Magnetic Minerals Research Articles

Quaternary Magnetic Stratigraphy of Deep‐Sea Sediments in the Western North Pacific: Influences of Paleomagnetic Recording Efficiency and Lock‐In Delay

AbstractUnderstanding past environmental changes in the western North Pacific is rather limited due to the general paucity of robust chronology for carbonate‐lacking pelagic clay sediments. Here, we present a new magnetostratigraphy of Quaternary deep‐sea sediments in the northern Mariana Basin. A comprehensive set of paleomagnetic, rock magnetic, and microscopic results reveal that paleomagnetic signals are mainly carried by detrital magnetic minerals of Asian eolian dust and volcanic origins. The volcanic materials, most likely from the Mariana Arc, are characterized by low coercivity (∼30 mT) interacting single domain (SD) and pseudo‐SD grains, associated with abundant dendritic magnetic crystals/inclusions. This volcanic component is a suitable remanence carrier but is less efficient in recording geomagnetic intensity than the higher coercivity eolian component. The relative paleointensity record derived with minimum rock magnetic artifacts shows comparable patterns with global templates. At the Matuyama‐Brunhes transition, a ∼2‐cm remanence lock‐in depth offset is identified from beryllium isotope records, and the estimated magnetostratigraphic age delay is small (∼8 kyr). Our results provide an improved understanding of remanence recording processes in carbonate‐poor deep‐sea clays and demonstrate magnetic stratigraphy as a valuable chronology in the western North Pacific region.

A magnetic measurement technique for small rare samples: Pre-study for Chang’e-5 returned and other extraterrestrial samples

Standard-size samples are usually used for traditional paleomagnetic studies. In some cases, small irregular samples are employed considering their amount and magnetic strength as well as experiment efficiency. With the development of deep space exploration, the demand for studying small and magnetic weak samples is increasing. In this study, we established a magnetic measurement technique for small rare samples. We designed low-background, sample-nondestructive and high-flexibility holders with various materials for different measurements of small samples. With the customized holders, we estimated uncertainty and reliability of magnetic measurements of small specimens from a terrestrial basalt. The results indicate that susceptibility and remanence of small specimens (e.g., 2-mm cubes) are more affected by measurement position than larger specimens (≥5 mm), which reminds us to pay special attention to consistency of the small specimen position during series of measurements. Moreover, susceptibility and remanence of small sister specimens (2-mm and 5-mm cubes) are more scattered than those of large ones (cube length ≥1 cm), mainly due to inhomogeneity of magnetic mineral abundance in the sample. Nevertheless, the average magnetic results of different-size specimens are generally consistent within error, indicating the inhomogeneity of small specimens can be averaged out and demonstrating the reliability of small samples during magnetic measurements. Finally, we tested our measurement system with a lunar meteorite, which mimics the Chang’e-5 returned samples in both size and mineralogy. The main minerals of the meteorite are plagioclase, pyroxene, troilite and kamacite. The isothermal remanent magnetization normalized paleointensity method recovered the expected laboratory field while the anhysteretic remanent magnetization corrected paleointensities are about 2-3 times the expected field, where the latter can be explained by inapplicability of the empirical f′ to the meteorite specimens. The anhysteretic remanent magnetization and IRM paleointensity calibration factor f′ and a of the lunar meteorite were calculated to be 3.89 and 3138 μT, respectively, which provides new constraints for the empirical values. The magnetic results of the lunar meteorite demonstrate the utility of our measurement system for small weak samples. This study provides technical support for paleomagnetic study of the Chang’e-5 and other extraterrestrial samples in the future.

Reversible Thermal Hysteresis in Heating‐Cooling Cycles of Magnetic Susceptibility: A Fine Particle Effect of Magnetite

AbstractThermomagnetic curves of magnetic susceptibility (κ) are key to characterizing magnetic properties. We report hump‐shaped κ‐T curves of magnetite‐bearing basalt during heating‐cooling cycles to ∼340°C, with a large thermal hysteresis and similar starting and ending values, even in multiple repeated cycles, ruling out changes in magnetic mineralogy. Based on FORC diagrams and published results of engineered materials, we propose that thermal hysteresis arises from configurations of magnetic moments in clusters of single‐domain particles due to dipolar coupling, with different collective behavior during heating and cooling. This effect modifies the hump‐shaped thermal relaxation behavior of the individual nanoparticles. FORC and κ‐T results indicate an increase in effective particle sizes after 700°C‐heating. Our results are a warning against premature interpretation of a decreasing trend in κ‐T curves by maghemite inversion. Instead, fine particle behavior should be considered when a hump‐shaped κ‐T behavior is detected.

