Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans-particularly well preserved in the arid environment of the Gobi region-allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is similar to 1 mm yr(-1) along the WIB and EIB segments and similar to 0.5 mm yr(-1) along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault.;Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at M-w 7.78-7.95.;Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of similar to 2500-5200 yr for past earthquakes along the different segments of the western Bogd Fault. This suggests that the three western segments of the Bogd Fault and the Gurvan Bulag thrust fault (a reverse fault bounding the southern side of the Ih Bogd range that ruptured during the 1957 earthquake) have similar average recurrence times, and therefore may have ruptured together in previous earthquakes as they did in 1957. These results suggest that the western part of the Bogd Fault system, including the Gurvan Bulag thrust fault, usually behaves in a 'characteristic earthquake' mode.
ISSN: 0956-540X

hal-00639467
https://hal.archives-ouvertes.fr/hal-00639467
https://hal.archives-ouvertes.fr/hal-00639467v2/document
https://hal.archives-ouvertes.fr/hal-00639467/file/rizzaGJI2011.pdf
DOI : 10.1111/j.1365-246X.2011.05075.x

Éditeur(s) : Actes du 6e colloque national BRG, La Rochelle, 2-3-4 octobre 2006
Résumé : Previous studies have shown heritable variation in larval developmental traits in the Pacific oyster Crassostrea gigas. In order to study the genetic consequences of production of oyster larvae in hatcheries, two factors, specific to hatcheries, were examined: the effect of discarding the smallest larvae (i.e. culling) and the effect of temperature (20°C versus 26°C). A mixed-family approach was used in order to infer the genetic composition of larval populations and family assignment, limiting possible environmental bias and allowing the study of a relatively large number of families using a limited number of larval tanks. Our results show that three multiplexed highly polymorphic microsatellite markers are a powerful tool for family assignment and, consequently, for the study of bivalve larvae genetics. Culling, by selective sieving of the smallest larvae is an advantageous practice at a phenotypic scale as it reduced variance in larval size, variance of developmental rate and time to settlement. Culling of 50% of the larval population only led to 15% less spat, showing a positive phenotypic correlation between larval growth and settlement success. However, culling represents a substantial risk for diversity loss, because it increases the variance of reproductive success among parental oysters. The effective population sizes of early settling cohorts of settlement were lower than those of later ones. Our results show that the settlement of slow growing larvae significantly contributes to minimizing the variability of reproductive success and therefore to maximizing genetic diversity. These results corroborate the low estimations of variability of broodstocks sampled in several French commercial hatcheries, relative to natural populations. The genetic composition of the larval population and the resulting spat was significantly different between the two tested temperatures, revealing genotype x environment interaction for survival. Similarly, genotype x environment interaction was also observed for larval growth as a higher temperature exerted a positive influence on the expression of genetic variability for this trait. Consequently, we can conclude that a temperature of 26°C coupled with culling, to common practice in oyster hatcheries, is likely to amplify the selection pressure for fast growing larvae. To test for this hypothesis, we compared larval developmental traits in the progeny of a hatchery broodstock closed for 7 generations, with the progeny of wild oysters and the two possible hybrids. Our results show that selection of fast growing larvae can counteract presumed inbreeding depression, due to higher mean relatedness among hatchery broodstock than in the wild. Genetic effects of intensive rearing conditions at larval stage are significant and should be taken into account in hatchery practices, especially in terms of genetic diversity management.
Afin d'étudier les conséquences génétiques des pratiques de production en écloserie d'huître creuse, deux facteurs ont été examinés : l'élimination des petites larves et la température. Nos résultats montrent que l'assignation de parenté par marqueurs microsatellites est un outil performant pour les études génétiques en phase larvaire de familles élevées en mélange. Bien qu'avantageux d'un point de vue phénotypique, le tamisage sélectif représente un risque de perte de diversité. La fixation des larves à croissance lente permet en effet de minimiser la variabilité du succès reproducteur et de fait, de maximiser la variabilité génétique. Ces résultats corroborent les estimations de variabilité sur les stocks d'écloseries françaises où l'on constate une diversité allélique inférieure à celle de populations issues du milieu naturel. La température exerce également une influence sur la précocité de l'expression de la variabilité génétique pour la croissance larvaire. Ainsi une température élevée associée à une procédure de tamisage peut amplifier l'effet sélectif. Enfin, la sélection de larves à croissance rapide semble démontrée, s'opposant à la dépression de consanguinité présumée. Les conditions d'élevage peuvent donc avoir un effet génétique significatif qui devrait être pris en considération dans les pratiques d'écloserie, notamment dans la gestion de la diversité génétique.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/acte-1505.pdf
http://archimer.ifremer.fr/doc/00000/1505/

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen’s segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal & India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes.
ISSN: 2045-2322

hal-01420404
https://hal.archives-ouvertes.fr/hal-01420404
https://hal.archives-ouvertes.fr/hal-01420404/document
https://hal.archives-ouvertes.fr/hal-01420404/file/hetenyi2016.pdf
DOI : 10.1038/srep33866

