The redox structure of Ediacaran and early Cambrian oceans and its controls

• 来源期刊: 科学通报（英文版）
• 年，卷（期）: 2020,（24）
• 所属期刊栏目: REVIEW
• 页码范围: 2141-2149
• 页数: 9页
• 语种: 英文

摘要

The rapid diversification of early animals during the Ediacaran(635-541 Ma)and early Cambrian(ca.541-509 Ma)has frequently been attributed to increasing oceanic oxygenation.However,the pattern of oceanic oxygenation and its relationship to early animal evolution remain in debate.In this review,we examine the redox structure of Ediacaran and early Cambrian oceans and its controls,offering new insights into contemporaneous oceanic oxygenation patterns and their role in the coevolution of environ-ments and early animals.We review the development of marine redox models which,in combination with independent distal deep-ocean redox proxies,supports a highly redox-stratified shelf and an anoxia-dominated deep ocean during the Ediacaran and early Cambrian.Geochemical and modeling evi-dence indicates that the marine redox structure was likely controlled by low atmospheric O2 levels and low seawater vertical mixing rates on shelves at that time.Furthermore,theoretical analysis and increas-ing geochemical evidence,particularly from South China,show that limited sulfate availability was a pri-mary control on the attenuation of mid-depth euxinia offshore,in contrast to the existing paradigm invoking decreased organic carbon fluxes distally.In light of our review,we infer that if oceanic oxygena-tion indeed triggered the rise of early animals,it must have done so through a shelf oxygenation which was probably driven by elevated oxidant availability.Our review calls for further studies on Ediacaran-Cambrian marine redox structure and its controls,particularly from regions outside of South China,in order to better understand the coevolutionary relationship between oceanic redox and early animals.