西昆仑山甜水海北湖砂楔的形成与环境演变

青藏高原是世界上中低纬度地区冰缘最发育的区域,其中西昆仑山甜水海地区广泛分布着砂楔群等冰缘现象.砂楔是寒冷气候条件的产物,对古气候和古环境的重建具有重要意义.文章通过分析甜水海北湖砂楔矿物特征发现,砂楔填充物基本属于近源堆积;14C测年结果以及粒度再结合砂楔形态分析得出,该砂楔的形成经历了13.9kaB.P.,11.9...     

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

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:33ka BP,30～26ka BP,20～16ka BP和8ka BP左右,当时的温度比今天分别降低8.4℃,12～13℃,10℃和7～10℃.     

Possible controlling factors in the development of seasonal sand wedges on the Ordos Plateau,North China

Wedge-like structures filled with silty sand penetrate Quaternary fluvial and aeolian sediments and, in places, Tertiary bedrock on the Ordos Plateau, North China. The wedges reflect thermal contraction cracking of either permafrost or seasonal frost during the Late Pleistocene and early Holocene. Wedges of about 1 m in depth form polygonal nets of 2-3 m in diameter(type B). They contrast with wedges of 3-4 m in depth that form polygons of 10-15 m in diameter(type A).This review focuses upon the highly variable size of the inferred polygon nets and discusses the problem of differentiating between seasonally and perennially frozen ground, or between seasonal frost and permafrost.