Magnetic susceptibility variations of the Edicaran cap carbonates in the Yangtze platform and their implications for paleoclimate

Magnetic susceptibility(MS)data were obtained from 11 sections of the Doushantuo(Edicaran)cap carbonate that directly overlies the Nantuo glacial diamictite in the southeastern margin of the Yangtze plat-form.The MS data revealed two regionally correlatable peaks at the bottom and top of the cap carbonate,sepa-rated by an interval of low values.The lower MS peak coincides with high percentage of insoluble siliciclastic residues that are compositionally identical to the matrix of the underlying diamictite,suggesting its origin con-trolled mainly by detrital components during the first phase of cap carbonate deposition at the end of the glacia-tion.The upper MS peak is associated with high clay content and iron sulfides,and can be interpreted as either derived from enhanced greenhouse weathering that could have brought more terrigenous components into the ocean,or the result of ocean anoxia at the late stage of cap carbonate deposition that could led to formation of abundant iron sulfides.The regionally consistent MS curves from the cap carbonates provided the first geo-physical record for the rapid climate change from icehouse to greenhouse conditions in the aftermath of the Neoproterozoic“snowball Earth”event.

Fabric characteristics of in situ sand with/without liquefaction verified by anisotropy of magnetic susceptibility

It is well known that fabric of sand may significantly affect mechanical behaviors and liquefaction resistance of sand.Various optical techniques are currently utilized to visualize the fabric,especially the distribution of the long axis of soil particles.However,none of these methods provides an ideal solution in laboratory tests and in situ observation.In this study,anisotropy of magnetic susceptibility(AMS)was first proposed as a convenient and efficient way to evaluate the liquefaction of clean sand.At first,investigations with scanning electron microscopy(SEM)and AMS were simultaneously conducted on two groups of soil specimens with different initial fabrics to verify the feasibility of the AMS technique.Then,80 in situ samples were collected to analyze the feature of liquefied and non-liquefied sand layers through AMS tests.It is clearly known from the test results that the natural sedimentary fabric was destroyed during liquefaction and the fabric anisotropy was greatly changed after liquefaction.The feasibility of evaluating soil fabric using the AMS survey was verified by the laboratory tests.Furthermore,the applicability of AMS in detecting liquefied layer in situ was confirmed for the first time.

Magnetic susceptibility of the Xifeng section and its paleoclimate significance

Magnetic susceptibility (MS) is one of the most important indicators of the East- Asia summer monsoon. Presented in this study is a high resolution magnetic susceptibility record from the Xifeng section, which consists of Quaternary loess-paleosol sequence and Pliocene red clay. Variations in magnetic susceptibility are well correlated with the δ18O record in deep-sea sediments and the eolian flux of Greenland. The climatic evolution in the Xifeng section shows that since the Late Tertiary, the driving force of the East-Asia paleo-monsoon is correlated with solar radiation on a 10-ka time scale .

Changes in magnetic susceptibility and grain size of Holocene sediments of the Pearl River estuary and climate changes reflected by them

Through the Pearl River Estuary Wan Qing-sha W2 core AMS 14^C dating of sediments, combining with paleomagnetic test, pollen analysis, and comprehensive comparison with other relevant records, the regional framework of Holocene age was established. Using the combined feature grain size and magnetic susceptibility proxies for the environment, climate change information in the area since about 6 000 cal yr BP was obtained. The result showed the area since the middle Holocene had experienced three stages climate changes of warm and dry - cool and wet temperature and humidity South area of China in the late Holocene climate （especially rainfall） had important changes, corresponding to the Northern Hemisphere solar radiation reducing, air temperature decreasing, Asian monsoon weakening, and it had close ties with activities to strengthen El Nino - Southern Oscillation events.

