Pulsed IRSL: A stable and fast bleaching luminescence signal from feldspar for dating Quaternary sediments

摘要

Elevated temperature post-infrared infrared stimulated luminescence (post-IR IRSL; pIRIR) dating method using feldspar has led to a significant advancement in dating Quaternary sediments, as this signal has been shown to be stable on geological time scales. In comparison to the conventional IRSL, the pIRIR signal is nearly free from anomalous fading, but it is more difficult to reset during daylight exposure; the latter characteristic may give rise to age over-estimation in some environments because of partial bleaching. The pulsed IRSL signal has also been known to be less affected by anomalous fading, when the signal is recorded during the off-time of LED stimulation pulses. In this study, we compare the signal bleachability, thermal and athermal stability, and age estimates derived using different measurement methods, i.e., pulsed IRSL measured at 50 °C (pulsed IR; subscripts refers to measurement temperature), continuous wave (CW) pIRIR and pIRIR signals, as well as the two IR signals measured as a part of the pIRIR protocols. This comparison is carried out for 3 samples taken from Late Quaternary fluvial sediments, which have independent age estimates from radiocarbon dating and tephrochronology. We observe that under exposure to solar simulator, the pulsed IR signal bleaches as rapidly as the CW IR, and much more rapidly than the pIRIR signals. Furthermore, the pulsed IR signal is also as stable as the pIRIR signals, especially when the middle part of the decay curve is used for signal intensity calculation.