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Mesozoic Salt Diapirism in Southeastern Bahamas as Evidenced by Geophysics


For several decades, Bahamas has intermittently attracted interest for hydrocarbon exploration. Only 6 test wells had been drilled, encountering thick upper Mesozoic and Cenozoic carbonates which, for the most part, are almost barren in hydrocarbon content. Because of the great depth to the older rocks; 3 to 4 km, these rocks were hardly drill tested. To the west, in Cuba, Jurassic and older strata have produced over 60,000 barrels of oil per day. Cuba currently has proven reserves of 181 million barrels of oil. Analyses of gravity, magnetic and processed seismic data in southeastern Bahamas provide independently clear evidence for the presence of Jurassic salt diapirism. The interpreted diapir is adjacent to a deep rift basin that may be a principal source of hydrocarbon generation. That basin has a drainage area of over 9000 sq km and a thickness of over 12 km. It appears to be part of a Triassic-Jurassic rift that extends southeast from Florida. In the vicinity of the interpreted diapir, calculations of thermal maturity from well log analysis validate the possibility of hydrocarbon generation and expulsion from the Middle Jurassic to the present.