Stratigraphic Framework And Environmental Evolution Since The Late Pleistocene In The East China Sea Shelf

Based on the theory of sequence stratigraphy,seismic stratigraphy and sedimentology,this research uses the regional geological data,drilling data and shallow stratigraphic data,to classify the stratigraphic sequence of the late Pleistocene in the East China Sea shelf.We are going to describe the characteristics of the seismic facies in the shallow stratigraphic section of the study area and the sedimentary features of the SFK-1 hole,furthermore,discuss and analyze the influence and control factors of the sea level change process and environmental evolution.According to the analysis of the reflection structure,wave group characteristics and formation reflection termination mode of shallow stratigraphic seismic profiles in the study area,I identified 14 seismic reflection interfaces and divided 13 seismic reflection units.From top to bottom,the reflection interfaces are: D0,D1-1,D1-2,D1,D1`,D2,D3,D4,D5-1,D5-2,D6,D7 and D8.The seismic reflection units are U1,U2,U3,U4,U5,U6,U7,U8,U9,U10,U11,U12 and U13.According to the characteristics of seismic reflection unit,combined with the lithology of SFK-1 well,the stratigraphic sequence is divided in I,II,III and IV,four groups with 8 subsequence sequences in total.Sequence I was composed of U1-U5,on behalf of the strata from Last Glacial Maximum to present;sequence II was composed of U6-U7,on behalf of the strata from the middle and late interglacial strata of the last glacial period to Last Glacial Maximum;sequence III was composed of U8-U11,on behalf of the strata in Interglacial period of the last glacial period;sequence IV was composed of U12-U13,on behalf of the strata in the middle and late stage of the interglacial period in Late Pleistocene.The main characteristics of the late Quaternary strata in the study area are the interactive development of marine strata and continental strata.According to the stratigraphic sequence,there have been four periods of transgressive regression in the East China Sea shelf since the late interglacial stage of Late Pleistocene,due to the change of climate periods,which correspond to sequence I to IV respectively.Each sequence period is further divided into a set of continental sequence and a marine sequence.The paleo channel is widely developed in the continental strata,and the tidal sand ridges are widely developed in the marine strata.The development rules of the ancient river channel and the tidal sand ridge may be positively related to the thickness of the stratum.The bedrock and shallow gas in the study area are mainly found around islands or nearshore areas in west and south of the study areas.The evolution of sedimentary environment of the East China Sea shelf since late Pleistocene has been further conjectured by comparing the distribution rules and changes of strata and special geological bodies.The evolution process of the marine regression environment since the late Pleistocene in the East China Sea shelf has been explained in detail.