Éditeur(s) : HAL CCSD Seismological Society of America
Résumé : International audience
Abstract The continuous record of large surface-rupturing earthquakes along the Dead Sea fault brings unprecedented insights for paleoseismic and archaeoseismic research. In most recent studies, paleoseismic trenching documents the late Holocene faulting activity, while tectonic geomorphology addresses the long-term behavior (>10 ka), with a tendency to smooth the effect of individual earthquake rupture events (Mw >7). Here, we combine historical, archaeological, and paleoseismic investigations to build a consolidated catalog of destructive surface-rupturing earthquakes for the last 14 ka along the left-lateral Jordan Valley fault segment. The 120- km-long fault segment limited to the north and the south by major pull-apart basins (the Hula and the Dead Sea, respectively) is mapped in detail and shows five subsegments with narrow stepovers (width < 3 km). We conducted quantitative geomorphology along the fault, measured more than 20 offset drainages, excavated four trenches at two sites, and investigated archaeological sites with seismic damage in the Jordan Valley. Our results in paleoseismic trenching with 28 radiocarbon datings and the archaeoseismology at Tell Saydiyeh, supplemented with a rich historical seismic record, document 12 surface-rupturing events along the fault segment with a mean interval of ∼1160 yr and an average 5 mm=yr slip rate for the last 25 ka. The most complete part of the catalog indicates recurrence intervals that vary from 280 yr to 1500 yr, with a median value of 790 yr, and suggests an episodic behavior for the Jordan Valley fault. Our study allows a better constraint of the seismic cycle and related short-term variations (late Holocene) versus long-term behavior (Holocene and late Pleistocene) of a major continental transform fault.
ISSN: 0037-1106

hal-00747401
https://hal.archives-ouvertes.fr/hal-00747401
DOI : 10.1785/0120100097

Éditeur(s) : HAL CCSD
Résumé : Several major earthquakes have struck the 2500 km long Himalayan range during the past century. However, both the maximum size of such earthquakes and the probability of occurrence of a magnitude 9 megaquake are still a mater of debate. In this framework it is of key importance to investigate the lateral segmentation of the Himalayan arc in order to deepen our understanding of the mechanisms that control such events as well as their extents. Besides the remarkably uniform tectonic set-up and the fact that most studies on the Himalayas have focused on Central Nepal, several indications of along strike changes can be gathered.This thesis brings new constraints on lateral variations of crustal structure and of deformation between western Nepal (~80°E) and eastern Bhutan (~92°E).The first part of this thesis focuses on the lateral variations of crustal structure. In the past three years we have carried out four land gravity campaigns. We have established 366 new gravity measurement points to fill the data gaps in central and western Nepal as well as in Bhutan. This new dataset, together with available seismological data, is used to constrain thermo-mechanical models of the bending of the India plate underneath the Himalayas. While the inferred crustal geometry does not exhibit major along-strike variations over central and eastern Nepal, the shorter wavelength flexure of the lithosphere in Bhutan is associated with a weaker upper mantle rheology.The second part focuses on the lateral variations of recent deformation in the Himalayas. Fifteen years of paleoseismological investigations have extended the catalogue of major Himalayan events over the last millennium. Combining these information with secular loading, we assess the spatial and temporal stress changes on the Main Himalayan Thrust along the orogen over the last nine centuries. Our calculations indicate that inter-seismic loading has now nearly overcome the Coulomb stress decrease caused by the great ~1100 medieval earthquake. Our results also point out that the 1897 Shillong plateau earthquake does not have a major influence on the stress accumulated on the Main Himalayan Thrust since then. In order to better characterize active tectonics in the Bhutan Himalayas where no studies were done so far, we carried out a morphotectonic analysis in the south-central part of the kingdom. We show that the same amount of Holocene deformation is accommodated on the frontal thrust in Bhutan as on the neighbouring portions of the Himalayan arc. We also find evidences for two major (M>8) earthquakes on this thrust in the Bhutan Himalayas during the last millennium. Our results therefore show that Bhutan cannot be considered as a seismic gap. They also challenge the interpretation of one single ~1100 medieval mega-event that would have ruptured the Main Frontal Thrust from central Nepal to eastern Bhutan.
Au cours du dernier siècle, plusieurs séismes majeurs ont affecté l'Himalaya. Cependant, la taille maximale de ces événements et la probabilité d'occurrence de méga-séismes avec des magnitudes proches de 9 sont toujours matière à débat. L'étude de la segmentation de l'arc Himalayen est donc primordiale afin de comprendre les mécanismes qui contrôlent ces séismes ainsi que leur extension spatiale. La compréhension du cycle sismique en Himalaya est aujourd'hui essentiellement basée sur des études menées au Népal central, ce qui limite notre connaissance de son fonctionnement tri-dimensionnel. Ce travail de thèse permet d'apporter de nouvelles contraintes sur les variations latérales de la déformation crustale dans la zone comprise entre l'ouest Népal (~80°E) et l'est Bhoutan (~92°E). La première partie de cette thèse est consacrée à l'étude des variations latérales de la structure lithosphérique. Quatre campagnes gravimétriques ont été réalisées entre 2010 et 2012. Elles ont permis d'étendre le réseau gravimétrique Népalais jusqu'à l'ouest Népal et d'établir le premier réseau gravimétrique Bhoutanais. Ce nouveau jeu de données, combiné avec les données sismologiques disponibles, permet de contraindre des modèles thermo-mécaniques de la flexure de la plaque Indienne sous l'Himalaya. Les résultats suggèrent qu'il n'existe pas de variations latérales majeures du comportement mécanique de la lithosphère Indienne entre le centre et l'est Népal contrairement au Bhoutan où une rigidité flexurale plus faible est nécessaire pour expliquer les données.La deuxième partie de cette thèse est consacrée à l'étude des variations latérales des déformations récentes dans le prisme Himalayen. Les études paléosismologiques menées depuis 15 ans en Himalaya ont permis d'étendre le catalogue des événements majeurs sur le dernier millénaire. En intégrant à la fois les contraintes disponibles sur ces séismes majeurs et le chargement séculaire, nous étudions les variations spatiales et temporelles de l'état de contrainte du chevauchemlent Himalayen principal le long de l'arc. Nos calculs montrent que même dans la cas où un méga-séisme se serait produit en ~1100 en Himalaya, le chargement séculaire a quasiment compensé la chute de contrainte associée. Les modèles montrent aussi que le séisme du Shillong ne joue pas un rôle majeur sur les contraintes accumulées sur le chevauchement Himalayen depuis 1897 au niveau du Bhoutan. Enfin, nous présentons les premières contraintes sur la tectonique active au Bhoutan. L'étude morphotectonique réalisée au centre du Sud-Bhoutan a permis de montrer que la majeure partie de la déformation Holocène est accommodée au niveau du front Himalayen, comme au Népal. Nous montrons aussi des évidences de ruptures de surface avec des décalages verticaux de plusieurs mètres associés à deux séismes majeurs sur le dernier millénaire. Ces évidences remettent en cause l'interprétation d'un méga-séisme en ~1100.
https://tel.archives-ouvertes.fr/tel-01002381

