submarine landforms and shallow acoustic stratigraphy of a 400 km long fjord shelf slope transect kangerlussuaq margin east greenland kangerlussuaq fjord is a relatively uniform steep walled basin whose floor has an almost smooth surface debris is supplied mainly from icebergs from the fast flowing kangerlussuaq glacier sedimentation after iceberg release from multi year sea ice is mainly by rain out of fine grained englacial debris streamlined glacial lineations and drumlins were produced at the sedimentary bed of an ice sheet that expanded into kangerlussuaq trough at the last glacial maximum lgm bedrock channels and crescentic overdeepenings indicate warm based ice and free water beneath parts of the former ice sheet cross cutting iceberg scour marks which characterise outer kangerlussuaq shelf were produced not only during deglaciation but also occasionally through the holocene by deep keeled icebergs from further north in east greenland the outward convex contours of the shelf edge and slope beyond kangerlussuaq trough and debris flows on the slope suggest a glacier influenced high latitude fan the distribution of streamlined subglacial landforms demonstrates that the greenland ice sheet extended throughout kangerlussuaq fjord and reached at least 200 km across the shelf in kangerlussuaq trough at the lgm streamlined landform orientation indicates ice flow from the interior of greenland down the axis of kangerlussuaq trough there is little evidence for discrete sedimentary depocentres in the trough implying that ice probably retreated rapidly from the outer and mid shelf during deglaciation

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

on the magnetocrystalline anisotropy of greigite fe3s4 the ferrimagnetic mineral greigite cubic fe3s4 is well known as an intracellular biomineralization product in magnetic bacteria and as a widely occurring authigenic mineral in anoxic sediments due to the lack of suitable single crystal specimens the magnetic anisotropy parameters of greigite have remained poorly constrained to the point where not even the easy axis of magnetization is known here we report on an effort to determine the anisotropy parameters on the basis of ferromagnetic resonance fmr powder spectroscopy on hydrothermally synthesized chemically pure greigite microcrystals dispersed in a nonmagnetic matrix in terms of easy axis orientations the fmr data are consistent with or or less likely a more general type with a g factor of 2 09 the anisotropy field is about 90 mt and in some samples may reach 125 mt compared to 30 mt for cubic magnetite this confirms the dominating role of cubic anisotropy on the magnetic properties of greigite which we show to be responsible for large sirm k values k1 is in the range 15 23 j m3 or 10 15 kj m3 yielding upper limits of 44 or 34 nm for the superparamagnetic grain size respectively

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

characterization of hematite α fe2o3 goethite α feooh greigite fe3s4 and pyrrhotite fe7s8 using first order reversal curve diagrams 1 first order reversal curve forc diagrams have become a standard tool in rock magnetism yet magnetite is the only magnetic mineral that is well characterized using forc diagrams we present forc diagrams for predominantly single domain sd synthetic aluminous hematite a fe2 xalxo3 and goethite a feal ooh and natural greigite fe3s4 and pyrrhotite fe7s8 to constrain interpretation of forc diagrams from natural samples hematite and goethite have low spontaneous magnetizations and negligible magnetic interactions while greigite and pyrrhotite have higher spontaneous magnetizations and can have strong magnetic interactions the coercivity of hematite systematically increases with al content only for samples produced using the same synthesis method but it is variable for samples produced with different methods even for similar al content this precludes use of magnetic coercivity alone to quantify the al content of natural hematites goethite has much higher coercivity than hematite for all measured samples sd and superparamagnetic sp behavior is common in natural greigite samples with peak coercivities ranging from

centennial scale variability of the british ice sheet implications for climate forcing and atlantic meridional overturning circulation during the last deglaciation evidence from paleoclimatic archives suggests that earth s climate experienced rapid temperature changes associated with pronounced interhemispheric asymmetry during the last glacial period explanations for these climate excursions have converged on nonlinear interactions between ice sheets and the ocean s thermohaline circulation but the driving mechanism remains to be identified here we use multidecadal marine records of faunal oxygen isotope and sediment proxies from the northeast atlantic proximal to the western margins of the last glacial british ice sheet bis to document the coupling between ice sheet dynamics ocean circulation and insolation changes the core data reveal successions of short lived 80 100 years high amplitude ice rafted debris ird events that were initiated up to 2000 years before the deposition of detrital carbonate during heinrich events he 1 and 2 progressive disintegration of the bis 19 16 kyr before present b p occurred in response to abrupt ocean climate warmings that impinged on the northeast atlantic during the early deglaciation peak ird deposition recurs at 180 220 year intervals plausibly involving repeated breakup of glacial tidewater margins and fringing marine ice shelves the early deglaciation culminated in a major meltwater pulse at 16 3 kyr b p followed by another discharge associated with he1 some 300 years after we conclude that temperature changes related to external forcing and marine heat transport caused a rapid response of the bis and possibly other margins of the eurasian ice sheet massive but short lived meltwater surges influenced the atlantic meridional overturning circulation thereby contributing to north atlantic climate variability and bipolar climatic asymmetry

