Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In orogenic systems, thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins (metamorphic, diagenetic, meteoric). This study focuses on the Monte Perdido thrust unit emplaced in the Paleogene Jaca thrust-sheet-top basin, in the SW-central Pyrenees. We aim to decipher the mechanisms and P-T conditions of deformation in fault zones and characterize the related fluid involvement, through combined microstructural, geochemical and microthermometry analyses. Two thrust faults cutting platform limestones, marls and siliciclastic turbidites of the lower part of the basin-fill (Paleocene-lower Eocene) have been studied. The fault zones are characterized by metre-thick shear zones with highly deformed, foliated clay-rich sediments. Foliation is underlined by preferentially oriented phyllosilicates. Several generations of shear and extension calcite, quartz and chlorite-bearing veins attest to fluid-rock interactions during a multi-stage deformation. Microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins, with mineralizing fluids in equilibrium with the host sediments. Our results suggest an essentially closed hydrologic system, and imply the absence of significant fluid flow along the studied fault zones. Microthermometric study on fluid inclusions present in calcite and quartz veins, and calcite-quartz oxygen isotopic fractionation determined for the first generation shear veins, allow a geothermal gradient of 34 degrees C/km to be estimated. Analytical results demonstrate an evolution of the fault zones in three stages. The first stage was related to the emplacement of the Monte Perdido thrust unit during the middle Eocene at a temperature of similar to 208 degrees C and a burial depth of similar to 5.7 km. The second stage corresponds to a fault reactivation at a temperature of similar to 240 degrees C and a burial depth of similar to 6.5 km. The latter deformation may have been related to folding of the Monte Perdido thrust unit during the emplacement of the underlying Gavarnie thrust unit during the late Eocene-early Oligocene, with deeper burial resulting from aggradation of the thrust-sheet-top basin-fill. The last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif.
ISSN: 0191-8141

hal-00644828
https://hal.archives-ouvertes.fr/hal-00644828
DOI : 10.1016/j.jsg.2011.06.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : This paper is the first presentation of a project called GHYRAF (Gravity and Hydrology in Africa) devoted to the detailed comparison between models and multidisciplinary observations (ground and satellite gravity, geodesy, hydrology, meteorology) of the variations of water storage in Africa from the Sahara and part to the monsoon equatorial part. We describe the various actions planned in this project. We first detail the actions planned in gravimetry which consist in two main surface gravity experiments: on the one hand the periodic repetition of absolute gravity measurements along a north-south monsoonal gradient of rainfall in West Africa, going from Tamanrasset (20 mm/year) in southern Algeria to Djougou (1200 mm/year) in central Benin; on the other hand the continuous measurements at Djougou (Benin) with a superconducting gravimeter to monitor with a higher sampling rate the gravity changes related to an extreme hydrological cycle. Another section describes the actions planned in GPS which will maintain and develop the present-day existing network in West Africa. The third type of actions deals with hydrology and we review the three sites that will be investigated in this joint hydrogeophysics project namely Wankama (near Niamey) and Bagara (near Diffa) in the Niger Sahelian zone and Nalohou (near Djougou) in the Benin monsoon zone. We also address the question of the ground truth of satellite-derived missions: in this context the GHYRAF project will lead to test the hydrology models by comparison both with in situ and satellite data such as GRACE, as well as to an important increase of our knowledge of the seasonal water cycle in Africa. We finally present preliminary results in GPS based on the analysis of the vertical motion of the Djougou site. The resulting absolute gravity changes related to the 2008 monsoon are finally given.
ISSN: 0264-3707

hal-00475660
https://hal.archives-ouvertes.fr/hal-00475660
DOI : 10.1016/j.jog.2009.09.014

