Provenance of Aeolian Sediment in the Taklamakan Desert of Western China, Inferred from REE and Major-Elemental Data

ARTICLE IN PRESS Quaternary International 175 (2007) 71–85 Provenance of aeolian sediment in the Taklamakan Desert of western China, inferred from REE and major-elemental data Xiaoping YangÃ, Bingqi Zhu, Paul D. White Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China Available online 24 March 2007 Abstract To identify the provenance of aeolian deposits in the extensive dune field in the Taklamakan Desert is of great importance for understanding the formation of this, the largest sand sea in China. The opinions from earlier studies are quite dipolar and are as follows: (a) local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages; and (b) strong homogenization of the sands in the entire Taklamakan on the basis of geochemical data from whole-rock samples. By separately examining the REE characteristics and major-elemental composition in coarse and fine fractions of the samples from aeolian deposits, this paper provides new data for interpreting sources of aeolian deposits in the Taklamakan. The sampling sites are distributed in four different fluvial systems, i.e. the areas of the Keriya River, Niya River and Cele River in the southern part and the northern margin near the Tarim River (Fig. 1). Our results show that there are some significant differences in concentrations of trace elements and in REE features between the coarse and the fine fractions of the aeolian sediment. The major-elemental and REE data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin. The fine fractions (mainly silts) are more homogenized. The regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin. This confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east–west direction. It should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea. In addition, little variation is found between old and young sands in two sediment sequences in the central part of the desert, indicating consistency of sand sources in a given site during the last 40 ka. r 2007 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction aeolian dust from the Asian continent is a major source of pelagic sediment in the western Pacific (Rea et al., 1998) To understand the formation of a landscape it is of great and an important part of the sediment in the central North importance to investigate the sediment sources, particularly Pacific (Kyte et al., 1993). In addition, the dust significantly in sand sea environments. Determining the sources of affects the chemical composition of seawater in the western aeolian sediment in the Taklamakan Desert, western China Pacific Ocean. It is recognized that the rare earth elements is crucial not only to the understanding of the formation of (REE) patterns of western Pacific Ocean seawater in the the sand sea but also to develop a better understanding of areas near Asia show close affinities to Chinese loess past and present global climate systems, because the (Greaves et al., 1999). In this context knowledge about the Taklamakan Desert is a large source for global dust sources of aeolian sediment in the Taklamakan has global production (Zhang et al., 2003). The mineral dust that is significance. being deposited in Greenland at recent times as well as Based on the major-elemental and mineral compositions during the Last Glacial period was recognized to be mainly and grain size distributions of the sand samples from from the Taklamakan and from the deserts of Inner southwestern part of the desert, Honda and Shimizu (1998) Mongolia (Svensson et al., 2000; Bory et al., 2003). The reconfirmed that the sand from the Taklamakan has higher feldspar/quartz and calcite/quartz ratios, finer grain sizes ÃCorresponding author. Tel.: +86 10 62008389; fax: +86 10 62032495. and less rounding than most desert sands (Zhu et al., 1981; E-mail addresses: [email protected], [email protected] Besler, 1991; Yang, 1991). However, the opinions about (X. Yang). sources and transport histories of the sands are divided 1040-6182/$ - see front matter r 2007 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2007.03.005 ARTICLE IN PRESS 72 X. Yang et al. / Quaternary International 175 (2007) 71–85 between (a) various sources of sand in each part of the the basin (Li and Zhao, 1964). Deep incision takes place desert because of different heavy mineral assemblages (Zhu along all rivers in foreland desert margins owing to et al., 1981; Yang, 1991, 2002) and (b) homogenized sands the uplifting of the surrounding mountains. During the in the entire desert because of consistent major-elemental Quaternary, the Keriya River incised 117 m into the and isotopic features in whole-rock samples (Honda