Sequence stratigraphic analysis and characteristics of Late Paleozoic coal accumulation in Dengfeng, Henan Province

Abstract：Principles and methods of sequence stratigraphy for outcrops and drilling cores were used to reconstruct the Upper Paleozoic sequence stratigraphic framework in Dengcao profile. Extensive investigation into outcrop and borehole data reveals that a total of 8 third-order sequence boundaries and 7 third-order sequences are developed in the Upper Paleozoic strata in the Henan part of southern North China Basin. S1 is equivalent to the Benxi Formation, S2 to the Taiyuan Formation, S3 to the Shanxi Formation; S4 and S5 to the Xiashihezi Formation, S6 to the Shanshihezi Formation, and S7 to the Shiqianfeng Formation. Within these sequences, the lowstand systems tracts are represented by conglomerates and sandstones of the delta plain distributary channel and lakeshore and the weathered crust of eluvial facies. The transgressive systems tracts are dominated by coastal-shallow lacustrine mudstones and siltstones and barrier island-salt lagoon and delta front, and the highstand systems tracts are mainly composed of carbonate rocks and mudstone-abundant successions. Coal accumulation of sequence 1～sequence 2 occurred mainly in the early transgressive or regressive period with poor sources, whereas coal accumulation of sequence 3～sequence 6 occurred mainly in the largest pan-sea with rich sources.