Preliminary investigations of outwash environments in the Tyne Valley: implications for Late Devensian (Dimlington Stadial) deglaciation     

Lynda Yorke  David G. Passmore 《Proceedings of the Geologists' Association. Geologists' Association》2007,118(2):201-211

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U-Series Chronology of Lacustrine Deposits in Death Valley, California   总被引：1，自引：0，他引：1  

Teh-Lung Ku  Shangde Luo  Tim K. Lowenstein  Jianren Li  Ronald J. Spencer 《Quaternary Research》1998,50(3):261-275

Uranium-series dating on a 186-m core (DV93-1) drilled from Badwater Basin in Death Valley, California, and on calcareous tufas from nearby strandlines shows that Lake Manly, the lake that periodically flooded Death Valley during the late Pleistocene, experienced large fluctuations in depth and chemistry over the last 200,000 yr. Death Valley has been occupied by a long-standing deep lake, perennial shallow saline lakes, and a desiccated salt pan similar to the modern valley floor. The average sedimentation rate of about 1 mm/yr for core DV93-1 was punctuated by episodes of more-rapid accumulation of halite. Arid conditions similar to the modern conditions prevailed during the entire Holocene and between 120,000 and 60,000 yr B.P. From 35,000 yr B.P. to the beginning of the Holocene, a perennial saline lake existed, over 70 m at its deepest. A much deeper and longer lasting perennial Lake Manly existed from about 185,000 to 128,000 yr B.P., with water depths reaching about 175 m, if not 330 m. This lake had two significant “dry” excursions of 10²–10³yr duration about 166,000 and 146,000 yr B.P., and it began to shrink to the point of halite precipitation between 128,000 and 120,000 yr B.P. The two perennial lake periods correspond to marine oxygen isotopic stages (OIS) 2 and 6. Based on the shoreline tufa ages, we do not rule out the possible existence 200,000 yr ago of yet a third perennial lake comparable in size to the OIS 6 lake. The²³⁴U/²³⁸U data suggest that U in tufa owes its origin mainly to Ca-rich springs fed by groundwater that emanated along lake shorelines in southern Death Valley, and that an increase of this spring-water input relative to the river-water input apparently occurred during OIS 6.  相似文献   

Lateral translocation of soil plasma through a small valley basin in the Northaw Great Wood,Hertfordshire     

R. J. Huggett 《地球表面变化过程与地形》1976,1(2):99-109

The paper looks at the process of lateral translocation in a small valley basin from the Northaw Great Wood, Hertfordshire. The valley basin comprises four lithostratigraphic units (London Clay and Pebble Gravel, and the others a mixture of these two), which were initially established in the field by a rough assessment of texture. Particle size analysis validated the lithostratigraphic units as delineated in the field; it was found unnecessary to alter the boundaries of the units. Patterns of lateral translocation of silt and clay (measured by the hydrometer method) and the amorphous colloidal hydrous oxides and hydroxides of Al, Fe, Mn and Si (measured in oxalate solution by atomic absorption spectrophotometry) are inferred from balance sheets of the relative gains and losses of the materials. Materials from horizons formed in lithostratigraphic units derived from London Clay are balanced against a clay dilution factor; those from the lithostratigraphic unit of Pebble Gravel against the dilution of sand on a clay-free basis. The results lead to the following conclusions about the process of lateral translocation: it has been a significant contributor to soil development; larger amounts of material have moved down-slope towards the hollow than over the nose because there has, theoretically, been more throughflow in the hollow; for some materials there has been less down-slope transport in lower horizons owing to less throughflow in them.  相似文献   

Slope form and basal stream relationships: Some further comments     

K. S. Richards 《地球表面变化过程与地形》1977,2(1):87-92

The nature and strength of the correlation between stream gradient and valley side slope angle are seen to vary according to the order of the stream segment. In addition, it is suggested that the relationship will depend on the efficiency of slope processes, and that this may contribute to tye different from of relationship obtained in different regions.  相似文献   

Pleistocene sediments,soils and landscape evolution at Stebbing,Essex     

Colin A. Whiteman  Rob A. Kemp 《第四纪科学杂志》1990,5(2):145-161

Pleistocene sediments and soils exposed at Stebbing in central Essex, England are described, analysed and interpreted. The sand and gravel units above Eocene London Clay and Upper Pliocene Red Crag are shown to be a high level member of the Kesgrave Formation, with a surface immediately beneath that of the Westland Green Gravels, which are tentatively assigned to the Pre-Pastonian ‘a’ Stage of the British Quaternary succession. The rubified, argillic soil developed in the surface of these fluvial deposits is a composite of the Valley Farm and Barham Soils and displays micromorphological evidence of several phases of clay illuviation, gleying and clay coating disruption. Originally truncated and buried beneath Anglian gelifluction deposits, cover sand and till, the soil has been exhumed in most places by subsequent erosion. The full succession, however, is preserved within large gulls that formed by periglacial cambering prior to this erosion. More recent loess incorporation and pedogenesis have modified the exhumed soil and the materials within the gulls.  相似文献   

