Subsurface DC resistivity mapping: approximate 1-D interpretation     

Youcef Meheni  Roger Guérin  Yves Benderitter  Alain Tabbagh 《Journal of Applied Geophysics》1996,34(4):255-269

Resistivity prospecting is the main tool used to investigate the shallow structure of the ground. A series of new techniques for determining the 2-D and 3-D geometry of the ground is now finding increasing use, but the light and simple Wenner prospecting technique remains a practical and efficient tool for rapidly mapping lateral variations in resistivity. When the resistivity changes are smooth, 1-D modelling can be used to interpret the data, and the criteria governing this approximation can be defined from synthetic data generated by a 3-D slab-model. For a Wenner array, two quadripole configurations can be used, Normal and Dipole-Dipole. For these two configurations the width of the transition zone, the apparent anisotropy effect and the precision of the resistivity values recovered from 1-D inversion differ. However the simultaneous inversion of both sets of data gives better results than for either configuration by itself. Two examples illustrate that in geological contexts where the thickness of the weathered zone causes the changes in the apparent resistivity value, this parameter can be recovered from 1-D inversion.  相似文献   

Hydrothermal alterations in the Echassières granitic cupola (Massif central,france)     

Thierry Merceron  Philippe Vieillard  Anne-Marie Fouillac  Alain Meunier 《Contributions to Mineralogy and Petrology》1992,112(2-3):279-292

Detailed petrographic and mineralogic investigations of an albite-lepidolite granite at Echassières (Massif Central, France; scientific deep drill program) shows the existence of hydrothermal stages which are closely related to the magmatic and structural history. According to fluid inclusion data, K-Ar datations and ¹⁸O/¹⁶O-D/H compositions of secondary minerals, two successive hydrothermal periods have been recognized. The early one (273–268 million years) produced a series of aluminous phyllosilicates: muscovite, pyrophyllite, donbassite, tosudite, kaolinite which are observed as vein deposits (<10 mm wide) and alteration products of primary minerals in wall-rocks. The vein system was sealed by monomineralic assemblages during a cooling period (400–150°C). This early hydrothermal alteration stage was controlled by interactions of rock with low salinity (1–10 wt% NaCl equivalent) fluids expelled from the granitic body during the cooling processes. The chemical properties of these fluids were the following: low pH, very low Mg and Fe and high Li, Na and K contents. Thermodynamic calculations show that the sequence pyrophyllite, Li-bearing donbassite, tosudite is mostly temperature dependent. From the chemical composition of secondary minerals and isotopic data it can be deduced that these fluids, which have a meteoric origin, have been expelled from the granite body during its cooling period and after interaction with it at high temperature. The late hydrothermal stage corresponds to deposits of fluorite and Fe-Mg rich illite (151 million years) in subvertical fractures. Temperature conditions did not exceed 250° C and fluids came through the surrounding metamorphic rocks into the granitic body. IIlite/smectite mixed-layer minerals have been identified in subvertical fractures which were opened during Tertiary periods. In the host micaschists, successive hydrothermal alterations took place during the cooling of the Beauvoir granite. Early magmatic fluids interacted with these micaschists. Locally, the metamorphic assemblage is replaced by a metasomatic one. Secondary topaz and (F, Li)-rich mica crystals were formed over a range of 450 of 150°C. Later hydrothermal fluids reacted with the country rocks to form phengite-biotite, chlorite-illite and kaolinite over a range of 300 to 150°C. Illite/smectite mixed-layer minerals crystallized in the roof micaschists and within the Beauvoir granite during the Tertiary alteration period. Meteoric water invaded open fractures producing supergene alteration mineral assemblages.  相似文献   

Comments on Lerche (1993) and Liu and Lerche (1993)     

Alan K. Burnham  Robert L. Braun  I. Lerche 《Mathematical Geology》1995,27(5):693-701

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Buchbesprechungen     

M. Pavoni  Robert Staub  Woker  Robert Staub  K. Wubrmann  J. Grönseth  Fritz Sulzer  R. Braun  H. Woker  H. F. Kuisel 《Aquatic Sciences - Research Across Boundaries》1959,21(1):123-132

