The relationship between organoclastic sulfate reduction and carbonate precipitation/dissolution in marine sediments

Pore fluid sulfate, calcium and magnesium concentrations in ocean drilling sites 981-984, 925-929 and 803-807 are modeled to estimate the rates of sulfate reduction and carbonate precipitation/dissolution. These sites represent scenarios where the sulfate reduction rate is high, moderate, and low. Results show that the rate of carbonate precipitation decreases with decreasing sulfate reduction rate. When sulfate reduction rate is sufficiently low carbonate minerals dissolve. Sulfate reduction produces H+ and bicarbonate which compete in driving carbonate minerals to dissolve or precipitate. The results suggest that the carbonate reactions are mainly driven by the produced H+ when sulfate reduction rate is low, and by the produced bicarbonate when the sulfate reduction rate is high.