Carbon isotope ratios of C_4 plants in loess areas of North China     

WANG Guoan  HAN Jiamao  ZHOU Liping  XIONG Xiaogang  TAN Ming  WU Zhenhai  PENG Jun 《中国科学D辑(英文版)》2006,49(1)

Recent stable carbon isotope studies have shown that the occurrence of C4 plants on the Earth was much later than that of C3 plants and there was a global ex-pansion of C4 biomass around 5―8 million years ago[1]. Although far fewer species use the C4 pat…  相似文献   

No apparent lock-in depth of the Laschamp geomagnetic excursion: Evidence from the Malan loess   总被引：2，自引：1，他引：2  

ZHU Rixiang  LIU Qingsong    PAN Yongxin  DENG Chenglong  ZHANG Rui & WANG Xianfeng . Paleomagnetism  Geochronology Laboratory 《中国科学D辑(英文版)》2006,49(9):960-967

Developing an accurate chronological framework is always a key issue in paleoclimatic studies. Magneto- stratigraphy has been a routine tool for such purposes. However, complexities arise for inter-profile correla- tions of magnetostratigraphy due to effects of the lock-in process. One good example is the “mystery” of the mismatching of stratigraphic locations of the Matuyama/Brunhes boundary (MBB) (occurred at ~780 ka) recorded in Chinese loess and marine sedi- ments. Tauxe et al.[1] con…  相似文献   

山西黄土塬区三维地震勘探的实际应用   总被引：2，自引：1，他引：2  

解团结 《中国煤田地质》2006,18(1):57-59

寿阳平头镇三维地震勘探区位于寿阳-阳泉构造堆积盆地的西北部，属黄土丘陵地貌，梁、峁比较发育，相对高差一般在30～50m。本区第四系覆盖较厚，纵横向变化大，且该地层中夹有砾石层和钙质结核层，难以成孔。地震激发与接收困难较大。通过多次的试验工作，最终确定采用变观措施来解决表浅层地震地质条件极差问题：避开黄土覆盖较厚地段，将炮点变观到较薄地段或者是基岩出露地段，并尽可能加深炮孔到理想激发层位。通过变观处理，记录品质明显提高。  相似文献   

单液硅化灌浆法加固豫西湿陷性黄土地基施工技术和质量控制          下载免费PDF全文

罗伟 《探矿工程》2007,34(10):55-57

通过总结单液硅化灌浆法加固豫西三门峡地区湿陷性黄土地基的多个成功工程实例,介绍了该法加固本地区湿陷性黄土地基施工工艺及施工质量控制措施。  相似文献   

高速铁路地基黄土微结构的分形研究   总被引：1，自引：1，他引：1  

任权  王家鼎  袁中夏  谷天峰 《水文地质工程地质》2007,34(6):76-78,82

基于分形理论,结合Photoshop等图像分析处理软件,在图像处理过程中选择适当的阈值,本文对郑州—西安客运专线地基黄土在动荷载作用下变形前后的孔隙微观结构进行分形研究。研究表明,黄土孔隙微观结构具有分形特征,揭示了黄土孔隙分形分维同孔隙比之间有近似直线的关系,且孔隙微结构分形分维越大,土体强度越大,反之越小。  相似文献   

Instability characteristics of the East Asian Monsoon recorded by high-resolution loess sections from the last interglacial (MIS5)   总被引：3，自引：0，他引：3  

Guan QingYu  Pan BaoTian  Gao HongShan  Li BingYuan  Wang JunPing  Su Huai 《中国科学D辑(英文版)》2007,50(7):1067-1075

The selection of high-resolution loess sections is needed in order to determine the climatic variability of the East Asian Monsoon during the last interglacial. Two sequences of S1 on the eastern and west-ern sides of the Liupan Mountain were both composed of five paleosol layers and four loess layers,indicating that there were five strong summer monsoon events and four strong winter monsoon events in MIS5. This corresponds with other records of the East Asian Monsoon,along with NGRIP and the North Atlantic records,implying that the climate of the Northern Hemisphere was very instable during the last interglacial. Two layers of paleosols and one layer of loess had developed during MIS5a and MIS5c. Compared with MIS5e,the climate in MIS5a and MIS5c fluctuated more intensively on a millen-nial scale,whereas the climate was relatively stable in MIS5e.  相似文献   

Luminescence dating of old (>70 ka) Chinese loess: A comparison of single-aliquot OSL and IRSL techniques   总被引：1，自引：0，他引：1  

J.P. Buylaert  D. Vandenberghe  A.S. Murray  S. Huot  F. De Corte  P. Van den Haute 《Quaternary Geochronology》2007,2(1-4):9-14

