| The provenance of eolian sediments is foundation for understanding its origin,transportation and climatic significance.Northern Xinjiang inland area is located in the Northwestern China,a geographical center of the Asian interior,and is influenced by westerly throughout the year.The Cenozoic deposits contain valuable archives about the aridification of inland Asia,the dust transportation pathways and the evolution of global climate change.They also can contribution to the debates about the effects of the uplifted Tibetan Plateau and the regression of the Tethys Ocean on the atmospheric circulation in Central Asia.In spite of the progress on the provenance of the surface sediments in northern Xinjiang,the source of these sediments are still insufficient studied and remain controversial.More detailed research with more proxies is needed.Rare Earth Elements(REE)has been widely used as trace elements in provenance studies of various sediments because of the similar chemical properties and little change during weathering,transportation and diagenesis.In this paper,through field investigation in northern Xinjiang(include the Ili Basin,the Tacheng Basin and the Junggar Basin)and the southeast of Kazakhstan,combined with its topography,wind direction circulation and so on,63 samples of various surface sediments and bedrocks were collected from different regions of the northern Xinjiang and the southeast of Kazakhstan.Among them,48 samples were surface sediments,including loess,desert sands,Gobi sands,surface soils,surface sediments from the rivers,and 15 bedrock samples.Different size fractions and REE analyses have been taken out to further explore the material sources and interrelations of the different sediments in northern Xinjiang.The preliminary results are shown as below:1.The total concentrations of rare earth elements in the samples of different regions in northern Xinjiang are significantly different and the ∑REE values vary from 59.00μg/g to 193.00 μg/g.And the LREE/HREE ratios of whole rock samples are changes intricately.Size-differentiated δEu values and UCC-normalized REE distribution patterns of the samples from different sites,differ from each other.These REE characteristics may suggest that the sources of the sediments in northern Xinjiang are diverse and local.Whether it is in northern Xinjiang or the southeastern of Kazakhstan,δCe values of the most samples from 0.95 to 1.08 and there are hardly any Ce anomalies in the samples,which reflect an overall arid climate leading to weak pedogenesis.2.REE characteristics,such as the UCC-normalized REE distribution patterns and the δEu values in different size fractions,integrated with knowledge of relevant topography and wind patterns present that the <2 μm particles of the surface sediments in the Ili Basin are deposited under the influence of the trumpet-like topography and the obstruction of the high Tianshan Mountains,which the dust from Central Asia transported by westerly winds over a long distance and is highly mixed.Moreover,the 2～16 μm particles are sensitive indicatiors for the change of local regions.Silt material from the uplift of the Tianshan Mountains by glacier grinding and weathering should be the major sources of the surface sediments from the rivers by rivers erosion strongly.Part of them exposed surface by the geological process in the downstream of rivers,and were carried to surrounding areas by local circulation,which formed into the Kazakhastan surface sediments.One part was carried into the southeast of Kazakhstan by fluvial system,and formed into the surface sediments.The other part were re-carried to the Ili Basin,it should be the sources of the >16 μm particles of the surface sediments.3.The southeast of Kazahkstan,located in the upper wind direction of southwest-west wind,is the main provenance area of the <32 μm particles of loess and surface soil in the Tacheng Basin.With the influence of the southeast wind in the near-surface winter and special topography of the southeast opening of the Tacheng Basin to the east,the Gurbantunggut Desert in the central of the Junggar Basin may the sources of the Gobi sands.4.δEu values and the UCC-normalized REE distribution patterns of the surface sediments from different sites,differ from each other in different size fractions.These REE characteristics may suggest that the sources of the sediments in the Junggar Basin are diverse and local.The dust from Central Asia transported by the northward branch of the westerly winds,which through the western pass of the Junggar Basin or around the western low mountains to the western basin,it may be the sources of the surface sediments in the <2 μm,2～16 μm and 16～32 μm particles.But the Gobi sands may also be affected by the dust from the Gurbantonggut Desert in the Junggar Basin.The debris derived from surrounding mountains are the main sources of the >63 μm particles of the Gobi sands and the surface soils in the western basin.The dust from Central Asia transported by westerly winds may also made a contribution to the <2 μm,2～16 μm and16～32 μm particles in the northern basin,however,it may be a broader source in this area.The differences of the UCC-normalized REE distribution patterns and the variation range of the δEu values in the 32～63 μm and >63 μm particles may be caused by the difference of original rocks in different strata and the uneven mixing.REE characteristics of the bedrocks and the >125 μm particles of the desert sands in the northern basin reveal that the silt production from the Altai Mountains are their major sources.The dust from Central Asia and the desert of the central basin may make a contribution to the <2 μm particles of the surface sediments in the eastern and southern basin.Debris produced by geological and weathering processes in the Baita Mountains and Karamari Mountains are the sources of the >32 μm particles of the surface soils and Gobi sands in the eastern basin,and the strong northwest wind from the northern and central basin has also important contributions to the sources.For the southern basin,silt production from the Tianshan Mountains by frost weathering and/or glacial grinding should be the major sources of the bedrocks and surface sediments from the rivers. |
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