Abstract:

Cap dolomite, overlying global later Neoproterozoic glacial depositions, occurs worldwide with significant 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.

Key words: dolomite, stable isotopes of C and S, mechanism discussion, the Three Gorges