Overdeepened valleys and basins are commonly found below the present landscape surface in areas that were affected by Quaternary glaciations. Overdeepened troughs and their sedimentary fillings are important in applied geology, for example, for geotechnics of deep foundations and tunnelling, groundwater resource management, and radioactive waste disposal. This publication is an overview of the areal distribution and the geometry of overdeepened troughs in the Alps and their foreland, and summarises the present knowledge of the age and potential processes that may have caused deep erosion. It is shown that overdeepened features within the Alps concur mainly with tectonic structures and/or weak lithologies as well as with Pleistocene ice confluence and partly also diffluence situations. In the foreland, overdeepening is found as elongated buried valleys, mainly oriented in the direction of former ice flow, and glacially scoured basins in the ablation area of glaciers. Some buried deeply incised valleys were generated by fluvial down-cutting during the Messinian crisis but this mechanism of formation applies only for the southern side of the Alps. Lithostratigraphic records and dating evidence reveal that overdeepened valleys were repeatedly occupied and excavated by glaciers during past glaciations. However, the age of the original formation of (non-Messinian) overdeepened structures remains unknown. The mechanisms causing overdeepening also remain unidentified and it can only be speculated that pressurised meltwater played an important role in this context.

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Abstract. Die morphologischen und sedimentären Belege aus dem Raum Lienz liefern starke Argumente gegen die bisher angewandte, fünfgliedrige Stratigraphie des Alpinen Spätglazials (ALG; ca 19–11.7 ka), dem Zeitraum nach dem Würm-Hochglazial (= Alpines Letztes Glaziales Maximum; AlpLGM). Die Resultate einer flächendeckenden geologischen Kartierung (inklusive Erfassung von Massenbewegungen) unterstützt durch geochronologische Methoden sowie Pollenanalysen zeigen, dass sich die ALG-Abfolgen in der Schobergruppe und den Lienzer Dolomiten jeweils in vier „unconformity-bounded units“ im Sinne der Allostratigraphie untergliedern lassen. Diese belegen drei klimato-stratgraphisch korrelierbare Phasen. Deltasedimente und Grund- bzw. Seitenmoränen von Lokalgletschern dokumentieren die Eiszerfallsphase unmittelbar nach dem AlpLGM. Nach der Eiszerfallsphase und vor dem Bölling/Alleröd (B/A)-Interstadial gibt es nur eine markante Phase der Gletscherstabilisierung, die mit dem Gschnitz-Stadial korreliert wird. Multiple Endmoränenwälle belegen aktive Gletscherzungen in der Jüngeren Dryas während des Egesen Stadials. Eine zuvor dem Daun-Stadial (prä-B/A-Interstadial) aufgrund von Schneegrenzdepressionswerten (∆ELA) zugeordneter Gletscherstand wurde mit 10Be auf 12.8 ± 0.6 ka datiert und entspricht dem Egesen-Maximum. Damit kann gezeigt werden, dass die bisherige Praxis ∆ELA-Werte zur stratigrafischen Korrelation über größere Räume zu benutzen nicht nur untauglich ist, sondern letztlich zu Fehlschlüssen hinsichtlich Paläoklima führt. ∆ELA-Werte werden nach wie vor als ein nützliches Werkzeug für Korrelationen im lokalen Maßstab betrachtet, so beispielsweise innerhalb einer Gebirgsgruppe mit vergleichsweise ähnlicher Topographie und Lithologie sowie unter Berücksichtigung von Einschränkungen wie z.B. dem Einfluss einer ehemaligen Schuttbedeckung. Jedenfalls zeigen unsere Resultate, dass eine stratigrafische Korrelation mittels ΔELA-Werten quer über die Alpen kein erfolgreicher Ansatz ist, der zu einer Verzerrung der Resultate und schließlich zu Zirkelschlüssen führt.

Drill cores from the inner-alpine valley terrace of Unterangerberg, located in the Eastern Alps of Austria, offer first insights into a Pleistocene sedimentary record that was not accessible so far. The succession comprises diamict, gravel, sand, lignite and thick, fine grained sediments. Additionally, cataclastic deposits originating from two paleo-landslide events are present. Multi-proxy analyses including sedimentological and palynological investigations as well as radiocarbon and luminescence data record the onset of the last glacial period (Würmian) at Unterangerberg at ∼120–110 ka. This first time period, correlated to the MIS 5d, was characterised by strong fluvial aggradation under cold climatic conditions, with only sparse vegetation cover. Furthermore, two large and quasi-synchronous landslide events occurred during this time interval. No record of the first Early Würmian interstadial (MIS 5c) is preserved. During the second Early Würmian interstadial (MIS 5a), the local vegetation was characterised by a boreal forest dominated by Picea, with few thermophilous elements. The subsequent collapse of the vegetation is recorded by sediments dated to ∼70–60 ka (i.e. MIS 4), with very low pollen concentrations and the potential presence of permafrost. Climatic conditions improved again between ∼55 and 45 ka (MIS 3) and cold-adapted trees re-appeared during interstadials, forming an open forest vegetation. MIS 3 stadials were shorter and less severe than the MIS 4 at Unterangerberg, and vegetation during these cold phases was mainly composed of shrubs, herbs and grasses, similar to what is known from today's alpine timberline. The Unterangerberg record ended at ∼45 ka and/or was truncated by ice during the Last Glacial Maximum.