Une mégaséquence d'émersion: la Lettenkohle (Trias Est de la France). Mise en évidence de marées par l'imbrication bipolaire de plaques de dessiccation     

Philippe Duringer 《International Journal of Earth Sciences》1987,76(2):579-597

Résumé Dès la partie moyenne du Muschelkalk supérieur, les faciès marins francs deviennent de moins en moins profonds. Avec l'avènement de la Lettenkohle, la transgression marine à son maximum dans le Muschelkalk supérieur, semble s'épuiser. Le caractère régressif est attesté par le relais de faciès récifaux, par des dépÔts littoraux et des marais cÔtiers. Cette évolution est marquée par l'édification d'une mégaséquence d'émersion complète. Des indices de marées sous forme d'imbrications bipolaires de plaques de dessiccation ainsi que des chenaux tidaux ont été observés. Certaines structures tidales ont été comparées avec celles de l'estran du Mont-Saint-Michel en Normandie (France).

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From the Middle Upper Muschelkalk the marine facies are becoming less deep. At the beginning of the Lettenkohle the marine transgression which had reached a maximum in the Upper Muschelkalk now seems to decline. Regression is evidenced by progressive replacement of reef facies by coastal deposits and supratidal marshes. The process results in the erection of the coarsening upward cycle of a progressive complete emergence.The trace of tides, i.e. bipolar desiccation clast fabric as well as tidal channels have been observed. Some tidal structures are compared with those of the depositional environment of Mont Saint Michel (Normandie).

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Zusammenfassung Schon im mittleren Oberen Muschelkalk zeigen die vollmarinen Fazies eine allmähliche Verringerung der Meerestiefe. Mit dem Auftreten der Lettenkohle scheint die im Oberen Muschelkalk optimale Transgression langsam abzuklingen. Ein progressiver übergang von einer marinen Riffbildung zu einem Küstenlandmoor veranschaulicht eine Regression. Dieser Vorgang bildet die Megasequenz einer progressiven totalen Emersion.Gezeiteneinflüsse werden an eingeregelten Trockenri\klasten und Rinnen beobachtet. Wattgefüge werden mit denen des heutigen Wattablagerungsmilieu des Mont Saint Michel in der Normandie verglichen.

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. . . , . - . , , Mont Saint Michel .

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Isotopic study of the Manaslu granite (Himalaya,Nepal): inferences on the age and source of Himalayan leucogranites   总被引：17，自引：1，他引：17  

Catherine Deniel  Philippe Vidal  Angel Fernandez  Patrick Le Fort  Jean-Jacques Peucat 《Contributions to Mineralogy and Petrology》1987,96(1):78-92

A detailed isotopic study of the Manaslu leucogranite was carried out. A U-Pb age of 25 Ma and a whole rock Rb-Sr age isochron of 18 Ma were obtained, suggesting that the magmatic activity lasted at least 7 Ma. Initial Sr isotopic ratios are very high (0.740 to 0.760) and initial Nd isotopic ratios are low ( _Nd ⁱⁿ : –13 to –16), and they show the existence of large isotopic variations even at the metre scale. These are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes (e.g. fusion, mixing by convection). These results also support the crustal origin of this leucogranite. The Tibetan slab paragneisses, whose Sr and Nd isotopic ratios are very similar to those of the granite at an age of 20 Ma, are the most probable parental material. Nd model ages for both the leucogranite and the gneisses are in the range 1.5–2 Ga. A model of formation of the Manaslu granite by coalescence of different batches of magma is in agreement with the present data.  相似文献   

Etude des Déformations et Inclinaisons du Sous-sol: Développements Instrumentaux et Applications dans la Région Sismique d’Arette,France     

Philippe Lesage  Pierre Antoine Blum  Marcel Vadell  Jean Francois Fels 《Pure and Applied Geophysics》1983,121(5-6):889-902

We present a modified version of a tilt and strain meter conceived to have great sensibility and good stability. These instruments were deployed in a cave at the seismic Pyrenean region of Arette (France). We set in evidence several types of phenomena, of which deformations brought about by water recharge filling up fissures on the massif are of importance. Owing to the redundance in the data, the study of the co-seismic deformations allows one to separate instrumental displacements and local readjustments from regional motions.  相似文献   

Evaluation of a high-resolution regional climate simulation over Greenland     

Filip Lefebre  Xavier Fettweis  Hubert Gallée  Jean-Pascal Van Ypersele  Philippe Marbaix  Wouter Greuell  Pierluigi Calanca 《Climate Dynamics》2005,25(1):99-116

A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model (RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than 60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations.  相似文献   

XMCD at Fe L<Subscript>2,3</Subscript> edges,Fe and S K edges on Fe<Subscript>7</Subscript>S<Subscript>8</Subscript>     

Isabelle Letard  Philippe Sainctavit  Catherine Deudon 《Physics and Chemistry of Minerals》2007,34(2):113-120

Pyrrhotite (Fe₇S₈) is a natural iron sulphide that can participate in rock magnetisation. Its electronic structure is not yet surely described. X-ray magnetic circular dichroism (XMCD) at Fe L_2,3 edges on Fe₇S₈, coupled with multiplet calculations, shows that iron is present only as Fe²⁺ in this magnetic iron sulphide. It reveals a strong magnetic orbital moment. XMCD at Fe and S K edges shows the quite strong polarization of both Fe and S in Fe₇S₈.  相似文献   

Characterizing flow zones in a fractured and karstified limestone aquifer through integrated interpretation of geophysical and hydraulic data     

