Stages of evolution of a Toarcian compacted claystone around galleries excavated between 1 and 124 years ago by the study of noble gases dissolved in pore water at the Tournemire Underground Research Laboratory (France)     

Bernard Lavielle  Jean-Michel Matray  Bertrand Thomas  Alexandre Dauzères  Fethi Bensenouci  Eric Gilabert 《Applied Geochemistry》2012

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Localization of saturated karst aquifer with magnetic resonance sounding and resistivity imagery   总被引：3，自引：0，他引：3  

Vouillamoz JM  Legchenko A  Albouy Y  Bakalowicz M  Baltassat JM  Al-Fares W 《Ground water》2003,41(5):578-586

To answer one of the main questions of hydrogeologists implementing boreholes or working on pollution questions in a karst environment--i.e., where is the ground water?--numerous tools including geophysics are used. However, the contribution of geophysics differs from one method to the other. The magnetic resonance sounding (MRS) method has the advantage of direct detection of ground water over other geophysical methods. Eight MRSs were implemented over a known karst conduit explored and mapped by speleologists to estimate the MRS ability to localize ground water. Two direct current resistivity imageries (DC-2D imagery) were also implemented to check their capability to map a known cave. We found that the MRS is a useful tool to locate ground water in karst as soon as the quantity of water is enough to be detected. The threshold quantity is a function of depth and it was estimated by forward modeling to propose a support graph to hydrogeologists. The measured MRS's signals could be used to calculate transmissivity and permeability estimators. These estimators were used to map and to draw a cross section of the case study site, which underline accurately the known karst conduit location and depth. We also found that the DC-2D imagery could underline the karst structures: It was able to detect the known cave through its associated faults. We prepared a computer simulation to check the depth of such a cave to induce resistivity anomaly which could be measured in similar conditions.  相似文献   

First assessment of the Caulerpa racemosa (Caulerpales, Chlorophyta) invasion along the French Mediterranean coast     

Ruitton S  Javel F  Culioli JM  Meinesz A  Pergent G  Verlaque M 《Marine pollution bulletin》2005,50(10):1061-1068

The introduced green alga Caulerpa racemosa var. cylindracea has been rapidly spreading in the Mediterranean Sea since 1990. It was first observed in France in 1997 (Marseilles). In early 2004, the stretch of the French Mediterranean coastline and the surface area affected by the invasion were estimated at about 83 km and 4014 ha, respectively. The depth range of colonized areas was usually 10-35 m depth. Shallow (0-10 m) and deep (down to 40 m) dense meadows were rarely observed. In contrast to the dead matte of Posidonia oceanica, which constituted the most widely colonized substratum, dense P. oceanica meadows and fine sand with large ripple-marks were not invaded. Few rocky areas were colonized and coarse sand bottoms were usually colonized below 20 m depth. All the colonized areas were exposed to human activities and more than 40% were fishing areas. Mild climate, suitable substrata, presence of vectors of dispersal and absence of efficient biological control make the French Mediterranean coast particularly vulnerable to the further spread of the alga.  相似文献   

Micrometeorological Measurements in a Street Canyon during the Joint ATREUS-PICADA Experiment     

Marcin Idczak  Patrice Mestayer  Jean-Michel Rosant  Jean-Francois Sini  Michel Violleau 《Boundary-Layer Meteorology》2007,124(1):25-41

In order to investigate the microclimatic conditions in a street canyon, a physical model was used to conduct the Joint ATREUS-PICADA Experiment (JAPEX) in situ experimental campaign. Four lines of buildings simulated by steel containers were installed to form three parallel street canyons at 1:5 scale, with width/height aspect ratio approximately 0.40. The reference wind and atmospheric conditions were measured, as well as the flow velocity and direction in the street. Preliminary results concern street canyon ventilation and thermal effects on in-canyon airflow, and show that vortical motions appear for reference wind directions perpendicular to the street axis. The presence of adjacent rows of buildings did not appear to significantly influence the flow character within the canyon for the case of a low aspect ratio corresponding to a skimming flow regime. The flow structure was not significantly affected by the thermal effects although some slight interference occurred in the lower part of the canyon. An analysis of horizontal temperature gradients indicated that a thin boundary layer develops near the heated facade. These facts imply that the thermal effects are considerable only very close to the wall.  相似文献   

On the computation of the barotropic mode of a free-surface world ocean model   总被引：1，自引：0，他引：1  

Eric Deleersnijder  Jean-Michel Campin 《Annales Geophysicae》1995,13(6):675-688

The free-surface formulation of the equations of our world ocean model is briefly described. The barotropic mode equations are solved according to the split-explicit method, using different time steps for the external and internal modes. Because the numerical algorithm is implemented on the B-grid, a spurious, free-surface, two-grid interval mode may develop. This mode must be filtered out. The properties of two filters are theoretically investigated and their actual performance is tested in a series of numerical experiments. It is seen that one of these filters may severely perturb the local mass conservation, rendering it impossible to enforce the impermeability of the surface or the bottom of the ocean. The dynamics of the external mode is also examined, by studying the depth-integrated momentum equations. The depth-integral of the pressure force due to the slope of the ocean surface is approximately balanced by the depth-integral of the force ensuing from the horizontal variations of the density. The depth-integral of the Coriolis force is an order of magnitude smaller, except in the Southern Ocean. Two variational principles are resorted to for computing the fictitious ocean surface elevation corresponding to the approximate equilibrium between the dominant forces of the barotropic momentum equations.  相似文献   

Microstructural criteria for reliable thermometry in low-temperature eclogites     

Jean-Marc Lardeaux  Jean-Michel Caron  Pascal Nisio  Guy Pquignot  Micheline Boudeulle 《Lithos》1986,19(3-4):187-203

