Évolution hydrogéomorphologique holocène de la Garonne maritime – Focus sur les sites de Langoiran et de lʼIsle-Saint-Georges (Gironde, France)

Abstract : This study concerns the lower Garonne River valley, a tidal area between La Réole and the Bec d’Ambès (92 km long). For the last few years, a palaeoenvironmental reconstruction was conducted on this fluvio-estuarine area in order to analyse the River spatiotemporal dynamics and to better understand environment-Human relationship. Until now, researches focus on the palaeohydrographical reconstitution at spatial (from the sites to the valley section) and temporal (from the Holocene to modern times) scales. On a tidal Garonne valley scale, textual and iconographical archives highlighted an important decrease of the number of fluvial islands since the 18th century. Locally, the River changed from a multi-channel to a single channel. On a Langoiran and Isle-Saint-Georges archaeological sites scale, further analyses allowed to relate the hydrographical evolution since the middle Holocene. These analyses associate (i) geomorphological data, derived from aerial photo-interpretation, topographical and geological maps, (ii) geophysical surveys (electrical conductivity), and (iii) stratigraphic data coming from the French subsoils database and 36 cores (4-10 m deep) we extracted from the two sites. Despite the important complexity of the hydrographical network, major palaeochannels have been identified in Langoiran and Isle-Saint-Georges. Many additional analyses (palynology, OSL dating, ostracology, electric survey tomography, microtopography from Lidar data) are ongoing but first results have already allowed to done a diachronic mapping of the alluvial plain and the sites, raising the question of the fluvio-maritime metamorphosis and its control factors.
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Submitted on : Friday, January 15, 2016 - 11:11:47 PM
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Séverine Lescure, Gilles Arnaud-Fassetta, Charles Le Coeur, Anne Colin, Sylvie Faravel, et al.. Évolution hydrogéomorphologique holocène de la Garonne maritime – Focus sur les sites de Langoiran et de lʼIsle-Saint-Georges (Gironde, France). Géomorphologie, 2015, 21 (1), p .57-72. ⟨https://geomorphologie.revues.org/10860⟩. ⟨10.4000/geomorphologie.10860⟩. ⟨hal-01257204⟩

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