Hard Isothermal Remanent Magnetization Research Articles

Changes in rock magnetic properties of sediments along the Carlsberg Ridge: Inferences on active/extinct vent fields

Hydrothermal vents at Mid Ocean Ridges (MOR) are known to leave metalliferous, bacterial, temperature-induced signatures in sediments. Knowledge of active/extinct vents along the Carlsberg Ridge (CR) is sparse; further conventional methods to distinguish relevant areas are tedious/expensive. We show that basic rock magnetic measurements, including magnetic susceptibility and laboratory-induced remanent magnetizations, can help to characterize sediment samples near and away from hydrothermally activity/extinct areas at the CR. Eight spade cores from the Carlsberg ridge (of which three are in the vicinity of the Tianxiu hydrothermal field and one from the ridge flank) collected on board R.V. Sindhu Sadhana during 77th and 83rd cruises are investigated for the present study. Two spade cores consist of top 2 cm and six core lengths ranged between 22 and 38 cm. Coarse fraction and magnetic minerals were separated and studied under a binocular microscope and scanning electron microscope (SEM). Magnetic susceptibility (χlf) of sediments ranges between 1.3 and 37.1 × 10−8 m3 kg−1 with higher values for ridge valley and lower values for ridge flank. Ridge flank sediments are associated with low χlf, Saturation Isothermal Remanent Magnetization (SIRM), Hard Isothermal Remanent Magnetization (HIRM) and high χARM/SIRM, which are taken as base values. Sediments in the vicinity of the Tianxiu hydrothermal vent field are associated with high χlf, SIRM, HIRM, and low Anhysteretic remanent magnetic susceptibility (χARM)/SIRM, coarse Stable Single Domain (SSD) and fine SSD & Mixture grains with magnetite as the dominant mineral. Similar signatures are observed in two more spade cores ∼250 km south of the Tianxiu vent field, suggesting new active/relict site/sites in the vicinity. Signatures like that of flank sediments are also observed in two cores from the ridge valley indicating, the absence of hydrothermal activity in the vicinity. In the marine environment, identifying/locating metalliferous hydrothermal sediment/sites along extensive MOR is expensive and time-consuming; rock magnetic could be a non-destructive method to shortlist the areas for detailed studies.

Environmental magnetic properties of core sediments in the Yellow River subaqueous delta and their chronologicalapplications

The Yellow River has shifted frequently in the downstream region since 1885; it has flowed into the sea through the Qingshuigou channel from 1976 onward, thus forming the latest delta lobe (1976–present). During the past ~40 years, the sediment load of the Yellow River has been greatly reduced because of human and natural activities, such as reservoir construction, soil and water conservation, and river avulsion. Beginning in 2002, the water-sediment regulation scheme (WSRS) has also changed the sediment loading patterns of the Yellow River. Several studies have reported on the erosion and deposition characteristics of the latest lobe of the Yellow River Delta over the past several decades, based on remote sensing methods and water-depth measurements. However, continuous sedimentary records of delta erosion and deposition and their responses to natural and human activities in the watershed are lacking. Here, we obtained three sediments cores, YD01, YD02, and YD03, from the subaqueous delta of the latest lobe of the Yellow River Delta. These cores contain sediments deposited from 1976 to 2018. We analyzed the environmental magnetism and lithological characteristics of these cores, and investigated their responses to natural and human activities in the watershed of the Yellow River, as well as possible applications to sediment dating in the Yellow River Delta. The results show that frequency-dependent susceptibility ( χ fd%) and anhysteretic remanent magnetization susceptibility ( χ ARM) values were high in core sediments deposited from 1976 to 1996, indicating abundant contents of fine single-domain (SD) and superparamagnetic (SP) magnetic particles, and therefore a dominant sediment supply from the Chinese Loess Plateau. Small decreases in χ fd% and χ ARM in sediments deposited after 1986 revealed slight reduction of the sediment load from the Yellow River, which was likely caused by sediment retention related to the construction of the Longyangxia Reservoir. Rapid rises in χ fd% and χ ARM occurred in core YD01 sediments deposited during 2002 and ~2007, likely in response to the implementation of the WSRS, which resulted in an increase in sediment transportation. Increases in hard isothermal remanent magnetization (HIRM) values, an indicator of high-coercivity magnetic minerals such as goethite and hematite, in cores YD02 and YD03 from 2002 to ~2007 may also represent the start of the WSRS. This is because the downstream riverbed of the Xiaolangdi Reservoir underwent intense erosion during the implementation of the WSRS, leading to large-scale transportation of coarse sediments enriched in goethite and hematite, which were deposited on the riverbed before the implementation of the WSRS. The lack of increased contents of fine SD and SP magnetic minerals in cores YD02 and YD03 compared with YD01 in the interval deposited between 2002 and ~2007 was attributed to erosion and redeposition in the areas around cores YD02 and YD03. Large drops in SD and SP contents after ~2007 were detected in all three cores, revealing intense erosion near the river mouth likely caused by river channel shift and reduced capability of the WSRS to remove sediments. Contents of SD and SP particles increased again in sediments deposited after 2014 in cores YD02 and YD03, likely related to erosion of the present (after 1996) Yellow River mouth and transportation of fine particles to the region near cores YD02 and YD03. In summary, the magnetic parameters χ fd% and χ ARM and the lithological characteristics of cores YD01, YD02, and YD03 recorded sediment delivery changes caused by four events in the Yellow River watershed: The main river channel shift in 1976, construction of the Longyangxia Reservoir in 1986, the beginning of the WSRS in 2002, and weakened capability of the WSRS to remove sediments after ~2007. The notable changes of χ fd%, χ ARM, and lithology at the 1976, 1986, 2002, and ~2007 horizons may be used as dating points in future research of sediment cores from the Yellow River Mouth.