Ohne Zusammenfassung  相似文献   

Wassermilben aus dem Amazonasgebiet (Hydrachnellae,Acari)     

Dr. R. Braun  Dr. H. Sioli  Karl Viets 《Aquatic Sciences - Research Across Boundaries》1954,16(2):161-247

Zusammenfassung Erstmalig aus dem Amazonasgebiet wurden nach den SammlungenSioli undBraun die Hydrachnellae untersucht. Von den 104 festgestellten Arten bzw. Unterarten waren 64 neu für die Wissenschaft; 5 neue Genera bzw. Subgenera wurden aufgestellt. Durch 171 ausgewertete F?nge wurden 1033 Individuen ermittelt, eine im Vergleich mit anderen Sammlungen geringe Menge sowohl im ganzen gesehen, als auch die Individuen pro Fang betrachtet, als auch im Hinblick auf die hohe Zahl der neuen Formen in der kleinen Individuenmenge. Als Ursache dieser Diskrepanz werden neben extensivem Sammelverfahren chemisch-physikalische Faktoren der Gew?sser vermutet. Die Amazonas-Wassermilben werden nach Biotopen-stehende und fliessende Gew?sser-untersucht; dazu kommen Angaben über Frequenz, über jahreszeitliche Verteilung und das Verh?ltnis der Geschlechter. Der besondere Chemismus der Amazonasgew?sser-die im allgemeinen niedrigen pH-Werte-, dazu die klimatisch bedingte inkonstanz mancher Faktoren scheint bei der wohl grossen Toleranz der Wassermilben diesen Faktoren gegenüber weniger direkt, vielleicht aber indirekt die Nahrungstiere und damit das zahlenm?ssige Auftreten der Hydrachnellae zu beeinflussen. Ein Vergleich der Wassermilben aus den bislang untersuchten tropischen Gebieten kann noch nicht zu allgemeinen Ergebnissen gelangen, weil einheitlich zutreffende Vergleichspunkte noch kaum gegeben sind.  相似文献   

On the stability of a slow deflagration front at the surface of a degenerate star     

A. Braun  R. Z. Yahel 《Astrophysics and Space Science》1980,69(1):217-225

On the surface of a degerate star, a slow nuclear combustion process with a wake of escaping matter can exist. The evolution of this process has been studied by solving the nonadiabatic, time-dependent hydrodynamic equations. It has been found that this flow is almost stationary and is stable against small spherical symmetric perturbations.  相似文献   

Tar ball frequency data and analytical results from a long-term beach monitoring program     

Owens EH  Mauseth GS  Martin CA  Lamarche A  Brown J 《Marine pollution bulletin》2002,44(8):770-780

Following the spill of fuel oils from the New Carissa in February 1999, approximately 300 km of beaches on the Pacific coast of North America were surveyed. A long-term observation program focused on the documentation of stranded tar balls in the vicinity of the spill site. Systematic beach surveys which were conducted over the period March 1999 to April 2001 and semi-logarithmic scale, time-series plots proved the most useful format for identifying trends. Beach monitoring continued through to August 2001. by which time 212 tar balls had been analyzed by GC/MS for their chemical characteristics. The samples of tar balls collected between February 1999 and August 2001 were qualitatively compared with New Carissa source oils (NCSO) and 101 (48%) were not consistent with NSCO. The presence of tar balls that are not related to an incident can confound attempts to define cleanup or endpoint criteria and to assess possible injury to natural resources.  相似文献   

北京地区单双频地基GPS大气水汽遥测试验与研究   总被引：5，自引：3，他引：5       下载免费PDF全文

谢璞  张朝林  王迎春  楚艳丽  张京江  王京丽  李矩  Ying Hwa Kuo  John Braun 《应用气象学报》2006,17(Z1):28-34

