2004 Vol. 10, No. 4

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FEATURES OF SPACE DISTRIBUTION OF THE FOREST LINE AND RELATIONS BETWEEN THE FOREST LINE AND CLIMATIC LIMIT OF PERMAFROST AND CLIMATIC SNOWLINE IN CHINA
JIANG Fu-chu, WU Xi-hao, WANG Shu-bin, FU Jian-li, WANG Yan, ZHAO Zhi-zhong
2004, 10(4): 289-299.
Abstract (225) PDF (495KB)(28)
Abstract:
The altitude of the forest line that is generally marked by the upper limit of the dark coniferous forest zone in the vertical zones of natural vegetation is controlled by the temperatures and their annual range.In this paper, based mainly on the heights above sea level of the upper limits of the modern dark coniferous forest zones in some mountainous regions and the climatic data obtained from 102 meteorological stations in China, the theoretic altitude of the forest line has been calculated and maps showing the altitude isolines of the forest line, the isolines of height differences between the permafrost limits and the forest line and the isolines of height differences between the modern climatic snowline and the forest line in China have been constructed respectively. On that basis, the primary features of spatial distribution of the forest line in China and its relations with the permafrost limits and climatic snowline are discussed.
LAKE-LEVEL CHANGE OF NAM CO,TIBET,SINCE THE LATE PLEISTOCENE AND ENVIRONMENT INFORMATION OF CLAY MINERALS IN LACUSTRINE DEPOSITS
ZHU Da-gang, MENG Xian-gang, ZHAO Xi-tao, SHAO Zhao-gang, MA Zhi-bang, YANG Chao-bin, WANG Jian-ping, WU Zhong-hai
2004, 10(4): 300-309.
Abstract (150) PDF (335KB)(7)
Abstract:
Field surveys of lacustrine sediments and lakeshore levees and leveling surveys of lake terraces at peripheries of Nam Co-the largest lake with the highest altitude above sea level in Tibet-indicate that there are 6 lake terraces below the lakeshore of Nam Co 48 m above the lake level and highstand la custrine sediments from 48 to 139.2 m above the lake level.Isotopic dating of the lacustrine sediments shows that the development of Nam Co and the evolution of the ancient large lake on the southeastern North Tibetan Plateau can be divided into three stages:① the ancient large lake stage at 116~37 ka BP, ② the outflow lake stage at 37~30 ka BP, and ③ the Nam Co stage since 30 ka BP.Clay minerals in lacustrine sediments of Nam Co since the late Pleistocene were analyzed by X-ray diffraction, and according to the analytic results, the paper discusses the environment information of clay minerals by using the ratio method, kaolinite method and X-ray diffraction method.The changes of the clay mineral composition show the climatic and environmental features of a dry temperate arid and semi-arid area.The study provide new data for the study of the lake evolution, climate change, paleogeographic change and the plateau uplift process.
QUATERNARY SPOROPOLLEN ASSEMBLAGES AND ENVIRONMENTAL EVOLUTION OF THE GONGHE BASIN ON THE NORTHEASTERN MARGIN OF THE QINGHAI-TIBET PLATEAU
SHI Wei, MA Yin-sheng, WU Man-lu, DU Jian-jun, ZHANG Xi-juan
2004, 10(4): 310-318.
Abstract (137) PDF (506KB)(9)
Abstract:
Relatively thick Quaternary strata are deposited in the Gonghe basin on the northeastern margin of the Qinghai-Tibet Plateau.They record Quaternary environmental changes in the basin in details.On the basis of an analysis of the characteristics of Quaternary depositional sequences and sporopollen assemblages in the Gonghe basin, combined with the thermoluminescent dating, the authors have studied the environmental change in the basin since the Quaternary and divided the change into two major phases:the early phase was one of lacustrine sedimentation (from the late part of the middle Pleistocene to 0.079 Ma), when the climate was relatively warm, and the late phase was one of fluvial sedimentation and eolian sedimentation (from 97.2 ka to the present), when the climate was relatively dry.The early phase may be further divided into three climatic stages and five climatic substages.Generally, in the Gonghe basin the climate has turned gradually from slightly warm to dry and the paleo-vegentation has changed gradually from forest vegetation to forest-steppe vegetation since the early Pleistocene.The main cause for this change is possibly that strong uplift of the Qinghai-Tibet Plateau since the early Pleistocene may have changed the southwest monsoon climatic pattern.