oscillating retreat of the last british irish ice sheet on the continental shelf offshore galway bay western ireland during the last glacial maximum the british irish ice sheet extended across the continental shelf offshore of galway bay western ireland and reached a maximum westward extent on the porcupine bank new marine geophysical data sediment cores and radiocarbon dates are used to constrain the style and timing of ice sheet retreat across the mid to inner shelf radiocarbon dated shell fragments in subglacial till on the mid shelf constrains ice advance to after 26 4 ka bp initial retreat was underway before 24 4 ka bp significantly earlier than previous reconstructions grounding line retreat was accompanied by stillstands and or localised readvances of the grounding line a large composite mid shelf grounding zone complex marks a major grounding line position with the ice grounded and the margin oscillating at this position by and probably after 23 ka bp the continental shelf was ice free by 17 1 cal ka bp but the ice sheet may have retained a marine margin until c 15 3 ka bp retreat occurred in a glacimarine setting and the ice sheet was fringed by a floating ice shelf collectively this evidence indicates a dynamic and oscillatory marine terminating ice sheet offshore of western ireland during the last deglaciation

the plio pleistocene geologic and climatic record of the kashmir valley india a review and new data abstract the kashmir valley located in the northwestern himalayas provides an intermontane valley fill comprising unconsolidated fluvio lacustrine sediments of more than a km thickness datable at 4 myr these sediments have been investigated for the last 7 years under an interdisciplinary multi agency project using a variety of proxy climatic data techniques and other analyses to decipher climatic change as a result of this study a variety of proxy climatic data from a long continental record is available now from northernmost south asia in this paper we briefly review the lithostratigraphic and chronologic framework of the sediment profile and proxy climatic data based on flora fauna stable isotopes pedology mineral magnetics and sedimentology lastly the climatic events are put in an absolute time frame for comparison with the global climatic trends the chronology is based on 14c thermoluminescence tl palaeomagnetic and fission track techniques

sediment chemistry and magnetic properties in an anomalously reducing core from the eastern mediterranean sea abstract in core kc19c 19 6 m long recovered in the abyssal plain between crete and cyprus in the eastern mediterranean a large number of organic rich layers sapropels occur which correlate to maxima in the insolation curve in contrast to other sites in the eastern mediterranean porewaters contain sulfide below a few meters below seafloor mbsf geochemical analyses were performed on the porewaters ammonium alkalinity sulfate manganese iron bisulfide chloride eh ph and sediments organic carbon barium total sulfur total iron manganese pyrite dithionite extractable iron in addition a series of magnetic parameters and ratios nrm arm irm in arm irm s ratio arm 20mt arm in were determined in the top of the sediments fe and mn hydr oxides occur at the oxic suboxic boundary just above the youngest sapropel si2 these hydr oxides appear to be more easily demagnetized by means of alternating fields than deeper hydr oxides which presumably are of detrital origin the transition from suboxic to anoxic sediments is located at 2 mbsf sulfide is produced possibly during sulfate reduction through anoxic methane oxidation at 17 5 mbsf from 17 5 mbsf sulfide migrates upward titrating reactive fe resulting in pyrite formation in the entire sediment column up to 2 mbsf at this depth the upward sulfide flux has been totally consumed by reaction with solid phase fe and dissolved fe ii diffusing downward from the suboxic zone above from 2 mbsf downward magnetic intensities are significantly reduced indicating reductive dissolution of fe oxide minerals and pyrite formation as a consequence no reliable nrm data can be obtained in the lower half of the core

late quaternary evolution and sea level history of a glaciated marine embayment bantry bay sw ireland ireland experienced a spatially complex pattern of relative sea level rsl changes and shoreline development caused by the interplay of isostatic and eustatic ice equivalent sea level processes since the last glacial maximum lgm using a combination of high resolution marine geophysical data vibrocores foraminiferal analysis and 10 ams radiocarbon dates we reconstruct the late quaternary evolution and rsl history of bantry bay a large 40 km long 5 10 km wide embayment in sw ireland the data indicate two infill phases one before and one after the lgm separated by glacial and lowstand sediments the pre lgm history is not dated and the depositional history is inferred a large sediment lobe formed at the outer edge of bantry bay as a lowstand ice proximal glacimarine outwash system as the ice retreated after the lgm at a sea level ca 80 m lower than present iceberg scour immediately west of this location likely relate to the break up of the local kerry cork ice cap long curvilinear ridges seen both offshore and on top of the sediment lobe probably formed as shoreface ridges under stronger than present tidal currents during a period of rsl stability pre 14 6 ka cal bp a subsequent infill phase is characterised by a basin wide erosional ravinement surface and the deposition of inter and sub tidal estuarine sediments although our data support the general trends our stratigraphic and radiocarbon data suggest a higher sea level between 11 and 13 5 ka cal bp than predicted by existing glacial isostatic adjustment models

greigite and the magnetic properties of sediments x ray diffraction spectra of freeze dried sediments from a lake in the english lake district positively identified the presence of greigite a magnetic iron sulfide fe3s4 mineral the sediments also show considerable loss of magnetic intensity when wet samples are allowed to oxidize several hypotheses have been proposed elsewhere to explain the intensity loss but an assessment of the evidence suggests that oxidation of greigite is responsible in these sediments data from several lakes and from laboratory experiments are used to deduce the environmental requirements for greigite formation these conditions of high labile c concentrations good sources of labile fe and s and an oscillating oxycline depth in the sediments are likely to be found only in mono or dimictic eutrophic lakes estuaries and salt marshes and are unlikely to be found in meromictic lakes unstratified lakes oligotrophic lakes or deep sea sediments

