New understanding of coal seam distribution law: Coal accumulation model controlled by paleoclimate evolution

It is very important for coal and coal-measure gas exploration to correctly understand the distribution law of coal seam and its main control factors in different coal accumulation models. Based on the review of the theories and models of paleogeographic coal control, coal accumulation in sequence stratigraphy, allochthonous coal accumulation and multiple coal accumulation theoretical system, a new coal accumulation model under the control of climatic revolution was proposed through the analyses of the Jurassic coal-bearing strata in the southern margin of Junggar Basin. The paleotemperature and paleohumidity during Badaowan Formation(coal accumulation period), Sangonghe Formation, Xishanyao Formation (coal accumulation period) and Toutunhe Formation in southern Junggar Basin show the low-high-low-high and the large-small-large-small variations, respectively, which are favorable horizons for analyzing the accumulation law of coal seam under the influence of paleoclimate evolution. According to the statistical analyses of the parameters, including the number and thickness variation of coal seams, and the distance from the first, last and thickest coal seams to the top and bottom interfaces of coal measures, it is considered that the paleoclimate change has an important control on the spatial distribution of regional coal seams. During the process from the warm and humid climate to the dry and hot climate, the number of coal seam layers decreases gradually, and the thickness of a single coal seam increases first and then decreases until it disappears. The coal accumulation intensity can be generally divided into four stages: medium, strong, medium and weak. The middle and lower parts of coal-bearing stratum comprise multiple thick coal seams, which are important horizon for coal exploration. For Badaowan Formation or Xishanyao Formation, coal seams were formed rapidly in the early stage of coal accumulation and disappeared slowly in the late stage, which should be closely related to the longer conversion time from wet air to dry air and the shorter conversion time from dry climate to wet climate with the continuous rise of temperature. uous rise of temperature.