Éditeur(s) : HAL CCSD American Association of Petroleum Geologists
Résumé : In reservoir engineering, hydrodynamic properties can be estimated from downhole electrical data using heuristic models (e.g., Archie and Kozeny-Carman's equations) relating electrical conductivity to porosity and permeability. Although proven to be predictive for many sandstone reservoirs, the models mostly fail when applied to carbonate reservoirs that generally display extremely complex pore network structures. In this article, we investigate the control of the three-dimensional (3-D) geometry and morphology of the pore network on the electrical and flow properties, comparing core-scale laboratory measurements and 3-D x-ray microtomography image analysis of samples from a Miocene reefal carbonate platform located in Mallorca (Spain). The results show that micrometer- to centimeter-scale heterogeneities strongly influence the measured macroscopic physical parameters that are then used to evaluate the hydrodynamic properties of the rock, and therefore, existing models might not provide accurate descriptions because these heterogeneities occur at scales smaller than those of the integration volume of the borehole geophysical methods. However, associated with specific data processing, 3-D imagery techniques are a useful and probably unique mean to characterize the rock heterogeneity and, thus, the properties variability.
ISSN: 0149-1423

hal-00950066
https://hal.archives-ouvertes.fr/hal-00950066
DOI : 10.1306/05221312134

Éditeur(s) : HAL CCSD Elsevier
Résumé : Reliable measurements of the intensity of the palaeomagnetic field are notoriously difficult to obtain. The approach generally taken is to produce multiple estimates per rock unit and assume that those which meet certain minimum standards of technical quality will combine to produce an accurate mean. However, here, using results produced from a package of 20th century basaltic lava flows from Mount Etna in Sicily, we demonstrate that this approach can fail. In this case, the application of typical sets of selection criteria actually introduces bias into the mean determination that we measure. We demonstrate that this is caused by two types of non-ideal behaviour acting in combination. The first is a result of the multidomain grains that the samples contain and the second is caused by differences in the natural and laboratory cooling rates. We discuss means of avoiding these sources of error in future palaeointensity studies performed on ancient rocks. We also develop a new, more general reliability criterion which is effective here and which we argue should be applied wherever possible in future palaeointensity studies in conjunction with standard criteria. It requires two distinct types of materials which both produce some good-quality palaeointensity measurements and uses their range of overlap to constrain the true palaeointensity. Both the application of this criterion and general reliability considerations require that future palaeointensity studies should measure many samples per cooling unit and that these should be as diverse in terms of their rock magnetic properties and cooling histories as possible.
ISSN: 0012-821X

hal-00407943
https://hal.archives-ouvertes.fr/hal-00407943
DOI : 10.1016/j.epsl.2007.03.017

Éditeur(s) : HAL CCSD
Résumé : Annual report
We present here the results of CRS reprocessing of a 3D real dataset acquired in 2001 on the Tournemire site in France, which is an experimental site for the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) to test geophysical imaging process in the context of geological nuclear waste storage. The main objective was to evaluate the ability of the methodology to recognize, in the carbonate cover of the experimental site clay layer, the prolongation of weak vertical-displacement faults seen in a tunnel within that clay layer. Previous seismic processing using the conventional common midpoint (CMP) approach did not provide satisfactory results in this cover, although the fault has beenrecognized in the carbonates underlying the clay layer. An original strategy was elaborated to define the best-possible parameters of the 3D Common-Reflection-Surface (CRS) stack. The procedure in- cluded refining the velocity search along a velocity guide, using a first CRS stack as the base of a subsequent curvature-parameter search, or a parameter smoothing before stacking. An optimal ap- proach was elaborated on a subset of the data, and furthermore applied to the whole dataset. The resulting image shows improved event continuity in the carbonate cover, which allowed for horizon picking after depth migration, as well as the estimation of post-stack geometrical attributes, such as coherency. The processing indicates a zone of degraded quality of reflection events lying in the N-S direction, above the known fault zone within the underlying formations. Such feature corresponds to an alteration zone at the earth surface. Further investigation at a higher resolution scale is planned to confirm whether this zone could be a spot of possible leakage
https://hal.archives-ouvertes.fr/hal-00857376

