Trinidad-Gulf of Paria: 'piggyback' halite-dissolution basins (11-0Ma) on a long-lived foreland-basin thrust belt (Campanian-Recent)
by Dr Roger Higgs,
Geoclastica Ltd
July 2005
Confidential - This document is for the exclusive use of XX and is subject to a confidentiality agreement between XX and Geoclastica Ltd. None of the contents may be passed to third parties outside XX.
EXECUTIVE SUMMARY
According to the popular "Pindell Model", the Jurassic-Cretaceous passive margin of Trinidad persisted until as late as Miocene time, whereupon it was destroyed by the obliquely colliding Caribbean Arc arriving from the west, initiating a foreland basin in Trinidad. In contrast, an exhaustive synthesis presented here of literature published since 1860 clearly shows a S-verging, S-migrating foreland basin in Trinidad starting 70 m.y. earlier (latest Cretaceous). This basin can be attributed to the published concept of slow (amagmatic) Protocaribbean subduction under the N-facing former passive margin, from Campanian time, pushing a "Slope Nappe" (former passive- margin slope and underlying rift fill and continental basement) up onto the former outer shelf, metamorphosing the shelf and rift succession there, and driving the foreland basin. In turn these metashelf and metarift strata were uplifted in Miocene time, as an in-sequence "Shelf Nappe" (present Paria-Northern Range; Oligo-Miocene cooling ages), further eroding the covering Slope Nappe and forcing the basin south. Nappe mountains fed olistostromes and turbidites southward to this Protocaribbean Foreland Basin from late Campanian (Galera Formation) to early Late Miocene time (Lower Cruse), ahead of a generally S-jumping thrust front. These sediments were deposited as submarine fan-deltas on the northern "active slope" of a S-migrating flysch trough, opposite a mud-rich "passive slope" and (beyond Trinidad) a presumed sandy southern shelf. The thrust front intermittently stepped back north, as shown by Central Range unconformities (e.g. sub-Nariva, sub-Brasso, sub-Tamana); other unconformities (sub-Chaudiere, sub-Cipero) record "pulling-in" of the forebulge due to changes in Protocaribbean relative motion.
The E-migrating Caribbean Arc "collision point" reached the longitude of NW Trinidad later (5 Ma, Pliocene, post-Lower Cruse) than stated by the Pindell Model (ca. 10 Ma), having begun its 1,100 km ESE (relative) transit along the Venezuela-Trinidad margin much later than the model asserts, starting from Guajira in the far west at 30 Ma (mid-Oligocene) rather than 60 Ma (Paleocene). This ESE motion obliquely along the ENE-trending Protocaribbean paleomountains of the central Venezuela-Trinidad sector of the margin caused oblique obduction of a Caribbean Arc nappe (incorporating the Villa de Cura Complex, Margarita and Tobago) onto the Slope-Shelf Nappe stack, through Early Miocene to Recent time (still in progress between the Margarita "suture point" and Tobago); thus the Caribbean took over diachronously as foreland-basin driver. The presently active (Caribbean) foredeep is confined to the far east (Deltana- Columbus Basin).
In Trinidad, Late Miocene (post-11 Ma) to Recent basins on the Caribbean- Protocaribbean nappe complex and its southern thrust belt (i.e. North Coast Basin, Gulf of Paria, Caroni and Southern Basins and their eastern-shelf continuations), interpreted in the literature as extensional or transtensional despite lacking volcanics, are reinterpreted here as synorogenic wedge-top basins, growing during nappe emplacement and shortening (ongoing). These are "pseudo-extensional" basins, formed by subsurface dissolution of a formerly unknown, thick (km), synrift, diapiric, lowermost Cretaceous halite interval in the Slope Nappe, Shelf Nappe and parautochthon, here named the "Carib Halite". In these basins, subsidence by buried- halite dissolution outweighs tectonic (shortening) uplift; subsequent reduction or cessation of halite dissolution (due to halite exhaustion?) has locally allowed uplift to overtake subsidence in Quaternary time (ca 1 Ma), forming the Central and Southern
Geoclastica ii Trinidad2005 Ranges. Massive underground halite dissolution coincided with the 11-0 Ma long-term glacioeustatic low (Haq), and reflects prodigious rainfall during each early-postglacial recovery, supplying fresh water to the subsurface along orogenically fractured aquifers connected to nappe- and thrust-belt mountain recharge areas.
