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Ressources du sous-sol et environnement en Bretagne. Genèse, géométrie et propriétés de différents types d'aquifères

Abstract : The superficial aquifers of the Armorican Massif constitute a non-negligeable part of the water reserves of Bretagne They can be devided into superficial fracture networks, weathered rocks, Tertiary and Quarternary sediment accumulations, in particular the sandy Ypresian, Mio-Pliocene and Pleistocene formations. The understanding of the origin, geometry and the possible connections between these different types of aquifers has, taking into account the present-day environmental problems, become a major issue. The cartography of the weathered rocks in the region of Landes du Mené shows that weathering profiles can be preserved over much larger surfaces than previously proposed. This mapping has made evident the existence of relative movement along the Quessoy/Nort-sur-Erdre Fault. The continuation of this mapping into the region of Ploërmel, south of the Landes du Mené, proves the progressive erosion of the weathered rocks, a phenomenon that has been interpreted as the result of Oligocene and/or Miocene marine transgressions. In these regions, the weathered rocks, mainly of lateritic origin, and the pedogenetic silcrets that locally cover them, caracterise the Eocene surface The caracterisation of the Eocene surface at the scale of the Armorican Massif has allowed for the construction of a first model of the distribution of the weathered rocks thanks to the count of the silcrets described in litterature. The study of the sandy formations shows that: - the Ypresian sands at Noirmoutier correspond to the migration of Gilbert type deltas in a lagunar environment. These deltas are covered by a sandy body with a poorly understood origin ; - the Mio-Pliocene sands of fluvio-estuarinne origin have been preserved as a network of paleovalleys during two cycles of varying the A/S ratio, following a general rétrogradational trend. - the Pleistocene sands at Pénestin have a fluvio-estuarine origin and could, partly, correspond to a paleo-Loire.
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https://tel.archives-ouvertes.fr/tel-00619366
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Submitted on : Tuesday, September 6, 2011 - 11:13:17 AM
Last modification on : Thursday, January 14, 2021 - 11:40:01 AM
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  • HAL Id : tel-00619366, version 1

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Nicolas Brault. Ressources du sous-sol et environnement en Bretagne. Genèse, géométrie et propriétés de différents types d'aquifères. Sciences de la Terre. Université Rennes 1, 2002. Français. ⟨tel-00619366⟩

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