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ABSTRACT: Organic Geochemistry of Sediments of the Deep Gulf of Mexico Basin

Jiasong Fang, Roger Sassen

Analysis of 716 core samples cored at DSDP (Deep Sea Drilling Project) Leg 96 in the Mississippi submarine fan and the Orca and Pigmy basins in the Louisiana continental slope using a Rock-Eval pyrolysis unit with a TOC (total organic carbon) module allows computations of hydrogen index (HI), total organic carbon, kerogen type, and oil generative capacity assessment.

No samples are obviously oil prone. TOC content ranges from 0.12 to 2.29%, with an overall average of 9.82%. HI values are generally less than 150 mg HC/g TOC. Tmax (maximum temperature of S2) values (average = 425°C) show the sediments are thermally immature throughout the study area. Hydrocarbon generative potential of the sediments ranges from 492 to 1107 ppm, with an average of 854 ppm. Higher PI (production index) values, ranging from 0.12 to 0.32 and averaging 0.15, suggest the presence of hydrocarbon seepage. Because of organically lean, thermally immature, and gas-prone terrestrial kerogen, there is little reason to assume that the sediments of the Mississippi fan can provide oil source rock for the Gulf of Mexico Basin, or that sediments of anoxic b sins in the Louisiana continental slope are analogs to past environments where source rocks for crude oil have been deposited.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990