ABSTRACT

In anoxic sediments, bacterially-mediated sulfate reduction can play a major role in both carbonate and sulfide mineral diagenesis. In order to understand better the complex interrelationships involved in these diagenetic processes, diagenesis of iron sulfide and carbonate minerals was studied in the poorly-sorted siliclastic-dominated sediments from Baffin Bay, Texas.

The production of pyrite dominantly takes place in the top 20 cm of sediment. A good correlation (r² = 0.76) is observed between the total inorganic sulfur (TRS) content of the sediments and the percentage of the sediment that is fine-grained (< 63 µm). Substantial upward fluxes of H₂S in some cores, high (> 0.8) degrees of Fe pyritization, and elevated C/S ratios compared to normal marine sediments indicate that reactive iron probably limits sulfide burial in sediments from this region containing more than about 1 wt. % organic carbon.

A major ( 10 fold) increase in CO₂ driven by sulfate reduction is closely related to a large decrease in dissolved calcium in the upper 1 m of sediment. The major decrease in dissolved calcium is probably due to the precipitation of calcium carbonate. Dolomite was observed in these sediments, and favorable conditions for its formation are present. However, a detrital origin for the dolomite cannot be ruled out.