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1.
Boualem Bayou Mohamed El-Messaoud Derder Bernard Henry Hamou Djellit Mohamed Amenna 《Comptes Rendus Geoscience》2002,334(2):81-87
Palaeomagnetic study, carried out in the Moscovian (~305 Ma) formation in the Edjeleh anticline, shows the existence of three magnetisation components. Two of them are probably Cenozoic and Permian remagnetisations. The third component determined by both well defined ChRMs and remagnetisation circles analysis passes the fold test. Because the folding started before or during the Stephano-Autunian, this third component is the primary magnetisation. Its palaeomagnetic pole (28.3°S, 58.9°E), close to other poles from the Saharan platform obtained from neighbouring periods but without palaeomagnetic tests, confirms the age of these last data. To cite this article: B. Bayou et al., C. R. Geoscience 334 (2002) 81–87. 相似文献
2.
In the Gran Paradiso massif (western Alps), the boundary between the Erfaulet orthogneiss and the overlying metasediments (Money Complex) is interpreted as a Late Palaeozoic intrusive contact. Major arguments in favour of this hypothesis are: (i) the obliquity of the sedimentary layering with respect to the contact; (ii) the presence of aplitic dykes within the Money Complex; (iii) the lack of a mylonitic zone; and (iv) rare relics of an early generation of garnet in the Money metasediments, interpreted as evidence of the contact metamorphism of the Erfaulet granite. To cite this article: B. Le Bayon, M. Ballèvre, C. R. Geoscience 336 (2004). 相似文献
3.
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
4.
IPCC reports provide a synthesis of the state of the science in order to inform the international policy process. This task is made difficult by the presence of deep uncertainty in the climate problem that results from long time scales and complexity. This paper focuses on how deep uncertainty can be effectively communicated. We argue that existing schemes do an inadequate job of communicating deep uncertainty and propose a simple approach that distinguishes between various levels of subjective understanding in a systematic manner. We illustrate our approach with two examples. To cite this article: M. Kandlikar et al., C. R. Geoscience 337 (2005). 相似文献
5.
Michel Magny Matthieu Honegger et Laurent Chalumeau 《Eclogae Geologicae Helvetiae》2005,98(2):249-259
Resume. Les fouilles archéologiques réalisées de 1998 à 2002 sur le site néolithique de Marin-Les Piécettes sur la rive nord-ouest
du lac de Neuchatel ont offert l’opportunité d’observer deux séquences sédimentaires intéressantes pour la reconstitution
des variations holocènes du niveau du lac, en particulier au cours de la période correspondant au changement de cours de l’Aar
en direction du nord-est, vers 5650–5500 cal BP. La géométrie des corps sédimentaires et les changements lithologiques permettent
de reconna?tre plusieurs phases majeures de bas niveaux relatifs du plan d’eau vers 6870, 5660, 5060–3990, 3580, 2280, 1640
et 1170 cal BP. Le site néolithique de Marin-Les Piécettes s’est développé vers 5454–5433 cal BP à la faveur d’un court épisode
de bas niveau du lac qui a interrompu une importante phase de haut niveau au début du Subboréal. Les événements paléohydrologiques
identifiés à Marin-Les Piécettes apparaissent cohérents avec ceux reconstitués sur le site de Montilier au bord du lac de
Morat, ainsi qu’avec les variations paléohydrologiques reconstituées à partir des lacs du Jura, du Plateau suisse et des Préalpes
du Nord fran?aises. Ceci suggère qu’ils témoignent d’un signal climatique. La séquence sédimentaire de Marin-Les Piécettes
met enfin en évidence la formation d’un cordon littoral sur la rive nord-ouest du lac juste après 5660 cal BP.
Manuscrit re?u le 22 septembre 2004 Révision acceptée le 11 mars 2005 相似文献
6.
Delphine Yeghicheyan Cécile Bossy Martine Bouhnik Le Coz Chantal Douchet Guy Granier Alexie Heimburger Francois Lacan Aurélie Lanzanova Tristan C. C. Rousseau Jean‐Luc Seidel Mickaël Tharaud Frédéric Candaudap Jérôme Chmeleff Christophe Cloquet Sophie Delpoux Marie Labatut Rémi Losno Catherine Pradoux Yann Sivry Jeroen E. Sonke 《Geostandards and Geoanalytical Research》2013,37(4):449-467
The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given. 相似文献
7.
