magnetic properties of hydrothermally synthesized greigite fe3s4 i rock magnetic parameters at room temperature summary greigite of variable purity has been synthesized hydrothermally at 140 c by injecting a mohr s salt solution into a sodium sulphide solution containing dissolved zerovalent sulphur ageing for 30 960 min and rapidly quenching oxygen was rigorously excluded during the synthesis scanning electron microscope sem observations yield a grainsize range up to 400nm the variable purity was deduced from a varying specific saturation magnetization 3 29 am2 kg i the mjm or ors os ratio varies between 0 3 and 0 4 which is indicative of fine grained greigite concurring with sem observations hysteresis measurements at low temperatures indicate the presence of grains that are superparamagnetic at room temperature coercivity parameters b 13 43 mt bo cr 37 73 mt are the highest obtained to date for synthetic greigite and compare well with those measured for natural greigite ranges for other rock magnetic parameters are discussed greigite hysteresis parameters overlap those of magnetite to a large degree a diagnostic interparametric ratio for greigite is its high o xin ratio the range of the present greigite is 40 75 kam

diagenesis and remobilization of carbon and sulfur in mid pleistocene organic rich freshwater sediment analyses of carbon and sulfur concentrations speciation of sulfur sulfur isotopic data and magnetic remanence properties are used to investigate the diagenetic history of carbon and sulfur in a pleistocene organic rich freshwater sediment the west runton freshwater bed norfolk uk although this unit is of freshwater origin on paleontological grounds bulk c s ratios for the sediment are low 2 to 7 indicative of diagenesis in a marine environment this apparent contradiction arises from two factors firstly much of the s is organically bound and bulk c s does not reflect an environment where pyrite is the dominant sink for diagenetic sulfide the basis for discrimination of marine and freshwater environments by the c s method secondly post diagenetic remobilization of s has occurred in the bed during a phase of oxic groundwater weathering sulfur has been leached from the upper part of the unit and is fixed as 1 ferrimagnetic greigite 2 pyritic s and 3 organic s lower in the section where reducing conditions have been maintained the lowest parts of the unit appear relatively unaffected by this process c pyritic s here is indicative of the original freshwater depositional environment and early diagenetic greigite is preserved we conclude that bulk c s ratios are not a reliable diagnostic tool for organic rich freshwater sediments since significant organic s concentrations can be present pyritic s must be determined specifically in organic rich sediment to give adequate distinction of depositional environment more worrying is the apparent ease with which s may be redistributed within a bed obscuring original depositional signatures whilst this is apparent when the sequence is examined in detail samples collected with less care or where less control is feasible e g drill chips or sidewall cores may yield erroneous data

high resolution palaeosecular variation in northern europe during the last 3200 years variations in the declination inclination and relative palaeointensity of earth s magnetic field during the last 3200 yr have been recorded from a sequence of annually laminated sediments in lake pohjajarvi lat 62 n central finland the magnetic mineralogy is uniform with only small variations in concentration of magnetite of pseudo single domain psd grain size the variations in direction were found to be very similar to records reconstructed from other lakes in finland and northwest russia while the relative palaeointensity curve can be correlated accurately with archaeomagnetic data from central europe

magnetic properties of sedimentary greigite fe3s4 an update greigite fe3s4 is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction it can also grow at any time when dissolved iron and sulfide are available during diagenesis greigite is important in paleomagnetic environmental biological biogeochemical tectonic and industrial processes much recent progress has been made in understanding its magnetic properties greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites the crystallographic c axis is the easy axis of magnetization with magnetic properties dominated by magnetocrystalline anisotropy robust empirical estimates of the saturation magnetization anisotropy constant and exchange constant for greigite have been obtained recently for the first time and the first robust estimate of the low field magnetic susceptibility is reported here the curie temperature of greigite remains unknown but must exceed 350 c greigite lacks a low temperature magnetic transition on the basis of preliminary micromagnetic modeling the size range for stable single domain behavior is 17 200 nm for cubic crystals and 17 500 nm for octahedral crystals gradual variation in magnetic properties is observed through the pseudo single domain size range we systematically document the known magnetic properties of greigite at high ambient and low temperatures and with alternating and direct fields and illustrate how grain size variations affect magnetic properties recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records including widespread remagnetizations

