【摘要】 新元古代南沱组冰碛层之上的“盖帽”白云岩在全球分布广泛, 碳稳定同位素表现出强烈的负偏移, 其成因被认为与甲烷的碳源有关。通过对湖北三峡庙河地区出露的“盖帽”白云岩的野外地质构造、碳 -氧稳定同位素和重晶石夹层的硫稳定同位素特征的研究, 发现除了明显的碳稳定同位素的负偏移之外, 重晶石的硫同位素值表现出明显的正偏移, 其数值可与现代海底甲烷喷气孔附近的自生重晶石矿物的同位素组成相对比, 进而认为“盖帽”白云岩的成因是末元古代“雪球”事件之后天然气水合物的释放与全球环境突变背景下的沉积产物。该研究成果将有助于对地史时期类似地质背景下古天然气水合物背景的识别和环境效应评价。更多还原

【Abstract】 Cap dolomite, overlying global later Neoproterozoic glacial depositions, occurs worldwide with (signi-)ficant stable carbon isotopic negative excursion caused most likely by the methane. Based on the study of rock textures and structures, and stable isotopes of dolomite and S isotope of barite interlayers within the cap dolomite outcropped in the Miaohe area in the Three Gorges, it is testified that the stable isotopes show a strong negative excursion, and the isotopes of sulfur show a significant positive excursion, which is similar to the reported data of authigenic barites formed in a modern seafloor gas hydrate environment. Therefore, it can be concluded that the cap dolomite was most likely formed in a special environment under which a huge gas hydrate dissociated with the breakup of “Snow Earth” in later Neoproterozoic. All of above analyses would be helpful to identify the proxies of paleo-gas hydrate deposition in some distinctive stratigraphic sections and to evaluate the global environment effect caused by gas hydrate in earth history.更多还原