河西走廊末次冰期砂楔的发现及其古气候意义  

The Discovery of Sand Wedges of the Last Glaciation in the Hexi Corridor and Its Paleoclimatic Significance

作　　者：王乃昂[1] 王涛[1] 史正涛[1] 胡刚[2] 高顺尉[2] 

机构地区：[1]中国科学院寒区旱区环境与工程研究所,甘肃兰州730000 [2]兰州大学资源环境学院,甘肃兰州730000

出　　处：《冰川冻土》2001年第1期46-50,共5页Journal of Glaciology and Geocryology

基　　金：国家自然科学基金重点项目!(497310 10 );国家重点基础研究规划项目!(G19990 435 0 1)资助

摘　　要：河西走廊砂楔主要形成在晚更新世冲洪积砾石层中 ,楔体内充填的风成砂14 C年龄证明其是末次冰期的产物 .在末次冰期 ,河西走廊年平均气温为 - 5～ - 7℃左右 ,较现在低 13～ 15℃ .这一估算数据与根据本区芒硝沉积层所推测的气温下降值是一致的 ,亦与最近有关北半球高、中纬度冰期降温幅度的研究相符合 .当时 ,河西走廊西段年降水量可能达到 10 0～ 2 0 0mm ,比现在平均年降水量增加约10Sand wedge is formed under cold climate, and is an important basis for reconstructing paleoenvironment. It has been reported constantly over the last 20 years in the Tibetan Plateau, North China and Northeast China. Fossil sand wedge groups at the end of the Late Pleistocene recently are found in Jiuquan, Anxi, Dunhuang and other areas in the Hexi Corridor now. The fossil sand wedges, found by the authors, were mainly formed in alluvial gravel stratum of bajada and piedmont alluvial plain. Based on the field incomplete statistics, the top-width of them is usually 12～30 cm, with a depth of 17～70 cm and a mean ratio of width to depth of 1∶1.61. Their morphometrics appear bottom-cuspate wedge, deep and narrow. Most of wedge bottom is single cusp. Eolian sand is filled in all wedge body. It is found from the granulometric composition of two sample groups that fine sand ranging from 0.25 to 0.125 mm is the maximum; followed by very fine sand ranging from 0.125 to 0.063 mm, and the physical clay, less than 0.002 mm, is less than 3%. A thin layer of grail overlies the top of the sand wedge groups. According to the morphological characteristics of profile, sand wedges have nothing to do with tectonic movement, fluvial erosion and drying crack of ground surface, but have something to do with disturbance caused by seasonal process of permafrost. 14 C dating of dripping carbonate within the sand wedges from the Anxi County shows that they were formed at about (22 500±190) a BP and (19 100±125) a BP, during the Last Ice Age. The study suggests that the Hexi Corridor was the southern periphery of the continuous permafrost zone with a climate rather cold and relatively moist at the Last Ice Age, because the region was situated in a transitional zone under the interaction of monsoon westerly. According to the temperature suggested by Romanovskiy for the formation of sand wedge within gravel, it is estimated that the annual mean air temperature during the Last Glaciation might be 11～15 ℃ colder tha

关 键 词：砂楔 末次冰期 古气候 河西走廊 晚更新世 风成砂 碳同位素 

分 类 号：P532[天文地球—古生物学与地层学]