Deciphering fluvial landscape evolution by luminescence dating of river terrace formation: a case study from Northern Bavaria, Germany
Kolb, Thomas; Fuchs, Markus; Zöller, Ludwig
published: Apr 1, 2016
ArtNo. ESP023106001002, Price: 29.00 €
Fluvial terraces are widespread geomorphic features, which formed dominantly during the Quaternary. Besides tectonics, the formation of Quaternary fluvial terraces is related to paleoclimatic changes and corresponding changes in fluvial discharge and sediment load. However, within the Pleistocene, the exact timing and the paleoenvironmental conditions for terrace formation are still under debate and traditional concepts are questioned. To shed light on the Pleistocene environmental conditions for terrace formation, we investigate their timing by establishing a local terrace chronostratigraphy based on numerical dating. The study is located in a small valley in northern Bavaria, Germany. Here, within a former interconnection between two headwater streams of the Main River, five Pleistocene terraces are distinguished. The terraces are interpreted as the result of a complex landscape evolution, which is characterized by an at least twofold river deflection. Fluvial and periglacial slope sediments are still widely preserved and can be used as sediment archives. The study is focused on dating the upper Pleistocene terrace (T2 level). Following traditional explanations, this terrace level has so far been interpreted as a Würmian (Weichselian) formation, developed during the last glacial maximum (LGM). Optically stimulated luminescence (OSL) ages obtained for fluvial deposits and hillslope sediments, however, indicate a significantly older age for the gravel accumulation. The correctness of the OSL ages is supported by radiocarbon AMS dating. These results point to significant Würmian (Weichselian) fluvial morphodynamics during early stages of the last glacial cycle (ca. 90 – 80 ka) as well as during the Lower and Middle Pleniglacial (ca. 64 – 30 ka). Furthermore, the results indicate that the response of fluvial systems to environmental changes is complex and strongly depends on local conditions, such as morphology and lithology, the regional hydrological setting in general or the alignment of river courses and the possibility of river deflection in particular.