Redox Conditions of the Late Ediacaran Ocean on the Southern Margin of the North China Craton

Abstract

Previous studies have revealed dynamic and complex redox conditions of the late Ediacaran ocean. Integrated analyses of Ediacaran successions on different continents can help to better understand global ocean redox conditions. In this study, we used iron and redox-sensitive trace elements (RSTEs) geochemical analyses to present the detailed redox conditions of the late Ediacaran Dongpo Formation on the southern margin of the North China Craton (NCC). Paleoredox reconstruction reveals a dominantly anoxic late Ediacaran ocean punctuated by multiple transient oxygenation events across the southern margin of the NCC. These transient oxidation events in the NCC may have contributed to the appearance of the Ediacaran tubular fossil Shaanxilithes. Based on the assumption that local iron speciation data in a global framework can track the mean and variance of paleoredox conditions through time, we additionally analyzed about 3300 new and published iron speciation data from fine-grained clastic rocks to infer the global redox change in Ediacaran–Cambrian oceans. Our statistical analyses indicated dynamic Ediacaran marine redox conditions and stepwise early–middle Cambrian ocean oxygenation. The appearance and rise of the Ediacaran biota and the diversification of metazoans corresponded temporally with the middle Ediacaran global ocean oxygenation and the early–middle Cambrian stepwise oceanic oxygenation, respectively. Our results highlight the coevolutionary relationship between ocean redox conditions and early animals.