1,720,981 research outputs found
Tectonics and exhumation of the Romanian Carpathians: inferences from kinematic and thermochronological studies
Full text linkThe ultimate topographic expression of intra-continental mountain chains is established during continental collision. The Romanian Carpathians provide a key location for understanding the mechanics of collision during slab-retreat because the nappe stacking was not overprinted by back-arc extension, as commonly observed elsewhere. A review of existing kinematic and low-temperature thermochronological data infers that the collisional mechanics is significantly different when compared with high-convergence orogens. The shortening at exterior of the orogen was entirely accommodated by back-arc extension, the area in between simply rotated and moved into the Carpathians embayment. The roll-back collision is driven by foreland-coupling, a process that gradually accretes and exhumes continental material towards the foreland. The topographic expression of the Romanian Carpathians is both inherited from latest Cretaceous – Paleogene times, such as in the Apuseni Mountains or South Carpathians, and overprinted by the Miocene exhumation associated with the roll-back collision, as in the East or the SE Carpathians. The migration of exhumation towards the foreland continued during Pliocene-Quaternary times and is still active modifying the present-day topography in the SE Carpathians. The Transylvania basin is one of the best examples available of vertical movements induced by deep mantle processes in what is commonly referred as dynamic topography
Interactions fluvio-marines et dynamique sédimentaire en zone d’embouchure fluviale
No full textCette thèse s’est construite autour du fait établi que la zone d’embouchure a joué un rôle central dans le développement du delta du Danube et de l’hypothèse selon laquelle les embouchures, étant des pourvoyeurs pour la côte en sédiments et en eau douce, sont essentielles à la compréhension des côtes sous influence d’embouchures. Cette thèse est basée sur des données de terrain, notamment des levés bathymétriques, des mesures de débit fluvial et de décharge sédimentaire, des données de vagues, vents et courants, ainsi que des profils topographiques et des images satellites. Une grande partie de cette thèse est consacrée à l’utilisation de Mike 21/3 by DHI (Danish Hydraulic Institute), un modèle couplant hydrodynamique et vagues. Les résultats montrent une réponse linéaire dans les changements bathymétriques en relation avec l’influence des inondations et des tempêtes, ces changements peuvent être prédits par un index innondation/tempète basé sur le débit fluvial, la décharge sédimentaire et la hauteur des vagues (R^2=0.84). Des simulations de modélisation exploratoire sont développée pour une gamme complète de conditions. La déflexion du jet est prédit en fonction de l’équilibre entre débit fluvial et courant longshore, ainsi le jet sortant est dévié (ou non-dévié) quand le courant longshore est dominant (ou dominé) sur le débit fluvial. Finalement, la thèse esquisse un schéma préliminaire du transport sédimentaire sur le lobe deltaïque de l’embouchure St. Gheorghe et décrit les actions nécessaires pour envisager au complet le système de transport sédimentaire, indispensable à une gestion réussie de cette côte deltaïque.This thesis started from the observation that river mouths play a central role in the development of the Danube Delta and from an intuition that river mouths, as suppliers of sediment and water to coastal areas are quintesential in understanding river-influenced coasts. The present thesis is based on field data which comprises bathymetric surveys, measured river water and solid discharges, wave and wind data, ADCP data, topographic profiles, satellite imagery. Also, a big part of the thesis is dedicated to using the Mike 21/3 by DHI (Danish Hydraulic Institute), a coupled hydrodynamic and wave model.Results show a linear response in bathymetric change in relation to the relative influence of floods and storms and that change can be predicted by a Flood/Storm index based on river water or sediment discharge and wave height proxies (R^2=0.84). Furthermore, the analysis is extended using exploratory modelling to a full range of conditions. Jet deflection is predicted by a balance of river jet discharge and longshore current discharge, such that the jet is deflected (undeflected) when the longshore current is much higher (much lower) than the river jet, and a ~45* deflection is predicted when the discharge of jet equals the discharge of the longshore current.Finally, the thesis sketches a preliminary scheme for the sediment transport at the wave-influenced Sf. Gheorghe lobe, taking into account the known sources and sinks, based on bathymetric measurements and numerical modelling results; and outlines the actions needed to envisage a full sediment transport scheme which is needed for a successful management of the deltaic coast
New Studies in Historical Geography and Geoarchaeology of Histria and the Danube Delta
No full textInternational audienc
Chilia-Lykostoma (Nord du Delta du Danube, frontière Roumano-Ukrainienne) : les apports des images satellitaires à l'histoire, archéologie et géoarchéologie de l'Europe
No full textInternational audienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
River Jets Versus Wave-Driven Longshore Currents at River Mouths
No full textNational audienceAt river mouths, fluvial jets and longshore currents (LSCs) generated by waves interact hydrodynamically. This idealized numerical modeling study simulates a large number of hydro-morphodynamic conditions (650) to explore the emergent hydrodynamics determined by different mouth bar volumes and geometries, river discharge, wave heights, and directions and their potential stress on river-mouth development. We find that in the absence of a river-mouth bar (RMB), interactions are driven by momentum balances, expressed either as the balance of wave momentum flux (Mw) and jet momentum flux (Mj), or the balance of river jet discharge (Q(Jet)) and longshore current discharge (Q(LSC)). When a RMB is present, the topography modifies the structure of the jet by spreading it, and we quantify this mechanism through the lateral jet transfer rate (LJT). Secondly, topography generates complex longshore wave-driven circulation as a result of the protruding shoreface which serves as a platform on which counter LSCs develop. The balance in Q(Jet)/Q(LSC) may be used as an indication of the type of circulation. High and oblique waves favor longshore circulation and RMB bypass, whereas low waves and normal-to-coast angles generate diverging LSCs on the mouth bar crest which interrupts the longshore circulation. A quantification of the dynamic diversion is proposed in the form of the non-dimensional Dynamic diversion index (DyD), which scales with the product of Mj and Mw, and can account for the absolute strength of hydrodynamic interactions occurring at river mouths. RMB morphology can affect DyD in multiple ways by strengthening or by weakening the interactions. The DyD effect seems to increase with increasing RMB size, indicating that the RMB scale regulates the interplay of the wave-driven circulation and the river jet which further controls the adjacent topography changes
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