Collaborative Research: Ocean Redox Evolution at the Dawn of Animal Life: An Integrated Geological and Geochemical Study of the Ediacaran Yangtze Platform in South China

最近的研究表明，埃迪卡拉纪（约635 ~ 542 Ma）的主要氧化事件触发了地球的第一次出现和演化。但是，由于缺乏关于埃迪卡拉纪海洋时空氧化还原变化以及埃迪卡拉纪生物对这种氧化还原变化的反应的详细文件，对所提出的联系的批判性评估受到限制。对埃迪卡拉纪扬子地台进行地质、地球化学和古生物学综合研究，旨在提高我们对保存罕见的化石沉积档案中海洋氧化还原变化、地球化学异常和早期动物进化之间相互作用的理解。本研究旨在验证以下假设：(1)深海在约551 Ma以前是缺氧/缺氧的；(2)大型海洋溶解有机碳（DOC）储层的幕式氧化导致地球化学异常的形成，包括异常的负碳同位素偏移；(3)埃迪卡拉纪生物时空分布与海洋氧化还原条件耦合。研究的目的是确定：(1)整个盆地的碳酸盐和有机碳同位素变异，以测试潜在的地表到深海的碳同位素梯度，该梯度可能比现代海洋大得多；(2)硫同位素的时空变异，以测试硫酸盐还原和硫歧化在整个盆地的持续和/或波动；(3)钼（Mo）浓度和Mo同位素、铁（Fe）形态和铁同位素的时空变化，以确定与稳定同位素漂移相关的长期氧化还原演化和潜在氧化还原波动；(4)埃迪卡拉纪化石时空赋存特征及其与地球化学边界/异常的关系。研究的最终目标是整合古生物学和地球化学数据，以测试埃迪卡拉纪生物氧化还原条件与时空模式之间的耦合关系。预期的数据将为我们了解与地球历史上重大生物创新有关的环境力量提供重要信息。该项目将部分支持来自内华达大学拉斯维加斯分校、弗吉尼亚理工学院、加州大学河滨分校和亚利桑那州立大学的四名博士生。该项目在四个不同机构的研究人员之间建立了新的合作关系，并为不同研究重点的学生提供了广泛的培训机会。研究成果将与四所院校的课程相结合，并将加强四所院校本科生对研究项目的参与。该项目还将促进与来自中国和加拿大机构的科学家的国际合作。

EAR 0745825COLLABORATIVE RESEARCH: Ocean Redox Evolution at the Dawn of Animal Life: An Integrated Geological and Geochemical Study of the Ediacaran Yangtze Platform in South ChinaABSTRACTRecent studies suggested that major oxidation events during the Ediacaran Period (ca. 635 Ma to 542 Ma) triggered the first appearance and evolution of the Earth?s earliest animal life, but critical evaluation of the proposed linkages is limited by the lack of a detailed documentation on spatial and temporal redox changes of Ediacaran oceans and the responses of Ediacaran organisms to such redox changes. An integrated geological, geochemical, and paleobiological study of the Ediacaran Yangtze platform is aimed at improving our understanding of the interplay between ocean redox changes, geochemical anomalies, and early animal evolution in a rarely preserved, fossiliferous sedimentary archive. The proposed research is designed to test the following hypotheses: (1) the deep ocean was anoxic/euxinic until ca. 551 Ma; (2) episodic oxidation of a large oceanic dissolved organic carbon (DOC) reservoir led to the formation of geochemical anomalies including unusually negative carbon isotope excursions; and (3) the spatial and temporal distribution of Ediacaran organisms was coupled with ocean redox conditions. Objectives of the research are to determine: (1) carbonate and organic carbon isotope variability across the basin to test a potential surface-to-deep ocean carbon isotope gradient that may have been much greater than in the modern ocean; (2) spatial and temporal sulfur isotope variability to test the persistence and/or fluctuation of sulfate reduction and sulfur disproportionation across the basin; (3) spatial and temporal changes of molybdenum (Mo) concentrations and Mo isotopes, iron (Fe) speciation and Fe isotopes to determine the secular redox evolution and potential redox fluctuation associated with stable isotope excursions; and (4) spatial and temporal occurrences of Ediacaran fossils and their relationships with geochemical boundaries/anomalies. The ultimate goal of the research is to integrate paleontological and geochemical data to test the coupling between redox conditions and spatial/temporal patterns of Ediacaran organisms. Anticipated data would provide important information for our understanding of the environmental forces related to a significant biological innovation in Earth history.The project will partially support four PhD students from University of Nevada Las Vegas, Virginia Polytechnic Institute, University of California at Riverside, and Arizona State University. The project develops new collaborations between researchers at four different institutions and provides a broad training opportunity for interactions among students with different research foci. Research results will be integrated with courses taught at four institutions and will enhance undergraduate involvement in the research project at four institutions. The project will also promote international collaborations with scientists from institutions in China and Canada.