Heavy mineral assemblages and sedimentation rates of eastern Central Asian loess: Paleoenvironmental implications

Abstract

Central Asian loess deposits record the evolution of aridification across the Asian interior. However, paleoclimatic proxies are strongly influenced by the variation of the dust source and accumulation process. In order to decipher the paleoenvironmental changes, a sensitive paleoclimatic proxy with clear source and accumulation process will be needed. In this study, heavy mineral assemblages and sedimentation rates were investigated in a 30-kyr loess section in the Ili Basin, Xinjiang, northwestern China. During Marine Isotope Stage (MIS) 2, trends in dust sedimentation rate were similar to those of the Chinese Loess Plateau (CLP), in anti-phase with Northern Hemisphere Summer Insolation (NHSI) at 65°N. Amphibole/epidote ratios (contents and mean grain size) were low during cold phases, such as the late Last Glacial Maximum (LGM) and Heinrich Event (H) 1; their ratios were higher during adjacent warm periods; this was attributed to aeolian sorting during transportation. Namely, greater sorting between amphibole and epidote occurred in warmer phases, and weaker sorting occurred in colder phases. The amphibole/epidote ratio could serve as a proxy for wind intensity, and thus the Siberian High (SH) intensity. Amphibole/epidote ratio was a more appropriate proxy to record wind intensity than dust sedimentation rate which was also influenced by sediment availability. A higher amphibole/epidote ratio corresponded to a more negative East Asian stalagmite δ18O, indicating an anti-phase relationship between the SH and East Asian Summer Monsoon (EASM) during the MIS 2.