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51.
Franoise Bergerat Pierre-Yves Collin Anne-Cline Ganzhorn Franois Baudin Bruno Galbrun Isabelle Rouget Johann Schnyder 《Journal of Geodynamics》2011,51(5):344-357
Instability structures, synsedimentary faults and turbidites have been studied in the Lower Pliensbachian succession of Saint-Michel-en-Beaumont, belonging to the Taillefer block, an ancient half-graben emplaced during the Liassic Tethyan rifting. Geometrical and mechanical analyses demonstrate that the instability structures occurred thanks to movements along spineless synsedimentary normal faults, when the turbiditic and limestone layers were already case-hardened and partly fractured by tension gashes even when the mudstones were still unlithified. Both the tension gashes and the synsedimentary faults are homogeneous in strike with the major regional faults and are in good agreement with the regional direction of extension for this period. The characters of the turbiditic beds, with erosive base, graded bedding, and incomplete Bouma sequence, are in favour of a seismic origin. Instability structures, spineless synsedimentary faults and turbiditic inflows are thus considered as seismites and interpreted as the result of high seismicity periods including some events with M > 5 in the general extensive ambiance of the Liassic Tethyan rifting. The analysis of the geometrical relationships between all these sedimentary features allows to distinguish the successive stage of occurrence of an instability structure, from the sedimentation of alternating marls and limestones, and sudden turbiditic inflows, then early case-hardening of the turbidites, until the important seismotectonic event generating the spineless normal faults, themselves triggering the fall of indurated blocks and locally the forming of breccias. The Ornon Fault, which constitutes the border of the Taillefer block, 15 km eastward, played a major role during the Liassic sedimentation and may represent the major seismic fault related to the seismites occurrence in the Beaumont basin. 相似文献
52.
Helios-1 and 2 spacecraft allowed a detailed investigation of the radial dependence of the interplanetary magnetic field components between 0.3 and 1 AU. The behaviour of the radial component B
ris in a very good agreement with Parker's model (B
r r
-2) and the azimuthal component B
also shows a radial dependence which is close to theoretical predictions (B
r
-1). Experimental results for the normal component B
and for the field magnitude B are consistent with those from previous investigations. The relative amplitude of the directional fluctuations with periods less than 12 hr is essentially independent of heliocentric distance, while their power decreases approximately as r
–3 without any appreciable difference between higher and lower velocity regimes.Also at Laboratorio Plasma nello Spazio, CNR, Frascati. 相似文献
53.
Aurélia Mouret Pierre Anschutz Bruno Deflandre Gwénaëlle Chaillou Christelle Hyacinthe Jonathan Deborde Henri Etcheber Jean-Marie Jouanneau Antoine Grémare Pascal Lecroart 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):528-540
The relationship between particulate organic carbon (POC) concentrations measured in modern sediment and fluxes of exported POC to the sediment surface needs to be understood in order to use POC content as a proxy of paleo-environmental conditions. The objective of our study was to compare POC concentrations, POC mineralization rates calculated from O2 consumption and POC burial rates. Benthic O2 distributions were determined in 58 fine-grained sediment cores collected at different periods at 14 stations in the southeastern part of the Bay of Biscay with depths ranging from 140 to 2800 m. Depth-dependent volume-specific oxygen consumption rates were used to assess rates of aerobic oxidation of organic matter (OM), assuming that O2 consumption solely was related to heterotrophic activity at the sediment–water interface. Heterogeneity of benthic O2 fluxes denoted changes in time and space of fresh organic material sedimentation. The most labile fraction of exported POC engendered a steep decrease in concentration in the upper 5 mm of vertical O2 profiles. The rupture in the gradient of O2 microprofile may be related to the bioturbation-induced mixing depth of fast-decaying carbon. Average diffusive O2 fluxes showed that this fast-decaying OM flux was much higher than buried POC, although diffusive O2 fluxes underestimated the total sediment oxygen demand, and thus the fast-decaying OM flux to the sediment surface. Sedimentary POC burial was calculated from sediment mass accumulation rate and the organic carbon content measured at the top of the sediment. The proportion of buried POC relative to total exported POC ranged at the most between 50% and 10%, depending on station location. Therefore, for a narrow geographic area like the Bay of Biscay, burial efficiency of POC was variable. A fraction of buried POC consisted of slow-decaying OM that was mineralized within the upper decimetres of sediment through oxic and anoxic processes. This fraction was deduced from the decrease with depth in POC concentration. At sites located below 500 m water depth, where the fast-decaying carbon did not reach the anoxic sediment, the slow-decaying pool may control the O2 penetration depth. Only refractory organic material was fossilized in sedimentary records at locations where labile OM did not reach the anoxic portion of the sediment. 相似文献
54.
55.
Emmanuelle Montarges-Pelletier Laurent Jeanneau Pierre Faure Isabelle Bihannic Odile Barres Bruno S. Lartiges 《Environmental Geology》2007,53(1):85-102
The Moselle river flows in the north-east of France, from Vosges Mountains to neighboring countries Luxembourg and Germany.