magnetic properties of muddy sediments on the northeastern continental shelves of china implication for provenance and transportation mud deposits are widespread in estuaries and on continental shelves and contain important information regarding interactions between terrestrial and coastal processes magnetic properties of muddy sediments from the northeastern continental shelves of china including shelves close to korean coasts were analyzed using bulk and size fractionated samples to elucidate muddy sediment sources and transport types concentration and granulometry of magnetic minerals were determined and all samples were found to be dominated by magnetite muddy sediments from the zhemin coast off the zhejiang and fujian coasts have the highest magnetic susceptibility and saturation isothermal remanent magnetization sirm values while those from the central and southeastern south yellow sea and the western korea strait have lower values reflecting lower magnetic mineral concentrations single domain ferrimagnetic grains dominate the magnetic particles in the central south yellow sea while superparamagnetic sp grains contribute significantly to the magnetic grains in the bohai sea sp and coarse multi domain md grains dominate magnetic grain assemblages in the north yellow sea and along the zhemin coast rock sediment particle size is not a major factor affecting the magnetic properties of the mud deposits in the study area rather terrigenous inputs and hydrodynamic transport processes primarily control the magnetic properties and sediments from the changjiang and huanghe rivers make the most significant contribution this observation applies to the whole study area although terrigeneous magnetic mineral concentrations decrease with increasing distance from the river mouths due to both sorting and mixing with other sediments with weak magnetic signatures bacterial magnetosomes also play a role in the central south yellow sea

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

paleomagnetism of two late pleistocene lake basins in colorado an evaluation of detrital remanent magnetization as a recorder of the geomagnetic field paleomagnetic studies of magnetite bearing lacustrine sediments from two late pleistocene sections age range about 12 000 23 000 14c years one at devlins park in the front range the other at triangle park in the northern end of the sawatch range colorado indicate that detrital remanent magnetization of fine grained silty clay sediments at both locations was capable of recording changes in the magnetic field over periods as short as 100 200 years whereas coarser grained silts in the triangle park section seem to be less efficient recorders of the geomagnetic field the remanence of the fine grained sediments contains an apparent inclination error of about 9 at both localities in addition locally operative depositional and or postdepositional processes have produced both intrabasinal and interbasinal systematic differences in the remanence records of up to about 30 in declination and 10 in inclination comparison of the directional data from devlins park with those from four other broadly contemporaneous north american lake basins reveals that although there are abundant minor and several major discrepancies there are general similarities in the longer wavelength features particularly of declination the differences in the records are attributable to depositional and postdepositional factors variable and secondary overprinting local field differences sampling techniques and incorrect stratigraphic correlations the overall similarity in the records probably reflects the influence of the geomagnetic field the greatest difficulty in determining the significance of the similarities and differences between the records from the various lakes is the present lack of precise age and stratigraphic control

the mineral magnetic properties of an annually laminated holocene lake sediment sequence in northern sweden detailed mineral magnetic measurements were conducted on a 9000 year varved lake sediment sequence in northern sweden lake sarsjon the results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments which is controlled to a large extent by the intensity of the spring snow melt in contrast the concentration of ferrimagnetic magnetite reflected by initial magnetic susceptibility and magnetic hysteresis parameters is positively correlated to the concentration of organic carbon which is most likely of an autochthonous origin this magnetite has magnetic properties that are characteristic of stable single domain magnetite grains produced by magnetotactic bacteria the paramagnetic susceptibility record clearly points to a climatic excursion in the early holocene between 6100 174 bc and 5700 167 bc which can be correlated to an d18o excursion a cold event in the greenland ice cores and lake sediments in southern germany an

