HORNUNG, T. (2006)

Conodont biostratigraphy of the Draxllehen quarry near Berchtesgaden (Tuvalian / Lower Lacian): implications for high variations of red limestone sedimentation on Hallstatt deep swells


Red limestone successions exhibiting a highly variable thickness, texture and different stratigraphical occurrence, are a common lithofacial feature of the Hallstatt Formation ('Juvavic Nappe'), which is well-exposed mainly in the central sectors of the Northern Calcareous Alps. Next to strongly condensed Julian and Tuvalian nodular red Hallstatt limestone sequences (thickness ~ 1 m) that are famous due to its richness of ammonoids, nautiloids and halobiid bivalves, the area around Berchtesgaden (SE Bavaria) exposes conspicuously thick, well-bedded, monotonous and macrofossil-depleted Tuvalian red limestone successions of a thickness of 25-60 m. As detailed biostratigraphic investigations remained restricted to the spectacularly ammonoid-rich but condensed sites near the Hallstatt type locality (e.g. Feuerkogel section) and ammonoid findings are known to be very sparse within the monotonous Hallstatt red limestones series, age-dating by modern means lacked so far. Conodont-biozonation of the approximately 25m thick red limestone succession exposed at the Draxllehen quarry near Oberau / Berchtesgaden resulted in a stratigraphically complete sequence encompassing all yet described conodont zones known from the Upper Carnian (Tuvalian) and the Carnian-Norian boundary. This resulted in two important conclusions: (a) the possibility of partly increased thickness of Hallstatt Red Limestone successions induced by tectonic doubling or tripling can be definitely excluded for the Draxllehen quarry and (b), as correlations to isochronous, stratigraphically more the less complete condensed sections showed, red limestone lithology infers a strong dependence of thickness and palaeo-morphology of synsedimentary Hallstatt deep swells.

submitted to: Austrian Journal of Earth Sciences, 99: 00-000, Vienna