Radiation-induced paramagnetic defects in natural kaolinites: Alpha dosimetry with ion beam irradiation     

Thierry Allard  Jean-Pierre Muller  Jean-Claude Dran  Marie-Thérèse Ménager 《Physics and Chemistry of Minerals》1994,21(1-2):85-96

Three types of paramagnetic radiation-induced defects (RID), namely A, A′ (Si-O^?-centers) and B (Al-O^?-Al center), had been identified in natural kaolinites by means of electron paramagnetic resonance spectroscopy. The A-center, stable at the scale of geological periods, was thought to be of particular relevance to quantify past transits of radionuclides in the geosphere. Alpha radiation being likely the main source of RID in kaolinite, the objective of this paper is to define the role of α-particles on the creation of RID and to test the use of A-centers for an α-dosimetry. Three kaolinites with different crystalline order and containing other clays as impurities were irradiated with He⁺ ion beams. The radiation dose range (0–750 MGy) was consistent with natural radioactivity in environments from the Earth's surface. Irradiation drastically enhanced the original signals due to RID. An important increase of concentration of the unstable B-center, partly due to unrealistic dose rate provided by accelerator ion beam, was observed from the lower doses. The most stable defects remained of the Atype all along experimental irradiations. The contribution of ancillary phyllosilicates to EPR spectra was negligible. The concentration of the three types of RID was related to radiation doses up to 30 MGy. Dosimetry growth curves for the A-centers exhibited variable efficiencies and saturation levels that were related to the structural order and the chemical purity of the kaolinites: the more ordered and purer the kaolinite, the higher the efficiency and the lower the saturation plateau. Moreover, these results are of geochemical significance: dosimetry based on A-centers could be directly used to quantify past migrations of radioelements in the geosphere, by determination of the naturally-cumulated doses (paleodose) of kaolinites.  相似文献   

Routes of plutonium uptake and their relation to biomagnification in starfish     

Jean-Claude Guary  Scott W Fowler  Thomas M Beasley 《Marine pollution bulletin》1982,13(3):99-102

The distribution of ^{239 + 240}Pu and ²³⁸Pu in environmental samples of starfish tissues is identical to the tissue distribution observed in experimental animals following uptake of plutonium directly from water. Plutonium in sea water has a strong affinity for the mucus-rich epidermal layer of starfish which contributes substantially to the relatively high levels of this transuranium nuclide measured in these invertebrates. Transfer of plutonium to starfish via food also occurs; however, the resultant tissue distribution is not consistent with that found in the natural environment where plutonium is available from both contaminated food and water. These data suggest that food chain biomagnification of plutonium by starfish does not occur in nature as has been previously hypothesized.  相似文献   

The recent fault scarps of the Western Alps (France): Tectonic surface ruptures or gravitational sackung scarps? A combined mapping, geomorphic, levelling, and Be dating approach     

Jean-Claude Hippolyte  Gilles Brocard  Marc Tardy  Grard Nicoud  Didier Bourls  Rgis Braucher  Gilles Mnard  Blaise Souffach 《Tectonophysics》2006,418(3-4):255-276

In the Western Alps, some recent scarps were previously interpreted as surface ruptures of tectonic reverse and normal faults that agree with microseismicity and GPS measurements. Our analysis shows that in fact there are hundreds of recent scarps, up to 30 m high and 2.1 km long, with only pure normal motions. They share the same characteristics as typical sackung scarps. The scarps are mainly uphill facing, parallel to the ridge crests and the contour lines. They are relatively short (less than 2.1 km) with respect to tectonic fault ruptures, and organized in swarms. They cut screes and relict rock glaciers with a slow (commonly 1 mm/year) average slip rate. In the Aiguilles Grives massif these sackung scarps clearly express the gravitational toppling of sub-vertical bedding planes in hard rocks. In contrast, the Belledonne Outer Crystalline Massif exhibits scarps that stem from the gravitational reactivation of conjugate tectonic faults. The recent faults extend to about 1600 m beneath the Rognier ridge crest, but are always above the valley floor. The main scarp swarm is 9.2 km long and constitutes the largest sackung ever described in the Western Alps. ¹⁰Be dating of a scarp and offset surfaces shows that > 4 m slip may have occurred rapidly (in less than 3800 years) sometimes between the end of the glaciation and 8800 ± 1900 years ago. This dating, together with the location of some faults far from the deep glacial valleys, suggests that sagging might have been triggered by strong earthquakes during a post-glacial period of probably enhanced seismicity. The Belledonne and Synclinal Median faults (just beneath the Rognier sackung) could have been the sources of this seismicity.  相似文献   

1 Determination of As,Bi, Sb,Se and Te in Fifty Five Reference Materials by Hydride Generation ICP-MS     

Gwendy E.M. Hall  Jean-Claude Pelchat 《Geostandards and Geoanalytical Research》1997,21(1):85-91

