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41.
Benoı̂t Waeles Pierre Le Hir Ricardo Silva Jacinto 《Comptes Rendus Geoscience》2004,336(11):1025-1033
Numerical experiments were performed to simulate the profile evolution of an intertidal mudflat with a 1D cross-shore morphodynamical model. First, the hydrodynamical forcing is a cross-shore tidal current due to semi-diurnal variations of the free surface elevation at the open boundary. Further, considering the conservation of the action density of surface gravity waves, a wave height (and resulting bottom shear stress) calculation is added to the morphodynamical model. Results of the numerical experiments show that the shape of the profile reaches equilibrium. The mudflat progrades continually when the forcing is tide only, whereas it can be steady under the simultaneous action of tide and waves. To cite this article: B. Waeles et al., C. R. Geoscience 336 (2004). 相似文献
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43.
Franois Chabaux Jean Riotte Anne-Dsire Schmitt Jean Carignan Pierre Herckes Marie-Claire Pierret Henry Wortham 《Comptes Rendus Geoscience》2005,337(16):4612
Major and trace element concentrations, as well as Sr and U isotope ratios, were measured in rainwater samples collected in three different locations in Alsace (East of France) and Luxembourg: a mid-altitude mountain site (Aubure Environment HydroGeochemical Observatory), an urban site (Strasbourg) and a peri-urban site located in an area of well developed industrial activity (Esch-sur-Alzette in Luxembourg). Results highlight the quite high spatial and temporal variability of the chemical and isotopic characteristics of rainwater at the regional scale. They also suggest a quite systematic contribution of a local component in the chemical composition of rainwater. In urban and peri-urban sites, the local component is certainly linked to human activities, as it is well illustrated in this study with the Esch-sur-Alzette samples. On the other hand, for the Aubure site, i.e. a small forested watershed of mid-altitude mountain, data presented in this study demonstrate the influence of the vegetation on the chemical composition of rainwater for alkali and calc-alkali elements, as well as for the Sr isotope ratios. Such a result questions the reliability of the method classically used to estimate the rainwater contribution on the river chemical budget. In addition, data of the present study confirm the very low content of uranium in rainwater and demonstrate, especially through the U isotope analysis of Aubure rainwater, the negligible effect of rainwater on U budget of river waters. This work thus outlines the property of U to be a geochemical tracer specific of weathering fluxes carried by rivers. To cite this article: F. Chabaux et al., C. R. Geoscience 337 (2005). 相似文献
44.
Philippe Ponel Russell Coope Pierre Antoine Nicole Limondin-Lozouet Chantal Leroyer Andr-Valentin Munaut Jean-Franois Pastre Frdric Guiter 《Quaternary Science Reviews》2005,24(23-24):2449-2465
Two Lateglacial insect sequences are described (a) from Conty, in the Selle valley and (b) from Houdancourt in the Oise valley, both in northern France. These investigations are part of a multidisciplinary investigation involving archaeology, sedimentology, geomorphology, geochronology and palaeontology (pollen, macroscopic plant remains, vertebrates, molluscs and insect fossils). The sequences of insect assemblages date from the latter part of the Bølling to the end of the Allerød periods. Environmental analysis of these faunas shows that rivers with riffles and pools meandered across flood plains. The river was extensively fringed with reedy vegetation. The only trees growing close to the river were of Salix and/or Populus. All the insect assemblages indicate that the thermal climates during the Bølling and Allerød periods were similar to one another and during both periods were very nearly as warm as that of the present day. No insect fossils were recovered from the sediments attributed to the Older Dryas interval though other evidence from these sites suggests that this event was decidedly colder than those immediately preceding and succeeding it. Comparisons are made between Lateglacial climatic patterns in northern France with those elsewhere in Europe. 相似文献
45.
Jacob Fosso Jean-Jacques Ménard Jacques-Marie Bardintzeff Pierre Wandji Félix M. Tchoua Hervé Bellon 《Comptes Rendus Geoscience》2005,337(3):315-325
Mount Bangou, an Eocene volcano (40K–40Ar ages between 44.7 and 43.1 ± 1 Ma) is the oldest dated volcano of the Cameroon Line. In this region, two magmatic series, evolving by fractional crystallization, show transitional affinities that are exceptionally known in this sector. Mineral compositions of basaltic rocks (scarce modal olivine and occurrence of normative hypersthene) as well as geochemical characteristics (low Ba, La, Ta contents and high Y/Nb ratios) are in agreement with this trend. The succession of magmas evolving in time from transitional to more typical alkaline compositions is evidenced in a continental setting. To cite this article: J. Fosso et al., C. R. Geoscience 337 (2005). 相似文献
46.
