Study on Depositional Model of Permo-Carboniferous Coal-bearing Strata in West Section of Northern Qilian Mountains

In order to reveal the depositional mode and coal accumulation law of Permo- Carboniferous coal- bearing strata in western part of the Northern Qilian M ountains, based on outcrop section, borehole cores, logging analysis and comprehensive mapping method, fluvial facies was recognized in the sandy conglomerate me mber of the Taiyuan Formation, and four types of facies including lagoon facies, tidal flat facies, carbonate platform and swamp facies were recognized in the Yanghugo n Formation and the coal- bearing member of the Taiyuan Formation. The sedimentary environments had experienced four stages, including terrigenous clastic system, peat swamp system, carbonate system and revival of terrigenous clastic system. The results showed that the lagoon- tidal flat coal- forming mode was proposed for the coal accumulation in the study area. The thick coal seam was mainly formed in the lagoon peat swamp, while the coal seam formed in the tidal flat coal- forming environ ment was thinner. The coal- accumulation center of the primary mineable coal groups of M5, M6 and M3, M4 which were formed in the coal- bearing member of Taiyuan Formation were mainly distributed in the area of the eastern Rixu- Qing Yang Gou- ALike belt and the western Wulingou- Yemaquantan belt.