NNT : 2013MON20074
tel-01002381
https://tel.archives-ouvertes.fr/tel-01002381
https://tel.archives-ouvertes.fr/tel-01002381/document
https://tel.archives-ouvertes.fr/tel-01002381/file/35970_BERTHET_2013_archivage_cor.pdf

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The lateral variation of the mechanical properties of continental lithosphere is an important factor controlling the localization of deformation and thus the deformation history and geometry of intraplate mountain belts. A series of three-layer lithospheric-scale analog models, with a strong domain (SD) embedded at various depths, are presented to investigate the development of topography and deformation patterns by having lateral heterogeneities within a weak continental lithosphere. The experiments, performed at a constant velocity and under normal gravity, indicate that the presence or absence of the SD controls whether deformation is localized or distributed at a lithospheric scale. Deformation and topography localize above the edges of the SD, while the SD region itself is characterized by minor amounts of surficial deformation and topography. The depth of the SD (within the ductile crust, ductile mantle lithosphere, or both) controls the pattern of deformation and thus the topography. The presence of a SD in the ductile crust or in the mantle results in limited surficial topographic effects but large variations in the Moho topography. Strong Moho deflection occurs when the SD is in the ductile crust, while the Moho remains almost flat when the SD is in the mantle. When the SD occupies the ductile lithosphere, the SD is tilted. These analog experiments provide insights into intraplate strain localization and could in particular explain the topography around the Tarim Basin, a lithospheric-scale heterogeneity north of the India-Asia collision zone.
ISSN: 0278-7407

hal-01172472
https://hal.archives-ouvertes.fr/hal-01172472
DOI : 10.1002/2014TC003756

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : The objective of this study was to analyse the factors explaining spatial variation in soil respiration over topographic transects in a tropical rain forest of French Guiana. The soil of 30 plots along six transects was characterized. The appearance of the 'dry to the touch' character at a depth of less than 1.2 m was used to discriminate soils exhibiting vertical drainage from soils exhibiting superficial lateral drainage and along with colour and texture, to define five classes from well-drained to strongly hydromorphic soils. Spatial variation in soil respiration was closely related to topographic position and soil type. Increasing soil water content and bulk density and decreasing root biomass and soil carbon content explained most of the decrease in soil respiration from the plateaux (vertically drained hypoferralic acrisol) to the bottomlands (haplic gleysol). These results will help to stratify further field experiments and to identify the underlying determinants of spatial variation in soil respiration to develop mechanistic models of soil respiration.
ISSN: 0266-4674

hal-01032046
https://hal.archives-ouvertes.fr/hal-01032046
DOI : 10.1017/S0266467406003415

Éditeur(s) : HAL CCSD Blackwell Publishing
Résumé : International audience
In the Causses platform (south-east France), Late Hettangian to Sinemurian deposits were interpreted previously as shallow-water carbonate ramp deposits. A new look at these deposits has shown a fault-controlled mosaic carbonate platform that is different from the carbonate ramp models. Within the platform mosaic, 15 lithofacies have been recognized, which are organized in four facies associations, including peritidal, restricted shallow sub-tidal, sand dunes and sub-tidal shelf facies associations. The rapid lateral and vertical facies changes, and the lack of consistent landward or seaward direction indicated by the pattern of facies changes, question the existence of a shoreline suggested by the traditional models for this region. Instead, the facies organization and cycle stacking pattern suggest deposition in a mosaic of intertidal islands between which sub-tidal restricted or open conditions could coexist in very close proximity. Such a platform mosaic would have been defined by tectonic activities along normal faults which segmented the shallow-water Causses platform. The facies and facies associations are arranged into metre-scale, peritidal and sub-tidal cycles that are also variable. Certain cycles show the same stacking pattern in all the sections and seem to be traceable over tens of kilometres. On the contrary, other cycles cannot be correlated; they are present only in specific sections and have a maximum lateral extension of 1 or 2 km. These metre-scale cycles stack to form four medium-scale cycles bounded by surfaces that display sub-aerial exposure features. Medium-scale cycles stack into two larger-scale cycles (tens of metres thick) and are bounded by well-defined karstic surfaces. Based on their lateral continuity and their stacking pattern, the metre-scale cycles are controlled probably by high frequency eustatic variations overprinting the topographic irregularities formed by differential subsidence of fault-bounded blocks. Episodic fault activities may reorganize the topography so that, even if eustatic changes may still be the major control of cycles, the expression and number of cycles could be different. Cycles of medium and large-scale are interpreted as being allogenic, controlled by changes in eustasy and/or subsidence rates as evidenced by their lateral continuity and the correlations of the large-scale cycles with third-order depositional sequences.
ISSN: 1469-3496

hal-00411940
https://hal.archives-ouvertes.fr/hal-00411940
DOI : 10.1111/j.1365-3091.2007.00896.x