Millennial-centennial Scales Climate Changes of Holocene Indicated by Magnetic Susceptibility of High-resolution Section in Salawusu River Valley, China

The upmost segment （Holocene series） of the Milanggouwan stratigraphic section （MGS 1） in the Salawusu River valley shows 11 sedimentary cycles of dune sands and fluvio-lacustrine facies, or dune sands and paleosols. The analysis of the magnetic susceptibility of this segment suggests that there are 11 magnetic susceptibility cycles with the value alternating from low to high, in which the layers of the dune sands correspond to the lower value of the magnetic susceptibility and the layers of fluvio-lacustrine facies and paleosols correspond to the higher peaks. The study reveals that the low and high magnetic susceptibility values indicate the climate dominated by cold-arid winter monsoon and warm-humid summer monsoon of East Asia, respectively, and the study area has experienced at least 22 times of milleunial-centennial scales climate alternation from the cold-arid to the warm-humid during the Holocene. In terms of the time and the climate nature, the variations basically correspond to those of the North Atlantic and some records of cold-warm changes in China as well. They might be caused by the alternation of winter and summer monsoons in the Mu Us Desert induced by global climate fluctuations in the Holocene.

Early Cretaceous Climate Changes Recorded in Magnetic Susceptibility and Color Index Variations of the Lower Liupanshan Group, Central China

This study carried out comprehensive analysis on sedimentology, magnetic susceptibility （7of） and color data of the continental sediments of the Liupanshan Group in Central China so as to obtain climatic change information during the 129.14-122.98 Ma interval. Based on the results of the Xlf and of the redness （a＊）, the section can be divided into two segments： （1） 129.14-126.3 Ma, with the lowest Xlf values and strongly variable relatively high values of redness and （2） 126.3-122.98 Ma, with high Elf values and relatively low redness. Analysis of the lithology and facies as well as the magnetic minerals and their contents points to a detrital origin of the magnetic minerals and this allow us to interpret the relationship between magnetic susceptibility variations and climate changes. Our study shows that the climate was significantly dry and hot during the whole studied interval although the interval between 126.3 Ma and 122.98 was a little bit cooler with increased humidity.

Characteristics of the Density and Magnetic Susceptibility of Rocks in Northern Borneo and their Constraints on the Lithologic Identification of the Mesozoic Rocks in the Southern South China Sea

Based on the volume magnetic susceptibility and specific gravity measurements and mineral and lithologic identification results for 540 samples,the rock type,density,and magnetic susceptibility of rocks from northern Borneo were analyzed,and the applicability of gravity and magnetic data to the lithologic identification of the Mesozoic strata in the southern South China Sea was assessed accordingly.The results show that there are 3 types and 25 subtypes of rocks in northern Borneo,mainly intermediate-mafic igneous rocks and exogenous clastic sedimentary rocks,with small amounts of endogenous sedimentary rocks,felsic igneous rocks,and metamorphic rocks.The rocks that are very strongly-strongly magnetic and have high-medium densities are mostly igneous rocks,tuffaceous sandstones,and their metamorphic equivalents.The rocks that are weakly magnetic-non-magnetic and have medium-very low densities are mostly conglomerates,sandstones,siltstones,mudstones,and coal.The rocks that are weakly magnetic-diamagnetic and have highmedium densities are mostly limestones and siliceous rocks.The Cenozoic rocks are characterized by low densities and medium susceptibilities;the Mesozoic rocks are characterized by medium densities and medium-high susceptibilities;and the pre-Mesozoic rocks are characterized by high densities and low magnetism.Based on these results and the distribution characteristics of the various rock types,it was found that the pre-Mesozoic rocks produce weak regional gravity anomalies;the Mesozoic sedimentary rocks produce negative regional gravity anomalies;whereas the Mesozoic igneous rocks produce positive regional gravity anomalies;and the Cenozoic igneous rocks produce positive regional gravity anomalies.The regional high magnetic anomalies in the southern part of the South China Sea originate from the Mesozoic mafic igneous rocks and their metamorphic equivalents;and the regional medium magnetic anomalies may be produced by the felsic igneous rocks and their metamorphic equivalents.Accordingly,the identification of the Mesozoic lithology in the southern South China Sea shows that the Mesozoic sedimentary rocks are distributed over a large area of the southern South China Sea.Thus,it is concluded that the Mesozoic strata in this area have the potential for oil and gas exploration.

