Framboidal pyrite evidence for persistent low oxygen levels in shallow-marine facies of the Nanpanjiang Basin during the Permian-Triassic transition

Abstract

Previous studies suggested that anoxia was a causal factor in the end-Permian mass extinction (EPME), marked by abrupt enrichment of pyrite framboids in the post-EPME microbialites of the earliest Triassic on shallow platforms, and that this dysoxic–anoxic phase followed a time of well‑oxygenated seafloors. Here, we report persistent dysoxia throughout the latest Permian and euxinia just before the EPME, based on a new redox history reconstruction study using framboidal pyrite size distribution as well as sulfur isotopic compositions of pyrites, from the Taiping section on the Pingguo Platform in the Nanpanjiang Basin in China. Further, we show that the EPME was followed here by rapid oxygenation, not an anoxic incursion. This revised redox history might be an unusual localized phenomenon when compared to other platforms, or it could be solid sedimentary evidence for redox oscillations outside the bioclast-enriched photic zone, which broadens our understanding of terrestrial–marine ecosystem interactions before and during the EPME.