Review     

Michel David 《Mathematical Geology》1979,11(6):721-722

  相似文献   

    

Michel David 《Mathematical Geology》1974,6(2):201-202

  相似文献   

Small Antarctic micrometeorites: A mineralogical and in situ oxygen isotope study     

Matthieu GOUNELLE  Ccile ENGRAND  Michel MAURETTE  Gero KURAT  Kevin D. McKEEGAN  Franz BRANDSTTTER 《Meteoritics & planetary science》2005,40(6):917-932

Abstract— We have investigated the texture, bulk chemistry, mineralogy, as well as the anhydrous minerals oxygen isotopic composition of 67 small Antarctic micrometeorites (AMMs) collected at Cap Prudhomme, Antarctica, and belonging to the currently poorly studied size fraction 25–50 μm. When compared to larger (50–400 μm) micrometeorites collected at the same site in Antarctica with the same techniques, no significant differences are found between the two populations. We therefore conclude that the population of Cap Prudhomme AMMs is homogeneous over the size range 25–400 μm. In contrast, small AMMs have different textures, mineralogy, and oxygen isotopic compositions than those of stratospheric interplanetary dust particles (IDPs). Because small AMMs (<50 μm) overlap in size with IDPs, the differences between these two important sources of micrometeorites can no longer be attributed to a variation of the micrometeorite composition with size. Physical biases introduced by the collection procedures might account for these differences.  相似文献   

Structural and geochemical data on the Rio Magno Unit: evidence for a new 'Apenninic' ophiolitic unit in Alpine Corsica and its geodynamic implications     

Elisa Padoa  Emilio Saccani  & Michel Durand-Delga 《地学学报》2001,13(2):135-142

The Rio Magno Unit (RMU) tectonically overlies the Schistes Lustrés units in south-eastern Alpine Corsica. It is represented by an ophiolitic sequence, showing remarkable differences with respect to the commonly recognized Corsican ophiolites. This unit can be distinguished from the Schistes Lustrés by the lack of HP–LT metamorphism, reflecting its different geodynamic setting, although both were involved early in the same tectonic events. Similarly, the RMU can be distinguished from the Balagne Unit by the presence of normal-MORB basalts and the scarcity of continent-derived sedimentary input, testifying to a different oceanic palaeogeographical setting. Moreover, the petrochemical and stratigraphic features of the RMU ophiolitic sequence show close analogies with the Internal Ligurides of the Northern Apennines. The RMU represents the first record of a nonmetamorphic 'Apenninic'-type ophiolitic unit in Alpine Corsica, supporting the hypothesis that the Alpine Corsica – Northern Apennine system represents a double-vergent accretionary wedge.  相似文献   

Geochemical influences on H40/1 bacteriophage inactivation in glaciofluvial sands     

Raymond?FlynnEmail author  Daniel?Hunkeler  Christine?Guerin  Christine?Burn  Pierre?Rossi  Michel?Aragno 《Environmental Geology》2004,45(4):504-517

Geochemical heterogeneities may cause spatial variations in virus inactivation rates resulting from interactions with minerals leading to differences in natural disinfection capacity within an aquifer. Column studies investigating the interaction of the bacteriophage H40/1 with natural sands sampled from the Kappelen test site (Kappelen), Bern, Switzerland indicated that inactivation rates are higher for adsorbed bacteriophages than for those suspended in groundwater. Moreover, breakthrough curves obtained from field-based tracer tests at Kappelen indicated that the adsorbed H40/1 is inactivated in-situ at comparable rates. Statistical analyses of mineralogical data failed to demonstrate significant spatial variations in aquifer composition either across the site or with depth. In contrast hydrochemical analyses of groundwater samples collected at Kappelen demonstrated that iron-reducing groundwater occurs below aerobic waters. Tracer breakthrough curves indicate that H40/1 survival is not affected by variable redox conditions. Investigation results suggest that spatial geochemical variability does not significantly affect H40/1s inactivation rate at Kappelen.  相似文献   

Alpine and late-hercynian geochronological constraints in the Argentera Massif (Western Alps)     

Michel Corsini  Gilles Ruffet  Renaud Caby 《Eclogae Geologicae Helvetiae》2004,97(1):3-15

