干旱区生态环境知识资源中心

The interbeddings of the aeolian sand dune facies and the fluvio-lacustrine and paleosol facies in the Milanggouwan stratigraphic section have been examined by a series of geological methods: including grain size, magnetic susceptibility, spore-pollen and fossil analyses along with various dating methods. The results showed a basic difference in depositional environments between the sand dune facies and the fluvio-lacustrine and paleosol facies. At least 27 cycles of alternate depositions of the aeolian dune sands and the fluvio-lacustrine facies and/or paleosols from 150 ka B.P. have been discovered in the Mu Us Desert. These cycles reflect the climatic variations that were induced by the growth and decline and confrontation between the winter monsoon and the summer monsoon of East Asia in the past 150 ka. The spore-pollen and magnetic susceptibility analyses suggest a great increase of rainfall (+40-120%) and temperature (2-6 degrees C) during the prevailing summer monsoon periods. This is the only sedimentary profile that represents the climatic variations of millennial scale in the desert areas of north China for the late Quaternary. The high-resolution results on paleo-monsoon variations from the section may indicate sensitive reactions of the margin desert to climatic changes. (C) 2000 Elsevier Science B.V. All rights reserved.