magnetic fabric variations in mesozoic black shales northern siberia russia possible paleomagnetic implications abstract a 28 m long section situated on the coast of the arctic ocean russia 74 n 113 e was extensively sampled primarily for the purpose of magnetostratigraphic investigations across the jurassic cretaceous boundary the section consists predominantly of marine black shales with abundant siderite concretions and several distinct siderite cemented layers low field magnetic susceptibility k ranges from 8 10 5 to 2 10 3 si and is predominantly controlled by the paramagnetic minerals i e iron bearing chlorites micas and siderite the siderite bearing samples possess the highest magnetic susceptibility usually one order of magnitude higher than the neighboring rock the intensity of the natural remanent magnetization m0 varies between 1 10 5 and 6 10 3 a m several samples possessing extremely high values of m0 were found there is no apparent correlation between the high k and high m0 values on the contrary the samples with relatively high m0 values possess average magnetic susceptibility and vice versa according to the low field anisotropy of magnetic susceptibility ams three different groups of samples can be distinguished in the siderite bearing samples i an inverse magnetic fabric is observed i e the maximum and minimum principal susceptibility directions are interchanged and the magnetic fabric has a distinctly prolate shape triaxial fabric samples ii showing an intermediate magnetic fabric are always characterized by high m0 values it seems probable that the magnetic fabric is controlled by the preferred orientation of paramagnetic phyllosilicates e g chlorite and mica and by some ferromagnetic mineral with anomalous orientation in relation to the bedding plane oblate fabric samples iii are characterized by a bedding controlled magnetic fabric and by moderate magnetic susceptibility and m0 values the magnetic fabric is controlled by the preferred orientation of phyllosilicate minerals and to a minor extent by a ferrimagnetic fraction most probably detrital magnetite considering the magnetic fabric together with paleomagnetic component analyses the siderite bearing and the high nrm samples about 15 of samples were excluded from further magnetostratigraphic research

apparent magnetic polarity reversals due to remagnetization resulting from late diagenetic growth of greigite from siderite summary a mixed polarity zone representing alternations between remagnetized and non remagnetized strata has been documented within the lower few metres of the crp 1 core ross sea antarctica detailed rock magnetic investigation of this interval indicates that the normal polarity remagnetization is carried by magnetostatically interacting single domain particles of a ferrimagnetic iron sulphide mineral while the reversed polarity magnetization of non remagnetized strata is carried by magnetite with a broad range of grain sizes and negligible magnetostatic interactions scanning electron microscope observations of polished sections indicate that the ferrimagnetic iron sulphide mineral is greigite fe3s4 based on microtextural relationships it is not possible to determine the relative timing of formation for much of the greigite however a significant proportion of the greigite has grown on the surface of authigenic siderite feco3 grains that occur as microconcretions and as cement surrounding detrital matrix grains in such cases microtextural relationships indicate that siderite post dates early diagenetic pyrite and that greigite post dates the siderite siderite usually forms in environments with abundant dissolved iron and carbonate but without dissolved pore water h2s this set of geochemical conditions occurs in methanic settings below the sulphate reduction zone in which early diagenetic pyrite forms we interpret the observed remagnetization of the lower part of the crp 1 core as due to a late diagenetic pore water migration event where abundant iron on the surface of siderite grains reacted with fluids containing limited dissolved sulphide thereby causing precipitation of greigite the distribution of siderite and associated greigite in the lower part of the crp 1 core is patchy which accounts for the apparent alternation of polarities this study is part of a growing catalogue of remagnetizations involving greigite which suggests that occurrences of greigite should be treated with caution in palaeomagnetic and environmental magnetic studies

rock magnetism and palaeomagnetism of greigite bearing mudstones in the italian peninsula magnetic measurements were carried out on a collection of samples from different geological settings throughout the italian peninsula the samples display magnetic properties that indicate the presence of ferrimagnetic iron sulphide minerals paired samples were also investigated to compare the palaeomagnetic behaviour with respect to different demagnetization treatments thermal static and tumbling alternating field af demagnetization greigite fe3s4 was positively identified in most samples in agreement with previous studies of greigite the sediments display thermal decomposition of the magnetic carriers at temperatures above ca 230 c resulting in decreased magnetic susceptibility values and maximum unblocking temperatures tub mostly in the range 320 350 c high saturation isothermal remanent magnetization sirm to low field magnetic susceptibility k ratios sirm k 10 ka m hysteresis ratios that are typical for single domain sd grains mrs ms 0 5 and b0 cr b0 c 1 5 where mrs is the saturation remanence ms is the saturation magnetization b0 c is the coercive force and b0 cr is the coercivity of remanence moderate coercivity with b0 cr values that range between 52 and 81 mt and a tendency to acquire a significant rotational remanent magnetization rrm we also found that greigite bearing sediments are particularly sensitive to field impressed anisotropy we propose a new magnetic parameter that can be used as a rapid mean to screen a rock sample for the presence of greigite which relies on its sd behaviour in field impressed anisotropy experiments in greigite bearing sediments the magnetic susceptibility measured in a given direction is increased by the application of a relatively high magnetic field 0 9 t in our experiments at right angles to this direction the susceptibility increase is directly correlated to the concentration of greigite in the sediment the comparative palaeomagnetic analysis of standard demagnetization techniques indicates that thermal demagnetization in close steps up to 350 380 c is clearly the most effective treatment for the isolation of the remanent magnetization carried by greigite whereas af demagnetization treatments display significant acquisition of unwanted magnetic remanences gyroremanent remanent magnetization grm and rrm at fields above ca 40 mt