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The timing of E–W extension of the Tibetan plateau provides a test of mechanical models of the geodynamic evolution of the India–Asia convergence zone. In this work we focus on the Kung Co half graben (Southern Tibet, China), bounded by an active N–S normal fault with a minimum vertical offset of 1600 m. To estimate the onset of normal faulting we combined high and medium temperature (U–Pb, Ar/Ar) and low temperature ((U–Th)/He) thermochronometry of the Kung Co pluton, a two-mica granite of the northern Himalayan granitic belt that outcrop in the footwall of the fault. Biotite and muscovite Ar/Ar ages , are close from each other [not, vert, similar 16 Ma ± 0.2 (Ms) and not, vert, similar 15 ± 0.4 Ma (Bt)], which is typical of fast cooling. The zircon and apatite (U–Th)/He ages range from 11.3 to 9.6 Ma and 9.9 to 3.7 Ma respectively. These He ages are indicative of (1) fast initial cooling, from 11.3 to not, vert, similar 9 Ma, gradually decreasing with time and (2) a high geothermal gradient (not, vert, similar 400 °C/km), close to the surface at not, vert, similar 10 Ma. The Kung Co pluton was emplaced at about 22 Ma (U–Pb on zircon) at less than 10 km depth and 520–545 °C. Subsequent to its shallow emplacement, the pluton underwent fast thermal re-equilibration ending around 7.5 Ma, followed by a period of slow cooling caused either by the end of the thermal re-equilibration or by very slow exhumation (0.02–0.03 mm/yr) from not, vert, similar 7.5 Ma to at least 4 Ma. In either case the data suggest that the exhumation rate increased after 4 Ma. We infer this increase to be related to the initiation of the Kung Co normal fault. A critical examination of previously published data show that most not, vert, similar N–S Tibetan normal faults may have formed less than 5 Ma ago rather than in the Miocene as assumed by several authors. Such a young age implies that E–W extension is not related to the Neogene South Tibetan magmatism (25 to 8 Ma). Consequently, models relating E–W extension to magmatism, such as convective removal of the lower lithosphere, may be inappropriate. We rather think that this extension is related with local accommodation of boundary forces and displacements.
ISSN: 0012-821X

hal-00311791
https://hal.archives-ouvertes.fr/hal-00311791
DOI : 10.1016/j.epsl.2007.01.029

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The cyanobacteria-derived neurotoxin β-methylamino-l-alanine (BMAA) represents a plausible environmental trigger for amyotrophic lateral sclerosis (ALS), a debilitating and fatal neuromuscular disease. With the eutrophication of water bodies, cyanobacterial blooms and their toxins are becoming increasingly prevalent in France, especially in the Brittany region. Cyanobacteria are monitored at only a few recreational sites, preventing an estimation of exposure of the human population. By contrast, phosphorus, a limiting nutrient for cyanobacterial growth and thus considered a good proxy for cyanobacteria exposure, is monitored in many but not all surface water bodies. Our goal was to develop a geographic exposure indicator that could be used in epidemiological research. We considered the total phosphorus (TP) concentration (mg/L) of samples collected between October 2007 and September 2012 at 179 monitoring stations distributed throughout the Brittany region. Using readily available spatial data, we computed environmental descriptors at the watershed level with a Geographic Information System. Then, these descriptors were introduced into a backward stepwise linear regression model to predict the median TP concentration in unmonitored surface water bodies. TP concentrations in surface water follow an increasing gradient from West to East and inland to coast. The empirical concentration model included five predictor variables with a fair coefficient of determination (R2 = 0.51). The specific total runoff and the watershed slope correlated negatively with the TP concentrations (p = 0.01 and p < 10− 9, respectively), whereas positive associations were found for the proportion of built-up area, the upstream presence of sewage treatment plants, and the algae volume as indicated by the Landsat red/green reflectance ratio (p < 0.01, p < 10− 6 and p < 0.01, respectively). Complementing the monitoring networks, this geographical modeling can help estimate TP concentrations at the watershed level, delivering a proxy for cyanobacteria exposure that can be used along with other risk factors in further ALS epidemiologic case–control studies
ISSN: 0160-4120

hal-01175538
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01175538
DOI : 10.1016/j.envint.2015.04.007
PUBMED : 25913322

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Understanding long-term variability in the frequency of intense storm activity is important for assessing whether changes are controlled by climate evolution. Understanding this variability is also important for predicting present and future community vulnerability and economic loss. Our ability to make these assessments has been limited by the short (less than 50 years) instrument record of storm activity. Storm-induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and storm activity on longer timescales. In this study, we present a record of these extreme climatic events that have occurred in the French Mediterrannean coast over the past 1500 years. The identification of these extreme events is based on the analysis of sediment cores from Gulf of Aigues-Mortes lagoons that contain a specific sedimentary and geochemical signature associated with intense storms.;Overwash deposits do not show any evidence of intense storm landfalls in the region for several hundred years prior to the late 17th century A.D. The apparent increase in intense storms around 250 years ago occurs during the latter half of the Little Ice Age, a time of lower continental surface temperatures. Comparison of the sediment record with palaeoclimate records indicates that this variability was probably modulated by atmospheric dynamics. The apparent increase of the superstorm activity during the latter half of the Little Ice Age was probably due to the thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large Central Atlantic/European domain and leading to a modification of the occurrence of extreme wind events along the French Mediterranean coast. A complete understanding of the relationship between climate fluctuations, storm activity, and the coastal response will be crucial to predicting the impacts of future climate change.
ISSN: 0031-0182

hal-00617525
https://hal.archives-ouvertes.fr/hal-00617525
DOI : 10.1016/j.palaeo.2010.11.009

