伊犁黄土物质来源研究及其对环境的指示意义

Though the loess record of Ili Basin provides an ideal archive of westerlies evolution, the provenance of loess material still remains controversial. Which atomospheric cirulucation plays a more important role in the dust transportion? The dust transported by the westerlies or the silt-sized particles carried by near-surface wind? It still remains deliberated, asking for more geochemical discussion and direct evidence from source regions. The physicochemical properties of climate proxies are closely related to the provenances of loess material, therefore, source tracing of loess in Ili Basin systematically is beneficial to understand the implications of climate proxies, and play crucial insight into the evolution of the westerlies and the history of atmospheric circulation. In this study, various sediments from such as topsoil/desert sands of Sary-Ishikotrau Desert, alluvial fan of Tianshan to the southeast of the desert, loess in southeast Kazakhstan, alluvial fan and loess of Ili Basin will be selected as research objectives, and will be extracted into four grain-size fractions taking 63μm, 20μm and 2μm as boundaries. The provenance of Ili loess will be explored through the analysis of geochemical and Sr-Nd isotopic properties of each fraction, combined with corresponding research of loess sequence in southeast Kazakhstan and Ili Basin. The project will provide important references for defining the paleoenvironmental implications of climate proxies and a more thorough understanding of westerlies evolution.

伊犁黄土是研究西风环流演变历史的理想载体，目前对于该区黄土的物质来源还存在许多疑问，是西风携带为主？还是由近地面风携带近源物质为主？尚缺乏来自地球化学的有力论证，并且没有来自"源区"的直接证据。不同的物质来源是影响气候代用指标理化性质的重要因素，系统追踪伊犁黄土的物源有助于正确解译气候代用指标的古环境意义，对进一步揭示西风气候演化与古大气环流历史具有重要的意义。本项研究根据研究区的主导风向，选取哈萨克斯坦的萨雷耶西克阿特劳沙漠、沙漠东南部天山山前洪积扇沉积和山麓黄土、伊犁地区山前洪积扇沉积以及伊犁黄土的表土样品，以63μm、20μm和4μm为界提取不同粒级组分，进行各相同组分的地球化学元素和Sr-Nd同位素组成特征对比分析，结合伊犁地区和沙漠东南部天山北麓典型黄土剖面的对应研究，探讨伊犁黄土的物质来源，为明确伊犁黄土气候代用指标的古环境意义和进一步探讨西风气候演化提供重要依据。

伊犁黄土是研究西风环流演变历史的理想载体，系统追踪伊犁黄土的物质来源有助于正确解译其气候代用指标的古环境意义，对进一步揭示西风区气候演化与古大气环流历史具有重要的意义。对伊犁盆地昭苏波马黄土（ZSP）、可克达拉沙漠沉积（TKP）和黄土高原朝那黄土（CN）的典型样品地球化学研究表明不同粒级组分的稀土元素（REE）含量、特征参数和Sr-Nd同位素的变化特征能够作为有效的指标，追踪风成物质沉积区的物质成分、输送体系和气候环境的变化。同时，醋酸淋溶的不同相态地化元素分析也表明酸不溶组分的稀土元素分馏特征可以更为敏感地指示物源信息，而酸溶组分的稀土元素特征对反映伊犁黄土不同来源的物质特征具有重要的参考意义。在此基础上，对伊犁-哈萨克斯坦东南部表层沉积物的不同相态REE参数特征分析发现，酸溶组分稀土特征反映了远源输送体系和近源输送体系下不同来源碎屑碳酸盐稀土的混合。伊犁河流沉积物、沙漠沉积物、基岩、哈萨克斯坦东南部各类沉积物仅为伊犁黄土提供了部分物源，伊犁黄土可能还存在更为广域的物质来源。这些高空远距离携带过来的物质，协同近地面西风向东搬运的哈萨克斯坦东南部粉尘物质，局地环流补充的南北天山、伊犁河谷物质，经过充分混合后在天山山前沉积下来。