关键词: 粒度, 磁化率, 气候变化, 全新世, 毛乌素沙地

Abstract: Located in the northwestern edge of the East Asian summer monsoon, Mu Us Sandy Land is sensitive to climate changes, which is an ideal area for studying paleoclimate changes and desert vicissitudes. Through the characteristics of the sediments grain size and magnetic susceptibility analysis of the Daliuta (DLT) section, based on data of OSL dating, we discussed the climate change process in Holocene of Mu Us Sandy Land. The results showed that:(1)The grain size composition of DLT section was mainly composed of medium (3.39%-73.84%) and coarse sand (1.46%-75.79%). In different sedimentary facies, the grain size components of aeolian sand were mainly medium (42.97%) and coarse sand (43.37%), the paleosol was dominated by silt (26.06%) and very fine sand (23.26%), the weak soil was dominated by medium (32.84%) and coarse sand (30.30%), and the lake-swamp sediment was mainly composed of fine (32.83%) and very fine sand (27.60%). In terms of grain-size parameters, the mean grain size ranged from fine to coarse in order of paleosol (2.86 φ), lake-swamp sediment (2.50 φ), weak soil (1.84 φ) and aeolian sand (1.04 φ), and the sorting coefficient also showed high value in paleosol (1.78) and low value in aeolian sand (0.60).(2)The magnetic susceptibility changed regularly in the whole section. The variation ranges of low, high frequency magnetic susceptibility (χ_lf,χ_hf) are similar, with the ranging from 2.50 to 115.66 (×10^-8m³·kg^-1) and 2.36 to 105.32 (×10^-8m³·kg^-1) respectively, and they showed the regularity of paleosol > lake-swamp sediment > weak soil > aeolian sand in different sedimentary facies. Meanwhile, the χ_lf was significantly positively correlated with the content of clay components and the mean grain size, and they showed consistent patterns of variation in vertical profile, which indicated similar climate changes.(3)The Holocene climate change in Mu Us Sandy Land has experienced at least 6 times distinct cold-warm fluctuations. Before 10.39×10³ yr BP, the climate of Mu Us Sandy Land fluctuated frequently, and there were 3 climate alternations of "cold-dry, warm-wet"; (10.39~9.34)×10³ yr BP, the climate was cold-dry and aeolian activities was strong; (9.34-8.68)×10³ yr BP, winter monsoon was weaker and summer monsoon was stronger than before, and pedogenesis was strong; (8.68-8.29)×10³ yr BP, the climate was cold and dry; (8.29-2.72)×10³ yr BP, the climate was warm and wet, after reached the warmest at (6.55-3.80)×10³ yr BP, it turned to cold and dry; (2.72-1.34)×10³ yr BP, the winter monsoon became stronger and the desert expanded again; since 1.34×10³ yr BP, the climate was close to modern climate. The climate change of Mu Us Sandy Land is related to the strength of East Asian winter and summer monsoons, which is the regional response to global climate changes.

Key words: grain size, magnetic susceptibility, climate change, Holocene, Mu Us Sandy Land