Soil genesis along a Catena in Southwestern Iran: a micromorphological approach.

In order to determine the role of topography and drainage condition on soil genesis, a micromorphological study was carried out along a catena in Kohgilouye Province, southwestern Iran. The catena in this study crosses the main physiographical units such as alluvial and colluvial fans, piedmont plain, plateau, river alluvial plain, and lowland. Seven representative soil profiles were described and studied accurately. Thin section observations, scanning electron microscope (SEM), and digital microscope studies were used in this study. The major contributing soil processes can be categorized as calcium carbonate leaching, clay eluviation, and formation of Fe-Mn oxides. Calcite depletion pedofeatures were the most striking aspect of the soil thin sections studied. In pedons that were located on more stable physiographic unit, a higher frequency of micritic calcite nodules was observed. The presence of needle-shaped calcite in aquic and non-aquic conditions throughout the soil profile suggests an appropriate broad range of pedoenvironmental conditions for the formation and stability of this mineral habit. The magnitude of calcite nodules that were impregnated with Fe-Mn oxides was higher in soils formed on more stable geomorphic units. Adjacent formation of needle-shaped calcite and cytomorphic calcite in some horizons may suggest the biogenic source of this mineral. In most thin sections of argillic horizons, clay films were cleared after a mild HCl treatment, suggesting masking of the clay coating by carbonates. [ABSTRACT FROM AUTHOR]