Loess depositional dynamics and paleoclimatic changes in the Yili Basin, Central Asia, over the past 250 ka

Abstract

Widely distributed loess deposits within the Tianshan Mountains are important archives for studying late Quaternary climate in this Central Asian region. However, insufficient age control for these regional loess records, especially over glacial-interglacial cycles, severely limits our understanding of loess depositional dynamics and accurate interpretation of paleoclimate conditions across central Asia. in this study, we applied K-feldspar optical dating, and magnetic susceptibility, grain size distribution, CaCO3 and color to loess-paleosol sections in the Yili Basin of the Tianshan Mountains to constrain loess depositional dynamics, identify timing of loess-paleosol formation and clarify the role of paleoclimate influence in this region since the late middle Pleistocene. Our results demonstrate that loess deposition started as early as 350 ka in the Yili Basin. Following river down-cutting associated with glacial-interglacial transitions and exposure of riverbed sediments, enhanced dust emission from flood plains played an important role in loess deposition. Very rapid loess deposition as high as 60–120 g cm−2 ka−1 on river terraces occurred during the last interglacial, when loess accumulation at different locations of the site had remarkably different rates, ranging from 10 to 100 g cm−2 ka−1. This heterogeneous behavior indicates that not only climatic changes influenced Yili Basin loess deposition and preservation but by complex interaction of local geomorphology, wind velocity, and changes of materials in dust origins. Depositional hiatuses frequently occurred during the past 250 ka, likely induced by strong erosion resulting from increased wind strength and dry-cold climate with poor vegetation cover in the region. Magnetic susceptibility, grain size distribution, CaCO3 and color analyses of the loess-paleosol sequences showed that paleosols formed around ~288 ka, 230–191 ka, 120–106 ka, 92–89 ka, and 84–71 ka. Hence, a generally moist climate characterized the Yili Basin before Marine Isotope Stages (MIS) 9, MIS 7, MIS 5d, MIS 5b, and the MIS 5-MIS 4 transition, respectively. This study suggests a climate pattern of moist interglacial and dry glacial periods in the Tianshan Mountains, whereas substages of interglacials had cold-moist and warm-dry climate characteristics.