Genesis, clay mineralogy and micromorphology of saline-gypsiferous soils in Kheirabad playa, Sirjan

Playa is an important landforms in desert environments and covers an extensive area in this type of ecosystem.  Playa landform is composed of different geomorphic surfaces. After orogenic activities and evaporation of water bodies remained from Thetis Sea, playa was formed and various evaporite minerals were precipitated. Minerals with lower solubility precipitated in upper parts were the origin of minerals for lower positions.   Kheirabad saline-gypsiferous playa in Kerman Province was selected to study physicochemical, clay mineralogy, and micromorphological properties.  Clay flat, puffy ground clay flat, wet zone and salt crust are among geomorphic surfaces identified by field studies and Google Earth images in Kheirabad playa.  Electrical conductivity at non-saline clay flats varied between 2.8 to 32.2 dS/m. Smectite, illite, palygorskite and kaolinite were detected in this geomorphic surface.  Euhedral gypsum crystals and calcite coatings were observed in gypsic and calcic horizons of this position, respectively. Electrical conductivity in saline clay flats varied between 33.5 to 160 dS/m.  Lenticular and interlocked plates of gypsum were among secondary gypsum crystals identified in this geomorphic surface using micromorphology. Maximum EC (314 dS/m) was investigated in puffy ground clay flat which is attributed to capillary movement of saline groundwater.  Illite, palygorskite, smectite, and kaolinite clay minerals together with calciticcrystalitic b fabric were found in wet zone geomorphic surface.  Electrical conductivity and percentage and size of gypsum crystals increased from upslope positions toward the center of the playa, but no such a trend was found for clay minerals.