Environment Changes revealed by grain size from Yudaokou in Bashang area since 8000 a B.P.

Bashang Yudaokou area belongs to a fragile eco-environmental zone that is very sensitive to climate change. It is of great significance to understand the climate change background in this area. Grain size is sensitive to climate and environment changes. The results of grain size can infer sediment formation and environment conditions. The chronological was established by five AMS¹⁴C dating. The grain size samples were collected from 2.8 m section to reconstruct environment variability since 8 000 a B.P. The chronology of the section was determined based on five accelerator mass spectrometry (AMS) ¹⁴C dating. The studied section encompasses the periods of 8 000~180 a B.P.. Environmental changes can be divided into three stages since 8 000 a B.P. in the Yudaokou area:(1)8 000~6 100 a B.P., the grain size indicates that the power is greater in this period, the dust is closer to the source area, the wind and sand activity is stronger. It is estimated that the climate is dry during this period and the regional vegetation is poor.(2)6 100 a B.P.~1 700 a B.P..At 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. It is estimated that the climate is humid during this period, the regional vegetation is better, and the wind and sand activity is weakened.(3)1 700 a B.P.~So far, the energy is relatively large, and the dust is relatively close to the source area. It is estimated that the climate is dry during this period, the regional vegetation is poor, and the sandstorm activity is strong.