通过对毛乌素沙地东缘大柳塔剖面地层沉积物粒度及磁化率特征的分析,结合光释光测年结果,探讨了毛乌素沙地全新世气候变化。结果表明:(1)剖面沉积物粒度组成以中砂、粗砂为主,古土壤中黏粒组分含量高(3.32%),风成砂中几乎不含黏粒组分(0.01%),粒度参数的平均粒径Mz和分选系数sigma也表现为古土壤高值、风成砂低值;(2)磁化率在全剖面呈有规律的变化,低频、高频磁化率在古土壤中呈高值,湖沼相、弱成壤次之,风成砂最小;低频磁化率chilf与黏粒(<2 mum)含量、平均粒径Mz呈显著正相关,垂向剖面上变化规律一致,指示了相似的气候环境意义;(3)毛乌素沙地在10.39 ka BP附近存在明显的3次冷干-暖湿气候波动; 10.39~ 9.34 ka BP,气候冷干,风沙活动盛行; 9.34~ 8.68 ka BP,冬季风衰退,夏季风增强,成壤作用强烈; 8.68~ 8.29 ka BP,气候寒冷干燥; 8.29~ 2.72 ka BP,气候整体温暖湿润,在6.55~ 3.80 ka BP达到鼎盛后转向冷干; 2.72~ 1.34 ka BP,冬季风占主导,沙丘活化,沙漠扩张; 1.34 ka BP至今,逐渐接近现代气候。毛乌素沙地的全新世气候变化是东亚冬、夏季风此消彼长作用下全球气候变化的区域响应。
英文摘要:
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 lakeswamp 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 Phi),lake-swamp sediment (2.50 Phi),weak soil (1.84 Phi) and aeolian sand (1.04 Phi),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 (chilf,chihf) are similar,with the ranging from 2.50 to 115.66 (*10~(-8)m~3·kg~(-1)) and 2.36 to 105.32 (*10~(-8)m~3·kg~(-1)) respectively,and they showed the regularity of paleosol>lake-swamp sediment>weak soil>aeolian sand in different sedimentary facies. Meanwhile,the chilf 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 *10~3 yr BP,the climate of Mu Us Sandy Land fluctuated frequently,and there were 3 climate alternations ofcolddry, warm-wet; (10.39~9.34) *10~3 yr BP,the climate was cold-dry and aeolian activities was strong; (9.34-8.68) *10~3 yr BP,winter monsoon was weaker and summer monsoon was stronger than before,and pedogenesis was strong; (8.68-8.29) *10~3 yr BP,the climate was cold and dry; (8.29-2.72) *10~3 yr BP,the climate was warm and wet,after reached the warmest at (6.55-3.80) *10~3 yr BP,it turned to cold and dry; (2.72-1.34) *10~3 yr BP,the winter monsoon became stronger and the desert expanded again; since 1.34*10~3 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.