Paléo-environnements holocènes et limites chronoclimatiques enregistrés dans un marais estuarien de la Gironde (France) [ Holocene paleo-environments and chrono-climatic limits recorded in a reclaimed marsh of the Gironde estuary (France).]

The Medoc peninsula acquired its present morphology during Holocene, following the building, to the west, of several generations of coastal dunefields, and by the filling up, to the east, of estuarian channels flowing into the main channel of the Gironde estuary. Sedimentological, palynological studies and 14C data from two sediment cores, taken in an ancient filled channel, provide evidences for the vegetation changes and the progressive infilling of tidal channels throughout the last 6700 years (6681-5444 B.C.). During the Atlantic period the reliefs, constituted by tertiary limestones and pleistocene fluvial terraces and surrounded with salt-marshes, were covered by forests of oak and hazel trees. The downstream and middle parts of the channel were always scoured by tidal currents. This channel became a continental marsh during the Gallo-roman period (2020 B.P. ± 60 or 55 B.C. - 65 A.D.). This change, together with an increasing anthropogenic modification of the environment, followed the formation of a shelly ndge, an index of high energy within the estuary. The sedimentation ended during the 17th or the 18th century as consequence of the reclaimation of the marshes of the North-Medoc.La presqu'île du Médoc s'est individualisée pendant l'Holocène par l'édification de plusieurs générations de dunes, sur la façade atlantique, et par le colmatage, à l'est, de chenaux estuariens, affluents de la Gironde. L'étude sédimentologique et palynologique de 2 carottes d'un chenal estuarien comblé, associée à des datations au 14C, a permis de reconstituer les variations de végétation et l'histoire du comblement progressif des chenaux tidaux depuis 6681-5444 av. J.-C. (6700 ± 70 B.P.). En particulier, l'époque gallo-romaine est marquée par un changement de la végétation locale, synchrone d'une modification hydrologique dans le domaine estuarien et de l'anthropisation du milieu.Diot Marie Françoise, Tastet Jean Pierre. Paléo-environnements holocènes et limites chronoclimatiques enregistrés dans un marais estuarien de la Gironde (France) [ Holocene paleo-environments and chrono-climatic limits recorded in a reclaimed marsh of the Gironde estuary (France).]. In: Quaternaire, vol. 6, n°2, 1995. pp. 63-75