Rare Earth Element Characteristics of Desert Sediments in Ili Valley and Their Environmental Implication
详细信息   
摘要

mal style="MARGIN: 0cm 0cm 0pt">man">For the similar chemical properties and little change during weathering, transportation and diagenesis, Rare Earth Elementsman’; mso-hansi-font-family: ’Times New Roman’">（man">REEman’; mso-hansi-font-family: ’Times New Roman’">）man">are widely used as trace elements in provenance studies of various sediments. At the same time,REE characteristics also can record the evolution of environment in detail, therefore,they are widely used as an important indicator in studies of paleoclimate. Relationships between REE characteristics and environmental change on eolian deposits have intensively been investigated in the Chinese Loess Plateau and the middle and lower reaches of the Yangtze River, however, their relationships between REE and paleoenvironment recorded by eolian sediments in arid Central Asia are still poorly understood. Ili Valley of Xinjiang dominated by the westerlies is an ideal place for understanding the climate change of Central Asia. The Kekdala section man’; mso-hansi-font-family: ’Times New Roman’">（man">TKP, 43man’; mso-hansi-font-family: ’Times New Roman’">°man">58man’; mso-hansi-font-family: ’Times New Roman’">＇man">13man’; mso-hansi-font-family: ’Times New Roman’">＂man">N, 80man’; mso-hansi-font-family: ’Times New Roman’">°man">32man’; mso-hansi-font-family: ’Times New Roman’">＇man">39man’; mso-hansi-font-family: ’Times New Roman’">＂man">E, elevation 605mman’; mso-hansi-font-family: ’Times New Roman’">）man">is located in the hinterland of Takelmukul desert man’; mso-hansi-font-family: ’Times New Roman’">（man">43man’; mso-hansi-font-family: ’Times New Roman’">°man"> 50man’; mso-hansi-font-family: ’Times New Roman’">＇man">00man’; mso-hansi-font-family: ’Times New Roman’">＂man"> -44man’; mso-hansi-font-family: ’Times New Roman’">°man"> 15man’; mso-hansi-font-family: ’Times New Roman’">＇man">40man’; mso-hansi-font-family: ’Times New Roman’">＂man">N, 80man’; mso-hansi-font-family: ’Times New Roman’">°man">5man’; mso-hansi-font-family: ’Times New Roman’">＇man">00man’; mso-hansi-font-family: ’Times New Roman’">＂man">-80man’; mso-hansi-font-family: ’Times New Roman’">°man">54man’; mso-hansi-font-family: ’Times New Roman’">＇man">30man’; mso-hansi-font-family: ’Times New Roman’">＂man">Eman’; mso-hansi-font-family: ’Times New Roman’">）man"> in the western of Ili Valley. The section is about 360cm thick and the whole section can be divided into 10 couples of alternative sand and paleosols. OSL dating showed that it developed since 3.7ka. This paper reports REE results of TKP section and discusses the relationship between REE of desert sediments and environmental change in combination with calcite. The results show that the EREE values vary from 32. 88μg/g to 238.58 μg/g with an average value of 130. 90μg/g, slightly higher than those of modern desert and lower than those of Chinese loess in averageman’; mso-hansi-font-family: ’Times New Roman’">（man"> 171 man’; mso-hansi-font-family: ’Times New Roman’">μman">g/gman’; mso-hansi-font-family: ’Times New Roman’">）man">. The REE distribution patterns in different units of the section are similar in shape, which are moderately rich in light rare earth elementman’; mso-hansi-font-family: ’Times New Roman’">（man">LREEman’; mso-hansi-font-family: ’Times New Roman’">）man"> and negative slopes. The ratios of LREE/HREE are close to each other, as well as 8Ce and 8Eu, with unclear Ce anomaly and moderately negative Eu anomaly. All these features indicate a consistence of profile material sources and arid/semi-arid environment. REE contents man’; mso-hansi-font-family: ’Times New Roman’">（man">including Ceman’; mso-hansi-font-family: ’Times New Roman’">）man">have good relationship with each other, so do EREE, LREE/HREE and calcite. These demonstrate that REE characteristics of desert sediments are closely related with climatic change and can be used as effective paleoclimatie proxies in this area. Therefore,the paleoelimate evolution of Ili valley in Xinjiang since Late Holocene was reconstructed. From 3.7ka to 2.1 ka the climate was characterized by dry with relatively warm and humid during 2.5 -2.3ka and 3.4 -2.9ka. It was warm and moist from 2. lka to 0.5ka with small fluctuations. Since then the Ili valley has experienced weak chemical weathering and poor pedogenesis environment with aridity and less precipitation.

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