hal-00857376
https://hal.archives-ouvertes.fr/hal-00857376

Éditeur(s) : HAL CCSD
Résumé : International audience
Mylonite bodies are exhumed extensions at depth of shallow structural level brittle faults. They are characterised by intense strain localisation involving large volumes of middle to lower continental crust. The analysis of shear zone geometry and microstructures is a useful tool to decipher deformation kinematics, though finite strain estimation is still relatively qualitative. Timing of the deformation has also been the focus of numerous studies using the complete spectrum of geochronometers. However, only rare examples provide geochronological data that can be unambiguously interpreted and cooling, recrystallisation and neocrystallisation are difficult to tell from each other. Thus, time-scales over which major mylonite zones develop and remain active under ductile conditions as well as their strain rate often remain poorly documented. We investigated two sections across the South-Armorican Shear Zone (SASZ), a crustal-scale pluri-km thick dextral shear zone active during a single tectonic event of late-Variscan age and associated with syntectonic granite emplacement.. Finite strain profiles on these cross-sections, quantified from average Quartz grain-size in 34 samples, show a strong deformation partitioning towards the center of the SASZ, with a decrease, for each section, from 150µm in slightly deformed zones to less than 7-5 µm in the core of the ultramylonite. Furthermore, toward the core of the SASZ, development of a penetrative shear band network progressively eliminates lenses of less deformed rocks and results in homogenisation of the Quartz grain sizes. In parallel, we performed in-situ UV-laser Ar/Ar dating on the fabric-forming white micas. White micas population can be decomposed into inherited muscovites carried by the folation and newly-formed, syn-tectonic substituted phengites located along the shear bands yielding 2 age groups for each sample. Along the profiles, the difference between these two ages evolves from 10-15 Ma in weakly deformed domains to zero toward the SASZ core. In addition, mylonite-forming phengites yielded the same age irrespectively of their position on the section or of the rock strain.. On the regional point of view, this study brings deformation-ages for the late-orogenic evolution of the South Armorican domain. Strain accumulated along the SASZ in a time-span extending to 300-298 Ma, i.e. contemporaneously with the activity of nearby major extensional shear zones. These results support a new model of crustal-scale shear zone activity, where the whole body of the shear zone is active throughout its history (defined as the largest age difference through the section), i.e. the actively deforming zone does not get progressively narrower. The strain distribution nevertheless evolves with time, with an increasingly large fraction partitioned in the ultramylonitic core.
EGU General Assembly
Vienne, Austria

insu-00839320
https://hal-insu.archives-ouvertes.fr/insu-00839320
BIBCODE : 2010EGUGA..12.9881A

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
An intensive water vapour intercomparison effort, involving airborne and ground-based water vapour lidar systems, was carried out in the framework of the COPS experiment. The main objective of this paper is to provide accurate error estimates for these systems. Comparisons between the ground-based Raman lidar BASIL and the airborne CNRS DIAL (Differential Absorption Lidar) indicate a mean relative bias between the two sensors, calculated with respect to the mean value of −2.13% (−0.034 g kg−1) in the altitude region 0.5-3.5 km, while comparisons between BASIL and the airborne DLR DIAL lead to a mean relative bias of 1.87% (0.018 g kg−1) in this same altitude region. Comparisons between the ground-based UHOH DIAL and the CNRS DIAL indicate a bias of −3.2% (−0.37 × 1022 m−3) in the altitude range 1.5-4.5 km, while comparisons between the UHOH DIAL and the DLR DIAL indicate a bias of 0.83% (0.06 × 1022 m−3) in this same altitude range. Based on the available comparisons between the ground-based Raman lidar BERTHA and the CNRS DIAL, the mean relative bias is found to be −4.37% (−0.123 g kg−1) in the altitude region 0.5-4.5 km. Comparisons between the ground-based IGN Raman lidar and the CNRS DIAL indicate a bias of 3.18% (0.55 g kg−1) in the altitude range from 0.5 to 4.5 km, while comparisons between the CNRS DIAL and DLR DIAL result in a mean relative bias of 3.93% (1.1 × 1022 m−3) in the altitude interval 0.5-4.0 km. Based on the available statistics of comparisons, benefiting from the fact that the CNRS DIAL was able to be compared with all other lidar systems, and putting equal weight on the data reliability of each instrument, overall relative values for BASIL, BERTHA, IGN Raman lidar, UHOH DIAL, DLR DIAL, and CNRS DIAL, with respect to the mean value, are found to be −0.38, −2.60, 4.90, −1.43, −2.23 and 1.72%, respectively.
ISSN: 0035-9009

