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1.
2.
François M. Costard 《Earth, Moon, and Planets》1989,45(3):265-290
In order to quantify the spatial distribution of volatiles on Mars, 2600 fluidized ejecta craters have been systematically measured, classified and mapped over the planet Mars, using 1 : 2 M scale USGS photomosaics. The latitudinal distribution of ejecta craters reveals that flower ejecta deposits (Type 1), together with low mobility ejecta, are frequently observed in the equatorial region and on ridged plains. Rampart craters (Type 2), with high mobility ejecta, occur at mid latitudes and exhibit a spatial relationship with polygonal patterns and pseudocrater areas. The increase of ejecta mobility with latitude attests for a concentration of volatiles at high latitudes. Statistical analysis shows that cratered uplands and ridged plains contain less volatile material near the surface than the underlying materials. In Chryse Planitia and Utopia Planitia the statistical study and the spatial relationships between polygonally fractured patterns, pseudocraters and the great number of high mobility ejecta deposits suggest the presence of a water-rich alluvial deposit close to the surface near the mouth of Chryse and Elysium channels. This result explains, on a more quantitative basis, the idea that fractured patterns were preferentially developed in a volatile-rich sedimentary deposits. The behaviour of volatiles, at 41 S, 257 W near Reull Vallis, exhibits a strong anomaly, with the presence of an abnormally volatile rich layer close to the surface. 相似文献
3.
François Farges 《Physics and Chemistry of Minerals》2009,36(8):463-481
Cr K-edge XANES spectra were obtained for a variety of Cr-bearing model compounds containing Cr(II), Cr(III), Cr(IV), Cr(V) and Cr(VI), in which the Cr-site symmetry is D4h, Oh and Td. The centroid position of the pre-edge feature is a better indicator of the Cr valence than the edge position. In Cr-rich oxides, higher-energy transitions must be excluded in order to refine a robust valence for Cr. The pre-edge for chromates is not unique and varies as a function of the CrO4 2? moiety distortion, which is often related to Cr-polymerization (monochromate vs. dichromate). Both the analogy with the Mn K-pre-edge information and ab initio FEFF calculations of the pre-edge feature for Cr(III) and Cr(VI) confirm the experimental trends. This methodology is applied to the Cr K-edge pre-edge feature collected in gems (emerald, spinel and ruby), the layered minerals fuchsite and kämmererite, two Cr-bearing aqueous solutions and a set of sodo-calcic silicate glasses used for bottling sparkling white wine. In emerald and fuchsite, the Cr-site is differently distorted than its ruby or spinel counterpart. In a Cr(III)-bearing aqueous solution and sodo-calcic glass, no evidence for Cr(III) with Td and C3v symmetry is detected. However, minor amounts of chromate moieties (most likely monomeric) are detected in a glass synthesized in air. Preliminary spectra for the wine bottle glass suggest that only trace amounts of chromates might possibly be present in these glasses. 相似文献
4.
Climate modelers have recognized the possibility of abrupt climate changes caused by a reorganization of the North Atlantic's current pattern (technically known as a thermohaline circulation collapse). This circulation system now warms north-western Europe and transports carbon dioxide to the deep oceans. The posited collapse of this system could produce severe cooling in northwestern Europe, even when general global warming is in progress. In this paper we use a simple integrated assessment model to investigate the optimal policy response to this risk. Adding the constraint of avoiding a thermohaline circulation collapse would significantly reduce the allowable greenhouse gas emissions in the long run along an optimal path. Our analysis implies that relatively small damages associated with a collapse (less than 1% of gross world product) would justify a considerable reduction of future carbon dioxide emissions. 相似文献
5.
