CHEMICAL WEATHERING CHARACTERISTICS AND PALEOCLIMATIC SIGNIFICANCE OF THE EOLIAN DEPOSITS IN CHENGDU PLAIN
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摘要: 对成都平原胜利红土剖面进行了系统的常量元素分析，并与川西典型黄土、古土壤样品的地球化学特征进行对比，研究本区风尘堆积所经历的化学风化作用过程，并对该序列化学风化特征的古气候意义进行探讨。研究结果表明，成都红土的常量元素组成与川西典型黄土、古土壤样品相似，与上地壳的平均化学成分也基本一致，说明成都红土与川西黄土一样，在堆积以前也经历了多次充分混合作用。在成都红土的形成过程中，Ca、Na元素大量淋失，含量很低，K、Mg也出现了不同程度的淋失，说明成都红土经历了斜长石和钾长石的化学风化过程。进一步的研究表明，成都黏土已达到中等风化的末期阶段，而网纹红土已进入强烈风化作用阶段。从整个序列的化学风化参数来看，距今1.13 Ma以来化学风化强度不断减弱，表明四川盆地及周围地区更新世中期以来有逐渐变干的趋势，与全球气候变化具有一致性。Abstract: The chemical composition of the eolian deposits mainly depends on the material composition of the source area and post-depositional in-situ pedogenesis. In this study, systematic major element composition analysis has been made Shengli red earth section in Chengdu Plain, and compared with the geochemical characteristics of typical loess and paleosoil samples from western Sichuan Province. The research results show that, similar major element composition between the Chengdu Red Earth and the loess-paleosoil samples from western Sichuan, and they are also comparable to the average composition of the Upper Continental Crust. These suggest that the Chengdu Red Earth, as same as loess from western Sichuan, were all derived from well-mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes. In the formation process of the Chengdu Red Earth, Ca and Na element experienced a large number of leaching and the content is very low, K and Mg also appeared different degree of leaching, explaining Chengdu Red Earth experienced chemical weathering process of plagioclase and potassium feldspar. Further study shows that, Chengdu clay has reached the later stage of medium degree of chemical weathering, and the vermiculated red soil has entered the strong weathering stage. From the chemical weathering parameters of the entire sequence, weakening chemical weathering intensity from 1.13 MaBP shows that Sichuan Basin and the surrounding area has gradually become drier since the mid-pleistocene, and has consistency with global climate change.
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Key words:
- Chengdu Red Earth /
- eolian deposits /
- chemical weathering /
- paleoclimate
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图 1 成都胜利红土剖面序列的主要化学成分
Figure 1. Main chemical compositions in the Shengli red earth profile in Chengdu
图 2 成都胜利红土剖面中成都黏土、网纹红土主要元素含量比较
Figure 2. Comparison between the main element contents in Chengdu clay and in reticulate red soil in the Shengli red earth profile
图 3 成都胜利红土剖面中成都黏土、网纹红土主要元素相对Al的比值变化特征
Figure 3. Ratio of main element contents in Chengdu clay and in reticulate red soil in the Shengli red earth profile to Al
图 4 成都胜利红土剖面中成都黏土、网纹红土主要元素平均含量的UCC标准化值变化特征
Figure 4. Ratio of main element contents in Chengdu clay and in reticulate red soil in the Shengli red earth profile to UCC
图 5 成都胜利红土剖面中成都黏土、网纹红土和甘孜黄土、古土壤的化学风化趋势
Figure 5. Chemical weathering tendency of Chengdu clay and reticulate red soil in the Shengli red earth profile, Ganzi loess and ancient soil
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