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251.
William L. Bandy Franois Michaud Jrme Dyment Carlos A. Mortera-Gutirrez Jacques Bourgois Thierry Calmus Marc Sosson Jose Ortega-Ramirez Jean-Yves Royer Bernard Pontoise Bertrand Sichler 《Tectonophysics》2008,454(1-4):70-85
To better understand the recent motion of the Pacific plate relative to the Rivera plate and to better define the limitations of the existing Rivera–Pacific plate motion models for accurately predicting this motion, total-field magnetic data, multibeam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May 2002 in the area surrounding the Moctezuma Spreading Segment of the East Pacific Rise, located offshore of Manzanillo, Mexico, at 106°16′W, between 17.8°N and 18.5°N. Among the main results are: (1) the principle transform displacement zone of the Rivera Transform is narrow and well defined east of 107o15′W and these azimuths should be used preferentially when deriving new plate motion models, and (2) spreading rates along the Moctezuma Spreading Segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the Moctezuma Spreading Segment, or this spreading center is not a Rivera–Pacific plate boundary as has been previously assumed. Comparison of observed transform azimuths with those predicted by the best-fit poles of six previous models of Rivera–Pacific relative motion indicate that, in the study area, a significant systematic bias is present in the predictions of Rivera–Pacific motion. Although the exact source of this bias remains unclear, this bias indicates the need to derive a new Rivera–Pacific relative plate motion model. 相似文献
252.
We document the mineralogical and geochemical composition of tephra layers identified in the late Quaternary sediments of Puyehue Lake (Southern Volcanic Zone of the Andes, Chile, 40°S) to identify the source volcanoes and to present the first tephrostratigraphic model for the region. For the last millennium, we propose a multi-criteria correlation model based on five tephra layers identified at seven coring sites. The two upper tephras are thin fine-grained green layers composed of more than 80% rhyodacitic glass shards, and associated to the AD 1960 and AD 1921-22 eruptions of the Puyehue-Cordon de Caulle volcanic complex. The third tephra is a sandy layer dominated by orthopyroxene, and related to the AD 1907 eruption of Rininahue maar. An olivine-rich tephra was deposited at the end of the 16th century, and a tephra characterized by a two-pyroxene association marks the second half of the first millennium AD. In addition, we detail the tephra succession of an 11.22-m-long sediment core covering the last 18,000 yr. The results demonstrate that the central province of the Southern Volcanic Zone has been active throughout the last deglaciation and the Holocene, with no increase in volcanic activity during glacial unloading. 相似文献
253.
Cheng Sibo Argaud Jean-Philippe Iooss Bertrand Ponçot Angélique Lucor Didier 《Mathematical Geosciences》2021,53(8):1751-1780
Mathematical Geosciences - An original graph clustering approach for the efficient localization of error covariances is proposed within an ensemble-variational data assimilation framework. Here,... 相似文献
254.
We present a geomorphologic analysis of an east‐west transect located east of the southern Andes of Argentina (~37°S). We observe a succession of zones that underwent erosion and deposition during the Pleistocene. If the proximal Andean foothills are incised, a proximal depozone receives sediments feeding the megafan of the Rio Colorado on the Chadileuvú plain. More distally, the abandoned palaeo‐valleys and bending of the valley floors reflect a localized uplift. Further to the east, another depozone corresponds to the Pampa Deprimida lowland. This pattern is consistent with the presence of a classical flexural geometry of the lithosphere. The distal uplift of the foreland corresponds in terms of location, length (150 km) and amplitude (240 m) to the Andean forebulge modelled by a geophysical approach. In this study, we identify the morphological imprint of this bulge and show its effect on the fluvial activity. 相似文献
255.