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : The Oman ophiolite consists of several massifs cropping out along a 500 km long band trending NW-SE along the coast of Oman; it is one of the best exposed sections of oceanic crust and mantle in the world. There is a gradient in igneous processes and composition in the ophiolite, with the northern massifs recording a polygenetic igneous history involving an increasingly important subduction component, whereas the southern massifs were formed primarily via a mid-ocean ridge basalt (MORB)-like, single-stage process at a submarine spreading ridge. In this study we use geochemical data from Wadi Tayin, which is one of the southern massifs of the Oman ophiolite, to constrain the composition and genesis of oceanic crust and upper mantle. The Wadi Tayin harzburgites are residues of partial melting that are as depleted as the most depleted mid-ocean ridge peridotites. They have low middle- to heavy rare earth element ratios, most probably reflecting melting close to and beyond the exhaustion of clinopyroxene. Like many abyssal peridotites, the Wadi Tayin samples show enrichment in highly incompatible elements, giving rise to U-shaped MORB-normalized trace element patterns. We favor the idea that this is caused by enrichment of highly incompatible elements along grain boundaries in peridotite, which may be the result of near-equilibrium partitioning between grain boundaries and grain interiors, rather than disequilibrium processes. Equilibrium partitioning between crystals and grain boundaries during melting and melt extraction is also our preferred explanation for ubiquitous high Pb contents relative to Ce and La in our samples as well as in most abyssal peridotites. The Wadi Tayin samples record substantial variability in terms of osmium isotopic composition and platinum group element (PGE) concentrations. The more radiogenic nature of the dunites and impregnated peridotites compared with the residual harzburgites may be due to relatively high Os-187/Os-188 in melt transported through the dunites. The presence of residual peridotites with whole-rock osmium isotopic compositions less radiogenic than MORB may be explained by melting of a veined (upwelling) mantle forming mixed melts in which much of the Os derives from veins with high Re/Os in a matrix of previously depleted peridotite. An important result of this study is that the shallowest samples are refertilized (i.e. anomalously enriched in incompatible elements), and record relatively high metamorphic closure temperatures. These observations suggest that migrating melt underwent crystallization during rapid cooling in the uppermost mantle during and immediately after ridge magmatism. A variety of geothermometers all yield the result that the stratigraphically highest harzburgites equilibrated at higher temperature than the deeper ones. The systematic decrease in closure temperature with increasing depth below the Moho transition zone probably reflects systematic variation in cooling rate as a function of depth in the mantle section. We hypothesize that the refertilization and higher closure temperatures recorded by the uppermost mantle samples are linked. More rapid cooling led to higher closure temperatures, and to partial crystallization of migrating melts in the shallowest part of the mantle section, yielding slightly elevated abundances of elements such as Ca and Na, and incompatible trace elements.
ISSN: 0022-3530

hal-00456056
https://hal.archives-ouvertes.fr/hal-00456056
DOI : 10.1093/petrology/egp077

Éditeur(s) : HAL CCSD Ecological Society of America
Résumé : International audience
The main theories explaining the biological diversity of rain forests often confer a limited understanding of the contribution of interspecific interactions to the observed patterns. We show how two-species mutualisms can affect much larger segments of the invertebrate community in tropical rain forests. Aechmea mertensii (Bromeliaceae) is both a phytotelm (plant-held water) and an ant-garden epiphyte. We studied the influence of its associated ant species (Pachycondyla goeldii and Camponotus femoratus) on the physical characteristics of the plants, and, subsequently, on the diversity of the invertebrate communities that inhabit their tanks. As dispersal agents for the bromeliads, P. goeldii and C. femoratus influence the shape and size of the bromeliad by determining the location of the seedling, from exposed to partially shaded areas. By coexisting on a local scale, the two ant species generate a gradient of habitat conditions in terms of available resources (space and food) for aquatic invertebrates, the diversity of the invertebrate communities increasing with greater volumes of water and fine detritus. Two-species mutualisms are widespread in nature, but their influence on the diversity of entire communities remains largely unexplored. Because macroinvertebrates constitute an important part of animal production in all ecosystem types, further investigations should address the functional implications of such indirect effects.
Ecology

hal-00911501
https://hal.archives-ouvertes.fr/hal-00911501
https://hal.archives-ouvertes.fr/hal-00911501/document
DOI : 10.1890/09-1534.1
OATAO : 10118

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Numerical programs for simulating flow and reactive transport in porous media is essential for predicting reservoir properties related to CO2 sequestration performance, subsurface storage and risk assessment. In this paper we solve the Navier Stokes' equation using finite difference method, on a simulated porous rock structure, to study the velocity distribution of fluid flowing through it under a constant pressure gradient. A reactive solute carried through the fluid is allowed to interact with the minerals in the rock. This chemical reaction dissolves the mineral which changes the rock structure thus affecting its flow properties. These changes of flow properties are studied with variation in reactive solute concentration and pressure field. The different mechanisms of dissolution responsible for the variation of flow properties for the different parameters is predicted. Before the onset of homogeneous dissolution, variation in porosity follows a power-law behaviour with change in permeability when the latter is scaled by the concentration of the reactive species. The simulation results are compared with available experimental data and found to give a reasonable match.
ISSN: 0022-1694

hal-00757760
https://hal.archives-ouvertes.fr/hal-00757760
DOI : 10.1016/j.jhydrol.2012.05.024