Where are the Volcanic Calderas in the Xiangshan Volcanic Basin of Jiangxi？ Implications from Anisotropy of Magnetic Susceptibility

Objective As the world＇s third largest volcanic type uranium ore field,the Xiangshan volcanic basin has attracted much attention for its large industrial value.The ore hosting rocks are mainly the early Cretaceous rhyodacite and porphyroclastic lava,as well as small amounts of high level intrusive acidic rocks and metamorphic rocks.

A New Model for Correlation between the Marine Benthic Oxygen Isotope and Red Clay Magnetic Susceptibility on the Chinese Loess Plateau

Objective Aeolian sediments on the Chinese Loess Plateau contain some of the best continental archives of palaeoclimate change in the Late Cenozoic. The consensus that alternating MS in loess-paleosols in China was due to the strengthening and weakening of the East Asian palaeomonsoon provides an excellent climate record when correlated with global ice volume. Significantly, new basal dates from the red clay underlying the loess-paleosol sequence indicate that wind-blown dust began to accumulate on the Chinese Loess Plateau at least 22 million years ago. There are differences of opinion,

EPR and Magnetic Susceptibility Investigation of Fe Ions in B_2O_3-SrF_2 Glass Matrix

The structural and magnetic properties of an oxide-fluoride mixed vitreous matrix 2B2O3-SrF2, were explored by using Fe impurities as probes. Information about the structural units involving iron ions, their valence state, the strengths and type of interactions involving them was obtained using EPR spectroscopy and magnetic susceptibility measurements.

Magnetic susceptibility measurements on metakaolin admixtured cement hydrated with ground water and sea water

The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of metakaolin and in a water/cement （W/C） ratio of 0.4 were prepared. The susceptibility at different hydration periods was determined by Faraday Curie balance and it was related to the changes in setting time and compressive strength of admixtured cement. Compared with sea water-treated cement paste, the magnetic susceptibility of ground water-treated cement paste is higher in value. The observed result shows that, irrespective of water, the magnetic susceptibility increases with increasing metakaolin percentage replacement level in cement.

Low symmetry aspects in spectroscopic and magnetic susceptibility studies of Tb^(3+)(4f^8) in TbAlO_3

The three sets of crystal field parameters （CFPs） obtained from spectroscopic and magnetic susceptibility studies of Tb3＋（4f^8） ions in TbAlO3 by Gruber et al. （J. Lumin. 128 （2008） 1271） were reanalyzed. These sets, fitted from experimental energy levels, are physically equivalent and correspond to specific choices of the axis system. Proper interpretation of experimental data for Tb3＋ ions at monoclinic C8 symmetry sites in TbAlO3 crystal requires clarification of several intricate low syrmnetry aspects, namely, （a） three equivalent forms of monoclinic CF Hamiltouian, （b） relative orientation of the crystallographic axis system w.r.t, the symmetry-adapted axis system, （c） monoclinic standardization of CFPs, （d） distinction between the actual and apparent low symmetry effects exhibited by CFPs, and （e） nominal nature of all fitted CFP sets. For this purpose, modeling of CFPs for Tb3＋ in TbAlO3 was carried out using at the first stage only the Coulomb, i.e. point charge, eonlribntions in the exchange charge model. The point charge model calculated CFPs disagree with the experimental CFPs, especially the rank k=6 CFPs. To explain this discrepancy and to verify the correcmess of the theoretical CFP calculations additionally the superposition model was employed. The methods of analysis and modeling of CFP sets for monoclinic symmetry cases proposed here proved useful for the studied case as well as might be used for other ion-host systems exhibiting monoclinic or triclinic local site symmetry. Partial results for Tb3＋ ions in TbAlO3 were presented here, whereas detailed results were given in a follow-up paper.

