Spatio-temporal distribution of Quaternary loess across Central Asia

Abstract

Central Asia (CA) is one of the main loess regions in the world and provides important information for the understanding of paleoclimate and paleoenvironmental changes. However, the spatio-temporal variability of the loess distribution is still not fully understood. Combining previous studies with our recent field investigations, we focus on the spatial distribution and ages of loess sediments in CA. Loess sediments are mainly distributed on the windward piedmonts of Central Asian high mountains, e.g. the Tianshan Mountains, Kunlun Mountains, and river terraces, with distinct pedogenic characteristics. The distribution of loess sediments is not only related to atmospheric circulations and regional climate but also closely related to landforms. Based on field observations and the pedogenic environment, we recommend that the loess distribution should be divided into three subregions (Western CA, Northern CA, and Eastern CA), which are approximately coincident with the 60% and 30% winter-half year's precipitation percentage contours, and also correspond to three loess depocenters with thicknesses over 200 m. Paleomagnetic, luminescence dating and AMS 14C geochronology indicated that most of the loess outcrops have developed since the last interglacial-glacial period; although CA loess sediments can span the entire Quaternary period and even extend into the Pliocene. AMS 14C can provide reliable ages for the last 25–30 kyr. Quartz OSL and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating techniques, based on well-bleached natural environmental materials, can provide reliable ages younger than 80 ka. The luminescence ages of older samples may be underestimated due to signal saturation problems. Dating of deposits at some elevated locations in CA shows rapid and discontinuous deposition, implying that caution is required in the interpretation of proxies and paleoenvironment. Spatial-temporal distributions of Central Asian loess luminescence ages indicate different clusters in different loess subregions, but generally the periods of strong dust activity occurred during cold glacial periods or stadials. New dating techniques should be developed to enable high-resolution paleoclimate reconstruction.