Interrogating the Paleogene sulfur cycle, carbonate-associated sulfate and pore water sulfate δ34S from Demerara Rise and Newfoundland Drifts
Friday, 19 December 2014
The isotopic value of seawater sulfate varied significantly throughout the Phanerozoic. Sulfate δ34S values decreased dramatically around 120 Ma from ~20‰ to ~10‰. During the Early Eocene (~55 Ma to 45 Ma) the δ34S composition increased from 18‰ to 22‰ and has remained largely invariant over the last 34 Ma. The two principal hypotheses that are invoked to explain this positive Eocene excursion: (1) a rapid increase in the flux of weathering-derived sulfate and an increase in sulfate concentrations, coupled with a compensatory increase in pyrite burial, or (2) an increase volume of anoxic waters and enhanced increase in pyrite burial. A clear understanding of this significant change in seawater chemistry is hampered by the relatively low temporal resolution of barite δ34S data during this period, and potential problems with the preservation of carbonate associated sulfate signals. Here we focus on increasing the temporal resolution δ34S isotope curve through this excursion using carbonate-associated sulfate data from IODP Expedition 342, Newfoundland Drifts, and ODP Leg 207, Demerara Rise. Initial data largely confirm the magnitude and timing of change observed in the barite δ34S records. Additionally, to better constrain the fidelity of CAS-derived δ34S values, we will present pore-water sulfate δ34S data sampled from Expedition 342 sediments.