EPR and Magnetic Susceptibility Studies of Cr^(3+) Ions in the 70TeO_2·25B_2O_3·5PbO Glass Matrix

By using EPR and magnetic susceptibility measurements, the Cr ion distribution in the xCr2O3.(1-x)[70TeO2·25B2O3·5PbO] glasses with 0＜x≤20 mol% was studied. EPR investigation evidencedthe presence of Cr3+ ions in agreement with the experimentally obtained atomic magnetic moment values. For concentrations x≤3 mol%, the isolated Cr3+ ions coexist with those coupledby dipole-dipole interactions. For x＞3 mol%, the Cr3+ ions participate in superexchange interactions and are predominantly antiferromagnetically coupled.

EPR and Magnetic Susceptibility Investigations of Fe Containing TeO_2-B_2O_3-SrF_2 Glasses

Iron ions were used as probes to explore the structural and magnetic properties of 70TeO2'25B2O3' 5SrF2 vitreous matrix. The distribution of Fe3+ ions on different structural aggregates was revealed by means of EPR, as depending on Fe2O3 concentration. Strongly distorted octahedral sites were detected for the isolated paramagnetic ions, and also clusters of Fe ions especially at high Fe2O3 content of samples. Magnetic susceptibility measurements evidenced both dipoledipole and superexchange type interactions involving iron ions. Mixed valence states of iron ions were also detected

Climatic periodicities recorded in lake sediment magnetic susceptibility data:Further evidence for solar forcing on Indian summer monsoon

The Indian summer monsoon exhibits considerable spatio-temporal variability.It is therefore important to understand its dynamics and the inherent periodicities.In this study,we have performed spectral and wavelet analyses of magnetic susceptibility data for sediments from Thimmannanayakanakere(TK)-a small lake in southern India.The main objective of this investigation is to identify and explain the possible origin of the prominent periodicities present in the magnetic susceptibility data.Significant periodicities in the TK χ_(lf)data are centered at 906,232,147,128,96,61,54 and 44 years,which might have a solar origin.The wavelet power spectrum of the raw and detrended χ_(lf)data confirms the findings of spectral analysis and also provides temporal variations of the significant cyclicities during the past3700 cal.years B.P.Positive correlation is documented between sunspot activity and TK xif data;crossspectral analysis of the reconstructed sunspot data and TK xif data suggest that there is a strong coherence between the two datasets as significant periodicities are documented in both.There is a good match between the TK xif and the reconstructed total solar irradiance data for the past 1200 years.However,an out-of-phase relationship is documented at certain time-intervals,which may be attributed to uncertainties in the age-depth model.The results obtained from this study show that solar variations are the main controlling factor of the southwest monsoon and,like other archives from different regions in India,the TK lake sediments have also recorded these solar signatures.

Contribution of the Magnetic Susceptibility to the Characterization of the Babouri-Figuil Cretaceous Basin

Magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion. This work, aims to show that, the magnetic susceptibility signature which exists in the cretaceous sediments of the Babouri-Figuil basin, resides mainly in the detrital constituents. Variations of amplitudes are observed, which can be useful for regional correlation.This amplitude variation results in the transgressive and regressive movements that give way to a fluctuation of detrital deposits because of erosion. Considering the sedimentological study, carried out, different microfacies have been identified in the basin, namely, fluvial facies and lake facies that sometimes contain fossils. The combination of detailed sedimentological analysis and sequence stratigraphy is based on the modeling of vertical and lateral variations within the basin. Finally, the interpretation of the magnetic susceptibility signal suggests that in the detrital domain, this signal is mainly controlled by environmental parameters such as the agitation of the water and the rate of sedimentation, as well as diagenesis.

