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

摘要地质记录研究表明，天然气水合物不稳定释放的阶段性甲烷可能是气候变化和海洋化学的一个重要因素。由于甲烷水合物存在于微妙的压力-温度平衡中，并构成地球表面最大的可交换碳库，海洋温度或海平面的细微变化可能导致失控的不稳定，对生物圈造成严重后果。这些事件最有可能发生在全球范围迅速变暖和/或海平面变化的时期。由于新元古代冰期（约850 Ma至600 Ma）的寒冷气候，这些事件的后果可以说是地球历史上研究这一现象的最佳时间间隔之一。这些事件的证据包括存在神秘的覆盖碳酸盐矿床，覆盖几乎所有新元古代的冰川和类似的nagmitude和持续时间的一个强大的碳同位素异常，预计这样一个全球性的甲烷释放events.The最令人信服的批评，这种甲烷水合物不稳定的假设是明显缺乏极端的碳同位素变化，在碳酸盐盖推断当地与甲烷渗漏。在现代渗漏和至少一些古代渗漏中沉淀的碳酸盐通常与13 C值相关，范围小于-25%。在现代和古代渗漏中常见的其他观察结果包括硫同位素异常和甲烷消耗微生物的生物标志物证据。来自中国南部新元古界帽碳酸盐岩地层（陡山沱组）的初步数据表明，这些缺失的证据线的元素确实存在于局部保存异常完好的渗漏样相的例子中。通过对中国帽碳酸盐岩的详细研究，为了解古渗漏过程提供了一个窗口。拟议的研究的更广泛的目标是测试的命题，这些渗漏是代表渗漏一样的织物在更多的成岩作用改变帽碳酸盐全球，和taht帽碳酸盐和冰后期碳同位素漂移提供了一个记录的灾难性的全球甲烷释放与全球变暖后新元古代雪球地球冰河时代。

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.