Recent 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.