Frequency-dependent Magnetic Susceptibility Research Articles

Iron Age ceramics from Thracian rock-cut complexes from Bulgaria – Mineral magnetic relics of technological production and use

The Gluhite kamani Thracian rock-cut complex in the Eastern Rhodopes Mountain is famous with its more than 500 rock niches carved in the rock at heights up to 20 m. Continuous habitation starting from the final Chalcolithic (the second quarter of the 4th millenium BCE) until the Late Classical – Early Hellenistic period (late 5th – 4th century BCE) provides unique opportunity for studying diachronic changes in pottery production and use. In this contribution, systematic analysis of a collection of 135 ceramic sherds from five archaeological periods at the site was carried out using a combined mineral magnetic and geochemical approach. Magnetic susceptibility (χ), frequency-dependent magnetic susceptibility (χfd%) and firing temperature (Tfire), determined using the magnetic susceptibility method, were combined with data from elemental XRF analyses. Thermomagnetic measurements, employed for identification of magnetic minerals revealed the dominant presence of (titano)magnetite with low Ti-content and/or a fraction of single-domain magnetite and in few cases hematite. Although varying in a wide range, median χ values of ceramic sherds from the Early Iron Age (EIA) periods show similar distribution, while for Late Iron Age (LIA) with the introduction of the wheel-thrown pottery, χ values are higher, presumably due to decreased amount of silica-rich clastics in the clay. Concurrently, χfd% values decrease in ceramics from the LIA, indicating predominant presence of stable single-domain magnetite in the iron oxide composition of the ceramics. Firing temperatures (Tfire) estimations display a systematic pattern of two groups – higher (Tfire between 760 and 800 °C) and lower (Tfire ∼ 400–––600 °C). During the EIA periods both Tfire groups are present, characterized by systematic gradual decrease of the median value of the low Tfire when going from EIA1 towards the EIA2. Wheel-thrown pottery from the LIA show low Tfire ∼ 400 °C only. Based on the differences in thermomagnetic properties of ceramics, their magnetic parameters and Tfire estimates, two possible hypotheses are suggested to explain the observed changes in EIA ceramic characteristics: i) utilization of two differently sourced clay materials (illite-dominated and montmorillonite-dominated) for production of ceramics fired at higher and lower temperatures, respectively; and ii) utilization of one raw clay source, while using two firing regimes – firing at higher temperature for prolonged time, and fast firing to high temperature with successive stage of longer firing at lower temperature. Differences in thermomagnetic properties of wheel-thrown pottery from the LIA period leads to the assumption for utilization of diverse clay source for their production, as compared clay sources for the Early Iron Age periods.

Recent environmental and morphosedimentary evolution of the mining-impacted Nalón Estuary (Asturias, N Spain): Disentangling natural and anthropogenic processes

Distinguishing between natural and anthropogenic processes in sedimentary records from estuaries with legacy pollutants is an essential task, as it provides baselines to predict future environmental trajectories of coastal areas. Here, we have addressed the recent transformation history of the mining-impacted Nalón Estuary (Asturias, N Spain). Surface and core sediment records from marshes and tidal flats were examined through a broad multidisciplinary approach, involving micropaleontological (benthic foraminifera), sedimentological (grain-size), geochemical (trace metals, major element Al and total organic carbon), physical (magnetic susceptibility, frequency-dependent magnetic susceptibility and large microplastics) and radioisotopic (210Pb, 137Cs and 239+240Pu) proxies. Results suggest that the interplay between natural (high fluvial influence and extreme hydrological events) and anthropogenic (coal and mercury mining disposals) factors induced strong sedimentation-erosion processes, further shaping the recent evolution of the estuary. Short-time scale and intense sedimentation processes were revealed by overall high sediment accumulation rates, the dilution of some geological signatures and the rapid formation of a marsh in the lower estuary bay. The increasing mining fingerprints during the 20th century were shortly interrupted by the catastrophic riverine flooding of 1938. Conversely, current erosional processes by fluvial influence led to the remobilization of contaminated sedimentary materials and exposure of mining-legacy Hg levels in tidal flats from the middle sector. Fluvial activity, floodings and taphonomic biases exerted a major control on benthic foraminifera since the 19th century, although Hg ecotoxicological effects on modern assemblages at certain areas within the estuary cannot be discarded. These findings, along with the documented enhanced erosion of marshes with ‘trapped’ pollutants (Hg, coal microparticles and microplastics), highlight the importance of monitoring the environmental and geomorphic processes taking place in historically-contaminated estuaries.

