tectonic and environmental evolution of quaternary intramontane basins in southern apennines italy insights from palaeomagnetic and rock magnetic investigations summary southern apennines is characterized by active extensional tectonics with ne sw stretching direction the seismicity of the region is very well understood and continuously monitored in contrast the onset of extensional tectonics is chronologically poorly constrained the aim of this study is that to give important constraints on the development of extensional regime and the onset of the continental deposition during quaternary in southern apennines we report the results of palaeomagnetic and rock magnetic analyses from four quaternary small intramontane basins in the picentini mountains southern apennines the sedimentary sequences are located at different altitudes from 600 to 1200 m a s l and were deposited in fluvial lacustrine environments we sampled 29 sites in clays and lacustrine limestones from tizzano piano del gaudo and acerno basins and in red palaeosoils and matrix supported conglomerates from the iumaiano basins in the clay and limestones samples magnetite titano magnetite hematite and iron sulphide have been recognized as the main magnetic carriers whereas magnetite and hematite characterize the iumaiano conglomerates and red soils palaeomagnetic results have been integrated with published radiometric data in order to constrain the age of each sedimentary basins sites from the iumaiano basin which represents the substrate of the tizzano and piano del gaudo basins show a reverse polarity and therefore have been attributed to the lower matuyama chron in contrast palaeomagnetic data from tizzano basin show a transition from reversed to normal polarity along the exposed section which has been interpreted as the matuyama brunhes transition sites from acerno and piano del gaudo basins show a normal polarity which according to radiometric and pollen data have been correlated to the brunhes epoch on the base of such results we discuss the tectonostratigraphic evolution of the basins and the role of extensional tectonics in this portion of the southern apennine during the quaternary

magnetic records of climate change sediments deposited on the sea floor on lake bottoms as well as on land as accumulations of windblown silt loess and as ancient soils paleosols formed in the loess possess many different properties that record past changes in climate geologically recoverable information on paleoclimate includes changes in global temperature as it may affect global ice volume and thus temperature of sea water net precipitation storm intensity wind speed and frequency as well as wind direction such information further contributes to interpretations about changes in oceanic and atmospheric circulation patterns as such the understanding of past climatic changes can provide baselines of natural climatic fluctuations as related to those that may be induced or influenced by human activities

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

rock magnetic criteria for the detection of biogenic magnetite abstract we report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron reducing bacteria magnetotactic bacterial mtb strains ms1 mv1 and mv2 and dissimilatory iron reducing bacterium strain gs 15 grown in pure cultures were used in this study our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain sd particles of magnetite from mtbs the most useful magnetic property measurements include 1 acquisition and demagnetization of isothermal remanent magnetization irm using static pulse and alternating fields 2 acquisition of anhysteretic remanent magnetization arm and 3 thermal dependence of low temperature 20 k saturation irm after cooling in zero field zfc or in a 2 5 t field fc from 300 k however potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero field and field cooled sirms on warming through the verwey transition t 100 k intact chains of unoxidized magnetite magnetosomes have ratios of fc zfc greater than 2 where the parameter is a measure of the amount of remanence lost by warming through the verwey transition disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the fc zfc ratio to around 1 similar to values observed for some inorganic magnetite maghemite greigite and gs 15 particles numerical simulations of fc zfc ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the fc zfc parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole sediment samples the strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made compared to techniques such as electron microscopy

