Chronostratigraphy and tectonostratigraphy of the Columbus Basin, eastern offshore Trinidad

The Columbus Basin, forming the easternmost part of the Eastern Venezuela B asin, is situated along the obliquely converging margins of the Caribbean a nd South American plates. The two primary structural elements that characte rize the basin are (1) transpressional northeast-southwest-trending anticli nes 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 elastic sediment supplied primarily by the Paleo-Orinoco Delta system. The delta prograded eastward over a stor m-influenced and current-influenced shelf during the Pliocene-Pleistocene, depositing marine and terrestrial elastic megasequences as a series of prog rading wedges atop a lower Pliocene to pre-Pliocene mobile shale facies. Biostratigraphic and well log data from 41 wells were integrated with thous ands of kilometers of interpreted two-dimensional and three-dimensional sei smic data to construct a chronostratigraphic framework for the basin. As a result, several observations were made regarding the basin's geology that h ave a bearing on exploration risk and success: (1) megasequences wedge bidi rectionally; (2) consideration of hydrocarbon-system risk across any area r equires 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) r eservoir quality of deep-marine strata is strongly influenced by both the t ype 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.