Iron mineralogy and speciation of sediment iron-bearing minerals in mangrove forest: Case study of Zhangjiang estuary, China

Few investigations of iron speciation exist in intertidal conditions with little attention given to understanding the geochemical behavior of Fe3+–Fe2+ and its biogeochemical processes. Here, one sediment core was collected in Yunxiao mangrove forests, Zhangjiang estuary, China and iron mineralogy was determined by magnetic methods and Mössbauer spectroscopy. Changes in magnetic susceptibility, susceptibility of anhysteretic remanent magnetization, and saturation isothermal remanent magnetization were linked to changes of pseudo-single domain soft coercive components with minor antiferromagnetic fractions and the presence of minimal concentrations of superparamagnetic particles was confirmed by the no frequency dependent of AC magnetization. A positive correlation between L-ratio and hard isothermal remanent magnetization is congruent with the distribution of high-coercivity antiferromagnetic minerals. At 295 K, the Mössbauer spectrum of specimens was well fitted with a single magnetic sextet, hematite and two magnetic doublets, paramagnetic Fe2+ and paramagnetic Fe3+. The usefulness of magnetic data and Mössbauer spectroscopy could offer valuable analytical tools for tracking changes of iron speciation and phase in the intertidal conditions.

Orbitally driven redox fluctuations during Cretaceous Oceanic Anoxic Event 2 (OAE2) revealed by a new magnetic proxy

Recent studies of the Cretaceous sedimentary records have documented that rapid redox changes between euxinic (sulfidic) and ferruginous conditions occurred during the perturbations to the global carbon cycle associated with oceanic anoxic events. This observation has major implications for the dynamics of and feedbacks on marine primary productivity and organic carbon burial during these events. The high-resolution rock magnetic study of a significantly expanded OAE2 interval in southern Tibet, presented here, provides further insight into the redox dynamics during the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) (~94 Ma). The ratio of hard isothermal remanent magnetization to magnetic susceptibility, HIRM/χ, is used as a proxy for bottom-water redox conditions and shows repeated fluctuations between relatively oxic and dysoxic/anoxic conditions in the eastern Tethys of the Southern Hemisphere during OAE2. Spectral analysis of a log (HIRM/χ) time series reveals cyclical variations at orbital frequencies and the subtle cyclic redox changes are found to occur within the obliquity frequency band. Moreover, variability in redox conditions at the onset of OAE2 correlates well with that recently documented for the OAE2 interval at Tarfaya, Morocco, implying that the cyclic redox variations spanned both hemispheres. Notably, the presence of obliquity signals, which dominantly influence high-latitude climate processes, in the tropics and subtropics of both the Northern and Southern Hemispheres further confirms previously hypothesized more vigorous meridional overturning circulation (MOC) during OAE2 and implies the interhemispheric/global nature of this major shift in oceanic circulation.

Why magnetite is not the only indicator of past rainfall in the Chinese Loess Plateau?

