Introduction
Magnetic susceptibility, a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field, has been applied successfully in various disciplines of geologic and environmental sciences to indicate the presence of ferrimagnetic minerals, such as magnetite and maghemite, in soils (Ayoubi & Mirsaidi Reference Ayoubi and Mirsaidi2019). This constant has also been employed effectively in various applications in soil science, such as soil development (Maher & Thompson, Reference Maher and Thompson1995; Grimley et al. Reference Grimley, Arruda and Bramstedt2004; Tazikeh et al. Reference Tazikeh, Khormali, Amini, Barani Motlagh and Ayoubi2017), soil contamination by heavy metals (Lu & Bai Reference Lu and Bai2006; Karimi et al. Reference Karimi, Ayoubi, Jalalian, Sheikh-Hosseini and Afyuni2011; Dankoub et al. Reference Dankoub, Ayoubi, Khademi and Lu2012; Naimi & Ayoubi Reference Naimi and Ayoubi2013), identification of soil moisture regimes (Valaee et al. Reference Valaee, Ayoubi, Khormali, Lu and Karimzadeh2016), differentiation of soil drainage classes (Mathe & Leveque Reference Mathe and Leveque2003; Asgari et al. Reference Asgari, Ayoubi and Dematte2018), and soil erosion and deposition processes (Mokhtari Karchegani et al. Reference Mokhtari Karchegani, Ayoubi, Lu and Honarju2011; Ayoubi et al. Reference Ayoubi, Ahmadi, Abdi and Abbaszadeh Afshar2012; Rahimi et al. Reference Rahimi, Ayoubi and Abdi2013).
Soil properties are affected predominantly by the lithology of the rocks and sediments of the soil parent materials. Hence, a characterization of soils developed on various rocks in arid and semiarid regions can inform management practices and environmental science applications (Lu Reference Lu2000; Rahardjo et al. Reference Rahardjo, Aung, Leong and Rezaur2004). Some researchers (e.g. Mullins Reference Mullins1977; Karimi et al. Reference Karimi, Haghnia, Ayoubi and Safari2017) have reported that magnetic susceptibility is one of the most important soil characteristics and that it is affected by lithology (Ayoubi et al. Reference Ayoubi, Adman and Yousefifard2018; Ayoubi & Karami Reference Ayoubi and Karami2019).
Magnetite and maghemite are the two main ferrimagnetic minerals that regulate the magnetic susceptibility of soils (Valaee et al., Reference Valaee, Ayoubi, Khormali, Lu and Karimzadeh2016). As such, the magnetic susceptibility technique can be useful for characterizing soil-forming processes (Ayoubi & Mirsaidi, Reference Ayoubi and Mirsaidi2019). In recent years, soil scientists and pedologists have employed magnetic susceptibility to broaden their understanding about soil evolution (Sarmast et al, Reference Sarmast, Farpoor and Boroujeni2017) and soil landscape processes (de Jong et al. Reference de Jong, Heck and Ponamarenko2005; Ayoubi & Mirsaidi Reference Ayoubi and Mirsaidi2019). Transformation of maghemite from goethite has also been proposed in acid sulfate soils as the mechanism by which the amounts of magnetic minerals can be increased in soils (Grogan et al. Reference Grogan, Gilkes and Lottermoser2003).
Various environmental variables, such as biological activities, topography, pedogenic processes, parent materials, landscape age, physicochemical properties, soil moisture regimes, and human activities, are factors driving the magnetic susceptibility variations observed in soils (e.g. Spassov et al. Reference Spassov, Egli, Heller, Nourgaliev and Hannam2004). Grimley & Vepraskas (Reference Grimley and Vepraskas2000) stated that the magnetic susceptibility is often much greater in soils subjected to a higher rainfall intensity and with better drainage. Favorable soil conditions can enhance the formation of ferrimagnetic minerals and increase the conversion of diamagnetic minerals into magnetite or maghemite.
