Sedimentary tectonics and subsidence modelling of the type Upper Cretaceous Gosau basin (Northern Calcareous Alps, Austria)

The Upper Cretaceous Gosau Group of the Austrian Northern Calcereous Alps records sedimentation and subsidence after Early Cretaceous thrusting. The Gosau basin in the Gosau-Russbach area is approximately 8 km wide and 10 km long. It is filled by more than 1000 m alluvial/shallow-marine deposits of the lower Gosau Subgroup (Upper Turonian-Lower Campanian). Facies and thickness changes within short horizontal distances suggest synsedimentary basin margin faulting. Extensional structures within the Triassic basement of the basin include fibrous gashes which indicate (W)NW-(E)SE directed extension of 6-18%. (W)NW-directed normal faults at the southeastern basin margin, a prominent SE-directed normal fault with a minimum fault throw of approximately 500 m at the NW basin margin, and dextral strike-slip at the southwestern margin suggest a pull-apart origin of the basin between NW/SE-trending, right-overstepping dextral strike-slip faults. Back-stripped tectonic subsidence curves yield values of total subsidence of 700 m in approximately 6 Ma. Forward computer modelling based on extensional models results in stretching factors ß between 1.09-1.15. Local extension along strike-slip faults is suggested as the main mechanism for basin formation.