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941.
Philippe Kister Michel Cuney Viacheslav N. Golubev Jean-Jacques Royer Christian Le Carlier De Veslud Jean-Claude Rippert 《Comptes Rendus Geoscience》2004,336(3):205-215
The average Pb/U ratio of the Shea Creek unconformity-type uranium deposit has been estimated at 0.071±0.015. The calculation was performed on a volume enclosing the orebody to take into account the possible radiogenic lead migration within the ore zone. Despite this precaution, this ratio is significantly lower than the expected ratio (0.211) assuming a main U deposition around 1315 Ma, as suggested by previous UPb isotopic dating. Although part of the radiogenic lead can be trapped as galena within the orebody, about 60% of Pb have migrated more than 700 m away from the orebody, preferentially along the unconformity. To cite this article: P. Kister et al., C. R. Geoscience 336 (2004). 相似文献
942.
Nathalie Volland-Tuduri Michel Brossard Ary Bruand Henri Garreau 《Comptes Rendus Geoscience》2004,336(11):1017-1024
Subrounded microaggregates 100 to 500 μm in diameter were collected in a Ferralsol located in the state of Goiàs. Observation of these microaggregates in dry conditions in scanning electron microscopy showed morphological characteristics that are representative of microaggregates described earlier in many Ferralsols. The shrinkage for drying of initially water saturated microaggregates was studied using an environmental scanning electron microscope. Results showed very small shrinkage for the microaggregates usually studied. However, the shrinkage varies since the volume of dried microaggregates was found to be 93 to 99% of their volume when they are saturated. To cite this article: N. Volland-Tuduri et al., C. R. Geoscience 336 (2004). 相似文献
943.
Marie-Dominique Loÿe-Pilot Michel Durand-Delga Hugues Feinberg Yves Gourinard Jean Magné 《Comptes Rendus Geoscience》2004,336(10):919-930
The earliest marine sediments of eastern Corsica, linked to the birth of the Corsica Basin, are represented by granitic breccia of the Saint-Antoine Formation and pelagic marls of the Alzelle Formation. They are dated as Mid-Burdigalian by nannoplankton and planktonic foraminifera (relative age and grade datings between 18.7 and 18.3 Ma). The Aghione Formation (Latest Burdigalian–Langhian) lies upon the Alzelle Formation. A component of the major East-Corsican faults, the Saint-Antoine Fault, underwent extensional activity during the Burdigalian and until the Late Miocene, when occurred the uplift of the Castagniccia antiform. To cite this article: M.-D. Loÿe-Pilot et al., C. R. Geoscience 336 (2004). 相似文献
944.
The Diagorou-Darbani Birimian greenstone belt includes (i) tholeiitic metabasalts with flat to slightly depleted LREE patterns, (ii) amphibolites having high contents in both compatible and incompatible elements with strongly fractionated spidergrams showing large HFSE negative anomalies, and (iii) metabasalts and amphibolites with intermediate features between the two previous groups. The chemical compositions of these rocks are not those of oceanic plateau basalts, but suggest a magmatic evolution from an arc environment to a back-arc oceanic basin. Source of the highly enriched amphibolites could be a depleted mantle metasomatized by slab-derived siliceous melts. To cite this article: A. Soumaila et al., C. R. Geoscience 336 (2004). 相似文献
945.
Anne Prieur Jean-François Bonnet Michel Combarnous 《Comptes Rendus Geoscience》2004,336(15):1323-1335
The role of forest ecosystems in the regulation of greenhouse effect at the global scale is developed here, from two points of view, sometimes considered as opposed: carbon storage and wood production for energy. A nomenclature is proposed to understand all the various mechanisms implied in carbon storage. A comparison is made between the effects on carbon emissions of storage alone and storage with wood fuel production. Use of wood energy is proved to be a ‘bonus’ that could optimise, in the middle and long terms, the use of fossil fuel reserves. To cite this article: A. Prieur et al., C. R. Geoscience 336 (2004). 相似文献
946.