Gaëlle SAUNIER Franck POITRASSON Bertrand MOINE Michel GREGOIRE Abdelmadjid SEDDIKI 《Meteoritics & planetary science》2010,45(2):195-209
Abstract– Although iron isotopes are increasingly used for meteorites studies, no attempt has been made to evaluate the effect of terrestrial weathering on this isotopic tracer. We have thus conducted a petrographic, chemical, and iron isotopic study of equilibrated ordinary chondrites (OC) recovered from hot Moroccan and Algerian Saharan deserts environment. As previously noticed, we observe that terrestrial desertic weathering is characterized by the oxidation of Fe‐Ni metal (Fe0), sulfide and Fe2+ occurring in olivine and pyroxene. It produces Fe‐oxides and oxyhydroxides that partially replace metal, sulfide grains and also fill fractures. The bulk chemical compositions of the ordinary chondrites studied show a strong Sr and Ba enrichment and a S depletion during weathering. Bulk meteoritic iron isotope compositions are well correlated with the degree of weathering and S, Sr, and Ba contents. Most weathered chondrites display the heaviest isotopic composition, by up to 0.1‰, which is of similar magnitude to the isotopic variations resulting from meteorite parent bodies’ formation and evolution. This is probably due to the release of isotopically light Fe2+ to waters on the Earth’s surface. Hence, when subtle Fe isotopic effects have to be studied in chondrites, meteorites with weathering grade above W2 should be avoided. 相似文献
256.
Zimin A. V. Atazhanova O. A. Romanenkov D. A. Kozlov I. E. Chapron B. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(12):1705-1711
Izvestiya, Atmospheric and Oceanic Physics - This paper presents the results of the analysis of the archive of radar images of Envisat Advanced Synthetic Aperture Radar (ASAR) and Radarsat-1,2 for... 相似文献
257.
Computational Fluid Dynamical Modelling of Concentration Fluctuations in an Idealized Urban Area 总被引:2,自引:2,他引:0
Turbulent mixing induces variability in concentration that is important in many applications, such as reactive plumes, risk
assessments or odour impact analyses (when the effects can have time scales on the order of a second). In urban canopies,
the variability may be modified by the presence of buildings. Our purpose is to study concentration fluctuation variance in
built-up areas using an Eulerian approach. We performed numerical simulations with the computational fluid dynamics model
Mercure_Saturne, which is a three-dimensional model adapted to atmospheric flow and pollutant dispersion. We use a k − ϵ turbulence closure and predict the concentration variance with a transport equation model. The model performance is evaluated
with the near-full scale experiment MUST (Mock Urban Setting Test), a field experiment conducted in Utah’s West Desert Test
Center. The modelled root-mean-square of the concentration fluctuations is compared to measurements for 20 of the MUST trials.
The model shows good agreement with the measurements, with the fraction of predictions within a factor of two of observations
of 60.1%, with better results for horizontal lines of detectors than for the detectors on vertical masts (with fractions of
predictions within a factor of two of observations of respectively 66.4% and 52.6%). The influence of different parameters
on the fluctuation variance is also studied and we show the importance of taking into account the stability of the stratification
when modelling the turbulent kinetic energy. 相似文献
258.
259.
Philippe Bertrand 《Comptes Rendus Geoscience》2002,334(8):521-528
The evolution of the atmospheric CO2 content is partly a response to the lack of balance between oceanic sedimentation and continental weathering, because the oceanic C reservoir tends to balance net inputs or losses from slow processes by rapid exchanges with the atmospheric reservoir. This response strongly depends on both amplitudes and time scales of the related processes. At Milankovitch or lower time scales, global models generally do neglect organic matter fossilisation, but such an assumption is only valid for oligotrophic systems. In eutrophic or mesotrophic systems, organic matter is not negligible and should be considered relatively to the carbonate sedimentation in order to know whether the impact of the sedimentation was a source or a sink for atmospheric CO2. To cite this article: P. Bertrand, C. R. Geoscience 334 (2002) 521–528. 相似文献
260.
Jean-Yves Boisson Lucien Bertrand Jean-François Heitz Yann Golvan 《Hydrogeology Journal》2001,9(1):108-123
In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron,
France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential
fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural
water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10–12 to 2×10–11 m2/s) and hydraulic conductivities derived from different types of laboratory tests (10–14 to 10–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements)
were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10–13 to 10–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical
coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural
flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling,
based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible
flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture
network do not permit reduction of uncertainties on these estimations at this stage.
Electronic Publication 相似文献