Study On Sedimentary Facies Characteristics And Evolution Of The He-8 Member In The Northeastern Margin Of Ordos Basin

In this thesis,using the theory and technical methods of sedimentary geology,sedimentary geochemistry and petroleum geology,the He-8 member of the Middle Permian Lower Shihezi Formation in the Upper Paleozoic of the Fugu Tianshengqiao section on the northeastern margin of the Ordos Basin is selected as the main research object.Based on previous studies,the field profile,geochemical element test data and drilling data were studied in depth.The material sources,sedimentary facies development characteristics and sedimentary evolution laws of the study area were studied in depth,and the following three main points were recognized:(1)Through the paleocurrent,debris components,cuttings components,cathodoluminescence,main quantity?trace element and rare earth elements,the source of the He-8 member of the study area is derived from the Yinshan ancient land on the northern margin of the basin.Then revolving back to the orogenic belt.The tectonic setting of the source area of the study area is dominated by the passive continental margin and there are active continental margins and continental island arcs.The REE partitioning pattern of the study area has good similarity with the Archean igneous rocks in the Yinshan-Daqingshan area in the northern part of the basin.The source rocks of the He-8 member are dominated by felsic rocks,and a small amount of neutral magmatic rocks exist.(2)The sedimentary facies of the He-8 member of the study area are accurately divided by sedimentary markers and geochemical markers,that is,the sedimentary facies of the braided river are developed from the lower part of the He-8 member to the upper-2 part of the He-8 member.The two types of subfacies of the river channel and the embankment are developed.It can be further divided into six types of sedimentary microfacies: retained sediment,heart beach,channel filling,abandoned channel,overshore sediment,and flood plain.The whole appears as a positive sequence sequence with inconsistent binary structure;The sedimentary facies of the meandering river are developed in the upper-1 part of the He-8 member,which develops two sub-phases of river channel and river diffuse,and can be further divided into three types of sedimentary microfacies: retained sediment,marginal beach and floodplain.The whole appears as a typical binary structure.Deposition sequence.(3)On the basis of the above research work,discuss the sedimentary evolution law of the He-8 member of the study area from the aspects of reference plane rotation,source supply,terrain slope and paleoclimate.It is clear that the evolution process of the meandering river from the braided river to the lower part of the He-8 member to the upper2 part of the He-8 member to the upper1 part of the He-8 member is combined with the sedimentary microfacies features and sedimentary microfacies plane spread feature of different periods in the He-8 member of the Sudong area,and the sedimentary evolution model of the He-8 member of the outcrop + drilling combination is established.