OMEGA long wavelength channel: Data reduction during non-nominal stages     

Denis Jouglet  François Poulet  Yves Langevin  Jean-Pierre Bibring  Brigitte Gondet  Mathieu Vincendon  Michel Berthe 《Planetary and Space Science》2009,57(8-9):1032-1042

The Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) instrument is a visible and near-infrared imaging spectrometer on board the European Mars Express (MEx) mission. The on-board calibration (OBC) performed at the beginning of observations on each orbit reveals that the photometric response of the C channel (1.0–2.5 μm) has been very stable since orbit insertion in January 2004. On the contrary the L channel (2.5–5.1 μm) response has varied significantly during the mission, and only orbits for which the response is close to nominal could be used with confidence. The spatial coverage of ice-free surfaces in this wavelength range is consequently limited to only ～30%, mainly during northern spring and summer. This paper presents the empirical method used to derive new instrumental transfer functions (ITF) for the non-nominal orbits. This method consists of analyzing the variation of the signal between several observations of a same region acquired at nominal and non-nominal calibration states. In the cases where the mineralogy and the atmospheric conditions between the two observations are the same, the variation in reflectance spectra is only due to the ITF variation, which provides a new ITF. We then associate these new ITFs with their corresponding OBCs to model a relationship between both. The resulting model enables us to provide a new ITF for each orbit for which the OBC is available. The new ITFs derived for the entire dataset have been validated (1) through a comparison of the C and L channel global albedo trends and (2) through a comparison of the surface temperatures derived from the L channel with those calculated from the General Circulation Model (GCM) numerical simulation of the LMD released in the Martian Climate Database. The non-nominal data processed with adapted ITFs for orbits up to 3050 increase the non-icy surface coverage of Mars to ～70% including all seasons.  相似文献   

Intense fracturing and fracture sealing induced by mineral growth in porous rocks     

Catherine Noiriel  François Renard  Mai-Linh Doan  Jean-Pierre Gratier 《Chemical Geology》2010,269(3-4):197-209

Mineral precipitation in the pores of a rock may exert a force, which is called crystallization pressure. This process has been studied experimentally and results bring a new look on the way fractures may develop and seal in natural systems. Cylindrical core samples of porous limestone and sandstone were left for several weeks in contact with an aqueous solution saturated with sodium chloride, at 30 or 45 °C, under axial normal stress in the range 0.02–0.26 MPa. The fluid was allowed to rise in the core samples by capillary forces, up to a controlled height where evaporation and precipitation occurred. The uniaxial deformation of the samples was measured using high-resolution displacement sensors. The samples were characterized using computed X-ray tomography, allowing therefore imaging in 3D the intensity and localization of the damage. Two kinds of damage could be observed. Firstly, small rock fragments were peeled from the sample surface. Secondly, and more interestingly, fracture networks developed, by nucleation of microcracks at the interface where evaporation occurred, and propagation to the free surface. Two families of fractures could be identified. A first set of sealed fracture parallel to the evaporation front is directly induced by crystallization pressure. A second fracture network, perpendicular to the evaporation front, accommodates the first set of fractures. An analytical model where fluid flow is coupled to evaporation, vapour transport, and localization of mineral precipitation explains the shape of this fracture network.  相似文献   

Troposphere-to-stratosphere transport in the tropics     

Jean-Pierre Pommereau 《Comptes Rendus Geoscience》2010,342(4-5):331-338

The analysis of the data collected over Brazil, Northern Australia and Africa from balloons, high altitude aircraft and satellites during the recent HIBISCUS, TROCCINOX, SCOUT-O3 and AMMA European campaigns, has led to significant revision in the understanding of troposphere-to-stratosphere transport. Repeated observations of strong updrafts of adiabatically cooled and washed-out tropospheric air rich in chemical and greenhouse gases by convective overshooting over the three continents, demonstrate the high frequency of occurrence of such events in contrast to their generally assumed scarcity. Moreover, global scale information provided by ODIN and CALIPSO satellite observations suggests that the mechanism could play a major, if not dominant, role in troposphere-to-stratosphere transport in contrast to the generally evoked slow ascent by radiative heating. Ignored by global scale models because of their limited extension and duration, convective overshootings might have a significant impact on the chemistry and climate of the stratosphere.  相似文献   

