Coal-accumulating environments and characteristics of inland coal measures: a case study of Jurassic coal-bearing area in Qilian Mountains and north Caidamu basin in Qinghai

By the detailed study of Jurassic depositional systems in coal-bearing area in Qilian Mountains and the north Caidam basin in Qinghai Province, the paper systematically summed up the main coal-accumulating environments of continental strata. The coal-accumulating environments of alluvial fan, meandering river, braided river, fan delta, meandering delta, braided delta and coastal lake had been mainly developed. The most favorable coal-accumulating environments in continental strata were systems of meandering river, meandering delta and coastal lake. The main features were as follows: the swamp behind bank in meandering river was important coal-accumulating environment, coal seams were presented as strip on plane, accumulated thickly vertically, extended far distance horizontally. The peat swamp developed in low-lying land between split streams of meandering river’s delta plain had good tapability, wide distribution along lake shoreline. In coastal lake coal-accumulating environments lakeshore line stretched far distance, on the plane coal was distributed as strip, vertically several sets of carbonaceous mudstone and coal seam were interbeded because of multi-cycle of the lake level changes at the same time. The research results provided the basis for accurate forecasts of the coal measures and the law of occurrence of coal and rocks.