Synergistic contribution of precipitation anomalies over northwestern India and the South China Sea to high temperature over the Yangtze River Valley   总被引：1，自引：0，他引：1  

Ge Liu  Renguang Wu  Shuqing Sun  Huimei Wang 《大气科学进展》2015,32(9):1255-1265

This study explores the characteristics of high temperature anomalies over eastern China and associated influencing factors using observations and model outputs. Results show that more long-duration (over 8 days) high temperature events occur over the middle and lower reaches of the Yangtze River Valley (YRV) than over the surrounding regions, and control most of the interannual variation of summer mean temperature in situ. The synergistic effect of summer precipitation over the South China Sea (SCS) region (18°-27°N, 115°-124°E) and the northwestern India and Arabian Sea (IAS) region (18°-27°N, 60°-80°E) contributes more significantly to the variation of summer YRV temperature, relative to the respective SCS or IAS precipitation anomaly. More precipitation (enhanced condensational heating) over the SCS region strengthens the western Pacific subtropical high (WPSH) and simultaneously weakens the westerly trough over the east coast of Asia, and accordingly results in associated high temperature anomalies over the YRV region through stimulating an East Asia-Pacific (EAP) pattern. More precipitation over the IAS region further adjusts the variations of the WPSH and westerly trough, and eventually reinforces high temperature anomalies over the YRV region. Furthermore, the condensational heating related to more IAS precipitation can adjust upper-tropospheric easterly anomalies over the YRV region by exciting a circumglobal teleconnection, inducing cold horizontal temperature advection and related anomalous descent, which is also conducive to the YRV high temperature anomalies. The reproduction of the above association in the model results indicates that the above results can be explained both statistically and dynamically.  相似文献   

云南大瑞铁路大保段地质灾害特征与诱发因素     

杨爱春  任贵良 《云南地质》2010,29(2):185-189,145

大瑞铁路大保段位于云贵高原西部边缘,著名的横断山脉南段,地势错综复杂。主要地质灾害崩塌、滑坡、泥石流,地质灾害的形成的本质因素是地形地貌、地层岩性、地质构造等;外部因素包括大气降水、植被破坏及人类工程活动等方面。  相似文献   

地震重灾区九寨沟黄木山滑坡稳定性分析及其防治对策     

李太军  李颖玲  蒲成华 《四川地质学报》2010,30(4):493-495

针对地震灾区九寨沟黄木山滑坡工程,分析了滑坡的岩土体特征,滑坡原因及其稳定性,简要的介绍了该工程的滑坡防治方案。  相似文献   

南疆开都河流域夏季径流量的变化及其特征分析     

魏瀛珠  赵巧华  欧阳潇然 《气象》2014,40(3):349-354

利用RegCM3模式对开都河流域2000-2006年夏季气候进行模拟,结果表明:模式对于流域夏季月降水总量和月平均气温的空间分布有较好的模拟能力。结合站点海拔高度值、实测值以及模拟量分别对降水、气温进行修正,并由此计算流域的面雨量和平均温度;结果表明开都河流域夏季面雨量与开都河同期实测径流量有较好的一致性,R~2达到0.97。对开都河流域夏季平均气温、面雨量以及径流量的分析表明,降水是影响流域夏季径流量的主要影响因子;而气温对于径流呈现负贡献的原因可能由于对温度敏感的小冰川大大减少,致使径流量随着温度增加而增加的关系减弱。此外,气温升高导致流域蒸散量的提高,可能是气温呈现负贡献的又一原因。  相似文献   

地形地貌对地震波放大效应数值模拟研究   总被引：2，自引：0，他引：2  

周兴涛  韩金良  施凤根  王昆 《工程地质学报》2014,22(6):1211-1220

采用FLAC3D 软件进行大量数值模拟,研究了地形地貌对地震波放大效应规律。结果表明:对于单面坡模型,斜坡较低时,坡体对天然地震波和简谐波的峰值加速度在竖直向和顺坡面向产生线性放大效应。斜坡较高时,若坡角低,两种波形的加速度等值线近似平行于坡面,天然地震波坡顶正下方极值性不明显,但随坡角增大而明显,坡面正下方可见若干条与坡面相平行具节律性的极小值条带,随坡角增大向一条极值带转化,简谐波在高低坡脚时坡顶面正下方区域内都出现等间距相间分布具节律性的极值条带,坡面正下方的极值带状性不如天然地震波明显,随坡角增大而消失; 若坡角高,两波形加速度放大系数顺坡面呈相间的极值圈分布。双面坡坡顶宽度越小,山脊越单薄,加速度放大效应越强烈,随坡顶宽度增大,坡肩加速度放大系数趋于稳定,双面坡对加速度放大效应强于单面坡。对加速度放大效应,多峰形双峰形单峰形,坡顶越不规则,加速度放大效应越强烈。V形河谷坡面上半部分加速度放大效应要强于U形河谷,U形河谷的谷底中部对地震波动力响应要强于V形谷。坡面局部不规则性只影响到坡面局部范围内的峰值加速度分布,坡高、坡角、坡顶几何特征为整个峰值加速度分布的控制因素。  相似文献