该文对北京地区单双频地基GPS大气水汽监测网布网依据、单频与双频地基GPS测量数据解算技术应用、GAMIT和Bernese地基GPS数据分析处理软件应用、远程遥控GPS数据采集与通讯系统、资料分析与数值同化应用等方面的工作进展进行简要介绍,重点讨论了单双频地基GPS大气水汽资料的解算技术及其应用效果。结果表明:在北京天气敏感区通过单双频地基GPS接收机合理组网布局,可构建并利用高分辨率电离层延迟订正技术将单频接收机的大气水汽监测精度提高到实用水平,为强降水天气预报提供有价值的产品。  相似文献   

Tracing of variabilities within a geological barrier by molecular organic geochemistry.: Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)     

Yann Hautevelle  Raymond Michels  Fabrice Malartre  Marcel Elie  Alain Trouiller 《Applied Geochemistry》2007

The Callovo-Oxfordian claystones located at 500 m depth at Bure (Meuse, France) are currently being investigated by Andra (the French National Radioactive Waste Management Agency) for testing the feasibility of long-term and deep geological nuclear waste disposal. In order to evaluate its potential as a geological barrier, it is very important to study, assess and describe its physico-chemical variability. The molecular biomarker composition of 150 samples of these claystones and their surrounding limestones carry diverse information on the sources of the sedimentary organic matter, the chemistry of the depositional environment, the preservation and diagenesis conditions. It also allows assessing the degree of lateral and vertical variability of the organic matter within these sedimentary series. The abundance of unsaturated biomarkers, the distribution of steroids and hopanoids and CPI values >2 prove the thermal immaturity of the organic matter. The co-occurrence of plankton, bacteria and land plant biomarkers indicate that the organic matter is a mixture of marine and continental contributions. The data also reveal that the organic matter was deposited under oxic and open-sea conditions except for a brief event of photic zone anoxia at the beginning of the Middle Callovian. In the claystones, the geosynthesis of diasterenes is favored to the detriment of the formation of steranes, especially in smectite-rich levels, and the organic matter is rapidly isolated from oxidizing then reducing conditions after the deposition due to the protective effect of clays. On the scale investigated, the claystones are characterized by a unique molecular facies and are thus homogenous from their organic content point of view. Yet, detailed investigation of specific molecular families indicates changes related to major claystone–limestone transitions. The homogeneity of these claystones can be explained by the paleogeographic position of their depositional setting and the plane and sub-horizontal paleotopography on which they were deposited. This study demonstrates the efficiency of organic geochemistry in the assessment of the variability of geological barriers.  相似文献   

Early Miocene adakite-like volcanism in the Balkuyumcu region, central Anatolia, Turkey: Petrology and geochemistry   总被引：1，自引：0，他引：1  

Elif Varol  Abidin Temel  Alain Gourgaud  Herve Bellon 《Journal of Asian Earth Sciences》2007,30(5-6):613-628

The Balkuyumcu region, located in the southwestern part of Ankara in the Izmir-Ankara suture zone (central Anatolia, Turkey), consists of basic andesitic, andesitic, dacitic and rhyolitic rocks extruded during the Early Miocene (20–22 Ma) as a result of post-collisional volcanism. Balkuyumcu volcanic rocks can be divided into two groups on the basis of their mineralogy and composition: The basic andesitic (BA) and andesitic, dacitic and rhyolitic (ADR) groups. The ADR and BA group of rocks have adakite-like and calc-alkaline characteristics, respectively. The ADR group has higher SiO₂ content, Sr/Y and La/Yb ratios and low MgO, Mg#, Y and Yb contents than the BA group. Both groups have nearly the same Sr, Nd isotopic compositions and display similar normalized multi-element patterns with enrichments in LILE and LREE, depletions in Nb, Ti, Zr, P and a lack of Eu anomalies. Major, trace element and Sr, Nd isotopic data indicate that both groups of rocks were derived from the same source but affected by different magmatic processes during ascent. The adakite-like rocks may have been produced by partial melting of thickened lower continental crust. Fractional crystallization also played a major role in their formation. However, the BA group rocks were derived from partial melting of lower continental crust that was probably delaminated. These rocks appear to have had limited interaction with mantle peridodite during ascent to the surface.  相似文献