Middle Pleistocene Glaciations in the northern Alpine Foreland - New insights from luminescene dating

The Quaternary spans the last ~2.6 million years and is characterised by marked climatic fluctuations. Reconstructing these past fluctuations is a fundamental requirement for understanding present and future climate change. The northern Alpine Foreland is a classic area of Quaternary research, but profound gaps of knowledge exist concerning the timing and extent of its glaciations. This particularly concerns glaciations older than ~50 ka due to a lack of numerical ages constraining the deposition of glacier related sediments. The major objective of the proposed study is to establish luminescence chronologies of glaciofluvial terraces in the German and Austrian Alpine Foreland. The focus is set on older terraces (~130-300 ka) formed during the Middle Pleistocene. Their formation is mainly climatically driven and often, they can be correlated with terminal moraines. Thus, the age of the terraces can be used to reconstruct the extent and timing of former glaciations and of climatic conditions. The study proposes to make use of recent advances in luminescence dating which bear great potential to extend the terrace chronostratigraphy to around 300 ka. A large, cross-border study area will allow regional correlations of the dated sediments as well as the reconstruction of past climatic gradients and regional differences in glacier dynamics. Further, correlations with marine climatic records and with the N-European Saale glaciations will provide important insights into the impact of past global climate change on terrestrial environments.

To bring more light into the local climate history of the Northern Alpine Foreland during the ice age, samples for Optically Stimulated Luminescence dating (OSL) were taken in the upper- and lower Austrian Alpine Foreland and in Southern Germany. After sample preparation in red light conditions all samples were tested to record the specific luminescence characteristics of quartz and potassium-rich feldspar.Because the Southern German and the Austrian samples displayed different characteristics, new methodological strategies had to be developed and applied. Single grain luminescence analysis of K-Feldspar and detailed mineralogical and geochemical investigations made it possible to date the samples and revealed an extensive chronological accordance of the samples from different regions.The majority of samples yielded ages of around 130-170 ka and thus belong to the time period of the Marine Isotope Stage (MIS) 6. For some samples the dating results pointed towards ages older than the MIS 8 from the same depositional units. Because of these discrepancies age, investigation in order to achieve independent age control had to be conducted: dating of methodologically comparable samples from a research drilling, comparative dating approaches using the in-situ cosmogenic isotopes, radiocarbon and pollen investigations.In the drilling glaciofluvial gravels, fine lake sediments and peat layers were encountered and allowed the application of the radiocarbon method together with OSL. Unfortunately the youngest and highest peat layer only showed minimum radiocarbon ages of more than 42.3 ka BP, which means that no exact numerical age could be determined using this method. Because of that, pollen were additionally investigated. Based on this analysis, the formation of the peat layers with the sampled pollen happened during the Early Würmian, which is in agreement with first OSL-dates.In order to establish an additional method for independent age control of OSL-samples, we investigated samples with a methodological combination of OSL and cosmogenic isotope dating using 26Al und 10Be. It was possible to prove that consistent ages form OSL and other age control methods were gained for Middle Pleistocene sediments. Thus, in the frame of this FWF-project a little bit more light was brought into the local climate history of the Northern Alpine Foreland.