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Magnetic properties of Jiaxian red clay sequences from northern {1. Loess Plateau and its paleoclimatic significance

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Science China earth {1. 2005年第8期48卷 1234-1245页

作者： QIANG xiaoke, AN Zhisheng, LI Huamei, CHANG Hong & SONG Yougui 1. {1., {1., chinese academy of sciences, {3., China 2. Guangzhou institute of Geochemistry, chinese academy of sciences, Guangzhou 51.640, China 1. chinese academy of sciences SKLLQG Institute of Earth Environment 710075 Xi’an China 2. chinese academy of sciences Guangzhou Institute of Geochemistry 510640 Guangzhou China

Detailed rock magnetism investigation of the Jiaxian red clay sequences indicated that there are common magnetic mineralogy properties in red clay and loess-paleosol sequences from the {1. Loess Plateau as well as the marked properties of themselves, magnetic min-erals mainly with magnetite, maghemite, hematite, and possibly limonite/goethite contributing to the magnetic behavior. Meanwhile, it is found that the strong paleosol in red clay sequences has a lower coercivity and higher content of ultra-fine ferrimagnetic grains than that of the weak pa-leosol, which is similar to loess and paleosol in upper Wucheng Loess sequences, and indicates that humid conditions and relatively strong pedogenesis play a significant role in the increase of ultra-fine magnetic minerals and transformation of the magnetic minerals. This suggests that, like Quaternary loess-paleosols, the change of characteristics of paleoclimatic conditions of the late Tertiary red clay deposits is fluctuant. In addition, the results of magnetic hysteresis properties show that the applied saturated field for samples from the Jiaxian red clay sequences is higher than that of the samples from eastern and southern {1. Loess Plateau. It is obviously shown that there exist more hard magnetic minerals and relatively weak biochemical processes in the Jiaxian red clay sequences on northern {1. Loess Plateau. We conclude that the paleocli-matic {3. is different between northern and eastern/southern {1. Loess Plateau, and it should be more arid in northern {1. Loess Plateau.

关键词： northern chinese Loess Plateau, red clay, magnetic property, paleoclimatic significance.

^(40)Ar/^(3.)Ar dating of shear deformation of the {1.anshuihe fault zone in west Sichuan and its tectonic significance

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Science China earth {1. 2004年第9期47卷 794-803页

作者： ZHANG Yueqiao1, CHEN Wen2, 3.& YANG Nong1 1. institute of Geomechanics, {1. academy of Geological {3., Beijing 100081, China 2. institute of Geology, {1. academy of Geological {3., Beijing 10003., China 3. institute of Geology and Geophysics, chinese academy of sciences, Beijing 100029, China institute of Geomechanics Chinese Academy of Geological Sciences Beijing 100081 China institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China

Based on field geological survey, structural measurements and classical Ar/Ar dating of mica, biotite and K-feldspar, we obtain cooling ages for Miocene left-lateral shear along the xianshuihe fault zone. The results document two thermal events during the sinistral shear. The early event (1.-1. Ma) corresponds to rapid cooling of the Zheduoshan granitic massif from above 700℃ to below {1.0℃. The late event (5-{1.5 Ma) corresponds to cooling of granites intruded along the eastern side of the fault zone. These dating results provide important thermochronological constraint on the timing of late Cenozoic eastward extrusion of the Chuan-Dian Block in the SE Tibetan margin.

关键词： xianshuihe fault zone, Zheduoshan granitic massif, sinistral shear deformation, 40Ar/3.Ar dating, late Cenozoic.

Chronology of Holocene lacustrine sediments in Co Ngoin, central Tibetan Plateau

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Science China earth {1. 2006年第9期49卷 991-1001页

作者： WU Yanhong1. WANG Sumin1. HOU xinhua1.{1.1. Key Laboratory of Lake Sedimentation and environment, Nanjing {1. of Geography and Limnology, chinese academy of sciences, Nanjing 21.008, China 2. {1. of Tibetan Plateau Research, chinese academy of sciences, Beijing 1.085, China {1. Graduate University of chinese academy of sciences, Beijing 1.00{1., China 1. Key Laboratory of Lake Sedimentation and environment Nanjing Institute of Geography and Limnology Chinese Academy of Sciences Nanjing 210008 China 2. institute of Tibetan Plateau Research Chinese Academy of Sciences Beijing 10085 China 3. Graduate University of {1. Beijing 100039 China

