calcite replacement of skeletals. Nodules however may be highly fractured and filled by anhydrite, suggesting pre-deep burial. Furthermore, thick dissolution seams occur between nodules and host sediment, suggesting chemical solution of carbonate against the already in-place chert. Therefore, formation could be in the shallow subsurface or even near-surface. Cementation or replacement of Solenopora by Silica 3 was probably very early, otherwise marine calcite spar would fill the moldic pores (Solenopora tubes), as most other voids in the Coronach Member are cemented relatively early by marine calcite. Silica 4 replaces Dimorphosiphon and is thus post-dissolution of aragonite. It also mimetically replaces calcite spar, therefore it post-dates calcite cementation/replacement. Generally, a lack of cement in the Coronach Member, particularly marine calcite, hinders "cement stratigraphy", which is used to place a more accurate timing on these minor siliceous cements. Timing of Silica 5 is probably very early since it is believed the source is unstable biogenic opal derived from siliceous sponges. The extremely gradational boundaries between Silica 5 mottles and dolostone and/or limestone suggests high porosity and permeability were high enough to not restrict the precipitation of silica contrary to the 187 small, dense nodules of Silicas 1 and 2. This suggests that Silica 5 is likely pre-shallow burial. Sources of silica were discussed above but the method of diagenetic replacement is unknown. Knauth (1979) proposed a mixing zone model, whereby dissolution of biogenic opal and mixing of marine and fresh waters produces fluids supersaturated with respect to quartz and undersaturated with respect to calcite and aragonite. This allows for dissolution of the carbonate as well as simultaneous precipitation of chert. It is proposed that dissolution, induced by decreasing pH, of the aragonite and/or high Mg-calcite matrix, in conjunction with redistribution of biogenic opal, produced these chert mottles; the by-product of this process was dolomite (Equation 6.4). 2CaC03|ar«g«onite] Si(OH)4(d|$solved silicon) Mg • 2+ CaMg(C03)2 [dolomite] + Ca + 2H20 + Si02{chert) (6.4) It is not apparent if CO2 from a mixing-zone model was the catalyst for decreasing pH. However, two types of possible vadose calcite cement (discussed below) may be evidence of a dropping water table that could have allowed for infiltration by fresh water. All types of silica have degraded reservoir-quality rocks, mainly by occlusion of moldic porosity and matrix replacement of carbonate. 6.3.4 Silica 6 Description and Interpretation Silica 6 is the only silica type found outside of Facies 2 and it forms a beige 10- cm thick bed at the disconformity at the top of the Coronach Member. The location of chert in Facies 5 (caliche horizon) suggests it may be a silcrete, a product related to weathering or soil-forming processes (van den Boorn et al., 2007). Summerfield (1983) 188 in Hesse (1990a) identified certain silcretes as forming in semi-arid environments with high evaporation rates, and the rise of highly alkaline pore-fluids by capillary action. These are criteria that fill well with the interpretation of the depositional setting for the Coronach Member. A second possibility however, is silica-bearing solutions were focused along the disconformity at some time post-burial (Hesse, 1990a). No thin sections were taken from this zone so it remains unclear what the source of silica may be. Regardless of the source, Silica 6 seems localized and has not affected porous reservoir rock, though it may provide a hydrocarbon seal in the absence of anhydrite. Timing of Silica 6 is largely unknown due to its obscured origin. 6.4 Calcite Description and Interpretation Seven types of calcite cement were observed in thin section; all from Facies 1 and 2. They are insignificant in terms of percentage of the total rock, thus isotope data only reflects general limestones composed of micrite matrix. Calcite 1 consists of fibrous, prismatic or bladed rinds of calcite that line the insides or outsides of skeletal grains, particularly brachiopods, ostracodes and bivalves (Plate 6.1k, B). It is found only in Facies 1 and 2. These types of cement are commonly developed in shallow, marine waters as aragonite or high magnesium-calcite (James and Choquette, 1990b). In a hardground sample from Facies 2 consisting of leached grains, calcite crusts are the only remaining feature to indicate the existence of skeletal organisms (Plate 6.8A). Plate 6.7. Calcite cement. A) Bladed calcite crystals (175pm) on inside and out side of shell wall of a brachiopod. Inside shell has also has sparry calcite. From 13- 23-6-11W2, 2586.75m, XPL. B) Close-up of a bivalve with fibrous calcite cement on the internal grain only. From 10-25-1-15W2, 3119.6 m, XPL. C) Calcite spar filling void space left by dissolution of Dimorphosiphon skeletals. From 13-23-1- 17W2, 3047.7m, XPL. D) Pseudospar calcite (stained red) replacement of unknown shell as well as infill cementation. Silica cement (Si) partially replacing calcite spar. From 10-25-1-15W2, 3119.6m, XPL. E) Large (225-1000pm) sparry calcite between mainly algal/microbial grains. From 6-5-6-19W2, 2714m, XPL. F) Calcite spar (stained red) and anhydrite (white) cementing an algal-packstone. Ibid., PPL. 190 Plate 6.8. Hardgrounds. A) Thin section example of a hardground (lower half of photo). The top of the hardground is composed of well-cemented allochems, some of which have been leached. The hardground has a sharp, slightly irregular surface and grades down into a mud-rich wackestone similar to the carbonates deposited above. From 16-23-2-1W2, 2524.6 m, XPL. B) A 1.5cm hardground with vuggy, possibly moldic, porosity. Several Trepostrome Bryozoans(?) are encrusting the top of the hardground. From 11-20-2-18W2, 2997m. 191 Calcite 2 occurs as small crystals in the matrix, generally 5% or less, that do not appear to be void-filling. This is likely the neomorphic product (recrystallization) of micrite mud (Bathurst, 1971), which is commonly perceived of as either a burial diagenetic or meteoric product (James and Choquette, 1990c). Although, Melim et al. (2002) have recently shown that microspar could be a cement forming around aragonite needles before they dissolve. Timing, therefore, is not evident. Calcite 3 is sparry, mosaic or anhedral crystals found between skeletal grains in biostrome facies (Sub-facies 2D) that completely occludes porosity (Plate 6.7E, F). Caclite 3 was only found in three thin sections had high percentages of the total rock ranging from 25% to 