Sedimentary Characteristics And Its Control To Sandstone Type Uramium Mineralization Of Zhiluo Formation In Dongsheng Area

Ordos basin is an important basin containing energy and nonmetallic mineral in china,and it has substantial oil,coal and natural-gas and uranium deposits etc.Dongsheng area is located in the northeast of Ordos basin.The lower member of Zhiluo Formation of Middle Jurassic is the main uranium-bearing strata in this area,and it is also the point of this dissertation.Based on field outcrop,well core,rock thin section,well log,analytic data and previous research results,it is systematically discussed that the classification and correlation of sequence stratigraphy,the facies indicators,the features of sandbody distribution,sedimentary facies features,as well as the relationship of sedimentary characteristic and sandstone type uramium deposit in the lower member of Zhiluo Formation of Middle Jurassic in Dongsheng area,Ordos basin.By the sequence stratigraphy theory and lithostratigraphy,this study systematically analyzes the stratigraphic features of Zhiluo Formation and presents the classified rules and identified symbol of the sequence stratigraphy,then makes sequence analysis on a single well and associated well and builds up the district sequence stratigraphic framework.This dissertation further discusses and systematically sums up facies indicators of Zhiluo Formation,such as the color,the detrital composition,the grain size and the sedimentary structure of sedimentary rock,making the conclution that the lower member of Zhiluo Formation sedimentary facies of the study area developed fluvial and delta facies.The palaeocurrent during sedimentation was north-west to south-east.The lower member of Zhiluo Formation was deposited in humid climate.According to characteristic of sandbody distribution,The largest distribution range of river channel lateral shift manifests as sand belt with large thickness and high sand ratio,while the region of small thickness and low sand ratio mainly deposited flood plain or interdistributary bay facies.Based on facies indicators and characteristic of sandbody distribution,the analysis method of “single well – section – plane” facies is used to restore the sedimentary environment for the lower member of Zhiluo Formation in the study area.Braid river subfacies – braid river delta plain subfacies is exit in the lower submember of the lower member and braid river subfacies – meandering fluvial subfacies – meandering river delta plain subfacies is exit in the upper submember of the lower member of Zhiluo Formation.According to the relationship of sedimentary characteristic and sandstone type uramium deposit,there are two requirements to become favorable areas of mineralization: river channel where hydrodynamic conditions change or the sedimentary facies change in the plane,and the bottom,the top or the superimposed position of channel sandbody in the section.