This study investigates the magnetic mineralogy of palaeosol S5 from Xifeng (XF), Linyou (LY) and Baoji (BJ) sections with increasing annual precipitation from north to the south on the Chinese Loess Plateau. Palaeosol S5 samples from these three localities are further prepared as magnetic extracts and separation residues. Low-temperature magnetic measurements including field cooled and zero field cooled (FC/ZFC) remanence, in-phase magnetic susceptibility, thermal remanent magnetization and room temperature saturation isothermal remanence magnetization (RTSIRM), with X-ray diffraction measurements are carried out for all magnetic extracts and separation residues samples. The asymmetric rounded 'hump' in cooling curves on RTSIRM and the 'tilted' Verwey transition on ZFC/FC curves suggest that partially oxidized magnetite is the dominant magnetic contributor, not pure maghemite or magnetite. Furthermore, The Verwey transitions on cooling curves slightly decrease and the increased slope of 'tilted' Verwey transition on ZFC remanence curves show that the degree of oxidation of magnetite between localities increases in the order XF-LY-BJ. Hard isothermal remanent magnetization, X-ray diffraction data and the difference of magnetization inwarming curves of RTSIRM suggest that both hematite concentration in magnetic extracts and goethite concentration in separation residues increase from XF to BJ. Frequency-dependent susceptibility and ZFC/FC curves show that BJS5 layer formed under high palaeoprecipitation has less superparamagnetic (SP) but more single domain to pseudo-single domain particles, because SP maghemite was dissolved and transformed into goethite by temporary waterlogging. The increase in hematite concentration is interpreted as due to SP maghemite oxidation or original goethite dehydration within dry soil environment. Therefore, transformation of maghemite to goethite in waterlogged phases of the S5 palaeosol led to the loss of magnetization.

Magnetic Response of Heavy Metal Pollution in Playground Dust of an Industrial Area

The use of mineral magnetic measurements as a potential pollution proxy is explored as an alternative means of monitoring heavy metal pollution in playground dust in industrial areas. Dust samples were collected from playgrounds in an industrial area in Nanjing. The magnetic properties of the samples were analyzed, and the total and acid-extractable concentrations of heavy metals were measured.Mineral magnetic concentration parameters[mean magnetic susceptibility (χlf) 939.31×10-8 m3·kg-1 and saturation isothermal remanent magnetization (SIRM) 16618.74×10-5 A·m2·kg-1] indicate that the dust samples contain high concentrations of magnetic minerals when compared to the non-industrial zone of the city. High and stable S-ratio values (mean 0.97, standard deviation 0.01) indicate the prominence of ferromagnetic minerals. Low values of anhysteretic remanent magnetization (χARM)/χlf(2.35) and χARM/SIRM (0.12×10-3 m·A-1) indicate predominantly coarse pseudo single domain (PSD) and multi-domain (MD) magnetic grain size assemblages. The playground dust is considered moderately to highly polluted, and the enrichment factor values for Cd, Zn, Cu, and Pb indicate extremely high contamination levels in the playground dust. Mineral magnetic parameters[χlf, SIRM, hard isothermal remanent magnetization (HIRM), χARM, and χARM/SIRM] reveal significant correlations with total and acid-extractable concentrations of the trace metals, and the correlations with total concentrations are stronger. The most significant correlations were found with mineral magnetic concentrations (χARM and SIRM) and total concentrations of the elements Mn, Ni, and Cr and the Tomlinson pollution load index (PLI) (0.69 ≤ r ≤ 0.86, P<0.01). Consistent spatial characteristics between them were also found, showing that the total concentrations of heavy metals and magnetic parameter values are higher in the playgrounds near and downwind of the power plant. Results of a principal component analysis indicate that anthropogenic activities (mainly from coal consumption by power plants) are the main sources for both heavy metals and magnetic minerals. In summary, significant correlations and consistent spatial characteristics between heavy metal contents and magnetic parameters and the same anthropogenic source for heavy metals and magnetic minerals confirm that magnetic parameters could be considered as efficient indicators for heavy metal contamination in the playground dust in industrial areas.

