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Abstract

A re-examination of the rock types and depositional environments of Trinidadian sediments, combined with a consideration of the structural controls on sedimentation and subsequent translation, have enabled the division of Trinidad’s stratigraphy into three stratigraphic groups: the Upper Jurassic through Maastrichtian Northern Range Group metasediments, the Cretaceous and Tertiary Trinidad Group sediments and the Cretaceous igneous and sedimentary rocks of the Sans Souci Group.

The Sans Souci Group rocks are stratigraphically and structurally distinct from Trinidad’s other rocks, and have probably been transported from the west with the Caribbean plate over many hundreds of kilometers. In contrast, the Trinidad and Northern Range Groups, which make up the majority of Trinidad, were deposited on the northern South American margin. Depositional environments interpreted from both groups suggest a rapid deepening around the Late Jurassic/Earliest Cretaceous time which may have been the result of the transition from a Middle/Late Jurassic phase of Proto-Caribbean rifting to Cretaceous passive margin development. The majority of the Late Jurassic through Late Eocene sedimentation history of both groups was on the outer shelf or middle to upper continental slope, and sedimentological variations appear to relate almost exclusively to long period eustatic variations in sea level and/or shifts in sediment pathways. Global oceanic anoxia, combined with upwelling and excessive fluvial run-off, at a time of high eustatic sea level, may explain the deposition of quality source rocks of the Gautier and Naparima Hill Formations from the Albian through to the Campanian time in Trinidad.

Deep-water passive margin sedimentation is interpreted to have continued in Trinidad through to Late Eocene/Early Oligocene time. Rapid shallowing, indicated by Late Eocene biostratigraphic data leads to an upward transition from the pelagic marls of the Navet Formation into shallow-water limestones and localised conglomerates in the San Fernando Formation. Following this, Early and Middle Oligocene sedimentation was very slow or non-existent. A similar shallowing and slowing of sedimentation is known from eastern Venezuela in the late Middle Eocene time, slightly earlier than in Trinidad, and at progressively older times farther west along the northern South American margin. Progressive west to east uplift induced by the passage of the flexural forebulge in front of the eastwardly migrating Caribbean plate, or in plane stresses resulting from the convergence of North and South America, both explain this diachroneity in uplift.

Trinidadian depocenters subsided rapidly in the Middle to Late Oligocene time, and up to 3 km of deltaic clastics and deep-water marls accumulated over 10 Ma (Late Oligocene to early Middle Miocene time). This is in sharp contrast to the thick passive margin sequence underlying these deposits that accumulated over an 80-Ma time period (Barremian to Eocene) and represents the onset of foreland basin sedimentation in Trinidad.

With the progressive approach of the Caribbean plate in Early to Middle Miocene time, the foreland basin was deformed causing depositional environments to generally shallow through the Early to Middle Miocene time. Thrust, and/or strike-slip pop-up highs locally reached the photic zone in the Central Range, resulting in deposition of early Middle Miocene inner neritic platform limestones of the Tamana Formation.

From the Late Miocene to Recent time, much of central and southern Trinidad subsided rapidly. In the last 5 Ma, up to 10 km of deltaic sediment accumulated in the Columbus basin to the south of Trinidad. The proximity of the Orinoco delta to the foreland basin is largely responsible for this rapid increase in sedimentation rate and may partially explain the subsidence. However, the subsidence observed in, and to the north and west of Trinidad may also be related to right-lateral strike-slip pull-apart basin development, possibly aided by a component of north-south extension as the Caribbean/South American plate boundary zone transforms into a zone of transtension.

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