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ARMENTROUT, JOHN M., RICHARD C. BECKER, and LARRY B. FEARN, Mobil Exploration and Development Technology Corp., WINSTON M. ALI, and DEREK G. HUDSON, Trinidad and Tobago Petroleum Company Ltd., and WILLIAM A. O'NEILL, TIM E. TYRRELL, and H. AUSTIN VONDERHOYA, Mobil New Exploration Ventures

ABSTRACT: Exploration Applications of Integrated Biostratigraphic Analysis, Plio-Pleistocene, Offshore Southern Trinidad

The Neogene depositional history of the Eastern Venezuela Tertiary Basin reflects dominance of north to northeast transport of deltaic sedimentation overprinted by complex tectonics. Exploration within this setting requires precise correlations and carefully constrained depositional models. The assessment of risk of exploration plays is facilitated by an understanding of depositional environments based on integration of biostratigraphy, seismic sequence stratigraphy, log-motif analysis and seismic facies mapping. Correlation of the offshore Trinidad Columbus and Carambola wells, and their use in calibrating seismic reflection profile analysis, illustrates this process of integrated stratigraphic interpretation.

The seismic reflection profiles are dominated by parallel continuous reflections and the tectonic overprint of phases of extension and compression. Locally developed unconformities and clinoforms of basin-slope scale identify what may be several sequence boundaries. Relative abundance plots of climatically controlled littoral and terrigenous derived palynomorph taxa show well developed arid-to-wet cycles. Biofacies analysis of benthic foraminiferal assemblages identifies patterns of shallowing and deepening environments. Integration of palynological and foraminiferal analyses defines two distinct associations/trends interpreted as environmentally significant:

a. Low sea-level association: Arid palynomorph assemblage and shallowing foraminiferal biofacies.

b. High sea-level association: Wet palynomorph assemblage and deepening foraminiferal biofacies.

Within the context of major marine incursions, these biofacies cycles, when integrated with seismic facies and wireline log stacking patterns, provide a framework for defining and correlating sequences. The distribution of seismic facies, log-facies and biofacies within each depositional sequence provides paleogeographic maps suitable for assessing the probable depositional environment, and also reservoir and seal potential within each structural closure.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.