Luminescence dating of pre-Eemian (pre-MIS 5e) fluvial terraces in Northern Bavaria (Germany) – Benefits and limitations of applying a pIRIR225-approach

Abstract

Quartz optically stimulated luminescence (OSL) and post-IR IRSL dating of potassium-rich feldspar separates were applied to fluvial sediments which had been supposed to be of pre-Eemian (pre-MIS 5e) age. Our aim was to establish a reliable chronology for the upper three terrace levels from a sequence of five fluvial terraces in a region of Northern Bavaria (Germany) characterized by a complex Pleistocene fluvial history. The investigated quartz samples proved to be in dose saturation and the calculated OSL ages could only be interpreted as minimum age estimations. The performance of the used pIRIR225-approach was tested by a set of bleaching experiments, dose recovery tests (DRT) and measurements of sample specific laboratory fading rates. Despite applying a pIRIR225-protocol, the phenomenon of ‘anomalous fading’ remained a major problem for age calculation in this study. Although various fading correction methods were applied, only the model proposed by Huntley and Lamothe (2001) could successfully be used. Overall, the corrected pIRIR225-ages were in good agreement with age constraints derived from stratigraphical and sedimentological findings. For some feldspar samples, however, the determined ages were far beyond a realistic age range for a meaningful interpretation when considering the (morpho-)stratigraphical setting. Although the reasons for these significant age overestimations are not clear so far, they might either indicate methodological limitations of the post-IR IRSL approach or point to serious problems attributed to the luminescence properties of the used K-feldspar separates or to the specific regional environmental settings during sample deposition. Despite these problematic findings, the numerical results derived from the post-IR IRSL measurements could be used to establish a preliminary chronological framework for the various evolutionary stages identified for the research area.