摘要
提要１９８７－１９９２年对喀喇昆仑山－昆仑山地区的考察结果再次证明，青藏高原西北部的强烈隆起始于上新世末──早更新世初，总上升幅度达３１００－３６００ｍ，强烈隆起具有整体性、阶段性和后期加速的特点，目前仍处于强烈隆起阶段，上升速率达４．２ｍｍ／ａ。青藏高原西北部及其北邻地区的自然环境随着高原隆起发生巨大变化，本区没有发现早更新世冰川遗迹，当时高原山地可能尚未达到雪线高度。中更新世冰川是本区三次冰川作用中时代最早、规模最大的冰川，具有海洋性冰川特征。晚更新世开始高原气候强烈变冷变干，冰川发育不良，形成大陆性冰川，未能形成统一大冰盖。昆仑山北坡的砂黄土是塔里木盆地南缘风沙堆积的同期异相地质体，其年代不超过１５８ｋａ。全新世黄土堆积速率增大。在最近２０ｋａ，高原内陆湖泊湖面波动下降，湖水咸化，甚至干涸。
Various new data derived from the investigations to the West Kunlun shan and Karakorum Shan area in the duration from 1987 to 1992 testify again that the intense uplift of west Tibetan Plateau began from the end of Pliocene to early Pleistocene (e. g. about 3.4 Ma) . A total amplitude of the uplift since that time is 3 100-3 600m which is similar to the Himalayas. The uplift is characterized by totality and stadiality and being accelerated in the late period. Present mean uplift rate along the high way from Yecheng to Shiquanhe is 4. 2 mm/a.according to the repeated measurement carried out in 1959-1961 and 1979-1981. It means that the North-western Tibetan Plateau is still in the intense uplift period at present day.Due to the intense uplifting, climate over the Northwestern Tibetan Plateau has been changed significantly which has exerted great impact on the development of glaciation, loess deposition. interior lakes and drainage system etc.Three glaciations can be recognized in the area. The earliest one appeared in early-middle Pleistocene and the later two occurred in the late middle Pleistocene and late Pleistocene respectively. The glaciation of the early Pleistocene which was referred by former investigators had never appeared in this area. The middle Pleistocene glaciers were well developed as a maritime monsoon glacier type in forms of piedmont glaciers or trellis valley glaciers. Glaciers in the later stages were changed to be continental style in forms of tongue, cirque and valley glaciers.They were consequently decreased in size since the late Pleistocene. It was impossible to develop an ice sheet on the Plateau during the last glaciation. This indicates that climatically it became colder and drier in the area in the late Pleistocene and Holocene stages followed by intense uplift.Loess deposits are scare to the south of the Kunlun Shan . but well developed and widely distributed on the northern side of the West Kunlun Shan with maximum thickness of 20m below an elevation of 4 200m asl. The loess began to deposit after 158kaBP. and accumulate more intensively in the Holocene. Evidences show that the loess on the northern slope of West Kunlun Shan is a correlative deposits of the sand dunes on the southern periphery of the TarimBasin under the environmental disintegration in the late Pleistocene and Holocene ages. The desertification in the Tarim Basin therefore might mainly be generated from the late Pleistocene time.Evidences show that there were many big ancient lakes which were combined with the existing isolated lakes in the Karakorum-West Kunlun Shan area during 40-20kaBP since about 20-18kaBP. most of them were separated into small isolated lakes because lake level was significantly dropped down. During the Holocene. processes of lake shrink became fast after the isolated lakes settled. For instances. the level of the Longimu Co has dropped down by more than 72m since about 11 kaBP. The intense lake shrinkage appeared in recent 20ka might be contributed to the continued uplift of the Plateau in late Pleistocene except the global changes.
出处
《地理学报》
CSSCI
CSCD
北大核心
1994年第4期289-297,共9页
Acta Geographica Sinica
基金
国家自然科学基金
关键词
青藏高原
第四纪
环境变化
North-western Tibetan Plateau, uplift, Quaternary environmental changes
