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Abstract: Structural Development of the Southern Basin, Onshore Trinidad: Implications for Hydrocarbon Entrapment

Leon J. Aden, Robert E. Bierley

Episodic compressional deformation across onshore southern Trinidad formed a complex spectrum of fold timing and fold types. Successful oil traps are not related to a specific time interval of structural formation, a specific oil expulsion event or a specific fold morphology. Traps that retained hydrocarbons may be related to seal facies.

The tectono-stratigraphic section of onshore southern Trinidad, south of the Central Ranges, is comprised of three generalized depositional packages. Firstly, a southerly sourced Cretaceous to late Oligocene passive margin sequence of deep-water sands, shales and marls; secondly, a northerly sourced late Oligocene through middle Miocene syntectonic sequence of shallow- to deep water sands and shales; and thirdly, a west-southwesterly sourced late Miocene through Pleistocene shelfal sequence.

Observations of compressional structures that folded these sediments during an early period of compressional deformation 25-10 million years before present suggest that all mudrock lithofacies could act as effective seals and trap hydrocarbons. Subsequent structural modification that occurred during a late period of compressional deformation between 5 million years and present day caused refolding and refaulting of these traps.

Restructured traps that were sealed by brittle, Mesozoic deep-water facies failed and hydrocarbons migrated to shallower structural levels. Restructured folds that were sealed by ductile, Tertiary shallow-water facies retained trap fill.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela