Geochemical Characteristics and Weathering Intensity of the Yanbandang Profile in Liyang Plain, the Middle Reach of the Changjiang River
Online published: 2013-01-31
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Based on detailed field survey, oxide contents analysis and optically stimulated luminescence (OSL) dating of the samples from the Yanbandang(YBD) profile in Liyang Plain, the geochemical characteristics of major elements, the weathering process and environmental change from late Pleistocene to mid-Holocene were discussed. The results showed that the content of oxide is mainly composed of SiO2, Al2O3 and TFe2O3 (Fe2O3+FeO) and their percentage are between 86% and 90.8%. Compared to the average upper continental crust composition, Na and Ca have been leached out strongly, while total Fe and Mn relatively enriched in the sediments of the YBD profile. The intensity of chemical weathering in the YBD sequence was significantly higher than that of loess and paleosol in Loess Plateau, slightly higher than Xiashu loess in Zhenjiang, almost equal to the Yucheng profile in Liyang Plain, but obviously lower than the red soil from Xuancheng profile in Anhui Province, which indicated a moderate chemical weathering intensity under warm and moist conditions. Changes of the Chemical Index of Alteration (CIA), the Eluvial Coefficient, the Coefficient of Weathering and Eluviations (BA), the Index of Compositional Variation (ICV) and the analysis of A-CN-K and A-CNK-FM ternary diagrams suggested palpable differences in weathering intensity of the strata. There are four stages of weathering process in the YBD profile: relatively stronger weathering, relatively weaker weathering, intensifying weathering, and relatively stronger weathering. The weathering intensity of the yellowish brown soil at the top and bottom of YBD profile were clearly higher than that of the black brown soil and the black soil. Since the chemical weathering intensity is sensitive to climate change, the geochemical parameters can be used to unravel the environmental change to some extent. The higher CIA value reveals that the climate is relatively warmer and wetter in the end of the MIS3a stage. It becomes cooler during the LGM, but gradually returns to be warm again in early-Holocene. The climate in the mid-Holocene was the warmest and most humid compared to the aforementioned periods.
Key words: Liyang Plain; Late Pleistocene; major elements; chemical weathering
GUO Yuan-yuan , MO Duo-wen , MAO Long-jiang , GUO Wei-min , GU Hai-bin . Geochemical Characteristics and Weathering Intensity of the Yanbandang Profile in Liyang Plain, the Middle Reach of the Changjiang River[J]. SCIENTIA GEOGRAPHICA SINICA, 2013 , 33(3) : 335 -341 . DOI: 10.13249/j.cnki.sgs.2013.03.335
Fig.1 Physiographic map of the Liyang Plain and the location of the Yanbandang(YBD) profile图1 澧阳平原概况及岩板垱剖面位置 |
Table 1 List of OSL dating data from the YBD profile表1 澧阳平原岩板垱剖面年代数据表 |
样品号 | 实验编号 | 所属地层 | 年代(ka B.P.) |
---|---|---|---|
YBD 9-1 YBD 9-2 YBD 10 YBD 11 YBD 12 YBD 13 YBD 14 YBD 15 | 080407 080408 080409 080410 080411 080412 080413 080414 | ⑦层上部 ⑦层下部 ⑥层中部 ⑤层中部 ④层中部 ③层上部 ②层中部 ①层中部 | 6.11±0.31 6.33±0.32 9.92±0.50 17.68±0.91 15.56±0.80 21.17±1.11 23.49±1.20 26.73±1.37 |
Fig.2 UCC-normalized patterns of major elements in different sediment layers at YBD profile in Liyang Plain(a), and comparison of UCC-normalized patterns between loess-paleosol in the Loess Plateau, Xiashu loess in Zhenjiang, yc profile in Liyang Plain and Xuancheng red earth in Anhui Province(b)图2 澧阳平原岩板垱剖面各层沉积物常量元素UCC标准化曲线(a)及其与黄土高原黄土–古土壤[2]、镇江下蜀黄土[10]、玉成剖面[18]和宣城红土[12]UCC标准化曲线的比较(b) |
Fig.3 A-CN-K (a) and A-CNK-FM (b) diagrams of sediments at Ybd profile图3 岩板垱沉积物A-CN-K和A-CNK-FM三角图解 |
Fig.4 The curves of CIA、eluvial coefficient、BA、ICV and LOI at YBD profile图4 岩板垱剖面CIA、残积系数、BA值、ICV及LOI变化曲线 |
The authors have declared that no competing interests exist.
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