Geological Features Of Original Carbonate Veins In Chuanlinggou Formation And Their Paleo-oceanic Implications

The Chuanlinggou Formation is characterized by gray-black sandstone in North China Platform.The nearly vertical carbonate veins that were rich for pyrites developed in the black shale layers were formed by anaerobic oxidation of methane (AOM) which was driven by ANME and SRB at early-synsedimentary diagenetic stage.Lots of framboidal pyrites and organic-rich muddy sediments showed the Chuanlinggou Formation was formed in the anoxic environment. The methane was produced by anaerobic microbial activity in the anoxic sediment and decomposition of organic matter under anoxic conditions.The bubble structures developed on carbonate in the Chuanlinggou Formation indicated that they were the petrochemical Community of ANME and SRB. The nearly vertical carbonate veins and authigenic pyrites developed in the black shale layers indicated that they may be related to the role of the AOM. The vales ofδ13C in the carbonates are significantly heavier than that of AOM related authigenic carbon- ate in Modern and Phanerozoic , but they are significantly lighter than that of most of the Proterozoic carbonate (+2‰~-2‰). The dots of Campbell model to 11 C、O isotope totally fell in the early diagenesis. It indicates that the form factor of carbonate is the anaerobic digestion of buried organic matter in the early diagenetic stage. To some extent, it may still reflect the important information in chemical conditions of the original sedimentary environment, although we can not exclude the superimposition of the late geological. If there was a huge DIC capacity in Mesoproterozoic ocean and it could form the buffer to stable carbon isotope fluctuations in the global. the lighter carbon isotope values in the Chuanlinggou Formation may reflected the short-term fluctuation caused by the increase of methane.There was special condition of the marine geochemistry in Mesoproterozoic(part- ial oxidation of the surface, hypoxia and sulfated of the bottom). This permanent hierarchical status provided the important environment for the growth of ANME and SRB, and the bury of organic matter in the Chuanlinggou Formation. The low concentration of sulfate and the methane emission activity effectively limited the depth of sulfate-methane transition zone (SMTZ) and the rate of AOM. So only a part of the methane could be consumed and formed minor carbonate veins. On these conditions, most of the methane may go into the atmosphere and become an important greenhouse gas, resulting in a long warm climate conditions in Mesoproter- ozoic.