粒度特征揭示的中全新世以来毛乌素沙地演化过程

通过对毛乌素沙地现代固定沙丘、半固定沙丘、半流动沙丘和流动沙丘的粒度特征分析，发现研究区沙地变化敏感粒度是>245 μm的沉积物粒度组分，尝试性地将其用于地质时期沙地演化研究。结合区域典型风成砂-古土壤剖面的沉积相特征，探讨了中晚全新世以来毛乌素沙地的时间演化过程及其特征。结果表明：中全新世以来毛乌素沙地存在多次活化扩张和固定萎缩事件，除7.5 ka BP前为流动沙地占优势以外，其余阶段多在半流动沙地、半固定沙地和固定沙地之间频繁转换，即使在全新世适宜期古土壤大规模发育期间仍存在局地短时间的沙地活化事件。

Desert Evolution during the Mid Holocene Reflected by Grain-size Variation of Aeolian Sand and Paleosoil Sequence Records from Mu Us Sandy Land

Based on the analysis of characteristics of grain-size from the modern fixed, semi-fixed, semi-shifting and mobile sand dunes in Mu Us Sandy Land, we find that the grain-size components greater than 245 μm is the sandy land environmentally grain-size sensitive components of experimental area, and it is tentatively applied to the study the sandy land evolution in geological time. In the meanwhile, combined with variation of the sedimentary fades in typical aeolian sand and paleosoil profile, we discussed the spatiotemporal changes of the Mu Us Sandy Land during the mid-Holocene period. The results indicate the region experiences the several activation/expansion and fixation/reduction. The sandy land was dominated by the mobile dune in 3.7-3.5 ka BP and before 7.5 ka BP, and the sandy land was in a frequently change period among fixed, semi-fixed, semi-shifting and mobile sandy land in other stages of the mid-Holocene, and regional sandy land activation still occur during Holocene Optimum when paleosoil development in large scale. The characteristics of sandy land change are consistent with the environmental evolution of adjacent loess plateau.