Topsoil's magnetic and electrical properties in a volcanic and tropical region.

Environmental monitoring by measuring topsoil's magnetic and electrical properties is one practical, quick, and low-cost approach. This method has been used worldwide as a proxy for the presence of potentially toxic elements. However, additional research must be conducted on diverse soil types, geology, and climates. We determined the magnetic and electrical properties of urban and agricultural topsoils in a volcanic region and analyzed them as possible proxies of potentially toxic elements for environmental monitoring. To identify topsoil characteristics, we employed the measurements of magnetic susceptibility and hysteresis, electrical conductivity, total dissolved solids, power of hydrogen (pH), particle morphology, and element contents that were statistically analyzed to identify relevant properties. The result was able to differentiate volcanic soils from urban, industrial, and agricultural areas as well. The value of low-frequency magnetic susceptibility (χLF) in soils from urban areas is higher than 866.0±249.9 ×10-8 m3 kg-1, while the value of χLF in agricultural areas is 208.0±67.8 ×10-8 m3 kg-1. This is reinforced by the relationship between low-frequency and frequency-dependent magnetic susceptibility (χLF-χFD%) in samples from urban areas that fall within the same cluster dominated by coarse-grained magnetic minerals originating from anthropogenic processes. In contrast, the agricultural area forms a separate cluster primarily influenced by pedogenic processes from acid igneous rock minerals. Caution is required for interpreting the magnetic signal due to the high contents of lithogenic magnetic particles inherited from the parent materials of Andisols.

Temperature- and frequency-dependent magnetic susceptibility on archaeological ceramics of the Tlatilca culture (Mexico City): A pilot study towards an archaeointensity approach

Temperature-dependent susceptibility curves are commonly used in archaeointensity studies to identify changes in the magnetic mineralogy of archaeological ceramics. In this pilot study, we investigated the low- and high-temperature thermomagnetic behavior and frequency-dependent susceptibility of eight ceramics from a Tlatilca culture archaeological site in Mexico City, after heating them at five different temperatures (from 120 to 440 °C). Our objective is to establish a correlation between the thermomagnetic behavior and the parameters that determine the magnetic grain-size and magnetic domain in similar style of ceramics from different occupations of the site. Our findings show that superparamagnetic grains (SP) degrade with increasing reheating temperature in ceramics, and we conclude that this behavior is related to details in artifact processing, such as the use of pastillage to represent headdresses, and an important aspect to consider when working with samples for archaeointensity procedures.

The firing temperatures of burnt clay from the Chinese neolithic cultural relics and its paleoenvironmental imprints

The impact of human-induced fires on the surrounding environment has been particularly significant during the Anthropocene epoch. Neolithic burnt clay, which is widely distributed in the archaeological relics of ancient civilizations across the Eurasian continent, provides pivotal information about the ancient firing stories. However, understanding of the paleoenvironmental imprints of fire in burnt clay has been largely limited by the lack of sufficient analytical data on comprehensive knowledge of ancient firing conditions. In this study, a detailed magnetic analysis was conducted on burnt clay materials from a Neolithic site in Fujian, southeastern China, which presented a burnt clay-based record of the Neolithic firing temperature in relation to paleoenvironmental conditions. Based on magnetic analysis, the ancient firing temperature was determined to be approximately 620 °C, which is comparable with other records from Eurasian Neolithic sites. Frequency-dependent magnetic susceptibility provides alternative indicative information for ancient firing conditions in addition to conventional magnetic susceptibility. Furthermore, magnetic properties of burnt clay may decode the in-situ source characteristics with respect to geological background. In addition, a potential link between temporal variations in ancient firing temperatures in burnt clay and surrounding paleoenvironmental changes is tentatively interpreted by local environmental feedback of temperature-moisture conditions and anthropogenic activity. This study further confirms the archaeological potential of thermomagnetic properties as useful indicators in paleoenvironmental studies. More work combining paleoenvironmental and archaeological archives is critically essential to understand ancient firing history in the context of environmental conditions.