Dearing (Reference Dearing1999) identified five basic types of magnetic behavior which can affect soil magnetic susceptibility; these are:
• ferromagnetic materials, including pure iron, that have highly ordered magnetic moments with a similar direction that generate a strong positive magnetic susceptibility;
• ferrimagnetic materials, such as maghemite and magnetite, that similarly exhibit intense magnetic moments and have unbalanced opposing forces;
• antiferromagnetic materials, such as hematite and goethite, that have well associated but opposing moments and generate a moderately positive magnetic susceptibility;
• paramagnetic materials, such as pyrite and biotite, that have weak positive magnetic susceptibility;
• diamagnetic materials, such as gypsum, calcite, quartz, and soil organic carbon, that have a weak negative magnetic susceptibility.
Accordingly, the main minerals that control enhanced magnetic susceptibility in rocks and soils have been identified as magnetite and maghemite (Mullins Reference Mullins1977; Maher Reference Maher1998; Dearing Reference Dearing1999; Cabello et al. Reference Cabello, Morales, Serna, Barron and Torrent2009).
As revealed by a literature review conducted prior to undertaking the study reported here, little attempt has been made to explore the relationships between magnetic susceptibility in various rocks and soil parent materials in arid and semiarid regions and the concentrations of magnetite and maghemite in those regions. Therefore, the main objectives of the present study were to: (1) characterize variations in the magnetic susceptibility of various igneous and sedimentary rocks; (2) determine the variations in the contents of ferrimagnetic minerals in rocks and the soils developed on the rocks using X-ray diffraction (XRD); and (3) evaluate the relationships between mineral presence/content and magnetic susceptibility in a semiarid region located in western Iran.
METHODS AND MATERIALS
Description of the study area
The study area is located in the Maku region, western Azerbaijan province, of northwestern Iran (approximately 45.5°E, 39.21°N) (Fig. 1). The average elevation of the selected area is 1634 m a.s.l. The average annual temperature and mean annual precipitation are 10°C and 270 mm, respectively. Pastures, irrigated farming, and dry land cropping are the major land uses in the study area. The predominant parent materials in the region are Eocene igneous rocks, Cretaceous sedimentary rocks, Permian sedimentary rocks (limestone), and Ordovician metamorphic rocks. The soil moisture regime in the study area is xeric and the temperature regime is mesic according to the Soil Survey Staff (2014).
Location of the study area in northwestern Iran, Azerbaijan province, Maku district, and locations of the study sites with respect to the various parent rock and soil materials
Soil sampling
Field studies were conducted and eight parent materials were collected from the study area (Fig. 1). The selected parent materials were igneous rocks that included granite, andesite, basalt, and ultrabasic and sedimentary rocks and deposits that included shale, limestone, marl, and the Qom formation. The Qom formation consists of partly consolidated, finely evaporated materials, including calcite, gypsum, and halite belonging to the early Miocene. Sampling sites were chosen for their similar geographical characteristics in terms of environmental features and nature, as well as similar vegetation cover, land use, elevation, slope, and slope aspect. All samples were collected from the back-slope landscape positions of pasture land that had 10–20% slope gradients with eastern slope aspects. Of the collected parent materials, ten samples were taken from the underlying parent materials along with the soils developed from the parent materials, with a total of 80 intact rock samples and 80 soil samples.
Laboratory analysis
The soil samples collected were air dried, crushed, and passed through a 2-mm sieve to remove coarse materials and plant litter prior to the laboratory analyses. Soil electrical conductivity (EC) of the saturated paste extracts was determined using an EC meter, and soil pH was measured in saturated soil pastes using a pH meter (Rhoades Reference Rhoades1982). The soil texture and particle-size distribution were determined using the pipette method (Gee & Bauder Reference Gee and Bauder1986). The soil organic material (SOM) content was determined by wet oxidation using chromic acid (K2CrO7–H2SO4) (Nelson & Sommers Reference Nelson, Sommers, Page, Miller and Keeney1982), and acid dissolution followed by back-titration was employed to measure calcium carbonate (CaCO3) equivalents (CCE) (Black et al. Reference Black, Evans, White, Ensminger and Clark1965).
