Environmental dynamics since the last glacial in arid Central Asia: evidence from grain size distribution and magnetic properties of loess from the Ili Valley, western China

Abstract

24The extensive loess deposits of the Eurasian mid-latitudes provide important terrestrial records 25 of Quaternary climatic change. As yet, however, loess records in Central Asia are poorly understood. 26Here we investigate the grain size and magnetic characteristics of loess from the Nilka (NLK) 27 section in the Ili Basin of eastern Central Asia. Magnetic parameters indicate very weak pedogenesis 28 compared with loess from other regions in Eurasia. The higher χlf values occur in primary loess, 29 rather than in weak paleosols, and the variations in magnetic susceptibility (MS) value correlate 30closely with the proportions of the sand fraction. We attribute this result to high wind strength at the 31 time of loess deposition. To explore the dust transport patterns further, we identified three grain size 32 end members (EM1, mode size 47.5 µm; EM2, 33.6 µm; EM3, 18.9 µm ) which represent distinct 33 aerodynamic environments. EM1 and EM2 represent the grain-size fractions transported from 34 proximal sources in short-term, near-surface suspension during dust outbreaks. Hemisphere summer insolation clearly illustrate local insolation-based control on wind dynamics in 43 the region, and humdity can also influence grain size of loess over MIS3 in particular. Although, the 44 polar front dominated wind dynamics for loess deposition in the region, the Central Asian high 45 mountains obstructed its migration further south. Our results may also support the significance of 46 the mid-latitude westerlies in transmitting North Atlantic climate signals to East Asia. 47 48

Evaluating the paleoclimatic significance of clay mineral records from a late Pleistocene loess-paleosol section of the Ili Basin, Central Asia

“…The NLK is >400 km from the deserts to the west of the Ili Basin (Fig. 1a), and, considering the unmixed end-member of loess grain-size distributions, we found that the fine sand end member is absent in the NLK loess (Li et al, 2017). This suggests that sand fraction may not have had significant impact on the grain size distribution patterns of the NLK loess.…”