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (40Ar/39Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60-100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8 Ma. The whole coastal area was uplifted at slow average rates (0.01-0.03 mm/y) in relation with a northeastward tilting of 0.2-0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.
ISSN: 0264-3707

hal-01053531
https://hal.archives-ouvertes.fr/hal-01053531
DOI : 10.1016/j.jog.2014.01.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Maguelone shore extends along the northern coast of the Gulf of Lions, west of the Rhone Delta and east of high-gradient coastal streams that have provided most of the clastic sediments to the Gulf of Lions margin since the early Miocene. This 10 km-wide area is constituted by a small coastal watershed (15 km long) in low-lying carbonate hills, a kilometre-wide marsh, a sandy beach barrier and a shoreface experiencing local low sedimentation rates. This onshore-offshore transition zone is a key area to understand the relationships between erosion, by-pass, deposition and preservation processes. Unlike the neighbouring Rhone deposits that display numerous thick deltaic sequences related to a continuous sediment flux, the Maguelone shore exhibits peculiar sedimentary bodies. The analysis of about 250 km of new VHR seismic profiles acquired over the study area, 9 short cores and outcrops data allowed us to determine the three-dimensional high-resolution geometry of the coastal system tracts from Quaternary to present-day. This revealed dominant denudation processes in the Upstream catchments associated with the formation of incised valleys during Quaternary lowstands. In addition, this study investigates the erosion and deposition mechanisms controlled by littoral hydrodynamics that have been taken place on this shore since the last transgression. In particular, metre-high and hundreds of metre-long sandy bodies constructed by alongshore hydrodynamics were identified and their effect on the morphodynamics of the whole littoral system is discussed. The Maguelone shore can be used as an experimental study for onshore/offshore dynamics under the influence of microtidal wave/current hydrodynamics and very low river-derived sediment flux during a eustatic cycle. Geometry of system tracts across flood plain to shoreface is usually considered to be controlled by relative sea-level changes, and is successfully analysed with 2D sequence stratigraphy cross-shore models. It is observed that in areas like the Maguelone shore, traditional sequence stratigraphy methods might not be fully relevant and need to integrate alongshore hydrodynamical processes.
ISSN: 0025-3227

hal-00421060
https://hal.archives-ouvertes.fr/hal-00421060
DOI : 10.1016/j.margeo.2009.06.008

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Geomorphic landscape features have been suggested as indicators of forest diversity. However, their explanatory power has not yet been explicitly tested at a regional scale in tropical rainforest. We used forest inventories conducted according to a stratified sampling design (3,132 plots in 111 transects at 33 sites) and holistic multi-scale geomorphological mapping derived from a Shuttle Radar Topography Mission digital elevation model to describe and explain spatial patterns in floristic composition across French Guiana (80,000 km2). We measured and identified 123,906 trees with DBH C20 cm and used constrained and unconstrained ordinations to analyze variations in the abundance of 221 taxa and 51 families. Variance partitioning and variograms were used to detect spatial patterns in species composition, compare the explanatory power of spatial and environmentalfactors, and select the variables that best explain forest composition. Strong floristic patterns corresponded to a major latitudinal gradient and significant sub-regional floristic structure. Geomorphological landscapes shaped by historic climate fluctuations and major geological events successfully captured these patterns and explained the variation in abundance of 80 taxa, corresponding to 65 % of the inventoried trees. Our findings suggest that long-term forest dynamics are under substantial ‘‘geomorphographic control’’. A geomorphological perspective on landscapes that incorporates current and past environmental filters and historical biogeographical processes could thus be used more systematically in tropical regions for regional planning and forest conservation
ISSN: 0960-3115

hal-01204224
https://hal.archives-ouvertes.fr/hal-01204224
DOI : 10.1007/s10531-014-0854-8
PRODINRA : 295767

