Identification and genesis of clay minerals in two paleosols from Sepahanshahr(Isfahan) and Emam_Gheis (Chahrmahal _Bakhtiari)

Existence and frequency of clay minerals is useful for reconstruction of paleoenvironment, because each mineral is formed and stabilized in special condition. The objective of this study was to identify clay minerals and their genesis in two paleosols from Isfahan and Charmahal-Bakhtiari. Through field observations and physico-chemical analysis, some horizons in these soils were selected for mineralogical studies. Soil and parent material samples were analyzed by XRD after necessary pretreatments. A few of samples were studied by scanning electron microscope and infrared spectrometer. The results indicate that mineralogical composition in surface horizon of Sepahanshahr profile is similar to parent material, whereas in the underlying paleohorizons palygorskite predominates. Lack of palygorskite in parent material on one hand and elongated shape of this mineral accompanied by calcite and gypsum in the paleohorizons on the other hand show that, it has formed pedogenicaly. In the soil surface of Emam_Gheis soil, the composition of clay minerals is also similar to parent material, but chlorite has been converted to vermiculite and subsequently to smectite, due to relatively high precipitation in this area. Presence of high amount of smectite in buried paleosol of Emam_Gheis probably indicates moister regime in the past.