ORIGINAL PAPER H. -J. Gawlick Æ F. Schlagintweit Berriasian drowning of the Plassen carbonate platform at the type-locality and its bearing on the early Eoalpine orogenic dynamics in the Northern Calcareous Alps (Austria) Received: 30 December 2004 / Accepted: 4 September 2005 / Published online: 1 February 2006 Ó Springer-Verlag 2006 Abstract The Plassen carbonate platform (Kimmerid- gian to Early Berriasian) developed above the Callovian to Tithonian carbonate clastic radiolaritic flysch basins of the Northern Calcareous Alps during a tectonically active period in a convergent regime. Remnants of the drowning sequence of the Plassen Formation have been discovered at Mount Plassen in the Austrian Salzkam- mergut. It is represented by calpionellid-radiolaria wa- cke- to packstones that, due to the occurrence of Calpionellopsis oblonga (Cadisch), are of Late Berriasian age (oblonga Subzone). Thus, the Plassen Formation at its type-locality shows the most complete profile pres- ently known, documenting the carbonate platform evo- lution from the initial shallowing upward evolution in the Kimmeridgian until the final Berriasian drowning. The shift from neritic to pelagic sedimentation took place during Berriasian times. A siliciclastic-influenced drowning sequence sealed the highly differentiated Plassen carbonate platform. The former interpretation of a Late Jurassic carbonate platform formed under conditions of tectonic quiescence cannot be confirmed. The onset, evolution and drowning of the Plassen car- bonate platform took place at an active continental margin. The tectonic evolution of the Northern Cal- careous Alps during the Kimmeridgian to Berriasian time span and the reasons for the final drowning of the Plassen carbonate platform are to be seen in connection with further tectonic shortening after the closure of the Tethys Ocean. Keywords Northern Calcareous Alps Æ Plassen carbonate platform Æ Berriasian drowning Introduction and Geological setting In the Northern Calcareous Alps the Plassen carbonate platform (Late Jurassic to Early Cretaceous) represent the first carbonate platform deposits since Late Triassic (e.g., Tollmann 1976). The type locality is Mount Plas- sen near Hallstatt in the Austrian Salzkammergut, located on the O ¨ K map no. 96 Bad Ischl. From the geological point of view the Plassen area is part of the Upper Tirolic unit (Fig. 1). Due to tectonic displace- ment and erosion, the Plassen Formation is recorded only in the form of isolated occurrences concentrated in the middle part of the Northern Calcareous Alps and reaching to the east as far as Vienna. The original paleogeography has been strongly modified during the post-depositional Tertiary tectonic cycle (Frisch and Gawlick 2003). Despite a lot of new knowledge about its geometry and evolution (Gawlick et al. 2005—with ref- erences), the Plassen carbonate platform is still far from being completely understood. Further detailed investi- gations will be necessary to reconstruct the original paleogeographic situation. After a period of systematic geological investigations from the mid-sixties to the beginning of the eighties of the last century, only little attention has been paid to the geodynamics of Late Jurassic shallow-water deposits. Until recent times, a relatively long period of non- deposition before and after sedimentation of the Plassen Formation was the generally accepted view in the liter- ature (e.g., Schweigl and Neubauer 1997, p. 306, ‘‘two great hiatuses’’, text-Fig. 2). Due to new tectonic con- cepts (e.g., Gawlick 1996; Gawlick et al. 1999; Frisch and Gawlick 2003), the Middle to Late Jurassic period became the focus of detailed re-investigations of the most important localities of the Plassen Formation and asso- ciated sedimentary rocks (e.g., Schlagintweit and Ebli 1999: Trisselwand; Ku¨gler et al. 2003: Falkenstein; Schlagintweit et al. 2003: Mount Plassen; Gawlick et al. 2004: Mount Krahstein; Gawlick et al. 2005: Barmsteine, type-locality of Barmstein limestones). These investigations H. -J. Gawlick (&) Æ F. Schlagintweit Department of Applied Geosciences and Geophysics: Chair of Prospection and Applied Sedimentology, University of Leoben, Peter-Tunner-Str. 5, A-8700 Leoben, Austria E-mail: gawlick@unileoben.ac.at E-mail: EF.Schlagintweit@t-online.de Tel.: +43-3842-4026317 Int J Earth Sci (Geol Rundsch) (2006) 95: 451–462 DOI 10.1007/s00531-005-0048-4