Frequency-Dependent Magnetic Susceptibility and Chemical Composition of Estuary Mangrove Sediment as Environmental Indicator of Ecosystem Degradation

Frequency-Dependent Magnetic Susceptibility and Chemical Composition of Estuary Mangrove Sediment as Environmental Indicator of Ecosystem Degradation

Identification of Sediment Formation Based on Magnetic Content and Element Composition of Mud Volcano in Sangiran Sediment using VSM and X-Ray Fluorescence

Based on trace geological history and several studies, the Sangiran mud volcano provides insight into the geology and hydrology of the region, aquifer system in the basin, groundwater flow patterns and characteristics, rock lithology, hydrogeology condition, and saltwater trap mapping. Related to these conditions, studies were conducted on the magnetic content and composition of the major oxide compounds in the Sangiran sediments. Sample analysis was based on geochemical methods. The methods consist of frequency dependent magnetic susceptibility and vibrating sample magnetometer (VSM) analysis. Geochemical analyses using x-ray fluorescence (XRF) analysis have been conducted and various elemental grades have been determined. VSM results confirm that the magnetic content of Sangiran sediments is partly dominated by Fe (17.66 percent) contained in hematite (Fe2O3). At the same time, the samples of Sangiran sediment were enriched by Si, Fe, Al, Ca, Cl, Ti, and K according to XRF measurements. The samples exhibited the highest Si and Fe concentrations in samples T1 (Si is 29.48 percent and Fe is 13.66 percent) and T7 (Si is 24.95 percent and Fe is 12.01 percent). Meanwhile, in the T4 sample, the highest concentrations were Si and Ca, 23.45 percent and 13.45 percent, respectively. Retrieved from the magnetic susceptibility measurement, this paper confirm that Fe content is one of the components of volcanic ash in the Sangiran sediment.DOI: 10.17977/um024v8i12023p009

Obliquity‐driven mountain permafrost‐related fluvial magnetic susceptibility cycles in the Quaternary mid‐latitude long‐term (2.5 Ma) fluvial Maros Fan in the Pannonian Basin

Magnetic susceptibility (MS) of the Quaternary long‐term mid‐latitude Maros fluvial fan (Pannonian Basin) was recorded to understand the stratigraphical features of source‐proximal fluvial depositional settings. Three fully cored 500‐m‐deep boreholes were sampled at 0.5‐m intervals; low‐field and frequency dependent MS were measured, and complementary hysteresis and SEM‐EDAX investigations were performed on selected samples. Logged susceptibility data were also used to log correlations established by a simultaneous comparison of wireline log and laboratory measurements. Time‐series analyses of the susceptibility records reveal a ~41‐ka and ~100‐ka cyclicity. Towards the source‐distal sections the intensity of the ~41‐ka cycles decreases, while that of the ~100‐ka cycles remains strong. Stratigraphical and spectral similarities were observed between the Maros fluvial fan and Chinese loess records; however, based on complementary magnetic data, the magnetic phase of the Maros Fan sections is related to the detrital magnetite that originates from the catchment during early postglacial permafrost degradations. The amplification of the ~41‐ka cycles can be attributed to the very high susceptibility values in source‐proximal settings and to the special stratigraphical feature of the distributive fluvial systems. This comprises the increased avulsion frequency on the fluvial fans in ‘glacial recession periods’, in concert with the ‘early postglacial’ occurrence of the permafrost‐related magnetite originating from the catchment. As a local phenomenon, this is significant since it records the obliquity‐driven variations in permafrost development in a catchment. However, fluvial and alluvial fans are widespread depositional landforms within the Eurasian mountain range and were possibly the same during the Quaternary deglaciations. Thus, obliquity‐driven magnetic susceptibility variations in source‐proximal fan deposits attached or adjacent to regions of loess deposition should also be considered when scanning for potential source material of aeolian deposits.

