Dust transport information and paleoclimatic changes revealed by the loess in Ranwu, south-eastern Xizang

Abstract

The loess accumulation process has great potential to record patterns of atmospheric circulation change, paleoclimate, and paleoenvironmental evolution. South-eastern Xizang is a climatically sensitive region and here, we analyze a loess profile at Ranwu in order to explore the processes and interactions of dust transport and paleoclimate evolution in the region. Based on parametric grain size end-member analysis, optically stimulated luminescence (OSL) dating, and environmental proxies we show that the Ranwu loess profile comprises five end members (EMs). EM1 represents the fine silt fraction transported by high-altitude westerly winds over long distances; EM2 represents the medium silt fraction accumulated by glacier winds; EM3 is the coarse silt fraction transported by local dust storms under the action of strong glacier winds; EM4 represents the very fine sand fraction transported by strong local dust storms, different wind strengths controls the relative proportion of EM3 and EM4 over time. EM5 is the coarse sand fraction formed from the product of strong weathering of gravels. OSL dating shows loess sedimentation at Ranwu started around 11.16 ka. The prevailing climate was generally warm and wet between 11.6 and 4.2 ka, with four cooling events at 10.50, 9.18, 7.85, and 6.37 ka. Extensive paleosol development between 8.2 and 4.2 ka, a change to dry and cold climate conditions was favorable for loess formation after 4.2 ka. The palaeoenvironmental changes and abrupt climate events recorded in the Ranwu loess sequence are consistent with Holocene global environmental changes.