the anisotropy of magnetic susceptibility in biotite muscovite and chlorite single crystals the anisotropy of magnetic susceptibility ams of single crystals of biotite muscovite and chlorite has been measured in order to provide accurate values of the magnetic anisotropy properties for these common rock forming minerals the low field ams and the high field paramagnetic susceptibility are defined for the high field values it is necessary to combine the paramagnetic deviatoric tensor obtained from the high field torque magnetometer with the paramagnetic bulk susceptibility measured from magnetization curves of the crystals this leads to the full paramagnetic susceptibility ellipsoid due to the anisotropic distribution of iron cations in the silicate lattice the ellipsoid of paramagnetic susceptibility which was obtained for the three phyllosilicates is highly oblate in shape and the minimum susceptibility direction is subparallel to the crystallographic c axes the anisotropy of the susceptibility within the basal plane of the biotite has been evaluated and found to be isotropic within the accuracy of the instrumental measurements the degree of anisotropy of biotite and chlorite is compatible with previously reported values while for muscovite is smaller than previously published values the shape of the chlorite ams ellipsoid for all the samples is near perfect oblate in contrast with a wide distribution of oblate and prolate values reported in earlier studies reliable values are important for deriving models of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks d 2003 elsevier science b v all rights reserved

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

a short reverse polarity interval within the jaramillo subchron evidence from the jingbian section northern chinese loess plateau 1 a high resolution paleomagnetic and rock magnetic investigation supported by scanning electron microscopy observations x ray diffraction determinations and anisotropy of magnetic susceptibility analyses has been carried out on a loess paleosol sequence from jingbian 37 4 n 108 8 e at the northern extremity of the chinese loess plateau the results indicate that the magnetic assemblage is dominated by pseudo single domain magnetite with associated maghemite and traces of a higher coercivity phase probably hematite the brunhes matuyama and upper jaramillo transitions have been carefully documented and a record of a short reverse polarity interval sri entirely within the jaramillo normal polarity subchron has been obtained the duration of the sri recorded over a stratigraphic interval of 48 cm is 10 1 kyr 29 kyr if the polarity transitions are included these results seem to exclude that rock magnetic variations are adversely affecting the recording process and compel us to reconsider the jaramillo subchron as characterized by a pair of normal polarity intervals interrupted by a short reverse polarity interval

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

revisiting the stratigraphic position of the matuyama brunhes geomagnetic polarity boundary in chinese loess article i nfo it is commonly accepted that the climate records in chinese loess can be correlated well with that in marine sediments however discrepancies for the stratigraphic position of paleomagnetic polarity reversal boundary seriously restrict an accurate teleconnection between these two archives for example the exact stratigraphic position of the whole matuyama brunhes mb transitional polarity zone remains uncertain in chinese loess in this study an accurate transitional zone of the mb reversal from the mangshan profile southeast margin of the chinese loess plateau clp was statistically determined using multiple subsets of parallel samples by integrating results from the central clp the whole mb transitional zone is consistently located across the pedostratigraphic and climatostratigraphic transitional zones between s8 and l8 over a wide region of the clp this conclusion further supports that the paleosol unit s8 should be teleconnected to the marine oxygen isotope stage 19 rather than 21 and thus unambiguously supplies an accurate age control in constructing a new loess time scale

multiple rapid polarity swings during the matuyama brunhes transition from two high resolution loess paleosol records 1 two high resolution magnetic records of the matuyama brunhes m b transition have been obtained from xifeng and baoji loess paleosol sequences in the chinese loess plateau the results of stepwise thermal and alternating field af demagnetizations confirm that both treatments are effective in isolating characteristic remanent magnetization chrm from specimens of loess paleosol sediments which suffer from weak pedogenesis and that af demagnetization clearly fails to isolate chrm from specimens of paleosol sediments which have undergone strong pedogenesis on the basis of virtual geomagnetic pole latitudes crossing the virtual geomagnetic equator the m b transition involves at least 15 rapid polarity swings rock magnetic experiments and anisotropy of low field magnetic susceptibility show that high frequency polarity swings during the m b transition cannot be attributed to rock magnetic and or sedimentary causes extrapolating a constant accumulation rate between the jaramillo matuyama and m b boundary ages the m b transition interval of both the xifeng and baoji sections is estimated to have a duration of more than 10 kyr durations of each short polarity interval are estimated to range from about 0 3 to 5 6 kyr our new results combined with previous paleomagnetic observations from lavas and marine sediments suggest that multiple rapid polarity swings occurred during the m b transition