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

kinematics of orocline tightening in the core of an arc paleomagnetic analysis of the ponga unit cantabrian arc northern spain 1 paleomagnetic and structural analyses of the western european variscan belt wevb suggest that the most viable kinematic model for variscan deformation in northern iberia is oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases e w in the late carboniferous and n s in the permian both in present day coordinates which resulted in the refolding about steeply plunging axes of initially north south trending thrusts and folds in the hinge zone and oroclinal tightening due to vertical axis rotation of the belt s limbs however the orocline model has yet to be critically tested in the wevb s core this study reports new paleomagnetic rock magnetic and structural data from the inner core of the wevb in order to test opposing kinematic models for the well documented fault and fold interference structures formed by late stage variscan deformation and to better understand the overall development of the wevb arc map scale structural features within the wevb core have a highly sinuous geometry characterized by transverse and thrust parallel fold systems formed by fault bend folding over footwall ramps the intersections of these two fold systems produce steeply plunging interference folds which are best exposed in the ponga thrust unit a total of 67 paleomagnetic sites were collected in the barcaliente formation of the ponga unit with emphasis placed on detailed spatial coverage of individual structural domains a multicomponent paleomagnetic remanence was measured which is interpreted to be composed of two components a low unblocking temperature recent viscous magnetization and a high unblocking temperature ancient magnetization that was acquired in the latest stephanian to early permian after initial d1 thrusting and folding bur prior to major secondary rotation rock magnetic experiments show that the characteristic remanence magnetization is carried by secondary authigenic pseudosingle domain magnetite these paleomagnetic results are used to determine the kinematics and geometry of postmagnetization deformation by restoring in situ magnetic vectors back to a defined reference direction on the basis of the restored ponga unit geometry the steeply plunging interference folds found in the wevb core are best described by a combination of secondary buckling of frontal ramp parallel hanging wall anticlines and modification of d1 lateral oblique ramps as frontal ramps during late stage north south shortening this combination of structural modification of the inner core of the wevb was necessary to accommodate oroclinal bending during the final amalgamation of pangea in the late paleozoic

stress dependent permeability of a de mineralised fracture in shale abstract the paper presents the results of laboratory direct shear tests on the hydro mechanical behaviour of an extensional fracture in shale the tests were conducted on fracture specimens obtained by mechanically splitting blocks of a naturally fractured shale along the cemented fracture and dissolving the calcite fracture filling with a strong acid the experiments consisted of radial fluid flow tests from a single fluid source along the fracture surface fracture samples were tested under different levels of effective normal stress and shear displacement the experimental results show significant reduction of fracture permeability during increasing contact normal stress across the fracture and after shearing of the fracture under constant high normal stress however the tested fractures never completely closed even under normal stresses close to or higher than the unconfined compressive strength of the intact shale the fracture permeability remained much higher than the intact shale or matrix permeability even when the fracture surface has undergone some gouge formation from local asperity failure during shearing the results indicate that fractures once created are difficult to close by mechanical loading in tight formations like shales fractures will always be conduits for fluid flow unless closed by cementation currently it is widely assumed that fractures in sedimentary basins stay open only when there is an overpressure which could keep the fractures hydraulically parted however the results presented here indicate that given a sufficient hydraulic gradient fluid can still flow along a fracture even in the absence of large overpressures

relationship between frontal dust storms and transient eddy activity in the northern hemisphere of mars as observed by mars global surveyor we have compiled a catalog of frontal dust storms in the northern hemisphere using mars orbiter camera daily global maps spanning 2 3 martian years of mars global surveyor mgs observations from 1999 to 2003 the most vigorous frontal storms that flush dust to the low latitudes occur in early mid fall and mid late winter away from the northern winter solstice while many streaks are observed in the polar hood during the winter solstice period no frontal dust storms are observed in the vicinity of the north polar region we have also analyzed simultaneous mgs thermal emission spectrometer tes temperature data and found statistically significant negative temperature anomalies associated with frontal storms in the lowest scale height of the atmosphere the geographical and seasonal distributions of temperature standard deviations associated with transient variations agree well with the distributions of frontal storms the correlation deteriorates with increasing altitude suggesting that lower level temperature waves are associated with the frontal dust storms specifically eastward traveling m 3 waves with periods of 2 3 sols appear to be closely related to the development of flushing frontal storms

modelling of localised gas preferential pathways in claystone a long term injection gas test on initially saturated claystone samples under isotropic confining pressure is modelled in a 2d hydro mechanical framework which includes the hydraulic anisotropy evidences of localised pathways through the sample have been observed experimentally which are difficult to reconcile with standard two phase flow models the presence of an embedded pre existing fracture is included in a continuum finite element model a hydro mechanical coupling between the fracture aperture permeability and the retention properties along the fracture is included in the model due to the increase in permeability and the decrease of the air entry pressure induced by the rise in fluid pressure at constant mean total stress the model provides good agreement with the experimental observations the discussion offers additional insight into the fluid flow mechanisms into the sample and the processes involved in the development of localised gas pathways this study allows conclusions to be drawn regarding the performance of the model and its practical limitations