The Holy Cross Mountains (Poland) terranes palaeoposition and depositional environment in Silurian—new insights from rock magnetic studies

SUMMARY The Holy Cross Mountains (HCM) in Poland, is an isolated natural outcrop of Palaeozoic rocks located within the Trans-European Suture Zone, a tectonic collage of continental terranes adjacent to the Tornquist margin of the Baltica. This uniqueness made the HCM a target for palaeogeographic research. Based on the facies differences, the HCM had been divided into two major units, the southern (the Kielce Unit) and northern (the Łysogóry Unit) part (SHCM and NHCM, respectively). Their position in relation to each other and the Baltica continent during Silurian times is still a matter of discussion, whether both parts of the HCM were separated terranes located along the Baltica margin or they shared in common palaeogeographic history. Here, we present the results of comprehensive rock magnetic measurements applied as a tool to interpret palaeoenvironmental conditions during deposition and burial and therefore allow discussion about the terranes’ relative position. To recognize the magnetic mineral composition and texture of studied Silurian graptolitic shales several rock magnetic measurements were conducted including low-temperature Saturated Isothermal Remanent Magnetization, thermal demagnetization of three-component IRM and hysteresis measurements, as well as anisotropy of magnetic susceptibility (AMS). The sampled rocks come from both units of the HCM. In all analysed samples we found single domain (SD) stoichiometric magnetite of mostly diagenetic (i.e. post-depositional) origin and goethite resulting likely from weathering. In turn, detrital magnetite, even if observed in previously investigated Silurian rocks from the Baltica margin, was not identified in this study, what we attribute to dissolution during diagenesis in the deep-water environment. Solely in the NHCM, SD hematite and maghemite grains were observed, which we interpret as detrital in origin. These grains have been preserved in the suboxic environment of the NHCM sub-basin bottom waters due to their resistance to dissolution in marine waters. Considering the deposition conditions (oxygenation of the near-bottom zone) rather similar for both HCM parts, we associate the presence of aeolian hematite grains solely in the NHCM rocks with a more proximal position of the NHCM than the SHCM in relation to the Baltica continent during late Llandovery (Silurian). This conclusion agrees with some existing palaeogeographic models. In addition to petromagnetic studies focused on the analysis of ferromagnets, AMS measurements were also carried out. The results indicate that the magnetic susceptibility is mainly governed by paramagnetic minerals, mostly phyllosilicates with small ferromagnetic contributions. Oblate AMS ellipsoid and distinct bedding parallel foliation indicate prevailing sedimentary-compactional alignment. Observed magnetic lineation of tectonic origin resulting from weak strain is related presumably to Variscian deformations.

Westerly-monsoon variations since the last deglaciation from semi-arid Ladakh region, Trans Himalaya, India

The semi-arid Ladakh region in the Trans Himalaya forms an environmental boundary between North Atlantic and monsoon forcings. Its location in the transient setting of these two climate systems enables to attest slight changes in the dynamics of these components of atmospheric circulation. Variation in climatic conditions from 19.6 to 6.1 ka using multi-proxy investigation (mineral magnetism, stable carbon isotope, palaeoprecipitation, sediment grainsize end member analysis, clay mineralogy and TOC) is studied from Khalsi palaeolake deposit in Ladakh. Considering the inherent uncertainty of radiocarbon chronology, the present study provides millennial to multi-centennial scale resolution of climate variation from the sediment sequence. The results indicate cold arid climate influenced by Westerly circulation for the last 19.6 to 11.1 ka, thereafter from 11.1 to 7.5 ka, monsoon forcings dominated the climate of the region, following the orbitally controlled solar insolation that influenced the position of ITCZ and formed the key driver of the variability of these atmospheric circulations. A short wet phase from ∼17.4 to 16.5 ka within the dominant Westerly period is attributed to the early wet phase of two-fold H1 event. Westerly regained strength from 7.5 to 6.1 ka during the mid-Holocene coinciding with decreasing insolation, weakening monsoon and enhanced El Niño activities.