divergent trends in land and ocean temperature in the southern ocean over the past 18 000 years reconstructions of land and ocean temperatures over the past 18 000 years in the high southern latitudes have shown conflicting trends analyses of temperatures on campbell island south of new zealand confirm this behaviour and lead to the suggestion that it reflects changes in the position and intensity of the westerly winds over the past 18 000 years sea surface temperatures for the southern ocean do not align with those of the adjacent high latitude landmasses during the late glacial period the ocean surface warmed rapidly to present day temperatures1 whereas the land warmed only slowly as evidenced by the lagged response of forest and glaciers2 3 however in the holocene epoch land based records suggest strong warming whereas marine records indicate that ocean surface temperatures cooled here we present reconstructions of summer temperature for campbell island in the southern ocean over the past 16 500 years based on fossil pollen we find a pronounced warming 12 500 11 000 years ago a cooling until 9 200 years ago and a rapid warming to a peak between 6 000 and 5 000 years ago followed by minor cool intervals from 5 200 4 000 3 000 1 700 and 700 100 years ago as expected our temperature reconstructions show a late glacial lag behind nearby records of sea surface temperature6 7 and opposing trends in the holocene we suggest that this discrepancy arises because land based reconstructions record summer temperatures whereas marine proxies generally reflect annual temperatures we conclude that the divergence of the records therefore reflects changes in the seasonality of atmospheric heat transport as atmospheric heat transport is tied to the southern hemisphere westerly winds we attribute our observed changes to shifts in the position and intensity of the southern westerlies

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

the chinese loess in xifeng i the primary study on magnetostratigraphy of a loess profile in xifeng area gansu province summary 1848 specimens were collected systematically from about 900 horizons in the loess profile of xifeng gansu province china the magnetostratigraphy is established on the basis of the palaeomagnetic results after thermal cleaning usually at 300 c this result has been found to be generally consistent with previous work in luochuan the susceptibility varies regularly with the appearance of loess and palaeosol in the profile and thus could be used as a criterion to classify the loess and palaeosol sequence

magnetic enhancement and palaeoclimate study of a loess palaeosol couplet across the loess plateau of china summary the origin of the milankovitch palaeoclimatic signal so dramatically recorded in the chinese loess remains uncertain at least five hypotheses have been put forward to explain the well documented enhancement of magnetic susceptibility in palaeosols which formed when conditions were warmer and wetter we report here a magnetic study of a prominent loess soil couplet l4 s3 at three widely separated sites where present day mean annual rainfall and temperature range from 350mm to 700mm and from 6 c to 13 c the properties determined are laboratory remanences isothermal irm anhysteretic arm viscous vrm including viscous decay room temperature susceptibility and thermomagnetic behaviour at fields beyond 100 mt the irm spectra are all essentially identical both in shape and in absolute magnitude suggesting a uniform magnetic component widespread across the plateau subtracting the signal of this component isolates a second component the amount of which varies by an order of magnitude between sites the magnetic properties of this latter material are remarkably similar to those reported for bacterial magnetite in geological sediments and modern soils viscous decay of vrm takes place in two distinct stages one of which falls to zero in 10min we attribute magnetic enhancement which is the source of the palaeoclimatic signal to in situ pedogenetic formation of magnetite which we characterize in our interpretation as two separate forms of bacterial magnetofossils the most magnetic sample requires a mass fraction of about half of one per cent of this biogenic material

reliability of the natural remanent magnetization recorded in chinese loess 1 chinese loess paleosol sequences undoubtedly have recorded geomagnetic events both polarity reversals and excursions however the fidelity of the rapid paleomagnetic field oscillations during a polarity reversal remains uncertain to test the reliability and consistency of the natural remanent magnetization records in chinese loess 10 subsets of parallel samples across the matuyama brunhes mb reversal boundary were obtained from the luochuan region in the hinterland of the chinese loess plateau our paleomagnetic results show diversified virtual geomagnetic poles vgps during the mb transition but consistent vgps outside of the transitional zone the anisotropy of magnetic susceptibility and rock magnetism results indicate that the sampled interval is rather uniform and undisturbed the discrepancies of the characteristic remanent magnetization within the mb transition are probably due to the low efficiency in aligning magnetic grains mainly pseudo single domain magnetite associated with the low field intensity nevertheless the stratigraphic location of the mb boundary can be confidently defined therefore we conclude that chinese loess paleosol sequences can record geomagnetic reversal events but the morphology within the polarity transition is rather questionable

a new model for transformation of ferrihydrite to hematite in soils and sediments this study was supported by the national key research and development program of china 2016yfa0601903 and the national natural science foundation of china grants 41504055 and 41430962 roberts acknowledges support from the australian research council grants dp110105419 and dp120103952

