Spatially associated red ferruginous (Lithic Ustorthent and Typic Ustochrept) and black soils (Lithic Ustorthent and Typic Haplustert) occur under similar topographic situation in close proximity in the basaltic Malegaon plateau of Nagpur district at an elevation of about 480 m MSL. Except the Vertisols, all other soils are noncalcareous. All the sola contain high amounts of coarse (< 2 μm) and fine clays (< 0.2 μm) which are dominantly smectitic. Presence of interstratified smectite-kaolin (Sm/K), even though in small amount, in the clay fractions suggests the formation of kaolin from smectite. Minor amounts of Sm/K and kaolin in ferruginous soils indicate a probable truncation of upper layers rich in these minerals. The formation of smectite and Sm/K in both the soils suggests that these soils were formed through a progressive landscape reduction process. The smectite and Sm/K were formed under humid climate of the geological past and are preserved to the present because of termination of the humid climate. The relatively higher soil pH condition of black soils has caused hydroxy-interlayering in vermiculite, an alteration product of mica. Chlorite in black soils is of pedogenic origin through a hydroxy-interlayer vermiculite stage.
Ferruginous soils, Vertisols, clay minerals and transformation
