Study On Permian Lithofacies Paleogeography In The Southeastern Margin Of Sichuan Basin

The research area of this paper is located in the southeastern margin of sichuan basin.The early Permian strata are generally absent and the middle-late Permian strata are widely developed.Although the Marine carbonate sedimentary facies,sedimentary patterns and lithofacies paleogeography of the Yangtze region have been studied,but the study on the sedimentary facies of the southeastern margin of sichuan basin in this paper is still lacking.Therefore,in this paper,the stratum in the study area was divided into multiple strata,and the permian strata in the area were sedimentary facies analysis through the field investigation of the southeastern margin of the sichuan basin,based on the measured stratigraphic profile,combined with previous research data.In this paper,the Permian sedimentary system of southeastern margin of sichuan basin is systematically studied by means of observation of field profiles,collection and statistics of geological data and sample analysis.The main tasks are as follows:identify the Permian marker layer in the study area,and divide the strata in the study area by the marker layer.The types of sedimentary facies in southeastern margin of sichuan basin and its adjacent areas were determined by analyzing the sedimentary facies,Transversal comparison of sedimentary facies was carried out.Based on the field measured profile and the collected 1:200,000 geological reports,the Permian lithofacies palaeogeographic map of southeastern margin of sichuan basin was compiled by using the principle of dominant facies.The sedimentary model of Permian groups in northwest guizhou province was established.Through the analysis and research,the following conclusions are drawn:?I thingk that the permian system in the study area mainly developed the coastal system,the carbonate platform system and the carbonate gentle slope system through the observation of a large number of field profiles and the combination of sedimentary facies markers,such as sediment lithology,color,sedimentary structure,paleontology and logging facies characteristics.The coastal system is divided into the coastal marsh and the coastal plain,the carbonate platform system is divided into the open platform,the confined platform and the platform edge slope,and the carbonate gentle slope system is divided into the shallow gentle slope and the deep gentle slope.?The distribution characteristics of sedimentary facies in the study area were distributed along the east and west as a whole.There are mainly 3 sedimentary facies belts in qixia formation.From south to north,there are restricted platform,open platform and gentle slope sediments,and carbonate platform sediments are mainly developed.In the south part of the study area,there are mainly restricted platform,shallow water carbonate platform sedimentary environment,and gentle slope facies sediments are mainly distributed in the north area of Tong4 well,chongqing.The maokou formation is still mainly carbonate platform.Influenced by the transgression from northwest China,the restricted platform area in the study area has collapsed to the south,and the open platform and gentle slope area have increased.However,the restricted platform still covers most areas in the south-central part of the study area.In the early period of wujiaping formation,influenced by regression,there were more coastal deposits in the south of the study area.In the changxing formation,the area of carbonate platform and gentle slope increased again due to transgression ? During the sedimentary period of liangshan formation,the paleoclimate was humid,and the lagoon facies and swamp facies were developed in the study area.With the deepening of seawater,the sedimentary facies from qixia formation to maokou formation gradually changed from restricted platform to open platform.,the sediments from the early argillaceous bioclastic limestone to bioclastic limestone,biological content and species increased significantly.In the late middle Permian,the dongwu movement caused the sea level of the south China plate to drop significantly,and the sedimentary discontinuity occurred between the maokou formation and the wujiaping formation,and the gufeng formation was absent.From the sedimentary period of Wujiaping Formation to the sedimentary period of Changxing Formation,a new round of transgression occurred,and the coastal marsh facies formed by the crustal uplift of the Dongwu Movement gradually developed into gentle slope sediments.At this point,the transgression continued until the early Triassic.