The Carib Halite dissolution "weld" can be identified in wells and exposures, but the halite itself is nowhere exposed, and where thought to be preserved is beyond drilled depths. The halite was deposited during the late-rift stage in a graben system that reached westward from Trinidad through northern Venezuela to Colombia (Bogotá halite). The age of the Carib Halite, constrained by fossils in strata below and above the dissolution weld, is early Neocomian (specifically late Berriasian and early Valanginian). This age is consistent with the lack of any indisputably Berriasian faunas among the recorded Jurassic-Cretaceous fossils ever found in Trinidad and Venezuela, and coincides precisely with a major eustatic sea-level low (Haq chart), that provided the halite-depositing graben with the required isolation from the world ocean. The deduced Neocomian age of the halite indicates that rifting in Venezuela and Trinidad persisted much later than proposed by Pindell and co-workers, who argued that Protocaribbean rifting ended (sea-floor spreading began) 20-30 m.y. earlier in the Jurassic (Oxfordian).
The missing halite explains, among many other diverse phenomena, the well known metamorphic-grade discontinuity (at the weld) in the Northern Range, and also in Paria Peninsula, separating (A) the Güinimita-Laventille-Lopinot-Toco post-rift suite, showing incipient metamorphism only (shales locally converted to slate and phyllite; limestones locally recrystallized, impeding dating due to alteration of fossils), from (B) metamorphic older rocks (Maracas, Maraval, etc.), showing prehnite- to greenschist metamorphism (including Sans Souci rift volcanics), with shales entirely converted to phyllite and schist.
These three "new" concepts, namely early northern orogeny (in fact a 1970s idea), "late" Caribbean Arc arrival (1980s), and massive halite dissolution, will profoundly
Geoclastica iii Trinidad2005 affect oil and gas exploration in Trinidad, changing interpretations and predictions of subsidence history, paleogeography, structure (halite décollement), traps (thrusting; dissolution collapse structures), heat flow (high thermal conductivity of halite), seismicity, previously unsuspected evaporitic source rocks, seals, etc. For example, rejecting the popular Gulf of Paria pullapart model, in favor of halite-dissolution subsidence, negates both a supposed 11 Ma change in Caribbean relative motion, from ESE to ENE, and major dextral slip (10s km) on mythical east-west master faults in Trinidad that have never been found and that cause severe dextral palinspastic disruption, with vital implications for oil exploration.
This report presents the Campanian to Recent evolution of Trinidad in detail, meticulously presenting the diverse evidence for deep-halite dissolution (from outcrops, wells and seismic profiles) and for long-lived northern provenance (based on southward fining, olistolith compositions, cannibalization and heavy minerals). The report is a painstaking synthesis of the literature, with the added benefit of the the author's 15 years of experience in the region, conducting outcrop and subsurface studies throughout Trinidad and Venezuela. Several enigmatic stratigraphic units are discussed in particular detail and demystified (e.g. Sans Souci, Toco, "Cherrycake", Soldado, San Fernando, Plaisance), as are the supposed El Pilar and Arima Faults. The report integrates and interprets a vast amount of published data, enhanced by outcrop observations by the author. Products include 14 new and original tectonogeographic maps (Maastrichtian through Quaternary) and five tables of data (olistolith compositions, heavy minerals, evaporite occurrences by formation, Trinidad-Venezuela halite-dissolution basins, and analagous basins worldwide). Aside from these benefits, the report can be used as a computer-searchable encyclopedia and literature source of Trinidad-Venezuela basins and formations. With onshore and onshore bid rounds scheduled in Trinidad for 2005-2006, plus the recently demonstrated continued potential for giant oilfield discoveries (e.g. Angostura, discovered 1999), no exploration company interested in this prolific petroleum province can afford to be without this report.
