Depositional Evolution Of Cretaceous Basin In Liupanshan Area

The Liupanshan basin is located at the junction of Qinling-Qilian-North China block,and at the northeast margin of the Qinghai-Tibet Plateau,its tectonic position is very important.But the basic investigation and exploration of the Liupanshan area are relatively weak.And the Cretaceous is an important stage of the tectonic evolution of China,the Cretaceous strata in the Liupanshan area is well developed,the study of the Cretaceous in the Liupanshan area not only provides clues to the evolution of the regional tectonic pattern,but also contribute to the northeastern Qinghai-Tibet plateau uplift research,and it can provides some help to the region's oil exploration work in Liupanshan area.In this paper,the sedimentary system of the Cretaceous in Liupanshan area was studied by field investigation and field analysis,through using sedimentology methods and provenance analysis to reveal the sedimentary evolution of the Cretaceous in Liupanshan basin.The stratigraphic evolution characteristics of the Cretaceous in the Liupanshan area were sorted out by field investigation.The sedimentary facies were subdivided by the analysis of the main sections measured in the field.The U-Pb chronological method of detrital zircon plays a very important role in the analysis of provenance,by using the debris zircon U-Pb chronology of two sandstone samples of the Li wa'xia formation and Ma dong'shan formation,the U-Pb ages of the two samples are similar,and they both have five age ranges between 200?350 Ma,350?530 Ma,670?1000 Ma,1000?2000 Ma and 2350?2650 Ma,and the corresponding peak ages are mainly 240Ma,430Ma,850Ma,1800Ma and 2500Ma.Compared with the age of the surrounding area,it was found that the peak age in the study samples was consistent with the age of several rock masses in the North Qilian-Qinling Mountains.Combined with the outcrop of ancient water,gravel analysis and other information,we speculated that the main source areas of Liupanshan Group are the North Qilian,North Qinling and Ordos plots.Based on the study of the Cretaceous sedimentary system in Liupanshan area and the comprehensive analysis of the source data,that the evolution of the Liupanshan basin is divided into three stages:the initial rift stage of the San'qiao and He shang'pu formation;the stable expansion stage of the Li wa'xia and Ma dong'shan formation;the atrophy stage of the Nai jia'he formation.