Study On Environmental Change From 200 To 80K A B.P. In Hanyuan Sichuan Province From Lacustrine Deposits Record

Based on the lithostratigraphic and geomorphology, sedimentlogy methods, this paper deals with the lacustrine deposits from the section in Baiyu village Dashu town of Hanyuan, Sichuan province. This section could be divided into eight depositional stages, including the three climatic cycles, so the depositional sequence of the Dashu—Baiyu section has been established.According to the grain-size frequency distribution analysis, the Dashu—Baiyu section is composed of clay, silt and fine sand, the median size value is 18.12μm. The grain-size frequency curves show the bimodal feature without coarse tail; compared with the grain-size characteristics and parameters of Daihai lake sediments, Xifeng loess and Xuancheng fluvial deposits, the depositional features in Dashu—Baiyu section are essentially similar to Daihai lake, but different from the other two sites, so the Dashu—Baiyu section was deposited in a lake environment.Through the high-resolution chronostratigraphic and depositional analysis, the resolution in the Dashu—Baiyu section could basically reach 1cm/100a. Deposition period is from 206.74 KaBP to 80.55 KaBP, i.e., from the late Middle Pleistocene to middle Late Pleistocene. Based on the interpolation and extrapolation methods, the high-resolution chronostratigraphic sequence is set up in the Dashu—Baiyu section.The median grain size value and magnetic susceptibility in the Dashu-Baiyu section show a positive correlation, but a negative correlation with the color L. The higher median grain-size value, magnetic susceptibility value and lower L value indicate a warm-humid climate with rich precipitation; the lower median grain size value and magnetic susceptibility, higher L values indicate a warm or cold dry climate with fewer precipitation.Within the period from 200 KaBP to 80KaBP, the paleoclimate in Hanyuan, Sichuan could be divided into three periods and eight stages: (1) the terminal period of the last but one interglacial Age (206.74 ~ 190.32 ka BP),dominated by warm, arid climate; (2) the last but one Ice Age (190.32 ~ 133.00 KaBP), dominated by warm-cold, humid climate, intercalated with a cold drier period; (3) the terminal interglacial age (133.00 ~ 80.55 ka BP) ,characterized by the large-scale fluctuations between the warm humid climate and warm dry climate, dominated by the warm and wet climate.The precipitation in Hanyuan was mainly controlled by the change of the Indian monsoon intensity under the influence of solar radiation. As for the temperature change, it is identical to the global climate. But the depositional record in Hanyuan is not fully coincident with the global change, reflecting the special regional characteristics of climate and environment.