potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

enhancement mechanisms of magnetic susceptibility in the chinese red clay sequence 1 little is known about the mechanisms of magnetic susceptibility enhancement for the red clay sequence on the chinese loess plateau clp in comparison to the overlying loess paleosol sequence here we present a rock magnetic study of the red clay sediments from the central clp our results show that frequency dependence of fd lf hf where lf and hf are measured at 470 hz and 4700 hz respectively lf and susceptibility of anhysteretic remanent magnetization arm are linearly correlated within the red clay sequence this linear correlation indicates that the pedogenic magnetic minerals of the red clay have a rather uniform grain size distribution as in the loess paleosol sequence and the grain size is independent of the degree of pedogenesis nevertheless red clay sediments are slightly more enriched in superparamagnetic magnetic particles than the overlying loess paleosol sediments as indicated by the higher slope of the regression line between fd and lf

magnetic and petrologic characterization of synthetic martian basalts and implications for the surface magnetization of mars 1 a suite of synthetic martian basalts is generated with the objective of providing fundamental material properties data for use in modeling and interpretation of mission data we systematically evaluate the effects of major element composition oxygen fugacity fo2 and cooling rate on phase chemistry and magnetic mineralogy grain size and intensity of remanent magnetization the range of experimental compositions and fo2 are chosen to bracket the range expected in the martian crust our results should therefore span the range of possible mineralogies textures and magnetic properties in rapidly cooled mars crustal materials two starting compositions are used for the sample synthesis 1 an fe rich al poor composition patterned after snc basaltic meteorites and 2 a composition based on thermal emission spectrometer tes data with a much lower fe al ratio the resulting magnetic phase in samples generated at the quartz fayalite magnetite qfm buffer is a spinel structured oxide with varying amounts of cr ti mg and al compositional differences depend on bulk composition cooling rate differences in crystallization sequence and the kinetics of silicate mineral nucleation and growth oxide abundance and magnetic intensity are most strongly influenced by fo2 with more subtle composition and cooling rate effects moderately oxidizing qfm conditions result in an intense magnetization 2 3 10 5 am2 kg 1 to 1 4 10 2 am2 kg 1 especially in the meteorite derived basalts however an increase of magnetic grain size into the multidomain range meteorite type and or low unblocking temperatures resulting from increased cr substitution tes type may affect the long term stability of the remanence in qfm samples

the late oligocene to early miocene early evolution of rifting in the southwestern part of the roer valley graben the roer valley graben is a mesozoic continental rift basin that was reactivated during the late oligocene the study area is located in the graben area of the southwestern part of the roer valley graben rifting initiated in the study area with the development of a large number of faults in the prerift strata some of these faults were rooted in preexisting zones of weakness in the mesozoic strata early in the late oligocene several faults died out in the study area as strain became focused upon others some of which were able to link into several kilometer long systems within the late oligocene to early miocene northwestward prograding shallow marine syn rift deposits the number of active faults further decreased with time a relatively strong decrease was observed around the oligocene miocene boundary and represents a further focus of strain onto the long fault systems miocene extensional strain was not accommodated by further growth but predominantly by displacements along the long fault systems since the oligocene miocene boundary coincides with a radical change in the european intraplate stress field the latter might have contributed significantly to the simultaneous change of fault kinematics in the study area

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

quantification of magnetic nanoparticles with broad band frequency magnetic susceptibility measurements a case study of an upper loess palaeosol succession at luochuan chinese loess plateau

the possible role of magnetic measurements in the discrimination of sahara sahel dust sources the mineral magnetic properties of deposited dusts collected along a broadly north to south transect across niger have been investigated on both a bulk and particle size specific basis dusts display a general north to south gradient in fine grained ferrimagnetic mineral magnetite maghemite concentrations with samples south of the sahara sahel transition south of 15 5o n generally containing greater concentrations than dusts from further north where the climate is much drier this distinction is seen especially clearly in the clay 2 m fraction which harbours the products of weathering and pedogenesis this gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils sands across a similar latitudinal range we suggest that the regional distinction in both dust and surface soil sand magnetic properties can be related to differences in weathering regime between the arid saharan parts of the transect and the sahel sites where higher rainfall has permitted stronger weathering and pedogenesis given that the weathering related magnetic signatures in the clays dominate the magnetic properties of the 16 m fractions in these samples and that this particle size component is most likely to be involved in long range transport magnetic measurements hold out the potential of discriminating sahara and sahel dusts deposited in remote areas copyright 2011 john wiley sons ltd

grain size distribution of pedogenic magnetic particles in chinese loess paleosols 1 variations in magnetic parameters of the long chinese loess paleosol sequences reflect paleoclimatic fluctuations however there remain ambiguities whether the magnetic proxies are controlled by the concentration or by the distribution of magnetic grain sizes we systematically investigated the frequency dependence of low field magnetic susceptibility fd and the decay rate dr dependence of anhysteretic remanence magnetization arm susceptibility arm dr for a set of representative loess paleosol samples from the yuanbao section western chinese loess plateau after removing the effect of aeolian coarse grained magnetites both fd and arm dr are nearly independent of the degree of pedogenesis indicating a presence of fine grained magnetic particles ranging from superparamagnetic to single domain with an almost constant grain size distribution therefore the magnetic enhancement of magnetic susceptibility or arm is caused dominantly by changes in the concentration of these fine grained pedogenic grains

magnetic properties of a soil from southeastern brazil in the presence of magnetic biomineralization by social insects abstract it is known that the migratory ant pachycondyla marginata and its prey the termite neocapritermes opacus synthesize magnetic minerals which may contribute to the magnetic characteristics of soil a comparative study of the magnetic properties of the minerals found in those species as well as their nests and surrounding soil aimed at investigating the contribution of the biogenic minerals to the magnetization of the soil partially oxidized magnetite t v 120 k was found in the pachycondyla marginata as shown by the verwey transition in the zfc fc and rtsirm curves low temperature remanence measurements of the neocapritermes opacus indicated the presence of maghemite and or titanomaghemite while partially oxidized pseudo single domain magnetites and or titanomaghemite were recognized in the soil and insect nests based on the similarity in the magnetic characteristic of the samples it is concluded that there is significant influence of biogenic mineralization upon the pedogenic contribution

frequency dependence of susceptibility in magnets with uniaxial and triaxial anisotropy characterization of minerals in rocks and soils provides a window into environmental processes and improves the interpretation of paleomagnetic measurements mineral composition size and shape can be constrained using magnetic measurements for small minerals a promising measurement is the frequency dependence of magnetic susceptibility the size and shape dependence of the in phase component and out of phase component are derived for arbitrarily oriented superparamagnetic and single domain magnets with uniaxial and triaxial anisotropy in a fluctuating field a single magnet has a thermal response parallel to the easy axis and instantaneous rotation of the moment perpendicular to it the size and temperature variations have the same form as in earlier theories in which all the magnets are aligned with the field and can be easily adapted to the methods of shcherbakov and fabian 2005 and egli 2009 for finding size distributions using multiple temperatures and frequencies these inversions are inherently non unique and complicated by non sd contributions but some robust constraints can be put on the volume distribution if the commonly used ratio fd is 10 or greater the anisotropy of the out of phase component opams has the same sense as thermoremanent magnetization trm and can be used to correct the paleofield direction along with the anisotropy of the in phase component ipams it can be used to gain quantitative information on the deformation of the host rock for the line plane or march deformation model opams and ipams are calculated and it is shown how they can be used to accurately represent the strain anisotropy

