Sequence-paleogeography and coal accumulation of the Carboniferous-Permian in the North China Basin.

The authors studied the depositional environments, sequence stratigraphy, paleogeography and coal accumulation of the Carboniferous-Permian paralic coal measures based on data from outcrop and borehole sections. The sequence boundaries were represented by regional disconformity, transgression direction switching surface, the base of incised valley fill sandstone, facies-reversal surface and associated paleosols. According to these sequence boundaries, the coal measures were subdivided into 7 third-order sequences and related systems tracts. For the paleogeography analysis, the contours of a variety of lithofacies parameters were drawn, including strata thickness, thickness ratio of sandstone and mudstone, limestone contents, and coal thickness. Based on these contours, the lithofacies paleogeography maps of each third-order sequence were reconstructed. The comparison of the contours of coal thickness with the distribution of facies units of the lithofacies paleogeography was made, and it revealed that the favorable coal-accumulating environments were deltas, fluvial plain and lagoon-tidal flat. Coal accumulation was strong in SQ2 (middle and upper Taiyuan Formation) and SQ3 (Shanxi Formation) with the coal accumulating centers were distributed in the Zhungeer, Datong, Shuozhou, Wuhai, Fengfeng areas, and the Beijing-Tainjin-Tangshan area. Coal accumulation in SQ4 (Xiashihezi Formation) and SQ5 (first member of the Shangshihezi Formation) was weak and the coal-accumulating centers were distributed in the southern part of the North China Basin, including Huainan and Huaibei coal fields. [ABSTRACT FROM AUTHOR]