Characteristics and evolution of sedimentary facies types of coal measures in Huainan coalfield——A case study of well 1001 in Xinji coal mine

Based on the core observation and sample collection of Carboniferous-Permian Taiyuan Formation, Permian Shanxi Formation and Xiashihezi Formation of well 1001 in Huainan coalfield, we carried out microscopic identification, particle size analysis and X-ray diffraction analysis of mineral composition. Based on the results of previous studies and microfacies analysis, we explored the characteristics and evolution of sedimentary facies types of coal-bearing rock series in Huainan coalfield. The results show:during early stage of Late Carboniferous, transgression and regression happened frequently, Taiyuan Formation in the study area developed, barrier coast and tidal flat depositional system, mud flat, mixed flat and limited subtidal flat microfacies coexisted, three large-scale transgressions occurred in general, which represented the filling stage of epeiric sea. During Early Permian the sea level dropped, in the study area, delta front depositional system, distal bar, mouth bar, distributary channel underwater, underwater natural levee and diversion bay microfacies symbiosis developed in Shanxi Formation, the delta continued construction under the destruction. In late stage of Early Permian, in Xiashihezi Formation delta plain depositional system developed, distributary channel, natural levee, peat swamps and swales microfacies coexisted. The study area entered into the continental delta depositional phase.