The Origin of Wushan Loess and the Characteristics of Soil Derived from It
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摘要:
目的 为探明巫山黄土成因,了解该类母质发育土壤的发生学特征。 方法 以典型巫山黄土及其发育土壤剖面为研究对象,通过野外调查采样和室内分析,详细考察剖面形态、颗粒组成、常量元素地球化学特征及其他相关理化性质,计算探讨硅铝率( Sa )、化学蚀变指数( CIA )、钠钾比( Na/K )、铁游离度等风化指标。 结果 (1)巫山黄土的颗粒组成以粉粒为主,平均含量为53.29%,与典型风尘沉积物相似,同时,巫山黄土与其他区域风成黄土的主要元素硅、铝、铁含量非常接近,上陆壳(UCC)标准化曲线也较为相似;(2)该剖面100 ~ 140 cm深度与其他深度相比,有机碳和硒含量较高,CaCO3相当物含量和δ13C值较低,推测在此深度堆积过程中的气候较为温湿,并可能出现过植物的生长;(3)巫山黄土剖面的 Sa 为8.73 ~ 9.17、 CIA 为65.96 ~ 69.10、 Na/K 为0.74 ~ 0.89、铁游离度为22.88% ~ 29.74%,与其他地区风成黄土相比,巫山黄土风化程度强于洛川黄土而弱于下蜀黄土和成都黏土,与汉江黄土和甘孜黄土十分接近。 结论 巫山黄土应为风积成因,处于中等化学风化程度,以脱盐基为主,脱硅富铁铝化程度弱,可能与汉江黄土或甘孜黄土同源。 Abstract:Objective In order to explore the origin of Wushan loess and understand the genetic characteristics of soils derived from this kind of parent material, Method the samples form typical Wushan loess profile were analyzed through field investigation and laboratory analysis for morphology characteristics, particle composition, characteristics of major elements, other physicochemical properties and weathering indexes such as silicon aluminum ratio (Sa), chemical indices of alteration (CIA), sodium potassium ratio ( Na/K) and iron free degrees. Result The results showed that: (1) The main particle composition of Wushan loess was silt, with an average content of 53.29%, which was similar to typical aeolian loess. At the same time, the contents of main major elements (Si, Al, Fe) of Wushan loess were close to those of aeolian loess in other regions, and the upper continent crust normalized patterns of major elements were also similar among them. (2) There were higher contents of organic carbon and Se, lower contents of Calcium carbonate equivalent and δ13C values in 100 - 140 cm soil layers, speculating that the climate was warm-wet and plant growth might have occurred during the deposition process of Wushan loess profile at depths of 100 - 140 cm. (3) For the Wushan loess profile, Sa were 8.73 - 9.17; CIA were 65.96 - 69.10; Na/K were 0.74 - 0.89; and iron free degrees were 22.88% - 29.74%. Compared with aeolian loess in other regions, the chemical weathering degree of Wushan loess was stronger than that of Luochuan loess, weaker than Xiashu loess and Chengdu clay, and very close to Hanjiang loess and Ganzi loess. Conclusion Wushan loess is of aeolian origin, in a moderate chemical weathering degree, mainly desalting base, and the degree of desilication and iron aluminum enrichment was weak. There may be the same source among Wushan loess, Hanjiang loess and Ganzi loess. -
Key words:
- Wushan loess /
- Aeolian origin /
- Major element /
- Pedogenesis
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表 1 巫山博物馆黄土剖面形态特征和颗粒组成
Table 1. Morphological characteristics and particle size composition of the Wushan museum loess profile