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Analysis of the microstructures in the km-scale mantle shear zone that separates the northern and the central parts of the Lanzo peridotite massif provides evidence of an evolution in time and space of deformation processes accommodating shearing in the shallow mantle within an extensional setting. This shear zone displays an asymmetric distribution of deformation facies. From south to north, gradual reorientation of the foliation of coarse porphyroclastic plagioclase-bearing peridotites is followed by development of protomylonites, mylonites, and mm-scale ultramylonite bands. A sharp grain size gradient marks the northern boundary. Early deformation under near-solidus conditions in the south is recorded by preservation of weakly deformed interstitial plagioclase and almost random clinopyroxene and plagioclase crystal orientations. Feedback between deformation and melt transport probably led to melt focusing and strain weakening in the shear zone. Overprint of melt-rock reaction microstructures by solid-state deformation and decrease in recrystallized grain size in the protomylonites and mylonites indicate continued deformation under decreasing temperature. Less enriched peridotite compositions and absence of ultramafic dykes or widespread melt-impregnation microstructures north of the shear zone and clinopyroxene and amphibole enrichment in the mylonites and ultramylonites suggest that the shear zone acted as both a thermal barrier and a high-permeability channel for late crystallizing fluids. These observations, together with chemical data indicating faster cooling of central Lanzo relative to the northern body, corroborate that this shear zone is a mantle detachment fault. All deformation facies have crystal preferred orientations consistent with deformation by dislocation creep with dominant activation of the (010)[100] and (100)[001] systems in olivine and orthopyroxene, respectively. Dynamic recrystallization produces dispersion of olivine CPO but not a change of dominant deformation mechanism. Evidence for activation of grain boundary sliding is limited to mm-scale ultramylonite bands, where solid-state reactions produced very fine grained polymineralic aggregates. Except for these latest stages of deformation, strain localization does not result from the microstructural evolution; the grain size decrease is a consequence of the need to deform a rock volume whose strength continuously increases because of decreasing temperature conditions. Strain localization in the intermediate levels thus essentially results from the more localizing behavior of both the deep, partially molten, and shallow parts of this extensional shear zone distribution.
ISSN: 1525-2027

hal-00644844
https://hal.archives-ouvertes.fr/hal-00644844
DOI : 10.1029/2011GC003627

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : The analysis of fine-scale spatial genetic structure (FSGS) within populations can provide insights into eco-evolutionary processes. Restricted dispersal and locally occurring genetic drift are the primary causes for FSGS at equilibrium, as described in the isolation by distance (IBD) model. Beyond IBD expectations, spatial, environmental or historical factors can affect FSGS. We examined FSGS in seven African and Neotropical populations of the late-successional rain forest tree Symphonia globulifera L. f. (Clusiaceae) to discriminate the influence of drift-dispersal vs. landscape/ecological features and historical processes on FSGS. We used spatial principal component analysis and Bayesian clustering to assess spatial genetic heterogeneity at SSRs and examined its association with plastid DNA and habitat features. African populations (from Cameroon and São Tomé) displayed a stronger FSGS than Neotropical populations at both marker types (mean Sp = 0.025 vs. Sp = 0.008 at SSRs) and had a stronger spatial genetic heterogeneity. All three African populations occurred in pronounced altitudinal gradients, possibly restricting animal-mediated seed dispersal. Cyto-nuclear disequilibria in Cameroonian populations also suggested a legacy of biogeographic history to explain these genetic patterns. Conversely, Neotropical populations exhibited a weaker FSGS, which may reflect more efficient wide-ranging seed dispersal by Neotropical bats and other dispersers. The population from French Guiana displayed an association of plastid haplotypes with two morphotypes characterized by differential habitat preferences. Our results highlight the importance of the microenvironment for eco-evolutionary processes within persistent tropical tree populations.
ISSN: 1932-6203

hal-01608324
https://hal.archives-ouvertes.fr/hal-01608324
DOI : 10.1371/journal.pone.0182515
PRODINRA : 403154
PUBMED : 28771629

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. A substantial fraction of the freshwater available in neotropical forests is impounded within the rosettes of bromeliads that form aquatic islands in a terrestrial matrix. The ecosystem functioning of bromeliads is known to be influenced by the composition of the contained community but it is not clear whether bromeliad food webs remain functionally similar against a background of variation in the understorey environment. 2. We considered a broad range of environmental conditions, including incident light and incoming litter, and quantified the distribution of a very wide range of freshwater organisms (from viruses to macroinvertebrates) to determine the factors that influence the functional structure of bromeliad food webs in samples taken from 171 tank-bromeliads. 3. We observed a gradient of detritus-based to algal-based food webs from the understorey to the overstorey. Algae, rotifers and collector and predatory invertebrates dominated bromeliad food webs in exposed areas, whereas filter-feeding insects had their highest densities in shaded forest areas. Viruses, bacteria and fungi showed no clear density patterns. Detritus decomposition is mainly due to microbial activity in understorey bromeliads where filter feeders are the main consumers of microbial and particulate organic matter (POM). Algal biomass may exceed bacterial biomass in sun-exposed bromeliads where amounts of detritus were lower but functional diversity was highest. 4. Our results provide evidence that tank-bromeliads, which grow in a broad range of ecological conditions, promote aquatic food web diversity in neotropical forests. Moreover, although bromeliad ecosystems have been categorised as detritus-based systems in the literature, we show that algal production can support a non-detrital food web in these systems.
ISSN: 0046-5070

