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Joshua W. Kasper Judith M. Denver Thomas E. McKenna William J. Ullman 《Hydrogeology Journal》2010,18(8):1855-1866
A numerical groundwater-flow model was used to characterize the source area and volume of Phillips Branch, a baseflow-dominated stream incising a highly permeable unconfined aquifer on the low relief Delmarva Peninsula, USA. Particle-tracking analyses indicate that the source area (5.51 km2) is ～20% smaller than the topographically defined watershed (6.85 km2), and recharge entering ～37% of the surface watershed does not discharge to Phillips Branch. Groundwater residence time within the source volume ranges from a few days to almost 100 years, with 95% of the volume “flushing” within 50 years. Artificial discharge from groundwater pumping alters the shape of the source area and reduces baseflow due to the interception of stream flow paths, but has limited impacts on the residence time of groundwater discharged as baseflow. In contrast, artificial recharge from land-based wastewater disposal substantially reduces the source area, lowers the range in residence time due to the elimination of older flow paths to the stream, and leads to increased discharge to adjacent surface-water bodies. This research suggests that, in this and similar hydrogeologic settings, the “watershed” approach to water-resource management may be limited, particularly where anthropogenic stresses alter the transport of soluble contaminants through highly permeable unconfined aquifers. 相似文献
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Ages of fractures in the Eye-Dashwa granite pluton north of Atikokan, Ontario, are estimated from analyses of their filling materials (pegmatite, aplite, hornblendeporphyry, epidote, chlorite, gypsum, diabase, iron oxides, carbonate and clays). The analyses include radiometric age determinations of filling materials, comparison of crystallization temperatures of filling materials with the expected temperature of the pluton through time, and paragenetic relations derived from textures. The major fractures (primarily epidote and chlorite-filled) were produced by penetrative deformation during cooling immediately after intrusion of the pluton. From 2.6 Ga to 2.4 Ga they transected the pluton and largely defined the present overall fracture network. Less severe penetrative deformation occurred about 1.1 Ga, when a few diabase dikes and small gypsum fractures developed. A second source of fracturing appears to have existed through most of geological time, and it reopened segments of old fractures within about 400 m of the present erosional surface. It is unknown whether the near-surface, or supergene, fractures formed more or less continuously through time or in distinct episodes, such as during glacial periods. Open fractures, which are most common in the near-surface layer, tend to transmit groundwater, but fracture sealing due to the accumulation of filling materials seems to occur with time. Underground excavations such as nuclear fuel waste disposal vaults, would be less susceptible to the incursion of groundwater, if they were located below the near-surface layer. 相似文献
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山东莒南后左山恐龙公园早白垩世恐龙足迹化石初步研究 总被引：8，自引：5，他引：8
山东省莒南县后左山恐龙公园内保存了数量众多、形态各异的恐龙足迹化石。该足迹化石群产于早白垩世大盛群田家楼组,主要是兽脚类、鸟脚类恐龙的足迹,尤以前者占优质。最大的一个为椭圆形,大小100cm×70cm,可能系鸟脚类恐龙的足迹。鸟脚类足迹大多为椭圆形,长轴一般30～40cm,常呈幻迹保存。最大的兽脚类足迹为三趾型,长49cm,宽35cm,是大型肉食龙类的足迹;最小的一个长8.5cm,宽4.5cm,可能是虚骨龙类的足迹。另外还发现了少量可能是驰龙的足迹,具有2个很长的趾(Ⅲ和Ⅳ趾),趾间角极小,二者几乎平行。鸟脚类恐龙足迹层位分布局限,但密度较大,产出的层面常发育泥裂、波痕,甚至冰晶痕,与泥岩、粉砂质泥岩等层位相关性较强。 相似文献
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Abstract factor analyses were performed on databases consisting of simulated samples from aqueousequilbria.The program COMPLEX was used to generate equilibrium species in a system of three reactantmetals and five reactant bases.Reactant concentrations and pH were drawn from random-normaldistributions so that sample data vectors comprised a multivariate log-normal distribution of equilibriumconcentrations.In addition,sample groups were created containing different distributions for pH andreactant concentrations.Equilibrium species were shown to contain variance contributed by change in pH among samples aswell as change in reactant concentrations.Factor modelling revealed the qualitative relationships amongthe species and how the relationships change with pH.Factors also revealed those reactants containingvariance in the data matrix.In some cases,reactant variance obscured relationships between pH and theequilibrium species.Since factor modelling of a simulated data matrix revealed the expected chemical equilibriuminteractions,a potentially powerful tool exists for investigating the effects of outliers and error. 相似文献