40%. Crystal sizes vary from 225^m to 1000|im and average 450p.m. The skeletal grains within these samples show excellent preservation, including aragonitic algae and Ortonella. This suggests Calcite 3 was emplaced very early, otherwise these taxa would break down. Sparry calcite may be found in shallow marine carbonates, particularly reefs and hardgrounds, but also takes similar forms where meteoric waters have infiltrated carbonates (James and Choquette, 1990a, c). A lack of dissolution features in these same samples rules out the latter. Furthermore, Calcite 3 crystals are cloudy under PPL suggesting a marine origin as opposed to a meteoric origin (Dravis, 2006). Calcite 4 is also a sparry cement but occurs as void-filling spar within shells or occlusion of moldic porosity left by partial to complete dissolution of unstable skeletal grains (Plate 6.7A-D). Aragonite grains are relatively unstable and may dissolve in the shallow burial environment (Machel, 2004) suggesting Calcite 4 is post-dissolution. Emplacement may have occurred anytime thereafter, as there is no evidence to suggest a 192 more accurate timing. Calcite 4 is found in both Facies 1 and 2 and is the most common calcite cement in Facies 2. Calcite 5 is a pendant and possibly meniscus-like cementation found near the top of Facie 2 (Plate 6.9). Both of these cement types are considered evidence for vadose diagenesis (James and Choquette, 1990c). However, Hillgartner et al. (2001) demonstrated effectively that meniscus cements can occur as a microbially-induced, subtidal cement and suggested the term meniscus-type to describe this variety. No other evidence exists to speculate on the origins of Calcite 5. Calcite 6 is the micritization of skeletal borders, a process of conversion of organic detritus to micrite within micro-bores created by algae, fungi or bacteria (Bathurst, 1971). These micritic envelopes sometimes produce a more resistant grain (Scholle and Ulmer-Scholle, 2006). Calcite 6 was only recognized where dolomite had completely replaced matrix and partially replaced skeletal grains (Plate 6.9C); however, there is no apparent relationship between dolomitization and micritization. Micritization usually develops on the seafloor (Bathurst, 1971), thus Calcite 6 formed very early in the diagenetic environment. Some peloids may be abiotic in origin (Bosak et al., 2004). Calcite 7 interpreted as a peloidal cement, which is only found in Facies 2. It contrasts markedly from other peloids in that it has a structure grumelous texture and is commonly associated with sparry calcites (Calcites 3 and 4). Timing is probably similar to Calcites 3 and 4 because of this close relationship. Criteria for the interpretation of peloids as a cementation product include 1) spherical shapes, 2) size limitations, 3) zonation produced by a sub-microcrystalline 193 Dolomicri to nuitiix IVIicrit'u.iiion • 250pm Plate 6.9. Other calcite cements. A) Crinoid ossicle showing calcite spar "pendant" cement. This geopetal indicator could be evidence of the vadose zone. From 10-25-1-15W2, 3118.05m. B) Possible meniscus-type calcite cement between a crinoid and a brachiopod fragment. This is also a vadose zone indicator. Brachiopod shell is marked by a zone of bladed cement (Bl). From 13- 23-6-11W2, 2586.75m. C) Micrite-alteration of red-stained skeletal grains along their edges, as shown by thin dark rims. See text for details. From 13-23-1-17W2, 3048.75m, PPL. 194 nucleus surrounded by larger euhedral calcite crystals, and 4) isolated sites of deposition, particularly inside skeletal cavities (Maclntyre, 1985). These criteria were recognized in some peloids suggesting they are indeed a type of cement. A few samples show peloids lining the insides of brachiopod valves (see Plate 5.16); biotic peloids, alternatively, would settle to the bottom of the shells only. Oxygen isotopes show that limestone samples (calcitic matrix) is depleted in 180 by 2-3.5%o relative to Late Ordovician marine calcite. Since all Coronach samples show the same depletion, it is likely that the Coronach Member has undergone isotopic re setting during burial diagenesis. These samples may have been modified by late diagenetic fluids, possibly Silurian waters, as strontium isotopes show values higher than established values for Late Ordovician seawater (Figure 6.3; Burke et al., 1982; Veizer, 1989; Veizer et al., 1999; Qing et al., 1998, 2001a; Shields et al., 2003; Young et al., 2009). Qing et al. (2001a) also attributed depleted 5180 values in matrix dolomites from the Yeoman Formation to burial diagenetic resetting. \ All types of secondary calcite have degraded reservoir quality by porosity- reduction. 6.5 Hardgrounds Marine hardgrounds are cemented beds at, or just below, the seafloor (Tucker and Wright, 1990). They were identified in a few cores and thin sections from Facies 2 (Plate 6.8). The common thread between the two examples in Plate 6.8 is the preferential calcitic cementation of grainstones. Early cementation at the seafloor has preserved grainstone beds from being dissolved in the subsurface. They are recognized in core or 195 thin section as containing moldic porosity and having flat tops and bases. Sometimes they are encrusted by algae and bryozoans. 6.6 Dissolution Several skeletal grains have undergone partial to complete dissolution due to their metastable skeletal mineralogy (i.e. aragonite). This has created moldic porosity that has been filled by secondary calcite spar, silica, or dolomite, as previously discussed. Timing of aragonite dissolution can be attributed probably to shallow burial depths, although aragonitic grains could survive to deep burial environments. Dissolution is a key diagenetic component in reservoir development, particularly for Facies 2 and 3, but it occurs sporadically. Primarily, it includes leaching of un-stable skeletals creating moldic porosity, though a dissolved matrix is sometimes observed. Where well-developed, moldic and vuggy porosity may reach 8% and 16% in Facies 2 and Facies 3, respectively, but porosity is usually less than 1% in Facies 2 while it averages 6% in Facies 3. 6.7 Compaction Compaction diagenetic processes include burial-related physical and chemical deformation in the first few hundred meters of burial (Choquette and James, 1990). In the Coronach Member, physical compaction consists of 1) mechanical destruction of skeletal grains and certain types of brecciation, and 2) compaction- and tectonically-induced fracturing (Plates 6.ID; 6.10; 6.11). 