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : Late Jurassic platform carbonates of Languedoc (southern France) are deeply incised by Late Miocene canyons, allowing the observation of karst systems filled with sediments containing evidences of marine origin. Field and structural relationships as well as new biostratigraphic data (planktonic foraminifera and calcareous nannofossils) provide a Latest Cretaceous-Earliest Paleocene age for the major karstification and a Paleocene (Danian-Selandian) age for the sedimentary filling. The ≥ 350 m vertical extent of this karst system and its subsequent marine filling gives a minimum amplitude for the base-level variation responsible for the karstification and then the marine flooding events. The observations suggest that at least, two marine successive events occurred in the Late Danian then in Selandian time. The large amplitude of base level is not in agreement with eustatic sea-level change, and the rate of base-level change is too fast for tectonic uplift and subsidence within the tabular, poorly deformed studied area. We propose a model of a silled endoreic basin, which was dessiccated and karstified over hundreds of meters, when it was disconnected from the World Ocean, and later suddently transgressed by the Paleocene sea and the karst flooded, when the bounding sill was submerged. Such a model is similar, although with significant differences, with the later Messinian-Zanclean event that affected the Mediterranean realm.
EISSN: 1777-5817

hal-00767556
https://hal.archives-ouvertes.fr/hal-00767556
DOI : 10.2113/gssgfbull.183.5.425

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : International audience
La Cabaña peridotite is part of a dismembered ophiolite complex located within the metamorphic basement of the Coastal Cordillera of south-central Chile, and is the only location in Chile were Cr-spinels have been described so far. The La Cabaña peridotite is part of the Western Series unit, which comprises meta-sedimentary rocks, metabasites, and serpentinized ultramafic rocks. This unit has been affected by greenschist-facies metamorphism with reported peak PT conditions of 7.0–9.3 kbar and 380°–420 °C. Within La Cabaña peridotite Cr-spinels are present in two localities: Lavanderos and Centinela Bajo. In Lavanderos, Cr-spinel occurs in small chromitite pods and as accessory/disseminated grains with a porous or spongy texture in serpentinite, whereas in Centinela Bajo Cr-spinel is present as accessory zoned grains in partly serpentinized dunites, and in chromitite blocks. All Cr-spinels display variable degrees of alteration to Fe2+-rich chromite with a variation trend of major elements from chromite to Fe2+-rich chromite similar to those observed in other locations, i.e., an increase in Fe2O3 and FeO, a decrease in Al2O3 and MgO. Cr2O3 content increases from chromite to Fe2+-rich chromite in chromitite pods from Lavanderos and chromitite blocks from Centinela Bajo, but decreases in ferrian chromite zones in accessory grains from Centinela Bajo. The minor element (Ti, V, Zn, Ni) content is mostly low and does not exceed 0.4 wt.%, with the exception of MnO (<0.9 wt.%), which shows a correspondence with increasing degree of alteration. Cr# (Cr/Cr + Al) versus Mg# (Mg/Mg + Fe2+) and Fe3+/Fe3++Fe2+ versus Mg# plots are used to illustrate the Cr-spinel alteration process. Overall, the Cr-spinels from Lavanderos (chromitite pods and disseminated grains) exhibit Cr# values ranging from 0.6 to 1.0, Mg# (Mg/Mg + Fe2+) below 0.5, and (Fe3+/Fe3++Fe2+) <0.4. Cr-spinels from chromitites in Centinela Bajo have Cr# and Mg# values that range from 0.65 to 1.0, and 0.7-0.3, respectively, and (Fe3+/Fe3++Fe2+) < 0.4. Accessory Cr-spinels from Centinela Bajo have Cr# and Mg# values that range from 0.55 to 1.0, and 0.6- < 0.1, respectively. The (Fe3+/Fe3++Fe2+) ratio is less than 0.4 in chromite cores and Fe2+-rich chromite, and >0.5 in ferrian chromite and Cr-magnetite. Interpretation of the data obtained and Cr-spinel textures indicate that the alteration of Cr-spinel is a progressive process that involves in its initial stages the reaction of chromite with olivine under water-saturated conditions to produce clinochlore and Fe2+-rich chromite. During this stage the chromite can also incorporate Ni, Mn, and/or Zn from the serpentinization fluids. As alteration progresses, Fe2+-rich chromite loses mass resulting in the development of a spongy texture. In a later stage and under more oxidizing conditions Fe3+ is incorporated in chromite/Fe2+-rich chromite shifting its composition to an Fe3+-rich chromite (i.e., ferrian chromite). Depending on the fluid/rock and Cr-spinel/silicate ratios, Cr-magnetite can also form over Fe2+-rich chromite and/or ferrian chromite as a secondary overgrowth. The compositional changes observed in Cr-spinels from La Cabaña reflect the initial stages of alteration under serpentinization conditions. Results from this study show that the alteration of Cr-spinels is dependent on temperature. The degree and extent of alteration (formation of Fe2+-rich and/or ferrian chromite) are controlled by the redox nature of the fluids, the Cr-spinel/silicate and the fluid/rock ratios.
ISSN: 0930-0708

hal-01172266
https://hal.archives-ouvertes.fr/hal-01172266
DOI : 10.1007/s00710-014-0335-5

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A large sand injectite network is very well exposed in the area of Bevons, Southeast France. The associated sandstone turbiditic channel–fill and the host marls are the Aptian–Albian rocks of the Vocontian Basin. The sand injection network is composed of dykes, sills and sedimentary laccoliths ranging in thickness from mm to pluri–m. The dykes and sills have vertical and horizontal lengths of up to and over 100 m and 1 km, respectively. Outcrop observations show that the architecture and morphology of the sand injectites in the marls is governed by the local stress field during injection, pre–existing faults, the host–rock lithology, compaction, and distance to the potential sand source(s). The main set of dykes is oriented N50–60° perpendicular to the minimum compressive stress σ3 during sand injection. Two other sets of dykes are intruded along pre–existing syn–sedimentary faults oriented N140–150° (set 2) and N90° (set 3) during the Apto–Cenomanian interval. Sills and dykes thin laterally away from their potential sand sources and thin laterally away from them. The vertical thickness variations of the dykes and wings are more complex, as thinning away from the sand sources is often compensated by thickening toward the palaeo–surface. Based on field observations and measurements, we characterized the 3D architecture of the sand injectites and showed that the injectites probably formed due to a forceful injection from an overpressured sand body sealed by low–permeability lithologies.
ISSN: 0191-8141

hal-01243488
https://hal.archives-ouvertes.fr/hal-01243488
DOI : 10.1016/j.jsg.2015.07.001

