Variability in sulfur isotope records of Phanerozoic seawater sulfate

Abstract

Key Points  6710 measurements of δ 34 S of sulfate in Phanerozoic sedimentary rocks were compiled and systematically updated to a consistent time scale  Records derived from evaporites, barite, and carbonate-associated sulfate are similar, but also contain dramatic short-term discrepancies  Variation created by diagenetic and depositional processes increases with age in all records, obscuring temporal trends in marine sulfate Plain Language Summary Sedimentary rocks deposited in ancient marine basins preserve a record of seawater composition. We compare the sulfur isotopic composition of three sedimentary materials that contain sulfatea major ion in seawater important for carbon and oxygen cycling. Evaporite salts, the mineral barite, and trace sulfate in limestone each reveal the same first-order trends over the last 541 million years, but also display substantial shorter order discrepancies that reflect how the materials capture and store paleooceanographic information. These discrepancies partially obscure understanding of the relationship between life, ocean chemistry, and climate.

Sulfide Dissolution and Awaruite Formation in Continental Serpentinization Environments and Its Implications to Supporting Life

“…(a) δ 34 S of sulfate against δ 34 S of the sulfide fractions (AVS and CRS) indicating later addition of sulfate either from modern or an ancient seawater sulfate reservoir. The light gray area indicates δ 34 S composition of Paleozoic to Mesozoic seawater (after Kampschulte & Strauss, 2004; Present et al., 2020). (b) Most samples from the Chimaera hydrothermal system are dominated by sulfate over sulfide and have a relatively narrow range in δ 34 S sulfate values.…”

“…(Note, Santa Elena and Chimaera peridotites were both serpentinized in the Cretaceous where δ 34 S seawater‐sulfate values were around 16–19‰; Present et al. [2020]). However, the abundance of vein‐like native copper forming in the center of serpentine veins (see Figure 3e) indicates that native copper formed during a later stage of fluid‐rock interaction.…”

“…These have been inferred to circulate through the lower lying Upper Paleozoic to Lower Mesozoic shales that are the source rock of the methane seeps (Hosgörmez, 2007). The δ 34 S composition of seawater sulfate in the Paleozoic and Mesozoic varied between +10‰ and +35‰ (Kampschulte & Strauss, 2004; Present et al., 2020) and hence could have contributed trace amounts of sulfate to the rock (Figure 6a). The input of modern seawater‐sulfate can, however, not be excluded.…”

Variability in Sulfur Isotope Records of Phanerozoic Seawater Sulfate

“…No new data were collected for this study. Data sets compiled for this research are tabulated in the supporting information and referenced below, and the compiled data are deposited in a freely accessible Open Science Framework repository available in Present et al (2020).…”

Variability in sulfur isotope records of Phanerozoic seawater sulfate

“…No new data were collected for this study. Datasets compiled for this research are tabulated in the Supplemental Material and referenced below, and the compiled data are deposited in a freelyaccessible Open Science Framework repository available in Present et al (2020).…”