Distribution and composition of loess sediments in the Ili Basin, Central Asia
Distribution and composition of loess sediments in the Ili Basin, Central Asia
复制标题
中亚伊犁盆地黄土沉积物分布及成分
DOI：
10.1016/j.quaint.2013.12.053
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发表时间：
2014-06-17
影响因子：
2.2
通讯作者：
An, Zhisheng
中科院分区：
文献类型：
--
作者：
Song, Yougui;Chen, Xiuling;An, Zhisheng
中亚的黄土沉积提供了区域气候和环境变化的重要记录。然而，与中国黄土高原（CLP）黄土沉积的深入研究相比，中亚东部伊犁盆地的黄土沉积却知之甚少。根据野外调查和现有文献资料，对伊犁黄土的分布、地层和成分进行了初步研究。伊犁黄土的分布明显受地形地貌条件的控制，主要分布在河流阶地、低丘地和天山山坡地。黄土的厚度从几米到两百多米不等。通过对伊犁黄土的粒度、地球化学、X射线衍射图谱和重矿物组合的分析，确定了伊犁黄土的成分特征。粒度分析表明，伊犁黄土主要由粉土（4-63 μ m）和少量的砂组成，比CLP黄土粗，并建议附近的物源。伊犁黄土的矿物组成以石英、长石为主，方解石、方解石、云母、白云石、角闪石等含量较少。重矿物有20多种，主要成分为角闪石、磁铁矿和绿帘石。伊犁黄土的常量元素以SiO_2、Al_2O_3、CaO含量高，Fe_2O_3、MgO、Na_2O、K_2O含量低为特征。与CLP黄土相比，伊犁黄土中Na 2 O相对富集，Na 2 O/Al 2 O3比值较高，说明风化作用较弱。稀土元素分布模式表明，伊犁黄土和CLP黄土均具有典型的上地壳成分，轻稀土富集，Eu负异常，重稀土亏损。重矿物组合和地球化学特征表明，伊犁盆地局部基岩对黄土沉积的贡献可能很小。(C)2014 Elsevier Ltd和INQUA。All rights reserved.
Loess deposits in Central Asia provide an important record of regional climate and environmental change. However, in contrast to the intensively investigated loess deposits on the Chinese Loess Plateau (CLP), loess sediments in the Ili Basin of eastern Central Asia are poorly understood. Based on field investigation and existing literature, this paper presents a preliminary study of the distribution, strata and composition of the Ili loess. The distribution of the Ili loess is clearly controlled by topographic and geomorphic conditions, mainly in the river terraces, low uplands, and slopes of the Tianshan Mountains. The thickness of the loess varies from several meters to over two hundred meters. To characterize the Ili loess composition, the authors analyzed its grain size, geochemistry, X-ray diffraction pattern and heavy mineral assemblage. Grain size analyses reveal that the Ili loess consists predominantly of silt (4-63 mu m) with a minor proportion of sand, which is coarser than the loess of the CLP and suggests a nearby provenance. The bulk mineral components of the Ili loess are dominated by quartz and feldspar with minor amounts of calcite, chlorite, mica, dolomite and hornblende. More than 20 types of heavy minerals were observed with major components of amphibole, magnetite and epidote. The major elements of the Ili loess are characterized by high abundance of SiO2, Al2O3 and CaO and minor amounts of Fe2O3, MgO, Na2O and K2O. Compared to the CLP loess, the Ili loess is relatively rich in Na2O and displays higher Na2O/Al2O3 ratios, suggesting weak weathering. The distribution patterns of REEs indicate that both the Ili loess and CLP loess are of typical upper crustal composition, with enrichment in LREE, negative Eu anomalies, and depletion of HREE. Both the heavy mineral assemblage and geochemistry indicate that the local bedrock of the Ili Basin may have contributed only a little to the loess sediments. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.