Mineral magnetic characteristics of the late Quaternary coastal red sands of Bheemuni, East Coast (India)

The voluminous red sand deposits of Bheemuni in the east coast of India provide record of coastal land-sea interaction during the late Quaternary climatic and eustatic oscillations. Limited information on the origin and depositional environments of these red sands and their chronology is available. We studied two inland to coast cross profiles from Bheemuni red sand deposits using mineral magnetism, color characteristics and Citrate-bicarbonate-dithionite (CBD) extractable pedogenic iron oxides over 23 horizons along with optically stimulated luminescence (OSL) chronology at 6 horizons. The oldest exposed bed had an optical age of ~48.9±1.7ka. Differential ages between the two parallel sections (SOS=~48.9±1.7 to 12.1±0.3ka and IMD=~29.3±3.5ka) suggest laterally shifting fluvial sedimentation.Both the profiles show significant amount of antiferromagnetic oxide (hematite) along with ferrimagnetic (magnetite/maghemite) mineral composition. The granulometric (/domain-) sensitive parameters (χFD, χARM, SIRM/χLF and χARM/χLF) indicate variable concentration of superparamagnetic (SP) and single domain (SD) particles between the two profiles. The higher frequency dependent and pedogenic magnetic susceptibilities (χFD and χpedo) in the younger (IMD) profile suggest enhanced pedogenesis under a warm-wet climate post ~29.3ka and also during Holocene. A combination of hard isothermal remanent magnetization (HIRM) and redness rating (RR) index indicates distinct but variable concentration of a) crystalline and b) poorly crystalline (pigmentary) hematites in both the profiles. We consider that the former (#a) is derived from hinterland red soils and possibly due to post-depositional diagenesis, and the latter (#b) precipitated from the dissolved iron under fluvial regime imparting the unique red coloration to Bheemuni sands. Partial to complete alteration of ferromagnesian minerals due to pedogenesis in hinterlands under warm-wet climate was therefore the principal source of reddening of the Bheemuni sands.

Estimating the concentration of aluminum‐substituted hematite and goethite using diffuse reflectance spectrometry and rock magnetism: Feasibility and limitations

AbstractHematite and goethite in soils are often aluminum (Al) substituted, which can dramatically change their reflectance and magnetic properties and bias abundance estimates using diffuse reflectance spectroscopy (DRS) and magnetic techniques. In this study, synthetic Al‐substituted hematites and goethites and two Chinese loess/paleosol sequences were investigated to test the feasibility and limitations of estimating Al‐hematite and Al‐goethite concentration. When Al substitution is limited (Al/(Al + Fe) molar ratio &lt; ~8%), the reflectance spectrum provides a reliable estimate of the goethite/hematite concentration ratio. New empirical relationships between the DRS band intensity ratio and the true concentration goethite/hematite ratio are estimated as goethite/hematite = 1.56 × (I425 nm/I535 nm) or goethite/hematite = 6.32 × (I480 nm/I535 nm), where I425 nm, I480 nm, and I535 nmare the amplitudes of DRS second‐derivative curves for characteristic bands at ~425 nm, ~480 nm, and ~535 nm, respectively. High Al substitution (&gt; ~8%) reduces DRS band intensity, which leads to biased estimates of mineral concentration. Al substitution and grain size exert a control on coercivity distributions of hematite and goethite and, thus, affect the hard isothermal remanent magnetization. By integrating DRS and magnetic methods, we suggest a way to constrain hematite and goethite Al substitution in natural loess. Results indicate that hematite and goethite in Chinese loess have Al contents lower than ~8% and, thus, that DRS can be used to trace hematite and goethite concentration variations.

Rock magnetic finger-printing of soil from a coal-fired thermal power plant.

We present seasonal rock magnetic data for 48 surficial soil samples collected seasonally around a coal-fired thermal power plant on the southwest coast of India to demonstrate how fly ash from the power plant is transported both spatially and seasonally. Sampling was carried out during pre-monsoon (March), early-monsoon (June), monsoon (September) and post-monsoon (December) seasons. Low- and high-frequency magnetic susceptibility (χlf and χhf), frequency-dependent magnetic susceptibility (χfd), χfd %, isothermal remanent magnetization (IRM), "hard" IRM (HIRM), saturation IRM (SIRM) and inter-parametric ratios were determined for the samples. Scanning electron microscopy (SEM) was used on limited number of samples. NOAA HYSPLIT MODEL backward trajectory analysis and principal component analysis were carried out on the data. Fly ash samples exhibit an average HIRM value (400.07 × 10(-5) Am(2) kg(-1)) that is comparable to that of soil samples. The pre- and post-monsoon samples show a consistent reduction in the concentration of magnetically "hard" minerals with increasing distance from the power plant. These data suggest that fly ash has indeed been transported from the power plant to the sampling locations. Hence, HIRM may perhaps be used as a proxy for tracking fly ash from coal-fired thermal power plants. Seasonal data show that the distribution of fly ash to the surrounding areas is minimum during monsoons. They also point to the dominance of SP magnetite in early-monsoon season, whereas magnetic depletion is documented in the monsoon season. This seasonal difference is attributable to both pedogenesis and anthropogenic activity i.e. operation of the thermal power plant.

