Analysison Paleographical Evolution of Carboniferous-Permian Lithofacies in Xishan Coalfield, Shanxi Province

The sedimentary environment of the Carboniferous-Permian coal-bearing strata in Xi shan coalfield is analyzed by means of drill cores logging data. Three main types of sedimentary systems and several types of sedimentary sub-environments and micro-environment are identified. The sedimentary system of the carbonate platform-lagoon-tidal flat were mainly developed in Benxi Formation in Late Carboniferous, while the sedimentary system of the carbonate platform-barrier island-lagoon-tidal flat in Taiyuan Formation mainly in Late Carboniferous-Early Permian. In the sedimentary period of Shanxi Formation in Early Permian, a regional regression occurred in Xishan coalfield, and a sedimentary system characterized by shallow water delta began to develop. The regional sedimentary environment changed from the epicontinental sea in the early stage, the sea-land interaction in the middle stage to the river-controlled delta in the late stage. Coal accumulation occurred in the deposition period of both Taiyuan Formation and Shanxi Formation. Lagoon, tidal flat and delta plain were the most favorable places of coal accumulation. Coal seams of Taiyuan Formation were produced in the lagoon-tidal flat, the thicker the sandstone, the thicker the coal seams, while coal seams of Shanxi Formation were produced in the delta plain, the thicker the mudstone, the thicker the coal seams.