Ediacaran sulfur cycle: Insights from sulfur isotope measurements (Δ33S and δ34S) on paired sulfate-pyrite in the Huqf Supergroup of Oman

The Ediacaran Period (635-541 Ma) was a time of dramatic environmental and ecological change. Sulfur isotopic records preserved in marine strata provide insights into these changes. Previous work using δ34S in pyrite and carbonate-associated sulfate in the Ediacaran-aged Huqf Supergroup (Sultanate of Oman) suggested increases in marine sulfate concentrations, changing microbial pathways and redox conditions, and a long-term increase in δ34S of sulfate delivery to the ocean. However, δ34S-based analyses on their own were insufficient to uniquely reconstruct these environmental and ecological changes. Here we present new paired δ34S and Δ33S data from carbonate-associated sulfate and pyrite in these strata. The results allow us to provide three new constraints on Ediacaran sulfur cycling. First, a notable increase Δ34SCAS-PY, previously attributed to possible disproportionation, in upper Buah strata is associated with Δ33S-evidence for an increase in sulfide reoxidation, indicating a transition to more oxidizing conditions, possibly associated with the onset of bioturbation. Secondly, Δ33S data indicate that a large positive shift in both sulfate and pyrite δ34S in Ara Group strata is mostly likely due to an increase in delivery of 34S-enriched sulfate to the basin. Finally paired δ34S-Δ33S data constrain possible changes in seawater sulfate concentrations, suggesting an increase in sulfate supply related to enhanced evaporite weathering, consistent with geological and geochemical observations that imply high [SO4] (∼17 mM) during deposition of the Ara Group.