hal-00572576
https://hal.archives-ouvertes.fr/hal-00572576
DOI : 10.1002/qj.697

Éditeur(s) : Basse-Terre : Imp. du Gouvernement
Siècle(s) traité(s) : 17
Provenance : Archives départementales de Guadeloupe
Permalien : http://www.manioc.org/patrimon/ADG18130
ADG18130

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The dating of the uplift onset of the Mongolian mountain ranges, the northernmost relief associated with the India-Eurasia convergence, is a fundamental issue to better understand the mechanisms of propagation of the Cenozoic transpressive deformation in Central Asia. Using apatite fission tracks we determined the timing and strain rates of the tectonics affecting the Gurvan Bogd system, in the Gobi-Altay, since the Middle Mesozoic to the Late Cenozoic. The region was firstly affected by a Lower-Middle Jurassic tectonic phase, characterized by a vertical crustal movement larger than 2 km. Then followed a protracted period without major crustal vertical movements until the last uplift phase. The peneplanation of the Jurassic relief produced an erosional surface that has undergone negligible denudation or sedimentation for more than 100 Ma. This same surface corresponds to the present summit plateaux of the massifs, standing about 2000 m above the surrounding region, which corresponds to the vertical movement produced by the ongoing uplift. Modelling of fission track data from the massifs of Ih Bogd and Baga Bogd shows that this uplift phase probably started at 5 ± 3 Ma. The Gobi-Altay mountain range appears therefore as one of the youngest mountain ranges in Central Asia, which is consistent with the idea of a northward propagation of the transpressional deformation from the Himalayan front to the Siberian craton. The Cenozoic uplift rate of the massifs is estimated to be between 0.25 and 1 mm/yr, which is slightly higher than the upper Pleistocene vertical slip rates of the bordering faults. This suggests that thrust faults observed within the massifs would increase the uplift rate inside the massifs compared to the uplift rate determined at their boundaries.
ISSN: 0012-821X

insu-00191116
https://hal-insu.archives-ouvertes.fr/insu-00191116
DOI : 10.1016/j.epsl.2007.04.047

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : Rock foundations of the Kephren and Kheops pyramids are examined in comparison with other Fourth Dynasty monuments: the Sphinx, Queen Kentkawes' monument and the Abu Rawash monument. This study is based on geological and topographical observations, photomontages and field measurements. The results, which are correlated with those of former studies, demonstrate the existence of natural hills used as substrata in the construction of the two great pyramids. The minimum volume of these hills can be estimated at 12% and 23% respectively of the volumes of the Kephren and Kheops pyramids. The use of worked rock hills appears to be a construction method under the Fourth Dynasty.
EISSN: 1777-5817

