There are various weathering indices consisting of the Chemical index of weathering (CIW), Chemical Index of Alteration (CIA), Chemical Proxy of Alteration (CPA). Typically, the value of these indicators increases by increasing weathering intensity. Magnetic susceptibility is a property that can be measured in a short time and according to various studies has a good relationship with some physical, chemical, evolutionary properties, drainage conditions, weathering and in some cases land use type. Therefore, in the present study, different forms of iron, magnetic parameters and weathering indices in different geomorphic surfaces of Chaldoran have been studied. The objectives of this study include (1) investigating changes in various forms of iron and magnetic susceptibility of soil; (2) the effect of drainage, land use and human (agricultural) activities on changes in soil magnetic susceptibility; 3) Investigation of weathering indices of CIW, CIA and CPA at different geomorphic surfaces.
Material and Methods
Based on the study of the predominant geomorphic surfaces of the region, including the piedmont plain (pedons 5 and 7), mantled pediment (pedon 6), alluvial fan (pedon 2), plains (pedons 1.3,4,9), flood plain (pedon 8) in figure 1 and a visual interpretation of Google Earth satellite images, topographic maps and field visits, the initial geomorphic surfaces of the sampling areas were determined. A total of 60 soil profiles were dug by supervised random sampling in different soil series, taking into account the entire study area. Also selected according to field studies and laboratory results, important and effective land characteristics, number of indicator pods. All excavated excavations were described according to the Soil Survey Staff (1993) and classified according to the Comprehensive Soil Classification of the United States (Soil Taxonomy, 1999) and the Keys to Soil Taxonomy (2010). Among the excavated Pedons, nine representative Pedons were chosen that mostly composed of quaternary sediments in terms of geology of the study area. In some parts, it could also be seen as veins of Limestone, Gabbro, Diorite and Basalt. Afterwards, soils were classified according to the soil taxonomy 2014 system. Sampling was performed in each control soil from top to bottom horizons and magnetic susceptibility was measured in all horizons. The soil samples were then dried at room temperature and passed through a 2 mm sieve after crushing. After that, the Soil Organic Carbon (SOC) using the Walkley-Black wet oxidation method, soil texture by pipette method, calcium carbonate equivalent by neutralization method , EC and pH of saturated extracts were measured using EC meter and pH meter, respectively. Besides, the amount of gypsum was measured using acetone method. Free iron (Fed) using dithionate bicarbonate citrate, non-crystalline iron (Feo) using ammonium acid oxalate, and total iron using nitric-perchloric acid (1:3) were extracted. The concentration of extracted iron was determined by utilizing the atomic absorption of Perkin Elmer AAnalyst 800. Furthermore, the magnetic susceptibility of soil (χ) at low frequencies 0.46 kHz, high frequency 4.6 kHz, (χ) was measured using MS2B Bartington magnetic susceptibility system.
Results and Discussion
The range of χlf of soils ranged from 42.90×10-8m3kg-1 (Horizon Ap, Pedon 1) to 1053.20×10-8 m3 kg-1 (Horizon C1, Pedon 1). The average χlf in the geomorphic units of the area is obtained in the form of flood plain> alluvial fan> mantled pediment> plain> piedmont plain. The χfd values of the studied soil samples were in the range of 0.07- 3.50%.
The range of changes in total iron is from 12.05 g kg-1 (Horizon C2, Pedon 1) to 42.60 kg-1 (Horizon Bss2, Pedon 9). Also, the mean of total iron in the studied Pedons is in the form of mantled pediment> alluvial fan> flood plain> piedmont plain = plain, respectively. Moreover, the mean Fed values in the studied geomorphic units were in the form of mantled pediment> plain> piedmont plain> flood plain> alluvial fan, respectively. The amount of Feo in the studied soils varied from 0.09 gkg-1 (Horizon C2, Pedon 1) to 0.75 gkg-1 (Horizon BC, Pedon 4). Furthermore, the average value of Feo in geomorphic units is flood plain> piedmont plain> alluvial fan> mantled pediment> plain, respectively. The range of changes in the Feo/Fed ratio in the studied geomorphic units was from 0.08 to 0.01. In addition, the range of changes in χlf value varied from 42.90×10-8m3 kg-1 on the Horizon Ap to 1053.20×10-8m3 kg-1 on the Horizon C1.
The range of changes in CIA index was from 60.82 (horizon C2, pedon 1) to 78.77 (horizon Bg, pedon 3). Moreover, the highest and lowest mean of CIA index were observed in flood plain and mantled pediment geoforms, respectively. Therefore, all horizons of excavated Pedon in the area have a CIA between 50 and 80, indicating that the soils of the area are in the phase of weak to moderate weathering. Another meteorological index used is the CPA index, which is somewhat complementary to the CIA index. The highest and lowest mean values of CPA index were observed in flood plain and mantled pediment geomorphic units, respectively. Meanwhile, the value of CIW index varied from 65 (horizon C2, pedon 1) to 87.20 (horizon Bg pedon 3).
The aim of this study was to evaluate the effects of soil formation factors on the amount and vertical distribution of magnetic susceptibility. Nine control excavations were excavated in five dominant geomorphic units of the region, including slope plain, covered pediment, alluvial fan, plain, flood plain in West Azerbaijan province located in IranThe obtained results of this paper confirmed that the parent materials, topography along with drainage, and land use status factors, had been known as the most important factors affecting the formation, evolution, and magnetic susceptibility of different geoforms in Chaldoran area. In most of the studied Pedons, the amount of magnetic susceptibility χ increased by increasing depth, whereas in some Pedons, the amount of χ was maximal due to the transfer of fine ferrimagnetic particles with clay particles in Horizon B. The soil drainage conditions and moisture regime had also greatly influenced both the magnetic susceptibility and Fed distribution. Overall, the aquic conditions in the studied soils reduced the susceptibility of the Fed rate. Meanwhile, the ferrimagnetic particles forming the soils of the area were of the type of multi-zone coarse particles (μm >110). Furthermore, the CIA, CIW and CPA weathering indices revealed a weak to moderate weathering phase in the area. Nevertheless, to better understand the magnetic properties of soils under different geoforms, it is better to explore the relationship of other magnetic parameters in the area.