The Soultz Enhanced Geothermal System (EGS) reservoir's response to chemical stimulation is assessed by numerical simulation of coupled thermo-hydraulic-chemical processes. To assess chemical interactions between host rocks and a mixture of HCl and HF as well as its potential effects on the Soultz EGS reservoir, new modelling efforts using the FRACHEM code have been initiated. This article presents the model calibration and results. Simulations consider realistic conditions with available data sets from the EGS system at Soultz. Results indicate that the predicted amount of fracture sealing minerals dissolved by injection of a mixture of acids Regular Mud Acid (RMA) was consistent with the estimated amount from the test performed on GPK4 well at Soultz EGS site. Consequently reservoir porosity and permeability can be enhanced especially near the injection well by acidizing treatment. 相似文献
6.
From outwash to coastal systems in the Portneuf–Forestville deltaic complex (Québec North Shore): Anatomy of a forced regressive deglacial sequence 下载免费PDF全文
Pierre Dietrich Jean‐François Ghienne Mathieu Schuster Patrick Lajeunesse Alexis Nutz Rémy Deschamps Claude Roquin Philippe Duringer 《Sedimentology》2017,64(4):1044-1078
Deglacial sequences typically include backstepping grounding zone wedges and prevailing glaciomarine depositional facies. However, in coastal domains, deglacial sequences are dominated by depositional systems ranging from turbiditic to fluvial facies. Such deglacial sequences are strongly impacted by glacio‐isostatic rebound, the rate and amplitude of which commonly outpaces those of post‐glacial eustatic sea‐level rise. This results in a sustained relative sea‐level fall covering the entire depositional time interval. This paper examines a Late Quaternary, forced regressive, deglacial sequence located on the North Shore of the St. Lawrence Estuary (Portneuf Peninsula, Québec, Canada) and aims to decipher the main controls that governed its stratigraphic architecture. The forced regressive deglacial sequence forms a thick (>100 m) and extensive (>100 km2) multiphased deltaic complex emplaced after the retreat of the Laurentide Ice Sheet margin from the study area ca 12 500 years ago. The sedimentary succession is composed of ice‐contact, glaciomarine, turbiditic, deltaic, fluvial and coastal depositional units. A four‐stage development is recognized: (i) an early ice‐contact stage (esker, glaciomarine mud and outwash fan); (ii) an in‐valley progradational stage (fjord head or moraine‐dammed lacustrine deltas) fed by glacigenics; (iii) an open‐coast deltaic progradation, when proglacial depositional systems expanded beyond the valley outlets and merged together; and (iv) a final stage of river entrenchment and shallow marine reworking that affected the previously emplaced deltaic complex. Most of the sedimentary volume (10 to 15 km3) was emplaced during the three‐first stages over a ca 2 kyr interval. In spite of sustained high rates of relative sea‐level fall (50 to 30 mm·year?1), delta plain accretion occurred up to the end of the proglacial open‐coast progradational stage. River entrenchment only occurred later, after a significant decrease in the relative sea‐level fall rates (<30 mm·year?1), and was concurrent with the formation and preservation of extensive coastal deposits (raised beaches, spit platform and barrier sands). The turnaround from delta plain accretion to river entrenchment and coastal erosion is interpreted to be a consequence of the retreat of the ice margin from the river drainage basins that led to the drastic drop of sediment supply and the abrupt decrease in progradation rates. The main internal stratigraphic discontinuity within the forced regressive deglacial sequence does not reflect changes in relative sea‐level variations. 相似文献
7.
RésuméPour étudier la tectonique des chaînes subalpines du Nord, et proposer un modèle cinématique régional, nous avons utilisé les résultats d’une expérience géophysique réalisée en 1985, et les observations géologiques de surface publiées à ce jour. Ces données ont été analysées de manière à préciser le style tectonique, le positionnement des failles par rapport aux horizons stratigraphiques et le schéma de branchement des failles. La construction simultanée d’une coupe interprétative, d’une coupe restaurée et d’une carte de branchement des failles a permis d’estimer l’amplitude du raccourcissement par la méthode des coupes équilibrées. Au niveau du Nord de la Chartreuse, la valeur minimale du raccourcissement global est de 14 km, 4 km étant associés au système chevauchant du Jura et 10 km à celui du massif des Bornes et des Bauges. Compte tenu des imprécisions existant sur les données utilisées, trois modèles cinématiques, qui correspondent à une plage de raccourcissement comprise entre 14 et 25 km, sont proposés. 相似文献
8.
