environmental conditions for the presence of magnetofossils in the last glacial maximum inferred from magnetic parameters of sediments from the ulleung basin east sea abstract magnetic characterization of sediments from the ulleung basin in the east sea japan sea was carried out to decipher changes in environmental conditions over the last 39 000 years magnetic susceptibility intensities of natural remanent magnetization nrm anhysteretic remanent magnetization arm partial arm parm and saturation isothermal remanent magnetization sirm were measured for selected samples irm acquisition hysteresis and first order reversal curve forc measurements were made the ratios of rock magnetic parameters such as arm sirm arm and s ratio were determined to identify magnetic grain size and mineralogical variations along with electron microscope observations of magnetic mineral extracts down core variations in rock magnetic parameters for the 5 21 m long sediment core reveal distinct intervals with different grain size concentration and composition of magnetic minerals the uppermost portion and the high magnetic intensity zone hiz in marine isotope stage mis 2 are characterized by higher concentrations of fine grained magnetite whereas the mis 1 and 3 intervals contain lower concentrations of coarser grained magnetic minerals with increasing influence of hematite and or iron sulphide minerals the hiz interval is inferred to contain high occurrences of fine grained bacterial magnetosomes based on geochemical proxies east sea conditions for the hiz interval coincident with the last glacial maximum lgm can be summarized as having low total organic carbon toc enhanced eolian contributions from terrestrial organic particles and iron bearing minerals under the influence of an intensified east asian winter monsoon along with iron reducing but not sulphidic conditions that favoured growth and preservation of magnetotactic bacteria the delicate balance between reductive dissolution of magnetofossils under sulphidic conditions and production and preservation of magnetotactic bacteria in overlying iron reducing sediments for the hiz interval is responsible for the resultant abundance variations of magnetosomes in the studied sediments

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

magnetic grain size and viscous remanent magnetization of pelagic clay unfossiliferous pelagic clay red clay cores from the pacific generally have unstable remanent magnetization except for tens of centimeters to several meters below the surface the origin of this instability has been considered to be viscous remanent magnetization vrm we conducted a rock magnetic study of a pelagic clay core from the south pacific which has the unstable to stable transition at about 1 5 m below the surface using the suspension method of yoshida and katsura 1985 we determined downcore variation of complete alignment magnetization cam and magnetic moment distribution geometric mean moment mg and log standard deviation log a assuming a lognormal distribution mean magnetic grain diameter was calculated from the mg using the saturation magnetization of magnetite 4 8 105 a m 1 on the assumption that all the magnetic grains are single domain magnetites of spherical shape this assumption is supported by thermomagnetic analyses isothermal remanent magnetization irm acquisition experiments and the ratio of cam to saturation irm the grain diameter ranges from about 0 02 to 0 15 m and decreases with depth below about 1 5 m the derived grain size holds even when the magnetites in the sediments suffered oxidation because the saturation magnetization of maghemite is close to that of magnetite the frequency dependence of magnetic susceptibility showed a downward increase in the amount of superparamagnetic grains on the other hand the magnetic viscosity acquisition coefficient normalized by the cam increases with depth we conclude that magnetic grain size can control the magnitude of the secondary magnetization vrm of pelagic clay it has been proposed that the major source of pelagic clay is atmospherically transported dust intensified global atmospheric circulation by the change of climate would raise the grain size of the magnetic minerals of the eolian component which can cause the unstable to stable transition of the remanent magnetization

regional patterns of magnetite authigenesis in the appalachian basin implications for the mechanism of late paleozoic remagnetization we report paleomagnetic and rock magnetic data from sedimentary carbonates of the appalachian basin that have implications for the mechanism of widespread late paleozoic remagnetization in this rock type sampling was accomplished mostly along two across basin transects one in devonian carbonates of new york state and the other in ordovician and mississippian carbonates of tennessee and alabama paleomagnetic investigations of the new york devonian carbonates along a transect from albany to buffalo indicate that these rocks were completely remagnetized in alleghenian time rock magnetic studies show that magnetite concentration varies in a regular fashion along the transect with a local maximum near syracuse and decreasing gradually to the east and west this pattern shows a striking correlation with the degree of diagenetic alteration of clay minerals in a devonian bentonite horizon which took place during alleghenian time we conclude that most of the magnetite present in these carbonates is of authigenic origin and that clay mineral alteration and magnetite authigenesis were coeval late paleozoic events that were controlled by the same diagenetic factors thermoviscous remagnetization processes cannot be ruled out in this setting in light of the observed degree of thermal maturity however our results suggest that chemical factors played a critical role in remagnetization since they allow us to infer that magnetite authigenesis and remagnetization are about the same age we propose a geochemical model for magnetite authigenesis wherein the iron is derived from detrital smectites during diagenetic illitization which is triggered by the introduction of potassium rich brines results from the tennessee transect from nashville to chattanooga show a very different pattern paleomagnetic studies indicate that late paleozoic remagnetization has affected ordovician carbonates of the nashville dome paleozoic carbonates in the overthrust belt near chattanooga also carry the late paleozoic remagnetization however mississippian carbonates between the dome and the overthrust belt are very weakly magnetized and show no evidence for late paleozoic remagnetization samples show only a present field magnetization or at one locality in northwestern alabama a dual polarity magnetization of probable mississippian age rock magnetic studies indicate that higher concentrations of magnetite are present in the remagnetized rocks of the nashville dome and the overthrust belt than in the nonremagnetized mississippian carbonates we therefore conclude that magnetite authigenesis and remagnetization are related events in this setting and that the remagnetization must be due to chemical processes the presence of a remagnetization shadow in the younger rocks now exposed between the fold thrust belt and the flexural arch is attributed to westward flow of magnetite forming aqueous fluids through deep sub carboniferous aquifers during alleghenian time upward migration of the fluids through the mississippian carbonates may have been prevented by the devono mississippian chattanooga shale an impermeable stratum that is present throughout the region

high resolution environmental magnetic study of a holocene sedimentary record from zaca lake california mineral magnetic studies of holocene lake sediments recovered from zaca lake in coastal southern california have yielded a 3000 year high resolution record of terrestrial hydrologic variability an

