Study On Sedimentary Facies And Lithofacies Palaeogeography Of The Middle-Late Permian In The Dejiang Area Of Guizhou

In recent years,China has made great breakthroughs and discoveries in the exploration of coal and oil and gas resources in guizhou,sichuan and xinjiang.The Permian strata in the upper Yangtze region,as one of the best developed reservoirs of important oil and gas and sedimentary minerals in south China,has a great prospect of exploration and development.The dejiang area of guizhou belongs to the northern guizhou uplift of the upper Yangtze plate,which indicates that the study of paleogeography in the area still has certain significance.Therefore,this paper takes the middle-late Permian strata in dejiang area as the research object,based on the field measured section and the correlation section,takes sedimentology,paleontology,petrology,geochemistry and other disciplines as the guiding theory,combines the field observation in the study area and indoor microscopic data of rock flakes composition,paleontology fossils and geochemical data,analyzes and summarizes the sedimentary environment and evolution characteristics,and obtains the following understanding:1)Based on the detailed investigation of the strata in the field and combining the latest rock strata and regional geology,the middle-upper Permian strata in dejiang area are further subdivided.The rock strata from old to new are liangshan formation?P₂l?,qixia formation?P₂q?,maokou formation?P₂m?and upper Permian united heshan formation?P3h?.2)Based on the field exploration and thin slice identification of the research objects,the relevant research data in guizhou and guangxi are summarized,and the rock types of the middle and upper Permian in the research area can be divided into carbonate rocks and clastic rocks.Carbonate rocks are mainly developed in qixia formation,maokou formation and heshan formation,and clastic rocks are mainly developed in part of heshan formation and liangshan formation.3)Combined with the characteristics of petrology,paleontology,sedimentology and sedimentary geochemistry,the characteristics of the backbone section and the auxiliary section were compared and analyzed,and the middle-late Permian sedimentary system in the study area was divided into barrier coastal system and carbonate platform system.Open platform subfacies can be subdivided into high energy shoal,low energy shoal,intershoal sea and platform depression;The subfacies of semi-confined platform can be divided into tidal flat and lagoon;Barrier coastal system can be subdivided into tidal flat microfacies and marsh microfacies in the study area.4)By using the relative ratio method and combining with the analysis of the Permian sedimentary system in the area,this paper has compiled 4 maps of the lithofacies paleogeography of the Permian in dejiang,guizhou.The paleogeographic units of liangshan period developed swamp and tidal flat successively from west to east;In qixia period,high-energy shoals,intershoal seas and low-energy shoals developed from west to east;The maokou transgression reached the maximum extent and inherited the qixia sedimentary environment as before,but the flint-limestone-mudstone-silicon-sedimentary assemblage can be seen in the middle of the study area,which is manifested as the taiwa sedimentary environment.The paleogeographic units of maokou period generally show high-energy shoal,intershoal sea,taiwa,intershoal sea and low-energy shoal from west to east;In the late middle Permian,dejiang area was uplifted to the land due to the influence of the sokurian movement,resulting in the disconformity contact between the maokou formation and the heshan formation.Then,with the beginning of transgression,the heshan period presented as a semi-confined platform,and the paleogeographic units from west to east were tidal flat and lagoon successively.