Luminescence dating of the Stratzing loess profile (Austria) – Testing the potential of an elevated temperature post-IR IRSL protocol

Abstract

Feldspar infrared stimulated luminescence (IRSL) signals saturate at ∼2000 Gy, i.e. ∼500–700 ka (assuming a dose rate of 3–4 Gy/ka, typical for loess) and it is therefore theoretically possible to date Middle Pleistocene loess. However, the accuracy of age estimates is hampered by anomalous fading, which leads to significant age underestimation. Fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses (as the growth curve approaches saturation). Recent studies have identified a post-IR IRSL signal that shows less fading and is thus less dependent on accurate fading corrections. This study builds upon these investigations and applies a post-IR IRSL SAR dating protocol to polymineral fine-grain samples of the loess/palaeosol sequence in Stratzing, Lower Austria. After a preheat at 320 °C (60 s) and an IR bleach at 50 °C (200 s) IRSL was measured at 290 °C for 200 s; the same set of conditions were used to measure the response to a test dose. Recycling ratios, recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation, although finite residual doses of up to 20 Gy are observed. For the oldest samples, the natural signal is in, or close to, saturation, indicating that fading is negligible in nature. This observation is inconsistent with the measured laboratory fading rates of 1–1.5%/decade and needs further investigation.