detrital and pedogenic magnetic mineral phases in the loess palaeosol sequence at lingtai central chinese loess plateau abstract a detailed rock magnetic investigation of loess palaeosol samples from the section at lingtai on the central chinese loess plateau clp is presented thermal demagnetisation of isothermal remanent magnetisation irm and curie temperature measurements suggest the presence of magnetite maghemite and hematite as remanence carrying components bulk and grain size fractionated samples have been analysed using coercivity spectra of remanence acquisition demagnetisation curves which identify four main remanence carriers in different grain size fractions of loesses and palaeosols a linear source mixing model quantifies the contribution of the four components which have been experimentally derived as dominating endmembers in specific grain size fractions up to two thirds of the total irm of the palaeosols are due to slightly oxidised pedogenic magnetite two detrital components dominate up to 90 of the irm of the loess samples and are ascribed to maghemite of different oxidation degree detrital hematite is present in all samples and contributes up to 10 of the irm the iron content of the grain size fractions gives evidence that iron in pedogenically grown remanence carriers does not originate from the detrital iron oxides but rather from iron bearing clays and mafic silicates the contribution of pedogenic magnetite to the bulk irm increases with the increasing degree of pedogenesis which depends in turn on climate change

magnetic mineral diagenesis abstract reduction oxidation redox reactions occur during burial because sediments contain reactive mixtures of oxidised and reduced components diagenetic chemical reactions represent the approach of all sedimentary components toward equilibrium and control the long term stability of sedimentary iron bearing minerals magnetic minerals are sensitive indicators of sedimentary redox conditions and of changes in these conditions through time with diagenetic effects ranging from subtle to pervasive despite the importance of magnetic mineral diagenesis in paleomagnetism rock magnetism and environmental magnetism and the usefulness of these subjects in the earth and environmental sciences there is no systematic single published treatment of magnetic mineral diagenesis this paper is an attempt to provide such a treatment for the full range of diagenetic environments magnetic mineral diagenesis during early burial is driven largely by chemical changes associated with organic matter degradation in a succession of environments that range from oxic to nitrogenous to manganiferous to ferruginous to sulphidic to methanic where the free energy yielded by different oxidants decreases progressively in each environment in oxic environments the most important diagenetic processes involve surface oxidation of detrital minerals and precipitation of fe3 bearing minerals from solution in ferruginous environments the most reactive detrital and authigenic iron oxides undergo dissolution often mediated by dissimilatory iron reducing bacteria which releases fe2 that becomes available for other reactions the fe2 in solution can diffuse upward where it is oxidised to form new authigenic iron oxyhydr oxide minerals or it can become bioavailable to enable magnetotactic bacteria to biomineralise magnetite generally at the base of the overlying nitrogenous zone alternatively dissimilatory iron reducing bacteria can produce extracellular magnetite within ferruginous environments in sulphidic environments iron bearing detrital mineral assemblages undergo more radical alteration hydrogen sulphide which is a byproduct of bacterial sulphate reduction or of anaerobic oxidation of methane reacts with the fe2 released from iron mineral dissolution or directly with solid iron oxyhydr oxide minerals to form iron sulphide minerals mackinawite greigite and pyrite authigenic growth of ferrimagnetic greigite has important implications for paleomagnetic recording secondary iron sulphide formation can also occur as a result of anaerobic oxidation of methane methane migration through sediments in association with biogenic or thermogenic methane production or in association with gas hydrate dissociation can disrupt the diagenetic steady state and give rise to greigite and monoclinic pyrrhotite formation that remagnetises sediments most of the above described diagenetic processes occur below 50 c with continuing burial above 50 c but at sub metamorphic temperatures magnetic minerals can undergo further thermally induced chemical changes that give rise to a wide range of mineralogical transformations that affect the magnetic record of the host sediment these changes include remagnetisations magnetic analysis can provide much valuable information concerning diagenesis in environmental processes the range of processes discussed in this paper should assist researchers in analysing sediment magnetic properties for which the assessment of diagenetic effects has become a necessary component