monitoring of helium and carbon isotopes in the western eger rift area czech republic relationships with the 2014 seismic activity and indications for recent 2000 2016 magmatic unrest abstract we report new data of the regional distribution pattern of total gas compositions as well as he and co2 isotopic compositions from 25 gas exhalations in the western eger rift and its surroundings additionally the first time series data from gas exhalations in a clay pit within the cheb basin cb are given at 21 degassing locations the first data were obtained 20 years ago from 7 locations within the degassing center cb and from 3 degassing sites belonging to the marianske lazn ml degassing center neon and argon isotope compositions were determined also co2 is the major component at all degassing sites the 13c values display a small range 1 7 to 5 1 and the 3he 4he ratios vary from 1 9 to 5 9 ra the highest 3he 4he ratios are found at locations along the pocatky plesna fault zone followed by the degassing site in the clay pit on the nova ves fault and the locations on the ml fault at the edge of the cb although gas flow and co2 concentrations in all degassing centers are very high the fractions of mantle derived helium are different with presently up to 94 in relation to the sclm 3he 4he of 6 32 ra in the cb up to 73 in the ml and up to 35 in the karlovy vary degassing center at the locations in the eastern part of the cb a clear progressive increase of the 3he 4he ratio has been observed since the first sampling campaigns there in 1993 and 1994 whereas at the other degassing sites the helium isotope ratio remained essentially the same the progressive increase of the 3he 4he ratio in the eastern part of the cb together with further short time increases up to 6 3 ra at one location bublak before both the 2000 and 2008 earthquake swarms indicate an ongoing magmatic process beneath this area which seems to be associated with the occurrence of seismicity the cb is located close to the nov kostel focal zone where since the beginning of our investigations four strong periods of seismicity with magnitudes 3 occurred the latest gas data confirm our earlier findings time series studies showed that in relation with seismic events decreased 3he 4he ratios were repeatedly observed due to admixed seismically released crustal helium presently the eastern part of the cb is the most active non volcanic region in the european cenozoic rift system with gas signatures similar to those found in free mantle derived gases from the east african rift system

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

gas transport properties through intact and fractured callovo oxfordian mudstones a series of controlled water and gas experiments was undertaken on samples of callovo oxfordian cox mudstone using a synthetic fluid and helium gas data from this study demonstrate that the advective movement of gas through cox is accompanied by dilation of the original fabric i e the formation of pressure induced microfissures at gas pressures significantly below that of the minimum principal stress flow occurs through a local network of unstable pathways the properties of which vary temporally and spatially within the mudstone the coupling of variables results in the development of significant time dependent effects affecting many aspects of cox behaviour from the gas breakthrough time to the control of deformation processes variations in gas entry breakthrough and steady state pressures may result from the arbitrary nature of the flow pathways and or microstructural heterogeneity under these conditions the data suggest that gas flow is along pressure induced preferential pathways where permeability is a dependent variable related to the number width and aperture distributions of these features this has important implications for modelling gas migration through low permeability clay rich materials

misinterpreting proxy data for paleoclimate signals a reply to srivastava and jovane 2020 srivastava and jovane 2020 have made several comments on our assessment of proxy data and challenged the outcome of shukla et al 2020 based mainly on interpretation of environmental magnetic p

high resolution analysis of early diagenetic effects on magnetic minerals in post middle holocene continental shelf sediments from the korea strait 1 two studied sediment cores from the korea strait contain mud sequences 14 m and 32 62 m in thickness that were deposited during the last 6 000 years the sediments have uniform lithology and geochemical properties however marked down core changes in magnetic properties suggest that diagenesis has significantly impacted the magnetic properties an expanded view of early diagenetic reactions that affect magnetic mineral assemblages is evident in these rapidly deposited continental shelf sediments compared to deep sea sediments the studied sediments are divided into four descending intervals based on magnetic property variations interval 1 is least affected by diagenesis and has the highest concentrations of detrital magnetite and hematite and the lowest solid phase sulfur contents interval 2 is characterized by the presence of paramagnetic pyrite and sharply decreasing magnetite and hematite concentrations which suggest active reductive dissolution of detrital magnetic minerals interval 3 is marked by a progressive loss of hematite with depth and coincides with the minimum magnetite concentration interval 4 has an increasing down core enhancement of authigenic greigite which apparently formed at depths of 3 30 m below the sediment water interface due to arrested pyritization reactions these results indicate delays of thousands of years for acquisition of magnetizations carried by greigite which suggests that studies of geomagnetic field behavior from greigite bearing continental shelf sediments should be conducted with care also virtually complete destruction of detrital magnetic minerals at depth suggests that magnetic studies of rapidly deposited shelf sediments are unlikely to provide a meaningful signature associated with syn depositional environmental processes

