Sedimentary Facies And Lithofacies Paleogeography Of The Nanhua System Datangpo Formation On The Northern Margin Of The Yangtze Platform

The Middle-Upper Yangtze platform formed stable crystalline basement and fold bases through the Jinning movement in the Greenwell orogenic period.From the Nanhua period,the Yangtze continent entered the evolutionary stage of the craton basin of the plate movement mechanism.In the Precambrian period,the Middle-Upper Yangtze Craton Basin started the evolution of a new sedimentary basin under the background of extension.According to the basic idea of “Earth structure control basin,basin control sedimentary facies”,taking the northern margin of the Yangtze platform as an example,this thesis mainly studies the sedimentation period of the Datangpo Formation of the Middle-Upper Yangtze Craton Basin,the filling sequence of the basin,and the sedimentary evolution,getting the evaluation of Hydrocarbon generation potential through comparative analysis of TOC values of the Datangpo Formation,and the main results achieved are as follows:(1)Through field surveys,a typical profile of the Doushantuo Formation of the Nanhua-Sinian system from the west-east Wutiao to the northern margin of the Yangtze platform is established.(2)The main exposed lithology of the Datangpo Formation in the study area is Carbonaceous shale,mudstone,silty mudstone,argillaceous siltstone,siltstone,sandstone.(3)According to its lithological characteristics,sedimentary structure and paleontological characteristics,the sedimentary facies of the Nanhua System Datangpo Formation in the northern margin of the Yangtze platform are divided into Fluvial facies,fan delta facies,shallow water shelf facies,deep water shelf facies and semi deep sea facies.(4)Using mapping method of the dominant facies,based on the study of sedimentary comparison,the lithofacies palaeogeographic map of the Nanhua System Datangpo Formation in the northern margin of the Yangtze platform is compiled and the sedimentary evolution characteristics of the Datangpo Formation in the study area is discussed on the basis of the lithofacies palaeogeographic map.(5)Through the comparison of organic carbon content in various regions,the highest value of local organic carbon content is 6.45%,with an average value of 3.92%,and the organic carbon content in most areas is less than 2.88%,with an average value of less than 0.38%.By analyzing the type of organic matter and the abundance of organic matter,this thesis discusses the favorable areas of source rocks and distant scenic spots in the study area to provide guidance for the next step of oil and gas exploration.