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

sem study of authigenic rutile anatase and brookite in proterozoic sandstones from sweden abstract scanning electron microscopic examinations revealed interstitial rutile anatase and brookite to be common in upper proterozoic sandstones of the visingso group in southern sweden anatase is observed as either single discrete crystals or as numerous crystals filling and lining pore space rutile and brookite occur predominantly as clusters of crystals within interstitial cements on detrital grains e g feldspar and quartz or as overgrowths on detrital and authigenic titanium oxides these titanium oxides have been formed diagenetically from percolating pore solutions rich in titanium ions the source of titanium ions is suggested to be mainly detrital fe ti oxides sphene and biotite grains

quantifying grain size distribution of pedogenic magnetic particles in chinese loess and its significance for pedogenesis quaternary glacial interglacial cycles have been imprinted on the chinese loess paleosol sequences through pedogenesis in order to accurately decode the paleoclimatic signals carried by these pedogenic particles it is essential to quantify the pedogenically produced magnetic particles in terms of mineralogy as well as grain size distribution gsd to date the gsd has not been accurately determined because of the dearth of available means for analyzing extremely fine grained nanometer scale pedogenic magnetic particles using low temperature techniques we systematically investigated the temperature dependency of fd defined as 1hz 10hz where 1hz and 10hz are ac magnetic susceptibility measured at 1 and 10 hz respectively from two characteristic loess profiles one located at the western chinese loess plateau and the other in the central plateau on the basis of neel theory for a shape anisotropy dominant grain and experimental analysis at low temperatures a quantitative gsd for pedogenic particles in chinese loess paleosols was constructed we found that the dominant magnetic grain size lies just above the superparamagnetic single domain threshold 20 25 nm and that the gsd is almost independent of the degree of pedogenesis this observation agrees well with other constraints from previous studies this new gsd model improves our understanding of the pedogenic processes in chinese loess enabling further explicit linkage of environmental magnetism to paleoclimate changes

p ed xrf geochemical signatures of a 7300 year old linear band pottery house ditch fill at vrable ve lke lehemby slovakia house inhabitation and post depositional processes abstract over the past decades multi element analyses have become increasingly important for archaeological and geoarchaeological research in particular the recent expansion in availability of portable ed xrf p ed xrf devices has allowed for the fast acquisition of large data sets in the presented paper we evaluate the quantitative measurement capability of a p ed xrf device through comparison with wd xrf sampling drying and homogenization sieving in a case study we measured the elemental contents of the archaeo sediment sequence fill of a trench of a ca 7300 year old linear pottery house at the site of vrable ve lke lehemby in southeastern slovakia based on a model applied at the nearby bronze age settlement mound of fidvar the p content of the archaeo sediment was considered as a proxy of palaeo demography however the measured p contents were much too small to reflect the metabolism of a reasonable number of inhabitants therefore in addition to the possibilities of shorter than expected duration of house occupation and incomplete garbage deposition within the ditches the post depositional settlement history is considered in detail furthermore bio cycling by plants during different subsequent phases of holocene landscape development forested agricultural field use has not been considered extensively in interpretations of the archaeological record so far but might have had a considerable influence on the shallow buried archaeological record a reconsideration of the interpretation of the geochemical record from a nearby bronze age site fidvar is thus suggested

an integrated study of the grain size dependent magnetic mineralogy of the chinese loess paleosol and its environmental significance 1 to investigate the grain size dependent properties of the magnetic minerals in chinese loess paleosol samples touxiangdao xining qinghai province china magnetic extracts were divided into two size fractions by gravitational settling on the basis of hysteresis measurements thermal demagnetization of low temperature saturation isothermal remanent magnetization and nonmagnetic studies sem and xrd we identified magnetic phases both in the grain size fractions of the magnetic extracts and in the less magnetic residues to provide more accurate and complete descriptions of all the magnetic components in the bulk natural samples the results show that the oxidation degree nonstoichiometry of magnetic minerals is strongly affected by both grain size and the paleoclimatic environment in which they were deposited and altered in ascending order of the oxidation degree of our samples we find 1 loess coarse particles lc are multidomain md magnetite with slight oxidation 2 paleosol coarse pc particles are also md magnetite but with a higher oxidation degree compared to lc 3 loess fine lf particles are pseudo single domain psd magnetite with a high oxidation degree and 4 paleosol fine pf particles are psd maghemite single domain sd and superparamagnetic sp maghemite mainly stay in the residues further thermomagnetic analysis of pf psd maghemite revealed that this natural maghemite has a curie temperature identical to that of magnetite and that the conversion efficiency of transformation from maghemite to hematite is only about 50 after a 700 c heating cooling cycle these new results identify the sources of multicomponent nrm in chinese loess sequences as well as clarify the paleoenviromental and paleoclimatic controls on the remanence components