Multi-criteria spatialization of soil organic carbon sequestration potential from agricultural intensification in Senegal     

Valentin Bellassen  Raphaël J. Manlay  Jean-Pierre Chéry  Vincent Gitz  Assize Touré  Martial Bernoux  Jean-Luc Chotte 《Climatic change》2010,98(1-2):213-243

On the eve of the 15th climate negotiations conference in Copenhagen, the pressure to assess all climate mitigation options is mounting. In this study, a bio-physic model and a socio-economic model were designed and coupled to assess the carbon sequestration potential of agricultural intensification in Senegal. The biophysical model is a multiple linear regression, calibrated and tested on a dataset of long-term agricultural trials established in West Africa. The socio-economic model integrates both financial and environmental costs related to considered practice changes. Both models are spatially explicit and the resulting spatial patterns were computed and displayed over Senegal with a geographic information system. The national potential from large-scale intensification was assessed at 0.65–0.83 MtC. With regards to local-scaled intensification as local projects, the most profitable areas were identified in agricultural expansion regions (especially Casamance), while the areas that meet the current financial additionality criteria of the Clean Development Mechanism were located in the northern part of the Peanut Basin. Using the current relevant mode of carbon valuation (Certified Emission Reductions), environmental benefits are small compared to financial benefits. This picture is radically changed if “avoided deforestation”, a likely consequence of agricultural intensification, is accounted for as the greenhouse gases sink capacity of projects increases by an average of a hundred-fold over Senegal.  相似文献   

Physical modelling of gelifluction and frost creep: Some results of a large-scale laboratory experiment   总被引：1，自引：0，他引：1  

Charles Harris  Michael Gallop  Jean-Pierre Coutard 《地球表面变化过程与地形》1993,18(5):383-398

An experimental slope was constructed in a 5 m × 5 m square refrigerated tank. The slope was formed of four sections, each consisting of regolith (soil) collected from a distinct bedrock lithology. The four lithologies utilized were granite, limestone, mudstone and slate. The slope was subjected to freezing and thawing from the surface downwards. Water was supplied at the base of the soil during freezing. Frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles, and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle. The experimental soils were non-cohesive; those derived from granite and limestone were respectively sandy and gravelly in texture, while those derived from mudstone and slate were silt-rich. Mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice. In the mudstone and slate soils, gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice. Mean per cycle rates of downslope soil transport for the granite, limestone, mudstone and slate soils were 5·8 cm³ cm^?1, 6·9 cm³ cm^?1, 21·2 cm³ cm^?1 and 31·2 cm³ cm^?1 respectively, units referring to the volume of soil passing a unit width of slope per cycle. Mass movement rates were shown to be strongly related to the silt content of the soils.  相似文献   

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   

Paleomagnetic record of two successive Miocene geomagnetic reversals in western Crete     

Jean-Pierre Valet  Carlo Laj 《Earth and Planetary Science Letters》1981,54(1):53-63

Two geomagnetic reversals(R→N followed by N→R) have been recorded in a sequence of Miocene marine clays of Tortonian-Messinian age in western Crete (Greece). The time span of each transition is found to be of the order of 5000–10,000 years. The transitional VGP paths are largely constrained in longitude either near the site longitude(R→N) or opposite to it(N→R). A normalized magnetization intensity record has also been obtained and its variations during reversals are found to be in excellent agreement with the predictions of Hoffman's phenomenological model.  相似文献   

Rosia Poieni copper deposit,Apuseni Mountains,Romania: advanced argillic overprint of a porphyry system   总被引：2，自引：0，他引：2  

Viorica?Milu  Jean-Pierre?Milesi  Jacques?Léon?LeroyEmail author 《Mineralium Deposita》2004,39(2):173-188

