Palynological Study Of Ning Shao Plain And Paleoenvironmental Significance Since Late Pleistocene

This study aims to study the paleoenvironment history of Ningshao Plain andYangtze Delta since the Late Pleistocene. Two sediments were retrieved from the tworegions respectively. One core with length of 45.2 m, was taken from Luojiang, 3 kmto north of Hemudu archaeological site on Ningshao Plain and the other core withlength of 22.9 m, was taken from Songze, 1 km to Songze archaeological site on thelower Yangtze delta. Based on the analyses of multi-proxies of environmental change,namely pollen, dinoflagellate cysts, freshwater algae, magnetic susceptibility, particlesize and organic carbon stable isotope, in combination with evidences fromarchaeological excavations and historical documents, the paleovegetation,paleoclimate, paleoenvironment since Marine Isotope Stages 3(MIS 3) and theinteractions between humans and the environment were discussed.Mixed broadleaved evergreen-deciduous forests developing during the MIS 3suggested a warm, wet climate. Climate of later MIS 3 turned to be cool indicated bythe expansion of conifers.Onset of the Last Glacial Maximum(LGM) was associated with sparsevegetation indicative of the coolest conditions. The cool was interrupted occasionallyby warm, wet conditions marked by mixed broadleaved evergreen-deciduous forestsin Ningshao Plain and mixed broadleaved evergreen-deciduous forests and meadowin the Yangtze Delta.From 13715 to 7626 a B.P., a warm, wet climate fostered the development ofmixed broadleaved evergreen-deciduous forests to grow on surrounding hills anduplands. A large expansion of subtropical evergreen-deciduous broadleaved forestsfrom 7626 to 4957 a B.E represented the mid-Holocene "hypsithermal". From 4957 to 4393 a B.P. the dominance of conifers and the reduction in broadleavedevergreen trees suggest cool, dry conditions corresponding to a Neoglacial periodelsewhere. There are alternate warm and cool climate fluctuations during all theHolocene time, but the extent of the climate fluctuations were not strong enough tochange the vegetation thoroughly. The uppermost hard clay that widely spreads in the late Quaternary strata of theYangtze Delta and Ningshao plain deposited during the LGM. High content ofConcentricystes shows that the formation of the hard clays was influenced by waterand the hard clays should be freshwaters deposits. This was different obviously fromthe Xiashu Loess on the hilly areas of the western Yangtze Delta.During 13715 to 6040 a B.P., 6040 to 4957 a B.P. and 4957 to 4393 a B.P. thesite where core Hemudu lay was influenced by sea water 3 times. The lake developedafter the LGM. It had been a saltwater lagoon since 13715 to 4393 a B.R and turnedto be fresh water lake after 4393 a B.P.. Swampland developed about 4350 a B.P.ago and the water of the lake dried up drastically after 1050 a B.R. Soil here wassalted seriously since MIS 3.There exists close correlation between human activities and the environmentalchanges. Environment changes play an important role in the development of Neolithicculture. Human should harmonize with the environment. The onset of themid-Holocene "hypsithermal" provided favourable conditions for the ancients tomultiply around Hemudu archaeological site. Hemudu archaeological site wasinundated by the flood about 5000 a B.P.. The durative transgression combined bythe change of Yaojiang's course salted the soil seriously and reduced the output of therice. About 5000 a B.E people had to abandoned this area.The increasing of Gramineae content shows that with the range expanding andintensity increasing of human activity, human activity has become one of theimportant factors to affect the environment.