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2016-01-29 - Colloque/Présentation - poster - Anglais - 1 page(s)

Dupont Nicolas , Kaufmann Olivier , "Reinterpretation of a Mons Basin geological cross-section based on ERT survey : the Hainin-Hautrage pumping station site" in 5th International Geologica Belgica Meeting, Mons, Belgique, 2016

  • Codes CREF : Sciences de l'ingénieur (DI2000), Prospection minière et pétrolière (DI2321), Géologie (DI1411), Sondages géologiques (DI2322), Hydrogéologie (DI1426)
  • Unités de recherche UMONS : Géologie fondamentale et appliquée (F401)
  • Instituts UMONS : Institut des Sciences et du Management des Risques (Risques)

Abstract(s) :

(Anglais) The Mons Basin overlies the Paleozoic basement and is composed by Upper Cretaceous chalks and calcarenites followed by Paleogene calcarenites, sands and clays. Thickness of this unit can exceed 300m. Sands, loess and alluvium deposited during Cenoizoic Era and overlie the Basin. Despite their limited geographical extend, the carbonate formations of the Mons Basin form an important aquifer, providing about 10% of the drinking water used in Belgium. Between 1935 and 1949, the TMVW water company set up a pumping plant of 15 wells in the western part of the Basin. The wells are approximately disposed along a 3.5 km North-South profile. The geological description of the wells and a synthetic cross-section of the pumping site was established by Marlière (1949). Recently, the SWDE water company wanted to check the pumping wells, and a geophysical survey was conducted to complete the geological data in this area. This survey contains 2D ERT sections that were interpreted to give detailed imaging of the subcropping formations. New discontinuities crossing both Upper Cretaceous and Paleogene formations have been highlighted and interpreted as unrecognized faults. An updated cross-section of the site is proposed, based on these new phenomena and the data from Marlière (1949). The main consequence of this reinterpretation is the replacement of the folds drawn on the primitive section by faults. Along the section, the geological formations are now disposed in monoclines separated by normal faults, in agreement with the tectonic context of the Basin. In particular, the Ypresian syncline which was drawn in the Basin axis is now interpreted as a graben. ERT sections show vertical offsets in the Paleogene sands and clays too, pointing at a later tectonic activity. In conclusion, this reinterpretation shows the potential complexity of the Mons Basin structure. Many fault systems have been already observed in quarries located in the area, but no previous exploration has recognized the Basin structuration on a kilometric scale so obviously. According to the analysis of these fault systems, the structure highlighted along the Hainin-Hautrage pumping site should be related to an extensive context, in agreement with a pull-apart system associated to the North Artois Shear Zone (Dupuis et al., 1989). Dupuis Ch. & Vandycke S. (1989). Tectonique et karstification profonde : un modèle de subsidence original pour le Bassin de Mons. Annales de la Société Géologique de Belgique, T112, pp.479-487. Marlière R. (1949). Le site géologique du Captage d’Hainin-Hautrage (Hainaut). Annales de la Société Géologique de Belgique, T73, B55-90.