The Research Of Sedimentary Structure And Spatial Distribution Of The Quaternary System Of Hangzhou

Quaternary is a very important period for the origin and evolution of human beings,the study area of Hangzhou is very important in the Yangtze River Delta area. Studying on the Quaternary depositional texture and it's spatially -distributing regularity in Hangzhou is very useful to recognize the primary factor controlled the Quaternary sedimentation and the properties and structure of Quaternary sedimentary,which can offer an important scientific basis in city planning and construction.On the basis of previous researches,this paper chose 1000 wells data optimally in Hangzhou area to analyze the Quaternary sedimentation in Arcgis using conventional geological methods of sedimentology,sequence stratigraphy, paleontology and geomorphology.And finally this paper compiled the Quaternary strata table of the study area synthetically,plotted the depth of the base rock, distribution of Quaternary sediment at the piedmont and gully and isopach map of the Q₃¹,Q₃²,Q₄¹,Q₄²,Q₄³ of the plain area,and also plotted two Quaternary geologic sections.Some innovative results are listed below:1,According to the lithologic characters,lithofacies,genetic classification and the geomorphy,the Quaternary system is divided into piedmont-gully's and plain's. The piedmont-gully's Quaternary sediment,which is about 3～20 meters in thick,is in the western hills of the study area.The plain's Quaternary sediment is widely distributed in the study area,which is about 30～60meters thick and become thicker from southwest to northeast.2,The Quaternary sediments of plain can be divided into five sedimentary cycles.The Late Pleistocene series Quantan group,at the bottom of the Quaternary System,is constituted by a fluvial facies-river and lake facies sedimentary cycle. The Late Pleistocene series Jiashan group,at the middle of the Quaternary sediment, is constituted by two fluvial facies-neritic facies-river and lake facies sedimentary cycles.The Holocene series Binhai group,at the upper of the Quaternary sediment, is divided into three parts,the under layer and middle layer are constituted by two littoral facies-river and lake facies sedimentary cycles,the upper layer is constituted by paludal facies,which was deposited at the lower-lying land like West Lake, Jiangcun-Gu dang,Xianghu lake,and coastal-estuary facies in other area.3,Folding and fault activities were weak in Quaternary and the tectonic activity had little influence on the Quaternary sedimentation.The ancient landforms,the evolvement of the river system and transgression were the main elements which controlled the Quaternary sedimentation in Hangzhou.The ancient landforms formed the basis of the Quaternary sedimentation.The evolvement of the river system and transgression individually or jointly controlled the Quaternary sedimentation of this area.4,The alternation of the climate was the main reason for the evolvement of the river systems and transgression,and it's also the reason why the Quaternary system of Hangzhou has the special sedimentary structure which is called soft interbed with hard layers.