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 petromagnetic study of miocene rocks bearing micro organic material and the magnetic mineral greigite sokolov and cheb basins czechoslovakia abstract the middle miocene sediments of the cypris series from the sokolov and cheb brown coal basins western bohemia were subjected to petromagnetic investigation during the laboratory thermal treatment at a temperature of 350 400 c the samples rich in micro organic material changed into carbonified samples which exhibited similar physical and technological properties to coal samples collected from the underlying coal seam the experimental results may have a bearing on several problems concerning the origin of fossil fuels and highlight specific rock properties which may have potential for identifying the micro organic content a strongly magnetic mineral greigite fe 3 s 4 was identified in magnetic zones above the coal seam the authigenic mineral greigite occurs in strata of greater thickness and it was found that a reducing environment generated by the presence of organic matter was required for the formation of the greigite metastable properties and the low coercivity spectra of this mineral are adverse for palaeomagnetic investigations

a stable chemical remanence in holocene sediments the ferrimagnetic iron sulphide greigite has been extracted from freshwater sediments from loch lomond and llyn geirionydd and identified by x ray diffraction and thermomagnetic analyses the authigenic greigite is probably the dominant carrier of a stable natural remanent magnetization in the freshwater sediments underlying marine sediments in loch lomond and in the lateglacial interstadial sediments from llyn geirionydd mineral magnetic analysis shows that greigite tends to have a higher sirm x ratio approximately 70 kam 1 than many natural magnetite assemblages this magnetic characteristic coupled with greigite s ability to oxidize easily and to change to a less magnetic mineral upon exposure to air may be used to indicate its presence in downcore magnetic profiles alternating field demagnetization cannot be used to distinguish chemical from detrital remanences in loch lomond or llyn geirionydd on account of the similar magnetic stabilities of greigite and magnetite the time lag between the acquisition of the primary detrital remanence and the secondary chemical remanence remains unknown and creates difficulties in understanding the record of paleomagnetic secular variation contained in these lake sediments

the detection of single domain greigite fe3s4 using rotational remanent magnetization rrm and the effective gyro field bg mineral magnetic and palaeomagnetic applications summary the intensity of rotational remanent magnetization rrm acquired by single domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization arm to calculate the effective biasing field bg that produced the rrm samples of single domain greigite had bg values between 137 and 84 t and a mdfrrm of c 80 mt by contrast a suite of natural and synthetic ferrimagnetic iron oxide samples including single domain magnetite and yfe3o4 tape particles acquired bg values between 3 and 14 t and mdfrrm ranged between 43 and 68 mt when rrm was acquired multidomain magnetite did not acquire a rrm bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes which revealed a minimum bg value of 24 t and a mdfrrm of 57 mt for the finest fraction 0 2 0 8 m in diameter in a geological example measurements of bg and mdfrrm were used to detect the presence of greigite in a 4 m long late weichselian sediment core variations in inclination declination and the intensity of the natural remanent magnetization nrm correlate with changes in magnetic mineralogy

gyroremanent magnetization and the magnetic properties of greigite bearing clays in southern sweden summary the acquisition of a gyroremanent magnetization grm by single domain sd greigite particles during alternating field af demagnetization is demonstrated previous palaeomagnetic studies failed to identify the presence of authigenic greigite in the glacio marine clays studied these clays formed the subject of an earlier debate about the validity of a late weichselian geomagnetic excursion the gothenburg flip in southern sweden the greigite carries a stable chemical remanent magnetization crm which coexists with a detrital remanent magnetization drm carried by magnetite af demagnetization could not isolate the primary remanence in the sediments where magnetite and greigite coexist due to the overlapping coercivity spectra of the two minerals and the inability to determine the time lag between sediment deposition and crm formation thermal demagnetization removed the crm at temperatures below 400 dc but this method was hindered by the unconsolidated nature of the sediments and the formation of secondary magnetic minerals at higher temperatures the results suggest that the low coercivity drm carried by magnetite was mistaken for a viscous component in the earlier studies hence the former debate about the record of the gothenburg flip may have been based on erroneous palaeomagnetic interpretations or non reproducible results af demagnetization procedures applied to samples suspected of bearing sd magnetic particles such as greigite should be carefully selected to recognize and account for grm acquisition

freshwater influx hydrographic reorganization and the dispersal of ice rafted detritus in the sub polar north atlantic ocean during the last deglaciation a sediment core from the north east north atlantic contains high resolution co registered foraminiferal 18o and ice rafted detritus ird records for the last deglaciation these reveal a distinct ice rafting event that occurred at the time of greenland interstade 1d gi 1d a feature also seen in other high resolution cores from the north atlantic the occurrence of a geographically widespread peak in ird at ice distal sites at a time when increased freshwater flux to the surface ocean is inferred to have caused rapid cooling suggests a mechanistic link between the processes analogous to the younger dryas gs 1 cooling episode the general absence of ird at southern locations at other times during gi 1 when the flux of icebergs from surviving ice sheets to northern locations continued suggests that the gi 1d ird peak represents a time of hyrdrographic reorganization which changed ird dispersal while numerous studies have suggested freshwater flux as a major driver of rapid climate oscillations observed around the north atlantic during the last deglaciation the evidence presented here both supports that mechanism and highlights the potential for rapid and major reorganization of the north atlantic s surface hydrography to explain changes in ird flux independently of ice sheet calving dynamics

