Clay Mineralogy of Gypsiferous Soils under Different Soil Moisture Regimes in Fars Province, Iran

This study investigated the relationship between clay minerals and different soilmoisture regimes in gypsiferous soils of fars province in southern iran. the overallclimate of the province is arid and semi-arid and, under this condition, parent material isthe most important factor affecting clay minerals distribution. beside this factor, climateconditions have determining role too. palygorskite, smectite, chlorite, illite, and kaolinitewere identified as the main clay minerals in gypsiferous soils, using xrd, tem and semanalyses. chlorite and illite were inherited largely from parent rocks and their abundancein soils with different moisture regimes was generally uniform. the presence of gypsumand saline and alkaline ground water in some pedons has favoured the neoformation ofpalygorskite from soil solution. palygorskite shows an increasing trend with depth thatmay be related to its authigenic formation in the presence of gypsum. the correlationbetween palygorskite percentage and gypsum content was estimated (r^2= 0.56). thehighest amount of palygorskite was observed in soils with aridic moisture regimes, and itslowest amount was estimated in soils with xeric moisture regimes. notably, withincreasing moisture, the length of palygorskite fibber decreased. high soil moisture andrainfall and low evaporation are reasons for instability of palygorskite relative to smectitein xeric moisture regime. large amounts of well-bundled and elongated palygorskite insoils of piedmont plain are related to their authigenic formation; while presence of slightamounts of short palygorskite fibres in lowlands suggest their transformation to smectite.results of soil and rock samples analyses showed that some palygorskite in all moistureregimes originated from parent materials. also, results indicated that thesmectite/(illite+chlorite) ratio increased with increase in moisture and the largest value(equal to 2.12) was observed in soils with xeric moisture regime.