Magnetic depletion and enhancement in the evolution of paddy and non‐paddy soil chronosequences

SummaryThe objective of this study was to understand the rates and controlling factors of magnetic depletion and enhancement during anthropogenic soil evolution. To this end, the study compared the dynamic changes in magnetic properties as well as iron oxide species of paddy and non‐paddy soil chronosequences with the same parent materials. A two‐way analysis of variance (anova) showed that paddy management resulted in significant (P &lt; 0.01) decreases in magnetic susceptibility (χ) and other magnetic properties. Paddy management‐induced χ losses increased gradually from 24 to 55% as the cultivation history increased from 50 to 700 years. The rates of χ decrease were most rapid within the first 50 years of paddy cultivation, after which the rate slowed. The rapid decline in χ is probably caused by accelerated depletion of fine‐grained maghemite and ultrafine magnetite by iron‐reducing bacteria during soil waterlogging and consequent reducing conditions. By contrast, a significant decrease in hard isothermal remanent magnetization (HIRM) occurred only after 700 years of paddy cultivation, which matches the time taken to leach CaCO3 from the profile. In contrast, although magnetic enhancement was observed in the non‐paddy surface horizon, there was no increasing trend at the millennium time‐scale, probably because of the large CaCO3 content of the soil. We show that magnetic properties of paddy and non‐paddy soil derived from calcareous sediments are mainly controlled by the changing soil moisture regime and soil carbonate status along different paths of soil development. Our study suggests that differences in soil moisture regime caused by land use are substantially more important than the period of cultivation.

Identifying the influence of urbanization on soil organic matter content and pH from soil magnetic characteristics

Soil magnetic characteristics are correlated with soil pH and organic matter content. Analyzing soil magnetic characteristics, organic matter content and pH can indirectly evaluate soil pollution caused by human activities. This study analyzed the soil magnetic characteristics, organic matter content and pH in surface soil samples from different land use types in Shihezi city, a newly and rapidly developing oasis city in Xinjiang of China. The aims of this study were to explore the possible relationships among the soil magnetic parameters and thereby improve the understanding of influence of urbanization on soil properties. Eighty surface soil samples at the depth of 0–10 cm were collected from 29 July to 4 August 2013. The results showed that the magnetic minerals in surface soil were dominated by ferromagnetic minerals. Spatially, the magnetic susceptibility (χ LF), anhysteretic remanent magnetization susceptibility (χ ARM), saturation isothermal remanent magnetization (SIRM) and “soft” isothermal remanent magnetization (SOFT) were found to be most dominant in the new northern urban area B (N-B), followed by built-up areas (U), suburban agricultural land (F), and then the new northern urban area A (N-A). The values of χ LF, χ ARM, SIRM and SOFT were higher in the areas with high intensities of human activities and around the main roads. Meanwhile, the property “hard” isothermal remanent magnetization (HIRM) followed the order of U>N-B>F>N-A. Built-up areas had an average pH value of 7.93, which was much higher than that in the new northern urban areas as well as in suburban agricultural land, due to the increased urban pollutant emissions. The average value of soil organic matter content in the whole study area was 34.69 g/kg, and the values in the new northern urban areas were much higher than those in the suburban agricultural land and built-up areas. For suburban agricultural land, soil organic matter content was significantly negatively correlated with χ LF, and had no correlation with other magnetic parameters, since the soil was frequently ploughed. In the new northern urban areas (N-A and N-B), there were significant positive correlations of soil organic matter contents with χ ARM, SIRM, SOFT and HIRM, because natural grasslands were not frequently turned over. For the built-up areas, soil organic matter contents were significantly positively correlated with χ LF, χ ARM, SIRM and SOFT, but not significantly correlated with frequency-dependent susceptibility (χ FD, expressed as a percentage) and HIRM, because the soil was not frequently turned over or influenced by human activities. The results showed that soil magnetic characteristics are related to the soil turnover time.

