Analyzing complex single grain feldspar equivalent dose distributions for luminescence dating of glacially derived sediments

Abstract

Overdeepened valleys are structures scoured into the underlying substrate by glaciers that have been subsequently filled with sediment, which recorded the environmental history of the adjacent landscape. Investigated here is an overdeepened structure that was formed beneath the Salzach Paleoglacier west of Freilassing, Bavaria (southern Germany). In a previous study, infinite infrared stimulated luminescence (IRSL) ages have been determined for the lower part of the core using a multi-grain approach. Applying single-grain feldspar luminescence dating allows to identify the unsaturated signals, previously masked by multi-grain signal averaging. Identification of the normally distributed leading edge in equivalent dose (D_e) distributions allows for the dismissal of low value D_e (LOVED) grains that appear to reflect underestimating outliers. Measurement of eleven samples distributed along the entire length of the core yielded two distinct age clusters, for which fading corrected IRSL₅₀ and uncorrected pIRIR₂₂₅ ages agree within uncertainties. Whereas the younger age cluster at the top of the sequence is attributed to Marine Isotope Stage (MIS) 3, the older age cluster is assigned to MIS 6. It is shown that single grain pIRIR measurements will allow to resolve the infill chronology of overdeepened structures in the Alps, at least for the last ca. 200 ka. Overall, the present study represents a further step towards understanding and handling complex D_e distributions often encountered in single grain feldspar luminescence dating. This contributes to better understand the frequently observed age offset between single grain and single-aliquot measurements.