hal-00512644
https://hal.archives-ouvertes.fr/hal-00512644

Éditeur(s) : HAL CCSD Springer
Résumé : Borehole logs provide in situ information about the fluctuations of petrophysical properties with depth and thus allow the characterization of the crustal heterogeneities. A detailed investigation of these measurements may lead to extract features of the geological media. In this study, we suggest a regularity analysis based on the continuous wavelet transform to examine sonic logs data. The description of the local behavior of the logs at each depth is carried out using the local Hurst exponent estimated by two (02) approaches: the local wavelet approach and the average-local wavelet approach. Firstly, a synthetic log, generated using the random midpoints displacement algorithm, is processed by the regularity analysis. The obtained Hurst curves allowed the discernment of the different layers composing the simulated geological model. Next, this analysis is extended to real sonic logs data recorded at the Kontinentales Tiefbohrprogramm (KTB) pilot borehole (Continental Deep Drilling Program, Germany). The results show a significant correlation between the estimated Hurst exponents and the lithological discontinuities crossed by the well. Hence, the Hurst exponent can be used as a tool to characterize underground heterogeneities.
ISSN: 1866-7411

hal-00617470
https://hal.archives-ouvertes.fr/hal-00617470
DOI : 10.1007/s12517-010-0129-y

Éditeur(s) : HAL CCSD
Résumé : Water vapour is highly variable in the atmosphere with concentration reaching saturation in the tropics and with dry areas over elevated continental region. Good knowledge of the amount of integrated water vapour in the air is necessary to predict phase changes and in particular precipitation. Water vapour variability measurements are still insufficient with standard observing systems. Moreover accurate GPS antenna positioning is affected by the refractivity index variation in the troposphere. Consequently, vertical positioning component estimation is difficult. This variation is directly linked to distribution of variables such as pressure, temperature and humidity along the path between satellite and receiver. Here we study more specifically heavy rains et notably Cevenols events. This thesis work consists to check the GPS measurement validity to quantify water vapour in comparison with measurements from radiosoundings and meteorological model outputs. GPS observations and flux surface information have been analysed to see if water vapour quantification by GPS allowed characterising heavy rain events (cumulative rainfall amount greater than 150 mm). Then, we tested the GPS data assimilation impact on cumulative precipitation forecasts using the high resolution Meteo France AROME model (2.5 km). Finally the quality and the contribution of GPS measurement on sea is evaluated for water vapour measurement. This study has been realised in the framework of VAPIMED experiment.
La vapeur d'eau varie largement dans l'atmosphère avec des concentrations allant de la saturation dans les tropiques à des zones presque sèches au-dessus des zones continentales élevées. Une bonne connaissance du contenu en vapeur d'eau dans l'air est nécessaire pour la prévision des changements de phases, notamment les précipitations. La mesure de la variabilité de la vapeur d'eau est une lacune des systèmes d'observation. Par ailleurs, il est apparu que le positionnement précis des antennes GPS était affecté par la variation de l'indice de réfraction dans la troposphère, ce qui rend particulièrement difficile l'estimation de la composante verticale. Cette variation est directement liée à la distribution des variables pression, température et humidité sur les trajets satellite-récepteur. On s'intéresse ici à l'étude des précipitations intenses et notamment aux épisodes Cévenols. Ce travail de thèse consiste à vérifier la validité de la mesure GPS pour la quantification de la vapeur d'eau en la comparant avec des mesures issues de radiosondage et des sorties de modèle météorologique. On cherche à analyser si la quantification de vapeur d'eau par GPS permet de caractériser les forts événements précipitants (cumuls supérieurs à 150 mm) à l'aide d'observations conjointes sur les flux de surface. On étudie ensuite l'impact de l'assimilation de données GPS issues d'un réseau GPS dense sur la prévision des cumuls de pluies dans le modèle à hauterésolution (2.5 km) AROME de Météo France. Finalement on évalue la qualité et l'apport de la mesure de vapeur d'eau par GPS en mer dans le cadre d'une campagne de mesure VAPIMED).
https://tel.archives-ouvertes.fr/tel-00444081

