Abstract

Arid soils in central Iran that evolved from the weathering of post-Tethyan sediments contain palygorskite. Clay fractions of gypsiferous soils and their associated sediments from different landforms from central Iran were investigated. Palygorskite was the dominant silicate clay mineral in clay fractions of the soils, and of Oligo-Miocene limestone, a less common parent rock. The Jurassic shale and Cretaceous limestone contain illite and chlorite with a trace amount of palygorskite. Association of large amounts of palygorskite bundles with gypsum in the gypsiferous soils studied, supports the hypothesis that palygorskite was probably formed after the initial precipitation of gypsum, that created a high pH and Mg Ca ratio. The major portion of the palygorskite present in colluvial and plateau soils was probably formed authigenically when central Iran was covered by post Tethyan shallow hyper-saline lagoons. Palygorskite in alluvial soils appeared to be essentially detrital.

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