rock magnetic signature of a miocene playa cycle in central asia and environmental implications the increased aridification of central asia during the miocene coincides in time with lake formations and the evolution of playa environments in the region however miocene continental climate dynamics and the forcing of aridification are still not well constrained neogene lacustrine mudflat deposits in the ili basin in southeast kazakhstan provide a well exposed paleoclimate archive here we present a detailed rock magnetic study of a middle miocene playa cycle deposited in a closed basin we use high resolution rock magnetic parameters lithological studies and geochemistry to reconstruct the playa environment and the depositional conditions the rock magnetic mineralogy of the playa cycle is controlled by hematite and two fine grained magnetite phases increased magnetic concentrations occur during dry mudflat conditions with a lower groundwater table and increased aridity the underlying processes controlling the observed variation in magnetic concentrations are a complex interplay of diagenetic processes during and after deposition the data support an authigenic origin of both magnetite phases one formed before and the other after sediment consolidation early diagenetic formation of fine grained magnetite by microbial activity is followed by post depositional formation of a secondary fine grained magnetite phase the rock magnetic results such as magnetic concentration dependent parameters arm sirm and s ratio indicate a sensitive record of ground water availability and aridity changes in the ili basin we suggest that they can serve as an effective proxy for detailed paleo environment reconstruction of playa evolution not only in the middle miocene ili basin but also in comparable floodplain playa lake settings

high resolution record of the upper olduvai transition from po valley italy sediments support for dipolar transition geometry abstract a detailed record of the upper olduvai polarity transition composed of 100 transitional directions has been obtained from the crostolo section in northern italy a careful examination of the rock magnetic properties of the sediments using standard paleomagnetic techniques thermomagnetic scanning electron microscopy microprobe x ray diffraction and mossbauer analysis shows that greigite is the main magnetic carrier of the remanence the correlation of a shift in the magnetic record to a small scale sedimentary feature observed in the section indicates that the magnetization was acquired at deposition or very shortly after the virtual geomagnetic pole vgp path is largely confined along a great circle over north and south america 90 west of the site and consists of three stages first the vgp moves to southern mid latitudes then after a period of standstill it comes back to almost true north and finally the south pole is reached in a third step although different from a record from the southern indian ocean this path is virtually identical to those obtained for the same transition from north pacific deep sea cores and partly coincides with a north atlantic record which suggests that a dipolar component may be present in the transitional field during the upper olduvai reversal a review of the recently obtained records of various transitions shows that in more than two thirds of the cases the vgp paths are similarly confined along a meridian over the americas or antipodal to them irrespective of the sampling site and of the sense of the transition although not deterministic this tendency suggests that a similar dipolar component might be present in the transitional fields of other reversals of different ages

magnetic hysteresis properties of greigite fe3s4 and a new occurrence in holocene sediments from swedish lappland a new occurrence of ferrimagnetic greigite fe3s4 is reported in freshwater holocene sediments from gaskkamus gorsajavri in swedish lappland the presence of greigite was inferred from the mineral magnetic analysis of sediment cores the greigite bearing sediments possess a high saturation isothermal remanent magnetisation to susceptibility sirm ratio a characteristic shared by other natural sediments known to contain greigite the hysteresis properties measured using a vibrating sample magnetometer of natural greigite extracted from lake sediments show much higher saturation coercivity b0 c and mrsms ratio values approximately 50 mt and 0 5 respectively than synthetic samples of greigite approximately 12 mt and 0 2 the results suggest that synthetic greigite samples contain crystals ranging from small non remanence carrying superparamagnetic grains to large multi domain grains in contrast the natural samples probably consist predominantly of pseudo single domain and single domain crystals capable of carrying a chemical remanent magnetisation however the unstable nature of greigite under laboratory conditions creates difficulty in characterising its physical attributes

a 13 000 year record of environmental magnetic variations in the lake and peat deposits from the chandra valley lahaul implications to holocene monsoonal variability in the nw himalaya abstract an 13 000 year old record of in situ peat bog and lacustrine sediments from a post glacial lake in the chandra valley of the lahaul himalaya is studied to generate the record of environmental magnetic signatures in response to indian summer monsoon ism variability in the nw himalaya the chronology of studied chandra peat trench cpt profile is based on 9 ams 14c calibrated dates cal yr bp the piece wise linear regression analysis of age depth model indicates non linear sedimentation with higher rates from 4142 cal yr bp to the present and lower accumulation during 12 880 4142 cal yr bp the mineral magnetism showed three dominant assemblages of magnetic minerals with varying concentrations in peat lake sediment sequence i e 1 mixed ferri and antiferromagnetic minerals between 12 880 and 11 019 cal yr bp 2 dominant antiferromagnetic mineralogy from 11 019 to 3172 cal yr bp and 3 significantly increased concentrations of mixed ferri and antiferromagnetic minerals from 3172 cal yr bp to the present with characteristically increased ferrimagnetic concentrations after 2032 cal yr bp the characteristic increase in antiferromagnetic mineral concentration accompanied by decreased ferrimagnetic concentration from 10 398 to 5770 cal yr bp suggest possible oxidation of magnetite to hematite under warmer climate conditions and corresponds to increased ism intensity during early to mid holocene warm wet climate in the nw himalaya the distinctly increased concentration of antiferromagnetic minerals from 6732 to 5770 cal yr bp indicates mid holocene climate optimum hco in the lahaul himalaya the strengthening and weakening of ism recorded in environmental magnetic signatures during 1260 852 cal yr bp 690 1098 ad and between 852 and 239 cal yr bp 1098 1711 ad corresponds to medieval warm period mwp and little ice age lia events respectively

