Research On The Environmental Background Between The Establishment Of The Hemudu Site And The Early Cultural Discontinuity

The core theme of Past Global Changes is to comprehend the interplay of human-climate-ecosystem of the past and to extract information for understanding the present and predicting the future.In the context of gobal warming,sea level changes and extreme climatic environment events had greatly affected the human beings and ecosystem.Facing changeable climate environment,human are in dire need of seeking more solutions from past human-environment relationship.The Yangtze Delta is one of the key areas for Neolithic culture and early rice domestication,where near the East China Sea.The Yangtze Delta's geomorphic evolution during the Holocen was controlled by sea level changes,which also had a significant effect both on the origin and development of Neolithic culture and rice cultivation agriculture in this region.What's more,because of the low elevation and a dense network of waterways,the Yangtze Delta was vulnerable to extreme climate and environment events,and can change the production and life style of prehistoric humans,then the develop trends and process of Neolithic culture,eventually.Thus,to explore the evolution of regional human-environment relationship,it is of great significance to clarify the Yangtze Delta's geomorphic evolution and extreme climate environment events.The Hemudu site is one of the most typical Neolithic site in the Yangtze Delta,which is rich in rice remains.However,the environment background of the Hemudu site and the full reason of Hemudu culture were still remained controversial,especially the full reason which includes climate change,transgression and flooding events.Consequently,it makes great importance to understand the response to environment changes of human activities through reconstructing the high-resolution geomorphic evolution and exploring the influence of extreme climate environment events to Hemudu site since Holocene.Based on a series of sedimentary cores which were drilled from Ningbo-Shaoxing plain,a basic understanding of the sedimentary system of this region was obtained.Then two cores from Hemudu site which named HMD 1601 and HMD 1602 were applied to fine analyses.According to the results of datasets,including sedimentary facies,AMS14C dating,particle size,element abundance and microfossil assemblage et al,five results were got:1)before 7800 cal a BP,the Hemudu site had been affected by seawater and may be a bayside environment.2)7800-7000 cal a B?During this period when sea level rose rapidly,the Hemudu site was completely submerged by the seawater,which indicates that this region may be in an estuary environment where salty-fresh water meets.At this time,only the low coastal hills and islands cradled limited number of the Hemudu ancestors with characteristic "marine".3)Geomorphic evolution changed dramatically at 7000 cal a BP.Sea level rise decelerated prominently,while sediments supply in the drainage remained high value,the combination of which led to land formation.Thus,the Hemudu site was established after the vast living space and fertile soil attracted the Hemudu ancestors to migrate to this region.4)7000?6500 cal a BP.This research argues that the Hemudu site was in a coastal freshwater marsh environment during this period,when the first cultural layer of Hemudu culture was formed and the terrestrial nature of the sendimentary environment was increased.The superior environmental conditions and abundant resources promoted the vigorous development of Hemudu culture in this period.The study area is also a frequent area where the Holocene extreme climatical-environmental events occurrenced.Analysis results of sedimentary facies,particle size,diatom and other indicators show that,the sand layer at the bottom of the neritic layer and the sand layer at the top of the cultural layer,which formed in 7400 cal a BP and 6600 cal a BP respectively,are all flood sediments.The diatom concentration of these two sand layers are significantly reduced,and their Zr/Rb ratio are shown as a peak.What's more,there are significant differences between the data of their grain size and the adjacent layers'.This study speculates that,during the period of around 7400 cal a BP and 6600 cal a BP,the extreme climatical-environmental events in the Hemudu area occurred frequently.Especially the storm and its flooding occurred at around 6600 cal a BP may be the main cause of the early culture disruption in the Hemudu site.The research indicates that the establishment and development of Hemudu Site is constrained by the natural environment.The evolution of geomorphic under sea level control and the impact of extreme climatical-environmental events are important factors in the development of Hemudu culture.