Hydrothermal alteration of surficial rocks at Los Humeros geothermal field, Mexico: a magnetic susceptibility approach

Utility of the geothermal surface manifestations (GSMs; thermal springs, geysers, fumaroles, and zones of hydrothermal alteration) in the studies related to the geothermal exploration is widely recognized. The identification of hydrothermally altered rocks and zones of alteration is very important because their presence indicates the type and size of the geothermal reservoir and existing thermal conditions. The use of traditional methods (i.e., geochemistry, mineralogy, and petrography) requires expensive equipment, time-consuming, and laborious sample preparation methods. Some of the rock magnetic parameters, like magnetic susceptibility (χlf) and percentage of frequency-dependent magnetic susceptibility (χfd%), are potential to become effective additional tools in identification of the hydrothermal rocks during the initial stages of geothermal exploration. Three chemical methods, Chemical Index of Alteration (CIA), loss-on-ignition (LOI), and the binary plot (CaO + Na2O + K2O) vs. (Fe2O3 + MnO + MgO), along with two rock magnetic methods, χlf and the binary plot (χlf vs. χfd%), are applied to nine intensively altered andesite reference rocks. All the five methods have correctly identified that 99 out of the total 350 studied rocks are altered. More altered rocks are distributed surrounding the several faults in the study area. Various faults (e.g., Los Humeros fault and the Loma Blanca fault) favor fluid flow and present strong hydrothermal alteration at the surface. However, there are no altered rocks on the surface region between the E-W trending Las Papas and Las Viboras faults. The presence of only the deeper fluid pathway toward the east in the surroundings of these two faults result into the almost absence of hydrothermal alteration along their strike at the surface. Consequently, there are not many altered rocks observed surroundings these two faults at the surface. These features suggest that the surface hydrothermal alteration at Los Humeros Geothermal Field (LHGF) is controlled by faults. χlf and χfd% are reliable, simple to measure, fast, cost-effective, and have the potential to become reliable additional tools for future exploration studies.

Magnetic susceptibilites of suspended sediment and microplastic abundance in a tropical volcanic estuary

Coastal and estuarine ecosystems are seriously threatened by pollutants, according to the literature. In the estuary, the zone that traps suspended particulate matter, namely, estuarine turbidity maxima (ETM), needs to be identified to prevent ecological threats, namely migration and species death. Magnetic measurements of sediments in volcanic rivers have also attracted attention because the sediment contains a high abundance of magnetic minerals. The method in this paper provides a low-cost, rapid, and nondestructive approach to environmental monitorings and assessments. However, the validity of magnetic measurements has not been investigated for their use in identifying the ETM zone in estuaries in volcanic regions. Therefore, this research aims to identify ETM zones in the estuaries of volcanic regions using magnetic properties to correlate the characteristics to microplastic abundance within suspended and surface sediments. The measurements consist of magnetic susceptibility at low frequency, magnetic susceptibility at high frequency, frequency-dependent magnetic susceptibility analyses, and acquisition of a hysteresis curve. Magnetic minerals were also identified using X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy. The results showed that the values of magnetic susceptibility at low frequency significantly correlate with total dissolved solids and microplastics abundance in sediments. The frequency-dependent magnetic susceptibility values were significantly correlated with total dissolved solids, microplastics abundance, turbidity, and microorganism cells. This phenomenon indicates that the magnetic properties of suspended sediments can be used to identify an ETM zone in estuaries in tropical volcanic regions.

Holocene synchronous evolution of precipitation and soil moisture as evidenced by paleosol deposits in the Ili Basin, Central Asia

Assessing the impact of precipitation and temperature on soil moisture changes during the Holocene is essential to understanding the regional ecological environment change in the arid Central Asia core (CAC). However, this assessment is challenging due to the lack of reliable precipitation records. Here, we present Holocene paired precipitation and soil moisture records from the same paleosol deposits with well-constrained optically stimulated luminescence chronology in the Ili Basin, CAC. We selected dolomite content and the δ13C of organic matter to reflect precipitation change, and redness, frequency-dependent magnetic susceptibility, and total organic content to reflect soil moisture changes. The results show that precipitation and soil moisture records exhibit internal consistency, suggesting a synchronous evolution in both during the Holocene. We deduced that precipitation dominated Holocene soil moisture variations in the CAC. The increasing precipitation during the Holocene in the CAC may be attributed to the southward migration of the midlatitude westerlies and increasing penetration of water vapor from the Asian monsoon region.

