Stratigratigraphic architecture and basin fill evolution of a plate margin basin, eastern offshore Trinidad and Venezuela

Garciacaro, Emilio José
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Eastward migration of the Caribbean plate relative to the South American plate is recorded by a 1100-km-long foreland basin which is oldest in the west (Maracaibo basin, 65-55 Ma) and youngest in the east (Columbus basin, eastern offshore Trinidad, 15-0 Ma). Regional transpression has caused lithospheric loading and flexure along the northern margin of South America creating a large foreland basin area which propagated from west to east as the Caribbean plate moved eastward relative to the South American plate. I have integrated 775 km of deep-penetration 2D seismic lines acquired by the 2004 BOLIVAR survey, 325 km of 1975 GULFREX seismic data, 8,000 km2 of industry 3-D seismic data, and published industry well data from offshore eastern Trinidad. Interpretation of seismic sections tied to wells reveals the following fault chronology: 1) middle Miocene thrusting along the Darien ridge related to highly oblique convergence between the Caribbean plate and the passive margin of northern South America; continuing thrusting and transpression in an oblique foreland basin setting through the early Pleistocene; 2) early Pliocene-recent low-angle normal faults along the top of the Cretaceous passive margin; these faults were triggered by oversteepening related to formation of the downdip, structurally and bathymetrically deeper, and more seaward Columbus basin; large transfer faults with dominantly strike-slip displacements connect gravity-driven normal faults that cluster near the modern shelf-slope break and trend in the downslope direction; to the south no normal faults are present because the top Cretaceous horizon has not been oversteepened as it is adjacent to the foreland basin; 3) early Pliocene-Recent strike-slip faults parallel to the trend of the Darien ridge and accommodate present-day plate motions. Active mud diapirism in the Columbus basin is widespread and is related to overthrusting and loading of upper Miocene-lower Pliocene age mud. Analysis of the 3-D seismic data reveals the presence of extensive gravity-flow depositional elements on the Columbus basin deepwater area, characterized by mass-transport deposits at the base, turbidite frontal-splay deposits, leveed-channel deposits, and capped by fine-grained condensed-section deposits. Deep basin wells drilled in recent years have proven that turbidites were transported into the Columbus basin deepwater during the Plio-Pleistocene. Analysis of these well results suggest that a deeper oil charge is present within the Columbus basin deepwater area. The primary uncertainty for this variable hydrocarbon system is whether fault or diapiric pathways connect the petroleum charge at depth with shallower reservoir rocks.