Mélina C.Z. Laurent Olivier Gros Jean-Pierre Brulport Françoise Gaill Nadine Le Bris 《Marine environmental research》2009,67(2):83-88
Large organic falls to the benthic environment, such as dead wood or whale bones, harbour organisms relying on sulfide-oxidizing symbionts. Nothing is known however, concerning sulfide enrichment at the wood surface and its relation to wood colonization by sulfide-oxidizing symbiotic organisms.In this study we combined in situ hydrogen sulfide and pH measurements on sunken wood, with associated fauna microscopy analyses in a tropical mangrove swamp. This shallow environment is known to harbour thiotrophic symbioses and is also abundantly supplied with sunken wood. A significant sulfide enrichment at the wood surface was revealed. A 72 h sequence of measurements emphasized the wide fluctuation of sulfide levels (0.1–>100 μM) over time with both a tidal influence and rapid fluctuations. Protozoans observed on the wood surface were similar to Zoothamnium niveum and to vorticellids. Our SEM observations revealed their association with ectosymbiotic bacteria, which are likely to be sulfide-oxidizers. These results support the idea that sunken wood surfaces constitute an environment suitable for sulfide-oxidizing symbioses. 相似文献
9.
Ontogenic variation and effect of collection procedure on leaf biomechanical properties of Mediterranean seagrass Posidonia oceanica (L.) Delile 下载免费PDF全文
Carmen B. de los Santos Bárbara Vicencio‐Rammsy Gilles Lepoint François Remy Tjeerd J. Bouma Sylvie Gobert 《Marine Ecology》2016,37(4):750-759
Leaf mechanical traits are important to understand how aquatic plants fracture and deform when subjected to abiotic (currents or waves) or biotic (herbivory attack) mechanical forces. The likely occurrence of variation during leaf ontogeny in these traits may thus have implications for hydrodynamic performance and vulnerability to herbivory damage, and may be associated with changes in morphologic and chemical traits. Seagrasses, marine flowering plants, consist of shoot bundles holding several leaves with different developmental stages, in which outer older leaves protect inner younger leaves. In this study we examined the long‐lived seagrass Posidonia oceanica to determine ontogenic variation in mechanical traits across leaf position within a shoot, representing different developmental stages. Moreover, we investigated whether or not the collection procedure (classical uprooted shoot versus non‐destructive shoot method: cutting the shoot without a portion of rhizome) and time span after collection influence mechanical measurements. Neither collection procedure nor time elapsed within 48 h of collection affected measurements of leaf biomechanical traits when seagrass shoots were kept moist in dark cool conditions. Ontogenic variation in mechanical traits in P. oceanica leaves over intermediate and adult developmental stages was observed: leaves weakened and lost stiffness with aging, while mid‐aged leaves (the longest and thickest ones) were able to withstand higher breaking forces. In addition, younger leaves had higher nitrogen content and lower fiber content than older leaves. The observed patterns may explain fine‐scale within‐shoot ecological processes of leaves at different developmental stages, such as leaf shedding and herbivory consumption in P. oceanica. 相似文献
10.
André Burnol Francis Garrido Philippe Baranger Catherine Joulian Marie-Christine Dictor Françoise Bodénan Guillaume Morin Laurent Charlet 《Geochemical transactions》2007,8(1):12
High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the
release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis.
Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted.
Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The
biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and
genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing
bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase
amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant
after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant,
or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial
solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst
X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction
revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results.
The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high
Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically
more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more
weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully
applied to recent experimental results on the release of arsenic from Bengal delta sediments. 相似文献