Assessment of the impacts of land-use change and slope position on soil loss by magnetic susceptibility-based models

Soil loss is a global environmental problem resulting from the erosion process caused by many factors, including land use and slope position. Estimation of total soil loss from agricultural fields is useful for understanding the consequences of historical and current erosion. The main purposes of the current study are to explore the application of magnetic measurements in the mapping and measuring soil redistribution in cultivated (MZ13) and forested (MZ17) transects in a Moroccan subcatchment, to develop a methodological approach correlating magnetic susceptibility (MS, denoted χ) variation to soil erosion/aggradation, and to discriminate the effects of land-use change and slope position on the total cumulative soil loss, assessed using three recently established erosion models based on an MS parameter. MS measurements were done on several soil cores collected at different slope positions including the summit (SU), shoulder (SH), back slope (BS), foot slope (FS), toe slope (TS) for Transects MZ13 and MZ17. A tillage homogenization (T-H) model, simple correlation model (SCM), and simple proportional model (SPM) based on χlf (where lf indicates low frequency) were applied to estimate soil loss for each slope position in the two transects. The results show that the correlation between χlf and χfd (which is the frequency-dependent magnetic susceptibility percentage) is positive and high for the two transects (R2 = 0.95; p < 0.01). The results confirm that the χlf enhancement of soils selected in calcareous parent material is related to the pedogenic processes with the formation of superparamagnetic particles distributed along the slope positions. The current study proves that it is possible to trace and monitor soil erosion and deposition using magnetic parameters (χlf and χfd%) for different slope positions along cultivated and forested transects. The results confirm that the soil losses strongly depend on land use and slope position. Higher erosion depth (d) estimated using the three erosion models are comparable and were about d(T-H, BS17L) = −154.9 cm, d(SCM, BS17L) = −142.3 cm, and d(SPM, BS17L) = −143.6 cm for MZ17 Transect, and about d(T-H, FS13M) = −156.3 cm, d(SCM, TS13L) = −143.8 cm, d(SPM, FS13M) = −145.9 cm for MZ13 Transect. The applied models indicate that the strong losses take place in the upper and lower slopes of the cultivated transect, and in the middle and lower slopes of the forested transect.

Magnetic signatures of a creosote oil contaminated site: case study in São Paulo, Brazil

Soils and groundwater contamination modifies the physical–chemical conditions of the environment, altering natural biogeochemical processes of the ground. As a result, several mineral transformations occur, in which iron plays a decisive role. The presence of iron enables the study of magnetic properties, improving the understanding of the geophysical signatures of highly dynamic environments (e.g., biogeochemical hotspots and contamination plumes). In this work, we seek to identify creosote biodegradation related to the precipitation of magnetic minerals on sediments at a contaminated site in São Paulo, Brazil. Several rock magnetism analyses were carried out to provide the magnetic mineralogy of the samples in terms of their composition, size, and abundance. We conducted high-temperature thermomagnetic curves, frequency-dependent magnetic susceptibility, anesthetic remanent magnetization (ARM) and isothermal remanent magnetization (IRM) data, superparamagnetic concentration and dipole moment (SPCDM), and scanning electron microscopy (SEM) analyses. The magnetic signatures of the contaminated samples suggest an increase of superparamagnetic grains in the water table fluctuation zone if compared to the magnetic signatures of the uncontaminated samples. Thermomagnetic curves of contaminated samples showed a lower heterogeneity of the magnetic mineral phases than the uncontaminated ones. This work contributes to the advancement of the understanding of how natural biogeochemical processes are impacted by human actions, such as soil contamination, and even by climate change, which should affect soil redox conditions in periods of drought and flooding.