Mineral magnetic and diffuse reflectance spectroscopy characteristics of the Deccan volcanic bole beds: Implications to genesis and transformations of iron oxides

Deccan volcanic bole beds are important indicators of paleoenvironmental conditions during Cretaceous–Tertiary volcanism. However, little attention has been paid to iron oxide characteristics of these lava flow hosted sediments. Therefore, in order to understand the genesis and transformation of various iron oxides in different colored bole beds, we studied the mineral magnetism and diffuse reflectance spectroscopy (DRS) characteristics of red, brown and green boles that are extensively exposed in the Deccan volcanic province (DVP) of Western India. Mineral magnetism and DRS characteristics indicate hematite (α-Fe2O3) as the major iron oxide in all the bole beds with traces of goethite (α-FeOOH) in many. Maghemite (γ-Fe2O3) was also present in red boles as well as in few brown and green boles. The higher concentration of magnetic minerals in red boles is due to the neo-formation of fine magnetic minerals produced from heating of the weathered sediments by the overlying lava flow. The increasing concentration of superparamagnetic (SP) fraction (indicated by frequency dependent susceptibility, χfd) with increased reddening of the bole beds (mean χfd for green, brown and red boles=~2.5, 11.1 and 19.3×10−8m3kg−1, respectively) facilitates the use of χfd as first order estimate for degree of heating in red boles. The paragenesis of ferrimagnetic and antiferromagnetic minerals in green and brown boles is indicated by good correlation (R2=0.78) between hard isothermal remanent magnetization (HIRM) and χfd suggests that green and brown boles have undergone some pedogenesis. The overall distribution of iron oxides in these bole beds indicate their genesis from incipient weathering of Fe–Mg minerals (e.g. olivine and pyroxenes) under humid conditions leading to the formation of ferrihydrite and goethite as precursors. Partial to complete heating resulted into oxidation of precursors and titanomagnetite to maghemite as the intermediate transformation phase and hematite as end product. The green, brown and red boles thus represent the transitional baking environments under various hydrous–anhydrous conditions and pedogenic processes. The genesis and transformation of various iron oxides in DVP bole beds may have significant implications for the characterization of such interflow sediments/paleosols from other igneous provinces (e.g. Israel, Karoo Flood Basalt, South Africa and Columbia River Basalt, USA). Further, complex genesis of the iron oxides in the DVP bole beds also envisages a great scope to study them as Martian analogues apart from their significance to paleoenvironment and demands more advanced rock magnetic and spectroscopic approaches.

Magnetic and diffuse reflectance spectroscopic characterization of iron oxides in the tidal flat sequence from the coastal plain of Jiangsu Province, China

In this paper, we present the results of research on a coastal lowland Holocene tidal flat sequence in order to explore the variations in magnetic mineralogy during the process of tidal flat sedimentation and subsequent land formation. Three cores (∼6 m in length) were collected from the coastal plain in Jiangsu Province, China, and investigated with magnetic measurements, diffuse reflectance spectroscopy (DRS) and free iron oxide (Fed) analyses. The tidal flat sequence shows a fining-upward trend, and the top ∼2 m of each core with redoximorphic feature was interpreted to be a salt marsh facies in origin. Unmixing of isothermal remanent magnetization acquisition curves identify magnetite and maghemite as well as high-coercivity hematite and goethite, with the latter iron oxides confirmed by DRS analysis. Enrichment of goethite, hematite and maghemite occurs in the salt marsh deposits in comparison to the lower intertidal and subtidal deposits, with goethite being the dominant iron oxide. The changes in hard isothermal remanent magnetization acquired in field above 100 mT field (HIRM100) and the S–100 ratio largely reflect the presence of medium-coercivity maghemite in absolute content and relative proportions, respectively. The approach used for iron oxide characterization may offer an efficient diagnostic tool for recognizing sediments or soils subjected to redox condition oscillation elsewhere and contribute to studies of iron cycling in (palaeo-)environmental researches.

