عنوان مقاله [English]
Introduction: Mineralogical composition, soil morphological properties, and magnetic susceptibility were affected along soil evolution in soils. That is why micromorphology helps in performing soil classification and evolution studies, as well as making soil management practices much more efficient. Clay mineralogy is a useful tool that helps in better understanding soil forming factors and processes. Soil magnetic properties are complex reflections of chemical, geological, and biological soil characteristics. Thus, knowledge about factors affecting magnetic susceptibility can help in better understanding and interpreting the results obtained in an area. Assessment of soil magnetic behavior might be used in pedology, soil mapping, investigation of soil process variations, parent material composition, sedimentary processes, soil drainage conditions, soil pollution, and separation and identification of soil unit boundaries. The present study was performed to investigate the effects of magnetic susceptibility, clay mineralogy, and micromorphology on soil characteristics, genesis, and evolution.
Materials and methods: Seven representative pedons were selected in sedimentary and igneous sections in uncultivated land use and physiographic units: hill, piedmont plain, alluvial plain, and lowland. Physicochemical properties measurements were performed on the collected samples from representative pedons using standard methods. The pedogenic (Fed) and amorphous (Feo) iron concentrations of the extracts were determined using a Vario Atomic Absorption Spectroscope (AAS) instrument. Undisturbed soil samples were selected for micromorphology studies and thin section preparation. Additionally, three soil samples were used for X-ray diffraction (XRD) analyses after carbonates, organic matter, and Fe were removed using Jackson (1965) and Kittrik and Hope (1963) procedures. Finally, the mass-specific magnetic susceptibility of soil samples was determined using a Bartington MS2 meter equipped with the MS2B Dual Frequency sensor, capable of taking measurements at both low (χlf at 0.46 kHz) and high (χhf at 4.6 kHz) frequencies.
Results and discussion: Salinization, leaching, and illuviation processes of gypsum and carbonates were observed in the studied pedons. The soils were classified as Aridisols (Soil Taxonomy system) and Solonchacks, Solonetz, Gypsisols, and Calcisols RSGs (WRB system) due to the presence of calcic, gypsic, salic, argillic, and natric diagnostic horizons. The presence of gypsum, carbonates, salt, clay accumulation, and argillic horizon reduces χlf values. The calcite coating located on the clay coating could probably be attributed to the presence of a climate with more available humidity in the past. The range of soil magnetic susceptibility was from 4.3×10-8 to 1264×10-8 m3kg-1. Gypsum infillings, different forms of gypsum, clay accumulation and coatings, and weathered calcite crystals were among the dominant micromorphological features observed in the studied pedons. Montmorillonite, chlorite, illite, kaolinite, quartz, and vermiculite minerals were observed in the studied pedons. Chlorite and illite minerals were dominant in the clay fraction of the studied soils, whereas a portion of these minerals was probably converted to vermiculite. Discontinuities observed in pedon 2 could be accounted for as proof of more available humidity in the past compared to the present time periods. Moisture has caused the removal of potassium and transformation of illite and chlorite to vermiculite. The dominance of illite and chlorite can be proof of initial weathering and evolution in the other studied pedons.
Conclusion: The χlf variations was related to depth trend and physicochemical properties. The χlf values showed a noticeable negative correlation with argillic horizon, gypsum content, carbonate calcium, and salinity. It seems that most of the clay minerals originated from the parent material in the present study, and pedogenic source has rarely taken place. Besides, the χlf and Fe contents were directly correlated. In general, the results indicated young soils with primary development stages in the area under study. Pedon 2 with buried polygenetic soils is an exception.