Interrogating the Paleogene sulfur cycle, carbonate-associated sulfate and pore water sulfate δ34S from Demerara Rise and Newfoundland Drifts

Abstract:

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.