remagnetization of carbonate rocks in southern tibet perspectives from rock magnetic and petrographic investigations netherlands organization for scientific research nwo with a rubicon grant 825 15 016 institute for rock magnetism irm at the university of minnesota instruments and facilities program of nsf erc starting grant 306810 nwo vidi 864 11 004

the different climatic response of pedogenic hematite and ferrimagnetic minerals evidence from particle sized modern soils over the chinese loess plateau abstract in recent years increasing interest in loess studies has focused on qualitative and quantitative paleoclimatic reconstruction using the imperfect antiferromagnetic mineral hematite however the linkage between the hematite formation and climatic variables remains controversial here we present the results of a comprehensive investigation of the magnetic properties and statistical analysis of a suite of clay and silt fractions of modern soil samples from 179 sites across the chinese loess plateau clp and adjacent regions our objective was to clarify the relationships between modern climatic variables and pedogenic hematite as well as pedogenic ferrimagnetic minerals first order reversal curve measurements were also conducted on representative particle sized subsamples from a n s transect to understand the differences in magnetic mineralogy between the two fractions our results show that pipette extraction separates the fine grained superparamagnetic sp and most of the single domain sd magnetic grains into the clay fraction and that the remaining silt fraction displays the magnetic properties of coarse pseudo single domain psd or a mixture of multidomain md psd and a few sd particles only the pedogenic clay fraction shows a strong correlation with climatic variables the application of redundancy analysis helps to distinguish the climate variables controlling the formation of ferrimagnetic minerals and hematite during pedogenesis on the clp pedogenic ferrimagnetic minerals are sensitive to mean annual precipitation while pedogenic hematite formation is preferentially dependent on mean annual temperature the confirmation of the temperature dependent nature of hematite on the clp provides a new possibility for quantitatively reconstructing the paleotemperature history of chinese loess paleosol sequences

rock magnetic records of the sediments of the eastern arabian sea evidence for late quaternary climatic change abstract rock magnetic measurements along with grain size acid insoluble residue air organic carbon oc caco3 and 18o of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of india magnetic susceptibility ms values in the surficial sediments reflect the land derived input and in general are the highest in terrigenous sediment dominated sections of the cores off saurashtra ratnagiri followed by the sediments off indus gulf of kachchh and then mangalore cape comorin the down core variations in mineral magnetic parameters reveal that the glacial sediments off the indus are characterized by low ms values s ratios associated with high air content low oc caco3 contents and relatively high 18o values while those off sw india are characterized by low ms values high s ratio associated with low air content and relatively high oc caco3 and 18o values conversely the early holocene sediments of all cores are characterized by high ms values s ratio associated with high air content low oc caco3 contents and gradually decreased 18o values these results imply that during the last glacial maximum lgm the cores off northwestern india received abundant continental supply leading to the predominance of eolian fluvial sedimentation in the sw region the influence of hinterland flux is less evident during this period but convective mixing associated with the ne monsoon resulted in increased productivity during the early holocene intense sw monsoon conditions resulted in high precipitation on land which in turn contributed increased air content ms values in the continental margin sediments a shallow water core off kochi further suggests that the intense sw monsoon conditions prevailed until about 5 ka the late holocene organic rich sediments of the sw margin of india were however subjected to early diagenesis at different intervals in the cores therefore caution is needed when interpreting regional climatic change from down core changes in sediment magnetic properties

testing the accuracy of absolute intensity estimates of the ancient geomagnetic field using copper slag material abstract the middle eastern copper slag is a promising new material for studying intensity variations in the geomagnetic field with high resolution and precision the purpose of this study is to test the accuracy of archaeointensity estimates determined using copper slag by addressing two questions 1 does slag material display the magnetic properties required for valid thellier experiments and 2 what is the accuracy of the archaeointensity estimates derived from thellier style experiments on optimal samples we address the first question through a comprehensive microscopic and magnetic study of representative archaeological slag samples in order to identify the properties responsible for optimal behavior in thellier experiments to address the second question we reproduced slag samples in the laboratory under controlled magnetic fields and analyzed them using the same izzi paleointensity technique used for the ancient slag microscopic analyses of the archaeological slag show that ferromagnetic phases occur as three dimensional dendritic structures whose branches consist of submicron elongated particles magnetic analyses show that these dendrites behave as an assemblage of shape controlled single domain like particles and that their magnetization is thermoremanent we conclude that slag material can be magnetically suitable for valid thellier experiments the laboratory produced slag material demonstrated similar magnetic and mineralogical properties as the archaeological slag izzi experiments showed that non linear trm acquisition even at field strengths similar to earth s and trm anisotropy are important factors to monitor during paleointensity studies of slag material anisotropy and non linearity are probably related to the dendritic shape of the oxide grains intensity estimates derived from three laboratory produced slag samples demonstrated accuracy to within 5 after applying the required corrections

experimental mixtures of superparamagnetic and single domain magnetite with respect to day dunlop plots day dunlop plots are widely used in paleomagnetic and environmental studies as a tool to determine the magnetic domain state of magnetite i e superparamagnetic sp stable single domain sd pseudosingle domain psd multidomain md and their mixtures the few experimental studies that have examined hysteresis properties of sd sp mixtures of magnetite found that the ratios of saturation remanent magnetization to saturation magnetization and the coercivity of remanence to coercivity are low when compared to expected theoretical mixing trends based on langevin theory this study reexamines day dunlop plots using experimentally controlled mixtures of sd and sp magnetite grains end members include magnetotactic bacteria msr 1 as the sd source and a commercial ferrofluid or magnetotactic bacteria a12 as the sp source each sp component was added incrementally to a sd sample experimental results from these mixing series show that the magnetization and coercivity ratios are lower than the theoretical prediction for bulk sp magnetic size although steric repulsion was present between the particles we cannot rule out interaction in the ferrofluid for higher concentrations the sp bacteria are noninteracting as the magnetite was enclosed by an organic bilipid membrane our results demonstrate that the magnetization and coercivity ratios of sd sp mixtures can lie in the psd range and that an unambiguous interpretation of particle size can only be made with information about the magnetic properties of the end members

