A simplified multiple aliquot regenerative dose protocol to extend the dating limit of K-feldspar pIRIR signal

Abstract

The post-infrared infrared stimulated luminescence signal (pIRIR) from K-feldspar shows significantly less athermal fading than the conventional IRSL signal, thus it has been widely used for dating Quaternary deposits. With the single aliquot regenerative dose (SAR) protocol, the test dose signal is influenced by the preceding regenerative dose, and the characteristic saturation dose (D0) of the pIRIR signal is mostly in the range of 200–600 Gy, depending on the size of the test dose. According to the D0 value, the dating range of pIRIR is restricted to <300 ka with the SAR protocol. Here we present a multiple aliquot regenerative dose (MAR) protocol using low-temperature thermoluminescence (TL) signal for inter-aliquot normalisation. The multiple-elevated-temperature (MET) pIRIR signals up to 290 °C are investigated. The D0 increases to 850–1300 Gy with this protocol, which should represent the intrinsic D0 of IR or pIRIR signals of K-feldspar. Based on the higher D0, this protocol has the potential to date samples with equivalent doses (Des) up to 2000 Gy, i.e. up to ∼600 ka considering a dose rate of ∼3.5 Gy·ka−1. Applications of this MAR protocol on two loess samples from the Chinese Loess Plateau provide ages consistent with expected ages up to 350 ka, with the MET-pIRIR signal at 290 °C. However, tests on three fluvial and alluvial samples show age overestimation with the new MAR protocol as well as SAR protocol, which may result from the hard-to-bleach property of the high-temperature pIRIR signals. Simulations of fading correction indicate that the age will be over-corrected when the laboratory dose response curve has a D0 smaller than the true D0 of the signal. Caution should be taken in fading corrected ages measured with the conventional SAR protocol, as the D0 values are always underestimated in this case.