Distribution of palygorskite in Cretaceous and Tertiary sediments and the associated soils in southern Iran

Little is known about the distribution and origins of palygorskite in soils developed on Tertiary and Cretaceous rocks and sediments and the associated soils in such areas as Fars Province, southern Iran, or the other Middle Eastern countries. The present study pursued the twofold objective of (1) identifying the distribution and sources of palygorskite in the soils developed on the above sediments and (2) determining the major soil properties influencing palygorskite distribution. Eight soil profiles developed on Cretaceous and Tertiary sediments and their parent materials were sampled and studied using XRD, SEM, and EDX analyses. The results revealed that most of the palygorskite was inherited from the respective parent materials although some seemed to be the product of neoformation pathways as a result of gypsum and calcite precipitation. Principal component analysis revealed that the most significant factors affecting the distribution and genesis of palygorskite in the soils developed on Cretaceous sediments are electrical conductivity (EC), clay, soluble Si, organic C, calcium carbonate equivalent (CCE), and smectite while those for Tertiary parent material-derived soils are the amounts of gypsum, illite, organic C, and CCE. Multiple regression analysis suggested smectite, pH, gypsum, and EC in the Cretaceous samples and the values of gypsum and soluble Ca and Si in the Tertiary soils as indicators to be used for predicting palygorskite content.