nonlinear preisach maps detecting and characterizing separate remanent magnetic fractions in complex natural samples natural remanent magnetization carriers in rocks can contain mixtures of magnetic minerals that interact in complex ways and are challenging to characterize by current measurement techniques here a non linear mapping scheme is described that efficiently enhances sensitivity and the resolution power of remanent preisach maps using this scheme a large dynamic range of magnetic moments and coercivities can be reliably resolved the method is applied to synthetic and natural standard samples containing magnetite and hematite as well as to natural samples from remanent magnetic anomalies where complex microstructures are observed it is shown that certain offset high coercivity patterns in remanent preisach maps may serve as fingerprints for exsolution structures of ilmenite in hematite or hematite in ilmenite and that in some magnetite bearing remanent anomalies the magnetite coercivity is increased beyond its intrinsic coercivity range experimental results and theoretical considerations indicate a minimal coercivity of about 10 mt for sd magnetite such that observation of lower coercivities implies psd or md grain sizes a diagnostic hematite pattern with a peak downwards offset of 17 2 of the intrinsic coercivity is found that is stable over a large range of intrinsic coercivities and may be related to shielding of internal defect or lamellar moments by a spin canting response to the internal field

shock induced metallic iron nanoparticles in olivine rich martian meteorites magnetic anomalies observed by the mars global surveyor mission are attributed to crustal remanence snc shergotty nakhla chassigny meteorites are likely samples of the martian crust and are amenable to mineralogical and magnetic measurements essential to the understanding of the origin of magnetic anomalies the recently discovered chassignite nwa 2737 and lherzolitic shergottite nwa 1950 display unusual magnetic characteristics that argue for a different magnetic carrier than the oxides and sulfides previously invoked in snc meteorites nwa 2737 the second member of the chassignite group is a dunite with unusually dark brown olivines and large magnetic susceptibility while chassigny contains green olivines and is nearly a pure paramagnet dark olivines are also found in nwa 1950 a lherzolitic shergottite which has singular magnetic properties when compared with other shergottites the dark olivine color is due to the presence of fe and feni metal nanoparticles identified both by tem and by magnetic measurements their size distribution encompasses the superparamagnetic to single domain transition at 30 k 10 nm range and explains the magnetic properties of the bulk rocks the formation of these nanoparticles is attributed to heating during the shock events that affected nwa 2737 and nwa 1950 the production of metal particles by shock induced reduction of olivine has been invoked on surfaces deprived of atmosphere but never observed on earth or mars therefore metal formed by shock in the heavily cratered noachian crust is a possible carrier for crustal magnetic remanence widespread surface formation of metal nanoparticles could provide the precursor for the oxidized particles goethite hematite observed in the martian soils c 2007 elsevier b v all rights reserved

magnetic minerals in calcic luvisols chromic developed in a warm mediterranean region of spain origin and paleoenvironmental significance abstract soil formation under aerobic conditions usually enhances magnetic signals mainly through neoformation of sub micron magnetite and or maghemite in order to better understand the nature and magnitude of the enhancement in this work we characterized the iron fe oxides and magnetic properties of two calcic luvisols chromic developed on calcareous orthoquartzites in a spanish region with a warm mediterranean climate weathering of the fe bearing minerals in the parent material mostly fe rich smectite had resulted in the neoformation of hematite and maghemite rather than goethite thus causing a substantial increase in magnetic susceptibility saturation magnetization m s and other magnetic signals the absolute frequency dependent magnetic susceptibility fd which is a typical proxy for the concentration of sub micron superparamagnetic pedogenic maghemite was strongly correlated with the concentration of hematite hm the estimated percent frequency dependent magnetic susceptibility fd was 15 7 this and various other magnetic indicators indicate that the grain size distribution gsd of the pedogenic maghemite is narrower around the superparamagnetic single domain threshold than is that of maghemite in soils and paleosols developed under other temperate climates e g the chinese loesss plateau where fd fd ratio fd the hematite goethite ratio and several indicators of the degree of weathering provides a better tool for paleoclimatic reconstructions than does the current use of alone

paleomagnetic field intensity derived from non sd testing the thellier izzi technique on md slag and a new bootstrap procedure abstract experimental techniques to determine paleomagnetic field intensity are based on a theoretical framework that is valid only for single domain sd ferromagnetic particles yet most of the available materials exhibit distinctly non sd properties designing the optimal paleointensity methodology for non sd is therefore a fundamental challenge in paleomagnetism the objective of this study is to experimentally test the izzi thellier absolute paleointensity method on small md recorders the test has two purposes 1 to describe the characteristic non sd patterns occurring in arai plots and 2 to identify the optimal approach in interpreting non sd behavior we carried out paleointensity experiments on 40 specimens from 4 synthetic re melted slag samples with identical magnetic properties mineralogy texture and non sd state produced under different field intensities we ran three batches of izzi experiments using different conditions that allow for a detailed characterization of the non sd behavior we find that the curvature of the arai plot is systematically dependent on the angle and the proportion between the field used in the paleointensity experiment btrm and the field in which the nrm was acquired bnrm straight line arai plot occur when the two fields are parallel and equal and seems to always give the true slope convex curves occur when btrm is parallel and significantly stronger than bnrm concave curves occur in all the other cases and yield two end case slopes that are always different than the true slope in addition zigzagged patterns increase with the angle the proportion between btrm and bnrm we test the accuracy of the best fitting line approach and conclude that best fitting line in curved plots cannot provide robust paleointensity estimates yet the two end case slopes in concave curves provide adequate constraints for the true value we introduce a new procedure to calculate a 95 confidence interval of the paleointensity from curved plots using bootstrap statistics we substantiate the new procedure by conducting two independent tests the first uses synthetic re melted slag produced under known field intensities 3 sd samples and 4 non sd samples the second compares paleointensity determinations from archeological slag samples of the same age 34 sd samples and 10 non sd samples the two tests demonstrate that the bootstrap technique may be the optimal approach for non ideal dataset

a new system for measuring alternating current magnetic susceptibility of natural materials over a wide range of frequencies a new measurement system has been developed for detecting frequency dependence of low field alternating current ac magnetic susceptibility in natural samples instead of employing intricate ac bridge circuits this system configuration is simple and consists of a set of primary secondary pickup and compensation coils a function generator and a two phase lock in amplifier this system can measure both in phase and out of phase components of ac susceptibility the operating frequency can be chosen at any value between 1 hz and 2 5 khz and the ac magnetic field intensity is changeable up to 1 0 103 a m the resolution is 1 10 8 m3 kg mass specific si for the 10 102 hz range and 2 5 10 8 m3 kg for 102 hz reconnaissance measurements made on chinese loess and paleosol samples revealed a stronger frequency dependence for the paleosol than for the loess over the entire frequency range this result suggests that the frequency dependence spectrum over wide band of frequencies can be useful especially in environmental magnetism as a new rock magnetic property to estimate the grain size distribution of superparamagnetic particles

