Study On Sedimentary Facies And Sand Body Distribution Rules Of He 8 Member Of The Upper Paleozoic Hedong Formation In Longdong Area Of Ordos Basin

In this thesis,the He8 Member of Upper Paleozoic in Longdong area of Ordos Basin is taken as the research object.Guided by basic theories and methods related to sedimentology,based on previous studies,making full use of field profile data,drilling core data,drilling core data and test analysis data,in-depth study of the material source,sedimentary facies development characteristics and sand body distribution law in the study area,and mading the following three main understandings:(1)Through peripheral paleoland characteristics,paleocurrent direction,detrital composition,rock debris type,heavy mineral analysis,and analysis of major trace elements,it is concluded that the source of the He 8 Member in the Longdong area originates from the ancient land of Yinshan in the north and northeast,and the Qilian orogenic belt in the southwest and the Qinling orogenic belt in the south.The provenance direction comes from the two main directions in the southwest and northeast and the secondary directions in the south.The provenance is dominated by the cyclic orogenic belt.This includes the tectonic setting of the provenance zone,which is dominated by passive continental margins,followed by active continental margins.(2)The sedimentary evolution characteristics of He 8 Member in Longdong area were clarified.The sedimentary facies types of He 8 Member in Long Dong area were clarified through the study of sedimentary signs,paleo-biomarkers and geochemical markers.That is,there are two types of sedimentary facies in the He 8 Member,mainly the Fensi River Delta sedimentary facies and the secondary lacustrine facies.The Fangsi River delta facies develops two types of subfacies,the Fangsi River delta plain and the Fangsi river delta front respectively.Among them,the Fangsi river delta plain has a relatively small area,and there are two types of sedimentary microfacies including distributary channels and interdistributary depressions.On the front edge of the Delta River,there are two types of sedimentary microfacies,namely underwater distributary channels and distributary bays.The lacustrine facies are only developed on a small scale in the middle of the study area,and shallow lake subfacies are developed,including two sedimentary microfacies of shallow lake mud and shallow lake sand bar.Combining the development features of sedimentary microfacies and the planar distribution features of sedimentary facies in He 8 Member of Longdong area,the corresponding sedimentary evolution model was established.(3)The sand body of the He 8 Member is distributed as a blanket.Both the upper He 8 and lower He 8 Members are developed six main sand body zones.They are all distributed in the southwest-northeast,north-south direction.The connectivity of the distributed sand bodies in the southwest-northeast direction is good,and the overall thickness is large.However,the scale,connectivity and extension of the sand body in the upper section of He 8 Member are worse than those in the lower section of He 8 Member.Among them,the thickness of each main belt in the lower section of the He 8 Member reached more than 15 meters,and the maximum thickness was 23 meters.Most of the main belts in the upper section of He 8 Member develop sand bodies with a thickness of about 10 meters and a maximum thickness of 15 meters.