Rise And Fall Of Paleoculture: The Eco-geological Study Of Cultural Layers In Yuchisi Site Of Mengcheng County

Sediments of archaeological sites are good materials to study ancient human activities and its corresponding environment.And they are playing an increasingly important role in the study of ancient human activities,ancient social development and subrogation,paleo-climatic and paleo-environmental changes and their impacts on human activities,etc.,due to its low dependence on archaeological remains and temporal continuity.The Yuchisi Site,which is in Mengcheng county of Anhui Province,central south of the Huaibei Plain,is an important gathering site for people between Yellow River and Huaihe River during the Neolithic period.A sediment profile named as YC1 was collected in Yuchisi Site,and analysis,including grain size,pollen-spore assemblage, total organic carbon and its isotope,amino acid,geochemical elements and lead isotope were performed on the samples.Combined with the results of traditional archaeological studies in Yuchisi Site,different human activities,climate changes,as well as their relationship were studied under the guideline of theories and methods of sedimentology,palynology,geology,geochemistry,paleoecotogy.Main conclusions are listed as following:(1) Based on the results of cluster analysis,principle component analysis and correlation analysis,we found that the variation of P,TOC,Cu,Ca,Mn,Zn,Sr,Na, Ni and soluble Sr in the cultural layers were conducted by the human activities.The Factorl extracted by principle component analysis could represent the population fluctuation during cultural periods,from 5050 to 4000 cal.yr.BR The result of Factorl shows,cultural subrogation(including the subrogation in interior Dawenkou Culture in Yuchisi Site) was well corresponding to decreased population in Yuchisi Site;since the beginning of Longshan Culture at 4400 cal.yr.BP,the population went on decreasing,until the end of it in Yuchisi Site.(2) The statistical results indicated that the variation of Al,Fe,Mg,Si,K and Ti in cultural layers was mainly affected by climate,and the Factor2 extracted by principle component analysis was a good index of Asian Summer Monsoon,which confirmed by the grain size and pollen analysis.From 5050 to 4400 cal.yr.BP,the Asian Summer Monsoon was relatively stable and strong,and the climate was warmer and more humid;From 4400 to 4000 cal.yr.BP,Asian Summer Monsoon turned weaker,and the climate was cooler and drier.The climatic event happened at 4400 cal.yr.BP,indicated the climate of Yuchisi Site turned from warm and humid to cool and dry.(3) The human impact factors should be considered when we study the climate changes on archaeological sediments.We should avoid to use the common proxies from Quaternary Geology directly,but select the proxies less influenced by human activity to reconstruct the paleo-climate and paleo-environment correctly.In this study, we didn't use the proxies,such as Ca,Sr,Na,Mn,which were largely affected by human activities in Yuchisi Site,but selected Al,Fe,Mg,Si,K and Ti to reconstruct the paleo-climate.The results are quite consistent with those by other methods,and have good relationship with the regional climate change.(4) The population of Yuchisi Site had good correlation with the summer monsoon:the stronger the summer monsoon,the larger the population,and vice versa. The primitive social development had close linkage with the climate,and the bad climatic condition was one of the most important reasons which led to the end of primitive culture.The results of population,amino acid and pollen-spore analysis, indicated that the Longshan Culture of Yuchisi Site was not developed from local Dawenkou Culture.(5) Stable carbon isotope compositions in organic matters showed that agriculture of Yuchisi Site was the mix farming of C₃ plant(rice) and C₄ plant(millet).From the beginning of Dawenkou Culture to the mid-late Longshan Culture,the proportion of cultivated millet slowly increased.But at the end of Longshan Culture,the proportion of cultivated rice obviously increased.The large reduction of agricultural production which may be led by the cooler and drier climate,might be one important reason for the end of Longshan Culture in Yuchisi Site.(6) Mercury variation in the YC1 profile was mainly affected by atmospheric deposit.Mercury accumulation rate was low before 4550 cal.yr.BP,and was mainly affected by climate:the cooler the climate,the higher the mercury accumulation rate in the profile.From 4530 to 4000 cal.yr.BP,Mercury accumulation rate was high,and the climate was not the dominate factor any more,but the ancient human activity was. The shift of mercury accumulation rate happened at about 4500 cal.yr.BP,indicating the coming of Chalcolithic Period in China.The results of lead isotope composition also showed that the lead in the cultural layers of Yuchisi Site likely came from the copper mining from South China(Yunnan,Sichuan,Hubei,Hunan or Guangdong Province) and its smelting,which was corresponding to the source of bronze material of early Shang and Zhou Dynasties.It also indicated the shift of Hg at about 4500 cal.yr.BP in study site was correlated to the development of metallurgical civilization.Based on the analysis of ecological and environmental indexes,and the use of statistical methods,this paper reconstructed the population variation of paleocultural periods of Yuchisi Site,discussed the climate change and the relationship between climate and cultural development,and suggested how to select climatic proxy when studying the archaeological sediments which may be helpful in the future study of environmental archaeology.In addition,the study of heavy metal transported by atmosphere provided natural evidence for the entrance of Chalcolithic Period in China, which was only proved by the statistical result of archaeological relics before,and this finding has enriched our understanding of the developmental history of Chinese metallurgic civilization.The eco-geological methods will play an more and more important roles in the future archaeological research.