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

Abstract

In this study, we present clay mineral records from a late Pleistocene loess-paleosol sequence in the Ili Basin, Central Asia, and assess their significance for paleoclimatic reconstruction. The results show that the clay minerals are mainly illite (average 60%) and chlorite (28%), with minor kaolinite (9%) and smectite (3%). Illite was of detrital origin with no obvious modification to its crystal structure. Increases in illite content in the loess are ascribed to wind intensity rather than pedogenesis. High proportions of illite in the clay fraction, and of muscovite in the bulk samples of the paleosol units, may lead to an overestimation of the weathering intensity. Kaolinite was likely inherited from the sedimentary rocks, while chlorite might have been inherited from both sedimentary and metamorphic rocks. The paleoclimatic signals of kaolinite and chlorite were unclear, due to reworking by both fluvial and eolian systems. Smectite was more likely formed by the transformation of biotite and illite, and its variation in the loess sequence was also controlled by wind intensity; this was largely due to aggregation and is unlikely to reflect moisture changes. Although the interpretation of paleoclimate evolution may contain some uncertainties, clay mineralogy does provide the possibility of tracing dust provenance.

Eolian dust dispersal patterns since the last glacial period in eastern Central Asia: insights from a loess-paleosol sequence in the Ili Basin

“…The raw grain size and magnetic susceptibility data for the Nilka loess section are publicly accessible on the GitHub repository: https://github.com/YueLi-ieecas/ Central-Asia-loess.git (Li et al, 2018).…”

“…In Central Asia, the loess deposits drape the piedmont slopes of the major mountain ranges -the Tian Shan, Alai, Altai, and Pamirs, from the Xinjiang province in China (Fang et al, 2002;Li et al, 2016Li et al, , 2015Liu, 1985;Song et al, 2014Song et al, , 2012 through Kazakhstan (Feng et al, 2011;Fitzsimmons et al, 2016;Machalett et al, 2006Machalett et al, , 2008, Kyrgyzstan (Youn et al, 2014), and Uzbekistan (Smalley et al, 2006), and into Tajikistan Li et al, 2016b;Yang et al, 2006). While recent years have witnessed increasing loessbased datasets in the region, the forcing mechanisms and the climatic conditions responsible for loess-paleosol sequences formation are as yet not systematically understood Li et al, 2016Li et al, , 2017Machalett et al, 2008;Song et al, 2018a, b).…”

Radiometric dating of late Quaternary loess in the northern piedmont of South Tianshan Mountains: Implications for reliable dating

“…The Ili Basin is located between the South Tianshan and North Tianshan Mountains, and contains loess deposits reaching 200 m thickness (Song et al, ), but most of the loess natural outcrops have developed since the last glacial period. In the past two decades, many researches have focused on the loess distribution in the Ili Basin (Li et al, ; Shi, ; Song et al, ; Ye, ) and the paleoclimatic significance of various proxies such as particle size (Li, Song, Lai, Han, & An, ; Song, Li, et al, ; Ye, Dong, Yuan, & Ma, ), magnetism (Chen et al, ; Jia, Xia, Wang, Wei, & Liu, ; Shi, Dong, & Fang, ; Song, ; Song, Nie, et al, ; Song, Shi, et al, ), elemental geochemistry (Chen et al, ; Zhang et al, ), and minerals (Li et al, ; Song, Zeng, et al, ), yet late Quaternary loess sediments in this basin remain poorly dated. This prevents us from addressing issues such as synchronicity of abrupt climatic/environmental events on millennial timescales since the last glaciation.…”

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

“…Located in the east of Arid Central Asia (ACA), the Ili Valley (42°14′–44°50′N, 80°09′–84°56′E) in the Xinjiang Province is one of the important loess deposits areas in China and loess in this valley (hereafter referred as “Ili loess”) ranges in thickness from a few meters to 200 m (Song et al, ). Recent years have witnessed much research on the Ili loess, with the focuses of the chronology (E et al, ; Kang et al, ; Qin & Zhou, ; Song, Lai, Li, Chen, & Wang, ; Song, Luo, et al, ; Song, Li, Zhao, Chen, & Zeng, ; Yang et al, ), distribution (Y. Li, Song, Yan, Chen, & An, ; Song et al, ), magnetic susceptibility (MS; Jia, Xia, Wang, Wei, & Liu, ; Y. Liu, Shi, Deng, Su, & Zhang, ; Shi, Dong, & Fang, ; Song, Nie et al, ; Song et al, ; Song, Shi et al, ), geochemistry (X. Chen et al, ; Honda, Yabuki, Suzuki, Ye, & Tatsumi, ; W. Zhang et al, ), and mineral composition (Y. Li, Song, Zeng, et al, ; Song, Zeng, et al, ; Ye, ; Zeng & Song, , ), and many important conclusions have been reached. For example, pertaining to the origin of the aeolian material and the pedogenetic processes it underwent.…”