superparamagnetism of two modern soils from the northeastern pampean region argentina and its paleoclimatic indications summary the magnetic susceptibility carried by pedogenic fine grained ferrimagnets has been widely used as paleoclimatic proxy to elucidate long term paleoclimatic variations for windblown terrestrial loess paleosol sequences however the magnetic properties of the lithogenic parentmaterialcanmaskthepedogenicsignals inthisstudy wesystematicallyinvestigatedthe origin of the superparamagnetism of two modern soils from the northeastern humid pampean region argentina developed on loess materials of different mineralogical composition the samples were treated with the citrate bicarbonate dithionite cbd reagent which is known to dissolve the submicron pedogenic ferrimagnets while leaving unaltered the coarse grained ones the magnetic material accounting for the frequency dependent magnetic susceptibility peak at about 50 k remained in the residuals and is independent of the pedogenic processes in addition pedogenic ferrimagnetic particles in the two soils have a magnetic signature comparable to that of the soils from the chinese loess plateau it is also suggested that the for the bulk samples does not seem to be a reliable paleoclimatic proxy for the pampean soils investigated in this study instead the cbd soluble magnetic signals could be more useful to detect paleoenvironmental variations in this region these new findings provide improved understanding of the magnetic assemblage in the pampean loess soils and make it feasible to retrieve the paleoclimatic signals carried by the pedogenic cbd soluble iron oxides after removing the effects of the lithogenic inputs

mineral magnetic properties of surface soils and sands across four north african transects and links to climatic gradients 1 in light of their earlier success in characterizing and differentiating soils sediments and atmospheric particulates magnetic measurements were carried out on samples of north african surface soils and sands the main aims were to document spatial variations in magnetic properties explore their possible links to climatic gradients and their likely basis and thereby help to differentiate potential sources for sahara sahel derived dusts samples were collected along four broadly north to south orientated transects located in egypt niger mali and benin and southern togo these transects cover major climatic gradients ranging from hyper arid to tropical across the rainfall range spanned by the niger and mali transects 800 mm yr there are significant north to south gradients in magnetic mineral concentrations this is seen most clearly in the concentrations of the finest ferrimagnetic minerals magnetite maghemite which are strongly represented in the clay fraction concentrations of the imperfect antiferromagnetic minerals predominantly haematite also increase with increasing rainfall by analogy with studies spanning a similar rainfall gradient in areas of more uniform lithology we suggest that the most likely cause for these trends is increased chemical weathering linked to the progressively wetter climate across the sahara sahel transition within the set of samples from egypt rainfall 100 to 5 mm yr there is a marked gradient in the coercivity of remanence in the antiferromagnetic minerals present with coercivity increasing southwards paralleling the trend toward increasing aridity given the strong spatial discrimination demonstrated especially in the niger and mali transects these potentially climate linked gradients hold out the promise of discriminating between dust source regions

characterizing the superparamagnetic grain distribution f v hk by thermal fluctuation tomography 1 in 1965 d j dunlop showed that the joint distribution of particle volumes and microcoercivities f v hk0 can be determined for magnetically monomineralic thermally stable single domain ssd ensembles by taking advantage of the joint temperature and field dependence of relaxation time we have developed a procedure that follows dunlop s strategy to obtain f v hk0 for ensembles containing both superparamagnetic and ssd grains based on backfield remanence curves measured over a range of temperatures each point on the derivative curves represents the integrated contribution from grains that lie along a corresponding blocking contour on the neel plot a suitable set of such line integral samples can be used to reconstruct the f v hk0 distribution using the methods of tomographic imaging samples of the basal tiva canyon tuff have narrow size distributions of elongate ti poor titanomagnetite tomographic inversion of the low temperature backfield spectra yield sharply peaked f v hk0 distributions from which we calculate modal grain dimensions in good agreement with those observed by transmission electron microscopy analysis of synthetic samples containing bimodal populations clearly distinguishes the two modes because our simplified forward calculations incompletely account for the effects of orientation distribution the width of the coercivity distribution at each temperature is underestimated and consequently the inverse calculations yield grain distributions that are overly broad frequency and temperature dependent susceptibilities calculated for the inverted f v hk0 distributions accord fairly well with measured susceptibilities for the weakly interacting tiva canyon samples less well for a moderately interacting paleosol specimen and poorly for a strongly interacting ferrofluid

paleogeographic and tectonic evolution of the pampia terrane in the cambrian new paleomagnetic constraints abstract paleomagnetic magnetic fabric and rock magnetic studies were carried out in the late middle to early late cambrian campanario formation exposed in nw argentina the study also presents preliminary results from the early cambrian metasediments of the puncoviscana formation and from mojotoro intrusive a new paleomagnetic pole c2 was computed for the campanario formation 23 6 n 346 5 e a95 7 0 n 11 sites from the localities of tilcara t terma de reyes r and el perchel ep including previous data from santa victoria oeste m in northernmost argentina a positive fold test was obtained for tilcara locality while a positive regional tilt test was obtained for mean site directions for the four localities this pole can be considered as the representative pole position for the pampia terrane for the late middle to late cambrian previous paleomagnetic data for the same formation from the iruya matancillas locality show an in situ clockwise rotation of about 30 around a vertical axis when compared with the mean pampia pole the same is observed when comparing the early ordovician pole for the santa rosita formation at those localities with the recently obtained coeval pole of the la pedrera formation indicating that local tectonic rotations affected that area these results suggest that previous paleomagnetic interpretations for these late cambrian and early ordovician rocks in the region as recording displacement of the pampia terrane in cambrian times are probably incorrect additionally two virtual geomagnetic poles were computed for the puncoviscana formation tp1 34 5 n 52 3 e a95 5 0 n 22 specimens and tp2 38 3 n 33 6 e a95 5 7 n 14 specimens and one for the mojotoro intrusive mo 9 1 n 345 6 e a95 16 4 n 11 specimens these and previous early cambrian paleomagnetic data from the pampia terrane differ from gondwana coeval reference directions in inclination and or declination lacking a simple pattern

holocene environmental reconstruction of sediment source linkages at crummock water english lake district based on magnetic measurements to reconstruct lateglacial and holocene environmental changes in the british uplands two c 5 8 m long sediment cores from crummock water nw england together with several hundred soil samples from the crummock water catchment were studied using magnetic techniques optically stimulated luminescence osl dating using fine silt quartz and 14c dating of terrestrial plant macrofossils were used to establish a chronology for the lake sediments a good agreement between optical and 14c ages indicates first that the osl dating method can be used to date lake sediments in the british isles second that macrofossil based 14c dating can be used to avoid the problem of old carbon error associated with bulk sample 14c dating of lake sediments and third that the established chronology is robust the lake sediment magnetic properties indicate a series of changes in sediment composition during the holocene which correlate well with sediment lithology water content and weight loss on ignition the first change corresponds to the lateglacial postglacial climatic shift at around 11400 years ago the subsequent suite of changes corresponds to a probable regional onset of human activity at 2000 bc and particularly to the intensification of human activity at around ad 900 a comparison of the lake sediment magnetic properties and those of the catchment soils shows a clear linkage for the lateglacial period and for the period after ad 900 in contrast detailed magnetic measurements of the early through mid holocene sediments suggest that their magnetic properties are dominated by bacterial magnetosomes