A Bartington MS2 dual-frequency sensor (Bartington Instrument Ltd., Oxon, UK) was employed to measure magnetic susceptibility (χ) at low (0.47 kHz; χlf) and high frequencies (4.7 kHz, χhf). For these analyses, all soil and rock samples were crushed and passed through a 2 mm sieve, following which ~10 g of the soil or crushed rock was placed into a 4-dram clear plastic vial (diameter 2.3 cm) (Dearing et al. Reference Dearing, Hay, Baban, Huddleston, Wellington and Loveland1996). The following equation was used to calculate the mean magnetic susceptibility of the dependent frequency (χfd):
XRD analysis was performed on crushed soils and rock samples using a Bruker AXS D8 Advance X-ray diffractometer (Bruker, Billerica, Massachusetts, USA) with Cu-Kα radiation. XRD measurements were performed using a step size of 0.022°2θ and a step time of 1 s. A scanning range of 10 to 80°2θ was used to obtain X-ray patterns. Relative peak positions were used to identify minerals, and peak intensities were used for semi-quantitative estimates of the ferrimagnetic mineral (magnetite and maghemite) contents (Soil Survey Staff 2014).
Statistical analysis
Descriptive statistics, which included range (minimum, maximum), mean, skewness, kurtosis, standard deviation, and coefficients of variation (CVs) were calculated using SPSS software version 19.0 (IBM Corp., Armonk, New York, USA). The correlations between soil magnetic susceptibility and soil properties were obtained also using SPSS version 19.0 (Swan & Sandilands Reference Swan and Sandilands1995), as were the correlations between ferrimagnetic mineral peak intensities and magnetic susceptibility in the soil samples.
RESULTS AND DISCUSSION
Variability in χlf in the studied parent materials
The results of the analysis of variance indicated significant differences (P < 0.05) between the χlf values of the rocks examined. Of all rock samples, the highest mean χlf values were found in ultrabasic rocks (2066.90 × 10−8 m3 kg−1) (Fig. 2a). Overall, igneous rocks (ultrabasic, basalt, andesite, and granite) had greater χlf values than the sedimentary parent materials (Qom formation, shale, marl, and limestone). The lowest χlf (1.17 × 10−8 m3 kg−1) value was observed in the Qom formation samples which were enriched in the diamagnetic minerals calcite, gypsum, and halite (Mullins Reference Mullins1977).
Comparison of magnetic susceptibility values measured at low frequency (0.47 kHz; χ lf) in samples from the studied parent materials (a) and the magnetic susceptibility values of the soils developed on them (b) in the study area. Different letters on the bars in each figure indicate a significant difference at the P < 0.05 probability level
The mean χlf values in the ultrabasic and basalt rocks were much greater (>1700-fold) than those in the other rocks studied. Among the igneous rocks, the ultrabasic and basic rocks, which contained much greater amounts of ferrimagnetic minerals such as magnetite, had the highest χlf values. Mooney & Bleifuss (Reference Mooney and Bleifuss1953) also compared the χlf values in igneous rocks and, similar to the present findings, observed that the basalt samples had the highest χlf value (1260 × 10−8 m3 kg−1), while granite had the smallest χlf (220 × 10−8 m3 kg−1). Mullins (Reference Mullins1977) stated that the magnetic susceptibility of igneous rocks is mainly correlated to the magnetite content in these rocks.
Aydin et al. (Reference Aydin, Ferre and Aslan2007) stated that the predominant source of magnetic susceptibility was ferromagnesian silicates plus ilmenite in an ilmenite-series of granites, and titanomagnetite in a magnetite-series of granites. These authors reported that the chemical composition (Fe/Mg ratio) and the abundance of constituent minerals controlled the magnetic susceptibility values of the rocks.