Droits : info:eu-repo/semantics/OpenAccess
tel-00444081
https://tel.archives-ouvertes.fr/tel-00444081
https://tel.archives-ouvertes.fr/tel-00444081/document
https://tel.archives-ouvertes.fr/tel-00444081/file/These_KBoniface.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Crystal growth driven by a flowing solution is modeled for a flow with low Reynolds number using a computational dynamic software. Considering equivalent crystallographic faces, the chemical flux is calculated along upstream and downstream faces. Upstream flux is higher compared to downstream and leads to a symmetry breakdown of the crystal shape and develops mirror symmetry parallel to the flow velocity. Moreover the ratio of these two fluxes (upstream / downstream) gives a quantitative relation between the relative crystal growth rate and the flow velocity. Thus, using an inverse method, the flow direction and velocity can be deduced by the study of the variation of the growth band thicknesses of equivalent crystallographic faces. This new method was applied to the formation of metasomatic tourmalinite associated with a leucogranite sill. The approach is complemented by a study of the chemistry of the tourmaline. In the studied case, the application of the new method gives the high fluid velocities in pores (10-3 - 10-4 m/s) during metasomatism. Equivalent Darcy velocities are estimated and discussed accounting for the major role played by the regional deformation. Finally, a two-stage tectono-hydrodynamic model is proposed for the metsomatism. The first stage is genetically linked to the sill injection, and the second is characterized by a wider event with hydrothermal flow passing along the leucogranite sills.
ISSN: 0012-821X

Droits : info:eu-repo/semantics/OpenAccess
insu-00352307
https://hal-insu.archives-ouvertes.fr/insu-00352307
https://hal-insu.archives-ouvertes.fr/insu-00352307/document
https://hal-insu.archives-ouvertes.fr/insu-00352307/file/Sizaret_et_al_final.pdf
DOI : 10.1016/j.epsl.2009.01.013

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A network of 54 survey GPS sites, 28 continuous GPS stations and three absolute gravity (AG) observation sites have been set up in the Alborz mountain range to quantify the present-day kinematics of the range. Our results allow us to accurately estimate the motion of the South Caspian block (SCB) for the first time, and indicate rotation of the SCB relative to Eurasia, accounting for the left lateral motion in the Alborz range. In light of these new results, it clearly appears that deformation rates vary along the range, the eastern part accommodating mainly left lateral strike slip (2 mm yr(-1) south of the range and 5 mm yr(-1) north of the range) with a very low range normal shortening rate on the Khazar thrust fault (similar to 2 mm yr(-1)), and the western part accommodating range normal shortening (similar to 6 mm yr-1) on the Khazar thrust fault with a left lateral component of similar to 2 mm yr(-1) north of the range and 1 mm yr(-1) south of the range. These present-day kinematics agree with geomorphologic estimated slip rates, but not the long-term deformation, corroborating the idea that the kinematics of the range have changed recently due to the change of SCB motion.;Modelling of the interseismic deformation suggests a deep locking depth on the central-western segment of the Khazar fault (similar to 30 km) in agreement with the Baladeh earthquake rupture and aftershock ranging between 10 and 30 km. Given this unusual deep locking depth and the 34 degrees dip of the thrust, a large part of the Alborz range is located above the seismically coupled part of the fault. Based on our AG measurements this part of the range seems to uplift at a rate of 1-5 mm yr(-1), in agreement with terrace uplift.
ISSN: 0956-540X

hal-00617146
https://hal.archives-ouvertes.fr/hal-00617146
https://hal.archives-ouvertes.fr/hal-00617146v2/document
https://hal.archives-ouvertes.fr/hal-00617146/file/djamour2010.pdf
DOI : 10.1111/j.1365-246X.2010.04811.x

Éditeur(s) : HAL CCSD Centre National de la Recherche Scientifique
Résumé : Avec l'augmentation récente de la population mondiale et des infrastructures en domaine littoral, les tempêtes et les cyclones sont devenus un des risques majeurs à l'échelle globale. La Méditerranée, et plus particulièrement le Golfe du Lion, ne sont pas épargnés par ces phénomènes. La tempête de 1982 par exemple, de catégorie 2 sur l'échelle de Saffir-Simpson est responsable du décès de quinze personnes et de plus de 400 millions d'euros de pertes économiques. La prévision de ces événements à partir de modèles climatiques est devenue primordiale. Le problème majeur dans cette approche est le manque de recul dans le temps pour calibrer ces modèles. Notre approche a donc été de reconstituer ces tempêtes du passé à partir de l'étude d'archives sédimentaires (paléotempestologie). Les lagunes du littoral languedocien sont les réceptacles de matériels terrigènes provenant des bassins versants en période de crues, mais aussi de sables transportés par la mer en période de tempêtes. L'étude des archives sédimentaires dans l'étang de Pierre Blanche nous a permis d'identifier et de reconstituer l'alternance des événements les plus extrêmes au cours des 2000 dernières années. La fréquence de ces tempêtes semble varier dans le temps et une augmentation significative est constatée durant la fin du Petit Âge Glaciaire.
ISSN: 1142-2904

