Collaborative Research: Testing the Methane Hydrate Hypothesis for the Aftermath of Severe Neoproterzoic Ice Ages

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AbstractStudies of the geologic record suggest that episodic methane release from destabilization of gas hydrates may act as an important factor in climate change and marine chemistry. Because methane hydrates exist in delicate pressure-temperature equilibrium, and constitute the largest pool of exchangeable carbon at the Earth's surface, the possibility exists that subtle changes in ocean temperature or sea level could result in a runaway destabilization with dramatic consequences for the biosphere. These events are mostt likely during times of rapid global-scale warming and/or sealevel change. By virtue of the extent of cold climate during Neoproterozoic ice ages (from ~850 Ma to 600 Ma), the aftermath of such events is arguably amongst the best intervals in Earth history for investigating this phenomenon. Evidence for such events includes the presence of enigmatic capping carbonate deposits that overlie almost all Neoproterozoic glaciogenic and a strong carbon isotopic anomaly of similar nagmitude and duration to that anticipated for such a global methane-release event.The most compelling criticism of this methane hydrate destabilization hypothesis is the apparent lack of extreme carbon isotopic variation in cap carbonates inferred locally to be associated with methane seeps. Carbonate precipitated in modern seeps and in at least some ancient ones is typically associated with 13C values ranging from less than -25%. Other observations that are common in modern and ancient seeps include sulfur isotopic anomalies, and biomarker evidence for methane-consuming microbes. Preliminary data from a Neoporterozoic cap carbonate formation in southern China (the Doushantuo Formation) indicate that elements of these missing lines of evidence are, indeed, present locally in an exceptionally well preserved example of seep-like facies. This study will provide a window into ancient seep-related processes by studying the Chinese cap carbonates in detail. The broader objective of the proposed research is to test the proposition that these seeps are representative of seep like fabrics in more diagentically altered cap carbonates globally, and taht cap carbonates and post glacial carbon isotopic excursions provide a record of catastrophic global methane release coincident with global warming following Neoproterozoic snowball Earth ice ages.