Éditeur(s) : HAL CCSD Société géologique de France
Résumé : The mechanical equilibrium of an orogenic wedge is maintained thanks to interactions between tectonic processes and surface processes. To better constrain the influence of erosion and sedimentation on the evolution of orogens, we performed a series of analogue models based on the tapered wedge principle, varying the amounts of erosion and sedimentation. The models develop by frontal accretion in the foreland basin and by simple underthrusting and subsequent underplating in the hinterland. The variations in rates of erosion and sedimentation strongly modify the extent, the morphology, the structures, the timing of development and the material paths in the different models. Under certain conditions, entire structural units can be formed and subsequently eroded out of the geological record, leading to important underestimations when restoring sections. Particles located in the converging lower-plate or in the upper-plate show complex uplift paths related to tectonic stages. The correlation between models and three Alpine tectonic cross-sections emphasizes the role of erosion and sedimentation on the dynamics and development of the orogen and adjacent Molasse basin. Along strike changes in the present structure of the orogen could be explained in part by differences in surface processes.
EISSN: 1777-5817

hal-00411140
https://hal.archives-ouvertes.fr/hal-00411140
DOI : 10.2113/gssgfbull.3.297

Éditeur(s) : OMICS Publishing Group
Résumé : Coastal tropical shrimp farming may impact the adjacent ecosystems through the release of large quantities of effluents rich in nutrients. In New Caledonia, mangroves are considered as a natural biofilter to reduce impacts on the surrounding World Heritage listed lagoon. Our main objective was to understand the influence of effluent discharge on the biogeochemistry of mangrove sediments. A monitoring of the physico-chemical parameters of mangrove sediments was carried out during a whole year, including active and non active periods of the farm. The parameters studied were: i) benthic primary production (Chl-a concentrations), ii) physico-chemical parameters of sediments (redox potential, pH, salinity, TOC, TN, TS, δ13C and δ15N), iii) concentrations of dissolved nitrogen, iron and phosphorus. A mangrove developing in the same physiographic conditions, presenting the same zonation, and free of anthropogenic input was used as reference. The concentration of benthic Chl-a measured at sediment surface in the effluent receiving mangrove was twice to three times that measured in the control zone whatever the season. We thus suggest that nutrients inputs significantly increased the phytobenthic production in the effluent receiving mangrove during the whole year, even after the cessation of discharges and because of natural seasonal dynamic of phytobenthos. Although the flow of surface OM was increased, the OM content at depth was not higher than in the control mangrove. However, the contribution of mangrove detritus to the sedimentary organic pool was higher probably as a result of higher density and much greater individual size of the mangrove trees. Unlike the control mangrove sediment, the effluent receiving mangrove sediment was not stratified, redox potential values were high and presence of Fe3+ was detected down to 50 cm depth, probably as a result of a larger root system, allowing a better sediment oxygenation and accentuated OM decomposition processes, and thus limiting ecosystem saturation.
Journal of Aquaculture Research & Development (21559546) (OMICS Publishing Group), 2014-07-03 , Vol. 5 , N. 5 , P. 1-13

Droits : 2014 Marchand C, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
http://archimer.ifremer.fr/doc/00251/36253/34801.pdf
DOI:10.4172/2155-9546.1000262
http://archimer.ifremer.fr/doc/00251/36253/