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In part of a large abandoned mining complex, electromagnetic geophysical surveys were used along with data derived from cores and monitoring wells to infer sources of contamination and subsurface hydrologic connections between acidic refuse deposits and adjacent undisturbed geologic materials.Electrical resistivity increases sharply along the boundary of an elevated deposit of pyritic coarse refuse, which is highly contaminated and electrically conductive, indicating poor subsurface hydrologic connections with surrounding deposits of fine refuse and undisturbed glacial material. Groundwater chemistry, as reflected in values of specific conductance, also differs markedly across the deposit's boundary, indicating that a widespread contaminant plume has not developed around the coarse refuse in more than 40 yr since the deposit was created. Most acidic drainage from the coarse refuse is by surface runoff and is concentrated around stream channels.Although most of the contaminated groundwater within the study area is concentrated within the surficial refuse deposits, transects of apparent resistivity and phase angle indicate the existence of an anomalous conductive layer at depth (>4 m) in thick alluvial sediments along the northern boundary of the mining complex. Based on knowledge of local geology, the anomaly is interpreted to represent a subsurface connection between the alluvium and a flooded abandoned underground mine. 相似文献
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A reclamation project at the abandoned Blackhawk Mine site near Terre Haute, Indiana, lasted about four months and involved the burial of coarse mine refuse in shallow (less than 9 m) pits excavated into loess and till in an area of about 16 ha. An abandoned flooded underground coal mine underlies the reclamation site at a depth of about 38 m; the total area underlain by the mine is about 10 km2. The potentiometric levels associated with the mine indicate a significant (2.7 m) and prolonged perturbation of the deeper confined groundwater system; 14 months after completing reclamation, the levels began to rise linearly (at an average rate of 0.85 cm/d) for 11 months, then fell exponentially for 25 months, and are now nearly stable. Prominent subsidence features exist near the reclamation site. Subsidence-related fractures were observed in cores from the site, and such fractures may have provided a connection between the shallower and deeper groundwater systems. 相似文献
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The geotechnical engineer is often faced with the problem of how to assess the statistical properties of a soil parameter on the basis of a sample measured in-situ or in the laboratory with the defect that some values have been replaced by interval bounds because the corresponding soil parameter values have turned out to exceed the capacity of the measuring instrument. Given such a censored sample the problem is to estimate the mean value, variance and certain fractiles of the distribution of the soil parameter as it would be measured by an instrument of unrestricted range. In many situations only a small censored sample is given. To estimate the characteristic value defined as a lower fractile value corresponding to a codified probability value, the geotechnical engineer is thus urged to supplement the information from the measurements at the actual location by considering whatever prior knowledge is available about the soil parameter distribution. The present paper shows how a characteristic value by computer calculations can be assessed systematically from the actual sample of censored data supplemented with prior information from a soil parameter data base. 相似文献
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白垩纪四足动物足印的生物地层学、生物年代学与遗迹相 总被引：3，自引：2，他引：1
从全球范围来看,白垩纪四足动物的足印多数是非鸟恐龙与鸟类留下的痕迹;少量足印来自翼龙、鳄鱼、龟、哺乳动物和其他四足动物。白垩纪的足迹化石以东亚(尤其是中国和朝鲜)和北美西部的最为人所知。南美(主要是阿根廷和巴西)也有一定数量广泛分布的足迹化石,欧洲、非洲与澳大利亚的白垩纪足迹组合则鲜为人知。以白垩纪四足动物的足印记录为基础,我们对两个全球足印生物年代重新进行了检查。早白垩世生物年代以蜥脚类与鸟脚类的足迹为特征。晚白垩世生物年代中的蜥脚类足迹较少,但是鸭嘴龙、暴龙和角龙的足迹增多了。另外,白垩纪足印化石的记录中记载了许多重要的生物地层学信息,如北美白垩纪中期蜥脚类恐龙的消失,以及白垩纪末恐龙的绝灭。越来越多来自东亚的白垩纪足印记录使我们对更精细的地方性白垩纪足印生物年代学有了初步印象。因此,以地方性四足恐龙(包括鸟类)遗迹属的地层分布为基础,可以识别出三个或四个足印生物年代。种类丰富并具有地方性特色的东亚的白垩纪鸟类动物的遗迹群,可能指示白垩纪时东亚存在着一个独特而繁盛的鸟类动物群。以足印化石为基础的这一假说有待进一步的验证。 相似文献
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