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Tectonic Evolution and Hydrocarbon Prospectivity of the Tobago Forearc Basin, Barbados Ridge, and Barbados Accretionary Prism

Abstract

This study utilizes 10,000 km of modern, high-resolution, deep-penetration 2D seismic data provided by the oil industry to define the tectonic evolution and hydrocarbon prospectivity of the Lesser Antilles subduction zone in the Barbados and Trinidad maritime zones. This zone includes the following tectonic and basinal components: (1) Paleogene Tobago basin, formed as a forearc basin in front of the Lesser Antilles volcanic arc; (2) Barbados submarine ridge and island of Barbados, that represents the Eocene Barbados prism accreted to the front of the Lesser Antilles volcanic arc; and (3) the Late Miocene inner forearc deformation belt (IFDB), a 400-km-long and 50- to 70-km-wide zone of westward-verging folds and thrusts that formed as a result of ongoing convergence between the Tobago Basin and Barbados ridge.

Limited production of oil and gas on the island of Barbados confirms the presence of a working petroleum system consisting of a continentally-derived, quartz-rich, turbiditic sandstone reservoir of the Eocene Scotland Formation; as well as the subsurface presence of both Tertiary terrigenous (type III) and possibly Cretaceous marine (type II) source rocks. We focus our study on the IFDB, which thrusts the western edge of the Barbados ridge westward over the east-dipping basement of the Tobago basin. At 11.75°N latitude near Tobago, the IFDB abruptly ends where it is erosionally truncated. Two styles of deformation are present in the IFDB that both result in large fold and faulted closers, involving equivalents to the Scotland Formation reservoir rocks on Barbados. Thin-skinned fold-and-thrust structures are observed deforming the western edge of the Paleocene-Miocene fill of the Tobago basin. Thick-skinned structures with shale diapirs are observed to the east along the edge of the Barbados ridge. The possible existence and type of source rocks below these large structures is discussed.