Analysis of Magnetic Material Abundance in Black Sand

The analysis of the magnetic material abundance on the black sand of Nyanyi beach revealed magnetic material content, grain size, density, magnetic mineral content, and magnetic susceptibility value.The results of this study can be used for black sand development inTabanan district. The black sand magnetic material was determined by the extraction method. Mineral content was tested by using XRF equipment, and the magnetic properties of black sand were determined by using a Bartingtons MS2 Magnetic Susceptibility Meter and a Vibrating Sample Magnetometer. The data were analyzed descriptively quantitatively. The results show thatNyanyi beach sand physically has a characteristic dark gray color, tends to be black, and shiny with a weight fraction of magnetic material reaching 95.52%.The density of the magnetic material is 2072.6 with varying grain sizes of 53 600 .The average value of magnetic susceptibility is 27.212x 10-with Fe2O3magnetic mineral content of 86.68% and the element of Fe is 89.41%.The values of saturation magnetization, remanance magnetization, and coervicity reach37.74; 4.64; 103.93 Oe.

Producing magnetite concentrate from iron tailings via suspension magnetization roasting: A pilot-scale study

ABSTRACT In the process of iron ore beneficiation, a considerable amount of iron was lost to the tailings, resulting in the waste of resources and environmental pollution. In this study, an innovative technology of pre-concentration followed by suspension magnetization roasting and low-intensity magnetic separation (PSRM) was used to recover iron from iron tailings. The iron grade of the roasted feed ores was increased from 15.68% to 33.19% by pre-concentration process. Subsequently, the suspension magnetization roasting was performed to transform the weak magnetic minerals into magnetite, and magnetite concentrate was obtained via low-intensity magnetic separation. The effects of feeding rate, roasting temperature, reducing gas CO flow rate, and fluidizing gas N2 flow rate during suspension magnetization roasting were investigated, and the pilot-scale equipment was conducted for 72 h continuously under the optimum roasting conditions. The phase transformation and magnetic property variations of the minerals before and after roasting were analyzed by X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM), respectively. The results showed that an iron concentrate with iron grade of 63.04% and total iron recovery of 48.40% was obtained under the optimum roasting conditions: feeding rate of 111.70 kg/h, roasting temperature of 550°C, CO flow rate of 4.0 m3/h, and N2 flow rate of 2.0 m3/h. The hematite and siderite in tailings were transformed into magnetite with an average magnetic conversion rate of 86.46%. This innovative PSRM technology provides an important reference for the resource utilization of solid waste and the recovery of iron from iron tailings.

Late-Middle Pleistocene Sedimentary Environment and Climate Variation in North Hebei Plain, China: Evidence from the SHBZK-1 Core

Thick Quaternary alluvial and floodplain sediments in north Hebei Plain provide important information for understanding local paleoenvironmental and paleoclimatic variations. A 120.8 m drilled core (SHBZK-1) was recovered to determine the late Pleistocene climatic fluctuations, sedimentary environment and their coevolutionary relationship. Laboratory analysis, including grain size distribution, magnetic susceptibility, and optical stimulated luminescence dating, was carried out. Lithofacies and grain size showed that the sediments are of fluvial origin and contain two subfaces: river sand bar and flood plain. The good correlation between magnetic susceptibility and grain size show that climate change is the main factor controlling the variation of sedimentary environment in Hebei Plain, rather than tectonic factors. Furthermore, variations of the magnetic susceptibility and lithofacies reflect the intensity and fluctuations of Asian monsoons and couple well with glacial-interglacial cycles, suggesting that the variation of ice volume in the Northern Hemisphere drives climate change in the Hebei Plain, which, in turn, regulates the variation of the sedimentary environment and facies through controlling precipitation changes, as well as the input amount of magnetic minerals. This research provides a useful continental archive for understanding the late Pleistocene environmental and climatic variation and suggests the prevalence of climate-driven environmental change.

