Possible Quaternary growth of a hidden anticline at the front of the Jura fold-and-thrust belt: geomorphological constraints from the Forêt de Chaux area, France

Stéphane Molliex (1, 2) , Olivier Fabbri (3) , Vincent Bichet (3) , Herfried Madritsch (4, 5)

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
2 LDO - Domaines Océaniques
3 LCE - Laboratoire Chrono-environnement (UMR 6249)
4 Institute of Geology and Paleontology
5 NAGRA - Nationale Genossenschaft für die Lagerung radioaktiver Abfälle

This study presents new constraints for Plio-Quaternary (post-2.4 Ma to present-day) anticline growth along the frontal zone of the Jura fold-and-thrust belt, in the Forêt de Chaux area, located 30 km SW of Besançon. The Forêt de Chaux area consists of a N080°E-elongated depression bordered by the Doubs and Loue rivers to the north and south respectively, and filled with Sundgau-type Pliocene alluvial deposits. The upper surface of the Pliocene deposits between the Loue and Doubs rivers is marked by a N065°E-trending ridge crossing the depression in a median position. A differential uplift along this ridge, post-dating the deposition of the gravels (2.4 Ma), is suggested by several geomorphological observations such as the opposite river migration on each side of the ridge as well as variations of drainage geometry and incision intensity. Geological and geophysical subsurface data indicate that the ridge roughly coincides with the axis of an anticline hidden beneath the Pliocene deposits. The observed uplift is presumably related to a post-2.4 Ma anticline growth. The fact that the azimuth of the hidden anticline axis is parallel to the strike of deep-seated Late Paleozoic basement faults and not to the local strike of the thin-skinned Jura structures indicates that the inferred post-Pliocene deformation could possibly be an expression of a recent thick-skinned deformation of the basement of the northern Alpine foreland. The focal depth (15 km) of the February 24th, 2004, Besançon earthquake supports the hypothesis of a basement fault reactivation.

Mots clés: Active tectonics; Active folding; Seismic hazard; Jura fold-and-thrust belt

Domaines: Tectonique; Milieux et Changements globaux

Stéphane Molliex, Olivier Fabbri, Vincent Bichet, Herfried Madritsch. Possible Quaternary growth of a hidden anticline at the front of the Jura fold-and-thrust belt: geomorphological constraints from the Forêt de Chaux area, France. Bulletin de la Société Géologique de France, 2011, 182 (4), pp.337-346. ⟨10.2113/gssgfbull.182.4.337⟩. ⟨insu-00633369⟩