Geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the Tibetan Plateau

Abstract

Aeolian sediments are an important archive for palaeoclimate reconstructions on the Tibetan Plateau. The accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases, respectively. During the last decade the number of OSL (optically stimulated luminescence) ages of aeolian sediments has been rapidly increasing. This study summarises the results from more than 300 individual OSL ages. Despite the widespread occurrence of aeolian sediments on the Tibetan Plateau nearly all OSL samples are located on the northeastern and the southern part. In most regions the strongest accumulation occurred during the late Glacial and in the early Holocene. This coincides with the strengthening of the Asian summer monsoon on the Tibetan Plateau and wetter climate conditions after the relatively dry glacial times. The development of a sufficient vegetation cover, acting as a sediment trap, seems to be an important requirement for the preservation of aeolian archives. Short dry periods like the Younger Dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions. The formation of palaeosols occurred mainly during the wet early and mid-Holocene, but the number of ages is relatively small. In contrast, a second phase of aeolian accumulation during the late Holocene was related to the weakening of the Asian summer monsoon and drier climate conditions. This indicates that the reaction of aeolian accumulation on the Tibetan Plateau depends on the previous climate state. A comparison between the OSL ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types. While the sand deposits in different basins resemble wet and dry phases, loess deposits show no common signal between the analysed areas. This indicates an influence of local factors, such as varying source areas and erosive processes on the slopes. In general, the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence.