Paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in Huangshui Valley, the northeastern Tibetan Plateau, China

Gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system. In this study, flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the Xining Region, northeastern Tibetan Plateau, China. These gravel deposits range in age from the modern Huangshui riverbed to Miocene-aged deposits overlain by eolian sediments. Our major objectives were not only to collect first-hand field data on the fluvial gravel sediments of the Xining Region, but also to the reconstruct the evolution of the fluvial system. These data may offer valuable information about uplift of the northeastern Tibetan Plateau during the late Cenozoic era. Reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130–180°. In addition, the lithological compositions in the higher gravel deposits differ significantly from the lower terraces, suggesting that the source areas changed at the same time. Eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1.55 Ma and 1.2 Ma. We suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period. Therefore, this study provides a new scenario of fluvial response to tectonic uplift: a reversal of flow direction. In addition, field observation and statistical analyses reveal a strong relationship between rock type, size and roundness of clasts.     

The response of lake-glacier variations to climate change in Nam Co Catchment, central Tibetan Plateau, during 1970–2000

Based upon the 1970 aero-photo topographic map, and TM/ETM satellite images taken in 1991 and 2000, the authors artificially interpreted boundaries of lake and glaciers in Nam Co Catchment, and quantified lake-glacier area variations in different stages by “inte-grated method” with the support of GIS. Results show that from 1970 to 2000, lake area in-creased from 1942.34 km2 to 1979.79 km2 at a rate of 1.27 km2/a, while glacier area de-creased from 167.62 km2 to 141.88 km2 at a rate of 0.86 km2/a. The increasing rate of lake in 1991–2000 was 1.76 km2/a that was faster than 1.03 km2/a in 1970–1991, while in the same period of time, the shrinking rates of glaciers were 0.97 km2/a and 0.80 km2/a respectively. Important factors, relevant to lake and glacier response to the climate, such as air tempera-ture, precipitation, potential evapotranspiration and their values in warm and cold seasons, were discussed. The result suggests that temperature increasing is the main reason for the accelerated melting of glaciers. Lake expansion is mainly induced by the increase of the gla-cier melting water, increase of precipitation and obvious decrease of potential evapotranspi-ration. Precipitation, evaporation and their linkages with lake enlargement on regional scale need to be thoroughly studied under the background of global warming and glacier retreating.     

MEASURING CHANNEL PLANFORM OF MEANDERING RIVERS

The traditional measure of river-channel sinuosity, P, is shown to vary with scale of measurement, the geometric character of the particular reach, and the starting point of the divider walk. Meander wavelength, L, suffers from non-reproducibility caused by the subjective identification of inflection points, a problem compounded by the irregularity of river meanders. Applicability of the angle measure technique (AMT) to the measurement of meander planform is demonstrated. The AMT considers variations in the complexity of meandering with scale, eliminating the dependence of results on scale of measurement. The AMT also samples the river at random points rather than sequentially, unlike the divider walk used to calculate P, avoiding the dependence of P on the starting position of the divider walk. The AMT also does not require subjective identification of inflection points as wavelength L does. Additionally, the traditional measures P and L are difficult to apply to manifestly underfit rivers. In this study, the AMT is applied to two underfit rivers and measures of meander size and sinuosity are calculated for each set of meanders. [Key words: sinuosity, meanders, wavelength, underfit river, fluvial geomorphology.]     

Assessing adaptability of planted trees using leaf traits: A case study with Robinia pseudoacacia L. in the Loess Plateau, China

Leaf trait patterns and their variations with climate are interpreted as an adaptive adjustment to environment.This study assessed the adaptability of planted black locust (Robinia pseudoacacia L.) based on the analysis of leaf traits and the comparison of its leaf traits with inter-specific ones existing in the same area.We measured some water and N use related leaf traits: leaf dry mass per unit area (LMA) and N,P and K concentrations based on both leaf area (Narea,Parea and Karea) and leaf mass (Nmass,Pm...     