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

inversion tectonics and magnetic fabrics in mesozoic basins of the western tethys a review abstract positive tectonic inversion of sedimentary basins has been recognized as one of the primary mechanisms of mountain building and intraplate deformation reconstructing the tectonic history of basins is relatively easy for the inversion stage but becomes more difficult for the basinal stage especially when strong deformation involving cleavage development is associated with the subsequent compressional tectonics since tectonic markers for the extensional episodes are not commonly well developed anisotropy of magnetic susceptibility ams has provided recently a tool for analyzing early stages in the evolution of sedimentary basins even in the absence of other outcrop scale mesostructures here we expose and discuss the applicability of magnetic fabrics by means of ams to different types of intra plate sedimentary basins in the western tethys region formed under extensional or transtensional regimes and which underwent different inversion styles total or partial inversion with or without cleavage development forming part of compressional thrust sheets etc owing to specific particular p t conditions and structural controls factors such as lithology magnetic mineralogy position within the sedimentary pile and deformation intensity are key to interpret the obtained magnetic fabrics in terms of tectonic evolution a basin classification is proposed according to inversion styles and magnetic fabrics where inversion did not involve cleavage development magnetic lineation is parallel to the stretching direction corresponding to the extensional stage the transition between non cleaved to inversion related cleaved units is marked by the switch of magnetic lineations from parallel to extension to parallel to the intersection lineation between cleavage and bedding these relationships are enhanced when extension and compression are roughly coaxial then favoring the clustering of axes of the magnetic ellipsoid even when extreme inversion occurs and the early extensional fabric is obliterated magnetic fabrics provide information about the interaction between preferred deformation directions associated with the main stages in basin evolution

rainfall dependent transformations of iron oxides in a tropical saprolite transect of hainan island south china spectral and magnetic measurements 1 the iron oxide content of soils and sediments controlled by weathering and pedogenesis is generally considered a reasonable indicator of climate previous studies in temperate zones have established a positive correlation in aerobic soils between ferrimagnets and low to moderate rainfall the correlation seems to be reversed under extreme climates with high rainfall here we present a transect of saprolitic soils from hainan island south china with high rainfall 1440 2020 mm yr little temperature variation 23 24 c and extreme weathering along this transect we observed that both hematite concentration and magnetic susceptibility decrease with increasing rainfall whereas goethite concentration displays a large increase however there is no systematic trend in the total amount of iron oxides related to chemical weathering intensity along the transect goethite is the favored mineral phase of iron oxide with increasing rainfall and accumulates at the expense of hematite and maghemite through the dominance of rainfall driven processes these pedogenic processes coincide with the fundamentals of previous nonmonotonic models of hematite magnetic susceptibility and rainfall control of an inflection point this study also verifies a common genetic relationship between hematite and pedogenic ferrimagnets across a wide climate range a conceptual model considering both rainfall and temperature is proposed to help interpret the mechanism of ferrimagnet formation and changes in the rainfall inflection point

nanogoethite as a potential indicator of remagnetization in red beds red beds are well known for recording stable natural remanent magnetization nrm however discriminating primary nrm from secondary remanence in red beds is difficult the paleogene nangqian red beds in eastern tibetan plateau variably record an overprint related to nearby magmatism and thus provide a great opportunity to characterize remagnetization in red beds through comprehensive rock magnetic mossbauer spectroscopic and petrographic analyses we find that remagnetization was controlled by temperature remagnetized red beds contain abundant authigenic hematite and goethite with some larger grains unblocking at the neel temperatures and the remainder nanoparticles unblocking at lower temperatures in contrast red beds retaining primary nrm are characterized by dominance of detrital hematite and magnetite presence of fine grained authigenic hematite and absence of authigenic goethite and magnetite high temperature behaviors of nrm susceptibility are indicative of remagnetization but the presence of goethite appears to be a more sensitive criterion for diagnosing remagnetization in red beds

contrasting behavior of hematite and goethite within paleosol s5 of the luochuan profile chinese loess plateau 1 the chinese loess paleosol sequence provides an excellent record of long term variations in the east asian paleomonsoon for representative loess profiles paleosol units have enhanced magnetic properties compared to loess units however at some depth intervals with special paleoenvironmental conditions selective depletion of antiferromagnetic afm minerals hematite and goethite could occur resulting in complexities in accurately linking variations in magnetic properties to long term fluctuations in paleoclimate to resolve this problem we directly measured the mass concentrations of these afm minerals using second order diffuse reflectance spectroscopy drs and then correlated the drs results to high field isothermal remanent magnetization hirm from paleosol unit s5 at the luochuan profile central chinese loess plateau our results suggest that a low hirm anomaly just below the sub paleosol unit s5s1 is caused by fluctuations specifically in goethite content while the hematite concentration exhibits a maximum over the same depth interval this appears to rule out significant loss of hematite to reductive dissolution and further indicates that hematite and goethite may respond differently to changes in the paleoclimate conditions

magnetic detection and characterization of biogenic magnetic minerals a comparison of ferromagnetic resonance and first order reversal curve diagrams australian research council grant number dp120103952 australia new zealand iodp consortium anzic grant number le0882854

curie temperatures of titanomagnetite in ignimbrites effects of emplacement temperatures cooling rates exsolution and cation ordering pumices ashes and tuffs from mt st helens and from novarupta contain two principal forms of titanomagnetite homogeneous grains with curie temperatures in the range 350 500 c and oxyexsolved grains with similar bulk composition containing ilmenite lamellae and having curie temperatures above 500 c thermomagnetic analyses and isothermal annealing experiments in combination with stratigraphic settings and thermal models show that emplacement temperatures and cooling history may have affected the relative proportions of homogeneous and exsolved grains and have clearly had a strong influence on the curie temperature of the homogeneous phase the exsolved grains are most common where emplacement temperatures exceeded 600 c and in laboratory experiments heating to over 600 c in air causes the homogeneous titanomagnetites to oxyexsolve rapidly where emplacement temperatures were lower curie temperatures of the homogeneous grains are systematically related to overburden thickness and cooling timescales and thermomagnetic curves are generally irreversible with lower curie temperatures measured during cooling but little or no change is observed in room temperature susceptibility we interpret this irreversible behavior as reflecting variations in the degree of cation ordering in the titanomagnetites although we cannot conclusively rule out an alternative interpretation involving fine scale subsolvus unmixing short range ordering within the octahedral sites may play a key role in the observed phenomena changes in the curie temperature have important implications for the acquisition stabilization and retention of natural remanence and may in some cases enable quantification of the emplacement temperatures or cooling rates of volcanic units containing homogeneous titanomagnetites

