Pliocene to recent uplift and shortening in the southern Rhinegraben is documented by deformation of Pliocene fluvial gravels, deposited on a nearly planar surface, as well as by progressive deflection and capture of rivers. This deformation is suggested to result from thick-skinned tectonic movements as evidenced by observations on seismic records, which demonstrate a spatial coincidence between en-Øchelon anticlines at the surface and faults located in the crystalline basement. These findings contradict the often invoked thin-skinned tectonism in the recent tectonic history of the Rhinegraben. In particular the transfer zone between the Rhinegraben and the Bressegraben is very suitable for reactivation under the present day stress field. Thickskinned reactivation of faults in the basement is also expressed by focal plane mechanisms of recent earthquakes showing strike-slip-rather than reverse faulting characteristics. This is of importance for the densely populated and industrialised southern Rhinegraben, previously affected by large earthquakes in historical times (e.g. Basel 1356).

The southern Rhinegraben represents a key area to unravel the Neogene paleohydrographic history of the northern Alpine foreland. At least, three successive main drainage systems are documented by the youngest sediments of the graben fill. They are respectively pre-, syn-and post-dating the folding of the Jura Mountains (about 10-5 Ma ago).Pliocene to recent uplift and shortening of the Pliocene fluvial gravel ("Sundgauschotter"), which accumulated on a nearly plain surface, and the progressive deflection and capture of rivers resulted from reactivation of preexisting Paleogene faults. The alluvial terraces along the major rivers of the Sundgau area show upward warping near the uplift areas. Furthermore, river beds responded to uplift by lateral shift.During the Pliocene-Pleistocene, fluvial drainage diverted stepwise from the initial, westwards directed course (towards the Bressegraben) to the N (into the Rhinegraben): Firstly, uplift in the south at the boundary between the Rhinegraben and the Jura Mountains induced a northwards directed migration of the middle Pliocene, E-W flowing paleo-drainage system. Successively, a late Pliocene/early Pleistocene lowering of the base level in the Rhinegraben north of Mulhouse resulted in the capture by southwards directed backward erosion of this system into the Rhinegraben, as likewise documented by the reconstitution of the paleo-drainage patterns in the Sundgau area. In addition, a gradually capture moving from NE to SW has been identified for the Sundgau catchment area. ZUSAMMENFASSUNGDie Morphogenese des südlichen Rheingrabens hängt stark mit der hydrographischen Entwicklung des zentralen Alpinen Vorlandes zusammen. In den jüngsten Ablagerungen der Grabenfüllung sind nämlich mindestens drei Hauptentwässerungssysteme dokumentiert. Die fluviatilen Sedimente vom mittleren Miozän bis zum Quartär wurden vor, während und nach der Hauptphase der Jurafaltung abgelagert (ca. 10-5 Ma).Eine Reaktivierung von paläogenen Brüchen während des Plio-Pleistozäns ist sowohl durch die Auffaltung der pliozänen Sundgauschotter als auch durch die fortschreitende Ablenkung und Anzapfung von Flüssen im süd-lichen Elsass (Sundgau) belegt. Alluviale Terrassen entlang der Hauptflüsse im Sundgau wurden in der Nähe von Antiklinalen gehoben und verstellt. Das weist darauf hin, dass die tektonische Aktivität zumindest bis in das Pleistozän anhielt.Die Rekonstruktion des Paläoentwässerungssystems zeigt, dass die Umlenkung des gesamten Flussnetzes im Sundgau, das während des Pliozäns nach Westen in den Bressegraben gerichtet war und sich dann nach Norden in den Rheingraben reorientierte, schrittweise stattfand: Infolge von Hebungen im Süden entlang der Rheingraben/Jura-Grenze migrierte der mittelpliozäne Hauptfluss nordwärts und die Absenkung im Rheingraben nördlich von Mulhouse während des Spätpliozäns und des Pleistozäns führte dann zur allmäh-lichen Anzapfung des Entwässerungssystems von Norden. fluenced the evolution of the adjoining Jura Mountains, when these were folded and thrusted since the Mi...

[1] Spatial variations of gradients in landscapes may be used to identify and quantify recent deformation. The problem with doing this is to determine whether tectonic or climatic forcing is responsible for these variations, especially for low uplift rate environments ((1 mm yr À1 ) where climate changes may have erased tectonic features. We evaluate the respective contribution of low uplift rate ($0.1 mm yr À1 ) and Pleistocene climate oscillations on gradient variations of two comparable river profiles crossing different uplift zones in the southern Upper Rhine Graben. We compare the observed points of discontinuity in river profile (knickpoints) and convex portions (knickzones) with those predicted by a detachment-limited model that includes stochastic short-term and cyclic long-term variations in climate, a bedrock detachment threshold and rock uplift. The detachment-limited model is chosen as it predicts the development of persistent knickpoints. Differing values of the shear stress exponent, erosion threshold, climate variability and uplift pattern have been checked. Our modeling suggests that climate changes had no significant effects on profiles and that anomalies are more likely due to anticline growth. This surprising result arises from the combination of a very low regional uplift rate and the detachment-limited assumption. The detachment-limited model implies an upstream propagation of knickpoints and knickzones generated by uplift at the outlet during dry climate periods of low erosion. The greater the uplift rate, the larger the variations in river bed elevation. Thus, for high uplift rate, knickpoints and knickzones generated by climate oscillations are more likely to hide tectonic features. This result seems counterintuitive because it suggests that tectonic knickzones will be better preserved in low uplift rate environments, provided that the lithology is homogeneous.Citation: Carretier, S., B. Nivière, M. Giamboni, and T. Winter (2006), Do river profiles record along-stream variations of low uplift rate?,

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