Analysis On Sedimentary Environment Of Middle Proterozoic Bingmagou Formation In Yichuan Of West Henan

North China Craton is one of the early formation of the global continental crust.Its formation and evolution has been a hot issue of research in the field of earth science, among which breakup and conjuction of Precambrian global plate is the key problem in the study. As the only strata record between the two events of volcanic eruption in Xionger Group and coastal sedimentation in Jixian System, research on Proterozoic Bingmagou Formation has important significance. For the Formations of Proterozoic Jixian System, predecessors have used a variety of methods to study their sedimentary evolution, sequence stratigraphy, hydrocarbon generation characteristics,origin and induced structure of microorganism. But research on Bingmaggou Formation is still relatively few. With the theory of sedimentology, stratigraphy and sediment granularity characteristic analysis, the sedimentary environments and geotectonic background of Bingmagou Formation in Yichuan area are studied in this paper. And the results are as follows:(1) The Bingmagou Formation in Yichuan area is about 670 m thick. According its lithology, it can be divided into two Sections: Lower and Upper Section. The Lower Section is about 120 m thick and consists of conglomerate, conglomeratic sandstone, coarse sandstone and other coarse clastic rock composition. Its sedimentary environment is suggested to be mud avalanche in a fan delta plain. The Upper Section is made up by a big regular rythem from coarse sedements such as fine conglomerate to fine siltstone, mudstone and such fine sediments. Probability value accumulation curves of the Upper Section change from "simple one suspended stage type " to "one suspended stage type," and then to "two or three-steps type". Besides, the C-M diagram of the Upper Section also reflects a turbidite deposit model. These all prove that the Upper Section reflects a frequent transition from debris flow to underwater distributary channel, underwater distributary interchannel and mouth bar deposits, it’s a fan delta front subfacies. The profile as a whole represents a big cycle from fan delta plain to fan delta front, and that the whole sedimentary environment is a offshore delta.(2) The craton of North China had been in extensional regime since the beginning of Xionger Group. The trigeminal rift system of Xionger Group was formed gradually in South of North China craton, which consists of Yushan rift trough parallel to the continental margin and Lvliang rift trough perpendicular to the continental margin. Fan delta sedimentation of Bingmagou Formation was formed because of some advantageous factors, such as the marginal position of the rift, large height difference, steep slope, near source and heavily tectonic activity. Its abouchement to massive transgression from south to north happened subsequently,and sedimentation of marine facies strata was formed on the top.