青海湖北岸原生砂楔的发现及其古气候意义

青海湖北岸刚察县城东与泉吉乡西发现原生砂楔群, 楔内充填物均为中细粒砂, 楔体底部中细粒砂ESR测年数据表明, 刚察县城东3个原生砂楔发育时代分别为(774±70) ka、(773±70) ka和(229±20) ka, 泉吉乡西1个原生砂楔形成时代为(197±18) ka, 反映该区至少发育两期原生砂楔, 其形成时代分别对应昆仑冰期和倒数第二次冰期. 基于原生砂楔的特殊形成环境, 估算青海湖盆地在昆仑冰期早期的年均温不高于-7.5~-10 ℃, 比现今至少低9.2~11.7 ℃, 中更新世早期青海湖盆地发育多年冻土, 青藏高原东北部可能已经进入冰冻圈; 倒数第二次冰期的年均温不高于-9.5~-10 ℃, 比现今低11 ℃以上.

Fossil sand wedges in the northern shore of Qinghai Lake: discovery and paleoclimatic implications

Qinghai Lake in the northeast of the Tibetan Plateau is the biggest inland lake and largest saltwater lake of China. The lake is at an elevation of more than 3 000 m with an annual mean temperature of 1.7 ℃. Around the lake there is no permafrost now, but ice-wedge casts and fossil sand wedges are discovered. Investigation in this area has found that there are many groups of fossil sand wedges in the northern shore of Qinghai Lake. One is located in the east of Gangcha County (37°15'43.7" N, 100°00'28.4" E), the another in the west of Quanji Township (37°14'22.2" N, 99°50'13.0" E). The fossil sand wedges found in the east of Gangcha County are named as GS1, GS2 and GS3, respectively. GS1 is 0.9 m in breadth and 1.9 m in depth, based on ESR dating, which formed during the Kunlun Glaciation (774±70) ka; GS2 is 1.4 m in breadth and 1.7 m in depth, which formed in the same layer of the profile in the east of Gangcha County, and based on the ESR dating, which also formed during the Kunlun Glaciation (773±70) ka; GS3 is 0.5 m in breadth, 1.0 m in depth, based on ESR dating, which formed during the Penultimate Glaciation (229±20) ka. The fossil sand wedges found in the west of Quanji Township is named as QS1, which is 2.3 m in breadth and 1.5 m in depth. The characteristics of QS1 are quite different from GS1, GS2 and GS3. QS1 is characterized by higher ratio of breath to depth and formed at (177±17) ka and (197±18) ka based on ESR dating, thus, it is believed that QS1 formed during penultimate glaciation. Research results of fossil sand wedges have environmental significances. It is estimated that the annual mean temperature in the northern shore of Qinghai Lake was probably -7.5~-10 ℃ in the Kunlun Glaciation and about -9.5~-10 ℃ in Penultimate Glaciation. Temperature reduction in glaciations were conspicuous. It is the first time to find that fossil sand wedges, which formed during the Kunlun Glaciation, in this region. The discovery has significance in Quaternary paleoclimate study and the study of permafrost distribution in the northeast of the Tibetan Plateau.