Sedimentary System Characteristics Of The Qixia Formation In The Middle Permian In Northwest Sichuan

The study area is located in the northwestern part of the Sichuan Basin,and the target layer is the Middle Permian Qixia Formation.The characteristics of sedimentary systems and sedimentary evolution have not been studied at full length because of relatively lagging oil and gas exploration and relatively few research work,in northwestern Sichuan.Based on the theory of sedimentology and Geophysics,sedimentary geochemistry and other methods,combined with field survey,exploration outcrop section,core,logging and geochemistry data,the top and bottom interfaces of the two stack of Qixia formation in the study area are identified,and the habitat and habitat are observed on the basis of stratigraphic division and comparison.The two section is divided into stratigraphic division.On the basis of this basic framework,using the outcrop data and logging data,the formation contrast of Qixia formation is constructed,and the distribution and longitudinal evolution characteristics of the strata are displayed on the plane.On the basis of field exploration and drilling core observation,through the study of the macroscopic and microscopic characteristics,the characteristics of the sedimentary structure and the geochemistry of the limestone of the Qixia formation,it is concluded that there are two main sedimentary facies types in the Qixia formation of the Northwest Sichuan: the platform margin and the open platform.Under the influence of tectonic activities,the platform margin is mainly developed at the northwest corner of the Longmen Mountain thrust zone.Geochemical data analysis is performed on typical sections to show the paleoclimate and paleoenvironmental characteristics of the northwestern Sichuan region.Field observations and observations,cores,sheet observations and descriptions,sample collections,and indoor analysis and appraisal were completed.Following the systematic completion of this series of work and following the principle of map compilation of lithofacies and palaeogeography,the two lithofacies paleogeographic maps of the Qixia Formation was prepared.The results show that there have been no major changes in the depositional environment,paleostructure,and paleoclimate of the Qixia Formation,and the two phases of deposition have been inherited.Under the influence of the tectonism of the Caledonian movement in the study area,the strong extension of the structure in the western Sichuan Basin formed a mantle barrier structure between the slope and the platform.In the context of this tectonic setting,it is indicated that the northwest of the study area is the continental shelf along the Guangyuan-Mianyang to the northwest,and the sedimentary facies of the platform marginal facies is developed along the Longmen Mountain thrust zone,and is the open platform carbonate sediment.The shoal developed within the platform,and the overall thickness of the strata from west to east is mainly thickened in the first member of the habitat.The thickness of the second member of the Qixia Formation remains basically unchanged,while the thickness of the strata in the northern and southern parts of the strata is relatively stable.The thickness of the southern strata is relatively stable.Both habitats are thicker than the others.