Pedological Investigation of a Litho-Toposequence in a Semi-Arid Region of Southwestern Iran

Resumo

A litho-toposequence of soils in a semi-arid region in southwestern Iran was investigated for their pedological properties. Nine representative pedons on different geomorphic surfaces, including river terrace, alluvial plain, pediment, and alluvial fan, were studied on stratigraphic ranges from Lower Miocene to Pliocene. The soils are dominated by carbonate, gypsum, and clay illuviation. More developed soils were found on the more stable surfaces. Illuviated clays at lower depth of stable geomorphic surfaces should be the result of the more humid climate of the past, where the carbonates have been removed completely. The occurrence of calcite coatings that are superimposed on the clay coatings shows the recalcification and carbonate precipitation processes. Smectite, illite, chlorite, palygorskite, kaolinite, and quartz clay minerals were identified in almost all geomorphic surfaces, but more palygorskite and less smectite were found in the older gypsiferous soils. Coating and infilling of gypsum and calcite crystals in voids and channels were common pedofeatures observed in the soils studied. Larger lenticular gypsum crystals were found in the soils with lighter texture located on the more stable geomorphic surfaces.