Revisiting the ‘Hole of Bad Aussee’: A key sedimentary record of Quaternary landscape dynamics in the Eastern Alps (Austria)

Abstract

Despite a long history of geologic research in the European Eastern Alps, Quaternary landscape evolution before the Last Glacial Maximum (LGM) remains poorly constrained due to the scarcity of dated sedimentary archives, particularly in inneralpine regions. In this study, we reinvestigate an 880-m-long drill core from Bad Aussee (Styria, Austria), originally drilled for salt exploration. Sedimentological, geochemical, and geochronological analyses allow us to identify three major depositional units spanning the last two glacial cycles. The succession starts with glaciolacustrine deposition during the penultimate glaciation (Rissian, Marine Isotope Stage 6), consisting mainly of glacially sourced material of local provenance (carbonates and evaporites). In contrast, the >500-m-thick overlying deltaic and lacustrine deposits (Early to Middle Würmian) indicate a source area dominated by crystalline rocks. This observation suggests that, for a prolonged period between the Last Interglacial and the Late Würmian (MIS 2), the Upper Enns Valley drained into today's Traun Valley, crossing the present-day drainage divide. Furthermore, the lack of glacial deposits indicates that glacial advances during this phase did not reach the Bad Aussee Basin. On top of the succession, a carbonate-rich subglacial till can be attributed to the LGM. While questions regarding the formation mechanism of this exceptionally deep and confined Quaternary basin remain, our results challenge the previously suggested model of subglacial dissolution and subsequent formation and rapid infill of a deep lake. Salt-related syndepositional subsidence could serve as an alternative explanation for the observed stratigraphy.