洞穴碳酸盐微层研究及其发展方向   总被引：4，自引：0，他引：4  

王先锋  刘东生 《地球科学进展》1999,14(3):286-291

近几年,在分辨率气候－环境变化研究中,洞穴碳酸盐微层逐渐受到人们重视。洞穴碳酸盐微层的类型较多,主要为年层。微层是在沉积条件发生高频率的周期性改变时形成的,要受到供水条件和碳酸钙浓度等多因素的控制。洞穴碳酸盐微层的稳定同位素组成,生长速率,微层结构与物质组分,微层厚度与灰度和光学特征等可以反映降水,温度,土壤成分及植被变化等信息。  相似文献   

Permeability Upscaling Measured on a Block of Berea Sandstone: Results and Interpretation     

Vincent C. Tidwell  John L. Wilson 《Mathematical Geology》1999,31(7):749-769

To physically investigate permeability upscaling, over 13,000 permeability values were measured with four different sample supports (i.e., sample volumes) on a block of Berea Sandstone. At each sample support, spatially exhaustive permeability datasets were measured, subject to consistent flow geometry and boundary conditions, with a specially adapted minipermeameter test system. Here, we present and analyze a subset of the data consisting of 2304 permeability values collected from a single block face oriented normal to stratification. Results reveal a number of distinct and consistent trends (i.e., upscaling) relating changes in key summary statistics to an increasing sample support. Examples include the sample mean and semivariogram range that increase with increasing sample support and the sample variance that decreases. To help interpret the measured mean upscaling, we compared it to theoretical models that are only available for somewhat different flow geometries. The comparison suggests that the nonuniform flow imposed by the minipermeameter coupled with permeability anisotropy at the scale of the local support (i.e., smallest sample support for which data is available) are the primary controls on the measured upscaling. This work demonstrates, experimentally, that it is not always appropriate to treat the local-support permeability as an intrinsic feature of the porous medium, that is, independent of its conditions of measurement.  相似文献   

Markov Processes and Discrete Multifractals   总被引：7，自引：0，他引：7  

Qiuming Cheng 《Mathematical Geology》1999,31(4):455-469

Fractals and multifractals are a natural consequence of self-similarity resulting from scale-independent processes. Multifractals are spatially intertwined fractals which can be further grouped into two classes according to the characteristics of their fractal dimension spectra: continuous and discrete multifractals. The concept of multifractals emphasizes spatial associations between fractals and fractal spectra. Distinguishing discrete multifractals from continuous multifractals makes it possible to describe discrete physical processes from a multifractal point of view. It is shown that multiplicative cascade processes can generate continuous multifractals and that Markov processes result in discrete multifractals. The latter result provides not only theoretical evidence for existence of discrete multifractals but also a fundamental model illustrating the general properties of discrete multifractals. Classical prefractal examples are used to show how asymmetrical Markov process can be applied to generate prefractal sets and discrete multifractals. The discrete multifractal model based on Markov processes was applied to a dataset of gold deposits in the Great Basin, Nevada, USA. The gold deposits were regarded as discrete multifractals consisting of three spatially interrelated point sets (small, medium, and large deposits) yielding fractal dimensions of 0.541 for the small deposits (<25 tons Au), 0.296 for the medium deposits (25--500 tons Au), and 0.09 for the large deposits (>500 tons Au), respectively.  相似文献   

Geomorphic aspects of groundwater flow   总被引：3，自引：0，他引：3  

Robert G. LaFleur 《Hydrogeology Journal》1999,7(1):78-93

 The many roles that groundwater plays in landscape evolution are becoming more widely appreciated. In this overview, three major categories of groundwater processes and resulting landforms are considered: (1) Dissolution creates various karst geometries, mainly in carbonate rocks, in response to conditions of recharge, geologic setting, lithology, and groundwater circulation. Denudation and cave formation rates can be estimated from kinetic and hydraulic parameters. (2) Groundwater weathering generates regoliths of residual alteration products at weathering fronts, and subsequent exhumation exposes corestones, flared slopes, balanced rocks, domed inselbergs, and etchplains of regional importance. Groundwater relocation of dissolved salts creates duricrusts of various compositions, which become landforms. (3) Soil and rock erosion by groundwater processes include piping, seepage erosion, and sapping, important agents in slope retreat and headward gully migration. Thresholds and limits are important in many chemical and mechanical groundwater actions. A quantitative, morphometric approach to groundwater landforms and processes is exemplified by selected studies in carbonate and clastic terrains of ancient and recent origins. Received, May 1998 · Revised, September 1998 · Accepted, October 1998  相似文献   