quantifying ultrafine pedogenic magnetic particles in chinese loess by monitoring viscous decay of superparamagnetism we propose a new approach for quantifying pedogenically produced ultrafine nanometer scale magnetic particles in chinese loess we have recorded the viscous decay t 100 s of imposed isothermal remanent magnetization irm assumed to be selectively carried by superparamagnetic particles jv application of viscosity measurements relaxometry to loess paleosol sequences from the se extremity of the chinese loess plateau reveals that jv aptly reflects contributions of viscous superparamagnetic sp particles to the total remanence carried by an assemblage of magnetic particles time decay of jv can be determined with a higher resolution than the conventionally used frequency dependent susceptibility fd for characterizing the relative abundance of sp particles the nearly logarithmic time decay of irm implies a rather broad grain size distribution of pedogenic particles in chinese loess that may range from a lower size limit of 10 nm to an upper limit of 40 nm with a prevalent grain size maximum of 21 25 nm numerical calculations of the time dependence of irm decay demonstrate that the actual contribution of fine grained pedogenic magnetite maghemite to the total remanence is at least twice as large as that estimated by both fd and our proposed jv parameter we therefore propose that determination of superparamagnetic contributions by the time dependence of irm viscosity is a useful technique for tracking pedogenic processes and hence paleoclimatic conditions of chinese loess

the superparamagnetism of yucca mountain tuff yucca mountain tuff contains small titanomagnetite grains with narrow size distributions in the superparamagnetic range schlinger et al 1988 magnetic measurements on three samples comprising hysteresis loops at low and ambient temperatures acquisition and demagnetization of isothermal remanent magnetization thermal demagnetization of the saturation remanence and of a low temperature thermoremanence and frequency and temperature dependent susceptibilities allow evaluation of the magnetic properties in terms of neel s 1949 single domain theory precise grain volume distributions have been obtained by applying the blocking volume concept to thermal demagnetization results in contrast an attempt to derive mean particle volumes by fitting a langevin curve to the room temperature magnetization curves fails probably because the precondition for the langevin function kv kt 1 is not met it is only for the sample with the smallest grains and in weak fields 20 mt that a langevin fit provides a reasonable volume estimate there is good agreement between the experimental results and the calculated frequency and temperature dependence of susceptibility thus verifying that neel s theory is sufficient for the magnetic description of single domain assemblages spanning the superparamagnetic stable single domain boundary however some deviations between modeled and measured susceptibilities exist and the physical causes may include size dependent anisotropy nonuniform magnetizations and also an uncertain preexponential time constant 0 while 0 10 11 s gives the best fit for the sample with the largest grains 0 10 9 s is more reasonable for the others thus 0 may indeed be size and temperature dependent as predicted by brown 1959 the commonly cited parameter fd frequency dependence of susceptibility reaches 30 at room temperature rt for one sample with a blocking temperatures just below rt while fd 0 at rt for a superparamagnetic sample with smaller grains these results thus exemplify that fd is not limited to 15 as a number of studies suggest and that fd 0 must not be taken to imply the absence of superparamagnetic grains

ferromagnetic resonance characterization of greigite fe3s4 monoclinic pyrrhotite fe7s8 and non interacting titanomagnetite fe3 xtixo4 ferromagnetic resonance fmr spectroscopy has become an increasingly useful tool for studying the magnetic properties of natural samples magnetite fe3o4 is the only magnetic mineral that has been well characterized using fmr this limits the wider use of fmr in rock magnetism and paleomagnetism in this study we applied fmr analysis to a range of magnetic minerals including greigite fe3s4 monoclinic pyrrhotite fe7s8 magnetically non interacting titanomagnetite fe3 xtixo4 and synthetic magnetite chains to constrain interpretation of fmr analysis of natural samples and to explore applications of fmr spectroscopy we measured the fmr signatures of a wide range of well characterized samples at the x and q bands fmr spectra were also simulated numerically to compare with experimental results the effects of magnetic anisotropy mineralogy domain state and magnetostatic interactions on the fmr spectra are discussed for all studied minerals our experimental and theoretical analyses of magnetically non interacting tuff samples and magnetically interacting chains enable quantitative assessment of contributions of magnetostatic interactions and magnetic anisotropy to the fmr spectra our results also indicate that intact magnetosomes are a unique system with distinct fmr signatures while fmr analysis is useful for characterizing magnetic properties of natural samples care is needed when making interpretations because of overlaps in a range of fmr signatures of different magnetic minerals with different magnetic properties our analyses will help to constrain such interpretations in rock magnetic studies

bubble nucleation in magmas a dominantly heterogeneous process abstract bubble nucleation is at the heart of magma ascent and degassing nucleation kinetics control how easily a magma exsolves its volatiles and thereby its explosivity close to the surface homogeneous nucleation i e without assistance from crystal substrates or other phases often requires attainment of large supersaturation pressures p n 100 mpa the change in pressure required for onset of nucleation while heterogeneous nucleation on pre existing crystals can occur at significantly lower values p n p n given experimental constraints on pressure conditions at the onset of nucleation decompression rate meters e g toramaru 2006 also relate the number density of bubbles in pyroclasts a readily obtained textural characteristic to rates of pressure change dp dt during ascent all these treatments require an explicit or implicit decision as to whether magma degassing was dominated by homogeneous or heterogeneous nucleation which is guided by the choice of surface tension values this contribution exploits the current textural datasets available for eruptions involving a variety of magma compositions to test the assumptions that homogeneous and or heterogeneous nucleation dominate bubble vesiculation in natural melts the comparison between pyroclast textures and those obtained via decompression experiments in the laboratory indicates that supersaturation pressures and decompression rates required for homogeneous nucleation are unrealistically high for natural magmas i review the arguments for and against homogenous nucleation and defend the alternate view that heterogeneous nucleation may dominate in all magma types including rhyolites in order to solve this central debate our focus needs to be shifted towards understanding the pre decompression phase equilibria and textural characteristics of magnetite in addition to the state of the melt structure

rock magnetic carriers of century scale susceptibility cycles in glacial marine sediments from the palmer deep antarctic peninsula abstract a 4200 year long magnetic susceptibility profile from the palmer deep records century and millennial scale variability in paleoenvironmental conditions along the western antarctic peninsula the susceptibility profile shows regularly spaced highs and lows over the last 3360 years b p then drops to uniformly low values these features are formed by the variable dilution of terrigenous material with biogenic sediments and shifts in magnetic mineralogy high susceptibility intervals are characterized by multi domain md pure magnetite low susceptibility intervals are characterized by pseudo single domain psd magnetite and titanomagnetite prior to 3360 years b p the magnetic mineral assemblage is dominated by fine psd titanium rich titanomagnetite and superparamagnetic particles suggesting a change in sediment provenance and or sediment transport processes the absence of md magnetite suggests a cessation in locally derived ice rated debris this horizon represents the transition from the mid holocene climatic optimum to the neoglacial period marked by an increase in glacial sedimentation

grain size dependent magnetic discrimination of iceland and south greenland terrestrial sediments in the northern north atlantic sediment record abstract we use isothermal and temperature dependent in field and magnetic remanence methods together with electron microscopy to characterize different sieved size fractions from terrestrial sediments collected in iceland and southern greenland the magnetic fraction of greenland silts 3 63 m and sands 63 m is primarily composed of near stoichiometric magnetite that may be oxidized in the finer clay