magnetic properties and metastability of greigite smythite mineralization in brown coal basins of the krusne hory piedmont bohemia finely dispersed forms of greigite or greigite smythite mineralization were found in layers a hundred and more metres thick in the miocene strata of the krusne hory erzgebirge piedmont brown coal basins under laboratory thermal treatment a pronounced instability of greigite or greigite smythite mineralization was revealed by the magnetic parameters conditioned by mineralogical metastability thermal treatment in oxidation conditions caused the most pronounced changes in magnetic parameters in a temperature range of 320 380 c in which a laboratory process of self reversal of remanence was observed the products obtained during thermal treatment were identified with the aid of x ray diffractographs co radiation fe filter when they were heated to 250 c no substantial changes were found while at 300 c the intensities of greigite became weaker and pyrite and marcasite originated to its detriment hexagonal pyrrhotite was generated in addition to pyrite and marcasite a total decomposition of bisulphides took place at temperatures above 400 c accompanied by the formation of various modifications of fe2o3 until finally at higher temperatures only fe2o3 was formed laboratory tests suggested self reversal of remanence in relation to the formation of pyrrhotite so far greigite or greigite smythite mineralization has been proven to exist in the bohemian massif solely in connection with miocene rocks containing fossil micro organic matter products of thermal alteration pyrite marcasite pyrrhotite and fe2o3 or fe3o4 depending on redox conditions may be expected in rocks of similar genesis but partly or completely carbonified as a result of a process of pyrolysis of the micro organic matter

gyromagnetic remanence acquired by greigite fe3s4 during static three axis alternating field demagnetization summary a magnetic study was carried out on lacustrine sediments from the zoigebasin tibetan plateau in order to obtain a better understanding of palaeoclimatic changes there gyromagnetic remanence grm acquisition is unexpectedly observed during static three axis alternating field af demagnetization in about 20 per cent of a large number of samples x ray divraction xrd analysis on a magnetic extract clearly shows that greigite is the dominant magnetic mineral carrier scanning electron microscopy sem reveals that the greigite particles are in the grain size range of 200 300 nm possibly in the single domain state greigite clumps of about 3 mm size are sealed by silicates fitting of xrd peaks yields a crystalline coherence length of about 15 nm indicating that the particles seen in the sem are polycrystalline grm intensities of most samples are of the same order as the nrm while others show much stronger grm although their magnetic properties are similar variation of the demagnetization sequence confirms that grm is mainly produced perpendicular to the af direction the anisotropy direction can be derived from grm but more systematic studies are needed for detailed conclusions an attempt to correct for grm failed due to high grm intensities and because smaller grm acquisition was also found along the demagnetization axis behaviours of acquisition and af demagnetiz ation of grm are comparable with those of nrm arm irm indicating fine grain sizes of remanence carriers

magnetic properties of biogenic soil greigite fe3s4 magnetic measurements were performed on soil samples which contained bacterial greigite the greigite containing soil horizon is characterized by sirm 70 ka m 1 and by q factors 5 alternating field af demagnetization curves of the nrm gave stable directions according to irm acquisition and alternating field demagnetization of the irm and arm the greigite in bulk soil samples shows single domain behaviour this sd behaviour is also confirmed by hysteresis and by frequency dependent susceptibility measurements the thermomagnetic behaviour was checked on extracted greigite the magnetic parameters of soil greigite are compared with parameters of sedimentary greigite and of bacterial magnetite

magnetic domain state and coercivity predictions for biogenic greigite fe3s4 a comparison of theory with magnetosome observations the discovery of bacteria that precipitate greigite within intracellular organelles magnetosomes offers new evidence about the origin of greigite in natural environments unlike magnetite only scarce information is available about the magnetic characteristics of greigite for this reason and the present inability to grow these microorganisms in pure culture it is not known whether or not the magnetosomes in the newly discovered greigite precipitating bacteria are of single domain sd size as are the magnetosomes from magnetite precipitating bacteria the hypothesis of natural selection for magnetotactic behavior predicts that the greigite bearing magnetosomes should also be single magnetic domains using previously reported magnetic properties and crystallographic features for greigite we have calculated the size and shape boundaries expected for sd and superparamagnetic spm behavior in this mineral for further characterization of the greigite crystals we analyzed the domain state at various length width ratios assuming crystal shapes of parallelepipeds and prolate spheroids magnetite was used as control for the current theories supporting these calculations we also present a simple algorithm to calculate the upper size limit of single domain grains our results show that the crystals of bacterial greigite characterized so far are located in the region close to the single domain superparamagnetic boundary and should have relatively low coercivity if these crystals contribute to the magnetization of sediments remanence produced by bacterial greigite could be mistaken for large multidomain magnetite in alternating field demagnetization studies