Assessing magnetic properties of biomonitors and road dust as a screening method for air pollution monitoring

Particulate matter (PM) pollution is one of the world's most serious environmental challenges. Among PM components, atmospheric heavy metals (HMs) are considered one of the main pollutants responsible for causing significant negative impacts on human health, and ecological quality. This study aimed to assess environmental magnetism as a simple and rapid method that can be used to evaluate heavy metal contamination in urban areas from the relationships between magnetic properties and heavy metal concentrations. For this purpose, road dust and leaf samples of two common evergreen species (Cupressus lusitanica/Casuarina equisetifolia) were sampled simultaneously for 2 years at sites with different levels of traffic pollution. The results found significant statistical correlations between the magnetic properties and the chemical substances of the plants studied, as Fe, Cr and V showed an r ≥ 0.9 and Cr and Zn r ≥ 0.7 with χlf in C. equisetifolia. The frequency-dependent magnetic susceptibility was found to be between 0% and 14% for plants, and 0% and 2% for road dust, suggesting a rather dissimilar particle size distribution for plants, and a less important contribution from the more hazardous ultrafine superparamagnetic magnetite for both. Confirming that magnetic analyses can be used to distinguish different degrees of urban air pollution.

The magnetic susceptibility of Pleistocene paleosols as a martian paleoenvironment analog

This work aims to introduce and test various semiquantitative field methods and environmental magnetic measurements to help prepare future planetary missions on Mars. For analog observations, paleosols of loess successions in various stages of soil development were investigated and were used as models to infer environmental change during environmental change on early Mars. Methods commonly used in terrestrial soils and sediment environments, such as soil development indices and low field and frequency-dependent magnetic susceptibility, are introduced and evaluated as potential proxies to constrain paleoenvironmental conditions and climate change on Mars billions of years ago. These methods include the following: 1) low field magnetic susceptibility, which may aid in the identification of weathered horizons (e.g., palaeosols) and provide insight into the degree of weathering intensity; 2) frequency-dependent magnetic susceptibility can constrain nanoscale magnetic contributions, including some with possible biogenic/bacterial origin, but its applicability to indicate the degree of pedogenesis is limited; and 3) the vertical distribution of low field magnetic susceptibility, i.e., the pattern of magnetic susceptibility curves, seems to work well in the indication of the balance between the sedimentary and pedogenic environment. Analysis of magnetic susceptibility curves may contribute to the identification of Martian paleosols, the characterization of the transition period between the soil-forming and subsequent sedimentary periods (Noachian-Hesperian and Hesperian-Amazonian transitions) and the identification of climate cycles; thus, these may be used as a frame of reference for evaluating paleoclimatic changes on Mars to e.g., the Noachian warm Mars and”Snowball Mars” periods.The results also suggest that the time dependence of the magnetic enhancement of paleosols seems to be nonlinear compared to the length of the pedogenic period itself, and magnetic susceptibility may work as a relative chronometric parameter, which can help to constrain the duration of pedogenic alteration and soil formation on Mars.

Nonlinear contributions to the dynamic magnetic susceptibility of magnetic fluids

• Higher order harmonic susceptibilities of magnetic fluids are obtained theoretically. • Mean spherical approximation is used with field strength expansion of magnetization. • Theoretical prediction is compared to the Langevin and Debye-Weiss limiting cases. • Field amplitude and frequency range of validity of the expanded MSA model is mapped. Based on our earlier analytical results for the magnetization of magnetic fluids with respect to the magnetic field strength, we propose an expansion method within the framework of mean spherical approximation (MSA) to obtain the coefficients of different nonlinear terms. Through a Fourier expansion of the frequency-dependent magnetic susceptibility the harmonic coefficients corresponding to the linear and nonlinear dynamic susceptibilities are calculated from the field expansion of magnetization. The frequency dependence of the higher order susceptibilities is determined on the basis of the Debye relaxation of magnetic dipoles. Our MSA based results are in line with the corresponding limiting case of the Debye-Weiss theory. We mapped the range of applicability of the expansion method concerning the field strength and frequencies. Our results show that under weak fields a 7th order expansion is sufficient to predict the magnitudes of the susceptibility components up to the 4th harmonic relevant for magnetic fluids.

