Research On Sedimentary Facies Of The Upper Permian Linxi Formation In Linxi-Zhaqi Area

This paper is guided by related theories such as sedimentology and sedimentary petrology.Under the premise of making full use of existing drilling,regional surveys and previous research results,combined with outcrops observation and indoor interpretation of date and laboratarry tests,To study the stratigraphic division and correlation,the depositional facies types,on this basis and the vertical and horizontal evolution of the depositional facies and their planar distribution characteristics were studied in detail.This paper is supported by a large number of outcrops work.Based on a large number of comparisons between the geological survey results of the research area and the neighboring area,the paper establishes a standard section based on the research results of the predecessors,and divide the Linxi Formatiaon into six members.And each menber will be study alone.On the basis of the regional depositional background,The study area is a trumpet-shaped foreland basin between Suzuoqi-Xiwuqi and the Northeastern margin of the North China plate,which is narrow in the West and wide in the East.Then,According to the lithologic characteristics(rock color,composition,vertical combination,etc.),sedimentary structure features and fossil features of Linxi Formation,Three types of depositional facies(lacustrine,delta and alluvial fan facies)and their subfacies and microfacies were identified of the Linxi Formation,their characteristics were described and analyzed in detail.Based on the vertical classification and horizontal correlation of depositional facies in Linxi formation outcrops,This paper firstly studied the types and analyzed the vertical and horizontal evolution of depositional facies in each members of Linxi Formation.It is considered that the Linxi Formation is a large transgression to regression cycle from the bottom to top,which cantains several secondary cycles.the most typical case is the Linxi formation in Linxi area,it shows the changing process from alluvial fan facies?shallow lacustrine subfacies?moderate lacustrine?deep lacustrine subfacies?shallow lacustrine subfacies.Influenced and controlled by factors of regional sedimentary structure,procenance direction and paleocurrent direction,the depositional facies belt of Linxi formation distribute along the southern side of the Suzuoqi-Xiwuqi magmatic arc and the northern margin of the North china plate,which extend in a trumpet shape from the west to the east.In the middle-late period of the Linxi formation(4th-6 th member),the shallow lacustrine subfacies advanced from southwest to northeast and superimposed on the moderate lacustrine?deep lacustrine subfacies,indicating that the lake basin shrank gradually at the end of Permian.