Soil-landscape relationship as indicated by pedogenesis data on selected soils from Southwestern, Iran

Abstract

Soils of semiarid regions of Dehdasht and Choram in Southwestern Iran have formed onalluvium derived from mixed calcareous-gypsiferous materials from Lower Miocene toUpper Pliocene. In order to characterize and classify the soils and to determine the soillandscape relationship in the area, nine pedons located on different physiographicpositions including plateau, river alluvial plain, piedmont plain, alluvial plain and alluvialfan have been described, sampled and analyzed. Physicochemical analyses, claymineralogy and micromorphological studies were performed. The results showed thattopography and parent material were two important soil forming factors affecting soilformation in the area. The soils were dominated by carbonate, gypsum, and clay illuviationand accumulation. More developed soils were found on the stable plateau and piedmontplain. Clay illuviation and argillic horizon development in soils of the more stable alluvialplain were assumed to be relict features from presumably more humid climates.Palygorskite, illite, chlorite, smectite, kaolinite, and quartz clay minerals were identified inalmost all physiographic surfaces, but more palygorskite and less smectite were found inthe soils with gypsiferous parent materials. Observations by SEM revealed the occurrenceof neoformed palygorskite as thread-like faces and coating of gypsum crystals and marlymatrix. Coating and infilling of gypsum and calcite crystals in voids and channels werecommon pedofeatures observed in the soils studied. Two different distribution patterns ofFe-Mn oxides were identified in aquic and non-aquic soils.