hal-00819103
https://hal.archives-ouvertes.fr/hal-00819103

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We analyze the kinematics of fault tip folding at the front of a fold-and-thrust wedge using a sandbox experiment. The analog model consists of sand layers intercalated with low-friction glass bead layers, deposited in a glass-sided experimental device and with a total thickness h = 4.8 cm. A computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation. Active deformation at the tip of the forward propagating basal décollement is monitored along the cross section with a high-resolution CCD camera, and the displacement field between pairs of images is measured from the optical flow technique. In the early stage, when cumulative shortening is less than about h/10, slip along the décollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium. In this stage of detachment tip folding, horizontal displacements decrease linearly with distance toward the foreland. Vertical displacements reflect a nearly symmetrical mode of folding, with displacements varying linearly between relatively well defined axial surfaces. When the cumulative slip on the décollement exceeds about h/10, deformation tends to localize on a few discrete shear bands at the front of the system, until shortening exceeds h/8 and deformation gets fully localized on a single emergent frontal ramp. The fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system. As long as strain localization is not fully established, the sand layers experience a combination of thickening and horizontal shortening, which induces gradual limb rotation. The observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds, relate finite deformation to incremental folding, and derive shortening rates from deformed geomorphic markers or growth strata.
ISSN: 2169-9313

hal-00138061
https://hal.archives-ouvertes.fr/hal-00138061
https://hal.archives-ouvertes.fr/hal-00138061/document
https://hal.archives-ouvertes.fr/hal-00138061/file/Bernard_et_al-2007-Journalsur Geophysical_Research__Solid_Earth_%281978-2012%29.pdf
DOI : 10.1029/2005JB004149

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Introduction The Latitudinal Gradient Hypothesis (LGH) foresees that specialized metabolites are overexpressed under low latitudes, where organisms are subjected to higher herbivory pressure. The widespread macroalga Asparagopsis taxiformis is composed of six distinct genetic lineages, some of them being introduced in many regions. Objectives To study (i) metabolic fingerprints of the macroalga and (ii) its bioactivity in space and time, both as proxies of its investment in defensive traits, in order to assess links between bioactivities and metabotypes with macroalgal invasiveness. Methods 289 macroalgal individuals, from four tropical and three temperate regions, were analyzed using untargeted metabolomics and the standardized Microtox (R) assay. Results Metabotypes showed a low divergence between tropical and temperate populations, while bioactivities were higher in temperate populations. However, these phenotypes varied significantly in time, with a higher variability in tropical regions. Bioactivities were high and stable in temperate regions, whereas they were low and much variable in tropical regions. Although the introduced lineage two exhibited the highest bioactivities, this lineage could also present variable proliferation fates. Conclusion The metabolomic approach partly discriminates macroalgal populations from various geographic origins. The production of chemical defenses assessed by the bioactivity assay does not match the macroalgal genetic lineage and seems more driven by the environment. The higher content of chemical defenses in temperate versus tropical populations is not in accordance with the LGH and cannot be related to the invasiveness of the macroalgae.
ISSN: 1573-3882

hal-01681538
https://hal.archives-ouvertes.fr/hal-01681538
DOI : 10.1007/s11306-017-1169-z

Éditeur(s) : HAL CCSD Wiley
Résumé : Tropical forests contain an important proportion of the carbon stored in terrestrial vegetation, but estimated aboveground biomass (AGB) in tropical forests varies two-fold, with little consensus on the relative importance of climate, soil and forest structure in explaining spatial patterns. Here, we present analyses from a plot network designed to examine differences among contrasting forest habitats (terra firme, seasonally flooded, and white-sand forests) that span the gradient of climate and soil conditions of the Amazon basin. We installed 0.5-ha plots in 74 sites representing the three lowland forest habitats in both Loreto, Peru and French Guiana, and we integrated data describing climate, soil physical and chemical characteristics and stand variables, including local measures of wood specific gravity (WSG). We use a hierarchical model to separate the contributions of stand variables from climate and soil variables in explaining spatial variation in AGB. AGB differed among both habitats and regions, varying from 78 Mg ha−1 in white-sand forest in Peru to 605 Mg ha−1 in terra firme clay forest of French Guiana. Stand variables including tree size and basal area, and to a lesser extent WSG, were strong predictors of spatial variation in AGB. In contrast, soil and climate variables explained little overall variation in AGB, though they did co-vary to a limited extent with stand parameters that explained AGB. Our results suggest that positive feedbacks in forest structure and turnover control AGB in Amazonian forests, with richer soils (Peruvian terra firme and all seasonally flooded habitats) supporting smaller trees with lower wood density and moderate soils (French Guianan terra firme) supporting many larger trees with high wood density. The weak direct relationships we observed between soil and climate variables and AGB suggest that the most appropriate approaches to landscape scale modeling of AGB in the Amazon would be based on remote sensing methods to map stand structure.
ISSN: 1354-1013

hal-01374829
https://hal.archives-ouvertes.fr/hal-01374829
DOI : 10.1111/j.1365-2486.2011.02432.x
PRODINRA : 183370

