The Dachstein paleosurface and the Augenstein Formation in the Northern Calcareous Alps - a mosaic stone in the geomorphological evolution of the Eastern Alps

The central and eastern areas of the Northern Calcareous Alps (NCA) are cha racterized by remnants of the Dachstein paleosurface, which formed in Late Eocene (?) to Early Oligocene time and is preserved with limited modificati on on elevated karst plateaus. In Oligocene time, the Dachstein paleosurfac e subsided and was sealed by the Augenstein Formation, a terrestrial succes sion of conglomerates and sandstones, which are only preserved in small rem nants on the plateaus, some in an autochthonous position. Thermochronologic al data suggest a maximum thickness of the Augenstein Formation of >1.3 km, possibly >2 km. The age of the Augenstein Formation is constrained by the overall geological situation as Early Oligocene to earliest Miocene. Fissio n track age data support an Early Oligocene age of the basal parts of the f ormation. The source area of the Augenstein Formation consisted predominant ly of weakly metamorphic Paleozoic terrains (Greywacke Zone and equivalents ) as well as the Late Carboniferous to Scythian siliciclastic base of the N CA to the south of the depositional area. To the west, the Augenstein Forma tion interfingered with the Tertiary deposits of the Inntal. Sedimentation of the Augenstein Formation was terminated in Early Miocene time in the cou rse of the orogenic collapse of the Eastern Alps. The Augenstein sediments were eroded and redeposited in the foreland Molasse zone. From Pannonian ti mes (similar to 10 Ma) on, the NCA and the denuded Dachstein surface experi enced uplift in several pulses. The Dachstein paleosurface has been preserv ed in areas, in which thick limestone sequences allowed subsurface erosion by cave formation and thus prevented major surface erosion.