Environmental Evolution And Human Activities In The Gonghe Basin During The Mid Late Holocene ——A Case Study Of Nankanyan Site

The northeastern Tibetan Plateau is an important channel for the expansion of prehistoric humans to the hinterland of the plateau,and it is also the frontier area for the cross cultural fusion among the various cultures on the plateau as well as the surrounding areas.Since the last glacial,diverse prehistoric civilizations had been emerged in many areas.However,cold and low oxygen environment on the QinghaiTibetan Plateau had hindered the expansion of human to the area,so the adaptation and survival strategy of ancient human beings on the Qinghai-Tibetan Plateau has attracted much attention in academia.At present,the studies are mainly focused on the areas like Hehuang Valley and Qinghai Lake Basin,while there are only few systematic studies on environmental evolution and human activities during the middle to late Holocene,especially during the Zongri Culture period in the Gonghe Basin.Nankanyan Site(NKY)is located in a closed river valley in the southwest of the Gonghe Basin.Through systematic field investigation at the site,stone products,pottery shred,animal bones and other environmental samples were collected.OSL dating,carbon debris,magnetic susceptibility,color,pollen,stone products,pottery shred,animal bones and other indicators were analyzed for understanding of the sequence of human activity in the area and their means of survival strategy.This paper presents a full aspect of the environmental background and the driving mechanism of human activities in the basin,and based on the existing archaeological data,it further discusses the relationship between the culture and environmental evolution in valley areas at different altitudes in Qinghai Tibetan Plateau.In precise,this paper draws the following main conclusions :(1)A total of 213 stone products were discovered at the Nankan site,including14 fine stone cores,12 fine stone leaves,15 stone leaves,6 stone tools,and 5 grinding stones.According to the typology of the stone tools,the site is mostly composed of fine stone tools,with few milled stone tools.There are 393 pieces of pottery shreds,of which33 pieces are Majiayao pottery,2 pieces are Banshan pottery and 358 pieces are Zongri pottery.According to the number of pottery pieces,the site is dominated by Zongri relics,and there are a small number of early and middle Majiayao cultural relics.According to the Majiayao type and Banshan type pottery pieces,the time span of the site is at least 5.3 ? 4.3 ka BP.Together with comprehensive analysis of the magnetic susceptibility,chromaticity,charcoal,animal bones of the site,it was concluded that there were three different period of prehistoric human activities in the area since the Holocene.A group of hunter and gatherer existed during 8 ? 6 ka BP,A group of Neolithic people existed during 5.2 ? 4.1 ka BP,and another group existed during the Bronze age around 4.3 ? 2.6 ka BP.It is extrapolated that this is a valley basin with rich cultural attributes and complete prehistoric cultural sequence.(2)According to the pollen results of the NKY profile,the evolution process of prehistoric vegetation along the Nankan area is roughly as follows: During the 13.7 ?10.5 ka BP stage,arbor pollen content was dominant,and spruce ranked the highest,indicating a forest expansion from the last glacial period to the early Holocene.During the 10.5 ? 4.7 ka BP stage,arbor pollen decreased,herb pollen content increased dramatically,indicating a gradual deforestation and expansion of grassland.At the same time,the pollen content of hygrophilous vegetation increased,indicating a development of wetland in the area.During the 4.7 ? 0.8 ka BP stage,arbor pollen content was low and herbs became dominant.Forests were still developed on the shady slopes in mountainous areas with high altitude,and the alpine meadow dominated by sedge expanded rapidly.Compared with previous studies,it is found that the vegetation evolution in the northeastern Tibetan Plateau has its own characteristics since the last glacial period.The main reason is that the closure of the basin and the relatively low altitude of area aggravated the thermal effect of the plateau,and the sinking airflow increases.With same precipitation,the evaporation of the basin increases thus the relative humidity is low in the basin.(3)Comprehensive analysis of the remains of ancient human activities at the site,during 8 ? 6 ka BP,hunting was the main mode of ancient human livelihood.With the climatic environment improvement,the Neolithic culture in the middle and lower reaches of the Yellow River began to spread to the northeast of the Qinghai-Tibet Plateau at about 5.5 ka BP.With the influence of the Yangshao culture and Majiayao culture,at the Gonghe Basin formed Zongri remain,a Neolithic remain with a plateau characteristics.The major mode of production was hunting and agriculture.At the same time,the study of animal archaeology shows that the wild animal resources of the site occupied an absolute advantage,and there was also evidence of consuming fish resources in the Yellow River,indicating a rich food resource in the area.A small proportion of sheep,goats,cattle and other bones revealed that the ancestors of Zongri might have involved in primary animal domestication and low intensity of animal husbandry,indicating primitive stage of animal domestication and husbandry.