Q56The Midlands of England: Economic Backwater or an Agricultural Powerhouse? Environmental Evidence from Prehistory to Modern Times Recorded in Sediments from Aqualate Mere, Central England, UK

ABSTRACT Archaeological and palaeoecological evidence relating to human activity in the English Midlands is scant compared to elsewhere in Britain. Knowledge of human activity in pre-Roman and Roman times is often fragmentary and disparate in parts of the region where it could be assumed that the resident population was small with little Roman impact. To examine these contentions, a palaeoenvironmental investigation from Aqualate Mere near Newport, Staffordshire, has been undertaken on the sediment record extending back to c. 1300 cal. BC. An analysis of microfossils, microscopic charcoal, sediment chemistry and mineral magnetism from a core dated by 14C, SCPs, 210Pb and 137Cs has provided an opportunity to reconstruct land use changes and atmospheric pollution from the later prehistoric period onwards. The results challenge the idea this region was a backwater as there is near-continuous agricultural activity around the mere since the Late Bronze Age through to modern times. This is characterised by phases of woodland decline, an intensification of farming, soil erosion, evidence for possible eutrophication and regional lead pollution.

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.

Monte Alban periphery (Oaxaca, middle Mesoamerica): New evidences on the early occupation trough archaeomagnetic study of pottery kilns

Aimed to obtain absolute chronology data for the early stage of Monte Alban, magnetic mineralogy and archaeomagnetic investigation were carried out of recently discovered pottery kilns. Oriented samples belong to four rectangular kilns, both single and double chambers, and one fire pit at the piedmont peripherical area. Susceptibility vs. temperature curves show market thermal instability while large pseudo-single domain grains seem to carry the major part of remanence for the kiln sample. Fire pit samples, in contrast, seem to be dominated by antiferromagnetic hematite. Alternating field demagnetization allowed to reach primary, characteristic magnetization components with reasonably well-defined mean archaeodirections. Possible archaeomagnetic age intervals were obtained considering currently available global models and local curves. The dates are consistent with the most important periods of occupation at the site, although the results may indicate that there was also a significant cultural presence in the Early Classic Period. Recently discovered kilns indicate constant manufacture of pottery. Although we cannot currently define the intensity of production, we believe that pottery could be a specialized activity in peripherical areas of Monte Alban to exchange ceramics or for its local consumption. Consequently, we propose that the piedmont area was an economically autonomous community whose inhabitants dedicated themselves to various tasks throughout their occupation.

Paleomagnetic study of the 1112 Ma Huanchaca mafic sills (SW Amazonian Craton, Brazil) and the paleogeographic implications for Rodinia supercontinent

During the Stenian Period (1200–1000 Ma) Rodinia was being formed, and the Amazonian Craton, presently in northern South America, was an important piece in this scenario. Recently a megacontinent named Umkondia composed by Amazonia/West Africa, Congo/São Francisco, Kalahari and India was proposed to have existed at 1100 Ma. We present a paleomagnetic study on the well-dated (U-Pb, baddeleyite) 1112 Ma mafic sills from the Huanchaca Intrusive Suite, western Mato Grosso State (Amazonian Craton) in order to test the proposed configuration of Umkondia. Alternating field (AF) and thermal stepwise demagnetization revealed northwestern characteristic remanent magnetization (ChRM) directions with low positive inclinations (mean: Dm = 303.2°, Im = 12.2°, N = 10, α95 = 14.5°, K = 12.0). A paleomagnetic pole was calculated for the Huanchaca sills (HU − 225.7°E, 30.1°N, A95 = 9.9°) which is classified with reliability index R = 5. Magnetic mineralogy experiments show that ChRM is carried by Pseudo single domain (PSD) magnetite. The Huanchaca paleopole favors the existence of the Umkondia megacontinent at 1100 Ma, which latter collided with Laurentia forming the Rodinia supercontinent around 1000–900 Ma.

