The Bleaching of Different K-Feldspar pIRIR Signals of Source Materials of Lacustrine Sediment – A Case Study from Bosten Lake Basin in Arid Central Asia

Abstract The residual ages and bleaching of K-feldspar post-IR IRSL (pIRIR) signals (pIR50IR170, pIR50IR290, and pIR200IR290) for a variety of modern sediment sources to the Bosten Lake basin in the southern Tian Shan of arid central Asia were assessed to identify the most appropriate facies to sample for ascertaining well-bleached, depositional ages associated with Quaternary paleolake development. Results indicate pIR50IR290 residual ages for pluvial fan, fluvial, and eolian sediments cluster at 40–6, 6–3, and 2–1 ka, respectively, and are depositional ages. Residual ages of pIR200IR290 signals are twice that of pIR50IR290 signals, while residual ages of pIR50IR170 signals are similar to that of pIR50IR290 signals for all samples. Eolian and fluvial samples show well-bleached, coarse-grained (90–125 μm) K-feldspar and poorly-bleached coarse grained K-feldspar from pluvial samples. High residual doses in fluvial and pluvial samples indicate it may not be advisable to apply pIRIR dating utilising different pIRIR signals to Holocene lacustrine samples. However, the residual ages measured for eolian deposits are small and can allow precise and robust assessment of paleolake development by targeting the K-feldspar pIR50IR170 signal to date Holocene samples and the pIR200IR290 and pIR50IR290 signals to date Pleistocene samples.