Origin and evolution of closed depressions in central Belgium,European loess belt     

T. Vanwalleghem  J. Poesen  I. Vitse  H. R. Bork  M. Dotterweich  G. Schmidtchen  J. Deckers  A. Lang  B. Mauz 《地球表面变化过程与地形》2007,32(4):574-586

Closed depressions (CDs) are lower lying areas where the sediment eroded from the surrounding soil surfaces draining towards the CD is trapped in the system. CDs have been reported in several regions of the European loess belt and are attributed either to natural processes (e.g. dissolution of subsurface horizons) or to human intervention (e.g. quarrying). Previous studies focussed mainly on cropland areas where, however, only few and largely filled in CDs remain. The objectives of this study were to i) assess the spatial distribution of CDs under forest and cropland, ii) to determine and compare the morphology of CDs under forest and under cropland, and iii) to determine the origin and age of these CDs under forest. In a study area located partly in ancient forest (13 km²) and partly in cropland (29 km²), a systematic survey revealed the presence of 71 CDs under forest (5·3 CD.km^?2) and 30 CDs under cropland (1 CD.km^?2). Comparison of their morphology showed that CDs under forest were significantly deeper, with steeper sidewalls and a smaller surface area because of the erosion and deposition processes acting on the CDs under cropland. By comparing CDs that had been under cropland for different time intervals, the rate of this morphological evolution could be reconstructed. Analysis of the soil stratigraphy of two representative CDs in the ancient forest area confirmed their origin as quarries. Most probably, calcareous loess was excavated since this soil horizon, about two to five meters thick, was completely absent within the CDs. Dating of the infilling of one CD by optically stimulated luminescence (OSL) shows that the CD filled in between the first century BC and the fourth century AD. This dating corresponds to the dating of sediment deposits in nearby, human‐induced gullies that were attributed to an agricultural land use phase between the 18th century BC and the third century AD.  相似文献   

三维地电模型数值模拟中视电阻率真假异常特征分析   总被引：2，自引：0，他引：2  

强建科  阮百尧  熊彬 《CT理论与应用研究》2002,11(1):6-9

本文概要介绍了三维数值模拟中双网格系统的剖分方法,并通过几种典型模型的有限单元法三维数值模拟计算（网格单元电导率分块均匀、电位三线性变化）,充分揭示了对称四极电阻率测深法三维地电模型视电阻率真假异常的分布规律,分析了产生真假异常的原因,并研究了真异常的形态与引起真异常的地质体位置的关系。  相似文献   

集值随机过程的样本函数连续性     

代宁  归庆明 《测绘学院学报》1999,(2)

讨论了集值随机过程Ｘ 的样本函数在闭收敛拓扑意义下的连续性,建立了此类性质与Ｘ 产生的实值随机过程ｄ（ｘ ,Ｘ） ,（ ｘ ∈Ｒｍ） 及其ＡＱＣａｓｔｉｎｇ 选择形成的向量值随机过程ｆｋ（ ｋ ≥１） 的样本函数连续性的等价关系。  相似文献   

湖南常宁县康家湾铅锌金矿硅化角砾岩岩石地球化学特征   总被引：8，自引：0，他引：8  

许德如  刘静  陈广浩 《地质科学》2002,37(3):356-364

湖南常宁县康家湾铅锌金矿床硅化角砾岩带由未硅化角砾岩—极弱硅化角砾岩—硅化角砾岩—强硅化角砾岩(似硅质岩)组成,产于侏罗系与下伏二叠系间的不整合面附近,角砾成份复杂,充填物和胶结物类型多样。随着硅化程度的加强,硅化角砾岩带SiO₂含量变化大,最高可达95.34%,而Al₂O₃、MgO、FeO、K₂O、Na₂O、CaO、CO₂和P₂O₅含量特别是MgO、CaO、CO₂和P₂O₅含量明显降低,且K₂O>Na₂O,TiO₂的含量显著偏低。硅化角砾岩带LREE/HREE比值为1.95～4.93,Ce(δCe=0.44～0.81)和Eu(δEu=0.58～0.89)均为弱负异常,属轻稀土富集型,但随硅化程度增高稀土元素含量显著减少:未硅化和弱硅化角砾岩稀土元素总量较高,为(176.82～318.93)×10^-10,与当冲组泥质岩配分曲线相似;硅化强烈的角砾岩稀土元素总量低,为(7.71～65.95)×10^-10,与下伏栖霞组灰岩稀土元素配分曲线极为相似。结合微量元素F、Ba、Cl、Cr、Ni、Sr、V研究结果及硅化角砾岩带自底部至顶部特有的下粗上细的韵律性层理构造,认为康家湾铅锌金矿床硅化角砾岩带是在地台体制向地洼体制转变期的大地构造环境下,由于地壳快速隆升,二叠纪灰岩、泥质岩、石英砂岩等岩石剥蚀,在古河流环境下搬运、沉积形成的。此  相似文献   