Interactions Between Depositional Regime and Climate Proxies in the Northern South China Sea Since the Last Glacial Maximum

AbstractSedimentary deposits from the northern South China Sea (SCS) can provide important constraints on past changes in ocean currents and the East Asian summer monsoon (EASM) in this region. However, the interpretation of such records spanning the last deglaciation is complicated because sea‐level change may also have influenced the depositional processes and patterns. Here, we present new records of grain size, clay mineralogy, and magnetic mineralogy spanning the past 24 kyr from both shallow and deep‐water sediment cores in the northern SCS. Our multi‐proxy comparison among multiple cores helps constrain the influence of sea‐level change, providing confidence in interpreting the regional climate‐forced signals. After accounting for the influence of sea‐level change, we find that these multi‐proxy records reflect a combination of changes in (a) the strength of the North Pacific Intermediate Water inflow, (b) the EASM strength, and (c) the Kuroshio Current extent. Overall, this study provides new insights into the roles of varying terrestrial weathering and oceanographic processes in controlling the depositional record on the northern SCS margin in response to climate and sea‐level fluctuations.

Magneto-mineralogical characteristics of mafite-ultramafites of the Middle Bug River area and Holovaniv suture zone of the Ukrainian Shield (overview)

Mafites and ultramafites manifest in the magnetic field as significant magnetic anomalies due to the high content of magnetite, titanomagnetite and iron-magnesium silicates. Studying the mineralogy and magnetic properties of Archean rocks formed deep in the lower crust and uplifted to the surface allows to understanding the sources of magnetic anomalies. Such rocks are known in the Ukrainian shield, in particular in the Middle Bug River region and in the Holovaniv suture zone (HSZ). We consider mafic-ultramafic assemblages of the rocks of this region, their mineral composition and magnetic characteristics, manifestations in the magnetic field, and the distribution of magnetic minerals. Several mafic-ultramafic associations of different ages, composed of effusive, sedimentary-effusive and intrusive formations, are recognized for the area the Pobuzkiy ore mining region. Most of them were transformed intensively by metamorphism of granulite (to eclogite) facies and by intense tectonic and diaphoretic processes. The main volcanics and volcanogenic-sedimentary rocks belong to the Tivriv stratum of the Paleoarchean Dniester-Bug and Neoarchaean Bug series. Mantle rocks were the protolith of the Tivriv stratum, which are similar in composition to oceanic basalts. The Pavliv stratum is considered as a part of the Dniester-Bug series. It is composed mainly of two-pyroxene crystal schists (sometimes amphibolized, often with significant magnetite content (up to 10 %)), magnetite-orthopyroxene crystal schists, and bodies of ferruginous quartzites. Both series contain gneiss complexes, as well as bodies of basite-hyperbasites. Mafic rocks are mainly represented by hornblende-pyroxene crystal schists and amphibolites. Ultramafite and mafit-ultramafite intrusive bodies were mapped in the central and northern parts of the HSZ where they are presented by rocks of the hyperbasite and gabbro-peridotite formations. The Holovaniv block of the HSZ is spatially coincident with the Holovaniv gravitational maximum and magnetic anomalies, which are probably caused by the rooting of mafit-ultramafits from the upper mantle along deep fault zones. Magnetic sources with increased magnetization were identified within the district of Haivoron. They are associated with pyroxene schists, gneisses, coarse-grained pyroxene schists, and ferruginous quartzites. The high values of magnetic parameters of the rocks of the Haivoron-Zavallya region are explained by the presence of eulysites and magnetite-hypersthene crystal schists. Within the area of occurence of charnockite-enderbite rocks, the magnetic field with increased intensity and a large-mosaic structure is observed. Differentiation of the magnetic properties of the rocks of the upper part of the Earth’s crust, the shape and low power of the sources indicate their possible primary magmatic formation in the form of massifs and dykes with further metamorphic transformations. Magnetite is the main magnetic mineral of mafite-ultramafites according to thermomagnetic analysis and ore microscopy. Several generations of magnetite are observed. Early generations (reliably magmatic) are present in the dark-colored minerals as point inclusions and emulsion discharges along fissures (disintegration structures of solid solutions). The increase of the amount of magnetite in all types of rocks is associated with superimposed secondary transformations. Redistribution of iron occurs in the recrystallization zones with the formation of clusters of secondary coarse-grained magnetite. According to the hypothesis, the magnetite of ferruginous quartzites has metamorphic origin, while the origin of the magnetite of iron-carbonate and iron-siliceous formations is a controversial issue. It depends on the determination of the genesis of the original substance.

