Genesis and clay mineralogical investigation of highly calcareous soils in semi-arid regions of Southern Iran

Abstract

This study outlines principal characteristics of soils occurred in the arid and semi-arid regions of Southern Iran. An outstanding characteristic of these soils is a prominent horizon of calcium carbonate accumulation at or near the depths of rainfall penetration. Objectives of this study were to discuss the genesis, morphological and physico-chemical properties of calcic horizons and mineralogy and classification of soils in semi-arid region. Five representative profiles were selected and soil samples were collected to determine the chemical and physical properties. Carbonate accumulation and clay eluviation-illuviation are the dominant processes in these soils. Calcium carbonate in the studied soils varied from continuous coatings with weakly cemented matrix which appears as few to common carbonate nodules (stage II) and to plugged horizon (stage III). Palygorskite, chlorite, illite, smectite and vermiculite minerals were observed in soil samples. Illite and chlorite are largely inherited from parent materials. Inheritance, transformation and neoformation from other minerals are the main pathways for the occurrence of smectite and palygorskite in the studied soils. Presence of kaolinite only in deeper calcic horizons suggested that these horizons developed in a tropical climate that shifted gradually towards semi-and conditions. The soils of study site were classified as Typic Calcixerepts, Petrocalcic Calcixerepts and Calcic Haploxeralfs, respectively. © 2008 Asian Network for Scientific Information.