山西大同、内蒙古鄂尔多斯冰楔、砂楔群的发现及其环境意义

Discovery of Ice Wedge and Sand-wedge Networks in Inner Mongolia and Shanxi Province and Their Environmental Significance

研究了山西大同、内蒙古东胜和乌审旗地区发现的大量冰楔假型、砂楔、寒冻裂隙和南部白城子附近的冰卷泥 .根据这些冰缘现象 ,并参考前人工作成果 ,划定了晚更新世晚期末次冰期时多年冻土的南界 ,并根据所获得的年代资料划分了 4次冰缘期 :33kaBP ,30～ 2 6kaBP ,2 0～ 1 6kaBP和 8kaBP左右 ,当时的温度比今天分别降低 8.4℃ ,1 2～ 1 3℃ ,1 0℃和 7～ 1 0℃ .

Periglacier is one of phenomena that are significant for the paleoenvironment reconstruction. According to the periglacial phenomena, such as ice wedges, sand-wedges, etc., the temperature and humidity condition in which the periglacier formed can be recovered. In this paper, the periglacial phenomena found in Datong of Shanxi Province, Dongsheng and weshenqi of Inner Mongolia are described in detail. According to the features of periglacial phenomena, the periglacial phenomena can be classified as four types, i.e., ice wedge cast, sand-wedge, frost crack and involutions. Based on the present research and former fruits, the south boundary of permafrost during the period of Last Glacier is identified stretching from Zhongning, Jingbian, Yulin, Datong, northern Beijing to Bohai Sea. Dating the samples collected from wedges, the following four periglacial stages are set up. (1) 33 ka BP, a small number of sand-wedges were formed, when the temperature reconstructed was about -1.5 ℃, 8.4 ℃ lower than that at present. (2) During 33～26 ka BP, a large number of sand-wedges were formed, when the annual average temperature was about -5 ℃, 12～13 ℃ lower than that at present. (3) During 20～16 ka BP, the humidity varied obviously from west to east, when the annual average temperature was 10 ℃ lower than that at present. (4) 8 ka BP, a small number of sand-wedges were formed, when the climate was dry and cold, and the annual average temperature was 7～10 ℃ lower than that at present. Besides, by the means of grain analysis, SEM, and so on, the sand filled in the ice wedges and sand wedges are studied. The experimental results showed that the sands have not experienced wind function. So it is believed that the sand filled in the wedges had not been transferred from the distance. The sand produced on the spot indicated that no wind activity followed chilliness climate.