Single-grain dating of potassium-rich feldspar grains: Towards a global standardised growth curve for the post-IR IRSL signal

Potassium-rich feldspar (K-feldspar) grains were extracted from 28 sediment samples from sites in Asia, Europe and Africa and the dose response curves - or growth curves - were constructed from the post-infrared infrared stimulated luminescence (pIRIR) signals emitted by individual grains. The samples exhibit large between-grain variation in both pIRIR signal intensity and the shape of the corresponding growth curves; the latter can be largely explained as a result of measurement uncertainties, including counting statistics and instrumental irreproducibility. This between-grain variation can be reduced by applying a least-squares normalisation (LS-normalisation) procedure, which allows a common growth curve - or global standardised growth curve (gSGC) - to be established for individual K-feldspar grains from the range of samples investigated. Equivalent dose (D-e) values for single grains can be estimated using the fitting parameters of the gSGC, together with measurements of the natural signal (L-n), one regenerative-dose signal (L-x) and their corresponding test-dose signals (T-n, T-x). The D-e values obtained using the gSGC approach are consistent at 2 sigma with those obtained from the individual growth curves constructed for each of the grains. The establishment of a gSGC greatly reduces the time required to measure a large number of grains for old samples, and it also overcomes the problem of D-e underestimation that can occur using a full single-aliquot (or single-grain) regenerative-dose (SAR) procedure when a large number of grains are rejected due to issues of 'saturation'. The construction of a gSGC may, therefore, potentially extend the dating range of pIRIR signals beyond the reliable limit of D-e estimation using the standard SAR method.