Soil-Landscape Relationship as Indicated by Micromorphological Data on Selected Soils from Karaj Basin, Iran

Soils of the arid–semiarid Karaj Basin in north-central Iran have formed on alluvium-colluvium derived from mixed calcareous-gypsiferous marls of Miocene and basic igneous rocks of Holocene age. In order to characterize and classify the soils and to determine the soil-landscape relationship in the area, sixteen pedons located on different physiographic positions have been described, sampled and analysed. According to field descriptions these soils all show evidences of carbonate accumulation to be classified as Calcids or Cambids. However, soils with well developed argillic and calcic horizons have been observed on apparently younger colluvial fans, whereas the less developed soils with calcic and cambic horizons occur on older upper alluvial plains. Due to the calcareous gravelly soil parent materials, clay films are mainly masked by carbonates and their identification in the field is mostly impossible. Also due to the adherence of these clay films to coarse gravels and their separation from the fine earth materials through sieving, they may not sometimes appear on the particle size distribution analysis. Yet under the microscope the soils show enough indicators to be characterized as argillic horizon and to classify the soils properly according to Soil Taxonomy as Argids instead of Calcids. Also, these findings point out the relatively older ages of these physiographic surfaces now they are covered by younger colluvial materials.