In the present study, the sedimentary rocks with large concentrations of diamagnetic minerals (halite, gypsum, and calcite) and paramagnetic minerals (e.g. aluminosilicate clays) had low magnetic susceptibility values that varied from 1.17 × 10−8 m3 kg−1 in the Qom formation to 6.26 × 10−8 m3 kg−1 in the shale deposits. These findings are similar to the observations of other researchers on sedimentary rocks and deposits throughout the world (de Jong et al. Reference de Jong, Kozak and Rostat1999; Ranganai et al. Reference Ranganai, Moidaki and King2015; Karimi et al. Reference Karimi, Haghnia, Ayoubi and Safari2017).
Magnetic susceptibility in soils and the contributions of parent materials
Descriptive statistics of the χlf values of the various soils developed on selected parent materials in the study area are given in Table 1. The χlf values in the soils developed on the ultrabasic rocks were the highest (range 1274.81 × 10−8 m3 kg−1 to 948.15 × 10−8 m3 kg−1) with a CV value of 23.38%. The lowest χlf values (~71.95 × 10−8 m3 kg−1) were observed in the soils developed on the limestone rocks (71.09 × 10−8 m3 kg−1), with a CV value of 33.21%. The mean χlf values in the studied soils are given in Fig. 2b. The mean magnetic susceptibility values in the studied rocks compared using the least significant difference statistical test revealed no significant differences (P < 0.05) between ultrabasic and basalt rocks. The LSD values obtained for granite and andesite, however, differed from those of the ultrabasic and basalt rocks. Among the sedimentary rocks, no significant differences were found, with the exception of marl which had the highest value (Fig. 2b). These results are consistent with the findings of other researchers in Iran and other countries (de Jong et al., Reference de Jong, Kozak and Rostat1999; Ranganai et al., Reference Ranganai, Moidaki and King2015; Karimi et al., Reference Karimi, Haghnia, Ayoubi and Safari2017). Mokhtari Karchegani et al. (Reference Mokhtari Karchegani, Ayoubi, Lu and Honarju2011) reported a mean χlf value of 62.59 × 10−8 m3 kg−1 for the sedimentary deposits in western Iran. Karimi et al. (Reference Karimi, Haghnia, Ayoubi and Safari2017) indicated that the soils developed on limestone and gypsiferous marls had a mean χlf value of 69.5 × 10−8 m3 kg−1 and that the soils developed on ultramafic rocks had a mean χlf value of 197.6 × 10−8 m3 kg−1.
Descriptive statistics for magnetic susceptibility measured at low frequency and the mean magnetic susceptibility of the dependent frequency of soils developed on the various parent materials studied
χlf, magnetic susceptibility measured at low frequency (units: 10−8 m−3 kg−1); χfd, mean magnetic susceptibility of the dependent frequency (unit: %); CV, coefficient of variation
The χlf values in the soils were compared to the soil parent materials, and the results indicated that the χlf values changed significantly after soil formation. A number of theories have been advanced to explain this increase in χlf values in the soils in comparison to the soil parent materials. One of the earliest theories, i.e., the effects of heat during fires, proposed by Le Borgne (Reference Le Borgne1955), was rejected here because no trace of fires in the study area was found. A second theory that has been put forward in recent decades is that of the accumulation of particles of material from atmospheric pollution (Blundell et al. Reference Blundell, Dearing, Boyle and Hannam2009; Karimi et al. Reference Karimi, Ayoubi, Jalalian, Sheikh-Hosseini and Afyuni2011; Naimi & Ayoubi Reference Naimi and Ayoubi2013) as a result of fossil fuel burning. However, this possiblity was also rejected because no urbanization or industrial activities have occurred near the studied soils. Two remaining processes which could account for the results include inheritance from parent materials and pedogenic processes (Mullins Reference Mullins1977; Blundell et al. Reference Blundell, Dearing, Boyle and Hannam2009).