Résumé : Bacteriological study of abyssal sediments: During the Demeraby mission of the N/O Jean Charcot in the western Atlantic Ocean, a study of the microflora of the digestive tracts of echinoderms (Holothuroidea of various genera, Asteroidea, Echinoidea) was compared with that of the surrounding sediment. The bacterial concentration observed in the digestive tracts of all the animals studied is higher than that in the surrounding sediments. The largest numbers were always found in the most anterior part of the digestive tracts of the holothurians. In some cases, the increase is considerable (7.10 versus 5.2. 10 cells per millilitre): It indicates a proliferation of bacterial cells in the anterior part of the digestive tract. As the sediment moves through the digestive tract, the bacterial level progressively decreases. In the most posterior part, the concentration is, however, always clearly greater than that in the surrounding sediment. In the case of the holothurian of the genus Deima, analysis according to the Adamsonian principle of comparison shows that the microflora isolated from the various parts of the digestive tract is composed of taxonomic groups showing little resemblance to those isolated from the sediment. In the case of the holothurian of the genus Pseudostichopus, no specialisation of the microflora from digestive tract contents appears with respect to that of the ingested sediment. Examination of metabolic activities suggests a juxtaposition of two types of communities: Free sediment - sediment in transit that complement one other in their enzymatic and nutritional behaviour Indeed, the strains of free sediment seem to be rather suitable for hydrolysing and using carbohydrates, while those of enteric communities prefer the hydrolysis of lipids and proteins and the assimilation of fatty acids, dicarboxylic acids, hydroxylic acids and certain amino acids. Moreover, the enteric microflorae possess a greater nutritional versatility that, linked with its total numbers, has a sizeable catabolic potential. .../... -2- Measurements of heterotrophic activity done by means of 14 C glucose tracers make it possible to show that the metabolic activities of the bacterial communities of superficial abyssal sediments vary according to zones. In the Amazon Cone, a clear glucose mineralization gradient over a distance of a few kilometres can be observed. In the abyssal plain of Demerara heterotrophic activities are slowed in relation to those of the superficial sediments of the Cone of the Amazon, even though the bacterial numbers and the depths are of the same order of magnitude in the two zones. The abundant microflorae associated with the various divisions of digestive tract contents of the Deima abyssal holothurian manifest little metabolic activity as regards the glucose. However, the bacterial communities of Pseudostichopus and Psychropotes manifest very strong heterotrophic activities, increasing from the oesophagus towards the cloaca. Current results are too fragmentary to allow us to observe possible physiological specialisation of enteric bacterial communities enabling the facilitation of digestion processes in the host. Conclusion: In the abyssal environment, characterised by poorly developed bacterial communities, microflorae associated with the digestive tract contents of echinoderms have considerably greater cellular concentrations. By means of their enzymatic equipment, these enteric communities, which complement those of the free microflorae of superficial sediments, can participate in the transformation of organic matter in the abyssal area. Study of the dynamics of microbial communities and their heterotrophic activities in shellfish farms: From experiments done on the water in the Arcachon basin, trials to quantify and describe the reactivity potential of bacterial communities were performed. Bacterial communities were defined by direct counts, counts after setting them up for cultivation, structure and diversity of these communities, dosage of AMP, ADP, ATP. Two opposite ecological conditions were considered: Autumn conditions (high temperature) and a winter conditions (low temperature). Tubs of sea water of 6 and 60 litres were enriched either with ammonium chloride or a mixture of amino acids, at about 500 uAtg N.L. The experiments lasted 24 hours, with sampling every 3 hours. The autumn community reacted rapidly (6 hours), the response to the enrichment in organic nitrogen being the highest. The structure of the community has unstable immature stages. On the contrary, during the winter experiment, no response could be perceived. This may mean that the latency phase is greater than 24 hours. The structure of this community has mature stages. In conclusion, bacterial communities react in the same way as macroscopic communities. Stable communities are diversified and correspond to mature stages of the ecosystem; the immature stages are unstable and less diversified. This type of experiment has made it possible to bring to light the rapidity of response of bacterial populations, and can be used to define the stability of a bacterial community in a precise biotope.
ETUDE BACTERIOLOGIQUE DES SEDIMENTS ABYSSAUX RESUME Au cours de la mission DEMERABY du n/o Jean CHARCOT en atlantique occidental , une étude de la microflore des tractus digestifs d'Echinodermes (Holothurides de différents genres, Astérides, Echinides) a été comparée à celle du sédiment environnant. La concentration bactérienne observée dans les tractus digestifs de tous les animaux étudiés est supérieure à celle des sédiments environnants. Les effectifs les plus importants sont toujours observés dans la partie la plus antérieure des tractus digestifs des holothuries. Dans certains cas, l'accroissement est considérable (7.10 contre 5,2. 10 cellules/ml) : il indique une prolifération des cellules bactériennes dans la partie antérieure du tractus digestif. Au.cours de la progression du sédiment dans le tractus digestif, la charge bactérienne décroit progressivement. Dans la partie la plus postérieure, la concentration est cependant toujours nettement supérieure à celle du sédiment environnant-. Dans le cas d'une holothurie du genre Deima, l'analyse selon le principe adansonien de comparaison montre que la microflore isolée des différentes parties du tractus digestif est constituée de groupes taxonomiques présentant peu de ressemblance avec ceux isolés du sédiment. Dans le cas d'une holothurie du genre Pseudostichopus il n'apparait pas de spécialisation de la microflore du contenu du tractus digestif par rapport à celle du sédiment ingéré. ¿ ¿ . L'étude des activités métaboliques suggère une juxtaposition de deux types de communautés : sédiment libre-sédiment en transit qui se complètent dans leur comportement enzymatique et nutritionnel. En effet les souches du sédiment libre semblent être plutôt aptes à hydrolyser et à utiliser les glucides, tandis que celles des communautés entériques portent leur préférence sur l'hydrolyse des lipides et protéines et 1'assimilation des acides gras, acides dicarboxyl iques, hydro'xy-acides et certains acides aminés. D'autre part les microflores entériques possèdent une versatilité nutritionnelle plus importante qui, liée à leurs effectifs, offre une potentialité catabolique non négligeable. .../... -2- Les mesures d'activité hétérotrophe effectuées au moyen de traceurs glucose 14 C permettent de montrer que les activités métaboliques des communautés bactériennes des sédiments abyssaux superficiels varient selon les zones. Dans le Cone de l'Amazone on observe un net gradient de minéralisation du glucose sur une distance de quelques kilomètres. Dans la plaine abyssale de Demerara les activités hétérotrophessont ralenties par rapport à celles des sédiments superficiels du Cone de l'Amazone, bien que les effectifs bactériens et les profondeurs soient du même ordre de grandeur dans ces deux zones. Les abondantes microflores associées aux différentes fractions du contenu du tractus digestif de l'holothurie abyssale Deima ne manifestent que peu d'activités métaboliques vis à vis du glucose. Par contre les communautés . bactériennes de Pseudostichopus et P syahropotes manifestent des activités hétérotrophes très fortes, croissant de 1'oesophage vers le cloaque. Les résultats actuels sont trop fragmentaires pour permettre d'observer une éventuelle spécialisation physiologique des communautés bactériennes entëriques permettant de faciliter les processus de digestion chez l'hôte. Conclusion: dans le milieu abyssal, caractérisé par des communautés bactériennes faiblement développées, les microflores associées aux contenus de tractus digestif des Echinodermes présentent des concentrations cellulaires considérablement plus importantes. Par leurs équipements enzymâtiques ces communautés entëriques complémentaires de ceux des microflores libres des sédiments superficiels, peuvent participer à la transformation des matières organiques du domaine abyssal. ETUDE DE LA DYNAMIQUE DES COMMUNAUTES MICROBIENNES ET DE LEURS ACTIVITES HETEROTROPHES DANS LES PARCS CONCHYLICOLES RESUME A partir d'expérimentations effectuées sur l'eau du bassin d'Arcachon, des essais de quantification et qualification du potentiel de réactivité des communautés bactériennes ont été effectuées. Les communautés bactériennes ont été définies par comptage directs, comptages après mise en culture, structure et diversité de ces communautés, dosage des AMP, ADP, ATP. Deux situations écologiques opposées ont étées considérées . Une situation automnale (température élevée) et une situation hivernale (température faible). Des bacs d'eau de mer de 6 et 60 litres ont été enrichis , soit avec du chlorure d'ammonium, soit avec un mélange d'acides aminés, à environ 500 uAtg N.l" . Les expériences ont duré 24 heures, avec des prélèvements toutes les 3 heures. La communauté automnale réagit rapidement (6 heures), la ' réponse à l'enrichissement en azote organique étant la plus importante. La structure de la communauté présente des stades immatures instables. Au contraire, au cours de l'expérimentation hivernale, aucune réponse n'a pu être perçue. Ceci peut signifier que la phase de latence est supérieure à 24 heures. La structure . de cette communauté présente des stades matures. En Conclusion, les communautés bactériennes réagissent de la même façon que les communautés macroscopiques. Les communautés stables sont diversifiées et correspondent à des stades matures de l'écosystème, les stades immatures sont instables et moins diversifiés. Ce type d'expérience a permi de mettre en évidence la rapidité de réponse des populations bactériennes, et peut être utilisé pour définir la stabilité d'une communauté bactérienne dans un biotope précis.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1981/rapport-1926.pdf
http://archimer.ifremer.fr/doc/00000/1926/

