Environmental Evolution Revealed By Grain Size And Sporopollen In The Yudaokou Area Since 8000 A B.P.

In recent years,due to the gradual deterioration of the global environment,the study of the earth's environment is imminent.Holocene is the period of human survival.It is great significance to study the environmental changes in Holocene for human beings to predict the future climate change.The Bashang area,as a typical transitional zone between agriculture and animal husbandry in northern China,is great significance for the study of Holocene environmental changes in northern China.The Bashang Yudaokou area belongs to a fragile eco-environmental zone that is very sensitive for climate change.It is great significance to understand the climate change background in this area.In this paper,the environment of Yudaokou bashang-area is reconstructed by grain size and pollen and spore since8000a B.P..The chronological time was established by five AMS¹⁴C dating.The relationship between human activities and the environment was discussed.Environmental changes can be divided into three stages since 8000 a B.P.in the Yudaokou area:Part One:(8000-6100a B.P.),at this stage the strong sandstorm activities and low vegetation coverage indicate climate drought.The large number of warm-loving pollen indicates a warm climate.The environment during this stage is stable,It may be that the environment has led to the development of agriculture.Part Two:(6100-1700a B.P.),During this stage,the grain size indicates that the energy is small,the dust is farther from the source area,and the coarse matter is reduced.The large number of pollen concentration indicates a warm wet climate.The warm wet climate is suitable for human survival.The Environmental changes can be divided in to two sub-stage.According to the archaeological research from 6100 to 3700a B.P.is the ancient agricultural civilization development period,In the second sub-stage(3700-1700a B.P.),the climate is drier than previous sub stage and rapidly towards drought.Part Three:(1700-0a B.P.)sand activity is strong,the sediment grain size significantly larger,vegetation is poorer.Moreover,the drought degree in the early stage(1700-900a B.P.)is stronger than that in the later stage(900-0a B.P.)so far.A large amount of evidence shows that the nomads in Bashang area began to expand southward during this period.Some cold event like that 4400a B.P.,3800-3500a B.P.3000-2800a B.P.and 1200a B.P.are recorded in bashang Area.