Evidence for recrystallization and fluid advection in the Maldives using the sulfur isotopic composition of porewaters, carbonates, and celestine

Abstract

The δ34S values of porewaters, carbonate associated sulfate, and celestine were analyzed from International Ocean Discovery Program Leg 359 Sites U1466, U1467, U1468, and U1471 drilled in The Maldives. These analyses reveal a complex diagenetic history in which the nature of the porewater gradients and their δ34S values varied multiple times during deposition and subsequent diagenesis, with changes recorded in the δ34S values of carbonate associated sulfate and celestine. The δ34S values of these components as well the pore fluids have been influenced by bacterial sulfate reduction which elevates the δ34S values while the concentrations of SO42− in the interstitial porewaters are drawn down. In most instances, the δ34S values of the carbonate associated sulfate and celestine bear little resemblance to the present day porewater δ34S values or those of the contemporaneous seawater. In cases where the δ34S values of the carbonate associated sulfate are similar to those of the porewaters, it suggests that neomorphism and/or recrystallization processes are taking place at the present time. Where δ34S values of the carbonate associated sulfate are similar to the original sediment values it is likely that either little diagenesis has taken place, or that it has taken place in an environment in which the pore fluids had a δ34S value not significantly different than the original sedimentary value. The δ34S values of the celestine at Site U1467 provide a further constraint in that it indicates formation at a time in which the pore fluids had an even more positive δ34S value, and thus a lower SO42−concentration and higher Sr2+ concentrations.