GEOCHEMICAL PATTERNS IN SEDIMENTS NEAR OFFSHORE PRODUCTION PLATFORMS

Patterns of the geochemical characteristics of sediments adjacent to t hree production platforms (22-150 m water depths) in the northwestern Gulf of Mexico were determined by the presence of the structure, the a mount and type of materials discharged from the structure, and the loc al hydrographic setting. Sediments close to platforms (<500 m) were en hanced in coarse-grain materials primarily derived from discharged mud s and cuttings. Hydrocarbon and trace metal (Ag, Ba, Cd, Hg, Pb, and Z n) contaminants were associated with these coarse-grain sediments. Con taminants were asymmetrically distributed around each platform in resp onse to the prevailing currents. Contaminant concentrations at most lo cations were below levels thought to induce biological responses. At a few locations close to one platform, trace metal (i.e., Cd, Hg) conce ntrations exceeded levels thought to induce biological effects. In dee p water (>80 m), sediment trace metal contaminant patterns were stable over time frames of years. A few metals (Pb, Cd) exhibited evidence o f continued accumulation in sediments over the history of the platform .