Éditeur(s) : HAL CCSD
Résumé : In this work on a complete transect of the west‐central Pyrenees, we combine low temperature thermochronology (apatite fission tracks, AFT) with a detailed structural analysis to describe vertical movements related to the thrusting system evolution, and to determine the influence of the latter on the sedimentation/burial/exhumation cycle of thesynorogenic deposits of the southern foreland basin (Jaca and Ainsa basins). AFT analysis from a transect of the south‐Pyrenean basin show the southward decrease of the fission track reset level from the southern edge of the Axial Zone to the South‐Pyreneanfrontal thrust, implying the southwards decrease of the burial amount from more than 5kmin the north to less than 3km in the south assuming an average geothermal gradient of 25°C.km‐1. The structural setting of the Jaca basin attests that the burial of the synorogenicsediments was mainly due to the sedimentary accumulation. AFT data from the northernpart of the basin display a late Oligocene‐early (middle) Miocene cooling event. Newinterpretation of industrial seismic reflection profiles across the Jaca basin suggests that the Oturia thrust is rooted in the Bielsa basement thrust, responsible for the early (‐middle) Miocene out‐of‐sequence tectonic reactivation of the southern flank of the Axial Zone (Jolivet et al., 2007). These results reveal a lower Miocene (Burdigalian ‐?Langhian) out‐of sequence episode of tectonic activity of the interior of the south‐Pyrenean foreland basin. AFT data from the Axial Zone and the North‐Pyrenean Zone confirm the general southwardmigration of the thrusting system, and also bring evidence of the late Oligocene‐lowe rMiocene out‐of‐sequence tectonic reactivation of the northern flank of the Axial Zone. All these results attest of a late Oligocene‐lower Miocene (Burdigalian‐?Langhian) "pop‐up" reactivation of the inner part of the west‐central Pyrenees, younger than the sealing of thesouth‐Pyrenean front (Aquitanian‐?Burdigalian) which is classically considered to mark the end of the Pyrenean compression. These results lead us to propose a new crustal scale evolution model of the west‐central Pyrenees in 3 stages: (i) From the Late Cretaceous to themiddle Eocene, the orogenic prism is characterised by the absence of relief, related to theinversion of Cretaceous extensional structures leading to the accretion of thin crustal units; (ii) The late Eocene‐Oligocene stage corresponds to the continental collision, marked by the creation of important relief associated with the accretion of thick crustal units; (iii) During the early Miocene, the inner part of the Pyrenean wedge is tectonically reactivated.
Ce travail de thèse concerne une transversale complète des Pyrénées centro-occidentales, où on a combiné la thermochronologie basse température (traces de fission sur apatites, TFA) avec une analyse structurale détaillée pour décrire les mouvements verticaux associés à l'évolution du système chevauchant, et pour déterminer l'influence de ce dernier sur le cycle sédimentation/enfouissement/exhumation des dépôts synorogéniques du bassin d'avant‐chaine sud (bassins de Jaca et Ainsa). L'analyse TFA complète les données déjà publiées dans la Zone Axiale et la Zone Nord‐Pyrénéenne, e tconstitue la première étude de ce genre dans un bassin d'avant‐chaîne pyrénéen. Les données TFA sur la transversale du bassin sud‐pyrénéen montrent une diminution vers le sud du degré d'effacement des traces de fission, traduisant la diminution vers le sud de la quantité d'enfouissement, supérieure à 5 km au nord et inférieure à 3 km au sud dans l'hypothèse un géotherme de 25°.km‐1. Le contexte géologique montre que l'enfouissement est principalement lié à l'accumulation des dépôts synorogéniques. Les données TFA de lapartie nord du bassin montrent un refroidissement d'âge Oligocène supérieur‐Miocèneinferieur (moyen). Par ailleurs, une nouvelle interprétation de profils de sismiques réflexiondans le bassin de Jaca montre que le chevauchement d'Oturia s'enracine dans lechevauchement de socle de Bielsa, responsable de l'exhumation tectonique hors‐séquencedu bord sud de la Zone Axiale au Miocène inférieur (‐moyen) (Jolivet et al., 2007). Cesrésultats attestent donc de l'exhumation tectonique hors‐séquence au Miocène inférieur (Burdigalien‐ ?Langhien) de la partie nord du bassin d'avant‐chaine sud‐pyrénéen. Des données TFA obtenues dans la Zone Axiale et la Zone Nord‐Pyrénéenne confirment lamigration générale vers le sud du système chevauchant, et mettent également en évidencela réactivation tectonique hors‐séquence du bord nord de la Zone Axiale à l'Oligocèneterminal‐Miocène inférieur. L'ensemble de ces résultats atteste donc de la réactivation en " pop‐up " de la parties interne des Pyrénées centre‐ouest à l'Oligocène supérieur‐Miocèneinférieur (Burdigalien‐ ?Langhien), postérieurement au scellement du front sud‐pyrénéen (Aquitanien‐ ?Burdigalien) classiquement considéré comme marquant la fin de lacompression pyrénéenne. Ces données nous ont permis de proposer un nouveau modèle d'évolution crustale des Pyrénées centro‐occidentales en 3 grandes étapes : (i) du Crétacé supérieur à l'Eocène moyen, le prisme est caractérisé par une absence de relief, en lien avec l'inversion de structures extensives crétacées conduisant à l'accrétion de petites écailles crustales ; (ii) la période Eocène supérieur‐Oligocène correspond à la collision continentale proprement dite, et est marquée par la création d'importants reliefs associés à l'accrétion d'épaisses unités crustales ; (iii) au Miocène inférieur, la partie interne du prisme pyrénéen est réactivée.
https://tel.archives-ouvertes.fr/tel-00772154

