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

Earth's biosphere witnessed the first major extinction event in the Phanerozoic during the Cambrian Age 4, with a genera loss up to similar 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 delta 98Mo (similar to+2.34 parts per thousand) 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. Marine life experienced the first major mass extinction during the Cambrian Age 4 (similar to 509-514 Ma) right after the Cambrian explosion, with a genera loss up to similar to 45%. The mass extinction was traditionally attributed to expanded marine anoxia in the global ocean based on lithological changes, but geochemical evidence for this scenario is still lacking. Molybdenum (Mo) isotopes can be used to track global marine redox states in ancient oceans. Herein, new Mo isotope data revealed transitory expansion of sulfidic waterbodies on in the global ocean at the major mass extinction intervals. Sulfidic waters enriched in H2S are lethal for marine animals. Therefore, expanded sulfidic waterbodies in the global ocean could have served as a major driver for the mass extinction event. Dynamic marine Mo cycling via Fe-Mn shuttles during the Cambrian Age 4 is revealedRobust Mo isotope evidence for expanded continental margin euxinia in the global ocean during mass extinctionFirm support to a causal link between expanded marine euxinia and the extinction event

Automated summary

This article supplements new geochemical evidence for expanded marine euxinia during the Cambrian Age 4 and provides firm support for a causal link between this environment and the extinction event.