Sedimentary Environment And Coal Formation Model Of The Late Paleozoic In The Northeast Of Qinshui Basin

The early Late Paleozoic development of terrigenous clastic-carbonate deposits in the central part of the North China Craton,and the Taiyuan and Shanxi formations as their early deposits,are important for exploring the evolution of the depositional environment of the southern margin of the North China Craton in the early Late Paleozoic.On the basis of field treks and with the help of borehole cores and logs,the depositional environment and coal-formation patterns of the Late Paleozoic coal-bearing rock systems in the Qinshui Basin were studied.The main coal-bearing formations in the study area are Taiyuan Formation and Shanxi Formation.The Taiyuan Formation mainly develops coarse-grained sandstone,medium-grained sandstone,fine-grained sandstone,siltstone,limestone,sandy mudstone,mudstone and coal seams;the Shanxi Formation mainly develops medium-grained sandstone,fine-grained sandstone,siltstone,sandy mudstone,mudstone and thin coal seams.Two sedimentary phases,such as barrier wall-offshore shelf and delta,were identified and further divided into six subphases,such as lagoon,barrier wall island,tidal ping,offshore shelf,divergent interbay and divergent river channel,among which tidal ping and the transition zone between barrier wall coast and delta plain are the most favorable environment for coal accumulation.The paleogeographic analysis shows that the dominant paleogeographic unit of the Taiyuan Group is the lagoonal-tidal ping,while the dominant paleogeographic unit of the Shanxi Group is the deltaic plain.The material sources in the study area mainly come from the paleolift highlands in the eastern part of the Qinshui Basin,and the sea intrusion comes from the northwest and southwest of the basin.The coal-forming mode of the Taiyuan Group is mainly the land surface seashore coal-forming mode,while the Shanxi Group is mainly the shallow-water deltaic coal-forming mode.