Composition of dust deposited to snow cover in the Wasatch Range (Utah, USA): Controls on radiative properties of snow cover and comparison to some dust-source sediments

Abstract Dust layers deposited to snow cover of the Wasatch Range (northern Utah) in 2009 and 2010 provide rare samples to determine the relations between their compositions and radiative properties. These studies are required to comprehend and model how such dust-on-snow (DOS) layers affect rates of snow melt through changes in the albedo of snow surfaces. We evaluated several constituents as potential contributors to the absorption of solar radiation indicated by values of absolute reflectance determined from bi-conical reflectance spectroscopy. Ferric oxide minerals and carbonaceous matter appear to be the primary influences on lowering snow-cover albedo. Techniques of reflectance and Mossbauer spectroscopy as well as rock magnetism provide information about the types, amounts, and grain sizes of ferric oxide minerals. Relatively high amounts of ferric oxide, indicated by hard isothermal remanent magnetization (HIRM), are associated with relatively low average reflectance (

Red palaeosols development in response to the enhanced east asia summer monsoon since the mid-pleistocene in South China: Evidence derived from magnetic properties and molecular fossil records

Although Pleistocene red paleosols are widely distributed in South China, paleoenvironmental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower (higher) χ but higher (lower) values of HIRM (hard isothermal remanent magnetization) and SIRM (saturation isothermal remanent magnetization)/χ has tight relationship with the intensity of pedogenesis, especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP (superparamagnetic)/SD (single domain) ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to the extremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon: (1) the most effective since the Middle Pleistocene; (2) moderately effective since 270 ka or so; (3) least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.

Rock magnetism, iron oxide mineralogy and geochemistry of Quaternary red earth in central China and their paleopedogenic implication

This paper presents a detailed investigation on the rock magnetism, iron oxide mineralogy and geochemistry of a Quaternary red earth (QRE) in central China. The magnetic profile of QRE showed a characteristic vertical variation pattern: the uniform red clay (URC) section (0.2–2m) of the profile had a higher magnetic susceptibility (χ) while vermiculated red clay (VRC) section (2–6m) had a very low χ (<30×10−8m3kg−1). Rock magnetism and differential XRD analysis revealed that magnetite/maghemite and hematite were the main magnetic carriers in the URC section. The major elements Fe2O3 and Al2O3 of QRE increased with depth while the SiO2 content decreased with depth, indicating a leaching of the mobile elements and an enrichment of the immobile elements. In comparison with the URC, the VRC has a greater depletion in the content of Na, Mg, K and Mg, indicating a stronger weathering intensity. The dithionite–citrate–bicarbonate (DCB) extracted iron (Fed), the ratio of Fed to total iron oxide (Fe/Fet), and the weathering indices of QRE confirmed that the VRC had experienced a stronger pedogenesis than the URC. Strong pedogenesis in the VRC resulted in a transformation of the highly magnetic maghemite to the weakly magnetic hematite, which was responsible for the weak magnetism and hard magnetic behavior of the VRC. Our studies suggest that the VRC had experienced a hot climate with a dry season following one that was warm and moister. Magnetic reduction of the VRC section resulting from the transformation of highly magnetic maghemite to weakly magnetic hematite appeared to be an important paleopedogenic process in the QRE. We concluded that the magnetic parameters, hard isothermal remanent magnetization (HIRM) and SIRM/χ of QRE, can be used for the analysis of paleopedogenic processes.

Soil Characteristic Response Times and Pedogenic Thresholds during the 1000-Year Evolution of a Paddy Soil Chronosequence

A paddy soil chronosequence consisting of five profiles derived from calcareous marine sediments with cultivation history from 0 to 1000 yr was studied to assess the dynamic changes in soil properties and major elemental mass balance during soil evolution and to understand the response rates of soil properties at different time scales. The threshold concept was applied to increase our understanding of paddy soil genesis processes. Results showed that 50 yr of paddy cultivation induced measurable accumulation of soil organic C (SOC) in the surface horizon and marked reduction of magnetic susceptibility (MS), soft isothermal remanent magnetization (IRMs), and Ca, Mg, and Na elemental concentrations. Complete removal of CaCO3 from profiles, measurable profile differentiation of free Fe oxide (Fed) and total Fe, clay illuviation, reduction of hard isothermal remanent magnetization (IRMh), and net losses of elemental P and Mn occurred during the 300- to 700-yr time period. Soil clay mineral composition and Si, Al, and K elemental concentrations showed little change in 1000 yr. The rapid changes in SOC, MS, IRMs, Ca, Na, and Mg within 50 yr primarily resulted from anthropogenic activities, which are extrinsic thresholds. The noticeable changes in horizon differentiation of Fed, clay illuviation, and the decrease in IRMh during the 300- to 700-yr time period indicate threshold values for carbonate, which is an intrinsic threshold. In conclusion, our data demonstrate that different soil components and properties have different transformation processes and associated rates influenced by anthropogenic activities and the soil carbonate status of the original soil.

