The Study On Sedimentary Microfacies Sequence And Genesis Of Microsparite Carboantes In Da Long Kou Formation Of Proterozoic, Middle Of Yunnan District

The thesis is part results of the Natural Sciences Foundation project of“The Great Geological Event of Worldwide change in Proterozoic: The Formation and Disappearance of Molar-tooth Carbonates”(40572073).The sedimentary geology of astronomy cycle theory proposed by MengXianghua and sequence stratigraphy are regarded as the main guidance. Through measuring the geological section of Dalongkou formation in meter-cycle method detailly by other members in Institute of Sedimentary Basin, associating with sedimentary microfacies analysis, different types of meter cycle and the superimposed of meter cycle, combining Fischer plot, the cyclic sequences of Dalongkou formation(the fourth section) in Luoshuidong section are divided into 20 third-grade sequences, which are merged into three second-grade hypercyclothem. And the cyclic sequences of Dalongkou formation(the fourth section) in Tadian section are divided into 8 third-grade sequences, the author did the comparision between the two different areas. At the early stage of hypercyclothem, it developed relative deep-water molar-tooth carbonates, during the late period, it appeared shallow-water algal pellet limestone, calcarenite(shoal environment), oolite limestone, on the top of the hypercyclothem, stromatolite limestone occur.The author did the sedimentary microfacies analysis using thin slice and associate with scanning electron microscope, X-ray microanalysis and other method .The thesis did some study on the petrology and sequence stratigraphy and microsparite carbonates(Molar-tooth structure) in the fourth segment of Dalongkou formation. By calculating the abundance of MT and the result of sequence analysis, it demonstrated that the molar-tooth carbonates produced in the process of transgression(TST) and early stage of HST with relative deep water.In the region of interest, it developed marine carbonates in the strata of Middle Proterozoic Era. The main rock type is limestone.By comparing stromatolite limestone and molar-tooth carbonates, it showed that they are the two different types of carbonates, which are affected by two kinds of ecosystem microbe. The stromatolite limestone is formed by Chlorophyta, which binds carbonate grain. The stromatolite limestone often occur in the sedimentary environment from upper part of subtidal zone to intertidal zone. From shallow to deep shallow sea, it can develop laminate, ripple, stylolite, coniform stromatolite. Whereas, the molar-tooth carbonates are the production of early diagenesis stage, the result of rapid crystallization. It consisted of microsparry calcite(the primary mineral is vaterite), with the diameter of 5-15μm. It has multifold shape, such as tadpole, banded, aggregate, filiform and so on. Different forms of MT creat in different depth of sea. Most appeared in shallow–deep slope of subtidal. Both of these two structures were likely to be affected by two different kinds of microbial colony.There are abundant organic material and pyrite in MT of Dalongkou formation, and the MT developing layers are the enclosing stratum of the major iron mine of Yunnan, which indicates that it was anaerobic environment when the MT developed. Molar tooth carbonates might be the particular sedimentary structure that arised by microbe-chemical interaction, and the microsparite carbonates probably have good hydrocarbon prospect.