rock magnetic properties of eemian maar lake sediments from massif central france a climatic signature the hypothesis of a climate variability within the last interglacial eemian suggested by oxygen isotope data of a greenland ice core grip was later supported by magnetic susceptibility organic matter and pollen signatures in the eemian lake sediments of the lac du bouchet france in the present paper we analyse in detail the rock magnetic properties of these sediments in order to determine the origin of the magnetic susceptibility variations furthermore in order to verify the empirical relation between magnetic susceptibility and climate we studied two eemian sequences from neighbouring lakes lac st front and ribains maar lake rock magnetic investigations mainly consisted of analyses of anhysteretic and isothermal remanent magnetizations along with hysteresis measurements carried out on pilot samples lac du bouchet susceptibility variations are at least partly affected by postdepositional magnetite dissolution lac st front sediments show a complex behaviour resulting in partly contradicting interpretations of rock magnetic parameters possible explanations may be the presence of a very fine grained magnetite or the presence of maghemite ribains maar lake sediments show a homogeneous magnetic mineralogy without major variations in most of the rock magnetic parameters susceptibility records of the three lakes were compared under the simplified assumption that magnetic susceptibility mainly reflects variations of the detrital titano magnetite input only a poor correlation between the three eemian susceptibility sequences is observed suggesting that local effects including dissolution and dilution effects may have altered the original detrital climatic signal the purely detrital origin of the lac du bouchet eemian susceptibility variations must thus be questioned but it nevertheless appears to be the only lake whose susceptibility variations can tentatively be correlated with the grip eemian oxygen isotope record

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

a study of gyroremanent magnetisation grm and rotational remanent magnetisation rrm carried by greigite from lake sediments summary further studies of gyroremanent magnetisation grm and rotational remanent magnetisation rrm have been conducted on lake sediments from the zoige basin in the eastern tibetan plateau in which greigite is the main carrier of gyroremanent magnetisation greigite has the greatest effective gyrofield bg of all magnetic minerals studied so far being several hundred t for a peak af of 80 mt this high bg value has the potential to be used as an indicator for greigite the grm produced during static alternating field af demagnetisation became close to its maximum at a peak af of 150 mt attempts to extract the natural remanent magnetisation nrm by algebraic elimination of the grm were unsuccessful above fields of about 30 mt because the grm became much larger than the remaining nrm the grm of a crushed sample was much reduced because of the destruction of the sample s anisotropy although as expected both rrm and bg were similar before and after crushing thus demonstrating that rrm and bg are independent of anisotropy measurement of the anisotropy of two samples from different depths showed that the deeper sample which acquired the higher grm also had the higher anisotropy presumably as a result of greater sediment compaction study of anisotropy of grm may help to elucidate the preferred alignment of greigite within the sample which is difficult to ascertain by other means

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

mineral magnetic record of environment in late pleistocene and holocene sediments lake manas xinjiang china a study of magnetic parameters was carried out on a late pleistocene and holocene sedimentary sequence 5 m from lake manas northern xinjiang china that has already been ana lysed for bulk sediment mineralogy stables isotopes from carbon ates and biogenic material magnetic minerals confirm major changes in palaeoenvironmental and palaeohydrological conditions that were deduced from other methods they also provide complementary information on changes in the lake system during the early and middle holocene the most important mineral mag netic change results from the authigenic formation of ferrimagnetic greigite fe3s 4 during the lacustrine episodes dated from 8 7 kyr b p to 5 5 kyr b p 380 335 cm and from 4 5 kyr b p to 3 5 kyr b p 320 285 cm respectively our data also indicate an abrupt break in sedimentary conditions which coincides with a short term retmxtowards dry climatic conditions around 3 5 kyr b p which was only suggested from other proxy data

crossover plots a useful method for plotting sirm data in paleomagnetism the effective grain size of magnetic minerals and therefore domain type controls the saturation isothermal remanent magnetization acquisition and subsequent demagnetization response and can be used to create crossover plots for paleomagnetic specimens where sirm is plotted as a function of the field applied using a logarithmic scale this paper presents templates of such plots for magnetite pyrrhotite hematite and goethite onto which sample data can be plotted for conventional paleomagnetic specimens to characterize their magnetic mineralogy and effective grain size

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

a new depositional model for ice shelves based upon sediment cores from the ross sea and the mac robertson shelf antarctica we document the similarity of depositional facies occurring in gravity cores recovered from two disjunct regions of the antarctic continental shelf the ross sea and the mac robertson shelf the facies sequence model is represented in two cores one collected during the 1995 1 cruise of the r v nathaniel r palmer core nbp95 tc 18 and the other collected by the rsv aurora australis during cruise 149 in 1995 core 149 39gc38 both cores show a succession of facies indicative of ice shelf retreat during the late pleistocene to holocene transition distinct lithofacies range in thickness from a few tens of cm to 1 m and consist of from bottom to top a coarse granulated sandy mud laminated silt and clay structureless silly clay poorly sorted sandy siliceous mud and siliceous mud and ooze these facies represent the passage of distinct depositional regimes across the core sites including sub ice shelf beneath a basal debris zone sub ice shell distal to a debris zone calving line transition and open marine this facies model represents an advance in our understanding of glacial marine stratigraphy for the antarctic continental shelf and will provide the basis for more realistic palaeoglacial reconstructions

