Study On Sequence Stratigraphy Of Upper Paleozoic Coal-bearing Formation In The Southeastern Part Of Ordos Basin

The paper is based on the sequence stratigraphy,the high resolution sequence stratigraphy,sedimentology and coalfield geology theory as the instruction.The research objects of the paper are in Benxi formation,Taiyuan formation and Shanxi formation of Upper Paleozoic coal-bearing formation in the southeastern part of Ordos Basin The study is on the sedimentary system,sequence stratigraphy and coal accumulation law.Six sequence boundaries are identified in the research area of Upper Paleozoic coal-bearing strata,and the Shanxi group,Taiyuan group and Benxi group are divided into six medium-term base-level cycles,which are named as the Bener sequence,Benyi sequence,Taiyi sequence,Shansan sequence,Shaner sequence and Shanyi sequence from bottom to up.The sequence stratigraphic framework of the research area is established.Five types of sedimentary systems are identified in the research area of Upper Paleozoic coal-bearing strata,which are braided river delta,meandering river delta,lake,barrier coast and the continental shelf.The Shansan sequence of the focused sections mainly develops three sedimentary systems of braided river delta,meandering river delta and lake,in which flood plain deposits develops widely.The Shansan sequence of the focused sections mainly develops barrier coast sedimentary system,in which peat develops widely.Analysis of plane distribution of Upper Paleozoic coal measure strata in the main coal seam of the NO.3 and No.11 is conducted,three coal centres of the No.3 coal seam are defined as the Resi Wan-Fengjia Ping area,Yaodian-Fengzhuang region and the majority large area of the southeastern Yanchang County and three coal centres of the No.11 coal seam are defined as the Anding-Pingqiao area,Ansai-Yanan and large area of the Y anchuan-Yanan-Y ichuan.The coal seam correlation of the main coal NO.3 and No.11 is conducted under the sequence stratigraphic framework in Upper Paleozoic coal-bearing strata according to the high resolution sequence stratigraphy and sedimentology theory.The features of spatial distribution,development law and distribution pattern under the sequence stratigraphic frame of the coal seam are summarized,and it is pointed out that the thick coal seam generally forms near the maximum flooding surfaces in the river delta environment and the the thick coal seam generally forms near the sequence interface in the barrier-lagoon environment.The coal accumulation models of the main coal seams are summarized.The No.3 coal seam belongs to fluvial delta coal-forming pattern,in which coal develops in coal accumulation place of the peat swamp in floodplain,abandoned channel filling marshes and some lake swamps,and the No.11 coal seam belongs to barrier-island coal accumulation model,in which coal seam forms in coal accumulation place of filling shallow lagoon or peat swamp behind barrier.