FGC－15型大直径单头潜孔锤钻具系统研制          下载免费PDF全文

蒋荣庆  殷琨  王茂森 《探矿工程》1995,(5):17-19,47

大直径单头潜孔锤与三通道气水龙头、主动钻杆、三通道钻杆、加重导正器配套，可实现大直径潜孔锤碎岩钻进、泵吸反循环排渣、泥浆护壁、压气闭路循环等相结合的先进钻进工艺，是解决大直径硬质基岩及卵砾石钻进的有效机具。文中介绍了钻具研制过程及设计内容。  相似文献   

The effects of closure on the moments of a distribution   总被引：1，自引：0，他引：1  

John C. Butler 《Mathematical Geology》1979,11(1):75-84

When percentages are formed from uncorrelated, normally distributed parent variables the moments of the percentage distribution may differ considerably from those of the parents. Equations can be derived which enable the approximation of the moments of a percentage variable in terms of the moments of the parent distribution, the row sum statistics, and the correlation between a part of a sum and the sum (the part-whole correlation). If the part-whole correlation is negative the mean and variance of the percentage are increased (relative to the means and variances of those variables with a positive part-whole correlation) and the percentage variable will exhibit a positive skewness. If the part-whole correlation is positive the percentage variable will be negatively skewed if, and only if, the part-whole correlation is greater than the ratio of the coefficient of variation of the row sum (T) to the coefficient of variation of the parent variable. The kurtosis of the percentage variable must be greater than that of the parent variable regardless of the sign of the part-whole correlation. It is obvious that the interpretation or explanation of the distribution of a percentage variable must include an assessment of the effects of percentage formation. However, at the present time the isolation of the percentage effect appears to be impossible unless the parent data set is available.  相似文献   

湘中地区硅化岩研究   总被引：2，自引：0，他引：2  

靳西祥  靳冰晔 《湖南地质》1995,14(2):91-98

湘中地区硅化岩，产出层位多，原岩组成多样，与锑矿化关系密切，空间上，锑矿化受早期硅化控制；时间上，锑矿化主要伴随早期硅化岩中的晚期硅化产生；成因上，硅化（岩）与锑矿化之间不存在必然联系，二者之内在联系，仅在碎裂硅化岩为矿质堆积提供了良好的空间。  相似文献   

地震监测台网的最佳理论设置初探     

魏永德  朱恩全  李福龙  岳明生 《东北地震研究》1994,(1)

本文所讨论的问题是在一个平面区域Ｄ内应如何设置地震监视台，使在该区域内任何一点发生地震，在距震源５０公里的圆周内，至少有４个地震台可监视地震情况，而且使区域Ｄ内设置的地震监视台个数最少．这里，首先对Ｄ为一有界闭区域，给出了在Ｄ内设置的地震监视台个数的下界，并且讨论了Ｄ为半径为５０的圆盘时，地震监视台的下确界以及地震台设置的设计方案．进而又讨论了当Ｄ为半径为５０ｋ公里时（ｋ＝２，３，……）时应设置地震台个数的下界．  相似文献   

A new approach to null correlations of proportions   总被引：1，自引：0，他引：1  

J. Aitchison 《Mathematical Geology》1981,13(2):175-189

Much work on the statistical analysis of compositional data has concentrated on the difficulty of interpreting correlations between proportions with an assortment of tests for nullcorrelations, for independence except for the constraint, F-independence of bounded variables, neutrality in the mean and in the median. This paper questions the appropriateness of characterizing the dependence structure of proportions in terms of such concepts, suggests an alternative method of modeling, develops necessary distribution theory and tests, and illustrates the methodology in applications.  相似文献   

闭合导线的不可靠性浅析     

姚排  窦承泽  梁作平 《吉林地质》2005,24(3):39-43

本文论证了闭合导线存在的不可靠因素；从理论上分析了产生的原因；提出了使用中应该采取的措施。  相似文献