Evolution of clay minerals in saline-sodic soils as influenced by topography and ground water table in northern Atrak watershed

Seven representative profiles, derived from loess materials, with different physiographic units and saline ground water table, were studied to determine the evolution of clay minerals in salt affected soils in northern Atrak watershed in Golestan Province. Soils were classified as Aridisols with Salids suborders. Due to arid climate with little leaching and weathering, soil clay minerals were mainly affected by parent material mineralogy. Mineralogical analysis showed that illite, chlorite, kaolinite and little amount of smectite were dominant clay minerals of parent materials. XRD analyses showed that the soils are somehow similar in the type but different in the abundance of clay minerals which is mainly due to drainage conditions. Chlorite, illite, smectite and kaolinite were detected on the X-ray diffractograms. Illite was found as the dominant clay mineral in all the soils. Illite, chlorite and kaolinite were found in C horizons and are mainly of inherited origin. Smectite increases in the soils with poor drainage conditions mainly due to the soil solution rich in basic cations which is suitable for its neoformation from soil solution. X-ray and TEM examinations revealed the occurrence of palygorskite in clay fraction of soils formed on plateaus. Absence of palygorskite in loess deposits elucidates its inheritance origin possibility. Favorable conditions such as sever salinity and alkalinity and old landform should have contributed in transformation of smectite and neoformation of palygorskite from soil solution.