地质历史时期天然气水合物分解释放的地质地球化学证据

Geological and Geochemical Evidence for Massive Dissociation of Gas Hydrate in the Geological History

巨量天然气水合物广泛赋存于大陆坡海底和高纬度永久冻土带沉积物中,是重要的环境影响因素。有些地质历史时期发生的重大地质灾变可能是由天然气水合物分解释放甲烷引起的。持续时间短暂且显著的全球性海相和陆相碳同位素的负漂移、甲烷起源的极负碳酸盐岩碳同位素值(特别是1δ3C<-40‰)、碳酸盐岩溶解、指示甲烷浓度异常的生物标志化合物、生物成因重晶石富集、类似冷泉碳酸盐岩发育的特殊沉积组构、海底垮塌及碳酸盐结晶扇(如文石)等是支持天然气水合物分解"假说"的主要证据。但这些证据还存在一定的局限性,该"假说"仍然存在较大的争论,因此需要进一步深入研究。

Gas hydrates as an important agent for climate change occur worldwide on the continental slopes and in permafrost regions.Based upon the study of the geology and geochemistry of the great geologic transitions,the dissociation of gas hydrates has been considered to probably result in global catastrophic events in the geological history.This idea is supported by global and relatively short-lived negative carbon isotope excursions,methane-derived carbon isotope values（especially δ13C-40‰） in carbonate sediments,carbonate dissolution,the biomarkers indicative of methane release,high accumulation rates of biogenic barite,an unusual suite of sedimentary structures and textures similar to those of cold seep carbonates,submarine sediment failures and crystal fans（e.g.aragonite）.However,the＂hypothesis＂remains controversial and the proposed evidence has their limitations;therefore,we need further research.