兰州大学机构库 >资源环境学院
青藏高原东部黄土的元素地球化学特征及其环境意义
Alternative TitleGeochemical Characteristics of Loess Deposits in the eastern Tibetan Plateau and its Environmental Implications
梁敏豪
Thesis Advisor杨胜利
2018-04-15
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword青藏高原东部 黄土 物源 元素地球化学 风化作用
Abstract

风尘堆积与大气环流、源区环境状况密切相关,是揭示古大气环流演化和古环境变化机制的理想地质记录之一。青藏高原东部主要受高原季风和西南季风的影响,其上广泛分布的黄土-古土壤序列,是研究青藏高原古环境变化与环流系统演化的理想材料。系统的研究高原东部黄土的元素地球化学特征,有助于深入理解高原黄土沉积特征、物质来源和环境意义。因此,本文详细分析了青藏高原东部黄土的常量、微量元素空间变化特征及其物源指示意义,进而探讨了末次冰期以来高原东部黄土的物源变化和化学风化过程。研究主要取得以下进展:

  在空间尺度上,对青藏高原东部地区典型黄土-古土壤和表土,进行了系统的常量、微量元素组成分析,结果显示,青藏高原东部黄土主要常量元素氧化物为SiO2、Al2O3、CaO和Fe2O3,黄土中SiO2和CaO含量差别较大;总体上川西地区常量元素组成与北方黄土高原黄土具有一定相似性。黄土、古土壤的微量元素含量差别较大,其中Rb、Sr、Ba、Zr、V占了微量元素的主要部分。与高原东部的风沙沉积、黄土高原黄土、河西走廊黄土进行对比,表明青藏高原东部黄土组分的常量元素之间的比值(SiO2/Al2O3、TiO2/Al2O3)、常量与微量元素之间的比值(Zr/Al、Zr/Ti、K/Rb、K/Ba)、微量元素之间的比值(Zr/Hf、Y/Nb)、常量元素三角图(Ca-Mg-K、Ca-Mg-Na)等与其他地区黄土有明显差异,而青藏高原东部黄土与高原表土沉积物及河流砂、风成砂样品元素特征比较接近。以上特征均指示了青藏高原东部黄土与黄土高原黄土物源的差异,其物源可能主要来自于青藏高原内部。

对川西高原的甘孜XS黄土剖面、金川MC黄土剖面进行系统的常量、微量元素组成分析,结果显示末次冰期以来甘孜地区的CaO、Na2O呈现逐步增加的趋势;而Al2O3、Fe2O3、MgO、K2O等趋势相反。在金川地区,自S2以来,SiO2、Na2O含量呈现出先减小后增加的趋势;而Al2O3、Fe2O3、MgO、K2O、CaO等趋势相反,其中CaO曲线波动较大,反映了金川地区在冰期间冰期的干湿交替变化。微量元素Co、Cr、Cu、Ni、V、Zn、Rb、Sr、Ba在甘孜XS剖面随深度微量元素含量不断增大,而金川MC剖面随深度先增大后减少,示踪元素比值表明川西高原黄土自身的常量元素比值(SiO2/Al2O3、TiO2/Al2O3、SiO2/ TiO2)、常量与微量元素比值(Zr/Al、Zr/Ti、Y/Al)随深度无明显变化,说明川西黄土物源无明显变化,相对稳定。

甘孜黄土化学蚀变指数(CIA)为56.73~68.53,处于低等风化阶段,金川黄土的CIA为61.34~71.37,处于中等风化强度。甘孜黄土-古土壤序列的风化强度,从末次冰期以来呈现减少的趋势,说明末次冰期以来黄土风化强度不断减弱。金川黄土-古土壤序列的风化强度随着冰期-间冰期的交替不断波动,CIA、化学蚀变替代指标(CPA)值在冰期时明显偏低,而在间冰期时较高。甘孜黄土CaO*/MgO、Na/K以及(Ca*+Na+K)/Al随深度减小的趋势,金川黄土CaO*/MgO、Na/K以及(Ca*+Na+K)/Al随深度先减后增的趋势,共同指示了末次间冰期以来川西地区逐渐变干的趋势。

