Sequence Stratigraphic Analysis Of Jiaxian-Wubu Deep Coal-Bearing Strata And Coal Accumulation Law In The Eastern Margin Of Ordos Basin

Based on the multiple borehole logging data,core data and well logging data in Jiaxian-Wubu area,this paper combined with the theoretical guidance of Sequence Stratigraphy,Sedimentology,Coal Field Geology and other disciplines,we established the sequence stratigraphic framework of the deep Carboniferous-Permian coal-bearing rock system in the Jiaxian-Wubu area,and the coal accumulation law in this area was discussed on the basis of the sequence stratigraphic framework,the factors affecting coal accumulation in different periods were also summarized.According to the color of sedimentary rocks,sedimentary texture and logging facies marks,5 sedimentary facies(including rivers,deltas,lakes,coastal and shallow seas),7 subfacies and 14 microfacies were identified in the Carboniferous-Permian strata of Jiaxian-Wubu area,and the characteristics of the sedimentary facies of the Benxi Formation,Taiyuan Formation,Shanxi Formation,Shihezi Formation and Shiqianfeng Formation were also discussed respectively.The Carboniferous-Permian system in Jiaxian-Wuu area was divided into 21 sequence groups and 6 composite sequences based on borehole cores and well logging data,and the sequence stratigraphic framework of the area was established.Among them:Sequence 1 was equivalent to the Benxi Formation in the study area;Sequence 2 and Sequence 3 ware equivalent to the Taiyuan Formation in the study area;Sequence 4,Sequence 5 and Sequence 6 ware equivalent to the Shanxi Formation;Sequence 7 to Sequence 15 ware equivalent The Shihezi Formation in the study area;sequence 16 to sequence 21 ware equivalent to the Shiqianfeng Formation in the study area.Based on the sequence stratigraphic framework,according to the factors influencing coal accumulation including paleo-structure,paleo-environment,paleo-plants and paleo-climate,the law of coal accumulation in different sequence groups was analyzed and considered:The thick coal seams in the Jiaxian-Wubu area are mainly distributed in the middle and lower part of the transgressive(water ingress)sequence group.After the sea retreat(lake retreat),a wide range of coastal platforms,shallow water delta fronts and cement-coated marshes in the delta plain ware formed.The environment and the diversion bay ware the main coal-gathering environments.Some discontinuous thin coal seams would be distributed in the middle and upper parts of the high-level sequence group,and no coal seams would be developed in the low-level sequence group.As a result of the combined action of paleogeography and other factors,paleostructure is the main factor.Among them,the rapid drying and heat of the paleoclimate was the main reason for the failure of coal accumulation in the research area during the Shihezi and Shiqianfeng periods.