| The estuarine regions,such as deltas,are facing the serious impact of extreme climate events such as inland floods and strom surges caused by global warming and accerating sea level rise.The intensive study of the occurrence and development process of coastal flooding in the delta region and its internal relationship with the succession of Neolithic culture can provide a theoretical basis for predicting the response of future hydrological environment changes in the region to climate and sea level changes and the evolution trend of human-land relationship,and actively response to the possible hazards of these natural disasters.During the mid-Holocene,Majiabang culture,Songze culture,Liangzhu culture,Qianshanyang culture and Guangfulin culture successively developed in the Hangjiahu Plain.The Liangzhu culture was highly developed and people built large-scale water conservancy projects,but it suddenly collapsed about 4500 years ago.Therefore,Hangjiahu Plain is an ideal place to study the changes of hydrological environment and the succession of Neolithic culture.In this study,a sediment core（ZK07）was obtained between the inner and outer walls of Liangzhu Ancient City,and cores ZK06 and ZK08 were collected on the northeast side of Liangzhu Ancient City and the north side of Maoshan site,respectively.To reveal the development process of coastal flooding at the end of Liangzhu culture and explore the response of Neolithic culture,AMS 14C and Optically stimulated luminescence（OSL）dating,grain size,organic carbon and nitrogen,stable carbon isotope,alkaline-earth metals extracted by acetic acid（HAc）of these three sediment cores were analyzed,I also collected previously published data of cores and sites in this area,and sorted out and analyzed their age datas.Main conclusions are obtained as follows:（1）Since the mid-Holocene,the environmental evolution of the C-type basin of Liangzhu Ancient City in the Hangjiahu Plain has successively experienced the intertidal-supertidal-coastal marsh-fluvial alluvial plain environment.During 6400-5600 cal.yr BP,as the ancient Taihu Bay was filled into land,the C-type basin of Liangzhu Ancient City enolved from intertidal to supertidal at about 5500 cal.yr BP.After that,the environment was stable until about 4600 cal.yr BP at the end of Liangzhu culture,and the Liangzhu Ancient city became a brackish swamp again.After about 4300 cal.yr BP,it became a fluvial alluvial plain.The evolution of the above sedimentary environment is mainly controlled by sea level fluctuations.（2）The flourish and collapsed of Liangzhu culture are closely related to environment changes.The formation of freshwater environment in the C-type basin of Liangzhu Ancient City and the middle and north of the Hangjiahu Plain after 5600 cal.yr BP provided the environmental basis for the rapid development of rice farming in the late Songze period,while the collapse of Liangzhu culture was closely related to the serious coastal flooding along the Hangzhou Bay during 4500-4300 cal.yr BP.In the time range of about 200 years,the occurrence of coastal flooding gengrally went through three stages:at first,the increase in local water levels led to the formation of a freshwater marsh;subsequently,salinity intrusions and local water levels increase further induced brackish marsh conditions;finally,the region was inundated by frequently extrame strom surges and river flooding.（3）At the end of Liangzhu culture,the coastal flooding is a response to global climate and sea level changes.At this time,the northern cultural factors appeared in the lower reaches of the Yangtze River,which is consistent with the cultural succession time in the lower reaches of the Yellow River and Huaihe River Basin.It suggests that the abrupt change of regional climate and environment in the late Liangzhu period may led to the prosperity of the Neolithic culture and southward migration of the population in the Haidai cultural area. |
