Reconstructing pre-LGM landscape evolution in the Eastern Alps (Austria): New insights from the Bad Aussee Basin

Le résumé fourni par la source

The erosive impact of glaciers during the Last Glacial Maximum (LGM) has largely obscured evidence of earlier, less extensive glacial advances within the Alps. While Alpine paleoclimate records show that the Marine Isotope Stage (MIS) 3 was characterized by pronounced changes between stadial and interstadial conditions, similar to the Dansgaard-Oeschger (D-O) cycles observed in ice-cores from Greenland, depositional evidence of glacial extent during this period remains scarce. Here, we present new data from a sedimentary archive in the inner-alpine Bad Aussee Basin in the Austrian Eastern Alps. Located close to the main accumulation areas of the former Traun Glacier, its topographic setting suggests that down-valley glacial damming is a major factor controlling the timing of depositional phases throughout glacial-interglacial cycles. Under present interglacial conditions, fluvial incision takes place.Our investigations are focused on an 880-m-long Pleistocene sedimentary record, recovered by a drilling intended for salt exploration and later included in the ICDP (International Continental Scientific Drilling Program) project DOVE (Drilling Overdeepened Alpine Valleys). Three distinct depositional phases can be distinguished. The basal Unit A (880–580 m), dominated by glaciolacustrine deposits, can be correlated with the Penultimate Glaciation (MIS 6) based on luminescence dating and consists of locally sourced material from the Northern Calcareous Alps. In contrast, Unit B (580–67 m) records a succession of lacustrine and deltaic sediments largely derived from the Austroalpine crystalline basement to the south of the Enns Valley. Luminescence results indicate that deposition took place mainly during MIS 3. Unit B exhibits several abrupt increases in total organic carbon (TOC), which we interpret as organic productivity events, followed by a gradual decrease. This TOC pattern closely resembles the D-O cycles, allowing a tentative correlation between individual events. Unit C (67–0 m) consists of subglacial till which we attribute to the LGM, although no numerical dating results are available.Based on the sedimentological, chronological and provenance data, this study presents a reconstruction of the pre-LGM landscape evolution of the Bad Aussee Basin with particular focus on the MIS 3 stadial-interstadial cycles. Placing our results in a broader regional context, we discuss the implications for glacial dynamics and drainage evolution in the Traun and Enns valleys.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.