吴吉春^1,,
盛煜¹,
赵林²,
王生廷¹
1. 中国科学院寒区旱区环境与工程研究所, 冻土工程国家重点实验室, 甘肃 兰州 730000
2. 中国科学院寒区旱区环境与工程研究所, 青藏高原冰冻圈观测研究站, 甘肃 兰州 730000

基金项目: 国家自然科学基金面上项目（批准号：41171058和41271084）和国家重大科学研究计划项目（973项目）（批准号：2013CBA01803）共同资助


详细信息

作者简介: 吴吉春, 男, 44岁, 博士/助理研究员, 普通冻土与冰缘地貌研究, E-mail:wujichun@lzb.ac.cn

中图分类号: P512.4⁺2;P534.63

收稿日期:2017-06-02
修回日期:2017-08-22
刊出日期:2018-01-30

Characteristics and implication of sand-wedges in Qaidam Basin, northeast Qinghai-Tibetan Plateau

Wu Jichun^1,,
Sheng Yu¹,
Zhao Lin²,
Wang Shengting¹
1. State Key Laboratory of Frozen Soils Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, Gansu
2. Cryosphere Research Station of the Qinghai-Tibetan Plateau, Cold and Arid Regions Environment and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, Gansu


MSC: P512.4⁺2;P534.63

--> Received Date: 02 June 2017
Revised Date: 22 August 2017
Publish Date: 30 January 2018


摘要
摘要:冰楔假形和原生砂楔是指示古冻土发育的重要证据。两者虽然具有相似的外观形态，但形成过程不同，在反映古气候、古环境和古冻土演化等方面具有不同的指示意义。在利用地层中的楔形构造推测古环境时，确定其类型是正确解读其环境意义的前提。本文讨论了柴达木盆地发现的楔形构造，通过楔形围岩和充填物中的一些微结构判断其属于原生砂楔，进而探讨了这些砂楔代表的环境意义和多年冻土发育状况。柴达木盆地中的砂楔主要形成在末次冰消期的Heinrich 1（H1）和Younger Drays两次降温事件期间。这表明，末次冰消期，柴达木盆地地表几乎全部被风沙覆盖，处于极端干旱的沙漠环境，年平均气温较现在降低6℃左右，多年冻土下界较现在下降了约1000 m。然而，多年冻土并没有占据整个盆地，在盆地中部和南部保留着大片融区，据此推测，即使末次冰期时期，柴达木盆地仍然保留一定面积的融区。末次冰期以来，青藏高原主体和祁连山两大现代多年冻土区并没有通过柴达木盆地连成一片。
关键词: 柴达木盆地/
砂楔/
末次冰期/
古环境/
古多年冻土

Abstract:Ice-wedges pseudomorph and relict sand wedges are important evidence for the former existence of permafrost. Similar appearance is shown in these two type periglacial features, but difference is present in their forming process. Accordingly, it is revealed that discrepant implication of palaeo-climate, palaeo-environment, and permafrost evolution. It must be validly classified of wedges when we reconstruct palaeo-environment based on periglacial wedges. In this article, we distinguished wedges as relict sand wedges based on micro-structure of filling material and host strata on the profile, and discussed palaeo-climate and permafrost occurrence during the Last Deglacial in the Qaidam Basin. Relict sand wedges were observed on profile which had been cut by building highway in Lenghu (38°51.23'N, 93°25.08'E; 2782 m a.s.l.)and Huaitou Tala (37°26.02'N, 96°14.02'E; 3760 m a.s.l.)regions, in northwestern and eastern margins of the Qaidam Basin respectively. Huaitou Tala wedges locate in a valley at 45 km west of Huaitou Tala town, and 100 km west of Delingha City. These wedges covered by loess depth of 50~70 cm, shaped by "V", top width range 30~120 cm, depth range 1.7~3.1 m. The wedges characterized by red-brown coarse sand infilling in green silt. The fissures can be found in the fillings from top to bottom of some wedges. The OSL dating of filling sand manifested these wedges have been cracked during 11.65±0.99~12.66±1.06ka B.P. Lenghu wedges top width range 20~50 cm and depth less than 100 cm, and they characterized by lamination in fillings and up bend of the host strata. The fillings in Lenghu wedge are 14.95±1.5 ka B.P. in age. Sand wedges in Qaidam Basin are identified that cracked by thermal contraction and filled by aeolian sand during Heinrich 1 and Younger Drays stadials. The Qaidam Basin had been paved by aeolian sand and very arid desert environment prevailed, and the mean annual air temperature had dropped by 6℃ during the Last Deglacial. Accordingly, permafrost low limit had descended about 1000 m. Nevertheless, permafrost had never occupied the whole basin floor, and it occurred in the periphery of the basin above 2800 m a.s.l. A patch of permafrost-free area persisted in the central and southern Qaidam Basin since the Last Glacial Maximum.
Key words:Qaidam Basin/
relict sand wedge/
Last Glacial Maximum/
palaeo-environment/
palaeo-permafrost



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