本研究对于认识青藏高原东部黄土-古土壤序列的元素地球化学特征及其古环境意义,理解高原黄土沉积过程、区域环境演化和古环境重建具有重要作用。

Other Abstract

Aeolian loess was closely related to the past atmospheric circulation and the environmental conditions. Loess is widely distributed in the eastern Tibetan Plateau(TP), which is one of the ideal material for the paleoclimate reconstruction, the evolution of monsoon circulation system and the effects of the TP. The detailed investigation on the geochemical characteristics of the plateau loess is great helpful to understanding the sedimentary processes, the sources area and the paleo-environmental implications. This paper conducted a systematic element geochemical analysis on the loess from the eastern TP, and the provenance significances and the chemical weathering processes since the last glacial period are discussed. It can be concluded as follows:

The geochemical analyses of the surface soils and loess deposits in the eastern TP show that the major elements SiO2, Al2O3, Fe2O3 and CaO, are consistent with typical loess from the Chinese Loess Plateau(CLP), with large variations of the SiO2 and CaO. The elements of Rb, Sr, Sr, Ba, Zr, V take the most part of trace elements in all samples, while the concentrations of trace elements in loess and paleosol are quite different. The comparisons of the provenance proxies of the SiO2/Al2O3、TiO2/Al2O3、Zr/Al、Zr/Ti、K/Rb、K/Ba、Zr/Hf、Y/Nb and the major elements ternary(Ca-Mg-K, Ca-Mg-Na) between the loess from the eastern TP and that of the CLP and the Hexi Corridor, have shown that the eastern TP loess has different source with the loess from other regions. Moreover, the elemental characteristics of the loess and surface soil, fluvial sediments, aeolian sediments from the eastern TP are quite similar. Thus, we can infer that the loess deposit is mainly from the inland of the TP.

The major and trace elements along the loess sequence from Ganzi have shown the increasing trends of the concentrations of the CaO and Na2O at Ganzi and the decreasing trend of the Al2O3, Fe2O3, MgO and K2O since the Last Glacial, which are similar with the loess from Jinchuan. The concentrations of the trace elements including Co, Cr, Cu, Ni, V, Zn, Rb, Sr, Ba increase along the depth at Ganzi, and those concentrations increase firstly with the depth then decrease at Jinchuan. The provenance proxies of the ratiosSiO2/Al2O3, TiO2/Al2O3, SiO2/ TiO2, Zr/Al, Zr/Ti and Y/Al have no obvious change along the depth at Ganzi and Jinchuan, which indicate that there is no significant change in the loess provenance in the eastern TP.

The CIA indexes of the Ganzi section vary from 56.73 to 68.53, indicating a slightly weathered stage, while the CIA indexes of the Jinchuan section vary from 61.34 to 71.37 showing a moderately weathered stage. The weathering strength of the Ganzi section shows a decreasing trend since the Last Glacial. The weathering strength of the Jinchuan section fluctuates continuously with the alternation of the loess and paleosol. The CIA and CPA are obviously lower during the Glacial and higher during the Interglacial. The ratios of CaO*/MgO, Na/K and (Ca*+Na+K)/Al decrease with depth at Ganzi and Jinchuan since L1, which indicates the gradually drying trend in the eastern TP since the Last Glacial.

This study will further our understanding on the geochemical characteristics of the loess-paleosol sequence and its paleo-environmental implications in the eastern TP, as well as in understanding the sedimentary process, regional environmental changes.

URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/240748
Collection资源环境学院
Recommended Citation
GB/T 7714
梁敏豪. 青藏高原东部黄土的元素地球化学特征及其环境意义[D]. 兰州. 兰州大学,2018.
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