四川螺髻山清水沟冰川槽谷演化及其影响因素

螺髻山地处青藏高原东南缘,是确切存在第四纪古冰川遗迹的典型山地之一,该区冰川地貌演化对于研究环境变化具有重要的科学意义。螺髻山东坡清水沟保存两套古冰川槽谷,分别为上槽谷和下槽谷,其中下槽谷保存完整,而上槽谷在3450~3600 m的阴坡部分出现缺失。采用野外地貌调查与模型分析相结合的方法,对冰川槽谷地貌进行分析,结果表明:清水沟槽谷的抛物线模型中,|A|值在1.3101~15.2064 之间变动,B 值变化于0.9695~3.2965 之间,且随着海拔由高到低,都存在着先变小后变大的规律,A、B值同时反映出在海拔3450~3600 m处冰川槽谷的演化不符合常态。分析认为岩性差异和河流溯源侵蚀是影响上槽谷形态的主要原因。对保存在清水沟上下槽谷内的高、低侧碛进行ESR年代测定,结果显示:高侧碛形成于58-84 ka BP左右的末次冰期早期,对应深海氧同位素4 阶段(MIS4);低侧碛形成于13-17 ka BP,属于于全球末次冰盛期晚期的产物。两次冰川作用分别塑造出两套冰川槽谷,即在末次冰期早期冰川作用形成上槽谷,末次冰期晚期形成下槽谷。

Evolution of glacial trough and influence factors of the Qingshui Valley in Luoji Mountain,Sichuan Province

Luoji Mountain located at the southeast margin of the Qinghai- Tibet Plateau is one of the typical mountains in China where Quaternary glacier relics exist. The evolution of glacier landforms in the area plays an important role in the study of regional environmental change. In the Qingshui Valley on the east slope of the Luoji Mountain, two sets of ancient glacial trough valleys, namely the inner trough valley and lateral trough valley, are preserved. The inner trough valley is relatively intact. However, the lateral trough valley between 3450 m and 3600 m in the shady slope is incomplete. Based on field investigation and model analysis, this study examines the evolution of the glacial trough valley. The model analysis shows that the A and B parameter values vary between 1.3101-15.2064 and 0.9695-3.2965 respectively and these values first increase and then decrease with decreasing altitudes. Both values indicate that the form of the glacial trough valley is atypical. The field investigation and model analysis indicate that lithology and headwater erosion have contributed to the shape of the trough valley. This study applied the ESR dating method to define the high and low moraine in the through valley. The result shows that the high lateral moraine was formed in ~58-84 ka BP, which was in the early stage of the last glacial cycle, corresponding to the Marine Isotope Stage 4 (MIS4). The low lateral moraine was formed in 13-17 ka BP, which was during the last glacial maximum (LGM), corresponding to MIS 2. During the last glacial cycle two glaciations developed two sets of trough valleys respectively, that is, the early stage of the last glacial cycle contributed to the formation of the lateral trough valley, and the late stage of the last glacial cycle contributed to the formation of the inner trough valley. The glacial sequences in the Qingshui Valley also show that the glacial activities took place here accorded with other mountains in the surrounding areas of the Qinghai-Tibetan Plateau.