深度(cm)
Depth土壤颜色
Soil color结构
Structure颗粒组成(美国制)
Particle composition (USDA)质地
Soil texture母质均一性值 Uniformity
value干态
Dry润态
Wet砂粒(%)
Sand粉粒(%)
Silt黏粒(%)
Clay0 ~ 20 10YR 5/4 10YR 4/4 小块状 32.84 42.41 24.76 壤土 −0.46 20 ~ 40 10YR 5/4 10YR 4/4 中块状 17.21 61.13 21.66 粉壤土 −0.03 40 ~ 60 10YR 5/4 10YR 4/4 大块状 26.20 51.29 22.51 粉壤土 −0.08 60 ~ 80 10YR 5/4 10YR 4/4 大块状 20.50 53.24 26.26 粉壤土 0.09 80 ~ 100 10YR 5/4 10YR 4/4 大块状 20.39 57.36 22.26 粉壤土 −0.24 100 ~ 120 10YR 5/4 10YR 4/4 大块状 18.30 54.71 26.99 粉壤土 1.04 120 ~ 140 10YR 5/4 10YR 4/4 大块状 19.99 56.52 23.48 粉壤土 −0.49 140 ~ 160 10YR 5/4 10YR 4/4 大块状 20.22 54.46 25.33 粉壤土 0.56 160 ~ 180 10YR 5/4 10YR 4/4 大块状 24.34 52.87 22.80 粉壤土 −0.27 180 ~ 200 10YR 6/4 10YR 4/4 大块状 23.22 52.72 24.05 粉壤土 − 400 ~ 500 10YR 6/4 10YR 5/6 大块状 29.48 49.43 21.09 壤土 − 表 2 巫山博物馆黄土剖面常量元素含量
Table 2. The major element contents of the Wushan museum loess profile
深度(cm)
DepthSiO2
(g kg−1)Al2O3
(g kg−1)Fe2O3
(g kg−1)MgO
(g kg−1)CaO
(g kg−1)Na2O
(g kg−1)K2O
(g kg−1)TiO2
(g kg−1)MnO
(g kg−1)0 ~ 20 651.68 124.44 52.93 13.84 35.05 11.45 21.37 8.00 0.76 20 ~ 40 651.12 123.63 52.79 13.27 35.30 11.28 20.82 7.94 0.73 40 ~ 60 659.12 128.09 54.66 13.20 32.92 10.65 20.66 8.12 0.69 60 ~ 80 650.11 123.65 53.34 13.47 36.06 10.87 20.89 8.00 0.75 80 ~ 100 661.73 128.01 54.74 13.58 27.54 11.04 20.96 8.17 0.76 100 ~ 120 658.87 124.44 53.29 13.08 27.48 11.45 20.91 8.09 0.75 120 ~ 140 664.44 126.72 54.34 13.21 25.30 11.83 21.09 8.30 0.80 140 ~ 160 635.80 122.87 52.31 13.44 42.01 11.05 21.02 7.94 0.77 160 ~ 180 650.88 122.29 52.17 13.34 36.67 12.25 21.06 8.00 0.80 180 ~ 200 655.09 121.27 51.51 13.58 35.88 12.03 20.53 8.07 0.80 400 ~ 500 645.89 120.32 51.13 12.90 45.35 9.77 20.02 8.01 0.73 最大值 664.44 128.09 54.74 13.84 45.35 12.25 21.37 8.30 0.80 最小值 635.80 120.32 51.13 12.90 25.30 9.77 20.02 7.94 0.69 平均值 653.16 124.16 53.02 13.36 34.51 11.24 20.85 8.06 0.76 标准差 8.05 2.56 1.21 0.26 6.07 0.69 0.35 0.11 0.03 变异系数 1.23% 2.07% 2.29% 1.97% 17.60% 6.16% 1.69% 1.33% 4.47% 表 3 巫山博物馆黄土剖面风化发育特征
Table 3. Chemical weathering indices in the Wushan museum loess profile
深度(cm)
DepthNa/K Sa CIA 铁游离度(%)
Free degree of Fe铁活化度(%)
Activity degree of Fe0 ~ 20 0.81 8.89 67.18 23.86 13.07 20 ~ 40 0.82 8.94 67.45 24.13 13.61 40 ~ 60 0.78 8.73 69.05 27.94 11.89 60 ~ 80 0.79 8.92 67.93 26.82 10.95 80 ~ 100 0.80 8.77 68.45 25.38 11.73 100 ~ 120 0.83 8.98 67.37 25.14 14.19 120 ~ 140 0.85 8.90 67.24 22.88 15.47 140 ~ 160 0.80 8.78 67.52 24.76 16.02 160 ~ 180 0.88 9.03 65.96 24.67 15.10 180 ~ 200 0.89 9.17 66.24 29.74 13.31 400 ~ 500 0.74 9.11 69.10 26.57 14.10 最大值 0.89 9.17 69.10 29.74 16.02 最小值 0.74 8.73 65.96 22.88 10.95 平均值 0.82 8.93 67.58 25.63 13.59 标准差 0.04 0.14 1.00 1.99 1.61 变异系数 5.38% 1.55% 1.49% 7.75% 11.87% -
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