gas migration through water saturated bentonite sand mixtures cox argillite and their interfaces france s deep seated nuclear waste repository consists of a natural barrier located at a depth of 500 m in a callovo oxfordian clayey formation this repository has artificial barriers that include

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

ferromagnetic resonance and low temperature magnetic tests for biogenic magnetite magnetite is both a common inorganic rock forming mineral and a biogenic product formed by a diversity of organisms magnetotactic bacteria produce intracellular magnetites of high purity and crystallinity magnetosomes arranged in linear chains of crystals magnetosomes and their fossils magnetofossils have been identified using transmission electron microscopy tem in sediments dating back to 510 570 ma and possibly in 4 ga carbonates in martian meteorite alh84001 we present the results from two rock magnetic analyses the low temperature moskowitz test and ferromagnetic resonance fmr applied to dozens of samples of magnetite and other materials the magnetites in these samples are of diverse composition size shape and origin biologically induced extracellular biologically controlled magnetosomes and chiton teeth magnetofossil synthetic and natural inorganic we confirm that the moskowitz test is a distinctive indicator for magnetotactic bacteria and provide the first direct experimental evidence that this is accomplished via sensitivity to the magnetosome chain structure we also demonstrate that the fmr spectra of four different strains of magnetotactic bacteria and a magnetofossil bearing carbonate have a form distinct from all other samples measured in this study we suggest that this signature also results from the magnetosomes unique arrangement in chains because fmr can rapidly identify samples with large fractions of intact isolated magnetosome chains it could be a powerful tool for identifying magnetofossils in sediments

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

an unsaturated hydro mechanical modelling of two in situ experiments in callovo oxfordian argillite abstract the unsaturated behaviour of callovo oxfordian argillite is investigated through the modelling of 2 in situ experiments the first test studies the influence of ventilation in a gallery on the hydro mechanical behaviour of the rock mass the second test consists in a gas injection in the rock mass from an experimental borehole a hydro mechanical model is described and used in the modelling of the experiments a review of the main hydro mechanical parameters of argillite is presented the numerical results highlight the need of a flow boundary condition reproducing the fluid transfers between the surroundings and the rock mass the influence of dissolved gas on the compressibility of the liquid phase is also emphasised

effect of citrate bicarbonate dithionite treatment on fine grained magnetite and maghemite mineral magnetic properties of soils and parent materials have been interpreted in terms of paleoclimate and rates of soil formation but it is important to understand which minerals contribute to the mineral magnetic signal citrate bicarbonate dithionite cbd treatment has been used to determine the amounts of fine grained often pedogenic ferrimagnetic minerals relative to coarse grained often inherited magnetic minerals however questions have been raised about the effect of particle size on the efficacy of cbd in dissolving magnetite and maghemite grains in this paper we use magnetic susceptibility and its frequency dependence and the low temperature behavior of a saturation isothermal remanent magnetization to track the dissolution of carefully sized magnetite grains we found that the standard cbd procedure dissolves fine magnetite particles ca 1 etm essentially intact thin oxidized coatings presumably maghemite are also dissolved by the cbd procedure these results support previous interpretations that the cbd procedure can be used to distinguish between pedogenic and lithogenic magnetic grains assuming that most pedogenic magnetic grains are sufficiently small ca 1 im these results also show that the standard procedure is too harsh to differentiate between 1 grm grains of magnetite and maghemite a modified cbd extraction that uses half as much dithionite reduces the magnetic susceptibility of 1 jam magnetite grains by only 10 this method may be useful in distinguishing between magnetite and maghemite grains in this size range

