Palaeogeography of the Eastern Tauern Window (Eastern Alps, Austria)

The Tauern Windows in the Eastern Alps is one of the most spectacular tectonic window, which formed after opening and closure of the Alpine Tethys between Europe and the Adriatic micro-continent. The herein described paleogeographical model is based on a new lithostratigraphic unit, the Wörth Formation, which formed as a local Jurassic black shale deepwater trough below the CCD on a strongly attenuated crustal basement. It developed as an oblique depression between the European continent and the Permian-Jurassic metasediments of the Seidlwinkl Nappe, which became an isolated element during opening of the Alpine Tethys. The Wörth Formation trough terminated to the NW within the European continent but maintained an open connection to the main Alpine Tethys towards SE. Different clastic sediments were derived from both sides of the trough: detrital mica-rich sandstones intruded by gabbroic laccoliths (167 Ma), olistoliths and re-sedimentation of Keuper beds, yet no indication of Triassic carbonates were derived from the northern side. In contrast, the deposits on the southern side are characterized by carbonate-bearing quartz-schists, breccias of Triassic carbonates, arkoses and tectonic slivers from the basement (Modereck crystalline).

Radiolarites and “Aptychen” limestones are useful marker lithologies for better lithostratigraphic interpretations. Until now Aptychen limestones got little attention, but could be recognized in all environment and most tectonic units from the Matrei Zone to the Klammkalk Zone. Rare locations have been detected, where at the base of the Glockner nappe a primary sedimentary succession of siliciclastic Jurassic into the typical marly “Kalkglimmerschiefer” lithology has been preserved. The Sandstone-Breccia unit is now understood as a continuously pro-grading accretionary wedge, containing considerable portion of clastics, derived from the southern border of Alpine Tethys and emplaced during post-Albian times on the northern parts of the Wörth Formation. White mica Ar ages, clustering regionally at 30 my and only little younger restricted apatite FT ages (see Spalding et al. Poster Session GD9.1) indicate early cooling due to a detachment process (see Brunner et al. Poster Session GD9.1) at the frontal part of the accretionary wedge.

The complex paleogeography has also important consequences for the tectonic evolution history:  It caused the contrasting structural architecture of the Glockner nappe W and E of the Rauris valley and the restriction of the HP-rocks (lawsonite pseudomorphs, eclogites) to the western side of Glockner nappe. The basement units of the eastern Tauern window should not interpreted as the direct continuation of the western basement. Earlier interpretations for different rifting ages in this part of Alpine Tethys, Jurassic in the S and Cretaceous in the N, lost their validity.