Neotectonics of the Roer Valley rift system. Style and rate of crustal deformation inferred from syn-tectonic sedimentation

Abstract

The Roer Valley rift system emerged since the Middle Miocene and fluvial sediments were supplied to it by the Rhine, Maas (Meuse) and local Belgian rivers. Ever since the emergence, thirty fluvial terraces of the lower Maas river have been formed due to regional uplift. Their age-altitude record shows strong evidence for an important acceleration of the tectonic activity at the end of the Pliocene (around 3 Ma), and for high-frequency oscillations superimposed on a general continuous trend. Three relaxation periods during the Quaternary were identified, the first from 1.5 to 1.2 Ma and two short ones around 5 ka BP and after 2 ka BP respectively. The reactivations, following these relaxation periods, appear to be of plate-tectonic importance. The observed accelerations in tectonic activity since the Late Pliocene through the Pleistocene to the present day, raise the question: are we at present living in a period of extremely high crustal dynamics? Floodplain positions of the rivers Rhine and Maas repeatedly changed in space and time. Strike-slip movements along the graben bounding faults explain this behaviour. The events point to punctuated changes in the stress field orientation, probably related to the interplay between Alpine and Ardennes-Rhenish Shield stress generators within the regional stress field.