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 Elsevier
Résumé : International audience
The barrier reef tract of New Caledonia is the second largest in the world enclosing lagoons of variable width. The Late Quaternary evolution of these barrier reefs and lagoons is poorly known. A recent high resolution seismic and multibeam bathymetry survey was carried out in the south-western lagoon from shoreline to open ocean across the barrier reef pass systems to perform sequence stratigraphy and to better understand the Quaternary evolution of the lagoon. Two depositional sequences bounded by type-1 erosional surfaces can be identified. The bounding surfaces delineate the bottom of two generations of incised valleys. System tracts comprising a complete succession of regressive, lowstand, transgressive and highstand tracts were observed only in the upper sequence. Chronostratigraphic and sedimentological interpretations of the seismic data are based on correlations with the chronology defined in the nearby cores drilled through the reefs and in the gravity cores previously recovered in the inner lagoon. Interpretation of seismic data is also carried out on the basis of correlation with multibeam bathymetric data. Our results indicate that the history of the New Caledonian lagoon probably does not exceed 200ka marked by two or three brief episodes each of immersion of about ten thousand years. The bathymetric data reveal that during successive low sea level stands, the lagoon was dependent upon erosional fluvial networks. The deep fluvial valleys were connected to the continental slope through the passes. Seismic records reveal that upstream palaeo-channels are not connected to the modern coastal rivers. In contrast, many aggrading deposits, including numerous stacking channels, and extending across the proximal part of the outer lagoon, can be identified. Examination of drainage network morphology suggests a progressive tilt of the outer lagoon. Such evolution reveals that the Nouméa lagoon which is one of the widest in the world is an exceptional modern example of a rimmed shelf providing data to analyze the past counterparts.
ISSN: 0031-0182

insu-00338953
https://hal-insu.archives-ouvertes.fr/insu-00338953
DOI : 10.1016/j.palaeo.2008.08.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fromthe Proterozoic to the Quaternary, the evolution of the Earthwas characterised by recurrent periods of glaciation.However, the margins of many ancient ice-sheets are poorly defined on palaeogeographic reconstructions.The extent and outlines of ancient ice sheets can be better understood through careful documentation ofsediments deposited at the ice-sheet margin. An outstanding example is provided herein based on an end-Ordovician archive in Libya (Tihemboka area, Murzuq Basin). The four sets of structures include: i) subglacialglaciotectonic structures and soft sediment deformations from flowing glacier ice, such as intraformational glacialstriae, intraformational deformation (shear planes, sheath folds), normal microfaults, and large-scaleglaciotectonic folds-and-thrusts; (ii) structures resulting from overpressured subglacial (meltwater) flowssuch as clastic dykes and tunnel valleys; (iii) proglacial depositional structures and facies related to highmagnitudemeltwater floods such as sandstone intraclasts, large-scale bedforms resulting from supercriticalflows, climbing-dune cross-stratification and kettle holes; and (iv) deformation structures resulting from freefloating and nonglacier ice such as ice-keel scours and ice-crystal marks. Such a set of structures points to anice-marginal (essentially continental) depositional setting, and provides an excellent suite of criteria to identifymargins of ancient ice sheets in the stratigraphic record. At a regional scale, a reconstruction through time andspace of the related depositional wedge is proposed. This corresponded to a seismic-scale (N120 m in thickness,40 km in length) ice-marginal wedge in front of an essentially warm-based ice-sheet inducing concomitantlarge-scale glaciotectonic deformation, glacial basin and tunnel valley downcuttings. The related ice-front wasassociated with high-energy meltwater flows feeding a network of deeply incised proglacial channels downstreamand, beyond them, a fluvioglacial deltaic system. Shallow ice-marginal permafrost most likely affectedthe depositional wedge. At a larger scale, the Tihemboka ice-marginal wedge is interpreted as related to a stillstandperiod over the Gondwana platform, developed over an estimated interval of a few thousands of years.Based on these data, the conditions that arose in a particularly favourable context for the development, the preservationand the identification of ice-marginal wedges in the geological record are reviewed. Significantmeltwater-derived sediment deposition and aggradation in an accommodation space resulting either frompreglacial inheritance, glacial downcuttings and/or glacio-isostatic lithospheric flexure, or active tectonic subsidence(>1 Myr) are required for their formation and subsequent preservation.
ISSN: 0012-8252

insu-01184739
https://hal-insu.archives-ouvertes.fr/insu-01184739
DOI : 10.1016/j.earscirev.2015.06.006

