Prof. Nicholas Christie-Blick
Earth Institute Contact: Prof. Nicholas Christie-Blick
We propose to test the hypothesis that widespread methane hydrate destabilization at the end of the late Neoproterozoic Nantuo glaciation (South China) resulted in a global scale release of methane capable of driving the oceans to anoxia and explaining the anomalous isotopic geochemical and physical record of cap carbonates overlying glacial deposits. This hypothesis, which represents an alternative to the popular, yet controversial, snowball Earth hypothesis (Hoffman et al., 1998), finds support in intriguing new carbon isotopic data from the basal Doushantuo cap carbonate. δ 13 C values ranging from +5> to -41> are found exclusively in primary calcite and in association with tepee-like (chimney) structures, sheet cracks, relict barite and framboidal pyrite, and they provide unambiguous evidence for the role of methane in these sediments.
The proposed research will include a combination of geological, organic and stable isotopic geochemical, and modeling approaches in 11 Nantuo glacial to postglacial sections distributed over 300 km across the edge of the Yangtze platform. Objectives are to determine 1) the isotopic and petrographic variability at millimeter to centimeter scale within and away from inferred methane seep facies; 2) the effects on stable isotopic and organic geochemical composition of dolomitization; 3) the origin of calcite within the cap carbonate using compound specific isotopic analysis of the organic fraction and isotopic determination of the sulfide and sulfate fractions; 4) detailed field analysis of inferred seep facies and their regional variation; 5) impacts of methane release on global biogeochemistry by means of numerical modeling; and 6) integration with findings from less well preserved examples from an ongoing study in Death Valley (California), Australia, and Namibia.
Intellectual Merit: The relationships between unusually severe Neoproterozoic glaciation, cap carbonates, associated carbon isotopic excursions, and biological evolution represent a longstanding enigma in Earth science. If new observations in the Yangtze platform of southern China bear out our preliminary data, the methane hydrate hypothesis may offer a way of reducing the environmental extremes that are implied by the snowball Earth hypothesis and that have proven problematic for interpretation of the paleobiological record. The proposed research is pertinent to our general understanding of gas hydrates in the Earth system and may provide one of the best supported examples of the influence methane hydrate destabilization can have on ocean chemistry yet reported. Methane is a greenhouse gas and may play an important role in climate change. The proposed research will be conducted by a multidiciplinary team with proven expertise in Neoproterozoic geology, geochemistry, modeling, and the logistics of working in China.
Broader impacts: The research will be spearheaded by one postdoctoral research scientist at the University of California, Riverside (Jiang), and will involve a second (Ridgwell). The project represents a continuation of several years of collaborative research and publication involving researchers at Columbia University, and new collaboration with Stanford University and University of Missouri. Laboratory work will provide opportunities for both undergraduate and graduate student involvement in the research specifically supporting three women (2 undergraduates, 1 graduate) employed in the UCR stable isotope and X-ray labs. Related studies in the Death Valley region of California are being integrated with courses at UCR including a course titled “Neoproterozoic Events” We anticipate continued collaboration with Chinese colleagues, a mechanism for disseminating both ideas and research approaches outside the U.S.
Cross Cutting Themes:
Hazards and Risk
University of California at Riverside
University of Missouri
National Science Foundation