Éditeur(s) : Université Bordeaux 1
Résumé : Les formations superficielles du plateau insulaire de la Martinique ont été cartographiées à l'aide de données acquises par l'utilisation de techniques complémentaires telles que le sonar à balayage latéral, les photographies sous-marines et les prélèvements à la benne. Ces formations sont constituées par des éléments carbonatés provenant du démantèlement des formations coralliennes actuelles et fossiles et d'éléments volcaniques transportés jusqu'à la mer par voies aérienne et fluviatile. Parmi les structures sédimentaires repérées dans les sables grossiers à très grossiers et dans les graviers, les plus significatives sont des mégarides symétriques, situées entre 20 et 60 m de profondeur. Elles présentent une hauteur comprise entre 0,20 et 0,60 m et une amplitude variant de 1 à 5 m. Le dépouillement des mesures de courantométrie, l'utilisation de statistiques sur les alizés, l'examen de données sur l'état de la mer et la modélisation des courants induits par les vents en période d'alizés et en période cyclonique ont abouti à la définition des caractéristiques des agents hydrodynamiques régnant sur le plateau insulaire de la Martinique. Les caractéristiques des corps sédimentaires permettent d'attribuer aux houles cycloniques plutôt qu'aux courants la responsabilité de leur formation notamment en période cyclonique. Les deux derniers cyclones les plus intenses ayant touché les côtes martiniquaises (David en 1979 et Allen en 1980) ont laissé des empreintes différentes en raison d'une intensité et d'une trajectoire différentes. Les courants de marée, les courants généraux et ceux induits par le vent occupent une place secondaire parmi les agents de remobilisation des sédiments et d'édification des mégarides.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00105/21587/19167.pdf
http://archimer.ifremer.fr/doc/00105/21587/

Éditeur(s) : HAL CCSD Ocean Drilling Programm
Résumé : This paper provides a summary of postcruise scientific results from Ocean Drilling Program (ODP) Leg 209 available to date, building upon shipboard observations and syntheses summarized in the Leg 209 Initial Results volume. During Leg 209, 19 holes were drilled at 8 sites along the Mid-Atlantic Ridge from 14°43´ to 15°44´N, mainly in residual mantle peridotite intruded by gabbroic rocks, in order to understand the tectonic and structural processes responsible for formation of oceanic lithosphere with abundant residual peridotite exposed on the seafloor coupled with a relatively low proportion of volcanic rocks. Based on proportions of recovered lithologies, the entire area may be underlain by mantle peridotite with ~20%–40% gabbroic intrusions and impregnations. Impregnated peridotites with olivine + two pyroxenes + plagioclase + spinel that apparently formed in equilibrium probably record crystallization from primitive mid-ocean-ridge basalt at pressures of 0.5–0.6 GPa. Metamorphic equilibria record isobaric cooling to ~1100°C at this pressure. Thus, the conductively cooled thermal boundary layer beneath the Mid-Atlantic Ridge in this region is >15 km thick. Combined crystallization and reaction with residual peridotite formed a series of impregnated peridotites recording increasing Na content at nearly constant Mg#; this process could explain some of the variation in fractionation-corrected Na (e.g., Na = 8.0) observed in mid-ocean-ridge basalts. Clinopyroxene textures and compositions record such impregnation processes, and they are particularly well documented for Site 1274. Other Leg 209 gabbroic rocks formed from extensive crystallization of highly evolved melts, indicating that a substantial proportion of melt entering the thermal boundary layer crystallizes entirely beneath the seafloor, with no volcanic equivalent. Alteration of peridotites occurred over a range of temperatures and is the result of three distinct processes: rock-dominated serpentinization with formation of brucite in olivine-rich lithologies, fluid-dominated serpentinization with formation of magnetite and no brucite, and fluid-dominated talc alteration with addition of SiO2 as well as H2O and oxygen. The latter two processes also exhibit detectable trace element metasomatism that is distinct in its character from the igneous impregnation described in the previous paragraph. Microstructures show that most residual peridotites were not ductilely deformed at temperatures less than ~1200°C. Structural and paleomagnetic data require tectonic rotations of relatively undeformed blocks; some rotations probably exceeded 60° around nearly horizontal axes parallel to the rift axis. Rotations occurred along several generations of high-temperature mylonitic shear zones extending deeper than 15 km depth and numerous faults at lower temperature. Early formed shear zones and faults were passively rotated around later features; such a process could have produced low-angle fault surfaces without slip on low-angle faults. This region provides end-member examples of processes that are common at many or most slow-spreading ridges. Osmium isotope ratios indicate an ancient history of depletion for residual peridotites from the 14°–16°N region along the Mid-Atlantic Ridge. Though depleted Os isotope ratios in peridotite have been reported elsewhere along the global ridge system, the values from this region are among the most depleted. In general, Os isotope ratios from mid-ocean-ridge basalts are systematically more radiogenic than Os isotope ratios from ridge peridotite samples, suggesting a polygenetic heterogeneous source for mid-ocean-ridge basalts. Geochemical studies of zircons from Leg 209 gabbroic rocks and impregnated peridotites, together with other ridge and arc-related zircons, indicate that ridge zircons have systematically lower fractionation-corrected U and Th concentrations compared to arc zircons. This observation provides a tool for interpreting the tectonic provenance of ancient detrital zircons and indicates an arclike provenance for Hadean detrital zircons. Geobiological studies and aerobiological studies were also undertaken during Leg 209. The geobiological work found no measurable microbial enhancement of olivine dissolution rate, possibly because the samples from Leg 209 were sterile. The aerobiological study determined that dust from North Africa, collected from the derrick of the JOIDES Resolution during Leg 209, contains a variety of abundant microorganisms.
Proceedings ODP, scientific results, 209

hal-00407966
https://hal.archives-ouvertes.fr/hal-00407966
DOI : 10.2973/odp.proc.sr.209.001.2007

