Les formations superficielles entre la Loire et le Loir (sud-ouest du Bassin parisien): les enseignements de l’analyse sédimentologique

• Jean-Pierre Larue ^[1] ; Édouard de Belizal ^[2]
  1. [1] Paris 12 Val de Marne University

     Paris 12 Val de Marne University

     París, Francia

     
  2. [2] Centre National de la Recherche Scientifique

     Centre National de la Recherche Scientifique

     París, Francia

     
• Localización: Norois, ISSN-e 1760-8546, ISSN 0029-182X, Nº. 240, 2016, págs. 43-57
• Idioma: francés
• Títulos paralelos:
  • Detritic deposits between the Loire River and the Loir River (Paris Basin): sedimentological study
• Texto completo no disponible (Saber más ...)
• Resumen
  • English

    In the Touraine area, the plateau which form the Loire-Loir interfluve stand at rather low and equal altitudes and bear locally detrital deposits which are not easy to identify (fig. 1, 2). The sedimentological study of those deposits makes it possible to distinguish several formations (fig. 3, 4 and tables 1, 2): The Château-Renault sands and the Montreuil sands look very much the same because of their bad sizing, their strong weathering and their heavy minerals distribution: a great deal of staurolite and not any garnet. The presence of pumice quartz, coming from the Mont-Dore eruption, makes it likely to date the Montreuil sands back to the Upper Pliocene. The Mazières sands, located north-west of Tours, come from the erosion of local marine deposits as it is proved by the morphoscopy and the absence of garnet and zircon which are present in the Faluns and the Sologne sands. The alluvial deposits, located in the north of Nazelles, are better grain-sizes and very rich in zircon and therefore may have been brought from upstream by the river Loire. The upper sands covering the Mazières sands are abundant in round and mat grains and heavy minerals of volcanic origin and have been brought by the wind from the alluvial deposits or the Val de Loire. If a part of the Montreuil sands certainly dates back to the Upper Pliocene, on the other hand their sedimentological characteristics invalidate the hypothesis of a flow upstream Loire towards the Atlantique in that period. The curving towards the Atlantique dis not take place until the ground was slightly abrased before the accumulation of the alluvial deposits which are preserved north of Nazelles (fig. 5). Coming from local substratum, those detrital formations, which are preserved on very closed levels, prove the relative tectonic steadiness in the Touraine area.

  • français

    L’analyse sédimentologique des formations détritiques tertiaires et quaternaires situées sur l’interfluve Loire-Loir, en Touraine, permet de caractériser plusieurs nappes détritiques. Datée du Pliocène supérieur par la présence de grains de quartz issus de ponces du Mont-Dore, la formation des Sables de Château-Renault et de Montreuil n’est constituée pour les autres dépôts que d’aports locaux, ce qui va à l’encontre de l’hypothèse d’un écoulement chenalisé de la Loire-amont vers l’Atlantique à cetre époque. Issus du remanierement de dépôts marins locaux, les Sables de Mazières sont probablement un peu plus récents. Les premieres alluvions quaternaires au nord de Nazelles, mieux classées, très riches en zircón, témoignent d’un transport fluviatile lointain effectué par une paléo-Loire chenalisé. Enfin, des sables soufflés, provenant des alluvions du Val de Loire, recouvrent localement les Sables de Mazières.