Geomorphological evolution of the Eastern Alps in response to Miocene tectonics

The Eastern Alps are divided into several geomorphological principal domain s, which are characterized by distinct elevation and slope angle distributi ons. High and rugged reliefs correlate with substantial exhumation since Mi ocene times and recent uplift; they characterize the western and central pa rts of the Eastern Alps. In the eastern part, remnants of paleosurfaces are preserved due to limited erosion (Early Miocene Nock: surface in metamorph ic lithologies) or predominant subsurface erosion by karstification (Early Oligocene Dachstein surface in the Northern Calcareous Alps). In the course of Miocene lateral tectonic extrusion the paleosurfaces were fragmented du e to tectonic block segmentation, and uplifted to different elevations. Lon gitudinal depressions follow important fault zones, which were active durin g extrusion tectonics. Polycyclic piedmont benchland formation, as proposed by several authors, was no important process during the uplift history of the Eastern Alps. A general west-east gradient can be established in terms of summit and mean elevations. This is mainly an expression of the Miocene tectonic processes. The geomorphological evolution of the Eastern Alps is sketched for three Mi ocene time levels starting with the Oligocene/Miocene boundary. The western Eastern Alps were already mountainous in Late Oligocene times. In the east ern part of the Eastern Alps, a northward-directed drainage system was fund amentally changed by the extrusion event. Thus, a new, east-directed draina ge system established in Middle Miocene time, following the main tectonic l ines. It formed the basis for the present-day drainage system in the easter n part of the Eastern Alps, whereas the drainage system of the western part did not experience fundamental changes since Late Oligocene times except a reduction of the catchment area of the Paleo-Inn river.