Rainer Dähn André M ScheideggerAlain Manceau Michel L Schlegel Bart BaeyensMichael H Bradbury Magali Morales 《Geochimica et cosmochimica acta》2002,66(13):2335-2347
Wet chemistry kinetics and powder and polarized extended X-ray absorption fine structure (EXAFS and P-EXAFS) spectroscopy were combined to investigate the mechanism of Ni uptake on montmorillonite, at pH 8, high ionic strength (0.2 M Ca(NO3)2), initial Ni concentration of 660 μM, and solid concentration of 5.3 g/L. Approximately 20% of Ni sorbed within the first 24 h; thereafter, the Ni uptake rate slowed, and 12% of the initial Ni concentration remained in solution after 206 d of reaction time. Powder EXAFS spectra collected on wet pastes at 1, 14, 90, and 206 d showed the presence of Ni-Ni pairs at ∼3.08 Å in an amount that gradually increased with time. Results were interpreted by the nucleation of a Ni phase having either an α-Ni-hydroxide- or a Ni-phyllosilicate-like local structure. The latter possibility was confirmed by recording P-EXAFS spectra of a highly textured, self-supporting montmorillonite film prepared in the same conditions as the wet samples and equilibrated for 14 d. The orientation distribution of the c*-axes of individual clay particles off the film plane, as measured by quantitative texture analysis, was 32.8° full width at half maximum, and this value was used to correct from texture effect the effective numbers of Ni and Si nearest neighbors determined by P-EXAFS. Ni atoms were found to be surrounded by 2.6 ± 0.5 Ni atoms at 3.08 Å in the in-plane direction and by 4.2 ± 0.5 Si atoms at 3.26 Å in the out-of-plane direction. These structural parameters, but also the orientation and angular dependence of the Ni and Si shells, strongly support the formation of a Ni phyllosilicate having its layers parallel to the montmorillonite layers. The neoformation of a phyllosilicate on metal uptake on montmorillonite, documented herein for the first time, has important geochemical implications because this dioctahedral smectite is overwhelmingly present in the environment. The resulting sequestration of sorbed trace metals in sparingly soluble phyllosilicate structure may durably decrease their migration and bioavailability at the Earth’s surface and near surface. 相似文献
947.
Michel L. Schlegel Kathryn L. Nagy Paul FenterNeil C. Sturchio 《Geochimica et cosmochimica acta》2002,66(17):3037-3054
The structures of prismatic (100) and pyramidal (101) growth faces of natural quartz crystals, and their modification upon annealing at T ≤ 400°C were investigated ex situ by atomic force microscopy (AFM) and in water by high-resolution X-ray reflectivity. AFM images revealed the presence of ∼ 0.1 to 1 μm-wide flat terraces delimited by steps of one to several unit cells in height. These steps follow approximately directions given by the intersection of growth faces. Modeling of X-ray reflectivity data indicates that surface silica groups on flat terraces have only one free Si-O bond each (presumably hydroxylated), except for some having two free Si-O bonds observed on a single (100) surface. Vertical relaxation of atomic positions (< 0.4 Å for terminal oxygens and < 0.2 Å for silicon and oxygen atoms fully coordinated to structural tetrahedra) is limited to a depth of 14 Å. Electron density profiles for all measured interfaces are consistent with a single layer of adsorbed water, with no evidence for additional organization of water molecules into distinct layers extending into the bulk solution. Similar interfacial structures were observed for natural and annealed surfaces of identical crystallographic orientation, indicating that extensive reconstruction of the silica network at the quartz surface did not occur under the annealing conditions. 相似文献
948.
949.
Laurent André Michel Franceschi Pierre Pouchan Olivier Atteia 《Comptes Rendus Geoscience》2002,334(10):749-756
New data on isotopic composition of sulphur and oxygen in dissolved sulphates are used to determine the origin of sulphate ions (SO42?) in the water of the Infra-Molassic Sands Eocene aquifer. Two very distinct origins appear: one is the gypsum dissolution, from the molasse, and the second is the pyrite oxidation, present at the bottom of and within the aquifer. These isotopic analyses helped, in agreement with hydrogeology, to identify geochemical basins whose properties modify the chemical water composition. They also highlight the existence of bioreduction areas. To cite this article: L. André et al., C. R. Geoscience 334 (2002) 749–756. 相似文献
950.
Michel Magny André Marguet Gilles Hervé Chassepot Yves Billaud 《Journal of Paleolimnology》2001,25(2):215-227
Early and late Holocene water-level changes in Lake Annecy, France, were reconstructed from a sediment sequence from Annecy. Two early Holocene successive rises in lake level at ca. 8900-8700 BP are recorded. Another increase in lake level, beginning at ca. 780 BP, is documented. The higher lake-level conditions in Lake Annecy during the 9th millennium BP, i.e. between the Preboreal oscillation and the 8200 yr event, appear to coincide with a more widespread cooling period which has been recorded in western Europe, in the Greenland ice-sheet and the North Atlantic ocean. The rise in lake level at ca. 780 BP can be related to the early Little Ice Age. 相似文献