Division And Correlation Of Jurassic Yan'an Formation In Dongsheng Coalfield Chaideng Prospecting Region

Chaideng prospecting region of Dongsheng Coal Field locates in the northeast of Ordos Basin. In stratigraphic division, the mesozoic-cenozoic belongs to Ordos Strata of Shanganning stratigraphic area. For tectonic position, it locates in the depression of Ordos platform and the mid-west of Dongsheng upheaval zone. And as a whole, it belongs to monoclinal structure of SW direction. According to study on the Chaideng prospecting region, this paper carries out stratigraphic division and correlation to the Yan'an formation that is coal-bearing strata inside the region, and confirm its geologic period.In the stratigraphic division, according to lithological combination, paleontology combin-ation and sedimentary cycle of coal-bearing strata of the Yan'an formation, this paper divides it into 3 members and 8 sub-members. The first member includes 2 sub-members; the second member includes 4 sub-members; the third member includes 2 sub-members. In the stratigrap-hic correlation, this paper carries out comprehensive comparison by making full use of some methods such as marker beds, coal seam spacing, lithological combination and tracing of seismic acoustic impedance etc., based on which the comprehensive maps of comparison of well connection are finished along 5 prospecting lines of NE-SW direction and 3 prospecting lines of NW-SE direction.These work achieve the result of all regional stratigraphic correlation, and supply important application value.Yanan famation's further exploration and development of coal resource.Controversy remains regarding the geological period of the Yan'an formation. This paper focuses on the Yan'an formation flora formed by a large number of paleobotany fossils which are found in this region. Based on their combination characteristics:Coniopteris hymenophylloides, Coniopteris tatungensis and Eboracia lobifolia usually present together; Coniopteris burejensis is distributed widely; the unprecedented prosperity of Coniopteris and Cladophlebis and high diversity, this paper confirms that the Yan'an formation flora belongs to the typical early-middle Jurassic Coniopteris—hoenicopsis flora.The flora was divided into two combinations:the lower combination in the member 1 is characterized by Sphenopsida,the deeper combinations in member 2 and 3 is characterized by Filicopsida and Ginkgopsida.And compare the Yan'an formation flora with North China's middle Jurassic flora: Mentougou flora of Beijing, Datong flora of Shanxi, the middle Jurassic flora of Irkutsk Basin in Siberia area and the middle Jurassic flora of Yorkshire in Britain.In this paper, the writer proposed new viewpoint of Yan'an Formation. Member 1 belonged to J12,member 2 and 3 belonged to J21. This paper solved the long-time unanswered question of Yan'an formation's geologic period.