Analytical data are reported for As, Bi, Sb, Se and Te in fifty five geological reference materials (RM). The method used is based on hydride generation inductively coupled plasma-mass spectrometry (HG-ICP-MS) following digestion of the samples in the mixed acid attack of HF-HClO₄-HNO₃-HCl. Analytes were separated from potential interferences by coprecipitation with La(OH)₃. This scheme results in method detections limits of: 1 ng g^?1 for Bi and Te; 6 ng g^?1 for Sb and Se; and 10 ng g^?1 for As. The average relative standard deviation (RSD) for three 0.5 g subsamples of each RM analysed by this method are: 3.7% for As in the range 0.35-187 μg g^?1; 5.6% for Sb in the range 0.03-22 μg g^?1; 6.8% for Bi in the range 0.002-48 μg g^?1; 7.2% for Se in the range 6-3610 ng g^?1; and 9.0% for Te in the range 2-445 ng g^?1.  相似文献   

Stress, failure and fluid flow deduced from earthquakes accompanying eruptions at Piton de la Fournaise volcano     

Martine Sapin  Alfred Hirn  Jean-Claude Lpine  Alexandre Nercessian 《Journal of Volcanology and Geothermal Research》1996,70(3-4)

In the present episode of eruptive activity, evidence from seismicity for sustained magma inflow from depth into the edifice of Piton de la Fournaise is lacking. Pre-eruptive main deformation and shallow seismicity help to identify very small volumes of magma that are in motion beneath the rim of the Dolomieu summit crater, and oriented along the azimuth of the future vents. Small magma pockets may reside in the cone above sea level, or may be expelled repeatedly, due to crystallisation in a small, low-velocity, aseismic region below sea level under the high-velocity central plug of the cone in which pre-eruptive earthquake swarms are located. In cross-section the hypocentres define two steep sheets diverging from the aseismic zone at sea level towards 1.5 km above sea level (or 1 km beneath the 2632 m high cone). However, failure induced by increased pressure in the suggested chamber does not account for the observed focal mechanisms.The occurrence and timing of magma transport are attested by eruption, and seismic activity may be related to magma transport. Focal mechanisms document strike-slip, not normal faulting or tensile failure. Vertical propagation of the edge of a feeder dike may enhance strike-slip motion above the edge, in a region where effective normal stress is decreased by thermally induced groundwater flow. The strike-slip mechanisms could also be caused by a tensile-shear widening of the horizontal section of vertical conduits.Fournaise strike-slip earthquakes occur in two orientations, with P axes orthogonal between them, within a single pre-eruptive event. Earthquakes are distributed in the same volume but mechanisms switch from one to another type systematically with time, indicating a reversal of stress conditions. The orientations of P axes with respect to the epicentral trend suggest that in the later parts of events leading to eruptions, a compression of the medium occurs after a dilation in the first part. The activated zone might respond successively to the arrival and the departure of the magma on its way from the reservoir at depth to the vent, radial to the cone.  相似文献   

The last interglacial ocean     

William F. Ruddiman  Rose Marie L. Cline  James D. Hays  Warren L. Prell  William F. Ruddiman  Ted C. Moore  Nilva G. Kipp  Barbara E. Molfino  George H. Denton  Terence J. Hughes  William L. Balsam  Charlotte A. Brunner  Jean-Claude Duplessy  James L. Fastook  John Imbrie  Lloyd D. Keigwin  Thomas B. Kellogg  Peter R. Thompson 《Quaternary Research》1984,21(2):123-224

The final effort of the CLIMAP project was a study of the last interglaciation, a time of minimum ice volume some 122,000 yr ago coincident with the Substage 5e oxygen isotopic minimum. Based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean, last interglacial sea-surface temperatures (SST) were compared with those today. There are small SST departures in the mid-latitude North Atlantic (warmer) and the Gulf of Mexico (cooler). The eastern boundary currents of the South Atlantic and Pacific oceans are marked by large SST anomalies in individual cores, but their interpretations are precluded by no-analog problems and by discordancies among estimates from different biotic groups. In general, the last interglacial ocean was not significantly different from the modern ocean. The relative sequencing of ice decay versus oceanic warming on the Stage 6/5 oxygen isotopic transition and of ice growth versus oceanic cooling on the Stage 5e/5d transition was also studied. In most of the Southern Hemisphere, the oceanic response marked by the biotic census counts preceded (led) the global ice-volume response marked by the oxygen-isotope signal by several thousand years. The reverse pattern is evident in the North Atlantic Ocean and the Gulf of Mexico, where the oceanic response lagged that of global ice volume by several thousand years. As a result, the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years. These regional lead-lag relationships agree with those observed on other transitions and in long-term phase relationships; they cannot be explained simply as artifacts of bioturbational translations of the original signals.  相似文献   

Dual-porosity elastoplastic analyses of non-isothermal one-dimensional consolidation   总被引：1，自引：0，他引：1  