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
We calculated the seismic properties of 47 mantle xenoliths from 9 kimberlitic pipes in the Kaapvaal craton based on their modal composition, the crystal-preferred orientations (CPO) of olivine, ortho- and clinopyroxene, and garnet, the Fe content of olivine, and the pressures and temperatures at which the rocks were equilibrated. These data allow constraining the variation of seismic anisotropy and velocities within the cratonic mantle. The fastest P and S2 wave propagation directions and the polarization of fast split shear waves (S1) are always subparallel to olivine [100] axes of maximum concentration, which marks the lineation (fossil flow direction). Seismic anisotropy is higher for high olivine contents and stronger CPO. Maximum P wave azimuthal anisotropy (AVp) ranges between 2.5 and 10.2% and the maximum S wave polarization anisotropy (AVs), between 2.7 and 8%. Changes in olivine CPO symmetry result in minor variations in the seismic anisotropy patterns, mainly in the apparent isotropy directions for shear wave splitting. Seismic properties averaged over 20 km-thick depth sections are, therefore, very homogeneous. Based on these data, we predict the anisotropy that would be measured by SKS, Rayleigh (SV) and Love (SH) waves for five endmember orientations of the foliation and lineation. Comparison to seismic anisotropy data from the Kaapvaal shows that the coherent fast directions, but low delay times imaged by SKS studies, and the low azimuthal anisotropy with with the horizontally polarized S waves (SH) faster than the vertically polarized S wave (SV) measured using surface waves are best explained by homogeneously dipping (45°) foliations and lineations in the cratonic mantle lithosphere. Laterally or vertically varying foliation and lineation orientations with a dominantly NW-SE trend might also explain the low measured anisotropies, but this model should also result in backazimuthal variability of the SKS splitting data, not reported in the seismological data. The strong compositional heterogeneity of the Kaapvaal peridotite xenoliths results in up to 3% variation in density and in up to 2.3% variation of Vp, Vs, and Vp / Vs ratio. Fe depletion by melt extraction increases Vp and Vs, but decreases the Vp / Vs ratio and density. Orthopyroxene enrichment due to metasomatism decreases the density and Vp, strongly reducing the Vp / Vs ratio. Garnet enrichment, which was also attributed to metasomatism, increases the density, and in a lesser extent Vp and the Vp / Vs ratio. Comparison of density and seismic velocity profiles calculated using the xenoliths' compositions and equilibration conditions to seismological data in the Kaapvaal highlights that (i) the thickness of the craton is underestimated in some seismic studies and reaches at least 180 km, (ii) the deep sheared peridotites represent very local modifications caused and oversampled by kimberlites, and (iii) seismological models probably underestimate the compositional heterogeneity in the Kaapvaal mantle root, which occurs at a scale much smaller than the one that may be sampled seismologically.
ISSN: 1869-9510

hal-01053516
https://hal.archives-ouvertes.fr/hal-01053516
DOI : 10.5194/se-5-45-2014

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Environmental variables affect many processes of fish biology and their fluctuations are thought to be one of the main factors in variability of fish stocks. Recent work has shown that the variability of the environment in the frequency domain (i.e., the environmental noise) can interact with endogenous processes (e.g., density dependence) and affect fluctuations of animal populations. In this study, we investigate whether fluctuations of large pelagics' time series are affected by environmental noise and whether life-history traits of species modulate this response. By analysing several environmental variables and a large dataset of tuna and billfish catch per unit effort (CPUE) time series from the Atlantic, we show that in environments dominated by long-term fluctuations (i.e., red noise) CPUE time series were less variable and displayed smoother fluctuations. Furthermore, larger, slower-growing and later-maturing species were found to be more sensitive to changes of environmental noise than species with a shorter turnover rate. Our results suggest that environmental noise interacts with fish biology; understanding how it is integrated into biological processes might provide important insights to understand the responses of fish stocks dynamics to exploitation and environmental changes. (C) 2010 Elsevier Ltd. All rights reserved.
Progress In Oceanography (0079-6611) (Pergamon-elsevier Science Ltd), 2010-07 , Vol. 86 , N. 1-2 , P. 267-275

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00011/12230/9083.pdf
DOI:10.1016/j.pocean.2010.04.025
http://archimer.ifremer.fr/doc/00011/12230/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The shallow-water bivalve Codakia orbiculata which harbors gill-endosymbiotic sulfur-oxidizing ?-proteobacteria can lose and acquire its endosymbionts throughout its life. Long-term starvation and recolonization experiments led to changes in the organization of cells in the lateral zone of gill filaments. This plasticity is linked to the presence or absence of gill-endosymbionts. Herein, we propose that this reorganization can be explained by three hypotheses: (a) a variation in the number of bacteriocytes and granule cells due to proliferation or apoptosis processes, (b) a variation of the volume of these two cell types without modification in the number, and (c) a combination of both number and cell volume variation. To test these hypotheses, we analyzed cell reorganization in terms of proliferation and apoptosis in adults submitted to starvation and returned to the field using catalyzed reporter deposition fluorescence in situ hybridization, immunohistochemistry, and structural analyses. We observed that cell and tissue reorganization in gills filaments is due to a variation in cell relative abundance that maybe associated with a variation in cell apparent volume and depends on the environment. In fact, bacteriocytes mostly multiply in freshly collected and newly recolonized individuals, and excess bacteriocytes are eliminated in later recolonization stages. We highlight that host tissue regeneration in gill filaments of this symbiotic bivalve can occur by both replication of existing cells and division of undifferentiated cells localized in tissular bridges, which might be a tissue-specific multipotent stem cell zone.
ISSN: 1059-910X

hal-01545915
https://hal.archives-ouvertes.fr/hal-01545915
DOI : 10.1002/jemt.22041