and forelands of Kunlun Mountains (Xinjiang Expedition Shimizu, 1998; Hattori et al., 2003). Based on the Team of Academia Sinica, 1978). Extensive sand dunes investigation of trace elements, in particular REE, and with various forms occur in the Taklamakan, known in major-elemental compositions in two grain size fractions of local folklore as a place for journey without coming back a larger number of samples from a wide geographical area due to its vast area of active dunes. However, the sand sea of the Taklamakan, this paper intends to provide new data is divided by various rivers originating from surrounding for deciphering the sources of aeolian sediment with spatial mountains. In the central and south Taklamakan, the and temporal considerations. rivers originating from the Kunlun Mountains flow mainly Trace elements including REE and major-elemental northwards. Large oases in the desert margins and long compositions have become robust techniques for examin- green belts along the river courses crossing the desert ing the sediment sources in deserts (Muhs et al., 1995; enable millions of people to live in the basin under an Pease et al., 1998; Honda and Shimizu, 1998; Wolfe et al., extremely arid climate. Due to their sensitive nature, lakes 2000; Pease and Tchakerian, 2002, 2003; Zimbelman and and river courses have undergone large-scale changes in Williams, 2002; Hattori et al., 2003). REE are useful tools response to climate fluctuations and human activities since for investigating sediment characteristics and provenance the Late Quaternary (Yang, 1991; Yang et al., 2002, because they are among the least soluble of the trace 2006a). elements and are less mobile during weathering than many This paper deals with desert areas along the Keriya other trace elements (Taylor and McLennan, 1985; River, Niya River and Cele River as well as the Tarim Rollinson, 1993), and also because the changes of River (Fig. 1). At present these rivers with their headwaters REE characteristics are mainly controlled by provenance located in Kunlun Mountains (Keriya, Niya and Cele) dry rather than diagenesis (Taylor and McLennan, 1985). In up in the Taklamakan, whereas the Keriya flows into the the case of aeolian sands, the difference in REE character- desert much further than the Niya and Cele rivers. The istics is largely controlled by compositions in minerals Tarim River, the longest River in the Tarim Basin, has because certain REE occur only in specific minerals. headwaters in the western Kunlun Mountains and Tian- shan Mountains and flows eastwards on the north margin 2. Regional setting of the desert along a tectonic graben. The discharge of all these rivers is largely dependant on melting glaciers and The Taklamakan Desert lies in the Tarim Basin of snow in the mountainous regions of upper reaches (Yang southern Xinjiang, with an area of 337,000 km2 being the et al., 2006b). largest sand sea in China (Zhu et al., 1980, 1981). Like desert research elsewhere (Goudie, 2002), the Unconsolidated sediments generally reach a thickness of classification of dune types in the Taklamakan is based 500–600 m, occasionally over 900 m in the south margin of on the surface appearance and their relationship to wind Fig. 1. Map of the study area showing the location of sampling sites. The right map is a zoomed view of the square marked in the left map. ARTICLE IN PRESS X. Yang et al. / Quaternary International 175 (2007) 71–85 73 directions (Zhu et al., 1981). The types of dunes in the plate; (d) samples were finally treated with 2 ml (1:1) HNO3 Taklamakan are quite diversified, including longitudinal and at this stage no residue was detected. The solutions dunes, barchains, barchan chains, pyramid dunes, dome- were finally transferred to clean flasks and were diluted shaped dunes, etc. (Institute of Desert Research of with 1% HNO3 to 50 ml. Sample preparation was Academia Sinica, 1980; Zhu et al., 1981; Ho¨vermann and performed at the Institute of Geology and Geophysics, Ho¨vermann, 1991; Ja¨kel, 1991; Wang et al., 2002). Under Chinese Academy of Sciences (CAS). ICP-MS analyses the influence of predominantly northern winds, the final were carried out at the Chinese Ministry for Nuclear direction of dune migration is towards the southwest in Industries, and the results are listed in Table 1. This ICP- most parts of the Taklamakan. It is only in the southwest MS offers very low detection limits (e.g. the lowest corner of the desert that the dunes migrate toward the detection limit for europium is 0.04 ng/ml in solutions) southeast (Zhu et al., 1981). The highest dunes in the and its analytical uncertainties (relative standard deviation) Taklamakan, being ca.

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