re arrangement of atmospheric circulation at about 2 6 ma over northern china evidence from grain size records of loess palaeosol and red clay sequences abstract recent studies have shown that the red clay sequence underlying the quaternary loess of the chinese loess plateau is wind blown in origin continuous atmospheric dust deposition in the past 7 0 ma has been documented to address the wind system that transported the tertiary red clay two north south transects were studied in the chinese loess plateau one of the transects was designed to study spatial changes in grain size of the last glacial interglacial loess records and the other to observe particle changes of the tertiary red clay underlying the quaternary loess the loess transect consists of nine sections and the red clay transect of four sections analyses of closely spaced samples show that there is a strong southward decrease in grain size of both loess and palaeosol horizons of the late pleistocene which is consistent with the idea that the aeolian materials of the quaternary in the loess plateau are transported by the northerly winter monsoonal winds grain size distribution of the red clay sequences however does not show such a change from north to south along the red clay transect the particle size distribution is almost identical in the four sections suggesting that the winter monsoonal winds might have played a less important role in transporting the red clay material it is suggested that the red clay may have been transported by the westerlies from the dust source regions of northwestern china onto the loess plateau a remarkable re arrangement of atmospheric patterns at about 2 6 ma therefore has been recorded by the red clay loess shift it is speculated that this re arrangement of atmospheric patterns may have been caused by the onset of glaciation in the northern hemisphere

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

new insights into magnetic enhancement mechanism in chinese paleosols article i nfo magneticsusceptibilityof chineseloess paleosolsequenceshasbeenextensivelyusedasareliablepaleoclimatic proxy for reconstruction of the asian summer monsoon system and its enhancement is usually attributed to neoformation of fine grained ferrimagnetic particles via pedogenesis but there is little understanding of either the formation process of such magnetic particles or their actual form and grain sizes to investigate these problems scanning electron microscope observations were conducted on magnetic extracts from pristine loess and strongly pedogenicpaleosol samples from xifeng onthe chineseloess plateau both magneticextracts commonly contained coarse grained detrital magnetite with grain size ranging from a few mt o several tens of m however the magnetic extract from the mature paleosol sample additionally included coarse silicate parti cles with ultrafine ferrimagnetic inclusions while that from the pristine loess sample did not the size of the ferrimagnetic inclusions mainly ranged from tens to hundreds of nanometers the temperature dependent susceptibility and hysteresis loops of the paleosol sample combined with the stratigraphic variations of rock magnetic parameters showed that the pedogenic maghemite inclusions should be a potential contributor to magnetic enhancements in chinese paleosols the fine grained ferrimagnetic inclusions have been pedogenically formed by weathering of coarse grained fe bearing silicate minerals our proposed magnetic enhancement mechanism is consistent with the accepted rock magnetic result that magnetic enhancement in chinese paleosols is caused by pedogenic maghemite grains in superparamagnetic and single domain size regions the presence of ultrafine ferrimagnetic grains as inclusions within coarse silicate particles is also consis tent with han and jiang s 1999 significant experimental result that magnetic enhancement in chinese paleosols is mainly contributed by the 0 5 m sediment fractions

dissolution behaviour of fine grained magnetite and maghemite in the citrate bicarbonate dithionite extraction method mineral magnetic properties of soils and sediments are increasingly used as proxy parameters for environmental and palaeoclimate analysis to investigate which magnetic minerals contribute to the environmental signal in the samples chemical techniques such as the citrate bicarbonate dithionite cbd extraction method have been introduced in environmental magnetism studies this technique is assumed to distinguish lithogenic magnetite from pedogenic maghemite mineral content in soils and sediments unfortunately interpretation of the cbd extractions is not straightforward because the procedure is sometimes more suitable for distinction between grain size than for distinction between minerals the procedure of the cbd extraction technique was investigated to determine the influence of extraction temperature and iron oxide concentration on the dissolution behaviour of the samples synthetic samples were extracted at three different temperatures 60o 70o and 80oc at similar iron oxide concentration 5 wt and for three different concentrations 0 1 wt 1 wt and 5 wt at the same temperature 60oc our results show that a lower extraction temperature reduces the dissolution rate for all samples while decrease in iron oxide concentration increases the dissolution rate thus the parameters in the cbd procedure have a major influence on the dissolution behaviour of the samples in practice this means that when natural samples of differing iron oxide concentration are extracted with this technique the results of the extractions cannot be compared therefore the outcome of this type of extraction experiment can only be accurately interpreted when the effect of the procedure on the dissolution behaviour is taken into account 1999 elsevier science b v all rights reserved

