Seismically induced shale diapirism : the Mine d'Or section, Vilaine estuary, Southern Brittany

• Published in: International Journal of Earth Sciences
• Main Authors: van Vliet-Lanoë, Brigitte, Hibsch, C., Csontos, L., Jegouzo, S., Hallégouet, Bernard, Laurent, M., Maygari, A., Mercier, Daniel, Voinchet, P.
• Other Authors: Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Université européenne de Bretagne - European University of Brittany (UEB), Géologie et gestion des ressources minérales et énergétiques (G2R), Université Henri Poincaré - Nancy 1 (UHP)-Institut National Polytechnique de Lorraine (INPL)-Centre de recherches sur la géologie des matières premières minérales et énergétiques (CREGU)-Centre National de la Recherche Scientifique (CNRS), Department of Geology, Eötvös Loránd University (ELTE), SAGE, Vie et Jaunay, Département de Géographie, Université de Brest (UBO), Department of geochronology, Mining and Geological Survey of Hungary (MBFSZ), Centre de Géosciences (GEOSCIENCES), Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2009
• Subjects: Shale diapirism; earthquake; saprolite; periglacial; neotectonics; Brittany; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; permafrost
• Online Access: https://hal.archives-ouvertes.fr/hal-00468265; https://doi.org/10.1007/s00531-007-0295-7

International audience The Pénestin section (southern Brittany) presents large regular undulations, commonly interpreted as evidence of periglacial pingos. It is an upper Neogene palaeoestuary of the Vilaine River reactivated during the middle Quaternary (middle terrace). It is incised into a thick kaolinitic saprolite and deformed by saprolite diapirs. This paper presents the arguments leading to a mechanistic interpretation of the deformations at Pénestin. Neither recent transpressive tectonics nor diagnostic evidence of periglacial pingo have been found despite evidence for a late paleo-permafrost. The major deformational process is shale diapirism, initially triggered by co-seismic water supply, with further loading and lateral spreading on an already deformed and deeply weathered basement, which allowed the shale diapirism to develop. Deformations are favoured by the liquefaction of the saprolite and a seaward mass movement and recorded, rather distant, effects of an earthquake (c. 280 ka B.P.) resulting from the progressive subsidence of the southern Armorican margin. These deformations triggered by an earthquake are similar to those induced by classical shale diapirism. They are probably common in tectonically active continental environments with shallow water table.