The Rosia Poieni deposit is the largest porphyry copper deposit in the Apuseni Mountains, Romania. Hydrothermal alteration and mineralization are related to the Middle Miocene emplacement of a subvolcanic body, the Fundoaia microdiorite. Zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions. Four alteration types have been distinguished: potassic, phyllic, advanced argillic, and propylitic. Potassic alteration affects mainly the Fundoaia subvolcanic body. The andesitic host rocks are altered only in the immediate contact zone with the Fundoaia intrusion. Mg-biotite and K-feldspar are the main alteration minerals of the potassic assemblage, accompanied by ubiquitous quartz; chlorite, and anhydrite are also present. Magnetite, pyrite, chalcopyrite and minor bornite, are associated with this alteration. Phyllic alteration has overprinted the margin of the potassic zone, and formed peripheral to it. It is characterized by the replacement of almost all early minerals by abundant quartz, phengite, illite, variable amounts of illite-smectite mixed-layer minerals, minor smectite, and kaolinite. Pyrite is abundant and represents the main sulfide in this alteration zone. Advanced argillic alteration affects the upper part of the volcanic structure. The mineral assemblage comprises alunite, kaolinite, dickite, pyrophyllite, diaspore, aluminium-phosphate-sulphate minerals (woodhouseite-svanbergite series), zunyite, minamyite, pyrite, and enargite (luzonite). Alunite forms well-developed crystals. Veins with enargite (luzonite) and pyrite in a gangue of quartz, pyrophyllite and diaspore, are present within and around the subvolcanic intrusion. This alteration type is partially controlled by fractures. A zonal distribution of alteration minerals is observed from the centre of fractures outwards with: (1) vuggy quartz; (2) quartz + alunite; (3) quartz + kaolinite ± alunite and, in the deeper part of the argillic zone, quartz + pyrophyllite + diaspore; (4) illite + illite-smectite mixed-layer minerals ± kaolinite ± alunite, and e) chlorite + albite + epidote. Propylitic alteration is present distal to all other alteration types and consists of chlorite, epidote, albite, and carbonates. Mineral parageneses, mineral stability fields, and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system. The alteration minerals reflect cooling of the hydrothermal system from >400 °C (biotite), to 300–200 °C (chlorite and illite in veinlets) and to lower temperatures of kaolinite, illite-smectite mixed layers, and smectite crystallization. Hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone. It was followed by phyllic overprint of the early-altered rocks. Nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones. The close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic-hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface.Editorial handling: B. Lehmann  相似文献   

Correlations and sequence stratigraphic model for Messinian carbonate platforms of the western and central Mediterranean   总被引：1，自引：0，他引：1  

Jean-Jacques?CornéeEmail author  Jean-Paul?Saint Martin  Gilles?Conesa  Philippe?Münch  Jean-Pierre?André  Simona?Saint Martin  Stefan?Roger 《International Journal of Earth Sciences》2004,93(4):621-633

Distance correlations of Late Tortonian–Messinian littoral carbonate complexes are proposed from the study of eight platforms in the western and central Mediterranean. Correlations are based on the identification of two major biological sedimentary cycles and of two index surfaces. Surface A is a maximum flooding surface during cycle 1 at around 6.7 Ma. Surface B is a regional marine planation surface at around 5.95 Ma, at the base of cycle 2 (Terminal Carbonate Complex). A general sedimentary model is proposed for the 7–5.6-Ma time-span. The boundary between cycles 1 and 2 is coincident with the onset of the Messinian Salinity Crisis, and appears to be related to major environmental–paleo-oceanographic changes in the Mediterranean, rather than to a major sea-level drop or to climatic change.  相似文献   

Un réseau fluviatile d'âge Burdigalien terminal dans le Sud-Est de la France : remplissage,extension, âge,implications     

David Besson  Olivier Parize  Jean-Loup Rubino  Jean-Pierre Aguilar  Marie-Pierre Aubry  Bernard Beaudoin  William A. Berggren  Georges Clauzon  Philippe Crumeyrolle  Yann Dexcoté  Nicolas Fiet  Silvia Iaccarino  Gonzalo Jiménez-Moreno  Cécile Laporte-Galaa  Jacques Michaux  Katharina von Salis  Jean-Pierre Suc  Jean-Yves Reynaud  Roland Wernli 《Comptes Rendus Geoscience》2005,337(12):1045-1054

An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005).  相似文献