Sedimentary System Of Qingshankou Nenjiang Formation In Western Slope Area Of Songliao Basin

The western slope area of Songliao basin is located in the west of Songliao Basin,which together with the central depression zone and southeast uplift area constitute Songliao basin.Since the last world,many geological researchers have carried out a lot of research work on the internal characteristics of Songliao basin.It has been proved that there are abundant oil reserves and uranium ore-forming areas in the study area.Because uranium deposits are mainly concentrated on sedimentary sand bodies,it is very important to study the sedimentary system of the western slope area.Based on the work of collecting many geological data,this paper analyzes the sedimentary facies,sedimentary system,tectonic environment and sand body distribution characteristics of Qingshankou Nenjiang Formation in western slope area by using the knowledge of sedimentology such as sedimentary facies and sedimentary system,combining with structural geology and stratigraphy,The purpose of this paper is to provide basic research for sandstone type uranium deposits.Based on the analysis of many field sections in the study area,and the thin sections of rock samples and the collected logging data,this paper analyzes that there are many sedimentary facies in the Qingshankou Nenjiang Formation,including alluvial fan sedimentary facies,fluvial facies,fan delta facies and lacustrine facies,Identify the sedimentary subfacies and microfacies in the study area.The results show that in the northern margin of Songliao Basin,the whole sedimentary system is greatly affected by the provenance,and at the same time,fan delta sedimentary facies and lake sedimentary facies are developed in many places in the supply area of the provenance.The second and third members of Qingshankou Formation in the western slope area are distributed in the southern margin as a whole in the form of thin mounds.The sandstone thickness in Baicheng Yingtai area is the largest,up to 260 m,which is the area with the largest thickness of sandstone in the whole study area.Fan delta facies deposits are formed between Baicheng and Yingtai,Delta plain and delta front are developed on a large scale.The Yaojia formation consists of fluvial delta deposits as a whole,delta front deposits in the northwest and large-scale lacustrine deposits in the southeast.From northwest to Southeast,the river delta delta front lacustrine facies change trend,lack of large-scale sand body deposition,the middle and West and southwest of the study area are high value areas of sandstone thickness.In the southwest,the distribution is duck tongue;It is fan-shaped in the middle.During the Nenjiang Formation,the west slope was lacustrine facies,lacking large-scale sand body deposition.Only a part of delta sediments developed in the middle,and fluvial facies developed in the northern margin.From south to north,there is a trend of semi deep lake shallow lake,and delta deposits are developed locally.Three high value areas of sandstone thickness are distributed in the north,northeast and southeast of the area.In the southeast,the distribution is duck tongue,and in the north and northeast,the distribution is semicircular.As a whole,the sandstone near Jingdu 12 is the thickest,and the thickest part can reach more than 120 meters,which is the thickest area in the study area.The developed depositional systems in the western slope area are: fan delta deposits in Qingshankou formation,sandy shallow lake lakeshore deposits in Yaojia formation and Nenjiang Formation.During the deposition period of the second and third member of Qingshankou formation,the Yingtai area of Baicheng was fan delta deposit,and the same thick sandy aquifuge was distributed above and below.In Yaojia formation,sandstone aquifuges are mainly developed,and multilayer delta dark sandstone aquifuges are developed on both sides.The whole Nenjiang Formation is lacustrine facies,the developed part is delta facies,the fluvial facies is developed in the northern margin,and the delta front sand body is thick.