A detailed magnetic record of Pleistocene climate and distal ash dispersal during the last 800 kyrs - The Suhia Kladenetz quarry loess-paleosol sequence near Pleven (Bulgaria)

Loess-paleosol sequences (LPS) from the Lower Danube area are valuable terrestrial archives of environmental change in SE Europe during the Pleistocene. A twenty-seven meters thick sequence has been sampled in Central North Bulgaria near the city of Pleven within the Suhia Kladenetz (SK) quarry. The sedimentary sequence consists of seven loess units and six interbedded paleosol complexes covering the last 800 kyrs. The continuous 2 cm resolution sampling depth interval enabled the recovery of several cryptotephras in addition to a ~ 20 cm thick tephra deposit observed in the field within the L2 loess unit. All cryptotephras are clearly identified in laboratory analyses by their strong magnetic signal, particularly well expressed by concentration – dependent anhysteretic susceptibility (χARM), isothermal remanence (IRM), low field magnetic susceptibility (χlf) and in some cases by frequency dependent magnetic susceptibility (Δχ), coercivity of remanence (BCR), and hard isothermal remanence (HIRM2.0–0.3T). Complementary optical and scanning electron microscope analyses of single grains from the tephra deposit and cryptotephra intervals reveal the presence of volcanogenic grains with smooth glassy surfaces and vesicular internal structure; fluidal grains with bulbous surfaces and dense irregular grains. Grain size sensitive magnetic ratios χARM/χlf, ARM/IRM100mT, IRM2T/χlf are not always discriminative, suggesting that (crypto)tephras do not have a single uniform source. Preliminary correlative age models are used to estimate ages for the (crypto)tephras and propose likely associated volcanic eruptions. Finally, strong pedogenic magnetic enhancement of the younger paleosols (S4, S3, S2 and partly S1) contrasts with the smeared and low magnetic signal of the older paleosols (S6 and S5). Moreover, an enhanced content of low-coercivity hematite observed from the upper part of the S5 paleosol upwards to the present and a sharp increase in the concentration of maghemite at the expense of magnetite observed for the S3, S2 and S1 paleosols provides strong evidence for a significant paleoenvironmental change. The timing of this change, based on the SK LPS age models, is compatible with the mid-Brunhes climate transition.

Studying the potential of rock magnetism to distinguish combustion structures of different type

Rock magnetism has a significant potential to elucidate archaeological issues related to firing process owing to the strong dependence of clay magnetic properties on firing conditions. The present study is an attempt to characterize some basic fuel installations (hearths, household ovens, pottery kilns, kilns for building ceramics and metallurgical ovens) by the most common magnetic parameters (magnetic remanence, initial magnetic susceptibility, Koenigsberger ratio, frequency-dependent magnetic susceptibility and viscosity coefficient), accumulating a set of relevant magnetic data for exemplary structures. Rasmussen method was used for firing temperature determinations.It is concluded that household ovens, used for cooking/heating activities only, were fired at temperatures below 500 °C. The acquired thermoremanence is in most cases partial TRM, generally less than 800 mA/m, the measured magnetic susceptibility does not exceed 300× 10−8m3/kg, and the corresponding Q ratios are mostly below 10. Experimentally baked clays show that already a firing at temperatures slightly above 500 °C yield much stronger and more stable TRM, and higher χ and Q ratio. Hearth and pottery kilns appear indistinguishable at this research stage, but systematically higher Q ratios were observed for the pottery kilns. Rising the temperature in the kilns for building ceramics and metallurgical ovens causes formation of a higher proportion of coarse-grained hematite and epsilon iron oxide, resulting in thermoremanence increase and magnetic susceptibility decrease.Firing temperatures determined for the household ovens corroborate well the observed magnetic parameters indicating a maximum operating temperature of not more than 460–470 °C. On the other hand, they appear to be underestimated when the highest firing intensity was expected (at T > 900 °C). This is indicative that further studies in this aspect are needed. The slags studied fail to produce any feasible result in terms of their firing temperatures, probably because of their strong inhomogeneity and/or complicated firing history. There is an excellent agreement between the estimated temperatures for clays baked in an experimental dual chamber kiln and the thermocouple readings. Differences in firing atmosphere between archaeological structures (or their experimental analogues) and laboratory furnaces probably have the least effect on low-temperature heated objects (i.e., household ovens) and the strongest on high-temperature ones where reducing conditions dominate that should be taken into account in the data interpretation. An overestimation of Tfiring can happen for low-temperature materials due to possible intense magnetic transformations above 600 °C.