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

carbon sulfur iron relationships in sedimentary rocks from southwestern taiwan influence of geochemical environment on greigite and pyrrhotite formation the importance of the magnetic iron sulfide minerals greigite fe3s4 and pyrrhotite fe7s8 is often underappreciated in geochemical studies because they are metastable with respect to pyrite fes2 based on magnetic properties and x ray diffraction analysis previous studies have reported widespread occurrences of these magnetic minerals along with magnetite fe3o4 in two thick plio pleistocene marine sedimentary sequences from southwestern taiwan different stratigraphic zones were classified according to the dominant magnetic mineral assemblages greigite pyrrhotite and magnetite dominated zones greigite and pyrrhotite are intimately associated with fine grained sediments whereas magnetite is more abundant in coarse grained sediments we measured total organic carbon toc total sulfur ts total iron fet 1n hcl extractable iron fea and bulk sediment grain size for different stratigraphic zones in order to understand the factors governing the formation and preservation of the two magnetic iron sulfide minerals the studied sediments have low ts fea weight ratios 0 03 0 2 far below that of pyrite 1 15 which indicates that an excess of reactive iron was available for pyritization observed low ts 0 05 0 27 is attributed to the low organic carbon contents toc 0 25 0 55 which resulted from dilution by rapid terrigenous sedimentation the fine grained sediments also have the highest fet and fea values we suggest that under conditions of low organic carbon provision the high iron activity in the fine grained sediments may have removed reduced sulfur so effectively that pyritization was arrested or retarded which in turn favored preservation of the intermediate magnetic iron sulfides the relative abundances of reactive iron and labile organic carbon appear to have controlled the transformation pathway of amorphous fes into greigite or into pyrrhotite compared to pyrrhotite dominated sediments greigite dominated sediments are finer grained and have higher fea but lower ts we suggest that diagenetic environments with higher supply of reactive iron lower supply of labile organic matter and consequently lower sulfide concentration result in relatively high eh conditions which favor formation of greigite relative to pyrrhotite

a 15 400 year record of environmental magnetic variations in sub alpine lake sediments from the western nanling mountains in south china implications for palaeoenvironmental changes abstract a detailed environmental magnetic investigation has been performed on a sub alpine sedimentary succession deposited over the past 15 400 years in daping swamp in the western nanling mountains of south china magnetic parameters reveal that fine grains of pseudo single domain psd magnetite or titanomagnetite are the dominant magnetic minerals in the lake sediments and surface soils collected from the catchment which suggests that magnetic minerals in lake sediments mainly originated from surface soil erosion of the catchment variation of surface runoff caused by rainfall is interpreted as the main process for transportation of weathered soils into the lake in the last deglacial period lgp 15 400 11 500 cal a bp the influx of magnetic minerals of detrital material may have been significantly affected by the severe dry and cold conditions of the last glacial maximum stabilised conditions of the catchment associated with increased vegetation coverage e g 8000 4500 and 2500 1000 cal a bp limited the input of magnetic minerals intensive soil erosion caused by increased human activity may have given rise to abnormal increases in multiple magnetic parameters after 1000 cal a bp because changes in runoff and vegetation coverage are closely related to asian summer monsoon asm intensity the sedimentary magnetism of daping swamp provides another source of information to investigate the evolution of the asm

