Subsurface Structure, Stratigraphy, and Hydrocarbon Basin Modeling of the Barbados Accretionary Prism

The Barbados Accretionary prism (BAP) is located along the eastern edge of the Caribbean plate and formed during the Late Cretaceous to Recent by westward subduction of Cretaceous oceanic crust of the Atlantic Ocean beneath the Lesser Antilles volcanic arc. The 300-km-width of the BAP over an along-strike distance of 600 km is related to high volumes of terrigenous clastic sediments delivered to the front of the prism and dammed by fracture zone ridges on the subducting, Atlantic plate. In Chapter 2, I evaluate the along-strike changes in the BAP as a response to oblique subduction of the two, elongated, fracture zones in oceanic crust (Tiburon Rise and Barracuda Ridge). Effects include: 1) closer spaced and imbricated thrust faults and associated folds along the areas of the deformation front that are in contact with the two subducting highs; 2) damming of the voluminous, clastic sediment supply from the Orinoco River that ponds along the southward slopes of the two fracture zone ridges and produce abrupt widening in the prism’s zone of frontal accretion - that in turn increases the wedge taper angles; 3) areas north of the Tiburon Rise and Barracuda ridge show an increased taper angle from 4°-6° while south of the Tiburon Rise and Barracuda Ridge that contain thick trench sediments or an overfilled subduction trench exhibit lower prism taper angles from 3°-4°. Tectonic reconstructions of the changing positions of the two fracture zones corresponding with the Atlantic basement highs over the past 25 million years reveal areas of the prism that have been affected by previous fracture zone collisions. In Chapter 3, I interpret ~16,000 line km of PSDM seismic data to construct 400-km-long cross-sections to better document: 1) the zone of active, frontal accretion; 2) the zone of initial stabilization in the center of the prism where imbricated thrust slices have been rotated to vertical; and 3) the zone of piggyback basins and westward backthrusting along the western edge of the prism; and 4) the Tobago-Barbados ridge (TBR) characterized by Miocene to Recent backthrusting that has uplifted the island of Barbados. Using this structural framework, I present a basin model for the TBR that predicts that the type II source rocks beneath the island of Barbados have reached the temperature associated with generation of oil at a depth of ~4 km and are generation gas at ~6 km. This generation of hydrocarbons is made possible by the uplift of the TBR above sea level which increased thermal stress in the subsurface. Direct hydrocarbon indicators documented from interpretation of seismic reflection data support the presence of mature source rocks at these predicted depths.