Éditeur(s) : HAL CCSD MAIK Nauka/Interperiodica
Résumé : Interaction between surface processes and deep tectonic processes plays a key role in the structural evolution, kinematics and exhumation of rocks in orogenic wedges. The deformation patterns observed in analogue models applied to natural cases of present active or ancient mountain belts reflect several first order processes that result of these interactions. Internal strain partitioning due to mechanical behaviour of a thrust wedge has a strong impact on the vertical component of displacement of tectonic units that in return favour erosion in domains of important uplift. Such strain partitioning is first controlled by tectonic processes, but surface processes exert a strong feed back on wedge dynamics. Indeed, material transfer in thrust wedges not only depends on its internal dynamics, it is also influenced by climate controlled surface processes involving erosion and sedimentation. Effects of erosion are multiple: they allow long term localization of deformed domains, they favour important exhumation above areas of deep underplating and combined with sedimentation in the foreland they contribute to maintain the wedge in a critical state for long time periods. The simple models illustrate well how mountain belts structure, kinematics of tectonic units and exhumation are determined by these complex interactions.
ISSN: 0016-8521

hal-00561361
https://hal.archives-ouvertes.fr/hal-00561361
DOI : 10.1134/S0016852110060075

Éditeur(s) : HAL CCSD
Résumé : The field campaign on the Sète coast deployed during the winter 2009 was used to understand the hydrodynamics on a double barred beach in the surf zone during storm periods. The large set of measurements collected at several position and depth were also useful to improve the 3D circulation model Symphonie that takes into account the atmospherics and wave forcings. Once implemented on the beach and supplemented with some additional parameterizations concerning the roller effects and the bottom friction, the model was tuned and validated in the surf zone. The role of the different processes was then analysed. Thus, the roller and the bottom friction are of primary importance in the dynamics of the circulation. Thanks to its 3D nature and once associated with a sediment transport model and a morphodynamic model, Symphonie will offer a good representation of the sediment transport.
Coastal Dynamics 2013
Arcachon, France

hal-00855035
https://hal.archives-ouvertes.fr/hal-00855035

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The contourite depositional system (CDS) along the southwestern Iberian Margin (SIM), within the Gulf of Cadiz and offshore areas of western Portugal bear the unmistakable signal of Mediterranean Outflow Water (MOW) exiting the Strait of Gibraltar. This locality records key information concerning the effects of tectonic activity on margin sedimentation, the effects of MOW dynamics on Atlantic circulation, and how these factors may have influenced global climate. Over the last four decades, numerous studies have been conducted on the late Miocene, Pliocene and Quaternary sedimentary stacking pattern of Neogene basins along the SIM for both academic and resources exploration purposes. However, understanding of the region rests primarily on basic seismic stratigraphy calibrated with limited data from only a few exploration wells. The Integrated Ocean Drilling Program (IODP) Expedition 339 recently drilled five sites in the Gulf of Cadiz and two sites on the western Iberian margin. The integration of core and borehole data with other geophysical databases leads us to propose a new stratigraphic framework. Interpretation of IODP Exp. 339 data along with that from industry sources and onshore outcrop analysis helps refine our understanding of the SIM's sedimentary evolution.We identify significant changes in sedimentation style and dominant sedimentary processes, coupled with widespread depositional hiatuses along the SIM within the Cadiz, Sanlucar, Doñana, Algarve and Alentejo basins. Following the 4.5 Ma cessation of a previous phase of tectonic activity related to the Miocene–Pliocene boundary, tectonics continued to influence margin development, downslope sediment transport and CDS evolution. Sedimentary features indicate tectonic pulses of about 0.8–0.9 Ma duration with a pronounced overprint of ~ 2–2.5 Ma cycles. These more protracted cycles relate to the westward rollback of subducted lithosphere at the convergent Africa-Eurasia plate boundary as its previous NW–SE compressional regime shifted to a WNW–ESE direction. Two major compressional events affecting to the Neogene basins at 3.2–3 Ma and 2–2.3 Ma help constrain the three main stages of CDS evolution. The stages include: 1) the initial-drift stage (5.33–3.2 Ma) with a weak MOW, 2) a transitional-drift stage (3.2–2 Ma) and 3) a growth-drift stage (2 Ma-present time) with enhanced MOW circulation into the Atlantic and associated contourite development due to greater bottom-current velocity. Two minor Pleistocene discontinuities at 0.7–0.9 Ma and 0.3–0.6 Ma record the effects of renewed tectonic activity on basin evolution, appearing most prominently in the Doñana basin. Several discontinuities bounding major and minor units appear on seismic profiles. Quaternary records offer the clearest example of this, with major units of about 0.8–0.9 Ma and sub-units of 0.4–0.5 Ma. Sedimentation is controlled by a combination of tectonics, sediment supply, sea-level and climate. This research identifies time scales of tectonic controls on deep-marine sedimentation, specifically over periods of 2.5–> 0.4 Ma. Shorter-term climatic (orbital) mechanisms control sedimentation at time scales of ≤ 0.4 Ma. The role of bottom water circulation and associated processes in shaping the seafloor and controlling the sedimentary stacking pattern on continental margins has to be seriously reconsidered in future multidisciplinary studies. This is not only because of the common occurrence of sandy contourite deposits in deep water setting and their economic interest for hydrocarbon exploration, but principally because they archive the heartbeat of the interior Earth and therefore have important sedimentary and paleoceanographic implications.
ISSN: 0025-3227

hal-01356166
https://hal.archives-ouvertes.fr/hal-01356166
DOI : 10.1016/j.margeo.2015.09.013

