Clay minerals in soil-loess sequences in Pasang area, Golestan province

Loess/soil sequences have been proven to be excellent paleoclimate indicators. Large areas of northern Iran are covered by loess deposits which provide a good condition to carry out research on paleoclimate, paleosols and discontinuities. The objectives of this research were to identify clay minerals of soil-loess sequences, to determine the role of climate change in clay mineral transformation and to estimate the relative ages of soil development based on archaeological information. Samples were analyzed by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The results showed that kaolinite, illite, quarts and feldspar were dominant in the fine clay, coarse clay and silt fractions. The type and the quantity of clay minerals in soils are highly correlated with parent material. Semiquantitative estimation indicated that different clay minerals are quantitatively different in the profiles. This may be due to different weathering rates caused by cool/dry and wet/warm periods. A high degree of chlorite to smectite transformation was observed in deep soil horizon (130–170 cm) where a developed horizon was buried. Differences between soil layers development were confirmed by comparison of oxalate and dithionite extractable Fe.