Evolution and significance of soil magnetism of basalt-derived chronosequence soils in tropical southern China

Soil samples were collected from eight basaltderived chronosequence soils with the ages of 0.01, 0.58, 0.92, 1.33, 2.04, 3.04, 3.76 and 6.12 Ma respectively from Leizhou Peninsula and northern Hainan Island of tropical southern China. Magnetic parameters of magnetic susceptibility (MS), percentage of frequency-dependent magnetic susceptibility (FDS%), anhysteretic remanent magnetization (ARM), saturation isothermal remanent magnetization (SIRM), soft and hard isothermal remanent magnetization (IRMs and IRMh) of the collected samples were measured to study the evolution and the significance of the magnetism with soil age. The results show that the magnetic parameters changed fast from Primosols to Ferrosols (0.01 - 0.92 Ma) but slowly at Ferralosols stage (1.33 Ma~), it suggests a stable phase occurred for soil magnetism at Ferralosols, the existence of this phase could be supported by the little changes in the contents of clay, Fet and Fed. Obvious differences existed in the values of magnetic parameters between Ferralosols and other soil types (Primosols and Ferrosols), FDS%: Ferralosols > 10%, Primosols and Ferrosols 8000 × 10 –8 SIm 3 ·kg –1

HIRM variations in the Chinese red-clay sequence: Insights into pedogenesis in the dust source area

Although extensive rock magnetic studies have been performed on the Chinese loess–paleosol sediments, few comparable studies have been applied to the underlying red-clay sediments. Because of this paucity of data, our understanding of the mineral magnetic properties of the red-clay sequence, and the paleoenvironmental information encoded in them, is limited. Here we report “hard” isothermal remanent magnetization (HIRM) variations from ∼8.1 to ∼1.2 Ma in the lower part of the loess–paleosol and the underlying red-clay sequences of the Chaona section on the Chinese Loess Plateau. The results indicate that there is a negative correlation between HIRM and frequency dependence of magnetic susceptibility χ fd ( χ fd = χ lf − χ hf, where χ lf and χ hf are magnetic susceptibility measured at 470 Hz and 4700 Hz, respectively) from ∼3.4 to ∼2.6 Ma and a positive correlation between these two proxies from ∼8.1 to ∼3.4 Ma and ∼2.6 to ∼1.2 Ma. We argue that the HIRM variations from ∼8.1 to ∼3.4 Ma and from ∼2.6 to ∼1.2 Ma reflect hematite availability in the dust source region, determined by the size of the area and climatic conditions of the dust source region. The negative correlation between HIRM and χ fd between ∼3.4 and ∼2.6 Ma suggests that magnetic enhancement during this time interval may be related to the alteration of hematite/goethite to magnetite/maghemite. We also find that HIRM data between 8.1 and 3.4 Ma show high coherence with the 100-kyr eccentricity signals, suggesting eccentricity forcing of concentration variations of hematite in the dust source area. Higher resolution samples are needed to determine if concentration variations of hematite in the dust source area are coherent with the orbital obliquity and precession forcing signals.

Tracking provenance change during the late Miocene in the eastern Mediterranean using geochemical and environmental magnetic parameters

Marls of the Metochia section (Gavdos, Greece) have been analyzed using geochemistry, environmental magnetism, and diffuse reflectance spectrometry to study late Miocene paleoenvironmental changes in the eastern Mediterranean region. Fuzzy c‐means cluster analysis (FCM), combined with nonlinear mapping (NLM), has been performed on a multiparameter data set to identify and characterize terrigenous source areas from North Africa and the Aegean margin. The parameters included in the FCM were selected on the basis of their univariate characteristics and their ability to trace input changes from regional source areas. The hard isothermal remanent magnetization (HIRM), calculated on a carbonate‐free basis, and the Ti/Al ratio are used to distinguish aeolian dust and transport mechanisms of material originating from North Africa. Mass accumulation rates of Al and Ni are employed to represent the input of terrigenous material originating from the Aegean region. CaCO3, calculated from Ca abundance, provides information concerning marine productivity and Mn/Al is used to trace reductive diagenesis in the marls. After performing the FCM and NLM analysis, a four‐cluster solution has the greatest stability and describes paleoenvironmental changes in both the African and European source areas. The cluster solution clearly reveals the change from input dominated by terrigenous material in the lower parts of the Metochia section to marine input at the top of the section but also reveals changes in paleoenvironmental conditions in North Africa from arid to more humid conditions at ∼8.2 Ma.