Origin and distribution of clay minerals in calcareous arid and semi-arid soils of Fars Province, southern Iran

Abstract

The clay mineralogy of soils and of the main calcareous sedimentary parent rocks of southern Iran were investigated to determine their origin and factors controlling their distribution pattern in soils. The results revealed that the soil-available moisture plays the major role in the distribution pattern of palygorskite and smectite clay minerals in the arid and semi-arid areas studied. There is an inverse correlation between palygorskite and smectite with regard to the soil-available moisture as expressed by P/ETº (ratio of mean annual precipitation to mean annual reference crop evapotranspiration). At P/ETº values >0.4 palygorskite transforms to smectite. Smectite is thought to be mainly of ‘transformed’ origin. It is detected in trace amounts in soils of more arid areas and increases in soils having greater available moisture. The general decrease in illite content with depth is related mainly to its transformation to smectite under favourable moisture conditions of the deeper horizons. Palygorskite is considered to be inherited in plateau soils of the arid regions whereas in saline and alkaline soils and soils with high gypsum, it is mainly of authigenic origin. The P/ETº and gypsum content show a significant correlation with the palygorskite content. The occurrence of kaolinite in some soils is due to its inheritance from the surrounding kaolinite-bearing Cretaceous rocks. Illite and chlorite abundance in soils is also largely related to their presence in parent rocks. The rare occurrence of vermiculite in the studied calcareous soils is mainly related to its lower stability under high pH, low Al activity and the presence of large amounts of Si and Mg in soils.

Response of some soil attributes to different land use types in calcareous soils with Mediterranean type climate in north-west of Iran

“…Changes in land use types and soil type did not cause noticeable modification in the XRD pattern of chlorite and kaolinite regarding the quantity and the intensity or in the position of peaks of them. This trend is not surprising, especially, in view of the fact that chlorite and kaolinite are very stable against weathering process in calcareous and alkaline soil like the region investigated (Khormali and Abtahi 2003;Rezapour et al 2009). Variability of illite and smectite was strongly evident following changes in land use and soil type.…”

Soil-landscape relationship as indicated by pedogenesis data on selected soils from Southwestern, Iran

“…Warm and humid climate with good drainage was reported for kaolinite formation (Nadimi and Farpoor, 2013;Khormali and Abtahi, 2003). Since such an environment could not be found in the area at present, kaolinite should have been inherited in the studied soils.…”

“…Soil clay minerals have two main sources: (1) neoformation and transformation by pedogenic processes, and (2) inheritance from parent rocks, or addition by eolian or fluvial processes to soil surface (Schaetzl and Anderson, 2005). Palygorskite, smectite, chlorite, illite, kaolinite, and vermiculite have been reported as dominant clay minerals in arid and semi-arid areas of Iran (Salehi et al, 2002;Khormali and Abtahi, 2003;Owliaie et al, 2006;Nadimi and Farpoor, 2013;Sarmast et al, 2016;Sarmast et al, 2017). Neoformation of palygorskite as a result of calcite and gypsum precipitation seems to be a major pathway for the occurrence of this mineral in the studied soils of southwestern Iran.…”

The mineralogy of paleosols in the Marília Formation and their importance in the environmental evolution of the Maastrichtian of the Bauru Basin in southeastern Brazil

“…The increase of calcite in the Bkm horizon implies changes in environmental conditions, such as an increase of leaching, precipitation and desilication processes, which leads to a climate with less arid characteristics. Khormali & Abtahi (2003) affirm the coexistence of carbonate pedogenic nodules with palygorskite and illuvial clay coatings in calcite crystals in the argillic horizon of aridisols in central Iran. These nodules suggest a link between pedogenetic carbonate, palygorskite and the argillic horizon, which formed when the climate was wetter than present day.…”