Abstract: Hochterrassen sind eine im nördlichen Alpenvorland weit verbreitete geomorphologische Form, denen traditionell eine Entstehung während der Riss-Kaltzeit zugeordnet wird. Allerdings sind oftmals unterschiedliche Terrassenniveaus innerhalb der Hochterrassen zu beobachten, deren Altersstellung noch unbekannt ist. Dieses Thema wird hier am Beispiel der Langweider und Rainer Hochterrassen im unteren Lechtal mit Hilfe relativer und numerischer Datierungsmethoden untersucht. Das morphologisch tiefste Teilniveau, welches nur am westlichen Rand der Rainer Hochterrasse erhalten ist, stellt höchstwahrscheinlich eine frühwürmzeitliche Übergangsterrasse dar. Das nächsthöhere Niveau der Jüngeren Hochterrasse muss älter sein als das letzte Interglazial. Dafür sprechen die warmzeitliche Parabraunerde, die in Resten am Top des Terrassenkörpers erhalten ist, und die würmzeitliche Lössdeckschicht, welche durch Lumineszenzmessungen und Paläoböden datiert werden kann. Die Jüngere Hochterrasse besteht aus zwei gestapelten Kieskörpern, welche mindestens zwei Akkumulationsphasen zugeordnet werden können. Der hangende Kieskörper entstand während der Sauerstoff-Isotopenstufe (MIS) 6 und der liegende Kieskörper zwischen MIS 7 und MIS 10 (oder älter). Es ist jedoch nicht geklärt, in welcher Aufschüttungsperiode während des Mittelpleistozäns die Ablagerung des liegenden Kieskörpers stattfand. Das höchste Teilniveau, die Ältere Hochterrasse zeigt auch eine Stapelung zweier Kieskörper, für diese liegen aber bisher keine numerischen Altersdaten vor

Abstract: The sedimentary infill of glacially overdeepened valleys (i.e., structures eroded below the fluvial base level) is an excellent but yet underexplored archive with regard to the age, extent, and nature of past glaciations. The ICDP project DOVE (Drilling Overdeepened Alpine Valleys) Phase 1 investigates a series of drill cores from glacially overdeepened troughs at several locations along the northern front of the Alps. All sites will be investigated with regard to several aspects of environmental dynamics during the Quaternary, with focus on the glaciation, vegetation, and landscape history. Geophysical methods (e.g., seismic surveys), for example, will explore the geometry of overdeepened structures to better understand the process of overdeepening. Sedimentological analyses combined with downhole logging, analysis of biological remains, and state-of-the-art geochronological methods, will enable us to reconstruct the erosion and sedimentation history of the overdeepened troughs. This approach is expected to yield significant novel data quantifying the extent and timing of Middle and Late Pleistocene glaciations of the Alps. In a first phase, two sites were drilled in late 2021 into filled overdeepenings below the paleolobe of the Rhine Glacier, and both recovered a trough filling composed of multiphase glacial sequences. Fully cored Hole 5068_1_C reached a depth of 165 m and recovered 10 m molasse bedrock at the base. This hole will be used together with two flush holes (5068_1_A, 5068_1_B) for further geophysical cross-well experiments. Site 5068_2 reached a depth of 255 m and bottomed out near the soft rock-bedrock contact. These two sites are complemented by three legacy drill sites that previously recovered filled overdeepenings below the more eastern Alpine Isar-Loisach, Salzach, and Traun paleoglacier lobes (5068_3, 5068_4, 5068_5). All analysis and interpretations of this DOVE Phase 1 will eventually lay the ground for an upcoming Phase 2 that will complete the pan-Alpine approach. This follow-up phase will investigate overdeepenings formerly occupied by paleoglacier lobes from the western and southern Alpine margins through drilling sites in France, Italy, and Slovenia. Available geological information and infrastructure make the Alps an ideal area to study overdeepened structures; however, the expected results of this study will not be restricted to the Alps. Such features are also known from other formerly glaciated mountain ranges, which are less studied than the Alps and more problematic with regards to drilling logistics. The results of this study will serve as textbook concepts to understand a full range of geological processes relevant to formerly glaciated areas all over our planet

Datierung - Datierungsmethode - Gletscher.