Sedimentary environments and coal accumulation aw of middle Jurassic in Duosuogongma Mining Area of Qinghai

Based on close relationship existed between sedimentary environment and coal accumulation of coal-bearing strata in Duosuogongma Mining Area,in or der to have coal accumulation law in the region,in combination with the data of the field outcrop section and borehole core section,the theory and method of sedimentol ogy and coal geology were applied to analyze the lithofacies,depositional environments,and coal distribution of the Jurassic coal-bearing strata.The results showed that the coal-bearing strata were mainly deposited in the braided river, braided river delta and lake environments,and the thick coal seams were formed in the braided river d elta environment.Coal accumulation were controlled by palaeo-tectonics and sedimentary environments.The Indochina Orogeny controlled the evolution of the basemen t of the Jurassic sedimentary basin,and the Yanshanian Orogeny controlled the development of the coal-forming basins.The braid river delta environments were develop ed during this stage, which favored the accumulation of two thick coal seams in the middle Jurassic Muli Formation. The coal-rich belt was distributed along the NW- SE direction,where the coal accumulating center was located in the southeastern part,around the Borehole ZK0-3 and ZK 11-3.