hal-00486349
https://hal.archives-ouvertes.fr/hal-00486349

Éditeur(s) : HAL CCSD Centre National de la Recherche Scientifique
Résumé : International audience
ISSN: 1142-2904

hal-00476106
https://hal.archives-ouvertes.fr/hal-00476106

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Transmission electron microscopy observations on olivine crystals deformed at moderate (≤1273 K) temperature evidenced dislocations interactions explaining the hardening observed in the experiments, but also recovery mechanisms by the absorption or emission of point defects. Thus we investigate the possibility that, at geological strain-rates, these recovery processes allow steady-state deformation by dislocation creep at low to moderate temperatures in the lithospheric mantle. We test this hypothesis using a 2.5-D dislocation dynamics (DD) model, which combines dislocation glide and recovery by climb. This model shows that diffusion-controlled recovery processes allow for steady-state deformation by dislocation creep in the lithospheric mantle at stresses <500 MPa. For stresses of 50–200 MPa, steady-state strain-rates of 10−15 s−110−15 s−1 may be attained at temperatures as low as 900 K. Fitting of the DD model produces a flow law, which represents a lower bound for the lithospheric mantle strength, since the models describe the deformation of an olivine single crystal in an easy slip orientation. Comparison of strain-rates and Moho temperatures inferred for different geodynamic environments and the predictions of this model-based flow law implies, nevertheless, that, except in incipient rifts, most of the observed deformation may be produced by stress levels ≤200 MPa, consistent with those inferred to be produced by convection. This convergence suggests that the present models, which explicitly calculate the time-dependent dislocation dynamics, may provide a correct first order estimate of the mechanical behaviour of the lithospheric mantle, which cannot be derived directly from any existing data.
ISSN: 0012-821X

hal-01277178
https://hal.archives-ouvertes.fr/hal-01277178
https://hal.archives-ouvertes.fr/hal-01277178/document
https://hal.archives-ouvertes.fr/hal-01277178/file/Boioli.pdf
DOI : 10.1016/j.epsl.2015.10.012

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A temporary network of 10 broad-band seismic stations has been installed in French Polynesia for the Polynesian Lithosphere and Upper Mantle Experiment (PLUME). All the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of French Polynesia in a manner which complements the geographic coverage provided by the regional permanent stations. The primary aim of PLUME is to image the upper mantle structures related to plate motion and hotspot activity. However, because of its proximity to all sites, the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity. The power spectral density (PSD) analyses of the seismic data recorded in French Polynesia show clear peaks in the 0.05– 0.10 Hz band (periods between 10 and 20 s), which corresponds to swell frequencies. Clear peaks in this frequency band are also observed in infrasonic data recorded on Tahiti. Ground motion analysis shows that the swell-related seismic noise (SRSN) is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore. The microseismic and the infrasonic 'noise' amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the National Oceanic and Atmospheric Administration (NOAA), wind-forced, 'WaveWatch' models. The swell direction can be estimated from SRSN polarization analysis but this has to be done with care since, for some cases, the ground motions are strongly controlled by the islands' anisometric shapes and by swell refraction processes. We find cases, however, such as Tahiti or roughly circular Tuamotu atolls, where the azimuth of the swell is in good agreement with the seismic estimates. We, therefore, demonstrate that the SRSN and the infrasonic signal observed in French Polynesia can be used in such cases as a proxy for swell amplitude and azimuth. From the continuous analysis of the data recorded in 2003 at the permanent seismic station PPTL in Tahiti, transfer functions have been obtained. This could provide a way to quantify the swell activity during the last two decades and, therefore, assist in the investigation of climate changes.
ISSN: 0956-540X

