Clay minerals in a soil chronosequence derived from basalt on Hainan Island, China and its implication for pedogenesis

• Published in: Geoderma Vol. 148; no. 2; pp. 206 - 212
• Main Authors: He, Y., Li, D.C., Velde, B., Yang, Y.F., Huang, C.M., Gong, Z.T., Zhang, G.L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.2008; Elsevier
• Subjects: Agronomy. Soil science and plant productions; Basalt; Biological and medical sciences; Clay minerals; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geochemistry; Silica-rich 2:1 minerals; Soil and rock geochemistry; Soil chronosequence; Soils; Surficial geology; Hainan China; Far East; Asia; China; Clay minerals; Basalt; Soil chronosequence; Silica-rich 2:1 minerals; illite; oxides; kaolinite; soil parent materials; X-ray diffraction; basalts; sheet silicates; silicates; framework silicates; soils; vermiculite; mixed-layer minerals; volcanic rocks; quartz; igneous rocks; smectite; hydroxides; gibbsite; islands; pedogenesis; clay minerals; tholeiitic basalt
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2008.10.007

A soil chronosequence consisting of six profiles formed on quartz tholeiite basalt ranging in age from 10,000 years to 1. 8 Million years (My) was studied here. Soil clays were identified using XRD diffractogram decomposition methods for samples obtained from the A and C horizons of profiles. The results showed that kaolinite minerals dominated in all the clay fractions. Gibbsite was prominent in the C horizons in the soils from older rocks. Clays in the A horizon of relatively young soils showed an initial stage of illite formation, followed by smectite mixed layer minerals (illite–smectites and then vermiculite–illite) and finally by vermiculite. The initial presence of illite is interesting as there is no magmatic micaceous or phyllosilicate phase in these basalts and the formation of illite we attribute to a secondary process, probably created by alkali transport by plant materials. The change in 2:1 clay mineralogy reflects the overall change in Si/Al ratios in the soils over longer periods of weathering. In all cases gibbsite is more abundant in the C horizons than the A horizons. The difference in gibbsite content between the A and C horizons we attribute to plant transport of siliceous phytolite material to the surface. Continued high rainfall over long periods of time removed the alkali faster than the plants could bring it to the surface, which led to continuous lowering of 2:1 minerals from younger to older in the soil chronosequence. Nevertheless a 2:1, silica-rich mineral persists in the clay assemblages although in very minor amounts.