196 Plate 6.10. Diagenetic breccia. Two examples of collapse-induced brecciation. Breccia's consist of dolomitized angular clasts. In (A) the clasts appear to have fallen from the roof of a cavity (black, dashed arrows) and either settled to the floor or are seemingly held in suspension, although grain-to-grain contacts (red arrows) indicate they are clast-supported. Interstices were later filled by brown-coloured mud. Above and below this zone is 70-90% replaced calcareous algae, based on identical morphologies to Solenopora Red Algae. Therefore, this feature is likely a growth-framework cavity. Core is 7cm across. From 11-20-2-18W2, 2995 m. B) A very similar dolomitized breccia where the angular clasts are not floating in a limestone matrix, but have brecciated in-place. Calcareous algae are also present above and below this feature suggesting a growth-framework cavity. Core is 9cm across. From 13-23-6-11W2, 2583.8m. Styolites Styolito Fracturing n / 250^m Plate 6.11. Compaction diagenesis. A) Crinoid ossicle in center of photo showing mechanical deformation (fracturing) and chemical dissolution (styolite), both as a result of deep burial diagenesis. From 12-2-7-11W2, 2549.2m. B) Horizontal styolite across middle of photo with advanced dissolution on left side. From 16-23- 2-1W2, 2524.6m. 198 Physical compaction features were noted in Facies 2. Two cores have a 5-10cm zone consisting of angular clasts ranging in size from 0.25cm2 to 2cm2 (Plate 6.10). Several grain-to-grain contacts suggests this breccia is clast-supported. The presence of calcareous algae above and below this feature indicates that this was a cavity, prior to its collapse, and was probably created by the growth framework of Solenopora, as opposed to dissolution of the carbonate by meteoric water. Other physical compaction features recognized include fractured grains (Plate 6.11 A). These are burial diagenetic processes, but they are known to form in sediments from just 10's of meters to 100's of meters of depth (Moore, 2001). Vertical fractures were noted in most facies, which post-dates all other diagenetic features except anhydrite cementation, which lines the fractures. Chemical compaction, or chemical solution, has produced mainly styolites and dissolution seams. Styolites are prevalent from Facies 1 through Facies 4 (Plate 6.1 IB). Bed-parallel styolites are more common in Facies 1 and 3, whereas high-amplitude styolites are common in Facies 2. These features are important to note because 1) reductions in vertical thickness of 20-35% are commonplace (Bathurst, 1971); 2) styolites may control groundwater and hydrocarbon migration (Tucker and Wright, 1990); 3) rocks prone to styolitization may suggest a relatively unstable mineralogy (Choquette and James, 1990). 6.8 Subaerial exposure Facies 5 at the top of the Coronach Member shows evidence of subaerial exposure. Exposure and weathering has in turn created a caliche horizon. The main diagenetic structures include mudcracks, sheetcracks, in situ brecciation, scour surfaces 199 and rip-up clasts (see Plate 5.26). Other evidence of lateration includes chalky or platy rocks and greenish white to orange colours. Mud rip-ups appear to be locally sourced, based on similar color to the host rock. Furthermore, these clasts are highly variable in size, and may have a flat or elongate morphology indicating in situ formation. A second type of mud rip-ups are of different color than the adjacent rock. These clasts typically "float" in the host rock. They are usually found above mud-cracked intervals and have probably been transported relatively long distances. Teepee structures are also present but less common (see Plate 5.26B). These 'pseudo-anticlines' are often the result of cementation and expansion (Tucker, 1991). Subaerial exposure is also evident in desiccated stromatolites (Sub-facies 3B; see Plate 5.21). 6.9 Pyrite Pyrite was found replacing parts of Solenopora in Facies 2 (Plate 6.4B) and as minor, thin laminae in Facies 1. It usually forms in reducing conditions, implying anoxic conditions. More precise timing of pyrite is difficult due to its extremely rare occurrence. Pyrite is recognized as gold-coloured in reflected light and anisotropic in plane light. It is considered too insignificant in the Coronach Member to have affected reservoir quality. 6.10 Diagenetic Summary Most of the diagenetic events listed in Table 6.1 have degraded reservoir quality (70%). Others are more complicated; for example Dolomite 1 has probably both enhanced and degraded reservoir quality. 200 The timing of one event to another is not always directly observed through petrography. Complicating the picture is evidence of recrystallization, including neomorphism and lack of zoning in any cements, as determined from CL. Recrystallization due to late diagenesis has likely reset isotopic signatures. However, many of the diagenetic events listed above can be related to specific environments of formation. This is based partly on the wealth of past studies on diagenetic models and interpretations. A summary of the most important processes in relation to reservoir enhancement and destruction are: a Four types of dolomite: Dolomites 1-3 are replacive and Dolomite 4 is a cement ° Six types of silica: Silicas 1-2, 4 & 5 are all replacive, Silica 3 is a cement and 4 may also double as a cement. Silica 6 may be either a replacement or a cement D Seven types of calcite: Calcites 1 & 3-7 are cements and Calcite 2 is matrix- replacive D Three types of anhydrite: all are cements and have degraded reservoir; Anhydrite 1 has created an effective hydrocarbon seal a Chemical and mechanical compaction, both reducing porosity and causing further cementation The main models and interpretations of the above diagentic events are summarized in Figure 6.9 and Table 6.3. 