The controls of sequence-paleogeography on coal petrology and quality of Yan'an Formation in Majiatan mining area

With Majiatan mining area as the research area, the sequence stratigraphic framework of Yan'an Formation in Majiatan mining area is established by the division and comparison of sequence, and then the sedimentation paleogeographic features of each third-order sequence were reconstructed. With the study on the distribution of coal petrology and quality, it is found that the plane and vertical distribution characteristics of coal petrology and quality are obviously controlled by sequence and palaeogeography. On the plane:the vitrinite content of the coal seam is higher in the delta plain environment in the south of the mining area, and the ash content is decreasing from the north to the south gradually by the control of the source area. Vertically, the composition and ash of the coal are changing in different sequences with the evolution of sedimentary environment. In the same sequence, the influence of different system tracts on the content of coal and rock components is segmented. The most favorable vitrinite formation is in the later stage of transgressive system tract, and the low level system tract is the most unfavorable to the formation of vitrinite.