Quartz OSL and K-feldspar post-IR IRSL dating of loess in the Huangshui river valley, northeastern Tibetan plateau

摘要

The northeastern Tibetan Plateau (NETP) is located in the climatically sensitive semiarid zone between the regions controlled by the East Asian monsoon and the Westerlies and loess deposits there may preserve a record of regional paleoenvironmental change. Establishing a robust loess chronology is critical for interpreting and correlating environmental records. In this study, quartz optical stimulated luminescence (OSL) and K-feldspar post-IR infrared (IR) stimulated luminescence (pIR-IRSL) dating methods have been used to date the Ledu loess section in the Huangshui river valley, on the NETP. In terms of quartz OSL dating, the results from both the 63–90?μm and 38–63?μm quartz fractions are consistent within errors. The reliability of the 63–90?μm K-feldspar pIRIR dating was confirmed by internal check using preheat plateau, dose recovery, anomalous fading, and residual dose tests. The results suggest that the K-feldspar pIRIR signals at stimulation temperatures of 170 and 225?°C were well bleached before deposition of Ledu loess. Comparison between quartz OSL and K-feldspar pIRIR dating indicates that quartz ages older than 50?ka (～150?Gy) may be underestimated. In establishing the chronological framework for the study section, we selected quartz OSL results for ages <50?ka and the K-feldspar pIRIR170and pIRIR225results for ages >50?ka. The results demonstrate that aeolian dust accumulated continuously between 67 and 25?ka, and there were two gaps in deposition, between 25 and 2?ka and from 80 to 67?ka.