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The growth of relief in active tectonic areas is mainly controlled by the interactions between tectonics and surface processes (erosion and sedimentation). The study of long-lived morphologic markers formed by these interactions can help in quantifying the competing effects of tectonics, erosion and sedimentation. In regions experiencing active extension, river-long profiles and faceted spurs (triangular facets) can help in un- derstanding the development of mountainous topography along normal fault scarps. In this study, we devel- oped analogue experiments that simulate the morphologic evolution of a mountain range bounded by a normal fault. This paper focuses on the effect of the fault slip rate on the morphologic evolution of the foot- wall by performing three analogue experiments with different fault slip rates under a constant rainfall rate. A morphometric analysis of the modelled catchments allows comparing with a natural case (Tunka half- graben, Siberia). After a certain amount of fault slip, the modelled footwall topographies of our models reaches a dynamic equilibrium (i.e., erosion balances tectonic uplift relative to the base level) close to the fault, whereas the topography farther from the fault is still being dissected due to regressive erosion. We show that the rates of vertical erosion in the area where dynamic equilibrium is reached and the rate of re- gressive erosion are linearly correlated with the fault throw rate. Facet morphology seems to depend on the fault slip rate except for the fastest experiment where faceted spurs are degraded due to mass wasting. A stream-power law is computed for the area wherein rivers reach a topographic equilibrium. We show that the erosional capacity of the system depends on the fault slip rate. Finally, our results demonstrate the pos- sibility of preserving convex river-long profiles on the long-term under steady external (tectonic uplift and rainfall) conditions.
ISSN: 0040-1951

hal-00646966
https://hal.archives-ouvertes.fr/hal-00646966
https://hal.archives-ouvertes.fr/hal-00646966/document
https://hal.archives-ouvertes.fr/hal-00646966/file/preprint_Strak_2011.pdf
DOI : 10.1016/j.tecto.2011.10.005

Éditeur(s) : HAL CCSD
Résumé : The evolution of mountain belt piedmont is controlled by interactions between tectonics, erosion and sedimentation. To study coupling between these processes, we analyze morphometric data collected in the eastern Tian Shan piedmont (NW China) and develop a new analogue modelling technique. The modeling approach uses an experimental set-up and analog material specifically designed to study simultaneously tectonic structures (faults, folds), detailed morphology (drainage basins, channels, alluvial fans, etc.) and stratified sedimentation. Measurement techniques based on laser interferometry and image correlation are also developed to quantify the topographic and kinematic evolution of models.
Our experiments allow a new approach for the study of piedmont morphotectonic evolution. Our results indicate that tectonics mainly controls this evolution. The propagation of deformation and the formation of relief both significantly influence the development of drainage networks, the evolution of drainage basins and the formation of morphotectonic markers. Particularly, a study of alluvial fans and watershed metrics suggests that there is a dynamical equilibrium between uplift, erosion and morphology. In addition, our results show that terrace nucleation is controlled by thrust activity and hydrography adjustments. Folding of terraces responds to a homothetic deformation pattern.
This new methodology brings promising perspectives in the fields of geomorphology, seismotectonics and sedimentology.
L'évolution d'un piémont de chaîne de montagnes est contrôlée par les interactions entre la tectonique, l'érosion et la sédimentation. Pour étudier ces processus, nous avons analysé des données morphométriques issues des piémonts orientaux du Tian Shan (NW Chine) et développé un nouveau type de modélisation analogique. Cette approche utilise un dispositif et un matériau expérimental spécialement conçus pour modéliser simultanément des structures tectoniques (failles, plis), une morphologie détaillée (bassins versants, rivières, cônes alluviaux, etc.) et une sédimentation stratifiée. Des techniques de mesure optique ont été également mises en oeuvre afin de quantifier l'évolution topographique et cinématique des modèles.
Les expériences réalisées offrent une opportunité inédite d'étudier l'évolution morphotectonique d'un piémont. Nos résultats montrent que la tectonique exerce un contrôle de premier ordre sur cette évolution. La propagation de la déformation et la formation des reliefs influencent en effet significativement le développement du réseau de drainage, l'évolution des bassins versants et la formation des marqueurs morphotectoniques. En particulier, l'analyse de la morphométrie des cônes alluviaux et de leurs bassins versants suggère qu'un équilibre dynamique s'installe entre la surrection, l'érosion et la morphologie. Nos résultats montrent également que l'apparition des terrasses est guidée par l'activité des chevauchements et les adaptations de l'hydrographie. Leur modèle de plissement répond à une déformation homothétique.
Cette nouvelle approche ouvre des perspectives d'étude prometteuses en géomorphologie, sismotectonique et stratigraphie.
https://tel.archives-ouvertes.fr/tel-00339145

tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145
https://tel.archives-ouvertes.fr/tel-00339145v2/document
https://tel.archives-ouvertes.fr/tel-00339145/file/These_Graveleau08.pdf

