50万a来沙漠-黄土边界带的环境演变

毛乌素沙漠与黄土高原接壤的沙漠－黄土边界带以其特有的古风成才－黄土－古土壤沉积系列记录了这一地区约50万a以来的环境演变．地层中的埋藏古风成砂是在冬季风极为强大时堆积的，古土壤是在冬季风萎缩、夏季风强盛时发育的，而黄土则是在上述两种极端气候的过渡状态下堆积的．研究结果表明毛乌素沙漠至少在50万a前就已经形成，但也并不是从一出现就持续至今，而是在第四纪气候振荡的作用下，历经“沙漠－非沙漠”的多次转变，其中沙漠明显扩大的时期至少有13次．

ENVIRONMENTAL EVOLUTION OF THE DESERT-LOESS TRANSITIONAL ZONE OVER THE LAST 0.5Ma

Besed of studying the sand-loess-palacosol series of Shboao profile, which is located in the desert-loess transitional zone of north China, the Mu Us Descrt evolution and the climatic flunctuations over the last 0.5Ma have been discussed, Our result indicated that:1. According to the sedimental records of Shimao profile, the oldest aeolian sand of desert-loess transitional zone formed at 0.5Ma B.P., so this probably means the earliest occuring time of Mu Us desert.2. The evolution of Mu Us Desert is controlled by the Quatcrnary climatic oscillation,and underwent changes from desert to non-desert or non-desert to desert. During the past 0.5Ma, at least 13 times of desert extension occurred, which are inferred by the 13palaeoeolian sand layers of Shimao profile.3. The strahgraphic sequence of the desert-loess transitional zone can be correlated with that of the Loess Plateau, but shows more sensitive to the past climatic changes: the sand layers sandwiched in glacial loess sediments and the loess or sand layers interbedded in interglacial palaeosols, all suggest that the sedimental succcssions in the transitional zone have a high resolution potential for recognozing not only the glacial-interglacial stages but also the within-stage climatic fluctuations.