Variability in Sulfur Isotope Records of Phanerozoic Seawater Sulfate

Abstract

The δ³⁴S of seawater sulfate reflects processes operating at the nexus of sulfur, carbon, and oxygen cycles. However, knowledge of past seawater sulfate δ³⁴S values must be derived from proxy materials that are impacted differently by depositional and postdepositional processes. We produced new time series estimates for the δ³⁴S value of seawater sulfate by combining 6,710 published data from three sedimentary archives—marine barite, evaporites, and carbonate‐associated sulfate—with updated age constraints on the deposits. Robust features in multiple records capture temporal trends in the δ³⁴S value of seawater and its interplay with other Phanerozoic geochemical and stratigraphic trends. However, high‐frequency discordances indicate that each record is differentially prone to depositional biases and diagenetic overprints. The amount of noise, quantified from the variograms of each record, increases with age for all δ³⁴S proxies, indicating that postdepositional processes obscure detailed knowledge of seawater sulfate's δ³⁴S value deeper in time.

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