Geoclastica iv Trinidad2005 CONTENTS EXECUTIVE SUMMARY i
1. GEOLOGICAL BACKGROUND 1 1.1. Present-day Caribbean Arc complex & its junction with S America 1 1.2. Present-day relative motion vector of the Caribbean Plate 2 1.3. History of plate-tectonic interpretations of northern S America, 4 culminating in the "Pindell Model" 1.4. Flaws in the Pindell Model 7
2. EVIDENCE FOR A NORTHERN SOURCE FROM CAMPANIAN TIME 10 2.1. Introduction 10 2.2. Northern olistostromes, fining south 11 2.2.1. Olistostromes 11 2.2.1.1. General 11 2.2.1.2. Mt Harris picnic area olistostrome (Chaudiere Fm) 13 2.2.2. Southward fining 14 2.3. Cannibalization 15 2.4. Sandstone mineralogy 16 2.4.1. Staurolite 16 2.4.2. Glaucophane 17 2.4.3. "Blue quartz" 21
3. PROTOCARIBBEAN INTERACTION WITH SOUTH AMERICA 22 3.1. Protocaribbean subduction (Campanian-Pliocene), causing uplift of 22 "Slope Nappe" then "Shelf Nappe", driving a foreland basin 3.2. Burial metamorphism, under Slope Nappe, of future Shelf Nappe 27 (Jur-Cret rift & passive-margin strata on Hercynian basement) 3.3. Remnants of the Slope Nappe 32 3.4. Current position of Shelf Nappe leading edge (Hercynian Front) 32 3.5. Dating of Shelf Nappe uplift from olistolith & conglomerate 35 compositions
4. CARIBBEAN INTERACTION WITH SOUTH AMERICA 37 4.1. Late arrival & obduction of the Caribbean Arc 37 4.2. The active foredeep: Deltana Basin, Columbus Basin 40 4.3. Past & present velocity of the Caribbean Plate 41 4.4. Caribbean Plate is not fixed in the mantle reference frame 42 4.5. Ablative subduction & trench rollback at the Caribbean- 42 Protocaribbean plate boundary
5. THE VANISHING SYNRIFT KILOMETRIC "CARIB HALITE" 44 5.1. Introduction 44 5.2. Neogene supraorogen basins attributed to buried-halite 46 dissolution, e.g. Gulf of Paria, Caroni, Southern, North Coast Basins
Geoclastica v Trinidad2005 5.3. Known occurrences of bedded evaporites in Trinidad 54 5.3.1. Anhydrite/gypsum 54 5.3.2. Halite 55 5.4. Indirect evidence for buried evaporites 56 5.4.1. Saline springs, e.g. the "Warm Springs" 56 5.4.2. High geothermal gradient indicated by "hot wells" 58 5.5. Evidence for dissolved or dissolving subsurface halite 59 5.5.1. Geomorphological evidence: Dragon's Mouth seaway 59 rupturing Northern Range-Paria mountain chain 5.5.2. Geological evidence 60 5.5.2.1. Block-faulted structural style of Neogene basins 61 5.5.2.2. Isolated structural highs below Neogene basins 64 5.5.2.3. Thrust-belt structural style 65 5.5.2.4. Collapse folds 67 5.5.2.5. Gypsum veins 67 5.5.2.6. High paleo-heat flow 68 5.5.2.7. Evaporitic source rock? 69 5.5.2.8. Collapse breccias 71 5.5.2.9. Barite cement 73 5.5.2.10. Mineralization 73 5.6. Carib Halite: distribution, thickness, tectonic setting, age 74 5.6.1. Distribution 74 5.6.2. Thickness 75 5.6.3. Tectonic setting 76 5.6.4. Stratigraphic position 77 5.7. Comparison with other halite-dissolution basins 83 5.7.1. Thickness of dissolved halite 83 5.7.2. Depth of halite dissolution 84 5.7.3. Rate of dissolution 84 5.8. Unique scale & extent of Carib Halite dissolution 85
