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) δ34S (i.e., δ34SCAS) from three Permian-Triassic boundary (PTB) sections in South China. We observe substantial δ34SCAS variation within single hand samples, with most samples having a δ34SCAS range exceeding 5‰ and some reaching ∼20‰. We also find evidence for mixing between low CAS abundance, high δ34SCAS and high CAS abundance, low δ34SCAS phases. A simple model of reduced sulfur oxidation and incorporation as CAS suggests that sedimentary redox oscillations may plausibly explain the δ34SCAS heterogeneity within many EPME carbonates; rapid variation in the δ34S of the marine SO42− 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 δ34SCAS heterogeneity.