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

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

gas flow through clay barriers a model for the simulation of gas flow in clayey rocks and clays is described gas migration is associated with the development of preferential paths along existing or pressure dependent discontinu

magnetic properties of tidal flat sediments on the yangtze coast china early diagenetic alteration and implications measurements of magnetic properties total organic carbon toc and total sulphur ts were performed on recent tidal flat sediments from the feng xian fx and bei bu gang bbg areas of the yangt

enhanced methane flux event and sediment dispersal pattern in the krishna godavari offshore basin evidences from rock magnetic techniques abstract detailed rock magnetic measurements such as susceptibility susceptibility of anhysteric remanent magnetization arm saturation isothermal remanent magnetization sirm soft isothermal remanent magnetization soft irm and hard irm hirm were carried out on the topmost sediment samples of 73 gravity cores collected in the krishna godavari kg offshore basin to understand the distribution of magnetic parameters and the associated diagenetic signatures related to upward methane flux the variation in magnetic parameters in the kg offshore basin fluctuates around the average value 105 10 8 m3 kg 1 arm 1 22 10 5 m3 kg 1 sirm 2040 10 5 am2 kg 1 soft irm 1807 and hirm 82 except at the location gc 07 15 767 n 81 814 e where the magnetic parameters arm and sirm drop to 1 6th 1 14th and 1 8th of the average near surface value indicating substantial loss in the concentration of primary magnetic iron oxide minerals anomalous low value of arm and arm sirm at gc 07 suggests that the magnetic remanence property is governed by coarser pseudo single domain psd or multi domain md grains to understand the nature of the anomalous magnetic parameters at gc 07 complete downcore variation of magnetic parameters was also studied the magnetic parameters were found to be even more depleted at all depths with susceptibility dropping at 5 2 mbsf to 1 200th of its average near surface value interestingly this core shows a rapid increase in the concentration of dissolved methane from 0 nm at surface to 153 nm at around 5 2 mbsf where the sulfate concentration is also reduced to zero the anaerobic oxidation of methane aom and the sulfate methane transition zone smtz occur between 4 2 and 5 2 mbsf based on the present day sulfate concentration profile the close association between the dissolution of magnetic iron oxide minerals and aom at gc 07 suggests that the reduced magnetization is primarily due to the release of hs by aom the magnetic iron oxide minerals are dissolved not only at smtz but also above the current depth of the smtz it is likely that the methane flux was higher in the past leading to upward shift of the smtz and the hs released by aom facilitated the dissolution of magnetic iron oxide minerals at shallower depths alternatively the hs diffusing upward from the current depth of smtz might have lead to dissolution at shallower depth therefore additional geological geochemical investigations are warranted at gc 07 to establish the dissolution mechanism of magnetic iron oxide minerals the variability in different magnetic parameters within the slope basin and channels shows systematic decrease in the concentration of magnetic minerals and increase in the abundance of stable single domain ssd magnetic grains with water depth the observed strong correlation between the silt fraction and the magnetic susceptibility for the slope basin and channels suggests that the variation in magnetic parameters is predominantly controlled by the sediment sorting transport process as finer particles are deposited in deeper water

a 130 000 year long pollen record from pittsburg basin illinois abstract pittsburg basin in south central illinois contains a sediment record extending from the present back to the end of the late illinoian glaciation when central illinois was covered with picea pinus forest during the last interglaciation a temperate deciduous forest more diverse than holocene quercus carya forest replaced the illinoian late glacial boreal forest prairie pollen types and the charcoal pollen ratio indicating fire frequency temporarily increased then forest with high juniperus percentages became dominant once more as the charcoal pollen ratio dropped after the last interglaciation the charcoal pollen ratio increased again and prairie and wetland surrounded pittsburg basin through the entire wisconsinan glacial age the area was still prairie in late wisconsinan time but with some picea and pinus during the holocene the region has been a mixture of prairie and quercus carya forest during the last interglaciation pittsburg basin was surrounded by vegetation different from that surrounding it during the present interglaciation rather than indicating substantial differences in climate between analogous phases of different glacial interglacial cycles this variation may be due to changes in fire frequency which could be caused by small changes in climate human activity or differences in soil