One of its tributaries, the Fensch river, drains a highly industrialized watershed, strongly impacted by mining, smelting
and surfacing activities. The objective of this work, part of a general research program on Moselle watershed (Zone Atelier
Moselle) was to assess the impact of the polluted Fensch river on the global quality of the Moselle river. For that purpose,
water, sediments and suspended particulate matter were sampled in both rivers, upstream and downstream the junction. Four
main sampling campaigns were carried out, in winter during a flood event and in spring at low water level. On a first step,
mineralogical analyses (XRD and FTIR) and chemical analyses (ICP-MS, ICP-AES), were performed on sediments, suspended particulate
matters and filtered waters. Major and trace elements concentrations were obtained on two different granulometric fractions
(0–2 mm and 0–50 μm) revealing the enrichment in heavy metals of fine particles. From one collecting campaign to another,
seasonal variations could be evidenced on suspended matter composition even though major minerals (calcite, quartz and kaolinite)
were always present. Furthermore, spatial variations were evidenced for Fensch and Moselle downstream sediments. Thus, very
fine-grained sediments, poorly crystallized, displaying at the same time higher metal concentrations and higher organic matter
content than in Fensch river material, were collected downstream, in a low hydrodynamic conditions zone, assumed as a preferential
sedimentary zone or even as a placer. Strong correlations could be revealed between iron content and contaminant concentrations,
confirming the origin of polluted material. 相似文献
56.
Hugues Raimbourg Bruno Goffé Laurent Jolivet 《Contributions to Mineralogy and Petrology》2007,153(1):1-28
Caledonian eclogite-facies metamorphism partially reworking Grenvillian granulite-facies anorthosite allows us to study the processes of garnet reequilibration at high pressure and to reconstruct the evolution of the unit near metamorphic peak conditions. Our results indicate that eclogite-facies metamorphism happened in two successive phases: first, inherited granulitic garnet was fractured and reequilibrated from their boundaries (crystal or fracture rims); then eclogite-facies minerals were crystallised in the fractures as overgrowths on inherited garnets. The reequilibration of inherited garnets is achieved through Fe2+Mg−1 exchange, whereas eclogite-facies garnets crystallised during the subsequent phase are notably richer in Ca than un- and re-equilibrated granulitic garnet. Pseudosection construction shows that this lack in Ca reequilibration cannot be related to variations in thermodynamic conditions (a
H2O, reacting system composition) between the two phases. From the compilation of the available data, the reequilibration of granulitic garnet seems to be controlled by the inefficient intra- and inter-granular transport properties of Ca compared to Fe2+ and Mg. While these kinetic factors confine garnet reequilibration to Fe2+Mg−1 exchange, the extent of reequilibration along this exchange vector is controlled by partitioning with adjacent omphacite. On the contrary to the diffusional reequilibration of granulitic garnet that lasted for several My according to our modelling of the diffusional relaxation, the strong compositional gradients between eclogite-facies and reequilibrated garnets, which are almost unaffected by diffusional reequilibration, provide evidence that rapid exhumation followed the crystallisation of eclogite-facies minerals. We propose that the movement reversal itself, from burial to exhumation, and associated deformation and fluid flow, triggered this crystallisation event. The resulting evolution near metamorphic peak conditions is therefore strongly asymmetrical: on the one hand, the prograde diffusional relaxation profiles indicate slow movement during the last stages of burial, whereas the unaffected retrograde overgrowth indicates fast exhumation rates. 相似文献
57.
Cancellation exponents and multifractal scaling laws in the solar wind magnetohydrodynamic turbulence 总被引:1,自引:0,他引:1
Some signed measures in turbulence are found to be sign-singular, that is their sign reverses continuously on arbitrary finer scales with a reduction of the cancellation between positive and negative contributions. The strength of the singularity is characterized by a scaling exponent , the cancellation exponent. In the present study by using some turbulent samples of the velocity field obtained from spacecraft measurements in the interplanetary medium, we show that sign-singularity is present everywhere in low-frequency turbulent samples. The cancellation exponent can be related to the characteristic scaling laws of turbulence. Differences in the values of , calculated in both high- and low-speed streams, allow us to outline some physical differences in the samples with different velocities. 相似文献
58.
Bruno Huber 《International Journal of Earth Sciences》1960,49(1):120-131
Zusammenfassung Die Dendrochronologie arbeitet mit der Jahresschichtung des Holzes. Der Zuwachs gleichzeitig wachsender Hölzer ist ähnlich. Diese Forschungsrichtung braucht viel Material zur Herstellung typischer Mittelkurven. Mit Hilfe der Überbrückungsmethode kommt man örtlich sehr weit zurück. Schwierigkeiten liegen in der gesetzmäßigen Abnahme der Ähnlichkeit von Jahresringkurven mit der Entfernung voneinander. Neben einer absoluten Chronologie sind in Deutschland relative Chronologien aus Jungsteinzeit und Bronzezeit erarbeitet worden. Die Dendrochronologie kann gewisse Aussagen über Klimaschwankungen machen. 相似文献
59.
Doppler tracking of an interplanetary spacecraft near solar conjunction is strongly affected by the plasma in the solar corona, the main competitive contribution in measurements of the gravitational deflection of light rays. With the simultaneous availability of carriers in X band and Ka band for interplanetary communications, the plasma contribution to the corona can be accurately eliminated and measured. If, as in the Cassini mission, three different observables are available, this can be done in two ways: one deals with the total plasma content in the electric approximation, even in the ionosphere and interplanetary space; another is limited to the corona, but has access to subtler effects, like the magnetic correction to the refractive index. This technique will allow important progress in the radio investigation of the solar corona. 相似文献
60.