Gengnian Liu

Quaternary geomorphological evolution of the Kunlun Pass area and uplift of the Qinghai-Xizang (Tibet) Plateau

Abstract There is a set of Late Cenozoic sediments in the Kunlun Pass area, Tibetan Plateau, China. Paleomagnetic, ESR and TL dating suggest that they date from the Late Pliocene to the Early Pleistocene. Analyses of stratigraphy, sedimentary characteristic, and evolution of the fauna and flora indicate that, from the Pliocene to the early Quaternary (about 5–1.1 Ma BP), there was a relatively warm and humid environment, and a paleolake occurred around the Kunlun Pass. The elevation of the Kunlun Pass area was no more than 1500 m, and only one low topographic divide existed between the Qaidam Basin and the Kunlun Pass Basin. The geomorphic pattern in the Kunlun Pass area was influenced by the Kunlun–Yellow River Tectonic Movement 1.1–0.6 Ma BP. The Wangkun Glaciation (0.7–0.5 Ma) is the maximum Quaternary glaciation in the Pass and in other areas of the Plateau. During the glaciation, the area of the glaciers was 3–5 times larger than that of the present glacier in the Pass area. There was no Xidatan Valley that time. The extreme geomorphic changes in the Kunlun Pass area reflect an abrupt uplift of the Tibet Plateau during the Early and Middle Pleistocene. This uplift of the Plateau has significance on both the Plateau itself and the surrounding area.

Glacial valley cross-profile morphology, Tian Shan Mountains, China

Abstract The morphology of glacial valley cross-sections can be described in terms of power law ( y = ax b ) or quadratic equations ( y = a + bx + cx 2 ) fitted to empirical data. The quadratic solution provides a more robust way of describing the morphology of glacial valley cross-sections, whereas the power law has more potential in understanding the cross-sectional shapes and their evolution. These two functions are used to study the cross-sectional morphology of glacial valleys in the middle and western Tian Shan Mountains and to discuss the comparison with fluvial channels. The major conclusions are: (1) Power law equation parameters ( a and b ) are sensitive to the origin selection with larger sensitivity in vertical and A ( A =ln a ) values. Conversely, c values of the quadratic equation are more stable regardless of different origins selected. (2) Hirano and Aniya [Earth Surf. Processes Landforms 13 (1988) 707–716] suggested two characteristic patterns in the relationship between the power law exponent, b , and the valley form ratio, FR . However, glacial valleys in these areas do not fit the Rocky Mountain model for b–FR values described by Hirano and Aniya for alpine glacial valleys. This indicates that this Rocky Mountain model cannot be applied to all alpine glacial areas. (3) The c values of the quadratic equation represent a curvi-linear trend with its corresponding FR s. At the same time, power law parameters ( A and b ) fit a closed linear relationship both from these areas and others in the published literature. (4) The cross-sectional shapes of glacial valleys show clear differences with fluvial channels by comparing A–b values of glacial valleys with the hydraulic geometry of fluvial channels. This implies that the A–b relationship and the variation range of b values (commonly with 1.5–2.5) may be helpful to differentiate valleys formed by different processes.

Analysis of the glacial geomorphological characteristics of the last glacial in the Tianger area, Tien Shan, and their paleoclimate implications

Abstract The Tianger area in the Tien Shan preserves many glacial landforms to which several methods of estimating ancient equilibrium-line altitudes (ELAs) can be applied. Thus it provides the opportunity to compare different methods and evaluate the correlation between the methods and their errors. This comparison provides guidance in the application of these methods in other mid-latitude alpine glaciated areas. In this paper we calculate characteristic ratios relating to the ELAs, including accumulation–area ratio (AAR), toe–headwall altitude ratio (THAR), terminus–summit altitude method (TSAM) and Höfer value, and their correlations with each other and the geomorphological characteristics. The AAR of a glacier is small when the slope of the bedrock beneath it is small and the area is large, and the AAR of a glacier with such characteristics is better correlated with its THAR, TSAM and Höfer value. Paleoclimate information derived from these characteristic ratios relating to ELAs is discussed. The glaciers and the glacial climate of the early and middle stage of the last glacial are more continental than those of the Last Glacial Maximum (LGM). Compared with those of the LGM on the Qinghai–Tibetan Plateau and surrounding mountains, the ELA characteristics of the early and middle stage of the last glacial in the Tianger area show more continental features.