Two Alpine eclogite bodies, sampled in metaophiolitic complexes of the Piemonte Zone, have been studied for geothermometry. It is demonstrated that temperature estimates, by both exchange thermometry and sizes of antiphase domains in omphacites, give rise to erratic results when the defect structures of the minerals are not taken into account. Microstructural criteria, by means of both optical and TEM microscopy, for reliable thermometry in low-temperature eclogites are disscussed. The dynamically recrystallized grains are the more suitable sites for the application of exchange thermometry, while only low-strained omphacites can be used for thermometry based on APD's.  相似文献   

The behavior of shape preferred orientations in metamorphic rocks: amphiboles and jadeites from the Monte Mucrone area (Sesia-Lanzo zone, Italian Western Alps)     

Benoit Ildefonse  Jean-Marc Lardeaux  Jean-Michel Caron 《Journal of Structural Geology》1990,12(8)

In the eclogitic micaschists of the Monte Mucrone area (Sesia-Lanzo zone, Italian Western Alps), we have measured in detail the eclogitic lineation at several outcrops. We present observations at the markers scale, this scale allowing the whole range of progressive deformations to be described. Populations of glaucophanes and jadeites show different statistical features which must be, at least for a part, produced by the distinct mechanical behavior for these markers during the alpine history. The glaucophanes show a positive correlation between the intensity of preferred orientation and their aspect ratio, due to a mainly rigid behavior. The observed differences in shape and orientation of jadeites also show different behavior, related to different retromorphic overprints. We briefly discuss the implications of these observations on the significance of metamorphic lineations.  相似文献   

The karst system of the Fontaine de Vaucluse (Southeastern France)     

Bernard Blavoux  Jacques Mudry  Jean-Michel Puig 《Environmental Geology》1992,19(3):215-225

The intake area of the Fontaine de Vauctuse system covers over 1,100 km²; its mean altitude is 870 m. The Lower Cretaceous limestones (1,500 m thick) give the system a very thick (800 m) unsaturated zone.Karstification is very well developed, both on the intake area (four sinkholes are more than 500 m deep) and on the lower part (sunken cave of 300 m depth under the spring). The bottoms of the sinkholes of the plateau do not reach the saturated zone of the karst, as their flows have chemical composition similar to seepage water. The maximum hydraulic gradient between the plateau and the spring is low, only 0.3%. Dye tracings allow assigning the Ventoux-Lure range (including its calcareous northern side with a southward dipping) and the Vaucluse Plateau to the intake area. The moisture balance, calculated for each altitude belt, shows that the effective rainfall strongly increases with altitude: 120 mm below 200 m, 1,300 mm over 1,800 m. The working of the system, studied by means of discharge, physical and chemical content, is one of a well-karstified milieu that reacts with a light inertia upon rainy periods. The system is made up of important reserves, peculiarly within the unsaturated zone, which maintain long decline and depletion episodes. Despite its large average discharge (21 m³·sec^–1), the spring is not harnessed and thus no general protection exists on the intake area. Only local protection is provided by protection areas around some piped little springs of the plateau. A Biosphere Preserve will protect as a whole the higher part of the intake area—Mount Ventoux.  相似文献   

A regional Bayesian POT model for flood frequency analysis     

Mathieu Ribatet  Eric Sauquet  Jean-Michel Grésillon  Taha B. M. J. Ouarda 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):327-339

Flood frequency analysis is usually based on the fitting of an extreme value distribution to the local streamflow series. However, when the local data series is short, frequency analysis results become unreliable. Regional frequency analysis is a convenient way to reduce the estimation uncertainty. In this work, we propose a regional Bayesian model for short record length sites. This model is less restrictive than the index flood model while preserving the formalism of “homogeneous regions”. The performance of the proposed model is assessed on a set of gauging stations in France. The accuracy of quantile estimates as a function of the degree of homogeneity of the pooling group is also analysed. The results indicate that the regional Bayesian model outperforms the index flood model and local estimators. Furthermore, it seems that working with relatively large and homogeneous regions may lead to more accurate results than working with smaller and highly homogeneous regions.  相似文献   

Genesis of the Dordogne (France) high-purity silica placers     

Laurent Désindes  Marc Durand  Laurent Bailly  Stéphane Jaillet  Vincent Bouchot  Marc Lespinasse  Marcel Pouliquen  Jean-Michel Ostermann  Jacques Leroy 《International Journal of Earth Sciences》2006,95(1):80-94

This article describes the formation of the principal French high-purity silica placer (source for electrometallurgy of silicon and ferrosilicon), the Boudeau deposit in Dordogne, and of one of its subordinate deposits, the Pays Brûlé deposit. Boudeau has always been considered to be a colluvial deposit, formed in a trap produced by extensional tectonism. The present work suggests a new genetic interpretation, based on a combined study of the deposits and their underlying rocks. It shows that the quartz gravel deposits, laid down by stream flow within braided channels, were reworked by karstic progressive sinking, and that the mechanism responsible for the increase in the thickness of the economic formations is cryptokarstic corrosion. This undercovers weathering process, which involves dissolution of karstifiable rocks (oolitic and bioclastic limestones) at their interface with a permeable, non-karstifiable cover composed of chemically pure quartz gravels in a sandy-argillaceous matrix. A typological study of the gravels provides a basis for tackling the problem of their origin and their purity. They seem to be derived mainly from the synmetamorphic quartz mobilisates of the stripped metamorphic units (the lower and upper gneiss units forming the western edge of the Massif Central). Lastly, a dynamic model is suggested for the genesis of the high-purity silica deposits of Dordogne.  相似文献