Provenance And Sedimentary System Analysis Of Jurassic In The Southern Margin Of Junggar Basin

Sandstone-type uranium deposits are one of the important strategic resources at home and abroad.The Junggar Basin is an important exploration area for sandstone-type uranium deposits in my country.The Jurassic strata develop typical uranium-bearing rock series.Therefore,the detailed analysis of the stratigraphic,provenance and sedimentary evolution characteristics of the Jurassic key uranium-bearing rock series in the Junggar Basin is of great significance and economic value for safeguarding Chinese energy resources,national defense and other national security.Based on the combination of field geological survey and indoor analysis,guided by the theories of stratigraphy,sedimentology and geochemistry,this thesis analyzes in detail the strata,provenance,sedimentary system and its evolutionary characteristics.Through detailed field surveys and field measurements,the development characteristics of the Jurassic strata in the southern margin of the Junggar Basin are systematically summarized.The Jurassic strata in the study area is divided into 6types of strata from bottom to top:Badaowan Formation（J₁b）,Sangonghe Formation（J₁s）,Xishanyao Formation（J₂x）,Toutunhe Formation（J₂t）,Qigu Formation（J₃q）and Kalazha Formation（J₃k）.Among them,the Lower Jurassic contains the Badaowan Formation and the Sangonghe Formation,the Middle Jurassic contains the Xishanyao Formation and the Toutunhe Formation,the Upper Jurassic contains the Qigu Formation and the Karazha Formation,and the Lower Jurassic and Xishan Formations.The lithology of the Yao Format ion is a set of coal-bearing clastic deposits;the Middle Jurassic Toutunhe Formation and the Upper Jurassic are a set of coarse-grained clastic rock deposits.The Kalazha Formation is seriously missing and only in the south.It is exposed in parts of the central and eastern part of the margin.On the basis of previous research results,through paleo-current measurement,light mineral and heavy mineral analysis,the provenance development characteristics of the Jurassic in the southern margin of the Junggar Basin are discussed.During the deposition of the Jurassic in the southern margin of the Junggar Basin,there existed the provenance area of the North Tianshan Mountains,the provenance areas of the Middle Tianshan Mountains,the source areas of the Zaire Mountains,the source areas of the Bogda Mountains,and the source areas of the Karameishan Mountains.During the Early Jurassic,the provenance system of the North Tianshan had absolute control over the sedimentation in the study area.During the period of the Sangonghe Formation,the middle Tianshan temporarily provided the source,while the Zaire Mountains on the northwestern margin and the Karameishan Mountains on the northeastern margin also provided sources;during the Middle Jurassic,the provenance area was transferred from the Middle Tianshan to the North Tianshan,and Bogda Mountain began to uplift and provided the source;during the Late Jurassic,with the Bogda Mountain further uplifting,at this time The provenance mainly comes from the North Tianshan Mountain and the Bogda Mountain.Through the identification of outcrop sedimentary facies,typical and comparative profile sedimentary analysis,and sedimentary facies plan compilation,the Jurassic lithofacies,sedimentary system types,characteristics and temporal and spatial evolution laws in the study area are systematically analyzed.The Jurassic in the study area mainly developed three typical sedimentary rock types:conglomerate,sandstone,and mudstone.A total of 13 lithofacies types and 8 lithofacies assemblage types were identified.There are six types of sedimentary facies in the Jurassic:alluvial fans,braided rivers,meandering rivers,fan deltas,braided river deltas,and lakes.Among them,the Badaowan Formation is dominated by fan deltas,braided river deltas and lakes,the Sangonghe Formation mainly develops braided river deltas and lakes,the Xishanyao Formation mainly develops braided river deltas,and the Toutunhe Formation mainly develops braided river deltas.The Qigu Formation mainly develops meandering rivers,meandering rivers and meandering rivers.The Kalazha Formation only develops alluvial fan facies in some parts of the central and eastern part of the study area.On the basis of the above analysis,the Jurassic sedimentary model of the study area was constructed,and the controlling factors of its sedimentary development were discussed.From the Early Jurassic to the Middle Jurassic Xishanyao Formation,the study area was in a weakly extended structure environment,with a warm and humid climate,a delta-lacustrine sedimentary system as a whole,and well-developed delta distributary channel sand bodies,lake-swamp facies The floodplain swamp facies developed industrial coal seams,which are the main coal-forming and oil-bearing strata.The rock color is mainly gray-green,gray,black and other reduction colors;the Toutunhe Formation from the Middle Jurassic to the Late Jurassic,The structural background of the study area is dominated by thrust,compression,depression and subsidence.The climate has turned to hot and arid.The river-lake sedimentary system has developed as a whole.The lake basin area has shrunk on a large scale.Seasonal rivers are unusually active.The rock color is mainly purple-red and brick.Oxidized colors such as red and reddish brown are the main ones.Many factors,such as tectonic movement,palaeoclimate,and provenance,jointly control the sedimentary evolution of the Jurassic in the study area.