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941.
B. Wilhelm F. Arnaud P. Sabatier O. Magand E. Chapron T. Courp K. Tachikawa B. Fanget E. Malet C. Pignol E. Bard J. J. Delannoy 《第四纪科学杂志》2013,28(2):189-199
A high‐resolution sedimentological and geochemical study of a high‐altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352 m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800–1300) and the current period of global warming. On a multi‐decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi‐centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multi‐decadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
942.
943.
西藏地堡那木岗矿区水系沉积物地球化学特征及找矿预测 总被引:1,自引:0,他引:1
利用SPSS等软件对矿区1:5万水系沉积物地球化学数据分析,选用平均值±3倍标准差(X±3S)作为上下限反复剔除原始数据的特值,使元素含量服从正态分布.最后以X+2S作为异常下限(T),以1T、2T、4T三级浓度分带,圈定Cu、Au、Ag、Mo单元素异常和Au-Ag-Mo综合元素异常,揭示矿区内水系沉积物地球化学异常特征.将异常区与矿区地质特征、矿床(点)套合分析,表明异常受地层、断裂、围岩蚀变控制,对寻找矿(化)体、断层、围岩蚀变带有指示作用.最终,优选2处远景区,分别为3号综合异常区中心北北西方向至北东向断裂附近,1号、2号综合异常区及其东侧组成一个走向为东西向的异常带. 相似文献
944.
We describe a juvenile specimen of a titanosaurian sauropod dinosaur consisting of two dorsal and three caudal vertebral centra, an ilium fragment, and an ischium unearthed in 1991 from Site Km 153.5 at BR-050 highway in the Serra da Galga region, municipality of Uberaba, state of Minas Gerais, Brazil. The outcrop at the site is assigned to the Serra da Galga Member of the Marília Formation (Bauru Basin: Bauru Group; Upper Cretaceous: Maastrichtian). Although the material is very incomplete, features such as strongly procoelous caudal centra suggest an affinity with the titanosaurian clade Lithostrotia. The extensive vertebral pneumaticity with deep pleurocoels and well-developed camerae supports the hypothesis that, in titanosaurs, the air sac system was already present and fully developed even at early ontogenetic stages. 相似文献
945.
Vertical soil arching, commonly known as the “trapdoor mechanism,” is a pervasive phenomenon in various geotechnical applications that can be evaluated through a variety of analytical and numerical approaches, most of which exist due to a variety of proposed arching mechanisms, many of which are focused on either purely frictional or cohesive soils. This study investigates the realized arching mechanisms and associated loads for trapdoors under both active and passive arching conditions in c′-ϕ′ soils through a series of dimensionless charts using both upper and lower bound limit analyses. An associated sensitivity analysis demonstrates that arching loads are highly dependent on collapse mechanism, a function of not only geometry, but soil shear strength, with cohesion affecting the realized mechanism and arching loads. 相似文献
946.
947.
A second‐generation, source‐to‐sink cellular automaton‐based model presented here captures and quantifies many of the factors controlling the evolution of aeolian dune‐field patterns by varying only a small number of parameters. The role of sediment supply, sediment availability and transport capacity (together defined as sediment state) in the development and evolution of an aeolian dune‐field pattern over long time scales is quantified from model simulations. Seven dune‐field patterns can be classified from simulation results varying the sediment supply and transport capacity that control the type and frequency of dune interactions, the sediment availability of the system and, ultimately, the development of dune‐field patterns. This model allows predictions to be made about the range of sediment supply and wind strengths required to produce the dune‐field patterns seen in the real world. A new clustered dune‐field pattern is identified from model results and used to propose an alternative mechanism for the formation of superimposed dunes. Bedforms are hypothesized to cluster together, simultaneously forming two spatial scales of bedforms without first developing a large basal dune with small superimposed dunes. Manipulation of boundary conditions produces evolving dune fields with different spatial configurations of sediment supply. Trends of spacing and crest length increase with decreasing variability as the dune field matures. This simple model is a valuable tool which can be used to elucidate the dominant control of aeolian sediment state on the construction and evolution of aeolian dune‐field patterns. 相似文献
948.
949.
The pores in shales are mainly on a nanometer scale, and the pore-size distribution is vital with regard to the preservation and exploitation of shale gas. This study focuses on the organic-rich lower Cambrian black shale in the Upper Yangtze Platform, South China and investigates their TOC, mineralogical composition and nanopore structure. Low-pressure N2 and CO2 adsorption experiments were conducted at 77.35 K and 273.15 K, respectively, and the nanopore structures were characterised by the modified Brunauer–Emmett–Teller, Dubinin–Radushkevich, t-plot, Barrett–Joyner–Halenda and density functional theory (DFT) methods. The results indicate the following. (1) The lower Cambrian shale has a high TOC content (1.77–7.23 wt%) and a high quartz content (27.7–51.6 vol%). The total specific surface area varies from 12.02 to 28.87 m2/g. Both the total specific surface area and quartz content are positively associated with the TOC content. (2) Shale samples with a higher TOC content have a greater number of micropores, resulting in more complicated nanopore structures. Micropore volumes/surface areas and non-micropore surface areas all increase with increasing TOC content, indicating that TOC is the key factor determining the nanopore structure of the lower Cambrian shale. (3) A combination of N2 and CO2 adsorption provides the most suitable detection range (~0.3–60 nm) and is both highly reliable and accurate with regard to nanopore structure characterisation. 相似文献
950.
文章对青海省达肯达坂山地区1∶5万水系沉积物测量所得数据进行R型因子分析,提取了5种具有代表性的因子组合类型,对各因子元素组合得分归类,绘制了测区地球化学分区图。通过判读分析,地球化学分区图反映了不同地质体中以相应元素组合类型为主的地球化学异常。研究对比组合分区与因子得分异常,有利于推断相关元素的浓集部位,也为确定找矿靶区提供了方向。 相似文献