Éditeur(s) : HAL CCSD
Résumé : At present, the forecasting of littoral evolution presents a considerable social stake. Many studies have been achieved to better understand coastal dynamics. Such dynamics are controlled by morphology, sediment supply, hydrodynamics, eustacy... at different time scales. At geological time scale, deposits geometry, controlled by eustacy and subsidence, is succesfully analysed where sediment supply is high. But the littoral zones present important sediment supply variability. In low sediment supply areas, the record of coastal tracts is smaller and harder to interprete. Analyses of about 250 kilometres of new VHR seismic profiles acquired along the languedocian coast (Northern Gulf of Lion, France), tens of short cores and outcrops data allowed us to determine the three-dimensional high-resolution geometry of the coastal tracts from Quaternary to present-day. This highlighted the role of alongshore dynamics in coast where direct sediment supply is low. The concepts of protected lagoon and isolated lagoon were broughted to the fore and the effect of inherited incised valley morphology was discussed. Last, a complementary study by analogue modeling of the channel incision processes controled by eustatic and climatic changes allowed to discuss the role of incised valleys in coastal areas.
Actuellement, la prévision de l'évolution d'un système littoral représente un enjeu social important. De nombreuses études sont réalisées afin de mieux connaitre la dynamique côtière et donc de comprendre les facteurs qui influencent son évolution. Cette dynamique est contrôlée par la morphologie, les apports sédimentaires, l'hydrodynamique, l'eustatisme... qui agissent à des échelles de temps différentes et avec de fortes interactions. A l'échelle géologique, l'architecture des dépôts, contrôlée par l'eustatisme et la subsidence, est parfaitement décrite dans les zones à forts apports sédimentaires. Par contre, dans les zones à faibles apports sédimentaires, l'enregistrement des cortèges côtiers est réduit et est difficile à interpréter. L'analyse de 250 kilomètres de profils sismiques THR sur le littoral languedocien (Nord du Golfe du Lion, France), de carottages et de données de terrain a permis de déterminer la géométrie en trois dimensions des cortèges sédimentaires côtiers depuis le Quaternaire jusqu'à l'actuel. Ces observations montrent l'importance de la dynamique longshore sur les littoraux pauvres en apports sédimentaires directs. De plus, l'étude d'un système lagunaire sur ce littoral met en évidence les concepts de lagunes protégées et lagunes isolées ainsi que l'importance des vallées incisées dans la génèse de ces environnements. Enfin, la modélisation en laboratoire des processus d'incision de chenaux sous contrôle eustatique et climatique permet de discuter le rôle des vallées incisées en milieu côtier.
https://tel.archives-ouvertes.fr/tel-00542897

tel-00542897
https://tel.archives-ouvertes.fr/tel-00542897
https://tel.archives-ouvertes.fr/tel-00542897/document
https://tel.archives-ouvertes.fr/tel-00542897/file/theseraynaldef.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In fold and thrust belts drainage organization and patterns of sedimentation depend conceptually on the ability or not for preexisting reaches to incise uplifting thrust sheets. In this study we investigate experimentally the dynamics of drainage network in a wedge submitted to shortening and erosion. It allows us to reproduce and to monitor the interactions between tectonics, erosion and sedimentation during the development of up to five successive thrust sheets. In the experiments channels adjust to uplift rate by both increasing their slope and narrowing their channels as it is observed in nature. The series of experiments shows that the proportion of persistent preexisting transverse channels increases with the ratio of rainfall over shortening rates. The experiments confirm the view that the competition between discharge and tectonic uplift controls along-strike variations in sediment flux in sedimentary basins by controlling the drainage organization. If the transverse channels draining a wedge are not diverted, a line-source dispersal system develops in front of the active structure. If channels are diverted in the backlimb of the frontal structure it results in point-sourced depositional systems separated by areas fed only by small channels developing in the front of the wedge. Fans accumulated in front of the active structures reveal two stages of sedimentation, one of progradation, while the frontal structure is active and a second one of valley backfilling and thrust sealing during internal deformation of the wedge. The experiments also suggest that spatial variations in rock uplift rate along a thrust front may be evidenced by minimum-discharge variations of persistent transverse channels.
ISSN: 0040-1951

insu-01252482
https://hal-insu.archives-ouvertes.fr/insu-01252482
DOI : 10.1016/j.tecto.2015.09.007

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : A study combining very high resolution seismic and sediment core data has been carried out on the Thau lagoon (Mediterranean coast, microtidal setting, SE France) in order to understand more clearly the dynamics and Holocene chronology of its closure through the different stages of its filling. One main seismic unit (U2) has been defined into the infill, above the rocky basement (U0) and a composite unit U1, which is interpreted as remnants of Pleistocene fluvial terraces or/and to early marine Holocene deposits. Unit U2, that reaches locally 9 m in thickness, rests conformably on U1 in the central part of the lagoon and onlaps U0 or U1 close to the edge of the lagoon. It is divided in two sub-units, U2-1 and U2-2. U2-2 rests paraconformably on U2-1 in the central part of the lagoon where the infill is the thickest, while a marked erosional unconformity is observed between U2-1 and U2-2 on topographic highs of the basement and on the seaward edge of the lagoon. A total of seven elementary sequences have been observed in U2-1 and U2-2.;According to core data, U2 consists in a series of mud-dominated sequences, with shell fragments dispersed at the base. The vertical distribution of the fauna into U2-1 and U2-2 reveals a lagoonal environment. However in U2-1, marine species are more abundant in the south of the lagoon. C-14 AMS dating provides three ages: similar to 6000 cal yr B.P. in the lower part of U2-1 on CAL1, 5400 cal yr B.P. just above the boundary between U2-1 and U2-2 on CAL4, similar to 3000 cal yr B.P. in the middle of U2-2 on CAL4.;A scenario to explain the lagoon infill stratigraphy and geometry is proposed. The beginning of the lagoon infill occurred with the initiation of the barrier construction, as soon as the sea-level rise slowed down significantly, i.e. between 7000-6000 yr B.P. The sediment-fill began into the back-barrier system, with a high rate of sedimentation for U2-1, according to the radiocarbon data. At 5400 yr B.P., the barrier is assumed to be totally closed leading to the deposition of the fully lagoonal U2-2 succession. The unconformity between U2-1 and U2-2 is interpreted as the result of a rapid landward retreat of the barrier. This severe retreat could be related to climate forcing and/or brutal change in sediment discharge driven by the Rhone River, which is the main sediment source of the longshore drift. In this scenario, the last sub-unit, U2-2, represents most of the late Holocene infill. In this framework, the elementary sequences observed in U2-2 could be related to high frequency climate changes of about 1000-1500 years periodicity according to C-14 dates.
EISSN: 1777-5817

hal-00486386
https://hal.archives-ouvertes.fr/hal-00486386
DOI : 10.2113/gssgfbull.181.2.197