201 5-15km 10-100 km Soil-related Weathering _ Capillary Evaporite Evaporation — y Dissolution Silcrate/ & —/ Evaporation & Penesaline ^Caliche Af^^aEvaporites Reflux Sabkha Dolomite Oscillating JSa&kuxsL. Siliceous Sponge Dissolution Shallow Burial o Deep Burial Mechanical Deformation Figure 6.9. Summary of diagenetic environments for a prograding depositional model. Those processes and diagenetic models creating or altering sediments are italicized; the products of diagenesis are in regular font. This sketch combines a snap-shot in time of the shallow environment and overlays the shallow to deep burial processes. Note overlapping diagenetic environments such as sabkha and reflux dolomite. Most near-surface diagenetic environments are controlled by geographic position along the ramp profile, including elevation and water table, as well as by depth and sea level position. These same diagenetic processes are expected to be no different in the aggradational model except that each major process occurs one at a time. Sub- Formal Name Fades Primary Uthology Diagnostic Features Diagenetic Environment Porosity Types Facies Breccia's, mudcracks, mud rip- Fades S Dolo/Calcimudstone Continental Exposure (Caliche) - uos. oxidation, black, arains Nil Individual to coalesced nodules Hypersaline Marine (Seepage- B Anhydrite of anhydrite Reflux Dolomite) Nil Facies 4 Cryptocrystalline Randomly oriented lath-like Hypersaline Marine (Supratidal A Dolomudstone crystals of anhvdrite Gvosum and Reflux Dolomite) Nil Disrupted, wavy, domal or flat Pene- to Hyper-Saline (Reflux Intercrystalline, B Dolomudstone laminations Dolomite) Vuggy Facies3 Calcitic to Dolomitic Organic-rich, hz, planar A Restricted, Penesaline Marine Mudstone laminations Nil Coronach Peloidal Calcitic Peloids, Planolites burrows, Restricted, Penesaline Marine D Member Wackestone ostracodes (Reflux Dolomite) Rare Vuggy Rare micritic mud; rounded & Shallow, Normal to Penesaline C Skeletal Grainstone abraded arains Marine Interparticle Facies 2 Algal-Stromatoporoid Very high fossil abundance and Shallow, Normal Marine (Marine B rudstone: Skeletal diversity Cement) Rare Moldic A Cherty Wackestone Chert nodules Marine Nil Laminations, kukersites, low Facies 1 - Calcimudstone skeletal diversity; Planolitgs & Marine Nil Palaeophycus traces Table 6.3. Expansion of Table 5.2 indicating near-surface diagenetic environments. Main porosity types are also included. 7.0 RESERVOIR CHARACTERIZATION 7.1 Introduction The preceding interpretations of depositional and diagenetic environments, plus the geological review of the Williston Basin hydrodynamics and Red River petroleum systems, sheds light on the potential for economic reserves of hydrocarbons in the Coronach Member of southeast Saskatchewan. Following is an integration of that data along with reservoir characterization. 7.2 Reservoir Development The highest quality reservoir rock in the Coronach Member has developed mainly in the stromatolites of Facies 3. Average core porosity and permeability indicates Sub- facies 3A has the best porosity and Sub-facies 3B has the best permeability (Figure 7.1 & Table 7.1). This data also suggests reservoir quality is primarily facies-controlled. Porosity types in Facies 3 include vuggy and intercrystalline. Peloidal sands, which constitute the majority of the sediment in Sub-facies 3B, were dolomitized early. Microcrystalline rims around peloids do not completely fill the pore space, leaving intercrystalline voids. Vuggy porosity is evident in core and thin section and appears to be associated with leaching of peloids. Vugs may have formed either during the dolomitization phase, or through flushing by fresh water (Machel, 2004; Moore, 2001). Though the original facies is a major control on reservoir development, the degree of dolomitization is another critical factor in assessing porous versus non-porous rocks. All facies above have been replaced by dolomite leading to cryptocrystalline grain sizes 204 Facies Porosity & Permeability 4.500 20.0% 4.000 Facies 2-4 Porosity - 18.0% Facies 2-4 Perm • 16.0% _ 3.500 • - 14.0% E 3.000 - 12.0% 2.500 10.0% S 2.000 • 8.0% 1.500 6.0% 1.000 4.0% 0.500 • s. - 2.0% 0.000 0.0% Facies 2 Facies 3A Facies 3B Facies 4 Figure 7.1. Core porosity and permeability data from all available cores. Facies 3B has the best average permeability while Facies 3A has the best average porosity. Not shown are Facies 1 and 5 due to lack of data. See accompanying Table 7.1. 205 Core Measured Porosity %) Facies 5 Facies 4 Facies 3B Facies 3A Facies 2 Facies 1 Count 1 26 28 13 152 0 Average 12.8% 7.4% 6.8% 10.1% 4.8% N/A Min 12.8% 0.1% 0.6% 0.5% 0.3% N/A Max 12.8% 17.8% 13.2% 17.8% 18.7% N/A Core Measured Permeability kmax) Facies 5 Facies 4 Facies 3B Facies 3A Facies 2 Facies 1 Count 1 21 28 13 139 0 Average 0.20 1.39 3.90 2.48 1.83 N/A Min 0.20 0.01 0.01 0.01 0.01 N/A Max 0.20 10.20 41.50 6.37 88.70 N/A Table 7.1. Core analysis data for all facies. 206 with lower reservoir permeability; although the primary sediment was likely very fine lime mud, which would have some control on the diagenetic grain size. Dolomitization at the top of Facies 2 is variable but has much larger crystal sizes. Porosity types include intercrystalline and moldic. Moldic porosity is the dominant type in Facies 2 because of the large number of metazoans present. Diagenetic interpretation indicates that development of moldic porosity is probably related to the dolomitization process, whereby dolomitizing fluids dissolved metastable carbonate cement. The average thickness of porous dolomitized Facies 2 is about lm. This adds thickness to the overall reservoir (Figure 7.2). Unfortunately, dolomitization of Facies 2 is very inconsistent and permeabilities are much lower than Facies 3. Calculating risked reserves for potential reservoirs should include Facies 3 and only Facies 2 if it is risked sufficiently high. A major limitation to economic reserves is the thickness of stromatolites. Facies 3 averages 1.5m thick. It reaches a maximum thickness of just 2.7m in the south-central part of the study area. Porosity contribution from Facies 2 is probably required to make economic hurdles. 7.3 Trapping Mechanisms Stratigraphic trapping is unlikely to yield significant reserves in the Coronach Member because of the hydrodynamic, updip northeastern flow of brines combined with northeastern up-dipping strata (discussed in Chapter 2). Structural traps on the other hand should not be affected by hydrodynamic flow and is evident in the multitude of structural traps that exist in the Yeoman Formation (Kreis and Kent, 2000; Harvey, 2003; Kohm and Louden, 1988). 207 Figure 7.2. NRK Bryant 15-8-5-7W2 litholog. Example litholog displaying core analysis and major fades. Dolomites (purple colors) have much better porosities than limestones (blue colors). Permeability remains high and probably reflects presence of fractures. See Appendix A for legend. 208 Khan et al. (2006), using hydrocarbon migratory models, suggested that Red River play types may extend considerable distances north of current producing fields. This can probably be applied to the Coronach Member. Most structural traps of the Red River Formation are related to faulting in the basement; the Red River is commonly draped over top of these basement "highs" creating structural closure (Figure 7.3). Many of the Red River Fields also line up along north-northwest and northeast trends (Kreis and Kent, 2000) and could be used as a prospecting tool. 2D-seismic is necessary to locate basement block-faulting responsible for Red River hydrocarbon accumulations, but 3D-seismic is needed to pinpoint them upon drilling (J. Arsenault, pers. comm.). 