Droits : info:eu-repo/semantics/OpenAccess
tel-00772154
https://tel.archives-ouvertes.fr/tel-00772154
https://tel.archives-ouvertes.fr/tel-00772154/document
https://tel.archives-ouvertes.fr/tel-00772154/file/thesemeresse.pdf

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
P>The Strait of Hormuz area is a transition zone between the continental collision of the Zagros (west) and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (east). Geology and recent GPS measurements indicate that about 15 mm yr-1 of relative motion in N10 degrees E direction is accommodated by two major fault systems: (1) the NNW-trending Minab-Zendan-Palami (MZP) fault system that connects the Main Zagros Thrust (MZT) to the inner Makran thrust system and the Frontal subduction thrust and (2) the N-trending Sabzevaran-Kahnuj-Jiroft (SKJ) fault system that bounds the Jazmurian depression to the west. We use dense GPS measurements along four transects across these fault systems in order to determine the strains spatial distribution. The northern GPS transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses (about 10 and 7.3 mm yr-1 in N10 degrees direction across the MZP and SKJ fault systems, respectively). For both fault systems, the elastic deformation spreads over shear zones that are several tens of kilometres wide. However, transects located close to latitude 27 degrees N reveal a much narrower shear zone (similar to 10 km) for the MZP fault system. Moreover, we confirm that most of the present-day strain is transferred towards the frontal subduction thrust rather than towards the inner Makran thrusts. In order to complement this new GPS velocity field with spatially dense measurements, we processed a set of ERS radar images by the radar interferometry (InSAR) technique. We used both a 'stacking' and a 'persistant-scatterers' approach to differentiate the ground deformation signal which spatial gradient is expected to be very low, from the atmospheric signal. Results from these interferograms appear to be relatively in agreement with the GPS-determined strain distribution. Nevertheless, they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram. Finally, we use a purely kinematic 'block model' inversion process to calculate slip rates and locking depths for each fault system from our GPS measurements. These models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m. So, we may wonder if the MZP fault system is not late in the interseismic phase of its earthquake cycle.
ISSN: 0956-540X

hal-00429386
https://hal.archives-ouvertes.fr/hal-00429386
DOI : 10.1111/j.1365-246X.2009.04321.x

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
We explore the tectono-magmatic processes in the western West Philippine Basin, Philippine Sea Plate, using bathymetric data acquired in 2003 and 2004. The northwestern part of the basin formed through a series of northwestward propagating rifts. We identify at least five sequences of propagating rifts, probably triggered by mantle flow away from the mantle thermal anomaly that is responsible for the origin of the Benham and Urdenata plateaus. Gravitational forces caused by along-axis topographic gradient and a ∼30° ridge reorientation appear to also be driving the rift propagations. The along-axis mantle flow appears to be reduced and deflected along the Luzon-Okinawa fracture zone, because the spreading system remained stable west of this major fault zone. North-east of the Benham plateau, a left-lateral fracture zone has turned into a NE–SW-trending spreading axis. As a result, a microplate developed at the triple junction.
ISSN: 0954-4879

insu-00304360
https://hal-insu.archives-ouvertes.fr/insu-00304360
DOI : 10.1111/j.1365-3121.2008.00824.x