Estimation of precipitation condensation latent heat in rainy season over Qinghai-Tibet Plateau

The basic data for this research comprise the outgoing long-wave radiation(OLR) data observed by the United States National Oceanic and Atmospheric Administration(NOAA) series satellites from June 1974 through December 2005 over the area of 75°-105°E and 25°-40°N(totaling 91 grid zones when the horizontal resolution is 2.5° longitude by 2.5° latitude) and the monthly rainfall data recorded,from 1961 through 2005,by 93 conventional meteorological stations on the Qinghai-Tibet Plateau.Based on the research of the relation between rainfall and OLR and climate regionalization,a mathematic model was established for each region and grid zone,which is applied to estimate the monthly rainfall and then to estimate the monthly latent heat resulting from the condensation of precipitation year by year from 1961 through 2005.The results indicated that the multi-year average precipitation is 401.5 mm and the condensation latent heat is 18.55×1020 J in the eastern part of the Qinghai-Tibet Plateau;the increasing rate of condensation latent heat is 0.218×1020J/10a in the recent 45 years;that is to say,it will increase 1.2 percent in each decade.Furthermore,the total condensation latent heat and its variation rate in the Qinghai-Tibet Plateau are slightly larger than in the east to the plateau.     

Distribution of uranium isotopes in the main channel of Yellow river (Huanghe), China

Uranium isotopes were measured in waters and suspended particulate matters (SPM) of the main channel of Yellow River, China that were sampled during four field trips between August 2005 and July 2006. The results show that the concentration of dissolved U (2.04–7.83 μg/l) and the activity ratio of ²³⁴U/²³⁸U (1.36–1.67) are much higher than the average U concentrations and activity ratios of global major rivers. Mass balance calculations using the results of simulated experiments and measurement data show that the section of the Yellow River between Lanzhou and Sanmenxia has its dissolved U derived from two sources: suspended sediments (68%) and groundwater/runoff from loess deposits (32%). Both sources are related to the heavy erosion of the Chinese Loess Plateau.     

青藏高原北部移动冰丘破坏桥墩的数值模拟

青藏高原北部常年冻土区断裂破碎带发育的移动冰丘对桥梁、涵洞、输油管道等工程设施具有不同形式的破坏作用。考虑移动冰丘与工程设施的相互作用,根据野外观测和实验资料设计模型,应用三维有限元数值模拟方法,计算移动冰丘冻胀产生的位移场、应力场和桥墩弯曲应力,分析桥墩破裂机理。结果表明,移动冰丘能够产生11～-21 MPa的轴向应力和15～-31 MPa的主应力,在桥墩周围形成不同规模的应力集中区,导致桥墩发生显著偏移。桥墩的偏移和弯曲能够在桥墩内部产生高达61.9～64.6 MPa的张应力和-45.0～-49.0 MPa的压应力,超过桥墩的强度极限。在粗细桥墩连接部位,外侧形成张应力集中区,最大张应力达26～30 MPa;内侧形成压应力集中区,最大压应力达-25～-28.8 MPa。粗细桥墩连接部位外侧的张应力超过了钢筋混凝土的抗张强度,产生与野外观测资料基本吻合的桥墩破裂和结构破坏。移动冰丘导致桥墩变形破坏的三维有限元数值模拟能够为常年冻土区桥梁工程设计和地质灾害防治提供力学参数和科学依据。     

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

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.     

西藏高原近40年的气温变化

利用西藏1961－2000年月平均气温、最高气温、最低气温资料，分析了近40年高原气温的变化趋势。结果发现，西藏大部分地区四季和年平均气温为升温趋势，尤其是秋、冬季；高原上普遍存在气温非对称变化现象，以Tmax、Tmin显著上升，但Tmin上升幅度大于Tmax为主要类型。Tmax上升主要表现在夏季，增暖以冬季最为明显，气温日较差降夏季外均显著减小。在各纬度带上均表现为升温，春、秋季升温最大，冬季次之。高海拔地区比低海拔地区升温强。近40年来西藏高原年平均气温以0.26℃/10a的增长率上升，明显高于全国和全球气温的增长率。20世纪60年代多异常偏冷年，90年代多异常偏暖年。     

Florogeography of mire plants in southern part of qinghai-xizang plateau and its adjacent areas

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