primary and secondary red bed magnetization constrained by fluvial intraclasts author s swanson hysell nl fairchild lm slotznick sp abstract 2019 american geophysical union all rights reserved the magnetization of hematite bearing sedimentary rocks provides critical records of geomagnetic reversals and paleogeography however the timing of hematite remanent magnetization acquisition is typically difficult to constrain while detrital hematite in sediment can lead to a primary depositional remanent magnetization alteration of minerals through interaction with oxygen can lead to the postdepositional formation of hematite in this study we use exceptionally preserved fluvial sediments within the 1 1 billion year old freda formation to gain insight into the timing of hematite remanence acquisition and its magnetic properties this deposit contains siltstone intraclasts that were eroded from a coexisting lithofacies and redeposited within channel sandstone thermal demagnetization petrography and rock magnetic experiments on these clasts reveal two generations of hematite one population of hematite demagnetized at the highest unblocking temperatures and records directions that rotated along with the clasts this component is a primary detrital remanent magnetization the other component is removed at lower unblocking temperatures and has a consistent direction throughout the intraclasts this component is held by finer grained hematite that grew and acquired a chemical remanent magnetization following deposition resulting in a population that includes superparamagnetic nanoparticles in addition to remanence carrying grains the data support the interpretation that magnetizations of hematite bearing sedimentary rocks held by g400 nm grains that unblock close to the neel temperature are more likely to record magnetization from the time of deposition this primary magnetization can be successfully isolated from cooccurring authigenic hematite through high resolution thermal demagnetization

frequency dependent ams of rocks a tool for the investigation of the fabric of ultrafine magnetic particles abstract in some geological processes new very fine grained magnetic minerals may originate the variation in content of these minerals is routinely investigated by frequency dependent magnetic susceptibility which is traditionally interpreted in terms of the presence of viscous superparamagnetic sp particles in addition to stable single domain ssd and multidomain md magnetic particles in addition the fabric of these grains can be investigated through the frequency dependent ams through standard ams measurement at different frequencies one can evaluate the contribution of sp particles to the whole rock ams appropriate methods were developed various rocks soils and ceramics showing frequency dependent magnetic susceptibility were investigated measurable changes of ams with operating frequency were revealed and attempts are made of their fabric interpretation

anomalous unblocking temperatures viscosity and frequency dependent susceptibility in the chemically remagnetized trenton limestone abstract chemical remagnetization of many carbonate rock units occurred by diagenetic alteration of iron sulfide precursors and by authigenesis of fine grained magnetite which can commonly be recognized by a distinctive set of rock magnetic attributes these carbonates also typically exhibit anomalously high unblocking temperatures for recent thermoviscous components that have overprinted the characteristic chemical remanence recent work has shown that departures from neel theory as applied in the model of pullaiah et al can generally be attributed to vrm carried by multidomain particles to which the theory does not apply in the remagnetized carbonates however rock magnetic data all point to an overwhelming dominance of fine superparamagnetic and stable single domain particles therefore we explore possible alternative causes for the anomalous unblocking temperatures including maghemitization and magnetocrystalline rather than shape anisotropy new blocking unblocking models for these cases however fail to match the observed behavior leading to the conclusion that the anomalous unblocking temperatures are indeed probably attributable to multidomain carriers a possible alternative explanation is an increase in coercivity due to maghemitization of single domain particles after acquisition of the viscous overprint causing a significant increase in their unblocking temperatures new frequency dependent susceptibility measurements at low temperatures allow us to focus on the time temperature behavior of the particles at the superparamagnetic stable single domain threshold and we find that these do closely follow the predictions of neel theory as formulated in the models of pullaiah et al and walton middleton schmidt

thermal demagnetization of partial thermoremanent magnetization three well characterized glass ceramic samples containing magnetite crystals of different domain states have been given partial thermoremanent magnetizations ptrms in the temperature interval 400 350 c for varying lengths of time 10 min to 5 days and in magnetic fields from 0 5 to 5 oe 0 05 0 5 mt the thermal demagnetization behavior of the ptrms changes with domain state in the sense that with decreasing coercivity increasing grain size demagnetization curves become less steep and may not completely demagnetize until heated to the curie temperature numerical calculations based on neel s single domain sd theory invoking field dependence and experimentally determined as well as theoretical volume distributions based on power laws have been performed to predict viscous magnetization acquisition and demagnetization temperatures we observe that experimental results do not match any of the theoretical predictions there is no discernible field dependence of demagnetization curves for the sd and pseudo single domain samples and even for the soft multidomain md sample in the field range investigated an important consequence for thermally derived paleointensity data is that they may not be entirely reliable especially if the sample remanence is due to md grains

fabrics facies and flow through a large volume ignimbrite pampa de oxaya chile the miocene oxaya formation exposed along the western andean slope in northern chile represents one of the largest ignimbrite provinces on earth in this study magnetic fabric data were acquired from a 1 km long core drilled vertically through a single cooling unit of the oxaya formation the ca 22 ma cardones ignimbrite samples for magnetic analysis were obtained every 20 m from the fine grained matrix of the core detailed measurements of the variation in bulk magnetic properties including natural remanent magnetization nrm susceptibility and anisotropy of magnetic susceptibility ams were used to monitor changes in magnetic mineralogy as well as changes in the strength and orientation of the magnetic fabric throughout the flow ams ellipsoid orientation and shape reflect rapid deposition from a concentrated granular fluidized flow and constrain both the location of the source caldera for this catastrophic eruption and processes of transport and deposition in this large volume ignimbrite after utilizing the magnetic remanence to correct for rotation about the core axis well grouped and imbricated petrofabric orientations reveal a well defined sw 247 transport direction down a proto western andean slope indicating syn or post welding flow and confirming the deformed lauca caldera as the likely source of the eruption systematic variations in fabric shape t and intensity p with depth reveal a predominately oblate fabric toward the top and base of the flow and predominately prolate fabrics in the center these vertical changes in fabric reveal that this massive apparently homogeneous deposit has a systematic layering this layering reflects depth dependent temperature variations temporal changes in the flow boundary zone during deposition and post depositional processes

the use of magnetic susceptibility and its frequency dependence for delineation of a magnetic stratigraphy in ash flow tuffs variations in the grain size amount and mineralogy of magnetic phases in layered volcanic rocks define a magnetic stratigraphy that can be identified by means of magnetic susceptibility measurements in ash flow tuffs grain size and other variables that control susceptibility are to a large extent a function of the cooling and alteration history the phases responsible for the susceptibility of ash flow tuffs consist of post emplacement high temperature precipitates of fe oxides in volcanic glass and the phenocrystic fe ti oxides at yucca mountain nevada laterally continuous high susceptibility approximately 10 sup minus 2 si horizons exist in the paintbrush tuff due to the presence of either precipitates or phenocrystic fe ti oxides the frequency dependence of magnetic susceptibility chi omega can be used to discriminate between horizons with multi domain phenocrystic material the chi omega exhibits a 26 decrease per decade of increasing frequency for precipitate grain sizes where the superparamagnetic single domain state gives way to stable single domain behavior and thus chi omega offers an indirect method for rapid estimation of magnetic grain sizes the interpretation of variations established by field and laboratory susceptibility data has been constrained by petrography and transmission electron microscopy tem