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

widespread occurrence of silicate hosted magnetic mineral inclusions in marine sediments and their contribution to paleomagnetic recording magnetic mineral inclusions occur commonly within other larger mineral phases in igneous rocks and have been demonstrated to preserve important paleomagnetic signals while the usefulness of magnetic inclusions in igneous rocks have been explored extensively their presence in sediments has only been speculated upon the contribution of magnetic inclusions to the magnetization of sediments therefore has been elusive in this study we use transmission electron microscope tem and magnetic methods to demonstrate the widespread preservation of silicate hosted magnetic inclusions in marine sedimentary settings tem analysis reveals detailed information about the microstructure chemical composition grain size and spatial arrangement of nanoscale magnetic mineral inclusions within larger silicate particles our results confirm the expectation that silicate minerals can protect magnetic mineral inclusions from sulfate reducing diagenesis and increase significantly the preservation potential of iron oxides in inclusions magnetic inclusions should therefore be considered as a potentially important source of fine grained magnetic mineral assemblages and represent a missing link in a wide range of sedimentary paleomagnetic and environmental magnetic studies in addition we present depositional remanent magnetization drm modeling results to assess the paleomagnetic recording capability of magnetic inclusions our simulation demonstrates that deposition of larger silicate particles with magnetic inclusions will be controlled by gravitational and hydrodynamic forces rather than by geomagnetic torques thus even though these large silicates may contain ideal single domain particles they can not contribute meaningfully to paleomagnetic recording however smaller silicate grains e g silt and clay sized silicates with unidirectionally magnetized magnetic inclusions can potentially record a reliable drm

nanosized authigenic magnetite and hematite particles in mature paleosol phyllosilicates new evidence for a magnetic enhancement mechanism in loess sequences of china

pedogenesis and paleoclimate interpretation of the magnetic susceptibility record of chinese loess paleosol sequences in the chinese loess paleosol sequences from luochuan haanxi province china variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base line level of the loess by using mineral magnetic properties and a soil chemistry extraction procedure we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis in effect loess deposition and pedogenesis are competing processes at all times and the presence of a paleosol simply indicates that the latter process was predominant these results imply that any interpretation of the paleoclimate record of loess paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

remanence acquisition efficiency in biogenic and detrital magnetite and recording of geomagnetic paleointensity relative paleointensity rpi variations of earth s magnetic field are widely used to understand geomagnetic field behavior and to develop age models for sedimentary sequences rpi estimation is based on a series of assumptions one key assumption that is rarely considered is that all magnetic particles in the sediment acquired a magnetization in an identical manner in this paper we test this assumption for sediments from the eastern equatorial pacific ocean that record well documented global rpi variations over the last 780 kyr the magnetization is carried by two stable single domain magnetic components which we identify as magnetite magnetofossils and titanomagnetite nanoparticle inclusions within larger silicate particles by analyzing signals carried by the two components separately we determine for the first time that magnetic nanoparticle inclusions can cause their host particles to record reliable but inefficient sedimentary paleomagnetic signals the magnetization carried by biogenic magnetite is acquired more efficiently than that carried by the nanoparticle inclusions variations in the concentration of both components are modulated climatically so that they record nearly identical rpi signals in many sediment types there is no correlation between the concentrations of different magnetic components so that variable remanence acquisition efficiency will complicate rpi recording our work demonstrates that detailed assessment of paleomagnetic recording by each constituent magnetic component needs to become a routine part of sedimentary rpi analysis

latest olduvai short lived reversal episodes recorded in chinese loess 1 a duplicate high resolution magnetic record was obtained from two parallel loess sections separated by about 300 m near baoji city southern chinese loess plateau this reveals at least eight short lived reversed polarity episodes in the uppermost part of the olduvai normal polarity subchronozone rock magnetic experiments and anisotropy of low field magnetic susceptibility confirm that the multiple occurrence of short lived reversals is not due to rock magnetic and or sedimentary causes assuming a constant accumulation rate within the olduvai subchron the short episode zone was estimated to span about 24 30 ka and 24 31 ka for the two sections respectively the duration of each short episode ranges from about 0 3 ka to 2 1 ka the present results together with previous worldwide observations show that the occurrence of numerous short reversals is peculiar to the latest olduvai subchron the geodynamo may have been in an anomalous state at that time

the role of maghemite in the enhancement of magnetic signal in the chinese loess paleosol sequence an extensive rock magnetic study combined with citrate bicarbonate dithionite treatment we have conducted a rock magnetic study of selected chinese loess samples before and after citrate bicarbonate dithionite cbd treatment our study is more extensive than previous ones and reveals new details of the magnetic carriers which are related to paleoclimate change three pairs of paleosol s1 the top paleosol layer in the lishi formation and loess l2 underlying s1 from three localities xining xifeng and jixian were investigated by using a variety of magnetic methods after the paleosols were treated with cbd which removes all maghemite grains and the finest grains of magnetite magnetic susceptibility decreased from 77 10 8 to 20 10 8 m3 kg in xining from 165 10 8 to 30 10 8 m3 kg in xifeng and from 180 10 8 to 25 10 8 m3 kg in jixian anhysteretic remanent magnetizations arm were reduced to less than one tenth of the original values in the three sites and saturation magnetization js decreased by about 60 in xining and 70 in xifeng and jixian these reduced values in the paleosols after cbd treatment are similar to those of the corresponding underlying loess samples which however did not show significant decrease after cbd treatment room temperature frequency dependence of susceptibility high temperature dependence of susceptibility and low temperature sirm demagnetization of the paleosol and loess samples before and after cbd treatment confirm that in addition to superparamagnetic sp particles magnetite and or maghemite the cbd removable magnetic carriers also include maghemite of grain sizes larger than sp