In the soils developed on igneous rocks, magnetic susceptibility originated mainly from the parent materials that had relatively higher χlf values in comparison to the sedimentary rocks. In the soils developed on the igneous rocks, dilution effects led to decreases in the χlf values in comparison to the parent rocks (Lu et al. Reference Lu, Xue, Zhu and Yu2008a,Reference Lu, Bai and Fub). It is possible that the formation of a number of diamagnetic minerals (e.g. calcite) and alterations to ferrimagnetic minerals (i.e. to paramagnetic minerals) during soil-forming processes are the main causes of decreased χlf values in the soils. In a study conducted on various igneous and metamorphic rocks in northwestern Iran, Yousefifard, Ayoubi, Jalalian, Khademi, & Makkizadeh (Reference Yousefifard, Ayoubi, Jalalian, Khademi and Makkizadeh2012) demonstrated that χlf values declined in all igneous rocks relative to the parent materials.
In the sedimentary parent materials, χlf values increased significantly in the soils in comparison to the parent materials. The χlf values in all soils developed on sedimentary parent materials were significantly enhanced, with values ranging from 1500% greater in limestone to >7000% greater in marl and the Qom formation. The enhanced χlf values in the sedimentary rocks are mainly attributable to soil-formation processes in the semiarid climate of the study area. These findings are consistent with those reported by Lu (Reference Lu2000) and indicate that the soils developed on igneous rocks had high magnetic susceptibility values, high absolute χ values, and markedly decreased χ values in comparison to the χ values of the parent materials. They also reported an increase in χ values in the upper soil horizons of the soils developed on sedimentary rocks in comparison to the χ values of the parent materials.
In the soils formed on sedimentary rocks, the χfd was > 4%. (see Table 1), indicating that super-paramagnetic particles were the prevalent magnetic minerals in these soils and that the χfd values could regulate the magnetic signal (Dearing Reference Dearing1994; Ng et al. Reference Ng, Chan, Lam and Wing2003; Jordanova et al. Reference Jordanova, Jordanova and Tsacheva2008). Highly positive significant correlations (P < 0.05) were obtained between the χlf and χfd values in the sedimentary rocks (Fig. 3), confirming that the χlf in these rocks increased through pedogenic processes that resulted in the formation of super-paramagnetic particles (Hu et al. Reference Hu, Su, Ye, Li and Zhang2007). Low χfd values were found in the soils that formed on the andesite, granite, basalt, and ultrabasic rocks (range 1.45–2.66%; Table 1), and no significant relationships were found between χlf and χfd in these soils (Fig. 3). These results confirmed that most of the ferrimagnetic minerals in the soils that formed on the andesite, granite, basalt, and ultrabasic rocks was inherited from the parent rocks. In contrast, the dilution influences that resulted from soil development led to a reduction in the χlf value in comparison with the respective parent rocks.
Relationships between χlf and mean magnetic susceptibility of the dependent frequency (χ fd) of soils that developed on various parent materials in the study area. The double asterisk indicates a significant difference at the P < 0.01 probability level. NS Not significant at P < 0.05
Correlation between soil properties and χlf
The observed relationships between magnetic susceptibility and soil properties (Fig. 4) revealed that all of the measured soil properties, including pH, EC, SOM, CCE, and clay content, were significantly and negatively correlated with χlf. The presence of SOM and calcite, both diamagnetic materials, reduced χlf values by weakening the effects of the magnetic materials (Marwick Reference Marwick2005). These findings are consistent with the results of other researchers, such as Naimi and Ayoubi (Reference Naimi and Ayoubi2013) who conducted a study in central Iran. Similar to the present findings, Dankoub et al. (Reference Dankoub, Ayoubi, Khademi and Lu2012) observed significant and negative relationships between χlf and EC in the arid regions of Iran. These authors attributed this phenomenon to the dilution effects of soluble salt minerals on the magnetic minerals in the bulk soils.
