ORIGIN AND DISTRIBUTION OF CLAY MINERALS IN CALCAREOUS, GYPSIFEROUS, SALINE SOILS AND SEDIMENTS OF BAKHTEGAN LAKE BANK, SOUTHERN IRAN

Pedogenesis and clay mineralogy of soils and rock samples were studied in a transect of calcareous, gypsiferous, saline soils and sediments of Bakhtegan lake bank in southern Iran. The main objectives of study were to determine the occurrence of clay minerals and factors controlling their distribution pattern and relative abundance in soils and parent materials. The soil parent material is highly calcareous in all regions. However, gypsiferous and saline soils mainly occur near the Bakhtegan Lake with much evaporitic sediments (gypsum and halite) and where there is a saline and alkaline ground water table. XRD, TEM, SEM and EDX analyses indicated that chlorite, illite, palygorskite, smectite and interstratified minerals are the dominant clay minerals in both soil and rock samples. The presence of illite, chlorite abundance could be attributed to the parent rock samples and inherited origin. Interstratified minerals of chlorite-smectite or illite-smectite are observed in clay fraction of soils situated in plains and down slope due to further weathering and transportation from upslope to down slope. Studies indicated the presence of neoformed, transformed and inherited forms of palygorskite in all soils. Studies have showed that arid soils in southern Iran were affected by post-Tethyan sediments and some minerals have evolved from the weathering of these sediments.