The applicability of two different approaches in the luminescence dating of old (>70 ka) Chinese loess is investigated. Both SAR-OSL ages obtained on 63–90 μm quartz grains and SAR-IRSL ages obtained on 4–11 μm polymineral grains, for samples collected from two sites in the Chinese Loess Plateau (Luochuan and Dongchuan) are presented. The characteristics of the luminescence signals stimulated by blue and infrared light are investigated in terms of dose response and dose recovery, and as a function of age. Additionally, anomalous fading measurements from the 410 nm IRSL emission in polymineral fine-grains are reported. An average value of g_2days amounting to 3% per decade was measured and seems to be independent of site location and age. For the samples from Luochuan, independent age control (pedostratigraphy and palaeomagnetism) is available. At both sites, the SAR-OSL ages are always lower than the SAR-IRSL ages after they have been corrected for anomalous fading. It seems that the quartz-based SAR-OSL ages are accurate for the younger ages, but that they underestimate the true age of deposition for loess that was deposited about 60–70 ka ago. The fading-corrected SAR-IRSL ages are in better agreement with the pedostratigraphic age control (75 and 130 ka) and allow dating beyond the quartz OSL range. Based on our results, we suggest that conventional SAR-OSL and SAR-IRSL protocols at these sites should be restricted to samples of ages not exceeding 40–50  and 100–120 ka, respectively.  相似文献   

准饱和黄土中暗穴水动力扩展响应的研究   总被引：1，自引：0，他引：1  

周新民  夏唐代  彭建兵 《工程地质学报》2007,15(1):56-61

为分析强降水过程中暗穴扩展机理,在野外调查资料的基础上,建立了准饱和黄土暗穴的扩展计算模型,概化为弹性准饱和土层中无限长圆柱形孔洞表面受水压力的动力响应问题。通过引入势函数,得到了Lap lace变换域中的应力、位移及孔隙水压力的解析表达式,并利用数值逆变换方法求得时域解,分析了降雨历时及饱和度等因子对暗穴动力响应的影响。结果表明,水动力是引起黄土暗穴扩展的主要因素,水压力作用历时对位移及应力有较大的影响,同时饱和度的细微变化对径向位移有显著影响。  相似文献   

地震诱发石碑塬黄土地层液化滑移距离研究          下载免费PDF全文

马星宇  王兰民  钟秀梅  蒲小武  刘富强  王谦 《地震工程学报》2020,42(6):1674-1682

为研究1920年海原地震中石碑塬地区液化滑移灾害的形成机制、滑移特征及滑移距离，对石碑塬液化滑移区进行钻孔勘探、取样以及探槽开挖。分别对钻孔及所取试样进行剪切波速测试及颗粒分析、室内动三轴试验，得出石碑塬液化滑移区地层分布情况、震时液化土体层位以及不同地震烈度条件下砂质黄土层的液化情况。综合分析钻孔勘探、颗粒分析、动三轴试验结果，揭示出海原地震中石碑塬黄土地层液化滑移灾害的形成机制：砂质黄土层液化后在自重应力以及地震力的共同作用下"托浮"第一古土壤层以及上部"粉尘化"的非饱和黄土层沿缓斜坡运动，并利用液化滑移地层滑距公式对滑移距离进行估算，得到结果为223.35 m，与实际情况较为相符。研究结果可为黄土地层液化滑移灾害的预防提供一定的借鉴意义。  相似文献   

真三轴条件下的原状黄土增湿变形特性     

方瑾瑾  冯以鑫  余永强  李震  林志斌 《岩土力学》2020,41(4):1235-1246

为了研究复杂应力条件下原状黄土的增湿变形特性，利用改进的非饱和土湿陷真三轴仪，在测量吸力条件下对原状黄土进行双线法分级浸水增湿试验，探讨力?水耦合作用下吸力的变化特性，研究真三轴浸水试验的增湿变形特性，以及吸力、净围压、中主应力和应力比对增湿变形的影响。研究结果表明：由ei-lgp压缩曲线确定了非饱和土的屈服点，屈服点之前，曲线的斜率近似相等；屈服点之后，曲线的斜率随着初始吸力的减小而减小，且非饱和土与饱和土的交点随着初始吸力的增大呈右下方移动趋势。等向压缩过程中，吸力随着净平均应力的增加近似呈线性减小趋势，初始吸力越小，吸力减小的速度越慢，且吸力变化量越小。均压分级浸水增湿时，吸力s随着浸水量w的增加而减小，增湿体变 随着浸水量w的增加而增大，不同净围压下的 -w关系曲线相互有交叉。交叉区域之前，净围压越大，增湿体变越小，而交叉区域之后，净围压越大，增湿体变越大。在同一净围压条件下，浸水量相同时，初始吸力越大，增湿体变越大。真三轴剪切增湿试验中，应力比k、中主应力参数b值和净围压?3皆对增湿变形有一定的影响。当q/p≤1时，增湿变形曲线前段下凹后段上凹，主要表现为体积增湿变形；当q/p>1时，增湿变形曲线只有下凹部分，主要表现为剪切增湿变形。增湿变形曲线的形态取决于k值和b值的不同组合。  相似文献