Chronology is the basis for using lacustrine sediments to reconstruct the history of en-vironmental change. Radioactive-nuclides such as 1.C, 21.Pb and 1.0}Cs dating are mainly used to establish the chronology for recent several ten thousand years. Because of being mixed with “dead carbon”, the measured 1.C age is always older than the actual age which is recognized as “reservoir effect”. Cs is a kind of active metal element, and easy to migrate vertically in the sediment that leads to the error of the time marker. 21.Pb dating should make sure to select CIC model or CRS model. On the Tibetan Plateau, most of the lakes are alkaline closed lake where Cs is more moveable in the sediment and the reservoir effect caused by “dead carbon” on 1.C dating is stronger. Based on the analysis on results of 1.C, 21.Pb and 1.0}Cs of the lacustrine sediments from Co Ngoin, central Tibetan Plateau, we use the simple regression method to re-calculate the 1.C calendar ages, and establish the time sequence for cores CE-1.and CE-2 with result of 21.Pb CRS model for the upper 3. cm and re-calculated 1.C calendar age for sediments bellow 3. cm. Since 1.00 cal. a BP, sedimentation inter-rupted for more than 1.00 years. According to this time sequence, variations of environmental proxies confidently reflect the major climatic events in Holocene.

关键词： 1.C, 21.Pb and 1.0}Cs, chronology, lacustrine sediments, climatic event, Co Ngoin, central Tibetan Plateau.

environmental characteristics of Mid-Holocene recorded by lacustrine sediments from Lake Daihai, north environment sensitive zone, China

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Science China earth {1. 2006年第9期49卷 968-981页

作者： SUN Qianli1.2, ZHOU Jie1. SHEN Ji3. CHEN Peng1.2, WU Feng1.2 & {1.E {1.uping1.2 1. State Key Lab of Loess and Quaternary Geology, institute of earth environment, {1., xi’an 71.075, China 2. Graduate University of {1., Beijing 1.003., China 3. Nanjing institute of Geography and Limnology, {1., Nanjing 21.008, China 1. State Key Lab of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi’an 710075 China 2. Graduate University of chinese academy of sciences Beijing 100039 China 3. Nanjing {1. of Geography and Limnology Chinese Academy of Sciences Nanjing 210008 China

Climate proxies, such as total organic carbon and nitrogen (TOC, TN), carbonate content (CaCO{1., grain-size and pollen of the sediment core retrieved from enclosed Lake Daihai which lies in the north China environment sensitive zone are analyzed to reconstruct the environment evolution of the area based on high-resolution radiocarbon chronology. The results reveal that the TOC and TN contents of the sediments correlate well with pollen percentage and pollen flux variations during the Holocene, and both reach their peak values simultaneously at 6.7―{1.5 ka BP (calendar age, 7.6―{1.6 ka BP). Since 6.7 ka BP, both the CaCO{1.and organic matter contents of the core have simultaneous variations, and their high values also occur during 6.7―{1.5 ka BP. While during 9.0―6.7 ka BP (calendar age, 1.―7.6 ka BP) relatively lower level of organic matter content and pollen flux corre- spond to the higher level of carbonate content. The above relations suggest that during 6.7―{1.5 ka BP, the productivity and effective precipitation were greatly improved in the lake drainage area, and this would probably strengthen the hydrodynamic conditions, enhancing organic matter, pollen and carbonate inputs from terrestrial sources. Such processes would account for the enrichment of both organic matter and carbonate in the sediments. While during 9.0―6.7 ka BP, the lower level of or- ganic matter, pollen flux but high carbonate content show depressed productivity and declined vege- tation coverage. The higher carbonate content at this stage would have probably resulted from the higher evaporation ratio of the lake water under relatively drier climate conditions. Therefore, it is in- ferred that during 6.7―{1.5 ka BP, the climate was more humid with abundant rainfalls and vegetation was more flourishing in the Lake Daihai area. This can be seen as Holocene Climate Optimum (HCO). As a result, this has evident discrepancies with the traditional notion that the HCO occurs at Early Holocene or early Mid

关键词： Lake Daihai, Mid-Holocene, lacustrine sediments, environmental characteristics.

Spectral analysis of quasi-stationary sea surface topography from GRACE mission

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Science China earth {1. 2005年第11期48卷 2040-2048页

作者： ZHANG Zizhan1.2 & LU Yang1.3.1. {1. of Geodesy and Geophysics, {1., Wuhan 43.077, China 2. Graduate School of the {1., Beijing 1.003., China 3. Unite Center for Astro-geodymics Research, {1., Shanghai 20003., China 1. institute of Geodesy and Geophysics Chinese Academy of Sciences 430077 Wuhan China 2. Graduate School of the chinese academy of sciences 100039 Beijing China 3. Unite Center for Astro-geodymics Research Chinese Academy of Sciences 200030 Shanghai China

