玉龙山西麓更新世冰川作用及其与金沙江河谷发育的关系

在玉龙山东麓更新世冰川作用研究的基础上,对其西麓和金沙江河谷中的古冰川与冰水沉积物的分布和特征进行了调查。结合ESR测年,划分出4次冰期,即0.7~0.6MaB.P.的玉龙冰期,0.53~0.45MaB.P.的干海子冰期,0.31~0.13MaB.P.的丽江冰期和晚更新世中晚期的大理冰期,其中玉龙冰期为规模较大的山麓冰川,丽江和大理冰期为山谷冰川,干海子冰期则为山麓冰川与山谷冰川的过渡类型。来自玉龙山西坡的玉龙冰期冰碛物充填于现今金沙江谷底的事实和大具金沙江下渡口西岸早更新世金沙江砾石层的发现表明,金沙江在早更新世早期即已存在,也说明了在该段金沙江河谷中多处发现的湖相沉积物是冰川沉积堰塞河谷而成石鼓古湖的结果。在该段金沙江河谷中仅发现拔河50m左右以内的4级河流阶地,且往往以这些湖相沉积为基座的现象,则是石鼓古湖被外泄后金沙江现代河谷形成的结果。

PLEISTOCENE GLACIATIONS ALONG THE WESTERN FOOT OF THE YULONG MOUNTAINS AND THEIR RELATIONSHIP WITH THE FORMATION AND DEVELOPMENT OF THE JINSHA RIVER

The Yulong Mountains (27°10'~27°40'N,100°09'~100°20'E), situated at the north of Yulong County, Lijiang City, Yunnan Province and the southeast margin of the Tibetan Plateau, are the southernmost mountains with existing glaciers both in China and Eurasia. Along the east, northeast and west feet, there is a series of relics of Pleistocene glaciations. Studying these glaciation relics and reconstructing their history of evolution have not only an important scientific implication for understanding the changes of glaciation, climate and environment and for discussing the uplift of the Hengduan Mountains and the Tibetan Plateau, as well as the development of the Jinsha River valley and the formation and development of Asian monsoon, but also major practical values for developing and protecting the tremendous resources of hydraulics and tourism in this area.Based on research of Pleistocene glaciations along the eastern foot of the Yulong Mountains where four glaciations had been recognized, i.e. the early Middle Pleistocene Yulong Glaciation (0.7~0.6MaB.P.), the middle Middle Pleistocene Ganhaizi Glaciation (0.53~0.45MaB.P.), the late Middle Pleistocene Lijiang Glaciation (0.31~0.13MaB.P.), and the middle-late Late Pleistocen Dali Glaciation, as well as on new ESR dates, the authors also discovered a series of relics of the four glaciations along the western foot, and are able to correlate them with glaciations on the Tibetan Plateau.The results show that the Yulong Mountains area was a part of the united peneplain from the Tibetan Plateau to the Yunnan-Guizhou Plateau, 500~1000m a.s.l. during the Miocene. In the Pliocene and the Early Pleistocene, the Yulong Mountains uplifted and the Lijiang Basin, Daju Basin, Shigu Valley and other basins subsided due to the fault activities along both the eastern and the western feet of the Yulong Mountains. At the same time, the ancient Jinsha River was formed in its present valley. In the early Middle Pleistocene, the Yulong Mountains had uplifted over the snowlines, and giant piedmont glaciers of the Yulong Glaciation, the largest glaciation in this area, occurred at their east, west and northeast feet. Because of barrier from moraines of the Yulong Glaciation, a glacial barrier lake, "Lake Shigu" was gradually formed in the former Shigu Valley. The glaciers in the Ganhaizi Glaciation were possibly piedmont or valley ones, but much smaller than those of the former. During the two interglacial periods in the Middle Pleistocene, some tributaries of the Jinsha River were formed. In the late Middle Pleistocene, the large-scale valley glaciers of the Lijiang Glaciation developed in the tributaries of the Jinsha River and three fluvioglacial fans from the west feet of the Yulong Mountains had possibly entered into the Lake Shigu and made its water level rise. In the Last Interglacial Period at about 80kaB.P., water of the Lake Shigu was wholly discharged and then the present Jinsha River and their four terraces (5~15m, 15~25m, 25~35m and 40~50m, respectively)were formed. In the middle-late Late Pleistocene, valley glaciers of the Dali Glaciation were also developed in the tributaries of the Jinsha River, but their scales were smaller than those of the Lijiang Glaciation.