SULFATE REDUCTION AND IRON SULFIDE MINERAL FORMATION IN GULF OF MEXICO ANOXIC SEDIMENTS

Sulfate reduction and iron sulfide mineral formation were investigated in Mississippi River delta and Gulf of Mexico continental shelf and slope sediments. Sulfate reduction rates and pyrite concentrations generally decrease exponentially with increasing overlying water depth. This is probably a result of decreasing sedimentation rates and organic carbon concentrations with increasing water depth. A linear relationship between sulfate reduction rates and organic carbon concentrations as well as normal marine C/S ratios indicate that organic carbon is probably limiting sulfate reduction and iron sulfide mineral formation in this region. Organic carbon reactivity appears to be substantially higher in Mississippi River delta sediments than in other sediments from this region. Mississippi River delta and Texas-Louisiana continental shelf sediments are the primary pyrite burial environments. Of the total pyrite deposition in the study area (approximately 6 x 10(11) g y-1), about 81 percent is deposited in Texas-Louisiana continental shelf sediments and about 15 percent in Mississippi River delta sediments. The remaining 4 percent is deposited in sediments on the continental slope and the western and southern continental shelf areas.