Framework of Sequence Stratigraphy Sedimentary System and Evolution of Yimin Formation in Yimin Depression

Well data, cores, logging, connecting with the characteristic of structure evolution are used to establish the sequence stratigraphic framework of the coal-bearing formation of Yimin Depression in Early Cretaceous. The coal-bearing formation can be divided into two three-order sequences and Yimin Formation, as one of the three-order sequences,is the most important object of study. Through cores description, research of Spontaneous Potential and Resistivity curve shape and analysis of sedimentary Cumulative Probability Size Curve, four facies including fan delta, braid river delta, sublacustrine fan and lake,and some subfacies are identified in Yimin Formation in the sequence stratigraphic framework. Coal-rich belts develop in the southwest delta plain and northwest interdeltaic bay in Yimin Depression. According to the characteristic of the development of coal and sedimentary system, two kinds of coal accumulation models, shallow lake and flood plain in delta front and interdelta, are concluded in Yimin Depression.