Research On Sedimentary Evolution And Ancient Environment In Fuzhou Basin In The Last 50,000 Years

Quaternary land,sea&land transition phase and marine sediments are widely distributed in Fuzhou Basin,recording rich paleo-climatic and environmental change information,providing rich data for the study of regional paleo-environmental change,and the sedimentary layer also records rich paleo-environmental paleo-climatic and geological structure evolution information of the basin.Therefore,the study of paleo-climmatology and sedimentary environment in Fuzhou Basin can not only speculate the future climate change development in the region,but also provide reference for human production and life.With the support of the National Natural Science Foundation of China and the authors,company,the boreholes of Gutian Road（ZK004）and Shoushan Road（ZKCS）were selected as representative boreholes,conducted AMS¹⁴C and OSL age tests,detailed lithographic analysis,environmental magnetism,clay turbidity water permeability test,geochemical elements and diatom powder identification according to the experimental conditions,lithology and age data,and established the standard stratigraphic framework of the basin since the Late Pleistocene.On this basis,the drilling data of Fuzhou Basin were standardized processing and data standardization,establish the stratum database to extract the sediment distribution characteristics and evolution rules of Fuzhou Basin since the late Pleistocene,and conducted correlation analysis and geographic analysis to generate representative 6 horizontal and 8 vertical geologic sections in the region and the spatial evolution trend of the basin.Finally,combined with the reconstructed global sea level changes and global ice volume evolution,the main causes of the Fuzhou sea invasion were explored.The following conclusions are drawn.（1）Through the study of a large number of drilling data in Fuzhou Basin,and the dating test and lithology analysis of representative boreholes ZK004 and ZKCS,combined with the engineering geological standard formation construction in Fuzhou area,the standardized layer sequence of the basin since the late Pleistocene was established.In addition,the basin strata were standardized,the formation data format and code were set,more than 10,000 drilling data were screened and standardized for more than 400 projects,transformed into historical strata data that can be used for scientific research and analysis,and the sedimentary strata database was established using Arc GIS.The mechanism of transforming engineering borehole into scientific research and analysis of drilling is established,which improves the utilization rate of existing sunk borehole data and saves the cost.（2）Through the experimental test of representative boreholes ZK004 and ZKCS environmental magnetism,geochemical elements,spore powder and diatom,the sedimentary phase in Fuzhou Basin since the late Pleistocene was divided into seven stages,forming three complete sea infestation-sea degenerative cycles.Under the background of inconsistent previous studies,it is confirmed that three sea invasion occurred in Fuzhou Basin since the late Pleistocene,namely"Changle Sea invasion","Fuzhou Sea invasion"and"Langqi Sea invasion".It is found that the main reason for Fuzhou sea infestation is regional tectonic settlement and uneven settlement within the basin,division in the Minjiang River,thin sea infestation in the south,and even missing in some places.（3）Using database analysis of the properties of the sediment information,such as the sediment cover elevation,bottom cover elevation,thickness and modern surface elevation parameters,using statistical correlation analysis software and gis geographic analysis software,and basin structure analysis,combined with the correlation between regional sedimentary evolution and tectonic activity,fracture distribution,reveal the basin formation evolution process.Through stratigraphic comparison,it is found that the hidden faults of Wushan Qian-Gutian Road and Xihong-Hudong Road,which were judged no active in the Holocene,are still active.This provides necessary decision support for urban development..（4）Detailed study of various characteristics of clay and silt sediments in Fuzhou Basin,and found that the geochemical elements,particle size distribution and rare earth elements of the clay layer are similar to the Quaternary alluvial loess and the hard clay of Yangtze River Delta,which shows that the clay layer in Fuzhou Basin may have the same eolian formation characteristics as them,and may be eolian deposition.