The patchwork loess of Central Asia: Implications for interpreting aeolian dynamics and past climate circulation in piedmont regions

Abstract

Reconstruction of mass accumulation rates (MARs) in loess deposits are widely used for interpreting long‐term aeolian transport and climate dynamics in terrestrial environments. However, these interpretations are often driven by a preponderance of reconstructions from individual or selected sites, which can bias our understanding of past climate, especially in the absence of other proxy information. Recent studies on MARs from multiple loess sites in Arid Central Asia (ACA) reveal disparities in the timing of peaks in accumulation between sites, as well as asynchronies with loess flux in the Chinese Loess Plateau (CLP). We investigate this issue by (1) dating five new sites from the western Ili Basin, therefore extending the spatial cover of loess chronologies across ACA and (2) combining that with MARs from >30 sites across ACA and the CLP over the last 60 ka. Our results indicate spatio‐temporal inhomogeneity in the timing and rate of loess deposition across the ACA, and highlight the importance of interrogating local and regional influences on dust supply and transport. Our synthesis of MARs from ACA and the CLP suggests that the timing of peak dust flux as an indicator of large‐scale climate dynamics is best derived from an aggregate of sites; this removes site‐specific bias where local processes or topographic settings outweigh the climate signature.

Variability in geochemical weathering indices in loess over the last full glacial cycle at Karamaidan, central Asia (Tajikistan)

“…Consequently, primary loess deposition at Karamaidan experienced a reduction in both temperatures and precipitations by approximately 15% and 17% respectively, compared to the preceding PS2 pedocomplex. These conditions appear to contradict the hypothesis that there was during the OIS 10.3389/feart.2024.1347910 3 an increase in precipitation favored by the northward expansion of the Asian monsoon and glacial expansion in the Tian Shan, but the spatio-temporal inhomogeneity and asynchrony of these events has recently been emphasized by other authors (Dave et al, 2023a). Of course it might also mean that the Wang's transfer functions, being based on data recorded form Chinese LPSS, are not sensitive enough for the local context.…”

“…Studies on the saturation behavior of fine-grained quartz suggest that this grain-size fraction does not saturate at high doses under laboratory conditions, and therefore tends to underestimate the true depositional age of samples beyond c. 60 ka (Timar-Gabor et al, 2017;Dave et al, 2023a). Therefore, for such samples we additionally measured the D e for fine-grained polymineral aliquots using the elevated temperature post-Infrared-Infrared-Stimulated-Luminescence (pIRIR) signal, to circumvent the issue of anomalous fading (Thiel et al, 2011).…”

“…The stratigraphic log, oxide geochemistry curves (percentage), and magnetic susceptibility are shown relative to depth; luminescence ages (quartz OSL in black circles/plain text; polymineral pIRIR in black dots/italics) are provided on the left. 2017; 2018; Dave et al, 2023a). An alpha efficiency value of 0.038 ± 0.002 for fine-grained quartz and 0.086 ± 0.004 for polymineral fine grains was used for all dose rate calculations (Rees-Jones, 1995).…”

“…There is an increasing balance of evidence indicating spatial variability in loess stratigraphy relating to spatial differences in accumulation rates and palaeo-topography, particularly in piedmont regions (e.g., Fitzsimmons, 2017;Dave et al, 2023a), although in aggregate it may still be possible to make regional correlations and identify "representative" type sections (e.g., Marković et al, 2015a). Even over scales of tens to hundreds of meters, variability in stratigraphy may be observed (e.g., Fitzsimmons et al, 2013;Fenn et al, 2021).…”

“…The Central Asian loess extends along an east-west transect along the piedmonts between the Asian high mountains to the south, and the desert basins to the north (Schaetzl et al, 2018). These deposits vary in thickness and age along the piedmonts (Prud'homme et al, 2021;Dave et al, 2023a). The thickest and longest loess deposits are located at the western end of the Central Asian piedmont, in Tajikistan, where loess up to 200 m thick has accumulated since the early Pleistocene (from 2.5 to 2.0 Ma), comparable to deposits on the Chinese Loess Plateau (Dodonov, 1991;2007;Forster and Heller, 1994;Dodonov and Baiguzina, 1995;Shackleton, 1995;Machalett et al, 2008).…”