Origin of Microsparite carbonates and the significance in the evolution of the Earth in Proterozoic
微亮晶（臼齿）碳酸盐成因及其在元古宙地球演化中的意义

The diagenesis and origin of Mierosparite(MT-Molar tooth)carbonates have been analyzed based on macroscopic and microscopic characteristics obtained with a variety of techniques.The study on petrology,mineralogy,geochemistry and organic geochemistry of the MT carbonates demonstrated that the MT carbonates were composed of micrometer-scale,equigranular and hexahedron microspars,and were formed by the early and fast lithificaiton during a rapid drop of atmospheric CO_2 pressure.There were two types of diagenesis which had been involved in formation of the MT carbonates;one took place in the soft mud of the sea floor where the differential compaction formed the ptygmatic fold structures or other complex shaped structures,another was the microsparite core of globules which were directly precipitated from sea water or was carried in by the carbonate gravity.All of above confirmed that MT carbonates were formed by biogeoehemical reaction in shallow sea.The MT carbonates were the most sensitive indicator of the paleo- atmospheric and paleo-oceanic conditions.The abundance of the MT carbonates can be measured and used to model the evolution of CO_2 level in paleo-atmosphere.Four-peak development stages of the MT carbonates were found in the Precambrian,including the Late Archaean Era,last stage of the Early Proterozoic,middle period of the Mesoproterozoic and Neoproterozoic.These four stages were coincident with the four stepping-down events of the CO_2 level in paleo-atmosphere.After these four stages,the CO_2 level dropped down to a lowest level in the Phanernzoic.Moreover,the MT carbonates are of importance for oil-gas resources perspective.