Coal-accumulation of lower member of Shanxi Formation in northeastern Ordos Basin

The coal accumulation of lower member of Shanxi Formation,northeastern Ordos Basin has been researched according to principle of base level cycle on basis of analysis of outcrops, core description, and well log, and sedimentary facies analysis, base level correlations condenses data controlling mapping were adopted. Coal forming has a dose relation to base level cycle and facies distribution,coal formed latter stage of short-term base level ascending cycle. Coal measttres distribution has a complementary relationship with distributary channel. In peat swamp far from distributary channel,coal layer has great thickness,with lower ash content,and lack of waste rock interlayer. Near the distributary channel,coal layer divarieation and pinch-out with high ash content, and transition to elastic rock. From Shah23 to Shan21,thick coal layer has a trend of retreat towards north,reflect that lower member of Shanxi Formation constituted mid-term base level ascending cycle.