hal-01388809
http://hal.univ-reunion.fr/hal-01388809
http://hal.univ-reunion.fr/hal-01388809/document
http://hal.univ-reunion.fr/hal-01388809/file/Barruol_swell_GJI2006.pdf
DOI : 10.1111/j.1365-246X.2006.02871.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The investigation of deformation rates on a mountain piedmont can provide key information for improving our understanding of the overall dynamics of a mountain range. Here, we estimate the shortening rate absorbed by a Quaternary emergent detachment fold on the southeastern piedmont of the Tianshan (China). Our work is primarily based on new 10Be cosmogenic exposure dating of deformed alluvial surfaces. The method we have developed combines depth profiling with sampling of surface cobbles, thereby allowing exposure time, erosion rate and inheritance to be simultaneously constrained. The exposure ages of the uppermost uplifted alluvial surfaces are around 140±17 ka140±17 ka, 130±9 ka130±9 ka and 47±9 ka47±9 ka, from west to east. A terrace lying below the 140 ka surface is dated at 65±5 ka65±5 ka. The ages of the uplifted and folded alluvial surfaces were then combined with estimates of shortening obtained using two distinct methods: (1) the excess area method, where sedimentation rates, extracted from magnetostratigraphic studies, are used to determine the amount of sedimentation after the abandonment of the river; and (2) a folding model derived from sandbox experiments. The late Pleistocene shortening rates are shown to be between 0.4±0.1 mm/yr0.4±0.1 mm/yr and 0.8±0.5 mm/yr0.8±0.5 mm/yr on the western part of the fold and 2.1±0.4 mm/yr2.1±0.4 mm/yr along its central part. The central part of the frontal Yakeng anticline therefore accommodates up to 25% of the total shortening currently absorbed across the whole Eastern Tianshan range (8 mm/yr). However, this situation seems to have prevailed for only the last 150 ka, as the shortening rate absorbed by this nascent fold was previously ten times slower. While the initiation of folding of the Yakeng anticline can be traced back to 5.5 Ma ago, the basinward migration of the active deformation front onto the Yakeng fold is a relatively recent phenomenon and appears to be diachronous from west to east, probably in relation to the tectonic activity of the folds in the hinterland.
ISSN: 0012-821X

hal-01306997
https://hal.archives-ouvertes.fr/hal-01306997
DOI : 10.1016/j.epsl.2015.11.041

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
An increasing number of field examples in mountain belts show that the formation of passive margins during extreme continent thinning may occur under conditions of high to very high thermal gradient beneath a thin cover of syn-rift sediments. Orogenic belts resulting from the tectonic inversion of distal margins and regions of exhumed continental mantle may exhibit high-temperature, low-pressure (HT-LP) metamorphism and coeval syn-extensional, ductile deformation. Recent studies have shown that the northern flank of the Pyrenean belt, especially the North Pyrenean Zone, is one of the best examples of such inverted hot, passive margin. In this study, we provide a map of HT-LP metamorphism based on a data set of more than 100 peak-temperature estimates obtained using Raman spectroscopy of the carbona-ceous material (RSCM). This data set is completed by previous PT (pressure and temperature) estimates based on mineral assemblages, and new 40 Ar– 39 Ar (amphibole, micas) and U–Pb (titanite) ages from metamorphic and magmatic rocks of the North Pyrenean Zone. The implications on the geological evolution of the Cretaceous Pyrenean paleomar-gins are discussed. Ages range mainly from 110 to 90 Ma, and no westward or eastward propagation of the metamor-phism and magmatism can be clearly identified. In contrast, the new data reveal a progressive propagation of the thermal anomaly from the base to the surface of the continental crust. Focusing on the key localities of the Mauléon basin, Arguenos–Moncaup, Lherz, Boucheville and the Bas-Agly, we analyze the thermal conditions prevailing during the Cre-taceous crustal thinning. The results are synthetized into a series of three regional thematic maps and into two detailed maps of the Arguenos–Moncaup and Lherz areas. The results indicate a first-order control of the thermal gradient by the intensity of crustal thinning. The highest grades of metamor-phism are intimately associated with the areas where subcon-tinental mantle rocks have been unroofed or exhumed.
ISSN: 1869-9510