During the last two decades satellite altimetry has offered an abundance of meas-urements of the sea surface resulting in the improvement of global mean sea surface height (MSSH) and marine geoid determination. On the other hand, with the launching of new genera-tion gravity satellites, some high accuracy long-wavelength gravity models are available. These breakthroughs give us a great opportunity for new estimation of quasi-stationary sea surface topography (QSST). In this paper, the new gravity model GGM01. derived from GRACE mission is briefly presented, and a new global high precision and high-resolution QSST is determined based on the GGM01. model and the global MSSH. The spectral features of the QSST esti-mated by GGM01. and EGM96 gravity model to degree/order 200 are discussed by spectral analysis. As a result, the QSST is mainly composed of long waves, medium waves partially and short waves scarcely, its power spectral structures are different between the zonal direction and the meridional direction, there are great differences between the two models, which maybe ex-plain why the ocean currents derived from the two gravity models by Tapley show different pat-terns.

关键词： quasi-stationary sea surface topography, mean sea surface height, GGM01. fast Fourier transform, spectral analysis

Impacts of permafrost changes on alpine ecosystem in Qinghai-Tibet Plateau

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Science China earth {1. 2006年第11期49卷 1156-1169页

作者： WANG Genxu1.3., LI Yuanshou2 , WU Qingbai2 & WANG Yibo3.1. institute of Mountain Hazards and {1., chinese academy of sciences, Chengdu 61.041. China 2. Cold and Arid Regions {1.al and Engineering Research institute, chinese academy of sciences, Lanzhou 73.000, China 3. Resource and {1. School, Lanzhou University, Lanzhou 73.000, China 1. institute of Mountain Hazards and {1. Chinese Academy of Sciences Chengdu 610041 China 3. Resource and {1. School Lanzhou University Lanzhou 730000 China 2. Cold and Arid Regions environmental and Engineering Research {1. Chinese Academy of Sciences Lanzhou 730000 China

Alpine cold ecosystem with permafrost environment is quite sensitive to climatic changes and the changes in permafrost can significantly affect the alpine ecosystem. The vegetation coverage, grassland biomass and soil nutrient and texture are selected to indicate the regime of alpine cold ecosystems in the Qinghai-Tibet Plateau. The interactions between alpine ecosystem and permafrost were investigated with the depth of active layer, permafrost thickness and mean annual ground temperature (MAGTs). Based on the statistics model of GPTR for MAGTs and annual air temperatures, an analysis method was developed to analyze the impacts of permafrost changes on the alpine ecosystems. Under the climate change and human engineering activities, the permafrost change and its impacts on alpine ecosystems in the permafrost region between the Kunlun Mountains and the Tanggula Range of Qinghai-Tibet Plateau are studied in this paper. The results showed that the per- mafrost changes have a different influence on different alpine ecosystems. With the increase in the thickness of active layer, the vegetation cover and biomass of the alpine cold meadow exhibit a significant conic reduction, the soil organic matter content of the alpine cold meadow ecosystem shows an exponential decrease, and the surface soil materials become coarse and gravelly. The alpine cold steppe ecosystem, however, seems to have a relatively weak relation to the permafrost environment. Those relationships resulted in the fact that the distribution area of alpine cold meadow decreased by 7.98% and alpine cold swamp decreased by 28.1.% under the permafrost environment degradation during recent 1. years. In the future 50 years the alpine cold meadow ecosystems in different geomorphologic units may have different responses to the changes of the permafrost under different climate warming conditions, among them the alpine cold meadow and swamp ecosystem located in the low mountain and plateau area will have a relatively

关键词： permafrost environment, alpine cold ecosystem, statistics relationship, climate change, impacts, Qinghai-Tibet Plateau.

Impact of land-use change on hydrological processes in the Maying River basin, China

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Science China earth {1. 2006年第10期49卷 1098-1110页

作者： WANG Genxu1.3. ZHANG Yu2, LIU Guimin2 & CHEN Lin3.1. institute of Mountain Hazards and {1., chinese academy of sciences, Chengdu 61.041. China 2. Cold and Arid Regions {1.al and Engineering Research institute, chinese academy of sciences, Lanzhou 73.000, China 3. Resource and {1. School, Lanzhou University, Lanzhou 73.000, China 1. institute of Mountain Hazards and {1. Chinese Academy of Sciences Chengdu 610041 China 3. Resource and {1. School Lanzhou University Lanzhou 730000 China 2. Cold and Arid Regions environmental and Engineering Research {1. Chinese Academy of Sciences Lanzhou 730000 China

