Luminescence dating of palaeoshoreline deposits from Khyargas Nuur, Western Mongolia: A comparative study of multigrain and single-grain K-feldspar dating

The evolution of lakes in western Mongolia and their responses to climate changes and glacial meltwater input remain poorly understood. This study evaluates the reliability of multigrain and single-grain K-feldspar post-infrared infrared stimulated luminescence (IRSL) (pIRIR) dating applied to palaeoshoreline sediments at Khyargas Nuur, western Mongolia. It specifically focuses on assessing the extent of pIRIR signal bleaching and proposes an improved methodology for dating shoreline sediments where quartz is unsuitable for luminescence dating. Multigrain pIRIR signals measured at 150°C (pIRIR₁₅₀) and 225°C (pIRIR₂₂₅) were used to date Holocene and older samples, respectively. Single-grain pIRIR dating was conducted for the first time in the region to assess bleaching conditions and refine age estimates. Our comprehensive methodological approach was essential for constructing a robust lake level chronology. Single-grain measurements, combined with the application of the minimum age model (MAM), allowed us to identify and correct for incomplete bleaching in several samples. Notably, many of the multigrain aliquots showed no clear signs of poor bleaching in their equivalent dose (D_e) distributions, which would have resulted in significant age overestimation if single-grain data had not been available. Without this approach, the chronology of lake level fluctuations could have been significantly misinterpreted. By addressing this issue, we confidently date the highest lake level at ~129 m above modern lake (a.m.l) to marine isotope stage (MIS) 5 (~89 ka) and a subsequent highstand (~118 m a.m.l) to the Late Glacial (~14 ka). Following this highstand, lake levels declined rapidly (~25 m/ka), reaching ~20 m a.m.l through the Late Glacial to early Holocene transition. During the late Holocene, the palaeolake experienced a gradual regression to ~7 m a.m.l before reaching its current elevation of 1029 m above sea level (a.s.l).