insu-01161826
https://hal-insu.archives-ouvertes.fr/insu-01161826
https://hal-insu.archives-ouvertes.fr/insu-01161826/document
https://hal-insu.archives-ouvertes.fr/insu-01161826/file/PL03457.pdf
DOI : 10.5194/se-6-643-2015

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : In this paper we present the potential of a new compact superconducting gravimeter (GWR iGrav) designed for groundwater monitoring. At first, 3 yr of continuous gravity data are evaluated and the performance of the instrument is investigated. With repeated absolute gravity measurements using a Micro-g Lacoste FG5, the calibration factor (−894.8 nm s−2 V−1) and the long-term drift of this instrument (45 nm s−2 yr−1) are estimated for the first time with a high precision and found to be respectively constant and linear for this particular iGrav. The low noise level performance is found similar to those of previous superconducting gravimeters and leads to gravity residuals coherent with local hydrology. The iGrav is located in a fully instrumented hydrogeophysical observatory on the Durzon karstic basin (Larzac plateau, south of France). Rain gauges and a flux tower (evapo-transpiration measurements) are used to evaluate the groundwater mass balance at the local scale. Water mass balance demonstrates that the karst is only capacitive: all the rainwater is temporarily stored in the matrix and fast transfers to the spring through fractures are insignificant in this area. Moreover, the upper part of the karst around the observatory appears to be representative of slow transfer of the whole catchment. Indeed, slow transfer estimated on the site fully supports the low-flow discharge at the only spring which represents all groundwater outflows from the catchment. In the last part of the paper, reservoir models are used to characterize the water transfer and storage processes. Particular highlights are done on the advantages of continuous gravity data (compared to repeated campaigns) and on the importance of local accurate meteorological data to limit misinterpretation of the gravity observations. The results are complementary with previous studies at the basin scale and show a clear potential for continuous gravity time-series assimilation in hydrological simulations, even on heterogeneous karstic systems.
ISSN: 0956-540X

hal-01526965
https://hal.archives-ouvertes.fr/hal-01526965
https://hal.archives-ouvertes.fr/hal-01526965/document
https://hal.archives-ouvertes.fr/hal-01526965/file/fores2016.pdf
DOI : 10.1093/gji/ggw396

Éditeur(s) : HAL CCSD
Résumé : While often criticized, independence remains the ultimate criterion for evaluating board composition, whether for regulators or shareholder activists. In this study, we examine the relationship between board independence and firm operating performance in a panel of French listed companies, paying particular attention to heterogeneity and endogeneity concerns. We take advantage of an original database, with a time-series dimension that can be used to mitigate heterogeneity and dynamic endogeneity issues through GMM estimators. In addition, this database can be disaggregated at the individual (director) level. This design enables us to introduce firm fixed effects and individual fixed effects in (firm) performance equations, thereby controlling for heterogeneity at the firm and individual levels. To our knowledge, this is the first paper so far to provide a systematic account on this issue for France. Our main result is to document a significant negative relationship between accounting performance and the independence status (irrespective of the person). This result supports the argument of an information gap suffered by independent board members, as developed by Adams and Ferreira (2007).
https://hal.archives-ouvertes.fr/hal-00919408

hal-00919408
https://hal.archives-ouvertes.fr/hal-00919408
https://hal.archives-ouvertes.fr/hal-00919408v2/document
https://hal.archives-ouvertes.fr/hal-00919408/file/cahier_de_recherche_2014-01.pdf