Luminescence-based chronologies for Palaeolithic sites in the Nihewan Basin, northern China: first tests using newly developed optical dating procedures for potassium feldspar grains
The Nihewan Basin in northern China is a key region in East Asia for the study of early human evolution, owing to the abundance of Palaeolithic sites with ages spanning the entire Pleistocene. However, most of the sites assigned to the Middle to Late Pleistocene have not been dated or are poorly dated, due to the lack of suitable numerical dating techniques. Optically stimulated luminescence (OSL) dating of quartz grains is commonly restricted to deposits younger than ~ 200 ka, but recent developments using the infrared stimulated luminescence (IRSL) emissions from grains of potassium-rich feldspar (K-feldspar) offer the potential to date Middle Pleistocene deposits using post-infrared IRSL (pIRIR) signals that do not suffer from 'anomalous fading'. In this paper, we report the first archaeological applications of the recently developed pre-dose multiple elevated temperature pIRIR (pMET-pIRIR) procedures for K-feldspar, which we applied to the sedimentary deposits at one Lower Palaeolithic site (Donggutuo) and one putatively Middle Palaeolithic site (Motianling) in the Nihewan Basin. Equivalent dose (De) values were measured, and non-fading signals were identified, using single-aliquot (SAR) and multiple-aliquot (MAR) regenerative-dose pMET-pIRIR procedures. For a sample from Donggutuo expected to be in field saturation, the natural pMET-pIRIR signals were consistent with, or close, to the laboratory saturation levels only when the MAR procedure was used. For the samples from Motianling, however, both the SAR and MAR procedures could be applied and these yielded indistinguishable De estimates. Our study shows that De values of up to 1500 Gy (or possibly 2000 Gy) can be measured using pMET-pIRIR procedures, corresponding to ages of up to 500 ka (or 650 ka) for deposits with environmental dose rates of ~ 3 Gy/ka, as is typical for this region. Our results also indicate that samples from a single study area (the Nihewan Basin) can respond differently to the same measurement conditions. As regards the archaeology of the Nihewan Basin, we date the upper part of the cultural layer at the Motianling site to 322 ± 33 ka and the underlying culturally sterile deposits to 370 ± 50 ka. These ages challenge the stratigraphic correlation of the stone artefacts to the Middle Palaeolithic and suggest that they should, instead, be assigned to the Lower Palaeolithic. Given this revised chronology, there is clearly a need to reassess the antiquity of other sites in the Nihewan Basin that have similarly been assigned previously to the Middle Palaeolithic. The pMET-pIRIR procedures tested in this paper show great promise as suitable chronometers for this task, and should be able to provide a timeline for human evolution and activities extending over the last half-million years in this key region of East Asia.