--> Abstract: Sources of Hydrocarbon-Rich Fluids Advecting on the Seafloor in the Northern Gulf Of Mexico, by B. Fu and P. Aharon; #90932 (1998).

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Abstract: Sources of Hydrocarbon-Rich Fluids Advecting on the Seafloor in the Northern Gulf Of Mexico

FU, BAOSHUN, and PAUL AHARON
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA, 70803

Hydrocarbon- rich fluids advecting on the seafloor through fault conduits are common in the northern Gulf of Mexico. In order to decipher the sources of these fluids we have initiated a program of coring these seep sediments using the submersible robot arm. Continuous porefluid profiles in 50 cm long cores were obtained by squeezing the sediments using a modified Jahnke device on board the surface ship.

Three types of hydrocarbon-rich fluids can be discerned on the basis of our present geochemical study. Fluids pertaining to the first type have normal Gulf of Mexico deepwater salinities (about 35.4 o/oo) and their 87Sr/86Sr ratios (0.70914, n=3) are identical to the overlying seawater (0.70917). These fluids originated as seawater trapped in the sediments with their chemical compositions being modified by microbial sulfate reduction and authigenic carbonate precipitation. Fluids of the second type are highly saline (1 16 o/oo to 150 o/oo salinity range), with 87Sr/86Sr ratios below that of seawater (0.70797 to 0.70897) and elemental chemistry compatible with halite dissolution. This type of fluids is interpreted to be derived by dissolution of subsurface salt diapirs during seawater convective circulation. Fluids of the third type have high salinity (range 52 o/oo to 155 o/oo), show high concentrations of Ba, Sr and Ca and lower than seawater 87Sr/86Sr ratios (0.70840 to 0.70862, n=8). The high radioactivity of these fluids is caused by enrichment in Ra. We propose derivation of the third type of fluids from deep-seated formation waters advecting on the seafloor. Whereas the first and second type of fluids occur in carbonate deposition areas, the third type is exclusively encountered in barite deposition areas.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas