A Study On The Relationship Between The Environment Changes And Human Activities During The Mid-Late Holocene In Ningfeng Plain

The Yangtze River Delta is one of the most important economic centers in China.The sea level rise caused by global warming has an important impact on the production and life of the region.The study of the Holocene environmental evolution and the relationship between the rise and fall of prehistoric civilization in this region can provide an important theoretical basis for the future economic development of the Yangtze River Delta and the study of human-land relationship.Xiawangdu and Hejia sites in Ningfeng Plain,south of Hangzhou Bay,Yangtze River Delta,are important sites of the late Hemudu Culture.In this study,the pollen analysis of the profile samples in the marginal area of the site,together with the analysis of charcoal,diatom and geochemical elements,combined with the AMS14C dating data and the stratigraphic chronological framework determined by archaeological and cultural stratification.It reveals the changes of sea level,environmental evolution and human activities in the middle and late Holocene in Ningfeng Plain.The results of palynology showed that the main type of vegetation in the site area is mixed evergreen broad-leaved and deciduous broad-leaved forests during Holocene.The warm and humid climate characterized by vegetation created conditions for the settlement of the ancestors of Hemudu.During the third cultural period of Hemudu(6000-5000 BP),wet herbs and algae showed that the area had a certain area of water and agricultural activities showed a trend of strengthening.The presence of Poaceae pollen grains with particle size>37 micron indicates that agricultural activities may occur in swamp environments affected by brackish water characterized by Spiniferitaceae and Amaranthaceae/Chenopodiaceae.In the late period of the third period of Hemudu culture,the comparative analysis of marine facies indexes such as sporopollen,diatom and geochemical elements shows that there is a certain degree of sea water influence in the study area,which may be the main reason for the abandonment of Xiawangdu site.The proportion of herbaceous plants(average more than 60%)was higher than that of shrubs(less than 30%)in the intermittent layer between the third and fourth cultures of Hemudu(6000-5000 BP),and the proportion of ferns dominated by Polypodiaceae increased.The palynological assemblage shows that the forest vegetation landscape of the mixed evergreen deciduous broad-leaved forest in the study area at this time,and there are a certain number of ferns under the forest,which also reflects the relatively warm and humid climate conditions of the Middle and Late Holocene in this area.During the four cultural periods of Hemudu,the Spiniferitaceae gradually decreased and disappeared,reflecting that the influence of sea water began to weaken and gradually disappeared during this period.From the fourth stage of Hemudu culture to Liangzhu culture,the pollen percentages of trees and shrubs decreased sharply,while the pollen percentages of herbs,especially Poaceae,increased sharply.The palynological assemblage shows that the ancestors' agricultural activities should have occupied an important position in this period.In Shang and Zhou Dynasties(about 1600 BC-1046 BC)and Song and Yuan Dynasties(960 AD-1386 AD),Brassicaceae(mean 6.1%)and Taraxacum(mean 4.6%)which were closely related to human activities increased,indicating that the impact of human activities on local vegetation was further strengthened.In addition,the analysis of the frequency distribution of pollen grain size in different strata of Xiawangdu site shows that rice farming was developed in the early stage of Hemudu culture(mainly between 27 and 34 microns),and rice farming was further expanded in Liangzhu culture period(the proportion of Poaceae with grain size between 34 and 39 ?m in size increased to 40%).According to the previous research results,a certain scale of rice planting paddy field has been formed in Liangzhu culture period in this area.