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
8.
Wafa Abouchami Stephen J. G. Galer Tristan J. Horner Mark Rehkämper Frank Wombacher Zichen Xue Myriam Lambelet Melanie Gault‐Ringold Claudine H. Stirling Maria Schönbächler Alyssa E. Shiel Dominique Weis Philip F. Holdship 《Geostandards and Geoanalytical Research》2013,37(1):5-17
Research into natural mass‐dependent stable isotope fractionation of cadmium has rapidly expanded in the past few years. Methodologies are diverse with MC‐ICP‐MS favoured by all but one laboratory, which uses thermal ionisation mass spectrometry (TIMS). To quantify the isotope fractionation and correct for instrumental mass bias, double‐spike techniques, sample‐calibrator bracketing or element doping has been used. However, easy comparison between data sets has been hampered by the multitude of in‐house Cd solutions used as zero‐delta reference in different laboratories. The lack of a suitable isotopic reference material for Cd is detrimental for progress in the long term. We have conducted a comprehensive round‐robin assay of NIST SRM 3108 and the Cd isotope offsets to commonly used in‐house reference materials. Here, we advocate NIST SRM 3108 both as an isotope standard and the isotopic reference point for Cd and encourage its use as ‘zero‐delta’ in future studies. The purity of NIST SRM 3108 was evaluated regarding isobaric and polyatomic molecular interferences, and the levels of Zn, Pd and Sn found were not significant. The isotope ratio 114Cd/110Cd for NIST SRM 3108 lies within ~ 10 ppm Da?1 of best estimates for the Bulk Silicate Earth and is validated for all measurement technologies currently in use. 相似文献
9.
The planet Mars lacks, today, a planetary, dynamic magnetic field, but strong, intense, localized magnetic fields of lithospheric origin, one to two orders of magnitude larger than the terrestrial lithospheric field, are present. This lithospheric magnetic field is the result of magnetization processes in the presence of a magnetic dynamo and of demagnetization processes after the dynamo shutdown, such as impact or volcanoes. This crude scenario can be more accurately specified by interpreting global and local models of the current magnetic field of Mars. Some specific areas are studied, including the intensely magnetized Terra Sirenum, as well as the magnetic anomaly associated with Apollinaris Patera. Magnetic minerals could be of primary and/or secondary origin; this latter would imply an early hydration of a basaltic crust. A scenario, in which Mars experienced a major polar wander due to the Tharsis bulge, prior to the cessation of its dynamo, is proposed and discussed. 相似文献
10.
Rivers, chemical weathering and Earth's climate 总被引:4,自引:0,他引:4
Bernard Dupr Cline Dessert Priscia Oliva Yves Goddris Jrme Viers Louis Franois Romain Millot Jrme Gaillardet 《Comptes Rendus Geoscience》2003,335(16):1141-1160
We detail the results of recent studies describing and quantifying the large-scale chemical weathering of the main types of continental silicate rocks: granites and basalts. These studies aim at establishing chemical weathering laws for these two lithologies, describing the dependence of chemical weathering on environmental parameters, such as climate and mechanical erosion. As shown within this contribution, such mathematical laws are of primary importance for numerical models calculating the evolution of the partial pressure of atmospheric CO2 and the Earth climate at geological timescales. The major results can be summarized as follow: (1) weathering of continental basaltic lithologies accounts for about 30% of the total consumption of atmospheric CO2 through weathering of continental silicate rocks. This is related to their high weatherability (about eight times greater than the granite weatherability); (2) a simple weathering law has been established for basaltic lithologies, giving the consumption of atmospheric CO2 as a function of regional continental runoff, and mean annual regional temperature; (3) no such simple weathering law can be proposed for granitic lithologies, since the effect of temperature can only be identified for regions displaying high continental runoff; (4) a general law relating mechanical erosion and chemical weathering has been validated on small and large catchments. The consequences of these major advances on the climatic evolution of the Earth are discussed. Particularly, the impacts of the onset of the Deccan trapps and the Himalayan orogeny on the global carbon cycle are reinvestigated. To cite this article: B. Dupré et al., C. R. Geoscience 335 (2003). 相似文献