http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Environmental controls on sulfate reduction and iron sulfide mineral formation
xviii, 190 leaves : illustrations ; 29 cm
Sulfate reduction and iron sulfide mineral formation were investigated in Atchafalaya Bay, Louisiana, the Mississippi River delta and Gulf of Mexico continental shelf and slope sediments. The primary objective of this investigation was to determine the factors controlling these processes in different depositional environments. The influence of dissolved sulfate concentration on sulfate reduction and iron sulfide mineral formation was investigated in the freshwater to seawater transitional environment of Atchafalaya Bay. High sulfate reduction rates were observed in sediments with a salinity range of 0.2 to 22. Unexpectedly high concentrations of AVS and pyrite-S were observed in sediments with low salinity. A complete reduction of dissolved sulfate did not occur in sediments with low salinity pore waters. However, the degree of sulfidization of iron was as high as 0.95, indicating that reactive iron possibly limits sulfide mineral formation in the low salinity Atchafalaya Bay sediments. Consequently, C/S ratios are higher in the low salinity sediments than in typical marine sediments, but not because of sulfate limitation as is commonly presumed. Sulfate reduction and iron sulfide mineral formation in the Gulf of Mexico are strongly influenced by the massive amount of sediments dominantly derived from the Mississippi River. Both sulfate reduction rates and pyrite-S concentrations decrease exponentially with increasing overlying water depth. This is probably a result of decreasing sedimentation rate and organic carbon concentration. The linear relationship between sulfate reduction rate and organic carbon concentration together with the normal marine C/S ratios indicate that the concentration of organic carbon is the primary factor controlling sulfate reduction and iron sulfide mineral formation in this region. Furthermore, due to a higher organic carbon reactivity, higher sulfate reduction rates are observed in the Mississippi River delta sediments as compared to those observed in the normal marine sediments. Texas-Louisiana continental shelf and Mississippi River delta sediments are the primary pyrite burial environments. Of the total pyrite deposition in the study area, i.e., 6.07x10^11 g/year, 81.1% is deposited in the Texas-Louisiana continental shelf sediments, and 14.8% is deposited in the Mississippi River delta sediments. The remaining 4.0% is deposited in sediments from the continental slope, and the western, southwestern and southern Gulf of Mexico continental shelf area.