Late Cenozoic Sedimentary Sequence And Basin Evolution Of The Jiujiang Basin,Jiangxi Province

The Jiujiang Basin is located in the northern part of Jiangxi Province,on the south bank of the Yangtze river and on the west side of the Lushan Mountain.The Quaternary system of the Jiujiang Basin is well developed,the genetic type is complex,and the lithologic facies changes greatly.The division of the Late Cenozoic sedimentary sequence of the Jiujiang Basin and its key analysis provide an important basis for exploring the material source and sedimentary evolution of the Jiujiang Basin,its is of great significance for the division of the Late Cenozoic sedimentary sequences in the region and the study of the climate environment since the Late Cenozoic in southern China.The Late Cenozoic strata(especially the Quaternary)of the Jiujiang Basin were selected as research objects.Based on a large number of geological surveys in the field,through studies of sedimentary strata,stratigraphic age,paleoclimatic changes,sedimentary sources,tectonic evolution,and basin evolution,The Late Cenozoic sedimentary sequences of the Jiujiang Basin were determined,the paleoclimate characteristics of the Jiujiang Basin were restored,the sedimentary sources controlling the Jiujiang Basin evolution were defined,and the Late Cenozoic sedimentary evolution of the Jiujiang Basin was analyzed.The major conclusions are as follows:(1)Determination of Late Cenozoic sedimentary sequences of the Jiujiang Basin: Through the study of the typical section of the Jiujiang Basin and the determination of the stratigraphic age,the Upper Cenozoic of the Jiujiang Basin,from the old to the new,is the Pliocene Poyang Formation,the Lower Pleistocene Dagu Formation,the Middle Pleistocene Yejialong Formation,and the Upper Pliocene Xingang Formation,the Holocene Lianxu Formation and the Holocene Poyanghu Formation.In view of the sedimentary characteristics,diagenesis and dating data of the gravel layer of the Lushan mountain,the gravel layer is divided into the Poyang Formation and the Dagu Formation,which belong to the Pliocene and the Lower Pleistocene.(2)Discussion on the climatic environment and provenance of the Late Cenozoic of the Jiujiang Basin: Through the analysis of the constant,trace and rare earth elements of loess and red clay in Xingcheng Avenue section in Jiujiang City,the wind characteristics of the two are further reflected,and the source of loess and iron-containing manganese red clay are more similar.Studies have shown that after the Middle Pleistocene,the climate of the study area changes from damp heat to dry and cold.Through the analysis of gravel structure of the Dagu Formation of Xingcheng Avenue,it is determined that the source of the material is from Lushan,which is an alluvial fan sediment.(3)Late Cenozoic sedimentary evolution of the Jiujiang Basin: It is determined by drilling that the Jiujiang-Jing'an fault controls the filling process of the Jiujiang Basin,and the basin evolution can be divided into three stages.First,the basin formation stage: The basin began to form,with Paleogene conglomerate and siltstone as the sedimentary basement of the basin;Second,The transition period of the basin: During the Neogene period,the Jiujiang Basin changed from formation to accepting filling,and the sediments in the basin were mainly Pliocene gravel layer;Third,the stable sedimentation stage: Early Pleistocene,the Dagu Formation is a stable sediment in the basin.After the Early Pleistocene,the aeolian deposits dominated the basin.