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Multi-proxy analysis of two marine sediment cores (MS27PT and MD04-2726) from the Nile continental slope provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in the Nile headwaters. Sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance, with sources oscillating between a Saharan aeolian contribution during the Last Glacial Maximum/deglacial transition and during the Late Holocene, and a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP). This study provides a new understanding of past environmental changes. Between 14.6 and 14.13 ka there was a major input of sediments from the Ethiopian Highlands, consistent with a stronger EAM at that time. Climate in the Nile basin was wetter between 14.8 and 8.4 ka, with a corresponding increase in Blue Nile water and sediment discharge via the main Nile into the Eastern Mediterranean. The gradual climatic transition from the AHP to the present-day dry climate was reflected in a decrease in Blue Nile sediment deposition and flood discharge between 8.4 and 3.7 ka, with aridity at a maximum between 3.7 and 2.6 ka. The onset of drier conditions in the Blue Nile basin seems to have begun before the 8.2 ka cooling event in the North Atlantic. We speculate that the climatic change from the wet AHP to the dry late Holocene may have been a result of a break in the low latitude dynamic equilibrium between climate, vegetation and erosion, which may in turn have affected the climate in higher latitudes. Reduced Nile flow may also have had an impact on Levantine Intermediate Water originating in the Eastern Mediterranean through an increase in intermediate water formation.
ISSN: 0277-3791

hal-01277950
https://hal.archives-ouvertes.fr/hal-01277950
DOI : 10.1016/j.quascirev.2015.10.030

Éditeur(s) : Springer
Résumé : The Golo Margin in eastern Corsica is dissected by four canyons and two gullies which fed turbidite systems. Study of the dispersal of surficial sediments and flow dynamic in the Golo system is based on Kullenberg and interface cores interpreted in relation to a previously published seismic dataset. Cores were described in detail and interpreted within a sedimentary and stratigraphic framework. During the last 42,000 years, gravity processes which occurred in the large systems with a canyon source were mainly slide-induced, differentiated turbulent surges and hyperpycnal flows. Processes occurring in the small system with a gully source are mainly hyperconcentrated and concentrated flows. Deposits from the Corsican Margin can intercalate with products of processes triggered on the Pianosa Ridge located in the eastern part of the basin. During relative sea-level lowstands or during periods of rapid or high-amplitude sea-level fall, only large canyons (South and North Golo) are supplied by carbonate-rich hyperconcentrated and concentrated flows which are channelled in incised valleys on the shelf. During periods of slow or low-amplitude sea-level fall and during sea-level rise, sediments are trapped on a shelf delta and intensely winnowed by shelf hydrodynamic processes. Sand-rich hyperconcentrated and concentrated flows occur. All the systems fed by a canyon are active simultaneously. Gullies form and are active only during periods of sea-level rise. During relative highstands of sea level (Holocene), all the system is draped by hemipelagic sediments. Relative sea-level changes and canyon location relative to river mouths have a strong influence on the nature of sediment input, and the initiation and type of gravity flows which, in turn, control morphology and geometry.
Geo-Marine Letters (0276-0460) (Springer), 2006-12 , Vol. 26 , N. 6 , P. 373-395

Droits : 2006 Springer
http://archimer.ifremer.fr/doc/2006/publication-3594.pdf
DOI:10.1007/s00367-006-0045-z
http://archimer.ifremer.fr/doc/00000/3594/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The structure and dynamic evolution of a mountain belt piedmont are controlled by strong interactions between tectonics, surface processes (erosion, sedimentation), and climate. Studying these couplings relies on detailed geometric and kinematic analysis of morphostructural markers (folds, faults, terraces, alluvial surfaces) and analysis of syntectonic sedimentation. To study quantitatively how these markers form, evolve and record deformation, we developed a new analogue modelling approach using a specific composite granular material. The originality stands in the simultaneous modelling of orogenic deformation mechanisms and erosion-transport-sedimentation processes, but also in the use of techniques allowing quantitative measurement of morphostructural evolution. This methodology opens new perspectives in the fields of geomorphology (relief dynamics), seismotectonics (study of active faults), and sedimentology (including sequential stratigraphy).
ISSN: 0010-7999

hal-00411972
https://hal.archives-ouvertes.fr/hal-00411972
DOI : 10.1016/j.crte.2008.01.005

Éditeur(s) : Elsevier
Résumé : A field survey was conducted on two intensive shrimp farms using similar technical practices: one (DF) historically affected by a vibriosis, the other (HC) in which the pathogen has been observed although no mortality event has occurred. Because historical data suggest that eutrophication process may directly or indirectly play a role in the disease outbreak, we focussed our research on its dynamics. A higher variability of the phytoplanktonic compartment linked to an imbalance in the molar N:P ratio was observed in farm DF compared to farm HC, implying a modification on the linkage between the bacteria and phytoplankton compartments at DF. The beginning of the mortality outbreak at DF followed a shift from picoto nanophytoplankton. The organic matter mineralization process at the water-sediment interface may explain the disturbance observed in the water column during eutrophication. The consequences of this disturbance on shrimps' health status and pathogen ecology are discussed. (C) 2009 Elsevier Ltd. All rights reserved.
Marine Pollution Bulletin (0025-326X) (Elsevier), 2010-03 , Vol. 60 , N. 3 , P. 402-411