The role of tephra additions on development of incipient soils from Livingston Island (Antarctic Peninsula) revealed by environmental magnetism

Soils from maritime Antarctica store important information about initialization of pedogenesis and role of the major factors of soil formation. Deciphering the interplay among all contributing agents is however challenging and needs involvement of an interdisciplinary approach. The main aim of our study is to contribute to this goal by assessing mineral magnetic signature of a collection of topsoils from Livingston Island and investigate the major contributing factors, determining their magnetic properties. A set of 23 soil samples from Hurd Peninsula at Livingston Island were studied. Magnetic susceptibility and frequency dependent magnetic susceptibility measurements, anhysteretic remanent magnetization, hysteresis measurements at room temperature and low temperatures were carried out. Identification of magnetic minerals was achieved through thermomagnetic measurements of magnetic susceptibility and analysis of Isothermal Remanence acquisition. Magnetic measurements were supplemented by geochemical analyses of total elemental composition by X-ray fluorescence spectrometry and selective Fe- and Al- extractions by Dithionite-Citrate-Bicarbonate and ammonium oxalate. Magnetic results indicate that composition of iron oxides in soils differs significantly from that of bedrocks by the presence of titianomagnetite fractions with high- and medium Ti-content, while rocks’ mineralogy is dominated by paramagnetic minerals or by coarse grained multi-domain magnetite. Titanomagnetite phases were ascribed to the input of tephra additions from the nearby Deception Island. Based on the magnetic susceptibility measurements at low temperatures it was concluded that a fraction of fine grained magnetite is present in soils, in addition to titanomagnetite. Geochemical data reveal differences between the composition of soils and main rock lithologies, which is also assigned to tephra input. Amount of ammonium-oxalate extractable iron and aluminum were higher than that extracted by dithionite, which was attributed to fast tephra weathering in cold polar climate.

Preliminary Investigation of Soil and Sediments Using Magnetic Susceptibility Method in Kogi State, Nigeria

Over the years, there has been significant increase in population and urbanization in Kogi State as a result of rural - urban migration. This has become a major threat to soil sustainability which is a natural non-renewable resource. The aim of this research is to carry out magnetic susceptibility mapping on the surface and subsurface soil of Kogi State using environmental magnetism techniques and geochemical analysis. The susceptibility test on rock samples and background soil samples within the study area shows an average of about 112.0 × 10^-5 SI. The magnetic susceptibility measurement on soil from Kogi State shows magnetic susceptibility enhancement of about (450.0 - 700.0) × 10^-5 SI. These values were dominant along the major towns, road pavements and commercial areas at the surface to a depth of about 50.0 cm in soil profiles. The 2D spatial distribution of magnetic susceptibility with depth reveals that these magnetic grains are distributed in the subsurface as a result of anthropogenic loading. The frequency-dependence of magnetic susceptibility (χfd%) values are very low (2 - 10.0 %) in most of the areas on the surface soil. These values indicate that the magnetic properties are predominantly contributed by the coarse multi-domain (MD) and stable single-domain (SSD) grains of anthropogenic origin. Atomic Absorbtion Spectrometer (AAS) analysis of these soil samples indicates the presence of Lead (300.0 - 900.0) mg/l and Cadmium (20.0 - 60.0) mg/l in large concentration at the surface soil in most part of the Kogi State. While Chromium show relatively low concentration on the surface soil. From the statistical correlation analysis, Lead and Cadmium show high positive correlation with magnetic susceptibility. These results suggests that the high enhancement of magnetic susceptibility on the surface and sub-surface soil in most part of Kogi State arise from anthropogenic activities rather than lithological and pedogenic processes and most likely cause by high concentration of Lead and Cadmium.