Coal facies evolution law controlled by sequence stratigraphy of Xishanyao Formation, eastern Junggar coal field

Based on the principle of sequence stratigraphy, the stratigraphic division of Xishanyao Formation in Xiheishan area is studied through the comprehensive analysis of the bore core and well logging data. As a result, such three system tracts as low-stand system tract, lake expanding system tract and high-stand system tract are recognized. Meanwhile, more para-stratigraphic sets are identified in each system tract. Therefore, braided river delta and lake depositional systems of Xishanyao Formation are deciphered into four subfacies and 8 microfacies under the constraint of sequence stratigraphic framework. Besides, coal quality and quantitative statistics of maceral are introduced in this study in order to identify the coal facies as moist forest swamp and dry forest swamp. The coal facies evolution law is controlled by the variation of lake level which was constrained under the framework of sequence stratigraphy in this area. As a main factor, the lake level determines the development of peat swamp, and then the evolution law of coal facies.