Single-grain K-feldspar luminescence dating of the late Quaternary rapid decline in the largest Lake over the Tibetan Plateau

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Well-preserved shorelines, situated at elevations ranging from tens to hundreds of meters above the current lake levels, are commonly found in the lake basins across the Tibetan Plateau (TP). These shorelines offer a valuable opportunity to reconstruct past hydroclimate changes, contingent upon precise age determination of palaeoshorelines. While single-aliquot luminescence methods have been extensively employed for dating palaeoshoreline sediments, both quartz and K-feldspar fractions, the application of single-grain (SG) dating techniques has been relatively limited, particularly in the case of water-lain sediments where partial bleaching must be taken into account. In this study, we applied the single-grain K-feldspar dating technique using the post-IR IRSL (pIRIR) protocol to a selection of palaeoshorelines from Qinghai Lake, the largest lake on the TP. Our primary objectives were to investigate the behavior of single-grain K-feldspar pIRIR signals and to establish precise timing for late Quaternary lake level fluctuations based on SG data. Our findings reveal a clear correlation between the De (equivalent dose) values of single grains and their fading rates. The higher fading rates observed in dim grains constitute the primary reason for the underestimation of De values. However, it appears that the internal K content of the grains cannot explain the relationship between fading rates and grain brightness. Finally, we utilized the 30% brightest grains for SG pIRIR De determinations, allowing us to reconstruct the historical water level fluctuations of Qinghai Lake. Our results indicate a pronounced decline in lake levels during the last interglacial-glacial transition, approximately 90,000 to 75,000 years ago. This decline can be attributed to the response of regional hydroclimate patterns to global environmental changes.