榆林剖面的热释光测年及其对这一地区干旱事件的讨论

用热释光测年方法对陕西榆林地区蔡家沟和石峁剖面的风成砂－黄土－古土壤序列进行了系统的测年，结果表明末次冰期的风成沉积中夹有三层古风成砂，由此反映了末次冰期中有三次沙漠扩大的气候干旱时期。根据年代测定结果最末一次干旱事件出现在１２～＜２７ｋａＢ．Ｐ．之间，基本上与末次冰期极盛期相当，可以与深海氧同位素阶段２对应。第二次干旱期出现在４８ｋａＢ．Ｐ．左右，大致与氧同位素阶段３的中期相当。最早的干旱期出现在５５～＜７５ｋａＢ．Ｐ．之间，与阶段４对应。令人感兴趣的是虽然与阶段２、阶段４对应的干旱期在世界上其它地区同样有记录，但是大致相当于阶段３中期的这期干旱事件却以榆林剖面反映最好，表现为末次冰期的间冰段期间，毛乌素沙漠也曾经大规模扩大，这从一个侧面说明了中国的沙漠－黄土边界带对气候变化的敏感性。此外，热释光测年结果还表明了末次冰期的沉积由风成砂与黄土迭覆而成，而末次间冰期则由古土壤与黄土迭覆而成，因此，无论是冰期还是间冰期，气候条件都不是以持续的干冷或温暖为特点，而是叠加了更次一级的气候变化。毛乌素沙漠在第四纪时期并非持续存在，而是在气候的调节下经历了沙漠出现与固定的多次转变

THERMOLUMINESCENCE CHRONOLOGY OF AEOLIAN SEQUENCES IN YULIN AND THE ARID EPISODES OF THIS REGION

Thermoluminescence technique had been used to date the age of the sand-loess-palaeosol series of Yulin, Shanxi Province. Our results indicate that there are three sand layers intercalated in the last glacial sediments, suggesting the recurring of three arid episodes during the last glacial time. The latest arid period occurred between 12 and <27 ka B. P., nearly coeval with the last glacial maximum, and could be correlated with stage 2 of marine oxygen isotope records. The second arid interval, with a TL age around 48 ka B. P., could be correlated with part of stage 3. The earliest arid episode with TL age between 55 and <75 ka B. P. corresponds to stage 4. Our results also indicated that although the arid evidence, corresponding to stage 2 and stage 4, can be found in other regions of the world, the arid episode interbedded in stage 3 can be only well documented by the sand-loess-soil profiles of Yulin. Thus, it reflect the high sensitivity of the Chinese desert-loess transitional zone to the Quaternary climatic changes. In addition, the TL results suggest that the last glacial sediments consist of alternatively depositing of sand and loess, and the last interglacial sediments consist of loess beds and palaeosols, these do reflect the climate is not only characterized by the glacial/interglacial stages, but also the within stage climatic changes. The existence of sand-loess-soil sequence reflect in some way the mobile dune sands of Mu Us Desert were only restricted to some periods of Quaternary, the extension and stabilization of Mu Us Desert are the results of cyclical climatic changes.