Nathalie Van Meir  David Jaeggi  Martin Herfort  Simon Loew  Philippe A. Pezard  Gérard Lods 《Hydrogeology Journal》2007,15(2):225-240

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An archaeomagnetic investigation of a Roman amphorae workshop in Albinia (Italy)     

Mimi J. Hill  Philippe Lanos  Annick Chauvin  Daniele Vitali  Fanette Laubenheimer 《Geophysical Journal International》2007,169(2):471-782

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A simplified approach for vulnerability assessment in moderate-to-low seismic hazard regions: application to Grenoble (France)   总被引：3，自引：2，他引：3  

Philippe Guéguen  Clotaire Michel  Laele LeCorre 《Bulletin of Earthquake Engineering》2007,5(3):467-490

Due to the moderate seismic risks in France, the building vulnerability assessment methods developed for high seismic risk countries could not easily be used here because of their cost and the low-risk perception among the public and officials. A light vulnerability assessment method is proposed and tested in Grenoble (France), based on classes and scores provided in the GNDT method but simplified in terms of visual screening and number of structural parameters used. Compared to the RiskUE method, the damage obtained by our approach shows that 90% of buildings have residuals smaller than 0.2, i.e. one grade of the EMS98 damage scale. A large scale survey is devised and conducted among the inhabitants of Grenoble in order to collect the main structural parameters. By comparing the results from the survey to the historical urbanization of Grenoble and to expert surveys performed in two urban districts, the information useful for the light method of vulnerability assessment can be rapidly collected by non-experts reducing substantially the estimate cost. The average damage is then computed using the GNDT formula considering the probable intensities which could be observed in Grenoble (VII and VIII). The average damage reaches 0.4 in the oldest part of Grenoble mainly made of masonry buildings and 0.2 in reinforced concrete suburbs where reinforced concrete predominates. The results are a relative vulnerability assessment that provides useful initial information for the urban zones of Grenoble where the vulnerability is higher. This method can be used to classify the seismic vulnerability in wide seismic-prone regions to a fair degree of accuracy and at low cost.  相似文献   

Inversion of interference hydraulic pumping tests in both homogeneous and fractal dual media     

Frederick Delay  Anne Kaczmaryk  Philippe Ackerer 《Advances in water resources》2007

This work proposes a complete method for automatic inversion of data from hydraulic interference pumping tests based on both homogeneous and fractal dual-medium approaches. The aim is to seek a new alternative concept able to interpret field data, identify macroscopic hydraulic parameters and therefore enhance the understanding of flow in porous fractured reservoirs. Because of its much contrasted sensitivities to parameters, the dual-medium approach yields an ill-posed inverse problem that requires a specific optimization procedure including the calculation of analytical sensitivities and their possible re-scaling. Once these constraints are fulfilled, the inversion proves accurate, provides unambiguous and reliable results. In the fractal context inverting several drawdown curves from different locations at the same time reveals more accurate. Finally, hydraulic parameters drawn from inversion should be taken into account to improve in various situations the conditioning of up-scaled flow in fractured rocks.  相似文献   

Adaptation of prestack migration to multi-offset ground-penetrating radar (GPR) data     

Donatienne Leparoux  Dominique Gibert  Philippe Côte 《Geophysical Prospecting》2001,49(3):374-386

In adapting the prestack migration technique used in seismic imaging to the inversion of ground‐penetrating radar (GPR) from time‐ to depth‐sections, we show that the theoretical integral formulation of the inversion can be applied to electromagnetic problems, albeit with three assumptions. The first two assumptions concern the electromagnetic characteristics of the medium, primarily that the medium must be perfectly resistive and non‐dispersive, and the third concerns the antennae radiation pattern, which is taken to be 2D. The application of this adaptation of the inversion method is confirmed by migrating actual GPR measurements acquired on the test site of the Laboratoire Central des Ponts et Chaussées. The results show good agreement with the geometry of the structures in the medium and confirm that the possible departure from the assumption of a purely resistive medium has no visible effect on the information concerning the geometry of scattering and reflecting structures. The field experiments also show that prestack migration processing is sufficiently robust with regard to the assumption of a non‐dispersive medium. The assumption of a 2D antennae radiation pattern, however, produces artefacts that could be significant for laterally heterogeneous media. Nevertheless, where the medium is not highly laterally heterogeneous, the migration gives a clear image of the scattering potential due to the geometry of structural contrasts in the medium; the scatterers are well focused from diffraction hyperbolae and well localized. Spatial geometry has limited dimensional accuracy and positions are located with a maximum error equal to the minimum wavelength of the signal bandpass. Objects smaller than one wavelength can nevertheless be detected and well focused if their dielectric contrasts are sufficiently high, as in the case of iron or water in gneiss gravels. Furthermore, the suitability of multi‐offset protocols to estimate the electromagnetic propagating velocity and to decrease the non‐coherent noise level of measurements is confirmed. Our velocity estimation is based on the semblance calculation of multi‐offset migrated images, and we confirmed the relevance of this quantification method using numerical data. The signal‐to‐noise ratio is improved by summing multi‐offset results after the addition of random noise on measurements. Thus the adaptation of prestack migration to multi‐offset radar measurements significantly improves the resolution of the scattering potential of the medium. Limitations associated with the methods used here suggest that 3D algorithms should be applied to strongly laterally heterogeneous media and further studies concerning the waveform inversion are necessary to obtain information about the electric nature of the medium.  相似文献