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Source Rock Potential of Fine Sediment Deposited in Eleuthera and San Salvador Deep-Sea Carbonate Fans, Bahamas

Andre W. Droxler, Mireille Vandenbroucke, M. Fabre, Richard A. Cartwright, Wolfgang Schlager

Organic matter analyses were conducted in late Quaternary fine sediments deposited in Eleuthera and San Salvador deep-sea carbonate fans (water depth ranging between 4,400 and 5,000 m) at the mouth of the two largest canyons draining most of Great and Little Bahama Banks. Higher content and better quality of organic matter are generally observed in fine carbonate turbidite material than in the intervening hemipelagic carbonate ooze or mud.

The hemipelagic carbonate ooze and mud (carbonate content between 80% and a few percent) are made of a mixture of planktonic tests, bank-derived fine aragonite and magnesian calcite, as well as fine terrigenous material transported southward from the North Atlantic by the Western Boundary Current. Their TOC (total organic content) values are low (in average between 0.30 and 0.45%). The organic matter quality is poor due to important alteration during a long transport and slow burial. The TOC values of the carbonate muddy turbidite, made almost exclusively of bank-derived fine aragonite and occurring in the valleys and lobes of Eleuthera mid-fan, range between 0.25 and 1.80%. The highest TOC values (1 to 1.8%) were measured in the most recent events (younger than 6,000 y.B.P.), where t e organic matter is exceptionally fresh due to the turbiditic sedimentation which prevents biochemical alteration. Its global composition is closer to the average composition of living marine organisms than the composition of common recent marine sediments. Its source rock potential for hydrocarbon generation is though to be high, and the intervening turbidite layers made of carbonate sands and gravel could serve as local reservoirs.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.