Marine redox evolutions and carbon isotope variations during the Guadalupian-Lopingian transition in the Yangtze Platform, South China

The Guadalupian (Middle Permian) witnessed a significant biocrisis or mass extinction which wiped out complex and large benthic faunas previously flourished in the long-term Carboniferous and Early-Middle Permian. The triggered pattern of environmental factors such as marine anoxia and volcanism on the mass extinction is still unclear. Here, we present conodont biozone, pyrite framboids size distribution, pyritic sulfur isotope and carbon isotopes data to address the relationship between carbon cycle, marine redox conditions and mass extinction. Our results show that two negative excursions of carbon-isotope occurred in the middle Capitanian and at the Guadalupian-Lopingian (G-L) boundary, the latter was a global signature. Long-term dysoxic-oxic conditions were developed in the early-middle Capitanian while persistent euxinia occurred at the G-L boundary, the former was probably related to the regional organic matter enrichment and high oxygen demand in bottom water; the latter was likely caused by global high nutrient input and primary productivity combined with deoxygenation related to large-scale volcanism eruption.