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THE DRY WET VARIATION SINCE ABOUT 4 ka B.P. REVEALED BY DAMUGOU SECTION LOCATED AT CELE OASIS DESERT TRANSITIONAL BELT

Cele, known as a typical oasis, is located at the southern rim of Taklimakan desert. Since late Quaternary, the oasis has undergone a great changes. The environmental change information have been recorded by the strata in oasis desert transitional belt. The paper, taking Damugou section as studying object, aims at establishing the environmental evolution history through research of Chronology, Sedimentology and Rb/Sr fluctuating features. (1) The alternation of fluvial sand layer and fine clay or silt clay layers reflected the increasing and decreasing processes of river discharge. The appearance of grey brown clay or silt clay layers indicated a relative humid climate which was favorable to the growth of vegetation. This vegetation has laid the foundation for the peat horizon formed in the section. The appearance of modern eolian sand dated at about 1 0 ka B.P. suggested that the climate was dry and with an aggravating tendency, which implied that the intensive development of desertification by Cele oasis just began at this period. (2) Several drying periods inferred from the Damugou section can be considered as the reflection of river discharge decreasing, oasis range shrinking and desertification aggravating, which resulted in many ancient city to be abandoned. For example, the Loulan city and the Haitou City et al were abandoned at the beginning of 5￣6 century, and this period was compatible with the drying period at about 1620±95 B.P. recorded by the section. At about 960±70 a B.P., the climate tended drier extensively, which resulted in another intensive desertification, and many ancient cities such as Milan, Dandanwulike (Ancient Cele City) were forced to be given up. (3) The dry wet fluctuating features suggested by Rb/Sr curve coincided well with the climatic changes reflected by the sedimentary subsequences. The drying tendency are more evidently reflected by Rb/Sr curve.