Palaeogeography and geodynamic evolution of the Gosau Group of the Northern Calcareous Alps (Late Cretaceous, Eastern Alps, Austria)

The sedimentation of the Late Cretaceous Gosau Group of the Northern Calcareous Alps records the complex geodynamic evolution of the northern part of the Austroalpine microplate. The tectonically controlled sedimentation and facies distribution were mainly governed by the oblique subduction of the Pennic-Ligurian ocean below the Austroalpine margin. Most of the Gosau successions comprise two distinct sedimentary complexes. The Lower Gosau Subgroup (upper Turonian-Campanian) is characterized by terrestrial to shallow-marine facies associations: alluvial fan and fan delta deposits, shallow-marine sandstones and sandy limestones, and storm-influenced nearshore and shelf deposits. During the early Santonian sea-level highstand, a great part of the Northern Calcareous Alps was covered by a shallow shelf sea. Palaeotransport directions point to source areas situated both to the north and to the south of the Northern Calcareous Alps. The Upper Gosau Subgroup (upper Santonian-Eocene) comprises deep-water hemipelagic and turbiditic deposits. Rapid subsidence into bathyal to abyssal depths started diachronously from the northwest (Santonian) to the southeast (Maastrichtian) after a short phase of deformation and erosion. Abyssal deposits in the northern parts of the Northern Calcareus Alps and north-directed palaeotransport indicate a tilting of the slope towards the north. This subsidence pulse is attributed to an event of subcrustal tectonic erosion, probably triggered by the subduction of a topographic high of the South Penninic ocean. The relationships of the Gosau Group of the Austroalpine unit to Late Cretaceous deposits of the Carpathians and Southern Alps are discussed in the framework of a plate tectonic model.