Intensified Northern Hemisphere Glaciation Facilitates Continuous Accumulation of Late Pliocene Loess on the Western Margin of the Pamir

Abstract

Thick eolian loess sequences in arid Central Asia (CA) contain a wealth of information on the intensity variations of midlatitude westerlies and the aridification history of the nearby deserts. In this study, detailed lithologic and magnetostratigraphic investigations suggest that loess deposits on the western margin of the Pamir Plateau began to accumulate at around 2.7 Ma, representing the most complete and oldest loess‐paleosol sequence in western CA. The widely distributed continuous loess deposition in the region suggests a rapid desiccation of CA during the late Pliocene. A synthesis of the initial timing and spatial distribution of late Cenozoic eolian deposits on the Eurasian continent further demonstrates that the dramatic increase in global ice volume exerted a dominant role in the expansion of eolian loess deposits in CA, China, and Europe, and middle Pleistocene expansion is a crucial precondition for the establishment of modern distribution patterns of the Eurasian loess belt.

Magnetic Proxy of Eurasian Loess Revealing Enhanced Physical Erosion Since the Mid‐Pleistocene Transition

“…In this study, we re-sampled the upper ∼70 m of the KMD section, which were deposited since the middle Pleistocene and were not investigated in Zan et al (2022). The KMD magnetic susceptibility record is well correlated with that of the CHM section in south Tajikistan (Ding et al, 2002) and the LC section on the CLP (T. Liu, 1985) (Figure S1 in Supporting Information S1).…”

“…Based on the comparison of magnetic susceptibility records between DK and CHM, the orbitally tuned age of the DK section was determined to be ∼0.8 Ma (Jia et al., 2018). In recent years, high‐resolution magnetostratigraphic studies extended the age of the KMD profile to ∼2.7 Ma (Zan et al., 2022). Climatically, Tajikistan has Mediterranean climate, characterized by hot and dry summers and cool and humid winters (Figure 1b).…”

中亚黄土粉尘与冰冻圈演化、太平洋生产力和全球变化的联系

“…在乌兹别克斯坦塔什干地区，100 m 黄土地层发 育有 10 套古土壤层(PC1~PC10；Pedocomplexes，简写 PC)；在哈萨克斯坦东南 部可以辨认出 8 套古土壤层 [18] . 最近对天山南麓塔吉克斯坦 Karamaidan 黄土地 层的研究发现 [23] ，该剖面可以清晰划分出 33 套黄土/古土壤旋回，且可以与黄土 高原第四纪以来的黄土-古土壤序列进行较好对比，是中亚西部目前已知的地层 序列最为完整的黄土粉尘记录(图 2). 而位于西风水汽背风坡的塔里木盆地，由 于气候极端干旱，年降雨量通常小于 100 mm，黄土粉尘在沉积后经历了比较微 弱的后期化学风化和成壤作用的改造，以砂黄土为主，详细的黄土-古土壤层划 分比较困难 13 .…”

“…而位于西风水汽背风坡的塔里木盆地，由 于气候极端干旱，年降雨量通常小于 100 mm，黄土粉尘在沉积后经历了比较微 弱的后期化学风化和成壤作用的改造，以砂黄土为主，详细的黄土-古土壤层划 分比较困难 13 . 早期的研究对中亚地区古土壤层是冰期发育还是间冰期形成存在 一定争议，目前通过多学科的综合分析，已普遍认为该地区古土壤的形成主要与 间冰期温暖湿润的气候条件密切相关， 土壤发育模式与中国黄土高原一致 [21,23,26] . [17] .…”

“…[17] . 塔吉克斯坦 Karamaidan 剖面古地磁定年结果显示，该地 区黄土粉尘于~2.7 Ma 开始出现 [23]. 高精度的古地磁测量和轨道调谐结果揭示， 西昆仑山地区 671 m 黄土序列的底部年龄为~3.6 Ma，是中亚地区已知的沉积速 率最高、年代最老的连续黄土粉尘记录 13 .…”