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

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.