Formation of clay minerals in andosoils under temperate climate

Abstract

The principal methods for studying clay minerals in andosoils differ especially by the succession of the pretreatments, i.e. differential dissolution of amorphous mineral cements before (first method) or after (second method) the dispersion and recovery of granulometric fractions.The first method permits a rapid total quantitative estimation of amorphous components and an accurate identification of crystallized clay minerals by means of X-ray diffraction. The second method only proves the presence of allophane and imogolite.The two methods were applied in two different laboratories on the same soils from the Massif Central. The comparison of the results emphasizes the profit of using the two methods, especially if hypotheses on the mechanisms of clay genesis are to be proposed.These results, if placed in the context of a more comprehensive study, suggest the existence of two principal phases of clay genesis, strongly connected to the evolution of organic matter in andosoils, as follows: (i) an early, prepedologic phase during which halloysites and smectites would form ; (ii) a late phase giving rise especially to some kaolinite and gibbsite.

Clay Sedimentology

“…The second stage corresponds to the widespread development of Fe-to Alsmectites (nontronite, montmorillonite, etc. Hetier et al (1977) also describe the formation of smectite during the first weathering steps of basalts in the Massif Central, France. Abundant volcanogenic smectites are commonly described in Europe from Mediterranean regions to Iceland, where they may occupy the largest part of soil profiles.…”

“…In temperate regions, halloysite can constitute significant amounts of some weathering crusts (e.g., Great Britain, Hathaway 1963, in Caroll 1970), of soils on basalts (Massif Central, France;Hetier et al 1977, Torrent et al 1982, or of direct alteration products of alkaline trachytic pumices (Central Italy; Quantin et al 1987). It also forms easily by weathering of airfall tephras, as Carroll 1970) in New Zealand (Lowe 1986).…”

Maximum altitude of Devensian glaciation on the Isle of Skye

“…It is known to develop under alpine conditions (Reynolds 1971) and is believed to form relatively rapidly on soils derived from volcanic rocks (Hetier et al 1977), particularly at sites where drainage is good and silica concentrations in soil water are low (Gardner 1972). However, the significant contrast in the representation of gibbsite in samples above and below the trimline on Skye implies that it is not a product of post-glacial weathering.…”

Clay mineralogy of seven dystrandepts developed from basalts in Northland, The French Massif Central and Western Oregon

“…If the Northland and Western Oregon soils whose parent material is not only basalt are excluded from the argument, the climo. sequence of soils in the French Massif Central (Cantal and Chaine des Puys (3,8,10 22), Velay and Vivarais (6)), Roumania (7), Southern Italy (11) and Tanzania (12): indicates that fairly humid and cool climatic conditions favor the formation of Andepts from basic igneous rocks such as basalt. FLACH et a/.…”

“…In Soil Taxonomy (1), Andepts are described as more or less freely drained Inceptisols that are formed mostly from pyroclastic ejecta, but sometimes from other pyroclastic rocks, sedimentary rocks, or basic extrusive igneous rocks. Reports have been published on Andepts or Andosols developed from basic volcanic rocks, mainly basalts and tuff (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) and from phyllite (14). Recent developments in the study of the clay mineralogy of Andepts from volcanic ash have been reviewed by WADA and HARWARD (15) and WADA (16)(17)(18).…”