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

characteristics and formation mechanism of pedogenic hematite in quaternary chinese loess and paleosols abstract hematite is an important iron oxide mineral in loess paleosol sequences in northwest china samples containing hematite and related minerals in the loess and paleosol units from chinese loess plateau were investigated using powder x ray diffraction xrd scanning electron microscopy sem and high resolution transmission microscopy hrtem the results show that there are at least three genetic types of hematite in quaternary loess paleosol sequences of northern china 1 weathering products of fe bearing silicate minerals such as chlorite and biotite that precipitated as aggregates of hematite nano crystals on mineral surfaces 2 oxidation products of eolian magnetite grains with hematite nano crystals closely associated with magnetite 3 coarse silt sized hematite grains present in the fresh loess hematite with a nanoporous texture indicates that dehydration of iron hydroxide ferrihydrite is the main mechanism for the formation of hematite coating during chemical weathering of fe bearing silicates it is proposed that nano phase hematite is primarily responsible for the red color of the paleosol units paleosol layers are also characterized by higher magnetic susceptibility and increased oxidation of eolian magnetite it is proposed that the major contribution to magnetic susceptibility is from the nano phase magnetite that may be related to microbial activity this research demonstrates that the study of mineral characteristics formation mechanisms and the relationship between hematite other iron oxides and fe bearing silicate minerals helps to understand better the geochemical process in loess both before and after dust deposition in addition our study helps to explain the correlation between magnetic susceptibility and paleoclimate in northern china during the quaternary

particle size contributions to bulk magnetic susceptibility in chinese loess and paleosol abstract the magnetic enhancement of paleosol is observed in the chinese loess the origin of this magnetic enhancement is still very uncertain it is however a key problem in correctly understanding the paleoclimatic significance of changes of magnetic susceptibility and in transferring the magnetic signals to paleoclimatic parameters two main models have been proposed to explain the mechanism of magnetic enhancement in paleosols a depositional model and a pedogenic model together with composition and concentration grain size distribution of magnetic minerals also plays an important role to the magnetic enhancement of paleosols systematic susceptibility measurements were carried out on the samples of the upper part s0 to top of l2 of three loess sections from jixian xifeng and xining along an east west transect in the loess plateau china the samples with the highest value of magnetic susceptibility in s1 and the lowest value in l2 of each section were selected as the representatives these representatives were separated into different grain size fractions based on stokes law for coarse grains and by centrifuge for fine grains measurements of magnetic susceptibility and mass have been carried out on these fractions results show that for the loesses magnetic susceptibility changes little in the fractions with different grain size and for the paleosols it increases with decreasing grain size the magnitude of changes is bigger in the east jixian and xifeng than that in the west xining the fraction with the finest particle size in paleosols does not show very high magnetic susceptibility values a new approach is used to estimate the contribution of each fraction to total magnetic susceptibility the contribution comes mainly from coarse grains 10 m for loess samples it reaches about 90 the main contribution comes however from the particles with medium size 10 0 2 m the very fine grained particle

effects of weathering on single domain magnetite in early pliocene marine marls rock magnetic parameters are often used to recognize variations in the original magnetic mineralogy and for normalizing purposes in palaeointensity studies incipient weathering however is shown to have a profound but partly reversible influence on the rock magnetic properties of the marls of the early pliocene trubi formation in southern sicily italy the remanence in the marls resides in single domain sd magnetite grains but the remanent coercive force hcr shows a strong variation and most values observed are anomalously high hcr range 36 188 mt the enhanced coercivities are attributed to stress in the magnetite grains induced by surface oxidation at low temperature upon heating to 150 c a reduction of coercivities occurs that can be explained by a stress reduction as a result of a reduction of fe2 gradient due to a higher diffusion rate at elevated temperature after heating to 150 c coercivities are quite uniform throughout the outcrop and the values are characteristic of sd magnetite hcr range 30 38 mt the bulk susceptibility increases by 4 24 per cent and the isothermal remanent magnetization irm decreases by 5 11 per cent the increase in anhysteretic remanent magnetization arm is large 20 242 per cent the magnitude of the changes is related to the degree of weathering another effect of heating the marl samples to 150 c is a substantial reduction of the coercivities of the secondary overprint in the natural remanent magnetization after heating separation of the secondary and primary components by alternating field demagnetization is more efficient the usual difficulties of thermal demagnetization above 300 c may thus be avoided by a combination of moderate heating to 150 c and subsequent alternating field demagnetization

