The mineralogical and stable isotope studies of the diagenetic carbonate and sulfide minerals from the Blake Ridge sediments retrieved during Leg 164 may shed some new insights on the diagenesis related to the occurrence of gas hydrates.
The oxygen isotopic compositions of the diagenetic carbonates show evidence that formation of gas hydrates has taken place in the entire sedimentary column above the BSR and have confirmed that gas hydrates are dissociated below the BSR and by the salt intrusion in the Cape Fear Diapir.
The chemical and carbon isotopic compositions of the diagenetic carbonates are controlled by the CH4-CO2 input-output balance, which depends on the bacterial reduction of sulfate and of carbonate.
During these bacterial reactions, large sulfur isotopic fractionation occurs between the sulfate source and the reduced sulfide that precipitates locally as pyrite concretions under partially closed-system conditions.