Chronostratigraphy and tectonostratigraphy of the Columnbus Basin, eastern offshore Trinidad

摘要

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) transpres- sional northeast-southwest-trending anticlines and (2) northwest- southeast-oriented, down-to-the-northeast, extension normal faults. The basin was filled throughout t4e Pliocene and Pleistocene by more than 40,000 ft (> 12,200 m) of clastic sediment supplied pri- marily by the Paleo-Orinoco Delta system. The delta prograded eastward over a storm-influenced and current-influenced shelf dur- ing the Pliocene-Pleistocene, depositing marine and terrestrial clas- tic qlegasequences as a series of prograding wedges atop a lower Pliocene to pre-Pliocene mobile shale facies. Biostratigraphic and welllog 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 explo- ration risk and success: (1) megasequences wedge bidirectionally; (2) consideration of hydrocarbon.system risk across any area re- quires 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 megas- equence 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 sub- aerial 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.