Constructing a cave sediment stratigraphy for the Dachstein Massif sheds light on landscape evolution (Eastern Alps)

The Dachstein in Austria is the second largest karst massif in the Alps. It is dominated by Upper Triassic limestone and 290 km of cave passages have been documented. For this study, five major cave systems on the northern edge of the Dachstein were investigated: Hirlatzhöhle, Mammuthöhle, Rieseneishöhle, Schönberghöhle and Günter-Stummer-Höhle. Thirty-five sediment profiles or exposures between 860 m a.s.l. and 1945 m a.s.l. were analysed with respect to stratigraphy, grain size, mineral composition and carbon content. Our study distinguishes the following main types of non-autochthonous sediments. The stratigraphically deepest sediment in the highest—and therefore oldest—cave (Ruin Level, c. 1900 m a.s.l.) is a dark clay with laterite-derived minerals, suggesting formation before c. 15 Ma, consistent with the previously proposed Eocene–Oligocene age. At intermediate elevations (Giant Cave Level, c. 1350 m a.s.l.), a poorly sorted channel facies forms the initial allochthonous sediment. In Hirlatzhöhle to the west, it is reddish-brown and dominated by para-autochthonous radiolarite components, while in the eastern caves, it is greenish (chlorite) and contains Augensteine sensu lato from metamorphosed rocks of the Niedere Tauern. Previous burial age dating of the quartz suggests an emplacement in the caves 4–6 Ma ago. In caves at this elevation, a dark brown fine-grained sediment of slack-water facies follows, which is probably a palaeosol derived from the allochthonous crystalline sediment cover. Above, rounded limestone gravel is at least partly attributed to glacial meltwater. At the top, and almost ubiquitous, is a bright clayey silt. It is carbonate rich and has a varve-like layering. This sediment is attributed to Pleistocene meltwaters and glacial backflooding. While it is normally a few tens of centimetres thick in the Giant Cave Level, it can reach a few metres in the Berger Level (c. 950 m a.s.l.) below. Only there is it partly overlain by Holocene carbonate sands.