a record of reversed polarity carried by the iron sulphide greigite in british early pleistocene sediments abstract palaeomagnetic measurements were made on samples extracted from a short sequence of early pleistocene estuarine clays now exposed in a sea cliff near sheringham on the north norfolk coast uk on the basis of earlier palynological work these clays had been ascribed a pastonian late tiglian age the clays show marked changes in colour from reddish brown at the top of the unit to blue grey in the middle and grey brown at the base the palaeomagnetic data vary in close association with these colour changes the top and basal brown clays show scattered normal directions of low intensity while the middle blue clays show strongly clustered reversed directions of much higher intensities some samples taken from the boundary between the middle blue and upper red clays show upon demagnetisation a normal overprint on a stable reversed polarity using high gradient magnetic extraction magnetic concentrates have been obtained from the strongly magnetic middle blue clays the presence of iron sulphide minerals in these concentrates was identified using energy dispersive x ray analysis during scanning electron microscopy more specifically x ray diffraction identifies greigite as the only detectable ferrimagnetic mineral in the magnetic concentrates rock magnetic measurements show clear qualitative differences in the magnetic mineralogies of the three clay subunits but absolute identification of the magnetic mineralogy of the weakly magnetic upper and basal brown clays has not yet been possible we interpret the sequence as a primary reversed polarity record this record is carried by the iron sulphide greigite as a chemical remanence acquired during syn depositional reduction of iron via the decomposition of organic material in these anoxic tidal clays subsequently the upper and basal subunits of the clay have been oxidised by permeation of groundwater from the adjacent coarse grained sediments most of the griegite in the oxidised margins of the clay has been altered as a result to a new less efficient magnetic recording material which thus carries a later scattered low intensity normal overprint

magnetic susceptibility mapping of the sudbury area ontario canada evaluating pollution distributions decades later this study evaluates the use of magnetic susceptibility and magnetic parameter measurements in assessing spatial and temporal variations of pollutants that emanated from mining industries in and around sudbury ontario canada for this purpose in situ magnetic susceptibility in situ was measured at 106 sites on a grid of 10 km 10 km and 5 km 5 km the in situ values ranged from 2 10 5 to 149 10 5 si and the highest in situ values were observed near the active copper cliff and inactive coniston mining sites the lowest in situ values were measured at increased distances from possible pollution sources therefore mapping of in situ magnetic susceptibility values is a proxy to polluted areas in and around sudbury to evaluate potential anthropogenic and or lithogenic input to in situ low frequency mass specific magnetic susceptibility lf variations with depth were classified into four different types of profiles for further investigation of magnetic minerals in the samples labo

a newly discovered submerged reef on the miyako sone platform ryukyu island arc northwestern pacific abstract bathymetric echosounder mapping and seafloor observations using a remotely operated vehicle were conducted on the miyako sone platform located northeast of miyako jima ryukyu islands northwestern pacific ocean this study aims to unravel the origin and development of the miyako sone platform a key field to reconstruct the biogeographic evolution and the geologic history of the ryukyu islands the resulting high resolution bathymetric map reveals details of the seafloor geomorphology including the spatial distribution of submerged terraces on the platform we report herein the discovery of a submerged reef the miyako sone reef on the platform whose top is at a water depth of 56 m extending in a north south direction for up to 1 km and with a minimum width of 500 m the reef consists of a central depression and a concentric marginal ridge topographic features analogous to spurs and grooves are recognized along the outer margin of the marginal ridge the miyako sone reef was drowned during a period of global postglacial sea level rise between 11 12 ka which may coincide with mwp 1b at 11 5 ka the increase in sea surface temperature in the ryukyu islands at 11 ka shows that the miyako sone reef formed during the final stage of the cooler postglacial period part of the miyako sone platform was likely a land bridge for the migration of terrestrial organisms from okinawa jima to miyako jima during low sea level stands after the deposition of the ryukyu group

sources of fine grained magnetic minerals in sediments a problem revisited progress in the discrimination of fine grained magnetic minerals in sediments and sediment sources using measurements of magnetic susceptibility at two frequencies and of magnetic remanence generated by a combination of direct and alternating currents is summarized the former measurements yield values for low field and frequency dependent susceptibility lf and fd respectively the latter generate an anhysteretic remanent magnetisation arm that when normalized to the dc bias field can be represented as the susceptibility of arm arm using quotients derived from lf fd and arm to generate bi logarithmic plots it is possible to discriminate between assemblages dominated by magnetic minerals formed through pedogenesis and those arising from the presence of magnetotactic bacteria that use chains of magnetic particles to seek optimum environments in surface sediments sediments to which both types of magnetic mineral contribute occupy positions between the envelopes of values typical of soil d

