Carbonate associated sulfate (CAS) δ34S heterogeneity across the End-Permian Mass Extinction in South China

Abstract The dynamics of the marine sulfur cycle across the End-Permian Mass Extinction (EPME) have been obscured by disagreement between sulfur isotopic records from different archives. Here, we attempt to resolve this disagreement with new measurements of carbonate associated sulfate (CAS) δ 34 S (i.e., δ 34 SCAS) from three Permian-Triassic boundary (PTB) sections in South China. We observe substantial δ 34 SCAS variation within single hand samples, with most samples having a δ 34 SCAS range exceeding 5‰ and some reaching ∼20‰. We also find evidence for mixing between low CAS abundance, high δ 34 SCAS and high CAS abundance, low δ 34 SCAS phases. A simple model of reduced sulfur oxidation and incorporation as CAS suggests that sedimentary redox oscillations may plausibly explain the δ 34 SCAS heterogeneity within many EPME carbonates; rapid variation in the δ 34 S of the marine SO 4 2 − reservoir is not necessary. Additional work to examine how synchronous changes in organic carbon fluxes, sedimentation rates, or other parameters that impact sediment redox and sulfur diagenesis is needed to evaluate the environmental implications of the δ 34 SCAS heterogeneity.