埃迪卡拉纪–寒武纪早中期整体海洋氧化还原状态连续演化重建

From late Ediacaran to early Cambrian, metazoan occurred for the first time in the Earth history, and quickly diversified and radiated, forming the Cambrian Explosion. Studies have indicated that oxygen concentration in the ocean increased pronouncedly. However, most redox proxies so far used can only reflect redox state of local marine environment. Because redox states of different areas in the ocean were probably different, and only part sediments of some certain areas in the ocean could be preserved as geological strata, data derived from local redox proxies recorded in marine strata of a period in different local areas often gave out different or even contradictory results. In other words, data of local redox proxies could not reflect global or holistic ocean redox state, and sometimes even would result in risks of taking a part for the whole. Although Mo isotope composition of sediments deposited under highly sulfide seawater can record open ocean composition and thus reflect oceanic redox state, sediments deposited under such condition were rare in the geological strata, and thus it is also difficult to obtain continuous evolution of global ocean redox state. Consequently, the evolution of oceanic redox state from the Ediacaran to Cambrian early-middle time is still not clear yet. This project plans to study/analyze U-isotope compositions of primary carbonates of the above stated period deposited under local oxic marine environment and not altered by diageneses, which is a newly developing redox proxy and can reflect redox state of the global ocean, and to combine with analysis of Mo-isotope compositions of black shales and carbonate deposited under local sulfide conditions, for the purpose to reconstruct the continuous evolution of redox state the holistic ocean in the period of Ediacaran to Cambrian early-middle time, and to provide clue for exploring the coevolution relationship between the Cambrian bioexplosion and the environment.

埃迪卡拉纪晚期–寒武纪早期，后生动物门类首次出现，并在相对很短的时期内分化和辐射，即寒武纪大爆发。对晚新元古代研究表明海洋氧化程度发生了显著升高，但多数氧化还原地球化学指标仅能指示海洋局部环境，而海洋不同部位的氧化还原状态是不同的，加之海洋地层的保存不均衡，故从不同地区地层剖面获得的局部环境指标结果往往是有差异的、甚至是矛盾的，因此用局部指标难以反映整体海洋氧化还原状态，甚至存在以偏概全危险；能够记录整体海洋氧化还原状态的Mo同位素的地层在时间上分布稀少，也不能获得海洋氧化还原状态连续演化。因此对该时期海洋氧化时间和过程仍不清楚。本申请拟采用新近发展的能指示整体海洋氧化还原状态的新指标（海洋氧化环境沉积的未发生成岩改变的碳酸盐岩U同位素），结合剖面中硫化黑色页岩和碳酸盐岩Mo同位素，重建埃迪卡拉纪–寒武纪早中期海洋氧化还原状态连续演化史，为探索寒武纪大爆发时期生物与环境共演化提供线索。

本项目研究恢复获得了埃迪卡拉纪晚期至寒武纪第三期海洋的U同位素，重建了该时期全球整体海洋氧化还原状态的演变，并通过分析测试和统计多种氧化还原指标获得了更长时间区间海洋氧化还原状态演变数据，揭示晚埃迪卡拉纪至早寒武纪全球海洋尤其浅海存在一个氧化过程，但氧化水平仍低于现代水平，并且存在多次波动。探讨了海洋氧化还原环境演变与寒武纪生命大爆发之间的关系，提出该时期海洋氧化过程及其波动对生物创新和多样化具有促进作用。发表标注本项目资助的SCI论文共7篇（其中包括NI 3篇），共已得到118次引用。