Mass Extinction Coincided With Expanded Continental Margin Euxinia During the Cambrian Age 4

Abstract Earth's biosphere witnessed the first major extinction event in the Phanerozoic during the Cambrian Age 4, with a genera loss up to ∼45%. The traditional view suggested that marine anoxia was the main cause of the biotic crisis, yet recent geochemical investigations yielded highly debated opinions on marine redox states during the Cambrian Age 4. Herein, we supplement new geochemical evidence for expanded marine euxinia at the extinction intervals on the Yangtze Platform, South China. Most importantly, modern‐level sedimentary δ98Mo (∼+2.34‰) records were most parsimoniously explained by transitory expansion of continental margin euxinia and concomitant intensification of sedimentary Mo sequestration via Fe‒Mn shuttles in the global ocean. The results clarify global marine redox conditions during the Cambrian Age 4, and lend firm support to a causal link between expanded marine euxinia and the extinction event.