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 Calcareous Alps r ecords sedimentation and subsidence after Early Cretaceous thrusting. The G osau 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 thick ness changes within short horizontal distances suggest synsedimentary basin margin faulting. Extensional structures within the Triassic basement of th e basin include fibrous gashes which indicate (W)NW-(E)SE directed extensio n 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 approxim ately 500 m at the NW basin margin, and dextral strike-slip at the southwes tern margin suggest a pull-apart origin of the basin between NW/SE-trending , right-overstepping dextral strike-slip faults. Backstripped tectonic subs idence curves yield values of total subsidence of 700 m in approximately 6 Ma. Forward computer modelling based on extensional models results in stret ching factors beta between 1.09-1.15. Local extension along strike-slip fau lts is suggested as the main mechanism for basin formation.