Base Level Cycle and Coal-Accumulation of Lower Member of Shanxi Formation of Permian in Northeast Part Ordos Basin

Coal accumulation of Lower Member of Shanxi Formation in Northwest part of Ordos basin has been researched according to the principle of base level cycle based on outcrops, core description, and well log. Sedimentary face analysis, base level correlation, condense data controlling mapping were adopted. Coal forming has a close relation to base level cycle, face distribution, and coal-forming latter stage of short-term base level ascending cycle. Coal measure distribution has a complementary relationship with distributary channel. In peat swamp far from distributary channel, coal layer has greater thickness, with lower ash content, and lack of waste rock interlayer. Near the distributary channel, coal layer is thinner and sparsely-distributed, with high ash content, and transition to clastic rock. From shan23 to shan21, thick coal layer has a trend of retreat towards north, showing that the lower member of Shanxi Formation constitutes mid-term base level ascending cycle.