PALEOGENE AND NEOGENE PALEOCLIMATIC CHANGES IN THE TURPAN BASIN,NORTHWEST CHINA
ZHANG Xi-juan, CHENG Jie, WANG Hai-zhi, YU Wen-yang
2004, 10(4): 319-326.
Abstract (200) PDF (246KB)(7)
Abstract:
The Paleogene and Neogene at the Lamjin section in the Turpan basin, Xinjiang, have a sedimentary thickness of~1779 m.This section is a good carrier for the study of the paleoclimate in this period in the basin.Major element geochemical analysis of the sediments in the section indicates the following:in the late Paleocene, the climate was warm and wet;in the late Eocene, it was also warm, but dry and wet alternately;in the Oligocene, it was warm and dry;in the Miocene, the climate was divided into two phases, being warm and wet in the early phase and cold and dry in the late phase;in the Pliocene, it was obviously dry.
DISCOVERY OF QUATERNARY REMNANTS OF GLACIATION IN THE NORTHERN SEGMENT OF THE LULIANG MOUNTAINS,NINGWU,SHANXI,AND THEIR SIGNIFICANCE
MENG Xian-gang, ZHU Da-gang, SHAO Zhao-gang, YU Jia, HAN Jian-en, MENG Qing-wei
2004, 10(4): 327-336.
Abstract (187) PDF (618KB)(19)
Abstract:
Lying at an average elevation of~2000 m above sea level and a relative elevation of a few hundred to about one thousand meters, the northern segment of the Lüliang Mountains, Ningwu, Shanxi, belongs to a medium mountain area.In the area Quaternary remnants of glaciation are very well developed and there are a great variety of types with distinctive features.They include U-valleys, knifeedge crests, horns, cirques and firn-basins, as well as many glacial erratic boulders, outwash sediments, moulins, deformed pebbles and streak pebbles in U-valleys.The discovery of abundant Quaternary remnants of glaciation in the northern segment of the Lüliang Mountains, Ningwu, Shanxi, not only proves the existence of many Quaternary glacial movements in the medium and low mountain areas in eastern China, but, as the scale of the glaciers are larger than was expected, the discovery also provides an important basis for the study of the paleoclimatic and paleoenvironmental evolution and important data and evidence for the division and correlation of China's Quaternary glacial stages.
VARIATION OF PRECIPITATION IN NAM CO,TIBET,SINCE THE LATE PLEISTOCENE AND ITSENVIRONMENTAL RESPONSE
SHAO Zhao-gang, MENG Xian-gang, ZHU Da-gang, WANG Jin, YANG Chao-bin, HAN Jia-nen, YU Jia, MENG Qing-wei
2004, 10(4): 337-343.
Abstract (175) PDF (225KB)(6)
Abstract:
Field surveys of the Nam Co-a large lake with the biggest area (1940 km2) and highest elevation above sea level (4718 m) in Tibet show that there are extensive lacustrine sediment around the Nam Co.Uranium-series and 14C dating indicate that the lacustrine sediments along the shores of the Nam Co are late Pleistocene and Holocene in age.The lake evolution was studied according to the change in distribution of lacustrine sediments of different ages around the Nam Co and the paleo-precipitation in the Nam Co drainage area was calculated.The study indicates that the climate in the study area turned from wet to dry since the late Pleistocene and that the precipitation has had a tendency of decrease since the Holocene.
INVESTIGATION OF THE EVOLUTION AND ENVIRONMENT CHANGE OF TYPICAL LAKES IN YUNNAN
SHI Zheng-tao, MING Qing-zhong, ZHANG Hu-cai
2004, 10(4): 344-350,365.
Abstract (197) PDF (1636KB)(12)
Abstract:
This paper introduces the primary results of investigations of seven lake systems and geomorphology of the lake areas in Yunnan.A total of 140 m of drilling cores were recovered from the wells in the seven lakes and bed mud samples were taken from some of the lakes.Investigation and study of the lake terraces, layered geomorphology and related strata indicate that there exist two to three distinct highstand banks and that many conch layers are distributed in the lakes, which are higher than dolinen and formed during the later Pleistocene.The sedimentary characteristics of the section at the top of Snake Mountain and previous dating data suggest that the deposition of the Sheshan Formation ended in the late part of the last glacial epoch.
