Mineralogy and Characteristics of Soils Developed on Persian Gulf and Oman Sea Basin, Southern Iran: Implications for Soil Evolution in Relation to Sedimentary Parent Material

There are relatively few comprehensive documents about the mineralogy of arid regions, and no study has been reported on the characteristics and mineralogical trends of the soils of arid regions in the Hormozgan Province, southern Iran. The objective of this study was to identify the variations in physical, chemical, and mineralogical composition of soils of the region lying between the southern part of Zagros and Persian Gulf to Oman Sea. X-ray diffraction, thin-section studies, and transmission electron microscopy with energy-dispersive X-ray spectroscopy were conducted to determine the relationship between mineral distribution and climate, along with an evaporate environment reflected by a variety of geological structures. On the basis of nature and composition, the soils can be classified into Alluvial soils rich in silt and Desert soils, sandy soils poor in organic carbon in which evaporate Tertiary Formations played an important role on the formation of contemporary minerals. The maximum portions of silt and sand fraction were composed of quartz and alkali-feldspars, whereas calcite and dolomite were elevated in soil samples without acid treatments. The clay mineralogy results revealed that detrital input and inheritance are possibly the main source of kaolinite, smectite, chlorite, and illite, whereas in situ neoformation during the Tertiary shallow saline and alkaline environment could be the dominant cause of palygorskite occurrences in the sedimentary rocks. The chemical composition of clay suspension, determined by electron microprobe analysis, corresponds to that of Mg-rich predominant palygorskite, with a degree of tetrahedral substitution from almost less than 2 to 23%. In conclusion, the soil mineralogy did not vary systematically with depth but showed spatial variations, and the relative influence of mineral distribution in topsoils can be summarized as follows: parent rocks > geomorphological setting > water table position > climate > physiography and soil evolution. The soils, in general, contained moderate to high amounts of weatherable minerals, indicating their early to intermediate stages of development.