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

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) delta S-34 (i.e., delta S-34(CAS)) from three Permian-Triassic boundary (PTB) sections in South China. We observe substantial delta S-34(CAS) variation within single hand samples, with most samples having a delta S-34(CAS) range exceeding 5 parts per thousand and some reaching similar to 20 parts per thousand. We also find evidence for mixing between low CAS abundance, high delta S-34(CAS) and high CAS abundance, low delta S-34(CA) phases. A simple model of reduced sulfur oxidation and incorporation as CAS suggests that sedimentary redox oscillations may plausibly explain the delta S-34(CAS) heterogeneity within many EPME carbonates; rapid variation in the delta S-34 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 delta S-34(CAS) heterogeneity. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

The dynamics of the marine sulfur cycle across the End-Permian Mass Extinction have been obscured by disagreement between sulfur isotopic records. New measurements of carbonate-associated sulfate delta S-34 reveal substantial variation and evidence for mixing within samples. This suggests that sedimentary redox oscillations may explain the heterogeneity in delta S-34 within many EPME carbonates.