Mineralogy and Genesis of Clays in Red‐black Soil Toposequences on Basic Igneous Rocks in Kenya

Abstract

The clay mineralogy of two red-black soil toposequences on basic igneous rocks in Kenya has been investigated. Besides some illite and amorphous material kaolinites predominate in the slope soils (ultisols) whereas smectites are the main clay minerals in the soils of the depressions (vertisols). The kaolinites are poorly crystalline and have high surface area. According to chemical analysis, IR spectroscopy, and D.T.A. the smectites appear to be a ferriferous member of the montmorillonite-beidellite series having approximately 0.5 FeSf in octahedral and 0.2 A1 per Olo(OH), in the tetrahedral position. The profile and slope distribution of kaolinites and smectites led to the conclusion that the smectites are the first weathering product and, depending on hydrological conditions governing the soil solution composition (Si, Mg, pH), either persist (depression) or are decomposed (slope) and followed by kaolinites.

Pedogenic Formation of Kaolinite-Smectite Mixed Layers in a Soil Toposequence Developed from Basaltic Parent Material in Sardinia (Italy)

“…K-S mixed layers in the studied soils were identified with increasing proportion of smectite layers downslope. This soil-clay mineral distribution, in relation to topography, is similar to that reported for (kaolinitic) red-black (smectitic) soil association in subtropical areas (Herbillon et aL, 1981;Kantor and Schwertmann, 1974). Drainage conditions induced by the slope gradient are thought to govern the soil clay mineralogical evolution.…”

“…Pedogenic formation of kaolinitesmectite (K-S) mixed layers was described in tropical and subtropical areas, primarily in the "red-black" soil sequences (Kantor and Schwertmann, 1974;Herbillon et al, 1981;Yerima et al, 1985). In temperate areas K-S mixed layers were reported but they are probably inherited from the parent rock (Wilson and Cradwick, 1972) or associated with polygenetic soil profiles (Jaynes et al, 1989).…”

The geochemistry of soils on a catena on basalt at Khon Buri, northeast Thailand

“…Catenary soil sequences derived from basalt have been studied widely (Yaalon et al, 1971;Kantor and Schwertmann, 1974;Beckmann et al, 1974;Fitzpatrick and Le Roux, 1977;Herbillon et al, 1981;Curi and Franzeier, 1984;Webb and Dowling, 1990;Bhattacharyya et al, 1992;Weitkamp et al, 1996;Righi et al, 1999). The spatial distributions of minerals and elements in soils formed from basalt are partly controlled by topographic position, especially in tropical regions (Yaalon et al, 1971;Kantor and Schwertmann, 1974;Fitzpatrick and Le Roux, 1977;Curi and Franzeier, 1984;Bhattacharyya et al, 1992;dos Anjos et al, 1995).…”

“…The spatial distributions of minerals and elements in soils formed from basalt are partly controlled by topographic position, especially in tropical regions (Yaalon et al, 1971;Kantor and Schwertmann, 1974;Fitzpatrick and Le Roux, 1977;Curi and Franzeier, 1984;Bhattacharyya et al, 1992;dos Anjos et al, 1995). For an Oxisol catena developed on a veneer of sediment underlain by basalt in Brazil, the soils on an upper slope position had relatively high hematite and gibbsite contents and those on a lower position had relatively high goethite and kaolin contents, because soils on the upper slope position were both more leached and relatively drier than those on the lower slope position (Curi and Franzeier, 1984).…”

Etude d'une smectite magnesienne de transition, a caracteristiques di et trioctahedriques et derivee de l'evolution superficielle d'une trachydolerite de Provence

“…Cette surface est plus faible que celle des smectites typiques. Cependant, des valeurs semblables ont &6 trouv6es pour des smectites isol6es de sols d6velopp6s sur roches ign6es basiques, off ces min~raux 2/1 sont les seules phyllites, h la fois en Allemagne par Schwertmann & Niederbudde (1969) et au Kenya par Kantor & Schwertmann (1974).…”