Holocene Stratigraphic Records And The Drivers For Rise And Fall Of Shell Mound Culture At The Jingtoushan Site,Yaojiang Valley Plain

The study of human-environment relationship is the key content of environmental archaeology.The coastal zone is densely populated and economically developed,but is facing a series of ecological and environmental problems such as storm surge intensification and seawater intrusion under the background of global warming and sea level rise.These will seriously affect and restrict the sustainable development of society and economy in the coastal zone.However,the coastal lowlands also faced environmental disasters in the prehistoric social stage.The Ningshao Plain,one of the birthplaces of Neolithic culture,is located in the coastal lowland of the south bank of Hangzhou Bay,eastern China.A large number of archaeological records in this area show that the emergence of natural deposits layers between cultural layers is associated with the catastrophic events caused by rising sea level,but ancient people have played a subjective initiative to adapt to environmental changes.Therefore,the study of the Neolithic site strata in the Ningshao Plain is helpful to understand the relative sea level changes and sedimentary environment evolution at the sites during the Holocene,to provide a good case support for exploring the connotation of human-environment relationship in prehistoric society.In this study,three profiles of the Jingtoushan site which is located in Yaojiang Valley Plain are taken as the research project,and they were carried out the analysis of chronology,sedimentology,geochemistry and microfossil.At the same time,the quantitative statistic of bioturbation had carried out in core CC with abundant biogenic traces,and several relative sea level curves were also collected and compared.Based on the high-precision AMS¹⁴C age results,we reconstructed the early to middle Holocene relative sea level change curves in the Hangzhou Bay,restored the sedimentary environment evolution of the Jingtoushan site under the control of sea level fluctuations,and discussed the rise and fall mechanism of the shell mound culture at the Jingtoushan site.The main progress and conclusions of the paper are as follows:（1）The strata of the three profiles at the Jingtoushan site showed different characteristics of sedimentary environment in the same period due to differences in paleotopography.The sedimentary environment of T609N profile evolved from supratidal zone to intertidal zone at 8250 cal yr BP,and become upper tidal flat at8010 cal yr BP.The T509S profile was always in supratidal environment from 8105 to7940 cal yr BP,and the land use at the location changed at about 8000 cal yr BP.The T309N profile belonged to the paleosol and terrestrial freshwater environment between 8020 and 7650 cal yr BP,which evolved into an intertidal environment after7650 cal yr BP.（2）The relative sea level changes at the Jingtoushan site during 8300～7650 cal yr BP experienced three stages:slow rise,accelerated rise and slow rise.Combined and compared with the previous results,it is found that there are two rapid rising events along the Hangzhou Bay between 9000 and 6000 cal yr BP,which occur in8500～8300 cal yr BP and 7600～7200 cal yr BP respectively,which were consistent with the global sea level change.（3）The rise and fall of shell mound culture at the Jingtoushan site is closely related to environmental changes and human activities.At 8300 cal yr BP,the rate of sea level rise was relatively declining,and abundant terrestrial and aquatic resources attracted ancient people to settle here.A large number of shells were collected and eaten resulting in the rise of shell mound accumulation.At about 7890 cal yr BP,quantitative statistics of bioturbation in core CC reflected the reduction of intertidal resources in the palaeobay at this time and the size became smaller caused by fishing pressure,which corresponds to the rate of shell mound accumulation decreased significantly in the late cultural period.Meanwhile,early rice agriculture was developed during the settlement,so it is speculated that the Jingtoushan residents used this to obtain a stable food source and gradually gave up collecting shellfish and other aquatic resources,resulting in the stagnation of shell mound accumulation.After 7650cal yr BP,the relative sea level rose again,which seriously threatened human production and life.Finally,the Jingtoushan people were forced to abandon the residence,and the cultural layer is buried by marine sedimentation.