  相似文献   

Shore litter along sandy beaches of the Gulf of Oman     

Claereboudt MR 《Marine pollution bulletin》2004,49(9-10):770-777

Beach debris abundance and weight were estimated from surveys on 11 beaches of the Gulf of Oman along the Omani coast. Debris were collected on two occasions from 100 m transects, sorted and categorized by origin and type. Overall contaminations ranged from 0.43 to 6.01 items m(-1) of beach front on different beaches with a mean value of 1.79+/-1.04 gm(-1) (95% C.I). In terms of weight, contamination levels ranged from 7.8 to 75.44 gm(-1) of beach front with a mean contamination of 27.02+/-14.48 gm(-1) (95% C.I). In terms of numbers of items, plastic debris ranked first on all beaches followed by either wood items or other organic materials such as cigarette butts. Industrial debris remained few on all beaches (<10%). Most debris had a local origin and, in terms of numbers, were associated with beach recreational activities whereas fishing debris represented the largest proportion of the debris in terms of weight. There were notable differences between beaches in the relative abundance of recreation-related and fishing-related debris.  相似文献   

Geostatistical mineral resources appraisal     

Michel Dagbert  Michel David 《Mathematical Geology》1977,9(3):313-317

  相似文献   

Variability of the gas transfer velocity of CO<Subscript>2</Subscript> in a macrotidal estuary (the Scheldt)   总被引：1，自引：0，他引：1  

Alberto?Vieira?BorgesEmail author  Jean-Pierre?Vanderborght  Laure-Sophie?Schiettecatte  Frédéric?Gazeau  Sarah?Ferrón-Smith  Bruno?Delille  Michel?Frankignoulle 《Estuaries and Coasts》2004,27(4):593-603

We report a large set of 295 interfacial carbon dioxide (CO₂) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From concomitant measurements of the air-water CO₂ gradient, we computed the gas transfer velocity of CO₂. The gas transfer velocity is well correlated to wind speed and a simple linear regression function gives the most consistent fit to the data. Based on water current measurements, we estimated the contribution of water current induced turbulence to the gas transfer velocity, using the conceptual relationship of O'Connor and Dobbins (1958). This allowed us to construct an empirical relationship to compute the gas transfer velocity of CO₂ that accounts for the contribution of wind and water current. Based on this relationship, the spatial and temporal variability of the gas transfer velocity in the Scheldt estuary was investigated. Water currents contribute significantly to the gas transfer velocity, but the spatial and temporal variability (from daily to seasonal scales) is mainly related to wind speed variability.  相似文献   

Dynamics of Small Earth-Approachers on Low-Eccentricity Orbits and Implications for Their Origins     

P. Michel  Ch. Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):93-112

The population of Near-Earth Asteroids (NEAs) appears to be overabundant at sizes smaller than 50m, compared to a power-law extrapolation from kilometer-sized objects. Several of these small NEAs are also concentrated on low-eccentricity orbits, where a few larger Earth-crossers are observed, and are called Small Earth-Approachers (SEAs). Their source region as well as the dynamical mechanisms involved in their transport close to the Earth on low-eccentricity orbits have not yet been determined. In this paper, we present our numerical and statistical study of the production and dynamical evolution of these SEAs. We first show that three main sources of Earth-crossers which are, according to recent simulations, the 3/1 and ₆ resonances in the main belt, and the Mars-crosser population, are not able to produce as many bodies on SEAs-like orbits compared to other Earth-crossing orbits as has been inferred from observations. From these sources, SEAs-like orbits are reached through the interplay of two required mechanisms: secular resonances and planetary close approaches. However, the time spent on these orbits remains smaller than 1 Myr as confirmed by the study of the evolutions of 11 observed SEAs which also reveal the action of various mechanisms such as close approaches to planets and/or secular resonances. Therefore, our results present some mechanisms which can be responsible for their production but none that would preserve the lifetime of the SEAs sufficiently to enhance their abundance relative to other Earth-crossing orbits at the level observed. The overabundance of the SEA population, if real, remains a problem and could be related to the influence of collisional disruption and tidal splitting of Earth-crossers, as well as to observational biases that might account for a discrepancy between theory and observation.  相似文献