6. ENIGMATIC FORMATIONS EXPLAINED BY THE NEW CONCEPTS 87 6.1. Introduction 87 6.2. Sans Souci & Toco Fms 87 6.3. "Cherry-cake conglomerate" 90 6.4. Soldado Fm & St Joseph Conglomerate 92 6.5. Eocene glauconitic sandstone (Mount Moriah) & redeposited 94 limestone (Vistabella) 6.6. Plaisance Conglomerate 101 6.7. San Fernando Fm redefinition 104
7. CONTROVERSIAL FAULTS EXPLAINED BY THE NEW CONCEPTS 106 7.1. El Pilar Fault 106 7.2. Arima Fault 109
Geoclastica vi Trinidad2005 8. CAMPANIAN-RECENT TECTONO-SEDIMENTARY EVOLUTION 110 8.1. Foreland basin tripartite tectonodepositional facies & 110 corresponding formation suites 8.2. late Campanian-Maastrichtian 111 8.2.1. Tectonics 111 8.2.2. Formations deposited 112 8.2.3. Remarks 113 8.3. Paleocene 113 8.3.1. Tectonics 113 8.3.2. Formations deposited 114 8.3.3. Remarks 114 8.4. Early Eocene 115 8.4.1. Tectonics 115 8.4.2. Formations deposited 115 8.4.3. Remarks 115 8.5. Middle Eocene 116 8.5.1. Tectonics 116 8.5.2. Formations deposited 116 8.5.3. Remarks 116 8.6. Late Eocene 116 8.6.1. Tectonics 116 8.6.2. Formations deposited 117 8.6.3. Remarks 117 8.7. Early Oligocene 117 8.7.1. Tectonics 117 8.7.2. Formations deposited 118 8.7.3. Remarks 118 8.8. Late Oligocene 120 8.8.1. Tectonics 120 8.8.2. Formations deposited 120 8.8.3. Remarks 120 8.9. early Early Miocene 121 8.9.1. Tectonics 121 8.9.2. Formations deposited 121 8.9.3. Remarks 122 8.10. late Early Miocene 122 8.10.1. Tectonics 122 8.10.2. Formations deposited 123 8.10.3. Remarks 123 8.11. early Middle Miocene 123 8.11.1. Tectonics 123 8.11.2. Formations deposited 124 8.11.3. Remarks 124 8.12. late Middle Miocene 124 8.12.1. Tectonics 124 8.12.2. Formations deposited 125
Geoclastica vii Trinidad2005 8.12.3. Remarks 125 8.13. early Late Miocene 129 8.13.1. Tectonics 129 8.13.2. Formations deposited 129 8.13.3. Remarks 129 8.14. late Late Miocene through Quaternary 130 8.14.1. Tectonics 130 8.14.2. Formations deposited 132 8.14.3. Remarks 132
9. OIL EXPLORATION IMPLICATIONS 135 9.1. Introduction 135 9.2. Revised paleogeographic maps 136 9.3. Oil source rock 136 9.4. Uplift-subsidence history of individual basins 136 9.5. Thermal-maturation models 137 9.6. Interpretation of structural style 137
10. REFERENCES 139
List of Tables (tables located at end of main text)
1. Trinidad olistostromes & identified olistolith-donor formations. 2. Heavy-mineral compositions of Trinidad formations. 3. Interpreted Trinidad-Venezuela-Colombia halite-dissolution basins. 4. Gypsum & anhydrite occurrences in Trinidad, by formation. 5. Halite-dissolution basins worldwide.