Relationships between magnetic susceptibility and some soil properties in the studied soils: (a) Clay content, (b) electrical conductivity (EC), (c) soil organic matter (SOM), (d) pH, ecalcium carbonate (CaCO3)
A positive significant correlation (r = 0.55, P < 0.01) was observed between χlf and sand content. This positive correlation confirmed the inheritance of magnetic minerals from the parent materials, especially in the igneous rocks. Yousefifard et al. (Reference Yousefifard, Ayoubi, Jalalian, Khademi and Makkizadeh2012) examined the relationship between magnetic susceptibility and soil properties in the igneous rocks of northwestern Iran and found positive and significant relationships (r = 0.66, P < 0.05) between sand content and χlf values. de Jong et al. (Reference de Jong, Kozak and Rostat1999) stated that magnetic susceptibility was more highly correlated with the subsurface soils when the distance from the parent materials was shorter .
Fe-oxide mineralogy and relationship to magnetic susceptibility
X-ray diffractometry is one of the principal techniques used to characterize the crystalline mineral phases (Whitting & Allardice Reference Whitting, Allardice and Klute1986; Cervi et al. Reference Cervi, da costa and deSouva Junior2014) and ferrimagnetic minerals in soils and sediments (da Costa et al. Reference da Costa, Bigham, Rhoton and Traina1999; Cervi et al. Reference Cervi, da costa and deSouva Junior2014). Distinguishing magnetite from maghemite using the XRD technique is difficult because magnetite and maghemite have similar crystalline structures and the small grain size of typical maghemite broadens the X-ray peaks (Carlson & Schwertmann Reference Carlson and Schwertmann1981). Therefore, in the present study, the shared XRD peaks were considered to indicate the co-occurrence of maghemite and magnetite. Previous researchers used XRD successfully to identify maghemite and magnetite in soils developed on igneous and volcanic rocks (da Costa et al. Reference da Costa, Bigham, Rhoton and Traina1999; Cervi et al. Reference Cervi, da costa and deSouva Junior2014).
The XRD patterns of the crushed rock samples are representative of igneous (ultrabasic and granite) and sedimentary (limestone) rocks. XRD analysis of the fine earth samples taken from the developed soils revealed mineralogical differences between the igneous and sedimentary rocks (Fig. 5). Specifically, Fe-oxide minerals, magnetite/maghemite (d spacing of 0.1488, 0252, and 0.296 nm), and hematite (d spacing 0.368 nm) were identified in the ultrabasic, basalt, granite, and andesite rock samples while, in contrast, no evidence was found to indicate the presence of these minerals in the sedimentary rock samples (Fig. 5e). Goethite (d spacing 0.418 nm), an Fe-oxide mineral, was also found in the granite (Fig. 5c).
XRD patterns of some of the soil samples used to identify iron minerals. (a) Ultrabasic rocks, (b) ultrabasic soil samples, (c) granite rock, (d) granite soil sample, (e) limestone rock, (f) limestone soil sample. Mt: magnetite, Mh: maghemite, Hm: hematite, Gt: geothite, CPS: counts per second
The mineralogy of soils developed on the igneous rocks was also studied, and the results showed similar patterns of Fe-oxide mineral occurrence in the soils developed as in the parent igneous rocks (Fig. 5b, d, vs. 5a, c), with maghemite/magnetite being the main mineral fraction in the soils. This result is similar to those of da Costa et al. (Reference da Costa, Bigham, Rhoton and Traina1999) and Cervi et al. (Reference Cervi, da costa and deSouva Junior2014), both of which studies reported that maghemite/magnetite constituted the main Fe-oxide fraction in the soils developed on basalt. An interesting observation in the present study was detection of the existence of Fe-oxide minerals, mainly maghemite/magnetite, in limestone (Fig. 5f), while no trace of iron oxide was found in the parent rock.
