Neotectonics and Morphotectonics of the southern eastern Upper Rhine Graben – the Cenozoic tectonic history of the Northern Markgräflerland, Germany

The Upper Rhine Graben (URG) is the central segment of the European Cenozoic Rift System. The present-day stress field is characterised by an approximately NW–SE orientation of the principle stress axis σ¹, which is responsible for sinistral transtensional conditions that affect the URG system. In the southern eastern segment of the URG, seismic activity indicates that neotectonic processes are ongoing, shaping the present-day relief. This study focusses on neotectonics, tectonic geomorphology and the tectonic evolution of this region since the onset of the main URG rifting in the Early Oligocene. We combined remote sensing, fieldwork and geophysical measurements (GPR, ERT). Our analysis reveals that kilometre-sized fault-blocks of the Variscan basement tilt northeasterly. This can be inferred from the asymmetrical hillshape of the fault blocks, which are characterised by southward-shifted crestlines and larger local catchments on the northern with respect to the southern hillslopes. Triangular facets are aligned along both NW–SE and NE–SW trending valley sides in the Variscan basement. They are most notable at the western entrance of the Lower Münstertal near Staufen indicating active normal faulting. Riedel-shear fault patterns, bent and shifted creek beds as well as fault scarps in alluvial deposits of the Staufen Bay prove neotectonic activity of the eastern URG boundary fault. Faults have been (re-)activated with different kinematics at different times due to repeated changes of the regional stress field since the onset of the main rift phase of the URG in Early Oligocene.