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00002/11368/8119.pdf
DOI:10.1016/j.marpolbul.2009.10.012
http://archimer.ifremer.fr/doc/00002/11368/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We developed a new granular material (MatIV) to study experimentally landscape evolution in active mountain belt piedmonts. Its composition and related physical properties have been determined using empirical criteria derived from the scaling of deformation, erosion-transport and sedimentation natural processes. MatIV is a water-saturated composite material made up with 4 granular components (silica powder, glass microbeads, plastic powder and graphite) whose physical, mechanical and erosion-related properties were measured with different laboratory tests. Mechanical measurements were made on a modified Hubbert-type direct shear apparatus. Erosion-related properties were determined using an experimental set-up that allows quantifying the erosion/sedimentation budget from tilted relaxation topographies. For MatIV, we also investigated the evolution of mean erosion rates and stream power erosion law exponents in 1D as a function of slope.;Our results indicate that MatIV satisfies most of the defined criteria. It deforms brittlely according to the linear Mohr-Coulomb failure criterion and localizes deformation along discrete faults. Its erosion pattern is characterized by realistic hillslope and channelized processes (slope diffusion, mass wasting, channel incision). During transport, eroded particles are sorted depending on their density and shape, which results in stratified alluvial deposits displaying lateral fades variations. To evaluate the degree of similitude between model and nature, we used a new experimental device that combines accretionary wedge deformation mechanisms and surface runoff erosion processes. Results indicate that MatIV succeeded in producing detailed morphological and sedi-mentological features (drainage basin, channel network, terrace, syntectonic alluvial fan). Geometric, kinematic and dynamic similarity criteria have been investigated to compare precisely model to nature. Although scaling is incomplete, it yields particularly informative orders of magnitude. With all these characteristics, MatIV appears as a very promising material to investigate experimentally a wide range of scientific questions dealing with relief dynamics and interactions between tectonics, erosion and sedimentation processes.
ISSN: 0040-1951

hal-00669904
https://hal.archives-ouvertes.fr/hal-00669904
DOI : 10.1016/j.tecto.2011.09.029

Éditeur(s) : Blackwell science
Résumé : An experiment was conducted in six earthen ponds with 20 shrimps m(-2) Litopenaeus stylirostris (Stimpson) during the warm season in New Caledonia to study the dynamics of wastes in relation with water exchange rate (WER). The nitrogen budget was established, taking into account the different forms of nitrogen in the water, sediment, feed and shrimp. Data from a wide range of treatments applied in unreplicated ponds were treated using regression analysis to establish the relationship between WER and partial nitrogen budget, sediment characteristics and shrimp performance. To compare effluent quality between treatments during the season, data were analysed using the non-parametric sign test. The water outflow was characterized by a decrease in the concentrations of N-mineral forms (TAN, NO2--NO3-), an increase in the concentration of organic soluble and sestonic organic forms (expressed in terms of particulate nitrogen, particulate organic carbon, chlorophyll a) compared with the water inflow. Increasing WER increased the amount of exported wastes and mainly in the organic forms and TAN can be considered as negligible. The nitrogen budget showed that 19-46% of nitrogen input (feed+water) was exported into the coastal environment. The results showed that the quality of the sediment decreased as WER decreased. The potential negative impact of the developing industry in New Caledonia on the costal environment could be partially reduced in a first step by decreasing WER. However, if applied in the farms, this practice should be linked to a close survey of the evolution of sediment quality.
Aquaculture Research (1355-557X) (Blackwell science), 2006-06 , Vol. 37 , N. 9 , P. 938-948

Droits : 2006 Blackwell Publishing, Inc.
http://archimer.ifremer.fr/doc/2006/publication-1811.pdf
DOI:10.1111/j.1365-2109.2006.01515.x
http://archimer.ifremer.fr/doc/00000/1811/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. In this paper, we present results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport, and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension, and strike–slip.Experimental results outline first that experimental morphologies evolve significantly at a short time scale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth, and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp, and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike–slip setting, the complex morphology of the wrench zone, composed of several interacting fault segments, enhances the interactions with the drainage network. Because of the widening of the main fault zone toward the surface, a significant amount of distributed deformation is observed along the wrench zone. Locally, where two terminations of fault segments interact, less than a quarter of the far field displacement can remain measurable using fault offsets, leading to a systematic underestimation of the real fault slip rate.These different experimental examples illustrate the great potential of the approach coupling deformation mechanisms and erosion–transport–sedimentation processes to investigate qualitatively and quantitatively the morphotectonic evolution of tectonically controlled landscapes.
ISSN: 0169-555X

hal-01243587
https://hal.archives-ouvertes.fr/hal-01243587
DOI : 10.1016/j.geomorph.2015.02.011