List of Figures (figures located at end of main text, after tables)
1. Present-day tectonic & basin map of Venezuela & Trinidad. 2. Schematic tectonic map of Caribbean region. Jordan 1975. 3. Tectono-geological map of SE Caribbean region. Mascle & Moore 1990. 4. Geological map of Trinidad. Saunders 1997a. 5. Stratigraphic chart of Trinidad. Saunders 1997a. 6. Cartoon paleoplate maps showing Caribbean relative motion since Paleocene. 7. Middle Eocene reconstruction of Caribbean region. Pindell et al. 1988. 8. Cretaceous-Recent Caribbean reconstructions. Lugo & Mann 1995. 9. Photos, Williamsville olistolith and "BioStrat olistolith". 10. Photos, Plaisance Conglomerate & olistostrome. 11. Photo, Mt Harris Forest picnic site olistostrome (Chaudiere Fm).
Geoclastica viii Trinidad2005 12. N-S section showing southward displacement of Cenozoic depocenters. Kugler & Saunders 1967. 13. Map of Hercynian orogenic belt of northern S America. Speed et al. 1997. 14. Photo, smoky quartz grains, Nariva Formation, Sandstone Trace. 15. Cretaceous-Recent N-S America relative motion. Müller et al. 1999. 16. Photo, upside-down Galera Formation sandstone bed with ?hummocky cross stratification. 17. Late Maastrichtian tectonogeographic map of Venezuela & Trinidad. 18. N-S paleo-sections of the Trinidad continental margin, showing development of Slope Nappe & Shelf Nappe. 19. Interpreted uppermost Jurassic-Lower Cretaceous stratigraphy of Trinidad & northern E Venezuela, showing inferred position of "Carib Halite". 20. Structural map of Gulf of Paria & Trinidad. Flinch et al. 1999. 21. Line drawings of Gulf of Paria seismic profiles. Flinch et al. 1999. 22. Cross section showing interpreted deep structure, Gulf of Paria. Flinch et al. 1999. 23. Model of basin filling above buried dissolving halite. Ge & Jackson 1998. 24. Photo, E Venezuela Chimana Fm (Cretaceous) with gypsum veins. 25. Photo, cherry-cake conglomerate, Toco Fm & Plaisance Conglomerate 26. Hypothetical forebulge migration. Allen & Allen 1990. 27. Hypothetical forebulge migration. Allen & Allen 1990 (after Tankard 1986). 28. St Joseph Conglomerate overlying sub-Chaudiere unconformity. 29. W-E schematic stratigraphic section, E Venezuela-Trinidad, with interpreted Eocene-Early Oligocene stratigraphy & depositional environments. 30. Graphic log of Plaisance Conglomerate. 31. Depositional environment model for the northern, "active slope" of the Venezuela- Trinidad flysch trough. 32. Late Maastrichtian tectonogeographic map, Trinidad. 33. Paleocene tectonogeographic map, Trinidad. 34. Early Eocene tectonogeographic map, Trinidad. 35. Middle Eocene tectonogeographic map, Trinidad. 36. late Late Eocene tectonogeographic map, Trinidad. 37. Early Oligocene tectonogeographic map, Trinidad. 38. Late Oligocene tectonogeographic map, Trinidad. 39. early Early Miocene tectonogeographic map, Trinidad. 40. late Early Miocene tectonogeographic map, Trinidad. 41. early Middle Miocene tectonogeographic map, Trinidad. 42. late Middle Miocene tectonogeographic map, Trinidad. 43. end Middle Miocene tectonogeographic map, Trinidad. 44. early Late Miocene tectonogeographic map, Trinidad. 45. late Late Miocene - early Quaternary tectonogeographic map, Trinidad.
Geoclastica ix Trinidad2005