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

rock magnetic and geochemical proxies for iron mineral diagenesis in a tropical lake lago verde los tuxtlas east central mexico magnetic and non magnetic mineral analyses were conducted on a lacustrine sequence from lago verde in the tropical coast along the gulf of mexico that covers the last 2000 years the site witnessed the transformation of the environment since the early olmec societies until forest clearance in the last century through these analyses we investigated the processes that affected the magnetic mineralogy in order to construct a model of past environmental changes and compare this model with the archeological record and inferred climatic changes in the northern hemisphere of tropical america volcanic activity has played a major influence on sediment magnetic properties as a purveyor of ti magnetites ti maghemites and as a factor of instability in the environment anoxic reductive conditions are evident in most of lago verde s sedimentary record direct observations of magnetic minerals and ratios of geochemical fe ti and ferrimagnetic f and paramagnetic p susceptibility data are used as parameters for magnetite dissolution p fe f and precipitation f ti of magnetic minerals intense volcanic activity and anoxia are recorded before a d 20 leading to the formation of framboidal pyrite increased erosion higher evaporation rates lower lake levels anoxia and reductive diagenesis in non sulphidic conditions are inferred for laminated sediments between a d 20 850 this deposit matches the period of historical crisis and multiyear droughts that contributed to the collapse of the maya civilization dissolution of magnetite a high organic content and framboidal pyrite point to anoxic sulphidic conditions and higher lake levels after a d 850 higher lake levels in lago verde broadly coincide with the increased precipitation documented during the medieval warm period a d 950 1350 in the northern tropical and subtropical regions of the american continent for the little ice age a d 1400 1800 the relatively moist conditions inferred are in concordance with the glacial advances recorded in central mexico higher erosion rates reflect destruction of the rainforest over the last 40 years

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

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

chronological constraints on the pre orogenic history burial and exhumation of deep seated rocks along the eastern margin of the variscan orogen bohemian massif czech republic key lithological units of the high grade eastern margin of the bohemian massif were dated using the u pb and pb pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the variscan orogenic root the protolith ages for metagranitoids orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from cambro ordovician to early devonian times probably related to discontinuous intracontinental rifting of neoproterozoic crust our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted neoproterozoic crust preserved farther to the east as the brunia microcontinent zircon ages for felsic granulites high grade gneisses of the lower crust and of a syn convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 ma exhumation of the lower crust to mid crustal levels was a localized process that occurred at 340 ma and was associated with crustal scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin both types of exhumation mechanisms were driven by deep level wedging indentation of the easterly brunia continent followed by deposition of heavy minerals and pebbles derived from high pressure rocks in the adjacent foreland basin final orogenic development was characterized by ne sw dextral transpressive shearing parallel to the brunia margin as well as dextral trans tension associated with activity along the elbe lithospheric fault these processes affected the marginal parts of the orogenic root and were accompanied by 330 to 325 ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries rotation of the assembled orogenic belt accompanied by lithospheric faulting driven by westerly subduction roll back may be the most plausible model to explain late deformation of the orogenic root

depth distribution of magnetofossils in near surface sediments from the blake bahama outer ridge western north atlantic ocean determined by low temperature magnetism 1 fe oxide and fe sulfide trace minerals in sediments and sedimentary rocks provide proxy records of biogeochemical processes record past variations in the geomagnetic field and can serve as proxies for climatic variations an important class of these fe oxides is produced by bacteria magnetic particles produced by magnetotactic bacteria have been proposed as a primary recorder of the geomagnetic field in many terrestrial marine sediments and have also been suggested to represent fossil evidence of life on the planet mars to better understand their distribution and preservation in the sediment column and their relationship to other biochemical processes we present rock magnetic data that document the occurrence and abundance of fossil biogenic magnetite magnetofossils in marine sediments from the blake bahama outer ridge magnetic hysteresis and low temperature magnetism both indicate that the occurrence of magnetofossils is closely linked to the depth of the modern fe redox boundary within the sediment column and that a fraction of the magnetic minerals in the sediment column above the fe redox boundary are in the form of intact and relatively unaltered chains of nanophase magnetite crystals below the fe redox boundary the abundance of these magnetofossils is markedly decreased the important conclusions of this work are to demonstrate that nondestructive rock magnetic methods can be used to successfully document the occurrence and relative abundance of magnetofossils in geologic materials

