Study on Sequence Stratigraphy of Jurassic Coal-bearing Measures in Hangya Area of North Qaidam Basin

In order to unveil the accumulation law of coal in Hangya area of Qaidam basin,By using borehole data,the paper studied its sedimentary facies,sequence stratigraphy and coal accumulation characteristics.A total of 5 rock types and 17 lithofacies types ware identified.Fluvial,delta and lacustrine depositional systems and related facies were recognized.Three sequence boundaries were identified based on the development of regional unconformity and the base of incised valley fill sandstones.The coal measures were subdivided into 2 third-order composite sequences,corresponding lower and upper members of the Shimengou Formation.The results showed that the interdistributary bay of the lower delta plain,and the back swamp of the fluvial-upper delta plain were the main environments for coal accumulation in Hangya area.In the basin margin,which was dominated by a fluvial-delta plain setting,the thick coal(G2) was developed around the maximum flooding surface,while the moderately thick coal(G3) was developed in the middle of the transgressive systems tract.In the basinal area,which was dominated by a lacustrine setting,the thinner coal(G1) was developed near the transgressive surface.