devensian late glacial and early flandrian environmental history of the vale of pickering yorkshire england pollen sedimentological and charcoal particle analyses are presented from devensian late glacial and early to mid flandrian deposits from a former lake in the vale of pickering yorkshire the combined analytical methods provide evidence for a short lived climatic deterioration towards the end of the late glacial interstadial followed by a brief recovery prior to the loch lomond stadial this deterioration may be correlated with one of the pre younger dryas cooling periods identified not only in other pollen sequences from britain and europe but from such diverse sources as foraminifera from the norwegian sea and electrical conductivity measurements from the greenland ice sheet loss on ignition and magnetic susceptibility data suggest that the loch lomond stadial was characterised by an initial prolonged temperature decline followed by a sudden more severe downturn resulting in particularly intense solifluction radiocarbon accelerator dating of the early flandrian marl deposits illustrates the problem of age determination in calcareous lakes and an estimate of the magnitude of hard water error is obtained the local population expansion of alnus glutinosa is dated to 7640 85 yr bp but there is possible evidence for a late glacial presence of the tree the significance of which is discussed in relation to other sites in east yorkshire 1996 john wiley sons ltd

mineral magnetic characterization of sediment sources from an analysis of lake and floodplain sediments in the catchments of the old mill reservoir and slapton ley south devon uk research on suspended sediment transport in the catchments of the old mill reservoir and slapton lower ley south devon has attempted to discriminate changing catchment sources on the basis of downcore variations in the mineral magnetic properties of lake reservoir and floodplain sediments here we examine these downcore variations and also explore the variability in catchment sources and the influence of topographic controls on mineral magnetic signatures of topsoils and subsoils particle size controls on the mineral magnetic signatures are explored by an analysis of a fractionated sediment sample whilst the possible impact of diagenesis is assessed by an examination of the mn profiles in the lake and reservoir sediments from this analysis it is evident that the mineral magnetic signatures of well sorted floodplain deposits are more likely to reflect the particle size composition of the transported material by contrast the mineral magnetic record in the sediment of slapton ley appears to be most strongly influenced by dissolution of magnetic minerals the sediment of the old mill reservoir provides the only suitable record for the application of a simple mixing model which is developed in order to quantify changes in the relative contribution of topsoil and subsoil through time the research has important implications for attempting to reconstruct sediment sources in highly eutrophic lakes and emphasizes the uncertainty in the application of simple mixing models 1998 john wiley sons ltd

the occurrence of greigite in sediments from loch lomond greigite has been identified in the sediments of loch lomond using x ray diffraction greigite is the dominant magnetic mineral in the oldest sediments recovered while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies a layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations probably as a consequence of magnetite dissolution associated with sulphide rich pore waters produced at the time of a marine incursion the greigite largely oxidises once the sediment is exposed to air but if freeze dried the greigite becomes surprisingly stable following freeze drying the greigite can be heated to 280 c in air before it alters and loses its strong ferrimagnetic properties

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

a geomagnetic excursion during the late matuyama chron the osaka group southwest japan abstract duplicate records of a geomagnetic excursion during the late matuyama chron were obtained from sediments gathered at the takatsuki and izumi sites in southwest japan the excursion is dominated by westerly declinations with shallow inclinations and was found just above the volcanic ash known as the azuki tuff in a marine clay layer of the osaka group the excursion occurred at about 0 85 ma a recently revised age for the azuki tuff by extrapolating constant sedimentation rates for the holocene marine clay dated by the radiocarbon method the duration of the excursion is estimated at about 240 yr with a range of 200 500 yr if we consider possible fluctuations in sedimentation rates the kamikatsura excursion previously reported around this time from the osaka group data is estimated to be a few tens of thousands of years older than the excursion reported in this study based on correlations of changes in sea level recorded in the sediments of the osaka group and the oxygen isotope record of deep sea cores these two excursions in japan together with short normal events reported in the southern ocean north america and china suggest that during the period from 0 87 0 84 ma the geomagnetic field may have been unstable and excursions or short reversals may have occurred regionally and sporadically over the earth

