5th Swiss Geoscience Meeting, Geneva 2007
Evidence for active folding at the northwestern front of
the Jura fold-and-thrust belt
Herfried Madritsch*,**, Frank Preusser*** Olivier Fabbri**, & Stefan Schmid*
*Geologisch-Paläontologisches Institut, Bernoullistrasse 32, CH-4056 Basel.
(herfried.madritsch@unibas.ch)
** Department of Geosciences, Universitè de Franche Comté, Route de Gray 16, F25030 Besancon cedex, France.
*** Institute of Geological Sciences, University of Bern, Baltzerstrasse 1, CH-3012
Bern.
The Jura Mountains are considered a type example of a thin-skinned forelandfold-and-thrust belt, representing the northwestern deformation front of the
Alpine orogen. The present-day activity of this fold-and-thrust belt, and its
recent style of deformation (thin- vs. thick-skinned tectonics), is subject of
ongoing scientific debates (e.g.: Becker 2000). Our study investigates the
northwestern front of this belt in Eastern France, where it interferes with the EoOligocene intracontinental Rhine-Bresse transfer zone. Low to medium
seismicity only vaguely defines recent deformation of this area. Nevertheless,
our tectono-geomorphic investigations allowed to detect long-term deformations
that took place during Pleistocene times.
The “Sundgau - Fôret de Chaux” gravels, deposited between 4.2-2.9 Ma by a
braided river system, represent a perfect post-Late Pliocene deformation
marker horizon (Petit et al. 1996). A post-depositional differential uplift is
marked by the widely erosion of these gravels throughout our study area. In
spite of this a detailed reconstruction of the former braided river channel could
be preformed, based on a regional heavy mineral analysis. The results indicate
that uplift and erosion are related with post-2.9 Ma folding throughout the area
of the Rhine-Bresse transfer zone. Even younger deformation is recorded by
paleo-meanders of the Doubs river near Besancon, which have been
differentially uplifted by active folding for at least 5 meters during the Mid to Late
Pleistocene! Absolute uplift rates associated with Pleistocene folding are
currently investigated by OSL-dating of oxbow meander deposits. While we
consider the main (pre-2.9 Ma) phase of Jura folding to have been purely thinskinned, the younger deformations are at least partly different in tectonic style.
Structural and geomorphic arguments, as well as the overall depth distribution
of instrumentally recorded earthquakes, indicate thick-skinned deformation
processes, induced by the reactivation of pre-existing basement faults
(Giamboni et al. 2004).
REFERENCES
Becker A. 2000. The Jura Mountains - An active foreland fold and thrust belt?
Tectonophysics 321, 381-406.
Giamboni M., Ustaszewski K., Schmid S.M., Schumacher M.E. & Wetzel,A.
2004. Plio-Pleistocene transpressional reactivation of Paleozoic and Paleogene
structures in the Rhine-Bresse transform zone (Northern Switzerland & Eastern
France). Int. J. Earth. Science, 93, 207-223
5th Swiss Geoscience Meeting, Geneva 2007
Petit C., Campy M., Chaline J. & Bonvalot J. 1996. Major paleohydrographic
changes in the alpine foreland during the Pliocene-Pleistocene. Boreas, 25,
131-143.