THE DROWNING SEQUENCE OF MOUNT BURGL IN THE SALZKAMMERGUT AREA (NORTHERN CALCAREOUS ALPS, AUSTRIA): EVIDENCE FOR A DIACHRONOUS LATE JURASSIC TO EARLY CRETACEOUS DROWNING OF THE PLASSEN CARBONATE PLATFORM

The Kimmeridgian to Tithonian Wolfgangsee Carbonate Platform as the northernmost platform of the Plassen Carbonate Platform sensu lato (s.l.) in the Northern Calcareous Alps was drowned in the Late Tithonian. The pre-drowning phase (Early Kimmeridgian to early Late Tithonian), the drowning phase and the post-drowning phase (both Late Tithonian) are preserved at Mount Burgl. The A) drowning event of the northern Wolfgangsee Carbonate Platform, the B) formation of a north-directed newly formed reef rim of the Plassen Carbonate Platform sensu stricto (s.s.) as well as the C) onset of resedimentation of enormous amounts of shallow-water debris from the central Plassen Carbonate Platform (s.s.) to the north, the D) enhanced subsidence with a prominent facies change at the Plassen Carbonate Platform (s.s.), and E) Tithonian normal faulting in the central Northern Calcareous Alps are more or less time-equivalent events. With respect to A)-E) we explain the Late Tithonian drowning of the Wolfgangsee Carbonate Platform as a result of the change in the overall tectonic regime: the compressional regime lasted until Late Oxfordian followed by a period of decreasing tectonic activity and relative tectonic quiescence in Kimmeridgian to Early Tithonian, and a subsequent extensional tectonic regime, that started around the Early/Late Tithonian boundary being responsible for the changes A) to E). The generally accepted model of a Kimmeridgian to early Early Cretaceous phase of tectonic quiescence during the evolution of the Plassen Carbonate Platform (s.l.), which formed a post-tectonic cover, must be replaced by a model of both diachronous platform onset and diachronous drowning in an active tectonic regime.