Investigations of the post-IR IRSL protocol applied to single K-feldspar grains from fluvial sediment samples

摘要

The post-IR IRSL protocol with single K-feldspar grains was applied to three samples taken from a fluvial sedimentary sequence at the archaeological site of the Dali Man, Shaanxi Province, China. K-feldspar coarse grains were extracted for measurement. Approximately 30-40% of the grains were sufficiently bright to measure, and after application of rejection criteria based on signal strength, recuperation, recycling ratio and saturation dose, ～10-15% of the grains were used for D _e calculation. The relationship of signal decay rate and form of D _e(t)with the recovery dose were investigated. The dose recovery ratios of the samples after initial bleaching with the four different light sources were within uncertainties of unity. No anomalous fading was observed. The over-dispersion of the recovered dose and D _e values were similar, suggesting neither incomplete resetting of the post-IR IRSL signals nor spatially heterogeneous dose rates significantly affected the natural dose estimates. The values of D _e obtained with the single K-feldspar grain post-IR IRSL protocol were in the range ～400-490 Gy. Combining all of the measured single-grain signals for each of the individual samples(into a 'synthetic single aliquot')increased the D _e estimates to the range ～700-900 Gy, suggesting that the grains screened-out by the rejection criteria may have the potential to cause palaeodose over-estimation, although this finding requires a more extensive investigation. Thermally transferred signals were found in the single K-feldspar grains post-IR IRSL protocol, and the proportion of thermally transferred signal to test-dose OSL signal(stimulation at 290 °C)from the natural dose was higher than from regenerative doses, and the proportion was grain- and dose-dependent. As such, TT-post-IR IRSL signals at 290 °C have the potential to cause dose underestimation, although this may be reduced by using larger test-dose irradiations. Our study demonstrates considerable potential in the post-IR IRSL method in providing chronological control in studies relevant to human evolution in the later-Pleistocene.