Optical dating of sand wedges and ice-wedge casts from Qinghai Lake area on the northeastern Qinghai- Tibetan Plateau and its palaeoenvironmental implications.

Sand wedges and ice-wedge casts in the Qinghai Lake area on the northeastern Qinghai- Tibetan Plateau ( 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 the Qinghai Lake area, we show that sand/ice wedges formed at c. 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° C relative to present during the sand/ice-wedge formation periods. This new work is partially corroborated by post- LGM proxy records from lakes and aeolian deposits reported from the northeastern QTP. It also significantly extends the palaeoenvironmental record in the region in the period before the LGM, when other proxy records are rare, allowing a better understanding of the palaeoenvironmental conditions on the northeastern QTP. [ABSTRACT FROM AUTHOR]