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

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

wind measurements in mars middle atmosphere iram plateau de bure interferometric co observations the iram plateau de bure interferometer has been used to map the co 1 0 rotational line in mars middle atmosphere absolute winds and thermal profiles were retrieved during the 1999 2001 2003 and 2005 planet s oppositions the observations sampled various seasons l 143 196 262 317 and 322 and different dust situations clear global storm regional storm the absolute winds were derived by measuring directly the doppler lineshifts the main zonal circulation near 50 km is dominated by strong retrograde winds with typical velocities of 70 170 m s strongly varying seasonally latitudinally and longitudinally in particular between morning and evening comparison of the retrieved temperature with a general circulation model indicates that the model often underestimates the temperatures in the middle 20 50 km atmosphere and overestimates them above 50 km

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

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 multi parameter rock magnetic record of the last glacial interglacial paleoclimate from south central illinois usa pittsburg basin a small kettle lake in south central illinois was formed after the retreat of the illinoian ice sheet 130 ka b p and the sedimentary record includes the last interglacial glacial cycle curie temperature measurements xrd analyses and thermal demagnetization of a low temperature j indicate that the magnetic fraction is characterized by rs oxidized magnetite and magnetic iron sulfides the grain size of the magnetic fraction was estimated from armrj ratios rs frequency dependent susceptibility and hysteresis parameters these measurements show that glacial sediments contain coarse grained presumably detrital material while interglacial samples have an additional fine grained magnetic component which cannot be explained by a single catchment or climatic process early interglacial samples show magnetic properties characteristic of authigenic biogenically produced magnetite while late interglacial samples are probably influenced by pedogenesis around the basin q 1997 elsevier science b v

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

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

sediment magnetic signature of the mid holocene paleoenvironmental change in the central okinawa trough abstract the kuroshio current kc has strong effects on local paleoclimate fluctuations and the paleoenvironmental evolution of the east china sea ecs in the okinawa trough the changes in the spatial position of its long axis and or current strength since the last glacial stage have been a controversial topic a multi proxy study including both magnetic and non magnetic grain size measurements and ams 14 c dating approaches has been carried out on samples from core y179 2 53 m long recovered from the central okinawa trough to investigate the possible kc related holocene paleoenvironmental changes in the trough the core spans about the last 12 000 years and comprises dominantly clayey silt and silt magnetic measurements indicate that pseudo single domain psd magnetite of terrigenous origin is the main magnetic carriers with no apparent alteration due to early diagenesis based on physical properties the core can be divided into three zones i 0 1 05 m 7 2 cal kyr bp compared with zone iii zone i contains less abundant but coarser magnetite particles and shows notable differences in magnetic and non magnetic mineral components zone ii shows transitional features between zones i and iii in terms of magnetic properties constrained by 14 c ages zone ii coincides with the middle holocene paleoenvironmental event in the okinawa trough 7 3 7 0 cal kyr bp which was either previously identified to be associated with the re entering of the kc into the trough after its shifting away during the last glacial maximum lgm or interpreted as the kc strengthening at the same time the down core variations of magnetic properties in core y179 agree well with the environmental changes caused by the middle holocene kc related event in the okinawa trough therefore our new results provide environmental magnetic evidence for the middle holocene event in the trough

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

quantifying the concentration of ferrimagnetic particles in sediments using rock magnetic methods 1 we have developed a quantification method that uses mainly room temperature rock magnetic measurements to calculate concentrations of ferrimagnetic particles in sediments our method uses saturation magnetization ms as a total ferrimagnetic concentration proxy the saturation remanence ratio mrs ms as a magnetic grain size proxy the anhysteretic remanence ratio a mrs to estimate inter particle magnetostatic interactions and the normalized susceptibility of the ferrimagnetic fraction f ms to calculate the proportion of ultrafine superparamagnetic particles this approach eliminates the effect of dilution of the magnetic properties by weakly magnetic matter and allows the calculation of direct concentrations or fluxes for dated sedimentary profiles of constituent ferrimagnetic components we test our method on a short sediment core from an urban minnesota lake for which we calculate ferrimagnetic fluxes of four magnetic components and compare their pre and post european settlement values our quantification technique can be applied for reconstructing past environmental changes in a range of sedimentary environments and is particularly useful for large sets of samples where detailed magnetic unmixing methods are unfeasible due to time or instrument constraints