glacimarine sedimentary processes and depositional environments in an embayment fed by west greenland ice streams abstract the extent and behaviour of the central west greenland sector of the greenland ice sheet gis during the last glacial maximum lgm and the following deglaciation remains poorly constrained to investigate deglacial marine environments and sedimentary processes in an area fed by several lgm ice streams we now report findings from a 3 5 khz sub bottom profiler survey acquired in and around disko bay in 2009 sediment thicknesses and volumes in three glaciated areas disko bay southern vaigat and egedesminde dyb are fully constrained for the first time acoustic facies types and distributions were also mapped the largest sediment thicknesses 256 m and widest variation in acoustic character was observed in disko bay adjacent to the mouth of jakobshavns isfjord significant sediment thicknesses were also observed in isolated basins in the egedesminde dyb trough and in a trough in southern vaigat strait up to 110 m given low modern sedimentation rates these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through disko bay and into both the jakobshavns and torssukatak fjord systems in central west greenland our results highlight similarities in deglacial sedimentary processes across the study area when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment laden meltwater plumes and melting icebergs we estimate the sediment flux for the palaeo jakobshavn ice stream while the ice margin was stable at a fjord entrance sill to be 1 6 3 6 10 7 m 3 a 1 assuming a flux at the upper end of our range for the torssukatak fjord system requires the grounded ice margin to be stable for about 450 years during retreat the sediment fluxes we estimate are within the range of previously calculated fluxes for other arctic and antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation even during periods of quasi stability retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice distal sedimentation by rainout of iceberg rafted detritus ird and hemipelagic material accumulation rates drop to 2 mm a 1 this study demonstrates the variability in glacimarine processes and environments on high latitude continental margins and highlights the importance of local factors such as bedrock morphology as well as glacio dynamic factors on sedimentation

magnetic enhancement of baltic sea sapropels by greigite magnetofossils magnetotactic bacteria mtb are known to biosynthesise single domain magnetite fe3o4 for geomagnetic navigation and their relict magnetosomes called magnetofossils can control the magnetic properties of lake and marine sediments magnetotactic bacteria also produce greigite fe3s4 magnetosomes but compared to those made of magnetite relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles we studied the magnetic properties of sediment cores from two basins the north central baltic proper and eastern gotland basin that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels which are a signal of past occurrences of anoxia and hypoxia in the baltic sea magnetic concentrates extracted from the laminated sapropels were characterised by transmission electron microscopy and energy dispersive x ray spectrometry and we identified only single domain greigite fe3s4 particles with a mean size of 55 75 nm which we interpret as magnetofossils due to diagnostic chains of individual particles separated by an intact dividing membrane the degree of magnetic enhancement in the laminated sapropels has a positive relationship with loss on ignition data which indicates a link between the production of greigite magnetosomes organic matter supply and preservation and redox conditions the coercive force of collections of non interacting greigite magnetofossils is 13 mt which is considerably lower than the magnetite counterparts 30 mt and strictly non bacterial and larger greigite single domain grains 60 mt the values of the interparametric ratios of sirm w warm sirm and warm w that we obtain for our greigite magnetofossils overlap with those previously considered to be diagnostic of magnetosomal magnetite the presence of bacterial greigite which is easily detected by magnetic measurements forms a proxy for hypoxia and anoxia thus aiding the palaeoenvironmental interpretation of how oxygen conditions in the baltic sea have changed over time

rock magnetism of greigite bearing sediments from the dead sea israel summary detailed magnetostratigraphic investigations were carried out on five sediment cores obtained from three sites on the northwestern shore of the dead sea israel the sediments are heterogeneous composed of fine clastic layers alternating with authigenic aragonite the magnetic remanence is carried by ti magnetite and greigite reflecting a detrital as well as an authigenic phase directions of the characteristic remanent magnetization were obtained from stepwise af demagnetization of the natural remanent magnetization and subsequent principle component analysis the acquisition of a gyroremanent magnetization in a noticeable amount of the samples could be linked to core disturbances the depth age models based on ams 14c datings on plant remains yielded an age of 10 04 ka cal bp for the base of the longest profile from site ein gedi a continuous lacustrine sediment sequence the profiles from the two other sites representing near shore sedimentation are interrupted by a hiatus in sedimentation comparison of the inclination and declination records from all dead sea cores and nearby sited lakes suggest that low frequency variations documented in the dead sea sediments are likely of geomagnetic origin

greigite detected as dominating remanence carrier in late pleistocene sediments lisan formation from lake kinneret sea of galilee israel summary a rock magnetic investigation of three sedimentary cores of lisan formation of late pleistocene age from lake kinneret sea of galilee northern israel demonstrates that the magnetization of these sediments is controlled by various degrees of a secondary chemical remanent magnetization crm carried by greigite fe3s4 this crm is superimposed on a primary detrital remanent magnetization drm that resides in ti magnetite this finding is independently confirmed by x ray diffraction xrd measurements performed on magnetic extracts of the sediments the domain state of the greigite is largely single domain behaviour sd thus dominating the magnetization therefore the magnetic record retrieve from of these sediments is not reflecting geomagnetic variations but rather chemical rock magnetic properties resulting from diagenetic processes the results of our study suggest that paleomagnetic record of greigite bearing sediments should be interpreted with caution because of the following reasons 1 geomagnetic secular variations can be biased due to large coercivity overlap between magnetite and greigite 2 alternating field af demagnetization can produce erroneous directions due to vector distortion by acquisition of a gyro remnant magnetization grm 3 estimation of relative paleointensity can be hampered by large scale variations in natural remnant magnetization nrm intensity caused by the acquisition of a secondary crm of unknown age and unknown extent superimposed on the drm the precipitation of greigite requires reducing conditions at the sediment water interface and or interstitial water associated with the presence of sulphur and iron oxides reducing conditions are typical of stratified lakes and other stratified water bodies such as the dead sea paleo lake lisan temporarily the eastern mediterranean sea the caspian sea the black sea and many other marine basins according to our findings paleomagnetic records from such environments carried dominantly by greigite therefore should be treated with care