Jincai Zhang  Jean-Claude Roegiers  Mao Bai 《Geotechnical and Geological Engineering》2004,22(4):589-610

A numerical solution, using the finite difference method, and based on a porothermo-elasto-plastic formulation for dual-porosity one-dimensional consolidation has been presented. The model is fully coupled to ensure the interactive behavior of fluid flow, heat flow and solid deformations in the conservation of momentum, mass and energy equations. A bi-linear stress-strain relationship is used to accommodate elastoplastic deformation behavior. A double effective stress law, proposed by Elsworth and Bai (1992), is applied to describe constitutive relationships among the stresses, pressures and temperatures. In order to examine the dual-porosity and thermal effects on the soil consolidation individually, isothermal and non-isothermal consolidations for a dual-porosity column are analyzed. In comparison to the single porosity approach, the present study shows that the pore pressure dissipation is faster and Mandel's effect (Mandel, 1953) is more pronounced at early times of the source disturbance for dual-porosity consolidation. One of the significant parameters affecting the dual-porosity consolidation is the fracture spacing (fracture density); the smaller the fracture spacing, the faster the column drainage.  相似文献   

Importance du choix des échelles de temps pertinentes pour l'étude du fonctionnement d'écosystèmes marins littoraux     

Nathaniel Bensoussan  Jean-Claude Romano  Bouazza El-Haikali  Michel-Guy Lafont 《Comptes Rendus Geoscience》2004,336(10):909-918

Semi-continuous (1/30 min) records of physicochemical parameters (T,S, DO and pH) have been measured at 1.50 m in Mediterranean coastal waters (Marseilles) from 1998 to 2000, together with meteorological parameters. Physicochemical data were studied in order to synthesise the information at different time scales (inter-annual, season, day, hour), particularly the semi-conservative DO and pH response to hydroclimatic variables. At a daily time scale, important circadian dynamic has been measured under all circumstances with a strong reactivity to irradiance change under the influence of biological activity. This work may contribute to the definition of new tools for coastal waters observation. To cite this article: N. Bensoussan et al., C. R. Geoscience 336 (2004).  相似文献   

Ground temperature changes in eastern Canada: borehole temperature evidence compared with proxy data     

Hugo Beltrami  Jean-Claude Mareschal 《地学学报》1993,5(1):21-28

Borehole temperature logs have been inverted to infer ground temperature histories (GTH) in eastern and central Canada. Regional ground temperature histories were obtained by simultaneous inversion of several temperature profiles from the same areas. Simultaneous inversion of 21 temperature logs sampled across all of eastern and central Canada yielded an average solution for this region. All but three of the studied sites show signs of warming in the last 150 years. This period of warming, which started after 1800 AD, was found throughout this part of Canada. The warming followed a cooler period corresponding to the little Ice Age. The inferred ground temperature histories exhibit long-term trends similar to those obtained from treering growth indices in nearby regions and stable isotope data in the southern hemisphere. The modern warming appears correlated with the atmospheric concentration of CO₂ as measured in ice cores.  相似文献   

Benthic indicators and index approaches in the three main estuaries along the French Atlantic coast (Seine, Loire and Gironde)     

Jean-Claude Dauvin  Guy Bachelet  Anne-Laure Barillé  Hugues Blanchet  Xavier de Montaudouin  Nicolas Lavesque  & Thierry Ruellet 《Marine Ecology》2009,30(2):228-240

The three main estuaries in the French Atlantic coast – the Seine, Loire and Gironde, all with high tidal regimes – are interfaces between the continental and the coastal ecosystems. The Seine and Gironde are highly contaminated, whereas the Loire remains in a more natural state. Both the Seine and Gironde have suffered from harbour construction, and as a result, their biological units are extremely compartmentalized. Benthic species and communities have adapted to tolerate temporal physical and chemical changes ( e.g. salinity, substrata, depth, and levels of fine particles and oxygen) and human activities ( e.g. dredging, shipping traffic, and habitat reduction). Although numerous bio-indicators and indices are used to define the ecological quality status (EcoQS) of coastal waters, very few of them were developed specifically for environments with a mosaic of conditions and salinity levels, including freshwater. The main problem appears to be that all the indices for determining anthropogenic stress examine the abundances of stress-tolerant species, which may also be able to tolerate natural stressors such as those occurring in estuaries. This paper takes a look at the development status of the benthic indicators and index approaches used in the three main estuaries along the French Atlantic coast. In addition, it examines the adaptation of the different benthic indicators to the taxonomic sufficiency principle, and the adaptation of the Benthic Opportunistic Polychaetes Amphipods index (BOPA) and the Benthic Opportunistic Annelida Amphipod index (BO2A) for use in the freshwater zones of transitional waters ( i.e. up to the upper limit of the tidal range). Several perspectives are discussed in light of the diverse disturbances and the heterogeneity of such stressed zones, such as the use of multimetric and scoring approaches.  相似文献