The magnetic susceptibility of soils in Kohgilouye, Iran

Abstract

Soil magnetic susceptibility (MS) and Fe were examined for several soils on calcareous parent material, reflecting key climatic conditions and drainage classes in southwestern Iran (Kohgilouye Province). Alfisols, in the eastern and northern parts, contained more pedogenic (citrate dithionite extractable) Fe (up to 60 g kg-1 on a minerogenic basis; 70 % of total Fe, as determined by lithium tetraborate fusion) and poorly crystalline Fe (up to 6 g kg-1 ammonium oxalate extractable) than the Inceptisols in the southern parts. Soil MS (χlf) ranged from 5 to 120 × 10–8 m3 kg-1, with A horizons exhibiting greater values than B horizons, and Alfisols higher than other soils. Pedogenic enhancement of χlf corresponded with preferential leaching of diamagnetics (primarily carbonates), as well as weathering of primary paramagnetics and neoformation of antiferromagnetics. Frequency dependence of MS (χfd), indicating ultrafine superparamagnetics, followed trends similar to χlf. Sequential heating of well-drained samples, from 25 to 500°C, resulted in enhancement of Χ (average of 21%), a ttributed to the conversion of antiferromagnetics to ferrimagnetics; between 500 and 700°C, Χ typically decreased (average of 15%). The Χfd of well-drained soils increased by an average of 5.3 percentiles by 700°C. Gleysolic soils exhibited less weathering (<51% of total Fe), higher proportions of poorly crystalline Fe (>0.15), lower Χlf (<25 × 10–8 m3 kg-1) and Χfd (<2%), as well as greater average enhancements of Χlf (265% at 500°C) and Χfd (8.4 percentiles at 700°C) on heating. Key words: Calcareous, iron oxides, citrate dithionite, ammonium oxalate, frequency dependence, thermal enhancement