Optical dating of sand wedges and ice‐wedge casts from Q inghai L ake area on the northeastern Q inghai‐ T ibetan P lateau and its palaeoenvironmental implications

Sand wedges and ice‐wedge casts in theQinghaiLake area on the northeasternQinghai‐TibetanPlateau (QTP) occur within alluvial gravel or river terrace deposits. In this study, we report the results of quartz Optically Stimulated Luminescence (OSL) dating of the infill of five relict sand wedges and one ice‐wedge cast. Combining our dating results with previously published luminescence ages of permafrost wedges in theQinghaiLake area, we show that sand/ice wedges formed atc. 62 ka,c.45 ka and between 30 and 15 ka, and that the mean annual air temperature (MAAT) was depressed by at least ∼3°Crelative to present during the sand/ice‐wedge formation periods. This new work is partially corroborated by post‐LGMproxy records from lakes and aeolian deposits reported from the northeasternQTP. It also significantly extends the palaeoenvironmental record in the region in the period before theLGM,when other proxy records are rare, allowing a better understanding of the palaeoenvironmental conditions on the northeasternQTP.