Exploration here of the contribution of Fe-oxide minerals to magnetic susceptibility in various soils revealed the presence of linear relationships between the peak intensity of maghemite/magnetite (d spacing 0.252 nm) and the χlf values. These relationships are presented in Figs 6 and 7 for igneous rocks and sedimentary parent materials, respectively. A positive and significant relationship was observed between peak intensity and χlf values in the soils developed on ultrabasic rocks (r = 0.60, P < 0.05), basalt (r = 0.71, P < 0.05), andesite (r = 0.74, P < 0.05), and granite (r = 0.75, P < 0.05). Significant and positive correlations were also found between peak intensity and χlf values in the soils developed on limestone (r = 0.82, P < 0.01), marl (r = 0.80, P < 0.01), shale (r = 0.83, P < 0.01), and the Qom formation r = 0.80, P < 0.01). da Costa et al. (Reference da Costa, Bigham, Rhoton and Traina1999) examined Brazilian soils and reported a significant and positive relationship (Rm2 = 0.89) between the maghemite content and magnetic susceptibility of the clay fractions. These significant correlations confirmed that ferrimagnetic minerals were the most important components that control magnetic susceptibility in the soils. These results also revealed that magnetic susceptibility measurements could provide valuable information to quantify ferrimagnetic minerals in semiarid regions with low concentrations of magnetic minerals.
Relationships between χlf values and X-ray peak intensity for magnetite/maghemite in various soils developed on igneous rocks. (a) Ultrabasic, (b) basalt (c) granite, (d) andesite
Relationships between χlf values and X-ray peak intensities for magnetite/maghemite in the various soils developed on sedimentary rocks and deposits. (a) Limestone, (b) marl, (c) shale, (d) Qom formation
Conclusions
(1) A comparison of the mean χlf values showed significant variations in the rock samples subjected to analysis. The highest χlf values were observed in the basalt and ultrabasic rocks that had the highest ferrimagnetic mineral contents, while the lowest χlf values were observed in the Qom formation deposits that were enriched with diamagnetic minerals (i.e. calcite, gypsum, and halite) and lacked ferrimagnetic minerals.
(2) The highest and lowest χlf values were observed in the soils developed on the ultrabasic and limestone rocks, respectively. In comparison to the respective soil parent materials, the χlf values in the soils decreased in the igneous rocks and increased in the sedimentary rocks. Increased χlf values in the sedimentary rocks were mainly due to soil-formation processes in the semiarid climate of the study area. Decreased χlf values were observed in the soils developed on the igneous rocks. This decrease was mainly attributed to the dilution effects induced by the soil-formation processes.
(3) The negative and significant relationships between magnetic susceptibility and soil properties, which included EC, SOM, CCE, and clay content were ascribed to the dilution effects of diamagnetic minerals, such as halite, organic matter, calcite, and phyllosilicates, respectively.
(4) The positive and significant relationships between maghemite/magnetite XRD peak intensity and χlf values confirmed that ferrimagnetic minerals were the most important components that control χlf values in the soils. These results suggest that χlf measurements can be used to quantify ferrimagnetic minerals in the soils of semiarid regions where low concentrations of magnetic minerals could be found. The quantification of magnetic minerals using magnetic susceptibility suggests that this relationship might be unreliable in soils with large quantities of diamagnetic minerals such as CaCO3, organic matter, halite, and gypsum. Therefore, removing the diamagnetic components from the soils might be necessary to identify or quantify effectively ferrimagnetic minerals using magnetic susceptibility
Acknowledgments
The authors greatly appreciated the financial support of Isfahan University of Technology.
Compliance with ethical standards
Conflict of Interest
The authors declare that they have no conflict of interest.