7.4 Reservoir Characterization Summary Based on the above interpretations and investigations, reservoirs of the Coronach Member are probably limited to structurally-trapped, dolomitized stromatolites throughout most of the study area. Areas to high-grade exploration efforts would include: 1) along the axis of the Coronach kukersite basin where hydrocarbon migration distance should be at its minimum, 2) in extreme southern Saskatchewan where more thermally mature source rocks are located, and 3) along trends of basement-block faulting, such as existing Red River oil pools (Figure 2.9). Facies 3 porosity and permeability from core analysis averages 7-10% and 2.5- 3.8mD, respectively (Table 7.1). Due to the limited thickness, additional reservoir-quality rock is required from Facies 2 to meet economic cut-offs. Facies 2 does commonly have 209 Pfjairie Cvaporite nnepegosis ro o Precambrian 1:42,100 Figure 7.3. Seismic profile of the Midale Field. Two economic pools in the Midale Field (Townships 6 & 7, Range 11W2) are defined by basement block-faulting, delineated by faults (in black). Hydrocarbon entrapment is due to structural closure. Vertical blue lines are locations of wells projected on the seismic profile. Modified from Urban (2001). porosity; however, its distribution is sporadic and may occasionally occur lower in the facies, thereby requiring more structural closure for hydrocarbon trapping. Migration of hydrocarbons from either the Yeoman Formation or the Coronach Member is not considered a limiting factor (discussed in Chapter 2). 7.5 Comparison to U.S. Equivalents In the U.S. the Coronach Member (Red River 'B') is a prolific producer as indicated in Tables 1.1 and 1.2. Oil pools consist mainly of structurally trapped laminate facies that are about 3m thick (Montgomery, 1997). These characteristics are very similar to the Coronach Member on the Saskatchewan side of the Williston Basin. However, several reasons are apparent from this study as to why the Coronach Member in the U.S. is substantially more prolific relative to Saskatchewan. a The U.S. has two large anticlines (Cedar Creek and Nesson) that are vastly larger than the basement-block structures that trap Red River oil in Saskatchewan. D Reservoirs in the U.S. are situated in areas more favorable relative to hydrodynamic flow. ° Average porosity and permeability in the U.S. is 8-26% and l-66mD (Montgomery, 1997). These values are higher than those from the Coronach Member, suggesting a more favorable diagenetic history for U.S. fields. u Based on geographic position within the basin, many Red River structures in the U.S. are well within the oil window. Q U.S. has a longer exploration history, due to the early discovery of Red River oil in 1951 along the Cedar Creek Anticline (Bogle et al., 1998). The above reasons may explain why production is lacking in Saskatchewan versus the U.S., but it does not explain the complete absence of production in the former. Based on observations of oil-staining in cores, it is apparent that reserves are present, but they may 211 not have been tested. Re-completion of deep wells overlying existing structural highs may prove there to be significant by-passed play in Saskatchewan. Areas of focus should include existing Red River fields. 212 8.0 CONCLUSIONS 1. The Late Ordovician Coronach Member in southeastern Saskatchewan was deposited on a gently-dipping ramp, which was part of a much larger epicontinental sea that covered most of Laurentia. Deposition is characterized by a shallowing-up and brining-up carbonate-evaporite sequence. 2. Sedimentation was in shallow to very shallow water, as well as on emergent areas, and characterized by initially high-sedimentation rates, low-energy conditions, and an arid to semi-arid environment. Shallow-water subtidal sediments characterized by reef mounds or biostromes are overlain by tidal flat stromatolites and supratidal, or possibly salina, evaporites. 3. Though sedimentation in shallow to emergent areas is evident, it is not clear if deposition occurred in an aggradational or progradational system. Evidence for the aggradation model includes a basin-centered anhydrite and widespread facies such as biostromes. Evidence for the progradational model includes prolonged exposure due to sea level fall, intertidal-like stromatolites, intra-sediment growth of gypsum and possibly anhydrite, deposition of peloids onto tidal flats from an adjacent subtidal setting, along with numerous modern analogues of progradational systems. 4. The Coronach Member has some of the oldest metazoan-constructed biostromes in the world. Carbonate build-ups are composed of Red Algal (Solenopora) 213 Framestones/Boundstones, Green Algal (Dimorphosiphon) Bafflestones/ Rudstones and Stromatoporoid Boundstones. However, no thickness anomalies are associated with these build-ups. Limited vertical accommodation space probably did not allow for build-ups to aggrade before they were killed by prograding tidal flats, increasing salinity, or both. These build-ups could be classified as either bed-like biostromes or low-relief reef mounds. Based on this study, a caveat should be applied to future studies regarding the classification of reefs, reef mounds, and mounds, if it can be shown that accommodation space has controlled aggradation. Laminites from the shallow-water to emergent tidal flats show indications of sediment agglutination by action of cyanobacteria. These are considered evidence of stromatolites. They constructed 1) domal features closer to or within the subtidal environment, 2) disrupted, crinkled and tufted features due to exposure, and 3) smooth, wavy features of the upper intertidal setting. Storms deposited peloids over tidal flats, likely during ebb flow, which were then trapped by cyanobacterial mats. Very fine, horizontal planar laminae with rare starved ripples may represent channel levees and the tops of beach ridges. These sub- environments are areas of high drainage, so trapping is mainly of fine mud as opposed to peloids. Early dolomitization of peloidal, stromatolitic boundstones has created the best reservoir quality in the Coronach Member in terms of porosity and permeability. 