腾格里沙漠南缘土门剖面末次冰消期层段粒度特征及其反映的古气候

腾格里沙漠南缘土门剖面41LD-52L层段由3层黄土状亚砂土、5层砂黄土、2层湖湘和2层古土壤组成,其年代为14 930~11 640 aBP,相当于末次冰消期。分析结果表明,整个末次冰消期层段以粉砂含量占绝对优势,分布范围/平均值21.69%~79.47%/50.33%;砂含量次之,为3.97%~75.37%/38.17%;黏土含量最少,为2.34%~34.02%/11.50%。各不同粒级沉积物、Mz、σ等在垂直方向上呈相反的镜像对称变化。该层段粒度(Mz)指示腾格里沙漠南缘末次冰消期经历了4个以东亚夏季风为主的暖湿气候(W1-W4)与4个冬季风为主的冷干气候(C1-C4),其中W2、W3和W4暖事件与格陵兰GRIP冰心记录的晚阿勒罗德(late Allerød)、早阿勒罗德和波令(Bølling)等暖事件对应;C1、C2和C3冷事件与新仙女木(Younger Dryas,YD)和阿勒罗德(Inter Allerød Cold Period,IACP)冷事件对应。同时,该指标指示的新仙女木冷期(12650~11640 aBP)与波令-阿勒鲁德暖期(14930~12650 aBP),可分别与格陵兰GRIP冰心氧同位素记录的新仙女木冷期、波令-阿勒鲁德暖期(B/A转换)在气候性质和相位上具有较好的对应关系。它们之间的良好的对比关系表明,腾格里沙漠南缘气候波动的驱动机制可能与格陵兰冰心代表的北半球高纬度热盐环流驱动机制密切相关。

GRAIN-SIZE DISTRIBUTION ALONG THETUMEN SECTION OF SOUTHERN TENGGER DESERT,NORTHWESTERN CHINA AND ITS PALEOCLIMATIC IMPLICATIONS DURING THE LAST DEGLACIAL

The Tumen sequence (41LD-52L) at the southern edge of the Tengger Desert in the northwestern China covers the time span of 14930-11640 a BP synchronously with the last Deglacial. It consists of 3 layers of loess-like sandy loams, 2 layers of sandy loess, 2 layers of lacustrine facies, and 2 layers of paleosol. The results of grain-size analysis show that silty sands dominate the major proportion ranging from 21.69% upto 79.47% with an average of 50.33%; Sands comes the second with a distribution range of 3.97%~75.37% and an average of 38.17%; The lowest proportion is clay, ranging from 2.34% to 34.02% with an average of 11.50%. Symmetrical changes in grain-sizes, Mz and σ are observed in vertical direction, indicating that the climate in southern Tengger Desert during the last deglacial had significantly varied for at least 4 warm-cold fluctuations, including warm-humid phase W1-W4 and cold-dry phase C1-C4. The W2, W3 and W4, are corresponding to the late Allerød, early Allerød and Bølling in the GRIP ice core record, respectively, while the C1, C2 and C3 are corresponding to Younger Dryas (YD) and Inter Allerød Cold Period(IACP). In addition, the Yonger Dryas(12650-11640 a BP) and Bølling-Allerød warm period (BA) (14930-12650 a BP) indicated by grain sizes are corresponded well and in phase with oxygen isotope records(δ18O) in GRIP cores, demonstrating that the driving force of such a change in southern Tengger desert is chiefly related to the thermohaline circulation in high nothern latitudes represented by Greenland ice core.