Éditeur(s) : Université d'Angers
Résumé : In oyster farming areas, organic matter fluxes toward sediment is increased. Pacific oysters (Crassostrea gigas) reject organic-rich faeces and pseudofaeces as a result of filtration process. Organic matter can be consumed by benthic fauna, but in excess it can entails the reduction of benthic faunal species richness, abundance and biomass. Organic matter degradation also induces hypoxic (or anoxic) conditions in the sediment, and production of ammonia and sulfides in toxic concentrations. The main objective of this study is to assess the effects of oyster farming on benthic intertidal ecosystems in the Pertuis Charentais. Benthic macrofauna, living (stained) foraminifera, and physicochemical characteristics of the water column and sediment were used as indicators to evaluate these effects. A multidisciplinary approach was conducted across the Pertuis Charentais at 3 different spatial scales: an oyster trestle (micro-scale), an oyster culture area (meso-scale) and various sites across the Pertuis Charentais (macro-scale). The study was also realised at 4 different temporal scales: some months for the spatial micro-scale, every two weeks for 2 years at meso-scale and once per season during one year at macro-scale. In this study, I found that oyster farming enriches sediment in fine particles, organic matter (up to 12 %), particulate organic carbon (15-20 µg mg 1) and leads to high microphytobenthic biomass. Moreover, the association of seasonnal warming (during spring and summer), remineralisation of accumulated organic matter and short-term hypoxic conditions leads to sulfides and ammonium production. Consequently, the benthic biodiversity decreases and the population dynamic is disturbed. The population dynamic disturbance is characterised by fast abundance rises followed by high mortality rates. In these conditions, tolerant benthic macrofaunal (Cirratulidae, Spionidae and Capitellidae) and foraminiferal (Ammonia tepida and Cribroelphidium gunteri) species are promoted. AMBI index confirms "medium" ecological quality of oyster farming areas. On the contrary, across the control sites, sensible species are maintained (Amphipods, Rosalina cf. vilardeboana). Comparison of oyster farming techniques shows that on-bottom culture is less disturbing for benthic ecosystem than off-bottom culture. Axial tomodensitometry, an innovative method, was used to describe in 3D the sedimentary column organisation. I show that oyster farming modifies the sedimentary column functioning. Indeed, the macrofaunal diversity decrease leads to the modification of the functional diversity of assemblages. Thus, the vertical distribution of living foraminifera is limited in oyster farming areas, because their distribution is tightly related to macrofaunal bioturbating modes.
Dans les zones ostréicoles, les flux de matière organique sont importants, l'huître Crasssotrea gigas rejetant sous forme de pseudo-fécès et de fécès de grandes quantités de matière organique. De ce fait, bien que cette matière organique puisse être consommée par la faune benthique, sa surabondance peut provoquer une réduction de la richesse spécifique, de l'abondance et de la biomasse et provoquer sur le plan des processus biogéochimiques des déplétions en oxygène et l'apparition de substances comme l'ammonium et les sulfures dont les concentrations peuvent devenir toxiques. L'objectif principal de cette étude était donc de déterminer l'impact de l'ostréiculture, grâce à plusieurs indicateurs, sur le compartiment benthique d'un écosystème littoral comme les pertuis charentais. Pour évaluer ces effets, la macrofaune benthique et les foraminifères vivants benthiques ont été utilisés en association avec des mesures des paramètres physico-chimiques de la colonne d'eau et du sédiment. Une approche pluridisciplinaire a ainsi été menée dans les pertuis charentais à trois échelles spatiales différentes : à l'échelle d'une table ostréicole (micro-échelle), à l'échelle d'un site ostréicole (méso-échelle) et à l'échelle des pertuis charentais (macro-échelle). Dans les trois cas, un suivi dans le temps a été associé à une étude de distribution spatiale, quelques mois à micro-échelle, tous les quinze jours pendant deux années à méso-échelle et une fois par saison pendant une année à macro-échelle. Ces différentes approches ont permis d'avoir une vision pertinente de la dynamique et de la réponse fonctionnelle de la faune benthique aux changements induits par la présence de l'ostréiculture. La présence des cultures ostréicoles dans les pertuis charentais enrichit les sédiments en particules fines, en matière organique (12 %), en carbone organique particulaire (15-20 µg mg-1) et favorise une production microphytobenthique élevée. Pendant la période chaude de l'année printemps-été, la reminéralisation de la matière organique accumulée associée à des hypoxies temporaires a favorisé la production de sulfures et d'ammonium. Dans les stations soumises à l'ostréiculture, la diversité des assemblages diminue. La dynamique des espèces est caractérisée par des augmentations rapides des abondances suivies d'épisodes de mortalité. Les espèces tolérantes de la macrofaune benthique (Cirratulidae, Spionidae et Capitellidae) et des foraminifères vivants benthiques (Ammonia tepida et Cribroelphidium gunteri) sont favorisées. Le calcul de l'indice AMBI confirme la qualité écologique moyenne de ces sites. Au contraire, dans la station témoin, les espèces sensibles sont favorisées (Amphipodes, Rosalina cf. vilardeboana). La comparaison de la technique de culture sur table et de culture à plat a montré que la culture des huîtres à plat est moins perturbante pour le milieu. L'étude de la bioturbation a montré l'influence qui existe entre le mode de bioturbation des différents groupes de la macrofaune et la répartition verticale des foraminifères vivants dans la colonne sédimentaire. La diminution de la diversité des assemblages de la macrofaune dans les zones soumises à l'ostréiculture modifient la diversité fonctionnelle de ces assemblages et affectent le fonctionnement de la colonne sédimentaire, limitant la répartition verticale des foraminifères dans ces zones.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2007/these-2582.pdf
http://archimer.ifremer.fr/doc/00000/2582/

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : The environment is impacted by natural and anthropogenic disturbances that occur at different spatial and temporal scales, and that lead to major changes and even disequilibria when exceeding the resiliency capacities of the ecosystem. With an annual mean flow of 1700 m(3) s(-1), the Rhone River is the largest of the western Mediterranean basin. Its annual solid discharges vary between 2 and 20 Mt, with flood events responsible for more than 70% of these amounts. In the marine coastal area, close to the mouth, both flocculation and aggregation lead to the formation of fine-grained deposits, i.e. the prodelta. This area is characterized by sediment accumulation rates up to 20-50 cm yr(-1) and high accumulations of particle reactive contaminants such as various man-made radionuclides released into the river by nuclear facilities or arising form prior atmospheric nuclear tests (1954-1980) and the Chernobyl accident (April 1986). This prodelta, however, cannot be considered as a permanent repository for particle reactive pollutants since it is subjected to reworking processes. Sediment dynamics had to be linked to the influences of hydrodynamic and atmospheric events such as high flow rates or storms close to the Rhone River mouth. An experiment was carried out during the winter 2006 based on the deployment of two ADCPs and six altimeters at the Grand Rhone mouth for several months. This type of installation has never been used before in this area because of the hard meteorological conditions and the strong fishing activities. However, results showed pluricentimetric rises of the sedimentary level just after river flood events and decreases during storms, generated by southeast winds. Radiotracers and grain size depth profiles helped to characterise the studied events and to establish inventories of sediments and radionuclides. A cruise (CARMEX) was carried out during this same period to collect water samples, suspended particles and sediment cores. The results enabled us to link both river flow and wind characteristics to events recorded on the sea floor, i.e. resuspension, accumulation, consolidation, etc. Deposits of 11 cm of sediments were estimated during flood periods and bottom shear stresses up to 5 N m(-2) were calculated during sediment erosion phases. (C) 2010 Elsevier Ltd. All rights reserved.
Continental Shelf Research (0278-4343) (Pergamon-elsevier Science Ltd), 2010-05 , Vol. 30 , N. 9 , P. 1095-1107

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00006/11695/8479.pdf
DOI:10.1016/j.csr.2010.02.015
http://archimer.ifremer.fr/doc/00006/11695/