214 6. Peloids are mainly of soft-pellet origin and their presence in the Coronach Member is solely a function of preservation. Pellets are found 1) in subtidal rocks, but only where skeletals have protected them (i.e. inside brachiopod shells) or where skeletals and/or early cementation is sufficient to provide a framework that resists compaction, and 2) on tidal flats, where early replacement/cementation by dolomitization has preserved them from the effects of burial compaction. Peloid grainstones from tidal flats are the main reservoir rock in the Coronach Member. 7. Algal production of lime mud was extremely high due to domination by Red and Green algae. Most mud was not lost to transport off-bank because of the vast intracontinental ramp-setting. Therefore, a significant amount of mud was deposited onto tidal flats and the basin may have been apt to infilling, overcoming the effects of subsidence, erosion, and solution. 8. An important reservoir-degrading cement is silica. It is found as I) complex chert nodules, beds, or mottles, 2) micro-quartz to mega-quartz replacement of skeletals or calcite spar, and 3) cementation of moldic porosity. The source of silica is most likely siliceous sponges composed of biogenic-opal. A chemical formula was proposed to explain the mottled features, whereby dolomite is likely a by-product of the process. Features developed through dissolution of metastable carbonate with simultaneous precipitation of chert have not been described before in early Paleozoic rocks. 215 9. Mottled textures are prevalent in the Coronach subtidal facies, but should not be confused with the dolomite mottles (or Tyndall Stone) of the Yeoman Formation. The latter is related to Thallassinoides burrows. The mottles of the Coronach Member have three origins: 1) Dolomitized Planolites' burrows; 2) Solenopora red algal and Ortonella nodular to encrusting masses, that have undergone secondary replacement; 3) complex, non-burrow related diagenetic features related to chert mottles described above. 10. Kukersites at the base of the Coronach Member occur in a similar sub-basin as Yeoman Formation kukersites, suggesting a continuation of a negative topographic area into 'Coronach time'. Petroleum geochemistry studies suggest these kukersites are thermally mature in extreme southern Saskatchewan and in North Dakota, providing a source of hydrocarbons for the Red River petroleum system. The recognition of kukersites in the Coronach Member implies the latter has its own source rock; thus, migration of hydrocarbons from the Yeoman Formation is not a necessary prerequisite for petroleum accumulations within the Coronach Member. Differences in depth between Yeoman and Coronach kukersites is only about 20m, therefore they should have similar oil windows, which occurs at depths as shallow as 2450m. An untested organic-rich rock formed by cyanobacterial laminites (Facies 3A) may also be a potential source of hydrocarbons in the Coronach Member. 216 11. A caliche horizon is present at the top of the Coronach Member. The features at the top of the Coronach Member include oxidized sediments (light brown to orange-brown color) that penetrate sharply down into reduced sediments (green to green-grey in color), in situ brecciation, mudcracks and sheetcracks, floating clasts of mud or quartz grains and cobbles, scour (ravine?) surfaces, and exposure surfaces. The caliche profile is dynamic; its reduction in "intensity" is measured by decreasing thickness towards the basin centre, which is a function of exposure time and topography. These criteria can be used to identify other, early Paleozoic caliche horizons. 12. Porosity is low throughout the Coronach Member for a number of reasons including: 1) long residence time in the burial environment (-450 million years), which has led to near total cementation; 2) depth of burial (2000-3000+ meters), which has led to pressure-solution features (styolites) and fractured skeletal grains (loss of moldic porosity); 3) over-dolomitization of carbonate supratidal muds; 4) high sedimentation rates leading to pore-filling by micritic mud; 5) siliceous cementation; and 6) sulphate emplacement. 13. Porosity has been created or preserved by 1) early reflux dolomitization of tidal flat peloidal muds, which withstood burial compaction better than adjacent subtidal limestones, leading to intercrystalline and vuggy porosity; 2) a combination of a) deposition of peloids by storms onto the tidal flats, which acted 217 as grains for development of intercrystalline porosity, and b) action of cyanobacteria to bind those peloids in place. 14. Dolomitization of the intertidal-supratidal sediments is thought to be early because of the preservation of peloids. Dolomite may have formed from two very similar models: 1) sabkha precipitation (penecontemporaneous) by highly- evaporated seawater, and 2) seepage-refluxion of evaporated seawater through the sediment. Brines likely became supersaturated with respect to magnesium after and during deposition of sulphates. A third dolomitization model invokes the alteration of subtidal deposits by penesaline seawater. Fluids may have been pumped into sediments by high-frequency sea level fluctuations. These dolomites have slightly different isotopic ranges, larger crystal sizes, and planar-s textures. Dolomitization of subtidal deposits has led to increased porosity and permeability over limestone equivalents, but this occurs over very thin intervals. Other dolomite types found in the Coronach Member are insignificant in terms of reservoir quality. 15. Carbonate geochemistry indicates all Coronach Member rocks may have had their isotopes reset due to burial diagenesis. Carbon-13 isotopes indicate dolomitization of stromatolites may have been partially mediated by cyanobacteria. Oxygen isotopes indicate dolomite samples, relative to limestone samples, were deposited from seawater or slightly evaporated seawater. Burial diagenesis has likely masked a better interpretation. Strontium isotopes for dolomites are well above 218 the normal seawater range for Late Ordovician seawater. A tentative hypothesis is that these samples were altered by Late Silurian seawater that percolated down through faults. 16. Hydrodynamic flow from southwest to northeast across the present-day Williston Basin has likely flushed up-dip stratigraphie traps on the northern side of the Williston Basin. Down-dip flow from topographic highs, such as the Black Hills, have aided in hydrocarbon trapping for those reservoirs in southern North Dakota and Montana. 