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

Abstract

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 N80°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 N65°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 24 th , 2004, Besançon earthquake supports the hypothesis of a basement fault reactivation.Propagation possible d'un anticlinal masqué au front de la chaîne plissée du Jura au Quaternaire : indices géomorphologiques dans le secteur de la forêt de Chaux, France.Mots clés: chaîne plissée, Jura, tectonique active, plissement actif, risque sismique RésuméCette étude présente de nouveaux indices en faveur d'une croissance, au cours du Plio-Quaternaire (post-2.4 Ma), d'un anticlinal situé au front de la chaîne du Jura, dans le secteur de la Forêt de Chaux à 30 km au sud-ouest de Besançon. La Forêt de Chaux correspond à une dépression allongée orientée N80°E et comblée par des dépôts alluviaux pliocènes de type Sundgau. Cette dépression est bordée au nord par le Doubs et au sud par la Loue. Le secteur situé entre ces deux rivières est marqué par la présence d'une ride orientée N65°E, qui traverse la forêt de Chaux d'est en ouest.Un soulèvement régional plus récent que 2.4 Ma le long de cette ride N65°E est suggérée par plusieurs indices géomorphologiques comme les variations de la géométrie du réseau de drainage, les différences de degré d'incision ou les migrations de rivières de part et d'autre de la ride N65°E. Des données de géophysique et de forages montrent que cette ride se superpose à l'axe d'un anticlinal masqué sous les dépôts alluviaux. Le soulèvement décelé semble donc résulter de la croissance post-2.4 Ma d'un anticlinal. L'azimuth de l'axe de l'anticlinal masqué est oblique aux directions locales des plis et des failles affectant la couverture...

Deciphering neotectonics from river profile analysis in the karst Jura Mountains (northern Alpine foreland)

“…Indeed, we propose that this k sn distribution reflects differential neotectonic activity across the Jura arc. Our observations are qualitatively in agreement with modern uplift estimates of 0.1-1.1 mm/year using leveling (Jouanne et al 1995(Jouanne et al , 1998 in the southern part of the High Range, and with long-term uplift estimates between 0.05 and 0.17 mm/year from morphological analyses in the External Range (Giamboni et al 2004b;Ustaszewski and Schmid 2007;Madritsch et al 2010b;Molliex et al 2011).…”

“…However, rivers are expected to potentially preserve topographic anomalies caused by uplift rate variations over about tens of thousands years (e.g., Whipple and Tucker 1999;Carretier et al 2006). Considering the total reset of most of the Jura rivers during the last ice extent, and according to previous studies (Nivière and Winter 2000;Carretier et al 2006;Madritsch et al 2010a;Molliex et al 2011), our analyzed river profiles are expected to have preserved the most recent tectonic disturbances.…”

“…Folding and thrusting took place between about 14 and 3.3 Ma according to stratigraphic and paleontological evidences (Becker 2000;Schmid 2006, 2007 andreferences therein). However, geomorphological evidence suggest that more recent deformations (i.e., Pleistocene to Holocene) occured along the northernmost frontal thrusts of the Jura (Nivière and Winter 2000;Giamboni et al 2004b;Carretier et al 2006;Nivière et al 2006;Schmid 2006, 2007;Madritsch et al 2010b;Molliex et al 2011). These authors highlight a Plio-Pleistocene N-S horizontal shortening in the external part of the Jura with an average uplift velocity of *0.05 mm/year at the front.…”

“…During the northwestward propagation of the Jura deformation in the Plio-Pleistocene (Madritsch et al 2010b;Molliex et al 2011), the former southwestwardflowing network maintained its initial course, corresponding to the present-day downstream part of the Doubs River (from Montbéliard to its outlet, see Figs. 1,3c).…”

“…However, recent geodetic studies based on GPS network analysis reveal horizontal velocities lower than 1 mm/year (Nocquet and Calais 2003;Walpersdorf et al 2006) associated with a main strain feature in favor of an arc-parallel extension. Moreover, geomorphological evidence of fold growth suggests a long-term mean uplift velocity of only *0.05 mm/year along the External Range, associated with a thick-skinned deformation mode (Giamboni et al 2004b;Ustaszewski and Schmid 2007;Madritsch et al 2010a;Molliex et al 2011).…”