摘要
对沙漠－黄土边界带的古风成砂－黄土－古土壤序列的研究表明，毛乌素沙漠至少在０．５ＭａＢ．Ｐ．就已出现，但也并非从其出现之初就持续至今。沙漠－黄土边界带的风成沉积所记录的沙丘活化和固定的多次转变是第四纪时期毛乌素沙漠对气候振荡响应的结果。五十万年来，沙漠－黄土边界带的石峁剖面记录了１３层古风成砂，代表了１３次沙漠大规模的南侵。沙漠的南侵不仅可以发生在冰期鼎盛之时，同样也可以发生在间冰期中的寒冷气候幕出现之时。此外，鉴于沙漠－黄土边界带具有气候敏感性的特点，石峁剖面的地层记录还表明了第四纪时期不仅有冷期与暖期的多次旋回，而且冷期和暖期发生时还有次一级的气候波动。
Deserts, especially those located in the semi-arid zone, are highly sensitive to climate change. The spatial shifting of the desert margin reflects the cyclic dry /wet variations. In China, Mu Us Desert is located to the northwest of the Loess Plateau-,the adjoining part of these two landscapes forms the desert-loess transitional zone,the aeolian sequence of this zone is characterized by the alternatively deposition of sand, loess, and palaeosol. The buried sand layers were accumulated when Mu Us Desert extended southward and, should indicate hyperarid climate. The palaeosols were developed when sand dunes were stabilized by vegetation and thus indicate humid climate. The loess beds were formed under the dominantly dry climate condition. Thus, the aeolian sequences of the transitional zone are very important sources of information for reconstructing the history of the Mu Us Desert.In this paper, environmental reconstruction for Mu Us Desert evolution is based on the study of the aeolian sequences at Shimao. This section lies in the desert-loess transitional zone, and is about 50km away from Yulin city, Shaanxi Province. The thickness of the aeolian deposits in Shimao section is 76.7m, overlying the Mesozoic sandstone. According to our magnetostratigraphical and pedological evidence, this section records the aeolian sequence of the last 0.5Ma.The results of our studies are summarized as follows.(1) The existence of buried sand layers in the eolian sequences of the desert-loess transitional zone is the geological evidence of the southeastwards extension of Mu Us Desert. The sand horizon, at the bottom of Shimao section, was estimated with an age of 0'5Ma B. P., thus Mu Us Desert occurred at least earlier than this time.(2) During the past 0.5Ma, thirteen sand intercalations have been recorded by the Shimao section, indicating there are thirteen times of desert expansion. Moreover, thegeological evidence suggests the desert expansion can not only occur during the glacial maxima, but also could occur during the cold intervals within the interglacial times.(3) Each layer of sand, loess, and palaeosol should represents an independent climatic event, thus the alternative deposition of sand, loess, and palaeosol indicates the cyclic Quaternary climatic fluctuations. Our results show that almost all the glacial sediments consist of loess and sand beds, these two kinds of aeolian deposits correspond to different climatic conditions, thus the climate of each gladal period is characterized by sighficant climatic variations. The interglacial soils, excluding the Holocene soil So, can be subdivided into two or three soil layers by the sand or loess intercalations. This indicates the warm climate of each interglacial time had been interrupted by the short cold-dry episodes. As there are two loess or sand intercalations occurring in S1, S3, and S5, this suggests the climate of each interglacial time, corresponding to oxygen isotope stage 5, stage 9, and stage 13, can be subdivided into three warm and two cold substage climatic episedes. Whereas, both stage 7 and stage 11, corresponding to S2 and S4, have two warm and one cold substages. Therefore,the eolian sequence of Shimao section suggests the climate of Quaternary is not only characterized by the glacial-interglacial stages, but also the within stage climatic oscillations.(4) The environmental evolution of Mu Us Desert is controlled by the Quaternary climatic changes. During the glacial maxima, coupling of the Siberian High with the Aleutian Low was greatly enhanced, both the strength and the persistence of winter monsoon were increased, the aeolian activity was intensified, and Mu Us Desert was extended to the Loess Plateau. Whereas, during the interglacial times, the relatively strengthened summer monsoon brought more humid air masses to the desert and thus favored the vegetation cover. As a result, the aeolian process was interrupted by the pedological process and soil formation, and this is marked by the northwest wards retreating of Mu Us Desert. Therefore, the activation an
出处
《第四纪研究》
CAS
CSCD
1996年第4期359-367,共9页
Quaternary Sciences
基金
国家自然科学基金
关键词
毛乌素沙漠
沙漠变迁
0.5Ma, Mu Us Desert, environmental evolution
