Li Chao, Shi Wei, Cheng Meng, Jin Chengsheng, Algeo Thomas J
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.
Sci Bull (Beijing). 2020 Dec 30;65(24):2141-2149. doi: 10.1016/j.scib.2020.09.023. Epub 2020 Sep 19.
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 environments 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 evidence indicates that the marine redox structure was likely controlled by low atmospheric O levels and low seawater vertical mixing rates on shelves at that time. Furthermore, theoretical analysis and increasing geochemical evidence, particularly from South China, show that limited sulfate availability was a primary 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 oxygenation 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.
埃迪卡拉纪（6.35 - 5.41亿年前）和寒武纪早期（约5.41 - 5.09亿年前）早期动物的快速多样化常常被归因于海洋氧化作用的增强。然而，海洋氧化作用的模式及其与早期动物进化的关系仍存在争议。在这篇综述中，我们研究了埃迪卡拉纪和寒武纪早期海洋的氧化还原结构及其控制因素，为同期海洋氧化模式及其在环境与早期动物共同进化中的作用提供了新的见解。我们回顾了海洋氧化还原模型的发展，该模型与独立的深海远端氧化还原指标相结合，支持在埃迪卡拉纪和寒武纪早期存在高度氧化还原分层的陆架和以缺氧为主的深海。地球化学和模型证据表明，当时海洋的氧化还原结构可能受低大气氧含量和陆架上海水垂直混合速率低的控制。此外，理论分析和越来越多的地球化学证据，特别是来自中国南方的证据表明，与现有观点认为远端有机碳通量减少不同，硫酸盐可用性有限是近海中等深度缺氧带衰减的主要控制因素。根据我们的综述，我们推断，如果海洋氧化作用确实引发了早期动物的兴起，那么它一定是通过可能由氧化剂可用性增加驱动的陆架氧化作用来实现的。我们的综述呼吁对埃迪卡拉纪 - 寒武纪海洋氧化还原结构及其控制因素进行进一步研究，特别是来自中国南方以外地区的研究，以便更好地理解海洋氧化还原与早期动物之间的共同进化关系。