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera-Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (~2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause-and-effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.
ISSN: 0954-4879

insu-00272075
https://hal-insu.archives-ouvertes.fr/insu-00272075
DOI : 10.1111/j.1365-3121.2007.00766.x

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
The East Sayan ranges are a key area to understand the interactions between the transpressive deformation linked to the far-field effects of the India-Asia collision and the extension linked to the opening of the Baikal Rift System. The active deformation that affects this range is very recent (around 5 Ma) but occurs in a very complex morphotectonic setting and the understanding of the Tertiary deformation relies entirely on a detailed knowledge of the pre-deformation situation. Using apatite fission track thermochronology, cosmogenic 10Be and morphological study on Tertiary lava flows we demonstrate that prior to the Oligocene the morphology of the East Sayan area was characterized by a wide, constantly rejuvenated erosion surface. Apatite fission track thermal modelling indicates that this surface started to form at least in Late Jurassic-Early Cretaceous (140-120 Ma). The long-term exhumation rates (several tens of million years) derived from apatite fission track data (17.5 m/Ma) and the short-term erosion rates (over a few hundred thousand years) derived from cosmogenic 10Be data (12-20 m/Ma) are coherent implying a near constant mean erosion rate since Late Jurassic. This constant, slow erosion prevented the formation of a lateritic-kaolinic weathering crust on the planation surface. By Oligocene-early Miocene times a long wavelength uplift that remains to be explained, induced incision that created shallow valleys later filled by basaltic lava flows. Finally, the present short-wavelength topography initiated during the Pliocene.
ISSN: 0743-9547

insu-00805603
https://hal-insu.archives-ouvertes.fr/insu-00805603
DOI : 10.1016/j.jseaes.2011.09.017

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
Résumé : Patagonia is well known for spectacular occurrences of a variety of glacial-derived landforms and deposits and for a long history of ancient glaciations. In this paper, we first review the diverse evidence that demonstrates the development of glacial-related sedimentary units within the Central Patagonian Cordillera since 7 Ma. Well preserved glacial landforrns at the top surface of mesetas on both sides of the Lago General Carrera-Buenos Aires are described: the Meseta Guenguel to the north, and the volcanic Meseta del Lago Buenos Aires to the south. The latter meseta corresponds to a 3 Ma old, morphologically inverted paleo-piedmont, based on Ar/Ar dates of the uppermost lava flows. It shows evidence of glacier advances to the NE direction. Over a distance of 20 km, glacial landforms observed by remote sensing data and digital elevation model define glacial tongues that were fed by the Cordillera reliefs to the west. These lobes are now beheaded from their westward sources along a morpho-structural corridor that bounds the Meseta del Lago Buenos Aires to the west. These remnants can be correlated with the oldest glacial landforms recognized north of Lago General Carrera-Buenos Aires, on the Meseta Guenguel that form the Chipanque moraine system. From these features it is concluded that the glacial drainage network of Central Patagonia has been strongly modified following relief inversion in response to erosion processes and to tectonic causes. Changes occurred after 3 Ma, from a smooth piedmont surface covered by an extensive ice mantle ending with ample glacial lobes, to the current series of deeply incised glacial valleys such as the Lago General Carrera-Buenos Aires depression. These new data bear important constraints on the history and development of the first glaciations in southern South America.
ANDEAN GEOLOGY

hal-00512682
https://hal.archives-ouvertes.fr/hal-00512682