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Growth hormone (GH) may stimulate water loss during exercise by activating sweating. This study investigated GH secretion and water loss during sequential cycling and running, taking postural changes into account. The two exercise segments had similar durations and were performed at the same relative intensity to determine their respective contributions to water loss and the plasma volume variation noted in such trials. Eight elite triathletes first performed an incremental cycle test to assess maximal oxygen consumption. Then, the triathletes performed one of two trials in randomized order: constant submaximal cycling followed by treadmill running (C 1 –R 2) or an inversed succession of running followed by cycling (R 1 –C 2). Each segment of both trials was performed for 20 minutes at ,75% of maximal oxygen consumption. The second trial, reversing the segment order of the first trial, took place two weeks later. During cycling, the triathletes used their own bicycles equipped with a profiled handlebar. Blood sampling (for GH concentrations, plasma viscosity and plasma volume variation) was conducted at rest and after each segment while water loss was estimated from the post-and pre-measures. GH increases were significantly lower in R 2 than C 2 (72.2650.1 vs. 164.06157 ng.ml 21 .min 21 , respectively; P,0.05). Water loss was significantly lower after C 1 –R 2 than R 1 –C 2 (11056163 and 12356153 ml, respectively; P,0.05). Plasma volume variation was significantly negative in C 1 and R 1 (26.1562.0 and 23.1665.0%, respectively; P,0.05), not significant in C 2 , and significantly positive for seven subjects in R 2 (4.0563.1%). We concluded that the lower GH increases in R 2 may have contributed to the smaller reduction in plasma volume by reducing sweating. Moreover, this lower GH response could be explained by the postural change during the transition from cycling to running. We recommend to pay particular attention to their hydration status during R 1 which could limit a potential dehydration during C 2 .
ISSN: 1932-6203

hal-01136734
https://hal.univ-antilles.fr/hal-01136734
https://hal.univ-antilles.fr/hal-01136734/document
https://hal.univ-antilles.fr/hal-01136734/file/Galy%20et%20al.%20-%202014%20-%20Sequential%20exercise%20in%20triathletes%20Variations%20in%20GH%20and%20water%20loss.pdf
DOI : 10.1371/journal.pone.0096145

Éditeur(s) : HAL CCSD
Résumé : International audience
Continental erosion and weathering destroy parts of the stratigraphic record. Analyses of the sedimentary filling of paleokarsts help completing the geological record of regions that have been submitted to post-depositional, long-term, continental evolution. Jurassic carbonate platform of Languedoc (South of France) has undergone several karstification phases from Cretaceous to Neogene. Later incision of canyons through the carbonate massifs allows to observe paleokarsts over 400m depth, within the massifs. Paleokarsts are partly filled with sediments. Some have yielded marine bioclasts (echinoderms, radiolars), foraminifera and nannofossils; others are composed of polygenic detrital sediments, including sources from the upstream Paleozoic basement (Cevennes). The age of the filling of successive paleokarsts can be constrained by structural relationships and by biostratigraphy. These findings suggests 1) the marine elements of the karstic filling relate to a Late Cretaceous to Early Paleocene interval, while 2) the Paleozoic basement-sourced-sediments were trapped in the karst during Miocene to Present. Karstic sediment containing Early Paleocene foraminifera and nannofossils are found in paleokarsts cavities distributed across the entire thickness of the carbonate massif (≥350m). This requires base-level lowering and associated karstification, followed by base-level rise and karst filling of at least 350 m amplitude, respectively. The time interval corresponding to the occurrence of foraminifera and nannofossils in karsts covers 10 Myrs ; surprisingly, no equivalent marine sediments are preserved on the surface. In addition, analyses of the different forams species suggests several (up to 3) distinct karstification and marine filling cycles. Finally, sedimentological facies analysis of the karst filling reveals the following succession of processes: low energy settling of mudstone, high energy reworking, transport and deposition of silts and sandstones within the karst system. Integration of geological, paleontological and sedimentological data, leads to a polyphase scenario in response to repeated base-level variations, more than 350m amplitude. Such an amplitude excludes eustacy, and the improbable repeated sequence of uplift and subsidence rules out tectonics, as driving forces for base-level change, respectively. We propose that the high-amplitude base-level changes results from a succession of desiccation-flooding events of an endorheic, silled, basin during Early Paleogene. The later detrital assemblage sourced in the Cevennes occurs on perched paleosurfaces and in karst cavities across the whole 350m-deep canyon walls. When found on paleosurfaces, they correspond to the south-flowing Early Miocene fluvial drainage, and can be correlated downstream with the marine, well dated, Early Miocene, sediments. When found within the karst cavities, they correspond to successive base-level surfaces connected to the progressive incision of the canyon. This canyon incision is coeval with a Late Miocene uplift of the hinterland.
24th International Karstological School "Classical karst" : Paleokarst
Postojna, Slovenia

hal-01306683
https://hal-brgm.archives-ouvertes.fr/hal-01306683
https://hal-brgm.archives-ouvertes.fr/hal-01306683/document
https://hal-brgm.archives-ouvertes.fr/hal-01306683/file/Abstract_IKS.pdf

