U-Series Chronology of Lacustrine Deposits in Death Valley, California

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.     

铁法煤田煤储层渗透性预测

煤储层的渗透性预测是煤层气开发前必须的储层评价工作。评价方法是依据围岩节理及煤层裂隙的宏观、微观统计分析,寻找区内裂隙发育带及其走向,预测高渗透区的分布。     

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

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.     

Slope form and basal stream relationships: Some further comments

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.     

Pleistocene sediments,soils and landscape evolution at Stebbing,Essex

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.     

Synergistic contribution of precipitation anomalies over northwestern India and the South China Sea to high temperature over the Yangtze River Valley

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.     

云南大瑞铁路大保段地质灾害特征与诱发因素

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。     

地震重灾区九寨沟黄木山滑坡稳定性分析及其防治对策

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。     

吉林浑江煤田构造分区分带特征及赋煤规律

运用煤田构造与控煤构造研究方法,从浑江煤田地质构造展布的平面差异性分析入手,揭示了本区地质构造展布的分区、分带特征,指出南北方向上分为三带,东西向分为两区,不同的区带内赋煤规律有显著差异。受到SE—NW向的挤压,浑江地区发育SW—NE向的断裂及褶皱,成为控制煤系赋存形态的主要因素。浑江煤田西区因中生代以来构造活动较强烈,断裂较发育,对煤系的后期改造破坏较强烈;而东部煤系赋存于向斜构造内,受断裂破坏较小,但保存面积少于西部。     

鹤岗煤田深部煤炭资源潜力分析研究

根据矿区已有地质资料,从构造、沉积古地理环境分析,认为鹤岗煤田深部与煤田现生产区属同一个沉积环境,其古构造条件、沉积体系及成煤环境相同,煤田深部预测区是生产区的延深。依据钻探、物探对深部构造及煤层的控制,证实煤田深部煤层发育较稳定,具有一定的煤炭资源潜力,值得进一步勘查和开发利用。