Late Quaternary loess deposition in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland and its palaeoclimatic implications

Abstract

The piedmont aeolian sediment in Central Asia is has been widely used for Quaternary palaeoclimatic reconstructions. Here we present detailed sedimentological and rock magnetic investigations on 188 samples from the~9.4m-thick Urumqi River section (URS) in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland. Optically stimulated luminescence (OSL) dating constrains the time-span of the URS loess sedimentation from c. 28 to c. 6.8 ka. This chronology implies that the onset of the URS loess sedimentation is approximately synchronous with the Shangwangfeng Glaciation (MIS 2) in the headwaters of the Urumqi River. Analyses of sediment grain size and rock magnetic parameters indicate that sediment grain-size composition controls magnetic properties of the URS loess, i.e. the wind intensity model, distinct from the pedogenic model interpreting the variations in magnetic properties of the loess in the Chinese Loess Plateau (CLP). Overall, the variations in sediment grain size and magnetic properties throughout the URS indicate that the present study area was dominated by a climate of strengthened wind associated with gradually intensified aridity during the latest Pleistocene. In contrast, the intensity of aridity and coldness during the early Holocene gradually became relatively weakened.

The relationship between environmental factors and magnetic susceptibility in the Ili loess, Tianshan Mountains, Central Asia

“…Under the cold climatic conditions, the strengthened westerly wind brings more original dust to the deposition area, and the local material contribution decreases, so that χ lf would be higher. Therefore, as well as detrital dust, the Ili loess is also influenced by local materials, and the mixture of different materials weakens the impact on χ fd or χ fd % in the Ili loess and loess in other regions, such as the loess sediments in northern piedmont of Tianshan Mountains (Lu et al, ; H. Zhao et al, ).…”

Origin of Late Quaternary Gravel and Drainage Basin Expansion in the Northern Chinese Tian Shan: Insights From Sediment Provenance Analyses

“…The climate during the late Cenozoic in the Tian Shan and its surrounding area was characterized by a trend of aridification (Sun et al., 2008). In the present studied area, sedimentological and rock magnetic studies on loess sediments have revealed the gradually intensified aridity of the climate since the latest Pleistocene (Lu et al., 2016). The present‐day regional climate is controlled largely by the mid‐latitude westerlies.…”

“…Weakly‐cemented Paleogene‐Neogene sedimentary strata are mainly exposed in the proximal foreland basin owing to folding and thrusting (Lu, Burbank, Li, et al., 2010, 2015) (Figure 1b), and a small amount of these strata are exposed sporadically in some small, uplifted intermountain basins (Deng et al., 2000; Jolivet et al., 2018). Late Quaternary alluvial deposits and aeolian loess often uncomfortably overlie the pre‐Quaternary strata involved in thrust‐related folds (Lu, Burbank, & Li, 2010, 2016).…”

Late Quaternary thrusting in the southern margin of the Chaiwopu Basin, northern Chinese Tian Shan foreland

“…As for terrace T 5 , an ESR sample taken from the layer of silt at the top of terrace gravels was dated to 142 ± 14 ka (Lu et al., 2014). This age is obviously older than the OSL age of 27.4 ± 3.1 ka of the sample taken from the base of loess covering the deposits of terrace T 5 (Lu et al., 2016), likely implying that the loess has not accumulated immediately after terrace abandonment. Given the uncertainty of the dates, we do not determine the time interval between terrace abandonment and loess deposition.…”