Sequence Stratigraphic Characteristics And Sedimentary Facies Of The Shahejie Formation On The Chengbei Slope

In view of the status quo of the limited research on the sedimentary facies of the Shahejie Formation of the Paleogene Period in Chengbei slope in Huanghua Depression,the in-depth research on the sequence stratigraphic characteristics and sedimentary facies of Shahejie Formation in Chengbei slope is carried based on sequence stratigraphy,structural geology,geophysics and sedimentology and other theories and methods to provide a reliable geological basis for the next exploration and development of the Shahejie Formation in this area.Based on taking into consideration different factors including structure,climate,sediment supply and eustatic lake level,it is identified that the Paleogene Period of the area researched can be divided into two 2 order sequences and that the Shahejie Formation can be divided into six 3 order sequences,and the stratigraphic frame of various 3 order sequences of the Shahejie Formation is established on the basis of the identification of the interface of different order sequences.The paper carries out systematic analysis of the provenance system during the sedimentary period of the Shahejie Formation by means of quantitative analysis of gravel composition,sandstone composition and heavy minerals etc.,through which it considers that the provenance mainly comes from the Chengning Uplift in the south of the area researched.The paper considers that the Shahejie Formation in the research area features in the braided river delta--lake sedimentary system,is mainly composed of braided river delta and lacustrine facies through a detailed analysis of lithology,sedimentary cycle,facies marker and other sedimentary characteristics and in combination with the sedimentary background in this area,from which 6 subfacies and 9 microfacies can be further identified.The plane distribution map of sedimentary facies of each 3 level sequence of Shahejie Formation in the research area has been prepared by taking the 3 order sequence as the mapping unit,and through the quantitative comprehensive analysis of single factors such as lithofacies type,sand thickness,etc.The paper further carries out the systematic research on the spatial and temporal distribution characteristics of the delta-lake sedimentary system of Shahejie Formation in the research area and considers that the braided river delta is mainly distributed in Yang'er Village Fault in the outer belt of Chengbei Slope Area-inner zone of Chengbei Slope Area,among which the braided river delta plain is mainly distributed in Yang'er Village Fault--Zhaobei Fault whereas the foreland of the braided river delta is mainly distributed in Zhaobei Fault--Zhangdong Fault.The Zhangdong Fault is taken as the boundary,from where the braided river delta is gradually transformed into a lake,on the basis of which,the paper establishes a model of sedimentary evolution of Shahejie Formation in the research area and considers that the SQ1-SQ2 features in the development of lake domain braided river delta,the SQ3 in the development of Lake-Lake retreat Braided River Delta,SQ4 in the development of lake domain braided river delta and SQ5-SQ6 in the lake domain braided River Delta.