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Calcareous Cwhannm. Cement 1 Chert*-darfc I Mixed lever daw I I I ^I Conglomerate • dark chert iMafitngtfcnfU- '£XWM'?)I Conglomerate - light chert ISynY-teririZL jCheftv-lrtOQlttc Chert-dark iChartv-vartoolcred Chert • foaaMfetou* 1sum- |8endv Chert-«gM I Claw mm- sa. Chert-MpoiWc {Dctornltc is^a- Chert • varicolored jfamxanou. ftnino I sit* Ctaystone • colored i£BSkiEtt>a Claystone • gray IQIeucflnHIc rial li II iri Coat JO^Mnu^ nnnnun Ferruginous Fossil* (Rock Buildars) 1 B 1 Aooraoaia oraini V • u iB jii ik in Gypeum as. p • I— 11 !• •• I Igneous • acidic /SI> r~\ • » !• • Igneous • basic /9s Alnae-ootoid a Qeitroeod Muddy IH8 (Mined HetsroMhlc State) burrowed tax •>» Muddy 1H8 (indeed tlelaroWNc Strata) •o,« JBL V I t JL Limestone • grain supported V I f • m fit T Mlscallanaou* Grain* ( Cement 1 • Mo** Mineral cryttel a Orthoclata m_ Anhydrite | • jOypailaraua j Qtauoonlta * Mnenl-darli a Plaglodaee n BarWc | • jllamaMttc | • X Bituminoue • UnonWc • Mtcaflafcae • MuaaovHe * Sand grain • Calcareoua X Pjflic w Owl-dark • Salt Porosity Typ* Track X Chart-light B Sidertle • Earthy • tow permeaMty • cvyetilt / graina leu tian 1 /1« mm m_ Octorrttc ft SHcaoue s FeneaM • void* (ram gae bubble! • ahrtnkage craeka • bMeeye texture m FamiBlnoM F Fracture X IntofcryMalRne * Inter^agmantil • Inlergcmulaf ( Sorting Track 1 VP 0 InteroolWc • Mtarpaletaldel | Vary poorty sorted • > 10 phi sin grade deaeee | f> J Mddie Poorty sorted • HO phi »ae grade daetet | 0 Organic • Srtdged • intafoaal M Moderately eortad - 3-6 phi rtae grade daaaaa | p Pinpoint • void* ieaa than 1/18 mm refM [ Moderately welsof led - 2-3 phi size grade cteeees | V Wigby • void» greater tian 1116 mm W J 242 OH Show Track Rounding Track • Evan MMno (75 • 100* of (ht rock * aMned) - iuoraaoaa m aotvent wA o ® ft ft ® Subangular wft WelRoundetf n P Framework Track F FVxveeoea • no vtaibla OH alaKng Framework to • rata between da He matorMpeetar than 1/16 mm and primary void War leeitftan 1/16 mm. ? Indicate* queaionatte inlarpretalan Trace FomII Track An Ar Al Aa Au Ba CB Cf Ch Ci Co Cora Track Taat Track cp ff °y IndfcatM Dm 0 Ea En bred Interval El be Oa Ql 1[Indtealaa Lost Cora 0 Olt H K I Ma Me Mtwfwitfcin Ne NaonanIM N O Sedlmenta n Structures Pa Pd PC PI Beddina / roiis Beddina Pi F*Y Ph P IX I.-L-I— LJ- mi,I,, Pm Pa Rh Re Ro Ru Sb Sc SM. Ry «f) •ft* Ta Tf S3 Td Th Tc Tp at TV TrypenHaa Z Zoophycoa Sfc Sadlmantary StructurM Sedimentary Structures 1 1 0 • c "OS \ Laminations T «*» Ctaaaeal rv -I -r "( S -v/V 3- tofsyfrlm Low«no»f i4«n , , •SB ==r Law anoia oam lam — PanMlamnaDoni it pA "V" Syneraia crack X Tfcepea ekudure /TP IMmarfca i Water Escape Wava rtppta 4am £S Wavy Ivrinationa Sedimentary Bedding Contact! EX FS GLOSS GRAD HO -EL. JL WAVY Wantworth Grain / Crystal Slza Scala Chart Canstrat/Amstrat Grain Slza Seal* Chart Mm* •tea Lower Uppar Dm Cleatfc Rocks CryetaMne Kocta Maa Ondao •tee Oretfee if Common Kama Common Mama LMt UmM Phi 11 Umfc Link PM (mm) (mm) {•5 [mm( (mm) « Clav CivMooivaMto 0.00097W 0.0030002 VarvFkta SW 0.0039062 0.0078125 •« Fine Sit FMvMorooviMiit 0,0076125 0.015625 •7 Vadium SW Madlum >«rmrwieta«hM 001S625 0.03125 •« *4 0.03125 0.062S *5 0.125 01475 •3 9 FlraSimiUmrt 0.1675 &£.. . „*JL UHUnSMMtU*mt 0.2S O.J7J *2 3 OS 10 •1 0 375 OS •2 10 2.0 O OS 0.76 Orantiaa 2.0 40 -1 8.0 -2 ao 10.0 -3 VMvCoaraaSrtftJooari 15 2.0 The too meeaure Phi is equal to Ite negatfve logertlhm to Vie 32.0 64.0 -5 baaa 2 c* tte atee in mMmel en Thua 1mm-0 PM and 1/2 rtm • *1 Phi and 1/4 mm» *2 Phi etc. Bauldara 2S60 -4K.-8 Tha siza measure PM ta aqua) to t» negative logarithm 10 tia bese 2 of the stta In Thus 1 mm • 0 Pht and 112 mm • *% Phi and 1/4 mm • •2 Phi ate. 243 Other Constituents argillaceous doloston* (Rock) halysitld coral (Fossil) Limestone grain supported (Rock) £ high-spired gastropod (Fossil) <3? Paleosol (Rock) articulated ostracod valves (Fossil) Anhydrite primary (Rock) pelmatozoan crinoid bioclasts (Fossil) argillaceous planar-bedded limestone (Rock) bivalve or pelycepod (Fossil) Matrix Supported Breccia (Rock) F undifferentiated bioclastic debris (Fossil ri Dolomite (Rock) Bioclastic (Fossil) calcareous dolostone (Rock) Bivalve (Fossil) Limestone mud supported (Rock) Pellet (Fossil) dolomitic limestone (Rock) HE Stromatoporoid (Fossil) disarticulated brachiopods (Fossil) Dolomite (Stringers) planolites or paleophycus (Fossil) Mudstone (Pebbles) Anhydirte cement (Accessory) § Paleosol (Clasts) Mud chips (Sedimentary Structure) Horizontal Decompaction Fractures am Nodular Bedding (Sedimentary Structure) vy Stylolite - High Amplitude Rip up clasts (Sedimentary Structure) • Anhydrite secondary (Grain) Scour and fid stmcture (Sedmentaiy Structure) Argillaceous (Accessory) W desiccation cracks (Sedimentary Structure) large codiacean algae (Fossil) planar lamination (Sedimentary Stmcture) cyanobacterial mat (Fossil) wavy lamination (Sedimentary Stmcture) calc red algae rhodophytes (Fossil) i water escape (Sedimentary Structure) disarticulated brachiopods (Fossil) M Anhydrite Cement fenestrate btyozoan (Fossil) Anhydrite • primary Nodule pelmatozoan crinoid bioclasts (Fossil) Anhydrite - secondary Nodule bioturbation with discrete burrows (Fossil) Chicken wire Stmcture Algae non descrlpt (Fossil) <£> Chert - light Nodule Intertidal (Fades) D Dolomitization Lagoonal (Facies) L Leaching Sabkha (Facies) M Mottled (dolomitization) Subtidal (Facies) \ Fracture Supratidal (Facies) J\r Stylolite - Undifferentiated Beach (Fades) 4/ir- Stylolite - High Amplitude Anhydrite primary (Grain) stromatolite (Fossil) fenestrate btyozoan (Fossil) 244 Oil Shows Sedimentary Structures i S 2 12? Rock and Fossil Accessories e oo Bindstone Framestone in BafBeetone CN Rud stone Carbonate Texture Ftoatstone Grainstone Packstone Wackestone Mud stone Interpreted Lithology Bedding Contacts I I Fades Classification 246 Cow Loo W*N Nama- Horn* « at Hoffar 1O-2&-1-10W2 Location: Ground' CoNar ( UWt: 101102500115W200 KB: (m) UTM Eaa»: Hot® tD; UTM North; Cor* Analysis Cora Analysis ParmaabHtty Porostty KV(mO| K80(mD) 247 248 Cor* Loo WcaNviw: 1S-2J-1-17W7 locrton Ground;Cottar (m| UW1.1011M500117W200 KB: (m) U7M Etac HotaC: UTM North. Cor* Analysl* Poro»lty Knaxtiw) Poroanj; Mhmn {%) wcssi KBO (nnO> 249 II II 1 i t i : ! >i » •J •:: j i .... i « . „'l.1 ~,t- - ~ t < •• - '«1 250 Cow Lea W*N Nam*; CDH-OEV TW Langbank Location: Ground / CoMar: (m) UWI: 1011S2801202W200 KB: (m) UTM Eaat: Hoi* ID. UTM North: 251 252 Cora Loa Wall Nam*: Charokaa at al Worfcman Location: Ground / Collar. (m) UWI: 101023400132W100 KB: (m) UTM East: Hole ID: UTM North: 253 Cof Loo VWINm 4-3-14-21SV2 iaeMon: Qicuntf / ZtHm (m) UW1: 10104Q201421W200 KB: Mot# 10: UTM North: Coro Anatysi* Porosity JOiuu_(rn0i. Pent, CMM (%) '.i1 !'«. 