Éditeur(s) : HAL CCSD
Résumé : This thesis aims to analyze the active tectonics and the seismic hazard for three main cities of NW Iran (Tehran, Tabriz and Zandjan) using morphotectonics and paleoseismology. Within the Tehran capital, we focused our analysis on the Mosha-North Tehran (M-NT) active fault system. Our investigations show that this fault system is mainly dominated by left-lateral faulting. Along the eastern part of the M-NT fault system, we found evidences of at least seven strong (M>7) paleoearthquakes during the past 10 ka (recurrence interval : 1100-1400 yrs). Our study along the central portion of the fault system (in Abali region) suggests that it corresponds probably to the source of the 1830 AD historical earthquake (M=7.1, Io= IX). Within Tabriz region, we studied the SE segment of the North Tabriz fault. We found evidences of at least three strong events, which occurred during the past 33.5 ka. The North Tabriz dextral fault corresponds to the central portion of a fault system (TFS), and contains two fault segments (NW and SE). Our paleoseismological analysis shows a variation of the slip rate, which decreases from NW to SE along the strike-slip fault. The western (Mishu) and eastern (Bozghush) terminations of the fault system correspond to oblique-compression zones. TFS belongs to the eastern portion of a regional fault system (GSKT), linking the active extension within the central part of the collision and the active compression to the East. Finally, we focus on the Zandjan area, where no important historical seismicitiy is recorded. There, based on morphotectonics analysis we discovered a large active fault network, whose southeastern part affects the Zandjan city. To conclude this work, we replace our observations within the general geodynamic framework of the Arabia- Eurasia collision. One of the striking pictures is the occurrence of opposite kinematics along the M-NT (and other range parallel faults within the south Central Alborz) and the North Tabriz fault systems that have the same trend. This shows the rapid variation of the regional stress field in the Northern Iran.
L'objectif de ce mémoire de thèse est l'étude de la tectonique récente et l'évaluation de l'aléa sismique pour trois villes importante, Téhéran, Tabriz et Zandjan, situées dans le nord-ouest de l'Iran. Dans la capitale de l'Iran, Téhéran, nous nous sommes concentrés sur le système de faille active de Mosha-Nord Téhéran. Nos travaux démontrent que ce système est essentiellement décrochant sénestre. Nos analyses paléosismologiques sur la portion est de ce système (dans la vallée de Tar) montrent au minimum les évidences de sept grands événements sismiques (M>7) pendant les derniers 10000 ans (l'intervalle de récurrence est de 1100 à 1400 ans). Les études que nous avons mené dans la partie centrale de ce système (région d'Abali) révèlent qu'il pourrait être la source du dernier événement sismique ayant affecté la ville de Téhéran en 1830 AD. Dans la région de Tabriz, nous nous sommes intéressés au segment SE de la faille décrochante dextre de Nord Tabriz où nous avons trouvé les évidences de trois grands séismes pendant les derniers 33500 ans. Nos études montrent que la faille Nord Tabriz qui est la portion centrale d'un système de faille (TFS) est constituée par deux segments NW et SE dextres. Notre étude paléosismologique suggère une variation de la vitesse qui diminue du NW vers SE le long de ces segments. Les extrémités ouest (Mishu) et est (Bozghush) de ce système correspondent à des zones compressives qui absorbent les déplacements horizontaux sur les segments NW et SE. D'un point de vue général la TFS est une partie d'un système de failles régionales (GSKT) qui relie une zone d'extension active dans la partie centrale de la collision Arabie-Eurasie et une zone de compression active à l'Est. Enfin, à Zandjan qui est une ville située dans une région de lacune sismique, nous avons découvert un important réseau de failles actives. Le tracé sud-est de ce réseau de failles passe par la ville de Zandjan. En conclusion, les localisations et les cinématiques des systèmes de faille étudiés sont discutées dans le cadre géodynamique général de la collision Arabie-Eurasie. On remarquera que la faille majeure de Nord Tabriz qui correspond essentiellement à un décrochement dextre a la même direction NW-SE que les décrochements sénestres présents dans la chaîne de l'Alborz (les failles de : Mosha, Talaghan et Manjil). Cette observation nécessite une variation de la direction de compression entre ces deux régions.
https://tel.archives-ouvertes.fr/tel-00539739

tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739/document
https://tel.archives-ouvertes.fr/tel-00539739/file/thesesoleymani.pdf

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy P - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
The Pyrenean mountain range is a slowly deforming belt with continuous and moderate seismic activity. To quantify its deformation field, we present the velocity field estimated from a GPS survey of the Pyrenees spanning 18 yr. The PotSis and ResPyr networks, including a total of 85 GPS sites, were installed and first measured in 1992 and 1995–1997, respectively, and remeasured in 2008 and 2010. We obtain a deformation field with velocities less than 1 mm yr−1 across the range. The estimated velocities for individual stations do not differ significantly from zero with 95 per cent confidence. Even so, we estimate a maximum extensional horizontal strain rate of 2.0 ± 1.7 nanostrain per year in a N–S direction in the western part of the range. We do not interpret the vertical displacements due to their large uncertainties. In order to compare the horizontal strain rates with the seismic activity, we analyse a set of 194 focal mechanisms using three methods: (i) the ‘r’ factor relating their P and T axes, (ii) the stress tensors obtained by fault slip inversion and (iii) the strain-rate tensors. Stress and strain-rate tensors are estimated for: (i) the whole data set, (ii) the eastern and western parts of the range separately, and (iii) eight zones, which are defined based on the seismicity and the tectonic patterns of the Pyrenees. Each of these analyses reveals a lateral variation of the deformation style from compression and extension in the east to extension and strike-slip in the west of the range. Although the horizontal components of the strain-rate tensors estimated from the seismic data are slightly smaller in magnitude than those computed from the GPS velocity field, they are consistent within the 2σ uncertainties. Furthermore, the orientations of their principal axes agree with the mapped active faults.
ISSN: 0956-540X

hal-01171752
https://hal.archives-ouvertes.fr/hal-01171752
DOI : 10.1093/gji/ggv052