Guadalupian (Middle Permian) ocean redox evolution in South China and its implications for mass extinction

Abstract The Guadalupian mass extinction was a long-term biocrisis that started in the early Guadalupian Epoch (Permian Period). Many studies of the causes of the extinction have focused on the late Guadalupian, although the entire Guadalupian should be studied to address its origins. The selective nature of the species removed during the Guadalupian extinction also remains a puzzle. Here, we present pyrite framboid size distributions, pyrite-sulfur isotopic compositions, and C-N-S profiles for the entire Guadalupian from South China to develop a record of ocean redox evolution to help understand the selective extinction. Our results indicate that euxinia was mostly persistent in the deep-water platform basin throughout the Guadalupian, which triggered long-term Early and Middle Guadalupian shallow-water dysoxia and frequent episodic Late Guadalupian euxinia events that resulted in a gradual long-term Early and Middle Guadalupian diversity decrease and selective Late Guadalupian extinction. The combined effect of euxinia and global regression led to selective extinction of taxa that had weakly buffered respiratory physiology and high growth efficiency, such as brachiopods, large fusulinids, and giant bivalves.