SOURCE ROCK AND MATURATION EVALUATION OF THE BARBADOS ACCRETIONARY PRISM

Organic material in specimens from surface and downhole sites and samples of oil and gas from Barbadian wells were studied for source potential and maturation history. The study involved: (1) visual examination of the kerogen; (2) measurement of total organic carbon content; (3) determination of vitrinite reflectance; (4) Rock-Eval pyrolysis assay; (5) geochemical measurement of pooled and extracted bitumens including carbon isotopic ratios (deltaC-13); and (6) gas chromatographic analysis of saturated gaseous hydrocarbons. Two types of kerogen occur in Barbados: terrestrial, presumably of South American origin, and marine planktonic. The two types are mixed in most samples. The terrestrial kerogens are dominant and occur in all wells in the basal complex and most of its outcrops. The planktonic organic matter occurs in exposed melange, hemipelagic rocks and rarely in terrigenous turbidites. The well specimens do not show significant maturation within the drilled depths, suggesting that pooled hydrocarbons originated from deeper levels of the prism and accumulated as a result of migration. Faults bounding the intraprism thrust sheets probably provided migratory paths for hydrocarbons and water, juxtaposed rocks of variable maturity, assisted in alteration and biodegradation, and led to the formation of structural traps. The composition of gases indicates that maturation conditions for gas generation may exist at great depths within the Barbados accretionary prism.