Sedimentary modulation of magnetic mineral records in the Central Bengal Fan

Submarine fan sediments are essential archives for understanding the interaction between continental weathering and climate change, but decoding multiple geological and environmental factors in such highly dynamic sedimentary environments is challenging. Here we present a high-resolution magnetic mineral record spanning the past ∼40 ka from the central Bengal Fan. Comprehensive rock magnetic and electron microscopic analyses are conducted to understand the origins of different magnetic mineral components in response to sedimentary and paleoclimate processes. Detrital magnetite and titanomagnetite are the dominant magnetic minerals in Bengal Fan sediments, whose abundance and grain size are primarily controlled by eustatic sea-level change. Increased Himalaya terrestrial input during Heinrich events is documented during sea-level low stand, but magnetic mineral variations and climate events are decoupled due to enhanced Indian hemipelagic sediment input since the last deglaciation sea-level rise. In addition, we identify an enriched biogenic magnetite layer near the Fe-redox boundary in the studied Bengal Fan sediment core, possibly related to relatively mild post-depositional diagenesis. Massive detrital inputs in the submarine fan sediments dilute the contribution of biogenic magnetite to the bulk magnetic record. Our results contribute to an integrated source-to-sink understanding of magnetic mineral components in continental margin submarine fans, which helps to construct multi-proxy Quaternary paleoclimate and paleogeography records in typical submarine fan deposits.

Evaluation of structural formation of granular materials using anisotropy of magnetic susceptibility

The structure of granular materials is one of the most important influential factors in mechanical behaviors. A few inevitable limitations exist in current optical measuring techniques, such as structure disturbance, operational complexity, and high cost. This study attempts to take a new application of the anisotropy of magnetic susceptibility (AMS) technique to investigate the structure of granular materials. To illustrate the feasibility of the AMS in detecting the structure, each of five different kinds of sand, including beach sand, river sand, aeolian sand, and calcareous sand, was reconstituted by moist tamping method and air pluviation method, respectively. Based on the structural features obtained from the optical and the AMS techniques, the validity and applicability of the AMS technique on granular materials with different magnetic mineral compositions were discussed systematically. It is found that the AMS technique is a feasible and efficient method to investigate the structure of granular materials both in laboratory tests and field sampling tests.

Combining mechanisms of black carbon and magnetic minerals in power plant fly ash

Black carbon (BC), one of the pollutants emitted from fossil fuel combustion, is closely associated with minerals and other hazardous substances. To date, little is known about the mechanisms between BC and magnetic minerals. Accordingly, further investigating the association between magnetic minerals and BC is necessary. In this work, the extraction of BC from fly ash and the magnetic fraction from BC was achieved by flotation and magnetic separation, respectively. The morphology, mineralogical composition, and magnetic properties of BC and magnetic fraction were characterized by FTIR, XRD, SEM-EDS, and vibrating sample magnetometer (VSM). The results show that BC and magnetic minerals have similar mineral compositions, rich in quartz, mullite, magnetite, and hematite. The magnetic minerals have prominent spherical characteristics and are distributed on the surface and inside the pores of BC with irregular honeycomb features. The VSM and XRD analyses show that Fe3O4 is the primary magnetic material. Moreover, large amounts of C, O, and Fe around and on the surface of magnetic spheres were detected by EDS, indicating that the spherical particles may be the structure of BC-coated Fe3O4. Pyrolysis experiments showed that the yield of the magnetic fraction in the pyrolysis product reached 60 %, far exceeding the theoretical yield of 12 % based on 5 % of doped Fe. This further proves that Fe3O4 was combined with a large number of organics during its formation, which may be due to coating and chemical adsorption. Quantum chemical calculations also confirmed this chemical adsorption between Fe3O4 with BC based on density flooding theory, in which adsorption energies ranged from −213.374 KJ/mol to −827.741 KJ/mol.

