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AAPG Bulletin, V.
Chronostratigraphy and tectonostratigraphy of the Columbus Basin, eastern
L. J. Wood1
1Bureau of Economic Geology, University of Texas at Austin, Austin, Texas 78713-8924; email: [email protected]
Lesli J. Wood is a research associate in the Bureau of Economic Geology's Industrial Associates Research Program at the University of Texas at Austin. She received her Ph.D. from Colorado State University in 1992, where she studied sequence stratigraphy of clastic shoreline and nearshore systems and their response to base-level changes. Wood joined Amoco Production Company in 1992, where she obtained extensive exploration and production experience in South America and the Caribbean and was a member of the Seismic Attributes Development Team working in clastic basins in Argentina, Brazil, Egypt, and Azerbaijan. Wood joined the bureau in 1997 as a member of the Deltaic Systems Research Group and is currently working in the modern Orinoco Delta in Venezuela, as well as in ancient fluvial/deltaic outcrops of the United States western interior.
The regional chronostratigraphic framework and tectonostratigraphic model for development of the Columbus Basin is a product of 3 years' regional work by many, many individuals. I would like especially to thank Peter Bentham, David Pocknall, Maria Henry, and Ken Ortmann for direct input into ideas, correlations, and implications. I would also like to thank Amoco Energy Company of Trinidad and Tobago for permission to publish the results of this work and the company geoscientists for many stimulating conversations regarding the geology of the Eastern Venezuela Basin. Much appreciation to M. Wade, F. Krause, and an anonymous reviewer, too, for reviews of this manuscript, as well as to Martin Jackson for conversations regarding the diapirs of the Columbus Basin. Finally, thanks to the graphics and editing staff at the Bureau of Economic Geology, University of Texas at Austin, for assistance in completing final figures and manuscript.
The Columbus Basin, forming the easternmost part of the Eastern Venezuela Basin, is situated along the obliquely converging margins of the Caribbean and South American plates. The two primary structural elements that characterize the basin are (1) transpressional northeast-southwest-trending anticlines and (2) northwest-southeast-oriented, down-to-the-northeast, extension normal faults. The basin was filled throughout the Pliocene and Pleistocene by more than 40,000 ft (>12,200 m) of clastic sediment supplied primarily by the Paleo-Orinoco Delta system. The delta prograded eastward over a storm-influenced and current-influenced shelf during the Pliocene-Pleistocene, depositing marine and terrestrial clastic megasequences as a series of prograding wedges atop a lower Pliocene to pre-Pliocene mobile shale facies.
Biostratigraphic and well log data from 41 wells were integrated with thousands of kilometers of interpreted two-dimensional and three-dimensional seismic data to construct a chronostratigraphic framework for the basin. As a result, several observations were made regarding the basin's geology that have a bearing on exploration risk and success: (1) megasequences wedge bidirectionally; (2) consideration of hydrocarbon-system risk across any area requires looking at these sequences as complete paleofeatures; (3) reservoir location is influenced by structural elements in the basin; (4) the lower limit of a good-quality reservoir in any megasequence deepens the closer it comes to the normal fault bounding the wedge in a proximal location; (5) reservoir quality of deep-marine strata is strongly influenced by both the type of shelf system developed (bypass or aggradational) and the location of both subaerial and submarine highs; and (6) submarine surfaces of erosion partition the megasequences and influence hydrostatic pressure, migration, and trapping of hydrocarbons and the distribution of hydrocarbon type.
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