254 \//sy//y/sA 255 Cort Loo W«IN*m*: 18-23-2-1W2 Location: Ground / Collar: UWI 111182300201W200 KB: (m) UTMEaM: HOMO: UTM North' Cora Analysis Cora Analysis Psmisablltty Porosity Kn**(mO) KV (m0> KftO(mO) 256 257 259 o ooooo ooooooooo ® ® ® ® ® ® ® Porosity Type > > n > > Dlagenesta « Sedimentary Structures Rocfc and Fossil Accessories Biidstone Framestone Bafftestona Rudstone Carbonate Texture Floatstone Grainstone Peckstone Wackestone Mudstone Interpreted LHhology Bedding Contacts Depth Sampled Facias Classfication 261 CgrtUg W*H Name: Suncar Oungra ®-16-2-14W2 LocaSon Ground / Coiar (m) UWI: 141M1M0314W300 KB: (m) UTM £aat* hoia O. UTM North: Cora Analysts Cor* Analysis Psrmoablltty Porosity Porotfty Maaaurad (*) >01 0.1 02 o.: Poroalty Hatkim (*) 9.01 kv (mo) Poroalty Caiculatad (%} „9J V hi, II I Ml••J ft H 262 263 265 Cors Log W»> Nwiw: Sa«fcott X >1 Mommiogftwd Locator Ground / CoUr. (m) UWI: 141121300219W20Q KB: Hoi* ID; l/TM North: Cors Analysis Cor* Analysis PsfmMblllty Porosity K90(mD) PorqMy M«Mur*di%J ).01 1000 0.1 0.2 03 KV(mO) PorocMy H*Mum >.01 1000 : 0.1 0.1 0.3 KmaxfmO} Porowtv cicuf >*d (%) >.91 , Jit}L_ M„ M I 266 267 Cort Log VW*I Nam*: 1V31^.11W2 Location. Ground / Coftar. (m) UW1; lS113nOOei1W2QO K8: Hot* ©: UTM North. Com Analysis Cors Analysis Psrmssblltty Porosity ? 8 ir Porw*y Mewwed £%) 6.': FofPMty CatartWd l%) 1.91 0.1 #JI Pore« I < d> f <$> t • &> • • • $ t * <|) I • • • *-A I 268 270 Esalss VM Nam*: Seaptra STIMN 8 Unit LocMkvt: OflSund / Coft*: (m) UWt 1310*3400304*300 KS: (m) UTMCMC HotoiD: UTM North: Cor* Analysis Cor* Analysis P*rm*abWty Porosity Pon+rty Mmtftd {%) 0.1 0 2 0. KV (mDi Poroafty CatcUatad (H) 0.1 0.2 0. PoroaHy HaMwm (%> .- 271 272 CortLoo MM Nanw NRK Bryartt Location: Orouvt/Coter (n<> UWI: t211»0M0607Wa00 KB: (m) UTMEaat: HotolO: UTM North Cor* Analysis Cor* Anslyai* Pmrnisabillty Porosity Kmax (mO) PoratMy Manured (%) KVOWPl PMM«y CMMMH (%) 111 K90 ImO) PorwMy HaHum (*) M «*•* U.t I + •///•S*vs/s/i 4 I I 273 274 Cof Log Waft Nana: 8.5-6-19W2 Ground l Cotor. (m) UWI: 14KMOS0001BW200 KB; (m) UTMEMt HOW © UTMNonh: Cor* Analysis Porosity If Kmc* ImO) KVlmO) KOO(mO) V/////M Y////////A f/s/s/////}} W///////J; —f/////////// ////////«#' /////////jy t 4> + Wf 275 276 278 •""trti 280 Cors Loo WelNwn# (-S-M7W2 Location. (Vnund / Coiar (m) UWt 10MW0M0S22W200 KB. (m) UTM EM: Hot* ID: UTM Mortfv Cor* Analysis Porosity jtvjsei- •.1 #J o.x Hofoawv mWum(%) a a ai a.a 281 282 284 I Appendix B: Isotope Data 285 Table B1: Carbon and Oxygen isotope data. M •HHH mm HI•i mmMl MMI llnK CC-1 2-34-1-32W1 2317.3m •0.81 -6.83 23.87 93% 0% 6% CC-2 2-34-1-32W1 2317.25 •0.39 -4.83 25.94 99% 0% 1% CC-4 16-23-2-1W2 2523.5m -0.26 -4.88 26.09 0% 98% 2% CC-5 16-23-2-1W2 2524.8m -0.10 -4.28 26.51 80% 20% 0% CC-9 12-13-2-19W2 2992.73m -3.29 -7.00 23.70 60% 40% 0% CC-10 12-13-2-19W2 2993.4m -1.20 -5.34 25.41 85% 15% 0% CC-11 3-16-2-10W2 3007.5m? -0.17 -5.29 25.46 0% 100% 0% CC-12 3-16-2-10W2 3012.45m 0.11 -7.34 23.35 100% 0% 0% CC-13 3-18-2-10W2 3013.25m 0.44 -6.93 23.77 80% 8% 12% CC-14 13-23-6-11W2 2583.7m 0.12 -4.27 26.52 0% 100% 0% CC-15 13-23-6-11W2 2586.75m -0.88 -6.50 24.22 95% 5% 0% CC-17 13-23-6-11W2 2589m -2.74 -6.57 24.15 55% 45% 0% CC-19 10-25-1-15W2 3113.4m 1.89 -4.71 26.06 0% 60% 40% CC-20 10-25-1-15W2 3114m 1.77 -4.69 25.68 0% 50% 50% CC-21 10-25-1-15W2 3115.8m 0.44 -5.17 25.59 0% 70% 30% CC-22 10-25-1-15W2 3117.2m -1.69 -6.48 24.24 0% 100% 0% CC-24 10-25-1-15W2 3118.05m -0.88 -7.42 23.27 94% 1% 5% CC-25 10-25-1-15W2 3119.8m 0.28 -6.53 24.19 85% 8% 7% CC-28 1-9-21-1BW2 5787ft -0.46 -5.14 25.83 0% 100% 0% CC-29 1-9-21-16W2 5789ft -0.46 -4.66 26.12 0% 100% 0% CC-30 1-9-21-16W2 5802ft 0.79 -5.44 25.31 70% 30% 0% CC-31 1-9-21-16W2 5800.1ft 0.51 -4.19 26.60 100% 0% 0% CC-33 6-5-6-19W2 2708.85m 0.78 -5.65 25.10 0% 90% 10% CC-34 6-5-6-19W2 2711.8m 0.13 -6.91 23.80 92% 3% 5% CC-38B 4-2-14-21W2 8902ft -0.41 -4.90 25.87 0% 87% 13% CC-39 4-2-14-21W2 8912.5ft 0.70 -5.49 25.26 40% 60% 0% CC-40 4-2-14-21W2 8921.5ft -0.58 -6.46 24.26 66% 24% 10% CC-43 12-2-7-11W2 2549.2m -0.37 -7.34 23.36 100% 0% 0% CC-44 12-2-7-11W2 2550m -0.26 •6.85 23.66 70% 25% 5% CC-46 6-5-8-22W2 2502.15m -1.16 -5.02 25.74 0% 100% 0% CC-47 6-5-8-22 W2 2508.75m 0.81 -3.78 27.02 15% 60% 25% CC-49 13-23-1-17W2 9984.5ft 0.22 -5.50 25.25 55% 45% 0% CC-50 13-23-1-17W2 9999.5ft -0.24 -6.93 23.77 93% 7% 0% CC-51 13-23-1-17W2 10003ft -0.24 -6.39 24.33 75% 25% 0% CC-55 11-20-2-18W2 2995m 0.64 •5.51 25.24 0% 100% 0% CC-56 11-20-2-18W2 2996.85m -0.18 -7.19 23.51 84% 8% 10% CC-57 2-11-10-9W2 7512.7ft -0.63 -4.46 26.33 100% 0% 0% CC-60 15-9-2-14W2 9971ft 0.60 -6.21 24.52 95% 0% 5% CC-66 1&-8-5-7W2 2651.8m 0.07 -5.12 25.65 35% 64% 1% CC-60 15-8-5-7W2 2854.3m 0.18 -6.97 23.74 98% 2% 0% CC-70 6-5-8-22 W2 8217.5ft -0.55 -4.81 25.96 100% 0% 0% cc-ao 15-6-5-7W2 2648.4m 1.27 -4.67 25.90 0% 100% 0% CC-81 15-6-5-7W2 2649.4m 0.69 -5.40 25.35 0% 100% 0% CC-82 15-6-5-7W2 26519m 0.34 -4.92 25.85 55% 45% 0% CC-83 8-16-2-14W2 3017.6m •0.25 -6.02 24.71 0% 100% 0% CC-84 11-20-2-18W2 2993.25m -0.01 -5.56 25.18 0% 100% 0% CC-85 11-20-2-18W2 2997.55m -0.30 -6.92 23.79 100% 0% 0% CC-86 6-5-6-19W2 2709.5m -1.32 •6.28 24.45 0% 100% 0% CC-87 16-23-2-1W2 2521m 1.38 -4.57 26.21 0% 100% 0% CC-88 16-23-2-1W2 2525.8m -0.39 -5.38 25.38 20% 78% 2% CC-89 15-9-2-14W2 9958.5ft -0.06 -5.38 25.38 0% 100% 0% CC-90 15-9-2-14W2 9993ft -0.04 -5.08 25.69 0% 100% 0% 510Ov«ww 3 1.03092 x 618OV-POB + 30.92 (Copteft, T. B., 1995) LiPo#3 LIPO#3 USC-1 LiPo#3 286 Table B2: Strontium isotope data. •1•1 W HUH mm CC1 2-34-1-32W1 2317.3m 0.70804 0.00001 93% 0% 6% CC2 2-34-1-32W1 2317.25 0.70945 0.00002 99% 0% 1% CC4 2-34-1-32W1 2523.5m 0.70833 0.00002 0% 98% 2% CC9 12-13-2-19W2 2992.73m 0.70821 0.00003 60% 40% 0% CC11 3-16-2-10W2 3007.5m 0.70838 0.00002 0% 100% 0% CC14 13-23-6-11W2 2583.7m 0.70798 0.00002 0% 100% 0% CC15 13-23-6-11W2 2586.75m 0.70814 0.00003 95% 5% 0% CC17 13-23-6-11W2 2589m 0.70870 0.00003 55% 45% 0% CC21 10-25-1-15W2 3115.8m 0.70821 0.00002 0% 70% 30% CC22 10-25-1-15W2 3117.2m 0.70895 0.00003 0% 100% 0% CC38 4-2-14-21W2 6902ft 0.70892 0.00003 0% 87% 13% CC43 12-2-7-11W2 2549.2m 0.70794 0.00003 100% 0% 0% COM 12-2-7-11W2 2550m 0.70798 0.00002 70% 25% 5% CC46 6-5-8-22W2 2502.15m 0.71003 0.00004 0% 100% 0% CC47 6-5-8-22W2 2508.75m 0.70824 0.00004 15% 60% 25% CC55 11-20-2-18W2 2995m 0.70841 0.00003 0% 100% 0% CC57 2-11-10-9W2 7512.7ft 0.70873 0.00003 100% 0% 0% CC80 15-8-5-7W2 2648.4m 0.70832 0.00001 0% 100% 0% CC81 15-8-5-7W2 2649.4m 0.70871 0.00003 0% 100% 0% CC84 11-20-2-18W2 2993.25m 0.70836 0.00001 0% 100% 0% CC85 11-20-2-18W2 2997.55m 0.70804 0.00001 100% 0% 0% CC87 16-23-2-1W2 2521m 0.70858 0.00003 0% 100% 0% CC88 16-23-2-1W2 2525.8m 0.70838 0.00003 20% 78% 2% 287 * 0* 0 + 0 • M * 0