magnetic characteristics of synthetic pseudo single domain and multi domain greigite fe3s4 1 we report the magnetic properties of pure synthetic pseudo single domain psd and multi domain md greigite and the grain size dependence of the magnetic properties of greigite for the first time the dominantly psd like and md like behavior are demonstrated by hysteresis first order reversal curve diagrams low temperature cycling ltc of room temperature saturation isothermal remanent magnetization sirm and low temperature sirm warming curves variations in a range of magnetic properties clearly correlate with grain size characteristic psd md behavior is preserved at low temperatures which coupled with the small decrease in remanence during warming rule out the presence of substantial superparamagnetic behavior in the studied samples ltc sirm measurements indicate a continuous demagnetization of remanence during cooling knowledge of this expanded range of magnetic properties of greigite should be widely useful in environmental magnetic and paleomagnetic studies

magnetic properties of sedimentary greigite fe3s4 new data are presented here that document the previously poorly known magnetic characteristics of sedimentary greigite fe3s4 several diagnostic magnetic properties can be used in conjunction to rapidly screen sediments to detect the presence of greigite such discriminants are necessary because greigite displays a similar or higher range of coercivities compared to most ferrimagnetic minerals and the commonly used method of alternating field demagnetization cannot be used to distinguish between palaeomagnetic remanence components due to greigite and other ferrimagnetic minerals sedimentary greigite has high ratios of the saturation isothermal remanent magnetization to magnetic susceptibility mrs which are accompanied by hysteresis ratios of mrsms 0 5 and bcr bc 1 5 ms is the saturation magnetization bc is the coercive force and bcr is the coercivity of remanence greigite has no low temperature phase transition whereas the ferrimagnetic iron sulphide pyrrhotite undergoes a major phase transition at about 34 k and unoxidized magnetite displays the verwey transition at 118 k low temperature measurements may therefore prove valuable in distinguishing between magnetite pyrrhotite and greigite although the absence of a low temperature transition cannot be taken as definitive evidence for the presence of greigite greigite also displays characteristic high temperature behaviour with a major drop in magnetization between 270 and 350 c determination of the mrs ratio is an excellent means of rapidly screening sediments to identify stratigraphic intervals that may contain greigite subsequent low and high temperature analyses can then provide unambiguous identification of greigite and enable the evaluation of the presence of other magnetic minerals

mineral magnetic study of late quaternary south caspian sea sediments palaeoenvironmental implications summary magnetic properties of sediments from a core 10 m long in the southern basin of the caspian sea have been investigated varying concentrations of greigite fe 3 s 4 dominate the magnetic fraction in late pleistocene sediments the synsedimentary formation of greigite indicates that the late pleistocene caspian sea was a brackish or fresh water poorly ventilated basin and suggests a water level higher than at the present the variation in magnetic parameters with the detrital magnetite bearing fraction remaining constant is interpreted in terms of greigite grain size variation and related to the slight variation in water salinity the holocene sediments are characterized by detrital magnetite this indicates better ventilation of the basin and suggests lower water levels than in the late pleistocene the gradual change in magnetic properties of the sediments between 90 and 60 cm depth with decreasing quantities of greigite indicates stepwise establishment of oxic conditions in the holocene

formation of greigite fe3s4 in the sediments of saline lake lop nur northwest china and its implications for paleo environmental change during the last 8400 years abstract we present the results of rock magnetic and sem edx analyses of the sediments of lop nur a former saline lake in the tarim basin china the aim of the study was to assess the impacts of authigenic iron sulfide minerals e g greigite on the sedimentary magnetic properties and their possible relationship with environmental and climate change five layers with relatively high values of arm sirm s ratio arm and sirm are identified within organic rich sediments the five layers are dated to ca 8150 7000 5300 4900 3600 3100 2750 2550 and 1820 1680 cal yr bp authigenic greigite is the dominant magnetic mineral within the five layers and it is present in the stable single domain state the magnetic properties of the intervening layers are dominated by detrital multidomain magnetite combined with results of a previous study we infer that the greigite bearing sediments were deposited during cold and wet periods which were probably related to the north atlantic cold events during the past 8400 yr during these periods greigite formation was likely driven by an enhanced organic matter supply but pyritization was constrained by the decreased sulfate content and high sedimentation rate the greigite and its diagnostic magnetic parameters e g sirm can be regarded as an indicator of the hydrological and climatic evolution of the tarim basin

mineral magnetic properties of artificial samples systematically mixed from haematite and magnetite summary detailed rock magnetic investigations were carried out on a set of samples with defined ratios of haematite and magnetite the measured parameters provide a reference for interpreting common rock magnetic parameters in investigations of sediments the contribution of haematite to the magnetic fraction must exceed 95 wt of the magnetic fraction when mixed with magnetite in order to visibly influence grain size and coercitivity indicative magnetic parameters coercivity of remanence bcr and coercive force bc do not change in the same way with increasing haematite content which results in a peak bcr bc value at around 99 5 wt haematite variations in haematite content can be ignored when interpreting most rock magnetic parameters especially grain size indicative parameters for samples where haematite contents range from 0 to 98 wt the s ratio is still the most sensitive parameter for estimating the relative amount of haematite in magnetite haematite mixtures a combination of s ratio the saturation isothermal remanent magnetization divided by the low field magnetic susceptibility sirm lf and bcr is the most effective way to identify haematite in natural samples our results agree with literature data and fill the gap between results obtained either from pure magnetite or haematite with comparable grain sizes