REMOTE SENSING CLASSIFICATION OF SURFACE FEATURES ON THE ROIG(E) PLATEAU
XU Gang, ZHAO Zhi-zong
2004, 10(4): 351-356.
Abstract (133) PDF (212KB)(9)
Abstract:
All materials have their characteristic spectral absorption peaks in remote sensing data.So missing and mixing of information that usually occurred in previous remote sensing classification may be greatly reduced by spectral identification.In order to solve the problem of the remote sensing classification of surface features on the Roigü Plateau, the spectral angle mapper classification of surface features was for the first time used in the ETM multispectral pansharp images.The steps of the classification are as follows:setting the standard of remote sensing data →selecting the swatches in the training area →using the minimum noise fraction rotation (MNF) to reduce the dimension and remove noises →using the pixel purity index (PPI) to purify the swatches →using the n-D visualizer to regroup the swatches →using the spectral angle mapper (ASM) to identify surface features.The classification results are as follows:the total accuracy of the class accuracy evaluation is 0.806 and the Kappa coefficient is 0.785.These accuracies conform to the technical requirements of 1:50 000 detailed land survey.
NUMERICAL SIMULATION OF THE STABILITY OF HIGH SAND LOESS SLOPES
ZHANG Yong-shuang, WANG Hong-cai
2004, 10(4): 357-365.
Abstract (141) PDF (302KB)(10)
Abstract:
Based on field investigation and lab tests, the main failure form of the sand loess slope and its impact factors on the northern Loess Plateau are summarized in this paper.Taking for an example from the construction of high-type highways in northern Shaanxi, a series of numerical simulations have been made using the elastico-plastic finite-element method to illustrate the influences of various factors, including the slope form, rainfall and earthquakes, on the stability of sand loess slopes under the conditions of excavation by different engineering works.The simulation results indicate that:with increasing slope angle or slope height, a slope becomes gradually less and less stable;a slope with a stepped form is more stable than that with a linear form, and is favorable for protection;rainfall tremendously influences the stability of a sand loess slope, and especially in the case of water logging at the slope foot, the stain value of the slope foot increases nearly 20 times than that in a normal state; earthquakes can make the values of both the stress and strain at the slope foot increase obviously with the growth of seismic acceleration.The simulation results provide a scientific basis for the high sand loess slope design and hazard control.
COMPARATIVE ANALYSIS OF THE METHODS OF INTERNAL FORCE CALCULATION OF THE PRESTRESSED CABLE LATTICE BEAM FOR LANDSLIDE CONTROL
MA Ying-juan, PENG She-qin, ZHOU Bin
2004, 10(4): 366-371.
Abstract (144) PDF (222KB)(6)
Abstract:
On the basis of the case study of a landslide prevention and control engineering work, a new model for design and calculation of the lattice beam suited to the layout of the engineering work is proposed.According to a comparative analysis of the results of calculation by using this model and the results of calculation by using the conventional Winkler elastic foundation beam and upside beam methods, the authors draw the conclusion that this model more closely conform to the actual manner of lo ad of the lattice beam.
TECTONIC CHARACTERISTICS IN THE PINGXIANG AREA IN THE JUNCTION BELT BETWEEN THE YANGTZE PLATE AND SOUTH CHINA PLATE
LIU Xi-yuan, ZHONG Da-hong, YUAN Jian-ya, XIE Qing-hui, LI Yi-chun
2004, 10(4): 372-379.
Abstract (147) PDF (277KB)(12)
Abstract:
The junction belt between the Yangtze plate and South China plate passes central Jiangxi. Since the end of the Yanshanian movement, nappe-thrusting predominated in the northern part of the Pingxiang area in the junction belt, forming large-scale thrust nappe structure, in its southern part a metamorphic-magmatic thermal dome and a series of glide fold zones and glide block structures formed under the action of gravitational gliding;and in the central part the junction belt of the stacked southern and northern structures formed.Coal measures are covered by these thrust nappes and glide nappes in many areas.This opens up a new sphere for looking for hidden coal fields.Furthermore, the junction belt is also a favorable cobalt polymetallic ore region.