Research On Environmental Evolution Of Jingbian Area Since Holocene

Jingbian is located in the transition zone between the Mu Us Desert and the Loess Plateau.It is the tail region of the East Asian monsoon and is sensitive to climate change.The black loess soil layer of Sandaogou section records the climate change in Jingbian area since the Holocene.The analysis of the granularity,magnetic susceptibility and pollen and other proxy indicators of the section reveals that the sandaogou section records the Jingbian area since the Holocene.Climate change and centennial-scale climate events,comparing the?¹⁸O content of Donggedong,the water vapor model in the core area of the westerly and the 30°N summer solar radiation,explore the driving mechanism of Holocene climate change.The following conclusions are obtained:(1)According to the dating results,the sandaogou palaeosoil profile began to deposit at 8.96 ka,all formed in the Holocene,recording the Holocene 8.96?1.74 ka climate evolution.(2)Through the analysis of the particle size test results of Sandaogou paleosol profile,the lithology of Sandaogou paleosol layer in Jingbian is clayey silt,and the particle size is larger than that of typical loess.The Paterson parametric end-member model is used to separate the particle size data of the Sandaogou profile into three components with environmental significance.EM1(7.962?m)is the long-distance background dust carried by the westerly wind,EM2(28.251?m)is the fine silt particles carried by the monsoon circulation,and EM3(44.774?m)is the near source material brought by the northwest winter monsoon.(3)Through the analysis of the magnetic susceptibility(quality)test results of the Sandaogou ancient soil profile,the correlation analysis between the magnetic susceptibility and the clay content(?4?m)shows that the magnetic susceptibility and the clay content are significantly positively correlated.Therefore,the level of the magnetic susceptibility is reflected The strength of the summer monsoon.Based on previous studies on the quantitative relationship between magnetic susceptibility and temperature and precipitation,the magnetic susceptibility-temperature model and magnetic susceptibility-precipitation model were selected to reconstruct the paleo-temperature and paleo-precipitation of the Sandaogou section.The Holocene climate change in Jingbian area presents a trend of cold-dry-warm-wet-cold-dry.The maximum annual average temperature is about 11.45?and the lowest is about 4.89?;the maximum precipitation is about 561.23mm and the minimum is about 380.161mm.(4)Through the processing and analysis of pollen samples,12 species of tree pollen,34 species of herb and shrub pollen,and 11 species of fern spores were identified.According to the cluster analysis of CONISS,seven sporopollen vegetation zones are divided.According to the geological age from old to new,they are Pinus-Artemisia-Selaginella sinensis sporopollen assemblage zone,Artemisia-chenopodiaceae-Grass sporopollen assemblage zone,Artemisia-Chenopodiaceae-Compositae-Selaginella combination zone,Artemisia-Chenopodiaceae-Selaginella sinensis combination zone,Artemisia-Chenopodiaceae-Compositae-Selaginella sinensis combination zone,Chenopodiaceae-Artemisia-Compositae Combination zone and Artemisia-Chenopodiaceae-Compositae-Taraxacum mongolicum combination zone.(5)Through the analysis of particle size,magnetic susceptibility and pollen index of Sandaogou section,the Holocene of Sandaogou section is divided into Early Holocene(8.9?7.8ka BP),Middle Holocene(7.8?3.0ka BP)and Late Holocene(3.0?1.7ka)Three stages.According to the change of particle size and pollen A/C value curve,five cold events in the Holocene were judged:8.2ka cold event,7.8ka cold event,5.8ka cold event,4.2ka cold event and 2.8ka cold event.Comparing the temperature-precipitation curve of the Sandaogou section reconstructed by the magnetic susceptibility and the?¹⁸O content of Dongge Cave,the water vapor model curve in the core area of the westerly wind and the 30°N summer solar radiation,it is found that the climate of the Sandaogou section is mainly affected by the East Asian monsoon and westerly in the Early Middle Holocene.In the mid-late Holocene,the climate of Sandaogou profile was mainly affected by solar radiation.