Stratigraphic sedimentary evolution of the middle and lower region of the Yongding Rive since MIS7 and its climate evolution since the Neolithic

Based on the core datas of A27 borehole and the characteristics of micropaleontology and sporopollen in the east of Langfang, combined with the AMS¹⁴C datas, analyzed the stratum, established the stratigraphic framework, since the MIS7, in the middle and lower region of the Yongding River. In addition, the stratigraphic and environmental effects under the oxygen isotope staging climate are discussed.The results show that stratigraphy can be divided into 8 sedimentary units(U1~U8), respectively, and have a good correspondence with the marine isotope stage, which correspond to the MIS1~MIS7 and late MIS8, in the Late Quaternary of the middle and lower region of the Yongding River. U1 unit is the lacustrine-valley-floodplain sediment formed during MIS1, U2 unit is the hard clay (the first hard clay) -incised valley-lacustrine sediment formed during MIS2, U3 unit is the lacustrine -valley-floodplain sediment formed during MIS3, U4 unit is massife sediment formed during MIS4 (including the second hard clay, exposed dewatered sediment), U5 unit is lacustrine and branch channel sediment formed during MIS5, U6 unit is incised valley during MIS6 with ephemeral Lake and marsh deposit, U7 unit is a lake-marsh deposit formed by MIS7, U8 is floodplain sediment formed during the late MIS8. It reshaped the sedimentary environment model since MIS7 and defined the geologic time scale in the late Quaternary.It is believed that rivers and lakes are coexisted in the Neolithic period, the lake reached its peak, and peat layer appears in its late era, in the middle and lower reaches of the Yongding River.Until the Shang-Zhou dynasties, the limnetic facies fade away and transform into flood plain facies under the influence of climate change.It can provide an important reference for regional palaeogeographic environment and ecological restoration.