Large-scale geological structures of the Egyptian Nubian Shield

Integration of potential field- and structural data make it possible to trace surface and subsurface large-scale geological structures of the Egyptian Nubian Shield (ENS). Obtained results indicate that the Northern Eastern Desert (NED) of the ENS is dominated by relatively younger (c. 580 Ma) E–W and NE–SW trending extensional structures that were controlled by the evolution and retreat of the Cadomian Arc. Density of such extensional structures increases with depth as displayed by the potential data. The prevailing structural trends in the Central Eastern Desert (CED) are NW–SE and WNW–ESE. Both trends are highly prompted by the timing of deformation upon the Najd Fault System, and are themselves dissected by a relatively younger NE–SW shearing trend. Lineament density in the CED is subordinate for both subsurface and near surface structures. The South Eastern Desert exhibits compressional and extrusion-related structures of two main prominent trends; WNW-to-NW (to the western part) and the N-, NNE- to NE (to the eastern part). The previously mentioned Neoproterozoic trends are remarkably influenced by the Oligocene–Miocene Red Sea-Gulf of Suez rift related fractures in the vicinity of the rift shoulder. The remarkable change in trends and densities of structural trends, especially in the NED, is interpreted in terms of concealing of the older structures by the younger extensional structures which in turns reflect an N-ward progressive deformation in the entire ENS. Gravity data are more appropriate in delineating the structural trends compared to the magnetic data which are largely affected by lithological variations and/or alteration zones and magnetic mineralogy.

Magnetic properties of gas hydrate-bearing sediments and their association with iron geochemistry in the Sea of Marmara, Turkey

The anaerobic oxidation of methane, a key geochemical process that is involved in the cycling of sulfate and iron (oxyhydr)oxides in marine sediments, results in the formation of iron sulfides. Although ferrimagnetic iron sulfides have been identified in seepage systems, the link between iron migration and sediment magnetic properties remains poorly understood. Here, we investigate two cores from the Sea of Marmara to evaluate biogeochemical iron cycling and iron sulfide mineralogy in gas hydrate-bearing sediments. Magnetic analyses indicate the presence of greigite and pyrrhotite in a core from a hydrate-rich site with a high hydrocarbon flux, which contrasts with a lack of these minerals in a core characterized by only mild seepage. This is supported by the results of rock magnetic and scanning electron microscope analyses of the sediments. The presence of authigenic greigite is critical for assessing local redox records and together with the occurrence of monoclinic pyrrhotite may suggest specific diagenetic processes in gas hydrate environments. Our analysis demonstrates the usefulness of these ferrimagnetic minerals, with a high saturation isothermal remanent magnetization to magnetic susceptibility ratio (SIRM/χ > 15 kAm−1) and a high index of hysteresis parameters (DJH > 0.2) indicative of magnetic mineralogy changes, for evaluating variability in the intensity of seepage fluxes and for estimating gas hydrate distributions.

Environmental Magnetic Characteristics and Heavy Metal Pollution Assessment of Sediments in the Le’an River, China

Environmental magnetism parameters have become a useful tool in addressing environmental issues. Due to the rapid, sensitive, economical and non-destructive characteristics of environmental magnetism, the present contribution focuses on magnetism parameters as proxy for heavy metal pollution, especially from their relationship with contents of heavy metal. We evaluated heavy metals pollution and examined environmental magnetism in the Dexing section of the Le’an River. The pollution load index (PLI) of Cr, Pb, As, Cu and Zn, as well as the concentration of other heavy metals, were analyzed, and the magnetic indexes of various sediments were analyzed. The results showed that the concentrations of all heavy metals far exceeded the local background values, and that the average contamination factor of Cu was as high as 22.88, making it the element of most serious contamination. The problem of heavy metal pollution near the mine is very serious. The content of magnetic minerals in sediments of Le’an River is relatively high and the composition of magnetic minerals is relatively stable. The stable-single domin (SSD) content is high at S1 and S10, indicating that ferromagnetic mineral content is relatively rich here, which dominates the magnetic characteristics of the sample. In general, it was found that environmental magnetism indicators did not exist in the Dexing section of the Le’an River that could clearly indicate the concentration of heavy metal pollution. Only a few heavy metals can be effectively indicated by magnetic parameters. IRM-20mT and S-ratio can be used as indicators of Cr, Pb, As, Cu and Zn, but they are not accurate. The correlation between Sr and magnetic indexes IRM200mT, IRM300mT, SIRM, IRM-300mT and HIRM is significant, which can be used as an indicator of Sr concentration. IRM20mT can also be used as an indicator of Hg concentration.