fe oxide microcrystals in welded tuff from southern nevada origin of remanence carriers by precipitation in volcanic glass although it is widely recognized that remanent magnetism in ash flow tuffs is carried by fine grained fe oxides the origin mineralogy and significance of such magnetic carriers are not well understood the authors have obtained transmission electron microscope images of distinctive fe oxide microcrystals in rhyolitic samples located 3 8 7 6 and 18 5 m above the base of a 110 m thick section of the miocene tiva canyon member of the paintbrush tuff the fe oxide microcrystals are lath shaped and increase in size from 20 x 140 nm in the lowermost sample near base of the member to 120 x 800 nm in the uppermost sample within the flow interior microcrystals in this size range are within or close to the range of single domain grain size for magnetite electron diffraction and analytical x ray data indicate that the microcrystals in the lower two samples are cubic fe oxides magnetite maghemite with less than 10 mol ti end member and that those in the uppermost sample are manganiferous hematite systematic variations in magnetic properties are consistent with the observed variations in size and mineralogy of the microcrystals these microcrystals are morphologically distinct from grains that the authors interpret to be fragments of phenocrysts the morphology and spatial distribution ofmore the microcrystals as well as their increase in grain size from the rapidly cooled base of the ash flow sheet into the flow interior are consistent with an origin by nucleation and growth from volcanic glass at elevated temperature subsequent to emplacement less

some examples of the middle triassic marine transgression in south western mediterranean europe in southwestern mediterranean europe ne spain sardinia and nw apennines e g monti pisani and punta bianca the middle triassic transgression on a margin of an intracratonic basin appears to be controlled by the different morphology and tectonic activity of the margin itself

paleointensity estimates from ignimbrites an evaluation of the bishop tuff 1 ash flow tuffs or ignimbrites typically contain fine grained magnetite spanning the superparamagnetic to single domain size range that should be suitable for estimating geomagnetic field intensity however ignimbrites may have a remanence of thermal and chemical origin as a result of the complex magnetic mineralogy and variations in the thermal and alteration history we examined three stratigraphic sections through the 0 76 ma bishop tuff where independent information on postemplacement cooling and alteration is available as a test of the suitability of ignimbrites for paleointensity studies thermomagnetic curves suggest that low ti titanomagnetite tc 560 c 580 c is the dominant phase with a minor contribution from a higher tc phase s significant remanence unblocking above 580 c suggests that maghemite and or titano maghemite is an important contributor to the remanence in most samples we obtained successful paleofield estimates from remanence unblocked between 440 c and 580 c for 46 of 89 specimens 15 sites at two of three total localities these specimens represent a range of degrees of welding and have variable alteration histories and yet provide a consistent paleofield estimate of 43 0 t 3 2 equivalent to a vadm of 7 8 1022 am2 the most densely welded sections of the tuff have emplacement temperatures inferred to be as high as 660 c suggesting that the remanence may be primarily thermal in origin though a contribution from thermochemical remanence cannot be excluded these results suggest that ignimbrites may constitute a viable material for reliable paleointensity determinations

quantifying paleoprecipitation of the luochuan and sanmenxia loess on the chinese loess plateau abstract paleoprecipitation is one of the most important paleoclimatic factors for monsoon studies magnetic properties of the chinese loess paleosol sequences have been demonstrated to be controlled strongly by the mean annual precipitation map in this study temporal variations of maps were systematically investigated for the luochuan lc and sanmenxia smx sequences from the loess unit l1 10 ka to the paleosol unit s5 620 kyr by applying the new climofunction map 8 06 fd hirm 254 where fd and hirm are frequency dependent magnetic susceptibility and hard isothermal remanent magnetization respectively for both the lc and smx sequences our climofunction indicates paleosols have higher maps than loess units and the maximum map value occurs in s5 indicating that the east asian summer monsoon was the strongest during the formation of s5 in agreement with previous studies overall maps of smx are higher than those of lc as smx is in the southeast of lc and receives more precipitation the positive correlation between the reconstructed maps and fd and arm suggests that precipitation is a key factor controlling degree of pedogenesis maps of paleosols from smx display a negative correlation with synchronous insolation maxima and a positive correlation with corresponding insolation minima however at lc maps have a less significant relationship with insolation this may be because the summer monsoon signals are relatively weak in lc and covered by local climate and environmental alterations in interglacials the summer monsoon associated with precipitation is controlled by the corresponding insolation maxima and minima in addition the map gradient between lc and smx is also modulated by the insolation amplitude

isothermal remanence experiments at room and at liquid nitrogen temperature application to soil studies a simple magnetic mineral identification technique is proposed which measures isothermal remanent magnetisation irm acquired in different field strengths at 293 k and 77 k magnetic parameters are introduced that use these irms in order to distinguish concentration and type of ferromagnetic minerals in different magnetic states the method determines easily contributions of superparamagnetic ferrimagnetic minerals in environmental magnetism studies in addition high coercivity goethite and possibly superparamagnetic hematite are identified the analysis of the magnetic properties of a soil profile on a late pleistocene terrace from the jarama river in central spain is given as an example

analysis of the field dependence of remanent magnetization curves 1 a new method to calculate and analyze coercivity distributions of measured acquisition demagnetization curves of remanent magnetization is presented the acquisition demagnetization curves are linearized by rescaling both the field and the magnetization axes an appropriate filtering of the linearized curves efficiently removes measurement errors prior to evaluating the coercivity distributions the filtered coercivity distributions are modeled using a set of generalized probability density functions in order to estimate the contributions of different magnetic components an error estimation is calculated for these functions with analytical and numerical methods in order to evaluate whether the model is significantly different from the measured data three sediment samples from baldeggersee switzerland and three samples of urban atmospheric particulate matter pm have been analyzed using this method it is found that the coercivity distributions of some of the magnetic components show significant and consistent deviations from a logarithmic gaussian function large deviations are found also in the coercivity distributions of theoretical af demagnetization curves of single domain and multidomain particles constraints in the shape of model functions affect the identification and quantification of magnetic components from remanent magnetization curves and should be avoided as far as possible the generalized probability density function presented in this paper is suitable for appropriate modeling of gaussian and a large number of non gaussian coercivity distributions

authigenic ferrimagnetic iron sulfide preservation due to nonsteady state diagenesis a perspective from perseverance drift northwestern weddell sea we document magnetic mineral diagenesis with high resolution magnetic susceptibility hysteresis isothermal remanent magnetization and other rock magnetic measurements through a shallow sulfate m