Groundwater processes and sedimentary uranium deposits   总被引：8，自引：0，他引：8  

D. K. Hobday  W. E. Galloway 《Hydrogeology Journal》1999,7(1):127-138

 Hydrologic processes are fundamental in the emplacement of all three major categories of sedimentary uranium deposits: syngenetic, syndiagenetic, and epigenetic. In each case, the basic sedimentary uranium-enrichment cycle involves: (1) leaching or erosion of uranium from a low-grade provenance; (2) transport of uranium by surface or groundwater flow; and (3) concentration of uranium by mechanical, geochemical, or physiochemical processes. Although surface flow was responsible for lower Precambrian uranium deposits, groundwater was the primary agent in upper Precambrian and Phanerozoic sedimentary uranium emplacement. Meteoric or more deeply derived groundwater flow transported uranium in solution through transmissive facies, generally sands and gravels, until it was precipitated under reducing conditions. Syndiagenetic uranium deposits are typically concentrated in reducing lacustrine and swamp environments, whereas epigenetic deposits accumulated along mineralization fronts or tabular boundaries. The role of groundwater is particularly well illustrated in the bedload fluvial systems of the South Texas uranium province. Upward migration of deep, reducing brines conditioned the host rock before oxidizing meteoric flow concentrated uranium and other secondary minerals. Interactions between uranium-transporting groundwater and the transmissive aquifer facies are also reflected in the uranium mineralization fronts in the lower Tertiary basins of Wyoming. Similar relationships are observed in the tabular uranium deposits of the Colorado Plateau. Received, May 1998 · Revised, July 1998 · Accepted, September 1998  相似文献   

试论造山带成山运动与环境变化调查方法--以东昆仑1:25万冬给措纳湖幅区调为例   总被引：1，自引：0，他引：1  

于庆文  李长安  张克信  古凤宝 《地质通报》1999,(1)

造山带演化可分为两个阶段：造山期和成山期。造山期地质调查一直是我国区调工作的重点,调查的内容以区内基础地质特征研究为主。而成山期地质调查过去一直被忽视,这也正是当前“扩大区调服务领域”所要探讨的问题。造山带成山期区域地质调查重点是：①造山带隆升的过程与特点;②山脉隆升的环境效应;③造山带现代构造运动与地质灾害。笔者结合东昆仑造山带１∶２５万冬给措纳湖幅和兴海县幅区调,对成山运动和环境变化进行讨论。  相似文献   

High-resolution observations of the J=1−0 transition of cyanoacetylene in Sgr B2     

M. R. Hunt  J. B. Whiteoak  D. M. Cragg  G. L. White  P. A. Jones 《Monthly notices of the Royal Astronomical Society》1999,302(1):1-8

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Effective collision strengths for forbidden transitions among the 3s²3p³ fine-structure levels of Cl IIIIII     

C. A. Ramsbottom  K. L. Bell  F. P. Keenan 《Monthly notices of the Royal Astronomical Society》1999,307(3):669-676

Effective collision strengths for the 10 astrophysically important fine-structure forbidden transitions among the ⁴S^o, ²D^o and ²P^o levels in the 3s²3p³ configuration of Cl  iii are presented. The calculation employs the multichannel R-matrix method to compute the electron-impact excitation collision strengths in a close-coupling expansion, which incorporates the lowest 23 LS target eigenstates of Cl  iii . These states are formed from the 3s²3p³, 3s3p⁴, 3s²3p²3d and 3s²3p²4s configurations. The Maxwellian-averaged effective collision strengths are presented graphically for all 10 fine-structure transitions over a wide range of electron temperatures appropriate for astrophysical applications [log  T (K)=3.3−log  T (K)=5.9]. Comparisons are made with the earlier seven-state close-coupling calculation of Butler & Zeippen, and in general excellent agreement is found in the low-temperature region where a comparison is possible [log  T (K)=3.3−log  T (K)=4.7]. However, discrepancies of up to 30 per cent are found to occur for the forbidden transitions which involve the ⁴S^o ground state level, particularly for the lowest temperatures considered. At the higher temperatures, the present data are the only reliable results currently available.  相似文献   

The sulphur depletion problem     

D. P. Ruffle  T. W. Hartquist  P. Caselli  D. A. Williams 《Monthly notices of the Royal Astronomical Society》1999,306(3):691-695

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The cooling of astrophysical media by H₂     

J. Le Bourlot  G. Pineau des Forêts  D. R. Flower 《Monthly notices of the Royal Astronomical Society》1999,305(4):802-810

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