Mathematical Model of Anisotropy of Magnetic Susceptibility (AMS)

Magnetic susceptibility of natural rocks and ores is important in many applications. In a few rock types magnetic susceptibility is independent of the direction in which a weak magnetic field is applied. Such rocks are magnetically isotropic. In most rock types, however, the magnitude of magnetic susceptibility in a constant weak field depends on the orientation of the magnetic field applied. Such rocks are magnetically anisotropic and such directional variation in magnetic susceptibility with these rocks is termed as anisotropy of magnetic susceptibility (AMS). Although attempts have been made on describing AMS using mathematical models, there is still a need to present a more consistent and united mathematical process for AMS. This paper presents a united AMS model by rationalizing the existing pieces of different AMS models through a consistent approach. A few examples of AMS from some types of natural rocks and ores are also presented to substantiate this united AMS model.

Magnetic susceptibility inversion method with full tensor gradient data using low-temperature SQUIDs

Full tensor magnetic gradient measurements are available nowadays. These are essential for determining magnetization parameters in deep layers. Using full or partial tensor magnetic gradient measurements to determine the subsurface properties, e.g., magnetic susceptibility, is an inverse problem. Inversion using total magnetic intensity data is a traditional way.Because of di culty in obtaining the practical full tensor magnetic gradient data, the corresponding inversion results are not so widely reported. With the development of superconducting quantum interference devices(SQUIDs), we can acquire the full tensor magnetic gradient data through field measurements. In this paper, we study the inverse problem of retrieving magnetic susceptibility with the field data using our designed low-temperature SQUIDs. The solving methodology based on sparse regularization and an alternating directions method of multipliers is established. Numerical and field data experiments are performed to show the feasibility of our algorithm.

Heavy Metals in Urban Soils of Xuzhou, China: Spatial Distribution and Correlation to Specific Magnetic Susceptibility

The investigation of the anthropogenic contamination by heavy metals of soils is very important for environmental planning and monitoring in urban areas. In the present study, surface soils (0-20 cm) samples from 167 sampling sites in Xuzhou (China) were collected in 2010 and analyzed for heavy metals including Zn, Pb, Fe, Mn, Cu, Cd, Sr, Ba Cr, Ni and Mo via inductively coupled plasma/mass spectrometry (ICP-MS). Compared with their levels in natural soils of China, these metals investigated exhibited a slight build-up in Xuzhou topsoils. The multivariate statistical analyses including factor analysis (FA) and cluster analysis (CA) were performed. The obtained results enabled the identification of two main groups of metals, discriminating Ni, Mo and Cr from Zn, Pb, Fe, Mn, Cu, Cd, Sr and Ba. Signifcant associations between Pb, Zn, Fe and specific magnetic susceptibility (c) indicated that specific susceptibility can serve as proxies for these metals levels in Xuzhou urban soils.

ANISOTROPY OF MAGNETIC SUSCEPTIBILITY AND IDENTIFICATION OF TILTED SEDIMENT CORES FROM THE BOHAI SEA

Anisotropy of magnetic susceptibility (AMS) is a well-developed technique increaseingly used in petro-fabric determination. ItS application to two Mackereth cores JX91-2A and JX91-2B, taken from thesame site in the central Bohai Sea, revealed 3D magnetic fabrics of the sediments as expressed with susce-ptibility ellipsoids. The flat seafloor and the relatively quiet depositional environment in the semi-isolatedBohai Sea should asult in a primary fabric with horisontally obate susocptibility el1ipsoids. Mormwr,the inaxing downcore totaI anisotropy comprising mainly of magntic foliation nsulting fIrom sedimentcompaction should also lead to flat ellipsoids. Therefore, the off-pole meam dindions of minimurn axes ofaseptibility ellipsoids on stermnets must indicate that the two coas are ti]ted re1ative to the flat anfloor.Use of Fisher statisties showh the tilt angles to be 14° for JX91-2A and 23°for JX91 -2B from whichthe tna depths of the coas were dedded accordingly.