authigenic monazite and detrital zircon dating from the proterozoic rocky cape group tasmania links to the belt purcell supergroup north america abstract the oldest known rocks in tasmania occur in the proterozoic rocky cape group a 10 km thick quartzarenite siltstone pelite dominated succession previously constrained to have been deposited between 1450 ma and 750 ma the rocky cape group contains the enigmatic fossil horodyskia string of beads and has the potential to place tasmania within supercontinent reconstructions detrital zircon and authigenic monazite grains dated via u pb laser ablation inductively coupled plasma mass spectrometry la icpms analysis yield a deposition window between c 1450 ma youngest zircon populations and c 1330 ma oldest authigenic monazite population for the 9 km thick lower middle units pedder river siltstone lagoon river quartzite balfour subgroup which hosts horodyskia detention subgroup the upper units 1 km include the irby siltstone which is younger than c 1310 ma this unit is likely separated from both the lower middle units and the overlying c 1900 ma grains were identified authigenic monazite age distributions are complex with multiple age domains within most samples the common pb corrected 206u 238pb ages defined by oldest grains in each sample identify three statistically significant groups 1 1358 1292 ma inclusive of two sigma errors lagoon river quartzite and pedder river siltstone 2 1283 1239 ma cowrie siltstone and balfour subgroup and 3 1085 9 ma detention subgroup we suggest monazite was precipitated during episodic fluid flow events at these three stages in various parts of the basin the original source for ree bearing fluids could be detrital monazite which is rarely preserved and or organic matter from the interbedded carbonaceous shales the rocky cape group has a shared provenance with the higher grade metasediments surprise bay and fraser formations of nearby king island the newly derived depositional ages also overlap and support the correlation of these rock associations on the basis of current datasets there are no obvious correlations that can be made with mesoproterozoic basins preserved in mainland australia instead an overlap in the timing of deposition similarities in detrital zircon signatures and analogous depositional environment suggests the c 1 45 1 37 ga upper belt purcell supergroup missoula and lemhi groups of western north america constitutes a plausible correlation with the tasmanian mesoproterozoic succession if the unexposed palaeoproterozoic basement of tasmania correlates with the transantarctic mountains region of east antarctica as previously proposed we suggest that the overlying mesoproterozoic sequences were deposited during rifting of the supercontinent nuna between proto australia including the mawson craton of antarctica and laurentia as predicted by the most recent palaeogeographic reconstructions both the tasmanian and western laurentian packages were affected by episodic post depositional fluid flow events between c 1 35 and 1 05 ga possible thermotectonic imprints of the subsequent assembly of rodinia

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

separation of pedogenic and lithogenic components of magnetic susceptibility in the chinese loess palaeosol sequence as determined by the cbd procedure and a mixing analysis summary magnetic susceptibility variations in the chinese loess palaeosol sequences have been used extensively for palaeoclimatic interpretations the magnetic signal of these sequences must be divided into lithogenic and pedogenic components because the palaeoclimatic record is primarily reflected in the pedogenic component in this paper we compare two methods for separating the pedogenic and lithogenic components of the magnetic susceptibility signal the citrate bicarbonate dithionite cbd extraction procedure and a mixing analysis both methods yield good estimates of the pedogenic component especially for the palaeosols the cbd procedure underestimates the lithogenic component and overestimates the pedogenic component the magnitude of this eect is moderately high in loess layers but almost negligible in palaeosols the mixing model overestimates the lithogenic component and underestimates the pedogenic component both methods can be adjusted to yield better estimates of both components the lithogenic susceptibility as determined by either method suggests that palaeoclimatic interpretations based only on total susceptibility will be in error and that a single estimate of the average lithogenic susceptibility is not an accurate basis for adjusting the total susceptibility a long term decline in lithogenic susceptibility with depth in the section suggests more intense or prolonged periods of weathering associated with the formation of the older palaeosols the cbd procedure provides the most comprehensive information on the magnitude of the components and magnetic mineralogy of loess and palaeosols however the mixing analysis provides a sensitive rapid and easily applied alternative to the cbd procedure a combination of the two approaches provides the most powerful and perhaps the most accurate way of separating the magnetic susceptibility components