Study On The Environmental Evolution And Prehistoric Cultures In Gonghe Basin And Gaomiaobasin During Mid-holocene

The environmental change and prehistoric human activities on the Qinghai Tibet Plateau is a hot topic in academic circles.Analyzing the intrinsic relationship between environmental evolution and cultural change in the past,helps us understand human's role in adapting to and changing the natural ecosystem,and the reverse effect of environmental change on human activities.This paper selects Gengahai Lake?Gonghe Basin,Northeastern Tibetan Plateau?and Dianziping Site?Hehuang Valley,Northeastern Tibetan Plateau?as the research objects.Based on the modern climatic data,the topsoil sporopollen,and the fossil sporopollen data of Gengahai,the precipitation change process in the middle Holocene was reconstructed applying the modern analogy method.In specific,the research includes-analyzing on the grain size,susceptibility,sporopollen,and carbon chips(AMS¹⁴C dating on five carbon chip samples)of the Dianziping Section?around4000-3500 aBP?;restoring the environmental conditions of Gaomiao Basin around3900 aBP with the indexes of high precision age and high resolution environmental indicators of DZP Site;discussing on the characteristics of the precipitation changes since the middle Holocene,the differences in the impact of prehistoric human production and living,and the information of vegetation environment and prehistoric human activities during the transition period of regional precipitation from humid to drought around 3900 aBP.Regional precipitation results show:a typical humid period in 6300⁵000 aBP,with 88 mm higher precipitation than modern time and the introduction of primitive millet farming into the region;a sub-humid period in 5000³900 aBP,with 65mm higher and the rapid spreading of millet farming;a declining period in 3900²900aBP,with 14 mm lower and a production mode shift to farming&husbandry coexistence;a modern-like period since 2900 aBP,with the formation of a stable agricultural and pastoral economy structure.3900 aBP is an important node of the regional precipitation change since the middle Holocene.To understand the cold-warm,dry-wet environmental characteristics of northeastern Tibet Plateau at then,the research also puts emphasis on the sporopollen analysis of DZP Site.Fossil pollen analysis results show:Gaomiao Basin is coniferous and broad-leaved mixed forest vegetation in the precipitation transition period?4050-3500 aBP?,with a cool and humid climate.Gramineae is the highest in pollen content,consists mainly of Pinus,spruce and Betula.The average content of Pinus is 62.6%and most samples are above 55%,and Spruce is 6%and 5.4%.Herbaceous pollen mainly consists of Artemisia,chenopaceae,Compositae,Gramineae,and dandelion.The average content of Artemisia is 10%and most samples are above 4.3%,and chenopaceae is 10.7%and 7.1%.Shrubs are mainly Ephedras,with the average content of 1.4%and most samples are above 0.7%.Human activities are frequent during 3900-3700 aBP,with the bursts of local and regional fire relics.A sudden increase in the value of magnetic susceptibility and effective humidity,and a position on the cultural layer of Qijia Culture,shows a possibility of ancient human beings interference with the magnetic material of the paleosol.A higher than 20%Gramineae pollen content suggests that the plants are human cultivated.Gramineae pollen content of DZP Section reaches the highest?28.9%?at 3800 aBP.Sediment information,cultural layer,pottery pieces and other artifacts show that there were human settlements in DZP,and they reclaimed farmland and grew crops.Research on Liuwan Cemetery and Gaomiao Basin shows that people in Qijia Culture Age used pine and cypress to build settlements and to make funeral utensils.The production mode in that time was mainly in farming.The rich coniferous and broad-leaved mixed forests around the Site provided enough timber resources for people.