Since the 1.60s, dramatic changes have taken place in land-use patterns characterized by the persistent expansion of cultivated land and a continuous decrease in natural woodland and grassland in the arid inland river basins of China. It is very important to assess the effects of such land-use changes on the hydrological processes so vital for water resource management and sustainable development on the catchment scale. The Maying River catchment, a typical arid inland watershed located in the middle of the Hexi Corridor in northwest China, was the site chosen to investigate the hydrological responses to land-use changes. The annual runoff, base flow, maximum peak flow, and typical seasonal runoff in both spring and autumn flood periods were selected as the variables in the hydrological processes. Statistical-trend analysis and curvilinear regression were utilized to detect the trends in hydrological variables while eliminating the climatic influence. The relationship between cultivated land-use and hydrological variables was analyzed based on four periods of land-use variation data collected since 1.65. A runoff model was established composed of two factors, i.e., cultivated land use and precipitation. The impact of land use changes, especially in the large ar- eas of upstream woodland and grassland turned into cultivated lands since 1.67, has resulted in a mean annual runoff decrease of 28.1.%, a base flow decline of 3..3.%, a drop in the maximum peak discharge of 3..77%, and mean discharge decreases in spring and autumn of 3..05% and 24.87% respectively, of which the contribution of cultivated land expansion to the influence of annual runoff amounts to 77%-80%, with the contribution to the influence of spring discharge being 73.-81., and that to the influence of base flow reaching 62%-65%. Thus, a rational regulation policy of land use patterns is vitally important to the sustainable use of water resources and the proper development of the entire catchment.

关键词： land-use change, arid inland river catchment, hydrological process, impact, Maying River.

Geochemical simulation of the formation of brine and salt minerals based on Pitzer model in Caka Salt Lake

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Science China earth {1. 2004年第8期47卷 720-726页

作者： LIU xingqi1. CAI Keqin2 & YU Shengsong{1.1. Nanjing institute of Geography and Limnology, {1., Nanjing 21.008, China 2. China University of Geosciences, Beijing 1.008{1. China {1. institute of Salt Lakes, {1., xining 81.008, China 1. Nanjing institute of Geography and Limnology Chinese Academy of Sciences 210008 Nanjing China 2. China University of Geosciences 100083 Beijing China 3. {1. of Salt Lakes Chinese Academy of Sciences 810008 Xining China

The geochemical simulation of the formation of brine and salt minerals based on Pitzer model was made in Caka Salt Lake. The evolution of the mixed surface-water and the mineral sequences were calculated and compared with the hydrochemical compositions of the brine and the salt minerals of the deposit in Caka Salt Lake. The results show that the formation temperature of the lake is between 0°C and 5°C, which is well identical with other studies. The mixing of salt-karst water with the surface waters, neglected by the former researchers, is very important to the formation of the lake, indicating that the initial waters resulting in the formation of the lake are multi-source. It is the first time to use Pitzer model in China for making geochemical simulation of the formation and evolution of inland salt lake and satisfactory results have been achieved.

关键词： Pitzer model,Caka Salt Lake,geochemical simulation,salt-karst water.

Physical mechanisms of plant roots affecting weathering and leaching of loess soil

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Science China earth {1. 2006年第9期49卷 1002-1008页

作者： LI Yong1.2, ZHANG Qingwen1.2, WAN Guojiang3. HUANG Ronggui3. PIAO Hechun3. BAI Lingyu2 & LI Lu2 1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, institute of Soil and Water Conservation, {1., Yangling 71.1.0, China 2. institute of Agro-{3. and Sustainable Development, chinese academy of Agricultural sciences, Beijing 1.0081. China 3. institute of Geochemistry, {1., Guiyang 550002, China 1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau Institute of Soil and Water Conservation Chinese Academy of Sciences Yangling 712100 China 2. institute of Agro-{1. and Sustainable Development Chinese Academy of Agricultural Sciences Beijing 100081 China 3. {1. of Geochemistry Chinese Academy of Sciences Guiyang 550002 China

Plant roots have potential impacts on soil mineral weathering and *** objective is to understand the physical mechanisms of plant roots affecting weathering andleaching of loess soil. Root densities were measured through the method of a large-size dug profile,and transport fluxes of soil elements were determined using an undisturbed monolith soilinfiltration device on the hilly and gully regions of the chinese Loess Plateau. The results showthat the improvement effects of soil {1. by plant roots are mainly controlled by the densityand weight of the fibrous roots with the diameters less than 1.mm. Plant roots have the strongereffects on soil physical properties than chemical properties. The principal components analysis(PCA) indicates that soil physical properties by plant roots account for 56.7% of variations in soil{1. whereas soil chemical properties and pH contribute about 24.2% of the soil *** roles of plant roots in controlling soil weathering and leaching increased in the followingorder: infiltration enhancement > increase of bio-active substance > stabilization of soilstructure. The effects of plant roots on soil mineral weathering and leaching can be quantifiedusing the multiple regression models with the high prediction accuracies developed in this study.

关键词： plant roots, soil weathering and leaching rates, soil environment field, principal components analysis (PCA), chinese Loess Plateau.