末次盛冰期和全新世大暖期毛乌素沙地的空间变化

SPATIAL VARIATIONS OF THE MU US DUNE FIELD(NORTH CENTRAL CHINA)DURING THE LAST GLACIAL MAXIMUM AND HOLOCENE OPTIMUM

沙漠/沙地边缘和内部的古风成沙层、砂质古土壤是重建晚第四纪以来地表变化的直接地质证据。位于我国北方半干旱区的毛乌素沙地,其地表过程对气候变化响应敏感。在对毛乌素沙地进行野外拉网式调查以及前人研究的基础上,我们在沙地南部和东部的沙漠-黄土过渡带发现了大量的埋藏古风成沙丘沉积,指示了干冷期沙漠扩张的最南、东界限;沙地内部广泛发育的砂质古土壤则表明在气候相对暖湿期地表植被生长,土壤发育,沙丘基本被固定。对14个典型风成沙/黄土/古土壤沉积剖面进行了光释光年代学样品的采集和测试,结合空间分析和他人研究结果,发现在末次盛冰期(约26~16ka),毛乌素沙地的流动沙丘向南、东扩张,扩张距离现代边界约30~50km,面积扩大至少约10000km^2,占现代沙地面积的25%;在全新世大暖期(约9~5ka),毛乌索沙地大部分被固定,发育了较厚的砂质古土壤。研究结果揭示了毛乌素沙地的地表过程对末次盛冰期和全新世大暖期气候变化的直接响应。

Relics of buried paleo-dune deposits and paleosols provide evidence for desert landscape evolution during Late Quaternary. Mu Us dune field located at semi-arid region of North China, near the northern limit of significant summer monsoon rainfall, is sensitive to climate changes. On the basis of extensive field investigations and previous studies in the Mu Us dune field,we found paleo-dunes and sand sheet layers interbedded within thick loess deposits in the loess-desert transition zone and northern Loess Plateau south and east to the dune field, indicating intensive dune migration to the south and east during arid and cold periods. Relics of paleosols are found distributed in the central and north dune field, implying enhanced vegetation and soil formation under relatively warm and wet climate conditions. 14 representative aeolian sequences were chosen for OSL dating to attempt to reconstruct spatial and temporal changes of the desert borders. Our preliminary results indicate that dunes migrated to the south and east into the Loess Plateau at around 26 - 16ka,with a maximum extension of about 30 -50kin relative to the present border, the area of mobile dunes extended at least 10000km2, accounting for about 25% of modern Mu Us dune field area. During Holocene Optimum（around 9 -5ka）,most of the mobile dunes in the dune field were stabilized by vegetation and soil. Spatial variations of Mu Us dune field during the Last Glacial Maximum and Holocene Optimum are interpreted as direct responses of the sand dune surface to climate changes.