Pierre Strzerzynski Stéphane Guillot Gabriel Courrioux Patrick Ledru 《Comptes Rendus Geoscience》2005,337(14):1284-1292
The structural analysis and the 3D modelling of Stephanian granites of the Pelvoux Massif characterize an emplacement along sinistral NW–SE- and dextral NE–SW-trending shear zones in the Pelvoux and in the Aiguilles Rouges–Mont Blanc Massifs, respectively. This Carboniferous shear system is consistent with a north–south extension direction known in the whole Variscan belt at this time. To cite this article: P. Strzerzynski et al., C. R. Geoscience 337 (2005). 相似文献
47.
Martin Thullner Philippe Van Cappellen Pierre Regnier 《Geochimica et cosmochimica acta》2005,69(21):5005-5019
The present study investigates the interaction between microbial growth and activity and the redox dynamics in natural porous media. The impact the transport regime has on this interaction is also addressed. Expressions for microbial growth are incorporated into a geochemical reaction network linking redox reaction rates to the activity of the microorganisms. A flexible simulation environment, the Biogeochemical Reaction Network Simulator (BRNS) is used for this purpose. Two reactive transport applications relevant to fields of contaminant hydrology and early diagenesis are simulated with the BRNS. Model results are evaluated based on a comparison with comprehensive datasets on the biodegradation of lactate in a sand column experiment and on the distribution of redox-sensitive chemical species in marine sediments of the Skagerrak, Denmark. It is shown that, despite quite different transport regimes, the geomicrobiological model performs equally well in the reproduction of measured chemical species distribution for both applications. This result emphasizes the broad applicability of the proposed approach. Our simulations support that the competitive behavior between various microbial groups is a process controlling the development of redox stratified environments. Furthermore, it is also shown that the transport regime is a key controlling factor for the degree of spatial correlation between microbial biomass distributions and redox reaction rates. Although all our simulations yield a pronounced stratification of the redox processes in the system, the biomass distribution is related to the associated reaction rates only in case of the advection controlled column experiment. In the early diagenetic application, mixing due to bioturbation is the dominant transport process for particulate matter, hence leading to fairly homogeneous distribution of bacterial biomasses which are unrelated to the spatial distribution of redox reaction rates. This homogeneous biomass distribution combined with the 1G carbon degradation model approach might explain why the steady state concentration profiles in such systems can be reproduced by diagenetic models without explicit representation of microbial growth. 相似文献
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49.
Jan Leitner Knut Metzler Christian Vollmer Christine Floss Pierre Haenecour Jnos Kodolnyi Dennis Harries Peter Hoppe 《Meteoritics & planetary science》2020,55(6):1176-1206
We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine‐grained chondrule rims in six Mighei‐type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM‐related carbonaceous chondrite Sutter's Mill. Sixteen O‐anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix‐normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O‐rich grains are enriched in 17O, and could originate from low‐mass asymptotic giant branch stars. One grain is enriched in 17O and significantly depleted in 18O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core‐collapse supernova origin showing enhanced 18O/16O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O‐anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O‐rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe‐rich silicates, one forsterite‐like Mg‐rich silicate, two Al‐oxides with spinel‐like compositions, and one Fe‐(Mg‐)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca2Mg[Si2O7]) or a an åkermanite‐diopside (MgCaSi2O6) intergrowth. 相似文献
50.
Optical long-baseline interferometry is a unique and powerful technique for astronomical research. Since the 1980’s (with I2T, GI2T, Mark I to III, SUSI, ...), optical interferometers have produced an increasing number of scientific papers covering various fields of astrophysics. As current interferometric facilities are reaching their maturity, we take the opportunity in this paper to summarize the conclusions of a few key meetings, workshops, and conferences dedicated to interferometry. We present the most persistent recommendations related to science cases and discuss some key technological developments required to address them. In the era of extremely large telescopes, optical long-baseline interferometers will remain crucial to probe the smallest spatial scales and make breakthrough discoveries. 相似文献