a multi proxy approach to reconstructing sedimentary environments from the sperchios delta greece this paper presents an integrated approach to assess holocene environmental changes in the sperchios delta sperchios rift central greece a multidisciplinary study was carried out applying established analytical methods as well as exploring new techniques to detect past environmental conditions in a fluvio deltaic depositional system a series of six deep boreholes up to 50 m long and four shallow cores up to 6 m long from across the delta plain were studied in detail sedimentary facies were defined by changes in grain size and macro and microfaunal composition variability in mineral magnetic composition documented by changes in bulk magnetic susceptibility and 77k 293k and remanence parameters s 300 and arm sirm ratios as well as down core elemental variations obtained by scanning micro x ray fluorescence xrf provide constraints on the depositional changes related to the evolution of the sperchios delta correlations between elemental data derived by xrf analyses and grain siz

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

fluvial sediments of the algeti river in southeastern georgia an archive of late quaternary landscape activity and stability in the transcaucasian region abstract in order to obtain information about landscape activity and stability during the late quaternary in the transcaucasian region fluvial sediments of the lower algeti river in se georgia were studied by means of geomorphologic sedimentologic and geochronologic methods these investigations show that sediments aggraded by the late pleistocene braided algeti river were strongly incised around the pleistocene holocene transition and subsequently a small scale pattern of diachronous fluvial terraces deposited by the now meandering river developed in the new valley during the holocene prior to ca 3 cal ka bp active phases of river channel aggradation and overbank sedimentation about 6 cal ka bp and 3 4 3 2 cal ka bp can be linked with climate driven vegetation changes i e stronger fluvial dynamics with sedimentation occurred during more arid and colder periods whereas the caucasian holocene climate optimum between 6 and 3 4 cal ka bp was characterized by stable geomorphologic conditions after 3 cal ka bp strongly increased human impact documented by former pollen studies is reflected by the fluvial dynamics as well i e an activity phase of strong overbank sedimentation 2 7 2 1 cal ka bp occurred during a period when forests in the lesser caucasus were burnt down two subsequent activity phases with fluvial sedimentation can be linked with historic events that probably both influenced vegetation distribution of the region i e a period of flourishing of georgia during the middle age and a time of large scale destruction of the country due to a persian invasion at the end of the 18th century ad respectively thus whereas no influence of tectonic events or fluctuations of the caspian sea level on the fluvial dynamics could be detected se georgia shows its fragile character with respect to climate and human driven vegetation changes similar to other semi arid landscapes of the mediterranean region

magnetic and chemical characterisation of a diagenetic magnetic mineral formed in the sediments of productive lakes abstract measurement of low frequency magnetic susceptibility in sediments from several lakes showed that a diagenetically formed magnetic mineral can contribute a significant amount to the intensity of bulk magnetic measurements on anaerobic sediments from productive lakes a single ferrimagnetic mineral containing stable single domains is responsible sequential chemical extraction showed that the mineral is not a carbonate phosphate or partially reduced oxide comparison of changes in magnetic properties with changes in sulphide concentrations suggests that the mineral concentration covaries with sulphide but is not actually a simple iron monosulphide

low temperature magnetic properties of greigite fe3s4 1 we provide comprehensive low temperature magnetic results for greigite fe3s4 across the spectrum from superparamagnetic sp to multidomain md behavior it is well known that greigite has no low temperature magnetic transitions but we also document that it has strong domain state dependence of magnetic properties at low temperatures blocking of sp grains and increasing thermal stability with decreasing temperature is apparent in many magnetic measurements thermally stable single domain greigite undergoes little change in magnetic properties below room temperature for pseudo single domain psd md greigite hysteresis properties and first order reversal curve diagrams exhibit minor changes at low temperatures while remanence continuously demagnetizes because of progressive domain wall unpinning the low temperature demagnetization is grain size dependent for psd md greigite with coarser grains undergoing larger remanence loss ac susceptibility measurements indicate consistent blocking temperatures tb for all synthetic and natural greigite samples which are probably associated with surficial oxidation low temperature magnetic analysis provides much more information about magnetic mineralogy and domain state than room temperature measurements and enables discrimination of individual components within mixed magnetic mineral assemblages low temperature rock magnetometry is therefore a useful tool for studying magnetic mineralogy and granulometry of greigite bearing sediments