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Source Rocks in the Caribbean Plate

Abstract

There is a consensus that source rocks in the Caribbean are principally Tertiary gas-prone with potential to generate huge gas volumes and subordinate amounts of oil. Indeed, vast thermogenic and biogenic gas accumulations and small oil fields confirm the existence of source rocks within the Caribbean. Unfortunately, given the complex tectonic setting, it is very difficult to determine what controls the Cretaceous and Tertiary source rock distribution, extent, quality, and organic content. This study provides an integrated geological and geochemical analysis, which documents the distribution, age, depositional facies, and types of source rocks along the Caribbean plate. Bulk rock geochemistry and petroleum geochemical characterization of source rocks in wells, fields, seeps, and outcrops were critical to better understand the hydrocarbon generative potential of the sedimentary basins and their petroleum systems. The principal source rocks that exist in the Caribbean basins are Tertiary in age, as proven by the petroleum systems in Cariaco Basin, Tobago Trough, Barbados accretionary prism, Dominican Republic, Jamaica Island, Nicaraguan Rise, Panama, the Lower Magdalena Basin (Sinu, San Jacinto and Plato and San Jorge Sub-basins), Guajira Basin, Urumaco Trough and Falcon Basin. These Tertiary successions contain typically transitional gas-prone source rocks with a mixture of type II/III kerogen. In Nicaragua and Barbados, however, Eocene oil-prone marine, Type II source rocks have been also identified. Although the Upper Cretaceous La Luna Formation (and its equivalents) is the most likely source rock along the northern South American plate, there are no evidences in the Caribbean Plate that suggest the presence of similar organic facies and depositional environment. Much has been proposed about the presence of a marine Cretaceous source rock associated with the global Late Cretaceous anoxic event, but the probable geographic distribution, thickness, and thermal maturity are uncertain. Even though Cretaceous source rocks have been identified in the Chorotega Block (Costa Rica), the Sinu Sub-basin (Colombia), and offshore Colombian and Venezuelan basins, their extension is very limited and not well constrained. These Caribbean Cretaceous sequences are excellent source rocks characterized by marine Type II kerogen, and record the anoxic event in the Late Cretaceous. However, they are not an extension of the La Luna prolific source rock.