Quaternary Characteristics And Sedimentary Environment Evolution In Bamencheng Area Of Tianjin City

In this paper,the Quaternary system in Bamencheng area in north-central Tianjin is taken as the research object.Combined with a large amount of geological work carried out in recent years,the Quaternary system characteristics in Bamencheng area are summarized,and then the evolution law of sedimentary environment is analyzed,which provides the basic basis for rational exploitation and utilization of emergency water sources,major engineering construction planning,prevention of geological disasters and improvement of ecological environment required by urban construction.On the basis of previous data,this study made full use of remote sensing interpretation,ground survey,geological drilling,sample testing and other means,and obtained a large number of original field data.On the basis of comprehensive analysis of the original survey data and test results,and fully absorbing the scientific research results and latest theories in recent years,the division evolution and basic characteristics of Quaternary strata in the study area are expounded.From the old to the new,the study area is divided into five group-level lithostratigraphic units,namely the upper Pliocene-Early Pleistocene Yangliuqing Formation,Early Pleistocene-Late Pleistocene Ouzhuang Formation,Late Pleistocene-Holocene Yangjiasi Formation,Holocene Gaowan Formation and Holocene Qikou Formation.The sedimentary facies system of the geological reference hole is divided,and the logging sedimentary facies model is established based on the logging data obtained.On this basis,the sedimentary facies analysis and vertical and horizontal comparison of all boreholes in the area are carried out,and the Quaternary sedimentary facies and sedimentary environment evolution research are completed.On the basis of regional geological survey data,and taking into account its material composition,genetic type,spatial distribution and change of lithologic facies,the evolution process of shallow Quaternary sedimentary facies and sedimentary environment has been carefully studied.According to paleogeography and petrography,the Quaternary stratigraphic structure in Bamenzheng area is divided into alluvial plain,alluvial plain and lake basin.Alluvial plain area is further subdivided into river channel zone and flood basin zone.The lake basin area is further subdivided into lakes and lake deltas.The alluvial-proluvial plain area is mainly divided into marine delta front areas.In addition,studies show that since Quaternary,there have been two relatively obvious transgression processes in Bamencheng area,namely,the first and second transgression layers,during which several corresponding ancient coastline changes have taken place.