Sedimentary Facies Of The Coal Measures In Northeastern Margin Of Ordos Basin And Coal Accumulation Mechanism

As the second largest sedimentary basin in China,Ordos Basin is a multicycle inner craton basin which is buried steadily and writhed heavily.Under the analysis of geological materials of east blank of Ordos Basin,observation of outcrops,thin section analysis and single well and well tie sedimentary facies analysis,Shanxi and Taiyuan formation strata and palaeoenvironment in Ordos Basin were analyzed.Alluvial,braided river,delta and meare deposit were founded in Shanxi formation in the eastern part of the basin.Braided river,swamp,and distributary channel of delta plain were considered as ideal coal formatting environment.Delta plain deposit is consisted by distributary channel,natural levee,crevasse splay and flood basin sediments.Swamp and peat swamp were widely distributed between river channels and domain most area of flood plain.Distributary channel and peat swamp are the most important coal formatting environments.Under the research of basic materials and well tie cut plane,the development of coal was analyzed.There are two coal beds in Shanxi formation,they distributes widely,but lack of continuity.There are three to four coal beds in Taiyuan formation,and two thick ones.It distributes widely and has a good continuity.On the base of single well and well tie sedimentary facies,coal formatting environment map were drawn and analyzed.Low-lying land in alluvial sediment,distributary channel in delta plain and peat swamp are favorable coal formatting environments.Based on the sedimentary facies research of Shanxi and Taiyuan formation in eastern part of the basin,characteristics of coal accumulation in these areas were concluded.Shanxi formation in eastern blank transformed from alluvial to braided river deposit from the north to south,and 'then transformed into braided delta in Jixian area where two sediments source meet.Low-lying land between alluvial and distributary channel or swamp in braided river deposits in the northern area is considered as favorable coal formatting environment.The primary sediment facies of Taiyuan formation is delta plain.Distributary channel is considered as a favorable coal formatting environment in that area.The controlling factors of coal accumulation,palaeostructure,palaeographic and palaeoclimate were also analyzed in this paper.