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

rapid directional changes associated with a 6 5 kyr long blake geomagnetic excursion at the blake bahama outer ridge geomagnetic excursions are recognised as intrinsic features of the earth s magnetic field high resolution records of field behaviour captured in marine sedimentary cores present an opportunity to determine the temporal and geometric character of the field during geomagnetic excursions and provide constraints on the mechanisms producing field variability we present here the highest resolution record yet published of the blake geomagnetic excursion 125 ka measured in three cores from ocean drilling program odp site 1062 on the blake bahama outer ridge the blake excursion has a controversial structure and timing but these cores have a sufficiently high sedimentation rate 10 cm ka to allow detailed reconstruction of the field behaviour at this site during the excursion palaeomagnetic measurements of the cores reveal rapid transitions 230th excess measurements to assess variations in the sedimentation rates through the sections of interest this provides an age and duration for the blake excursion with greater accuracy and with constrained uncertainty we date the directional excursion as falling between 129 and 122 ka with a duration for the deviation of 6 5 1 3 kyr the long duration of this interval and the fully reversed field suggest the existence of a pseudo stable reversed dipole field component during the excursion and challenge the idea that excursions are always of short duration

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

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

magnetic record of deglaciation using forc pca sortable silt grain size and magnetic excursion at 26 ka from the rockall trough ne atlantic research supported by us nsf grants 0850413 and 1014506 and the european research council under the european union s seventh framework programme fp 2007 2013 erc grant agreement no 320750 the uk nerc and bgs funded the recovery of core md04 2822

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

improved determination of marine sedimentation rates using 230thxs measurements of excess 230th 230thxs have proved to be a useful tool in constraining changes in sedimentation rate and improving our understanding of the fluxes of other components into marine sediments to obtain the initial activity of 230thxs 230thxs0 in sediment the total measured 230th must be corrected for the presence of 230th associated with detrital minerals for ingrowth from uranium bearing authigenic phases and then also corrected for the decay of 230thxs since deposition we describe a number of improvements in the way these corrections are applied to obtain more accurate determinations of 230thxs0 we present a new method for the determination of a local estimate for the detrital 238u 232th activity ratio suggest more appropriate values for the isotopic composition of authigenic uranium and question the assumption of secular equilibrium in detrital material we also present a new freely available matlab script called xsage that can calculate 230thxs0 from user supplied datasets of uranium and thorium isotope activities from sedimentary samples following the theoretical approach described xsage can determine variations in sedimentation rate between stratigraphic horizons of known age and thus produce high resolution age models using a monte carlo approach the program calculates uncertainties for these age models and on the durations of intervals between tie points an example of the application of the xsage program using a previously published record is provided

magnetic characteristics of loess paleosol sequences in tacheng northwestern china and their paleoenvironmental implications abstract systematic rock magnetic data including magnetic mineralogy and magnetic concentration magnetic susceptibility laboratory induced magnetic remanences are presented from the loess paleosol sequences in tacheng northwestern china to explore the specific paleoenvironmental significance of magnetic characteristics in the xinjiang loess results show that ferrimagnetic minerals such as magnetite and maghemite dominate the magnetic properties in the tacheng tc section similar to the magnetic mineralogy of loess deposits in the chinese loess plateau clp the magnetic particles in the tc section are characterized by multi domain md and pseudo single domain psd behavior representing the detrital primary mineral phase the absolute contents of pedogenic ultrafine superpara sp ferrimagnetic particles are very low in the tc section indicating that pedogenesis has a limited contribution this is quite different from the magnetic enhancement of loess deposits in the clp variation of magnetic susceptibility and median grain sizes could be interpreted by the predominance of paleowind intensity as well as provenance variation a similar pattern was also found in other places in xinjiang such as talede section in yili basin and bole section in the western tianshan our results suggest that variation of detrital inputs might have played a pivotal role in the enhancement of magnetic susceptibility while pedogenesis was probably responsible for the increase of finer single domain sd particles in paleosol units the arm sirm ratio could serve as an indicator for reflecting the degree of pedogenesis in xinjiang loess

oligocene paleoceanography of the south atlantic paleoclimatic implications of sediment accumulation rates and magnetic susceptibility measurements paleoceanographic changes during the oligocene in the south atlantic have been examined using paleomagnetic rock magnetic carbonate content and sediment accumulation rate sar data we show that magnetic susceptibility ms is largely controlled by carbonate content at deep sea drilling project site 522 which in turn is the primary control on sar at the site over 5000 ms measurements were averaged over magnetostratigraphic polarity intervals for use as indicators of carbonate content and sar proxies the study produced three primary results 1 a spectral analysis of the ms data from one upper oligocene core reveals two dominant periodicities 44 7 10 4 kyr and 26 4 3 6 kyr which approximate milankovitch obliquity 41 kyr and precession 23 kyr periods 2 four pulses of increased sar lasting 1 to 2 m y punctuate the section implying longer term climatic changes these events are also seen in the contessa quarry section of the italian tethyan oligocene and 3 two of the sar maxima correspond to times of global cooling and possible ice volume increases at 31 and 36 ma

the last glacial aeolian record of the island of susak croatia as seen from a high resolution grain size and rock magnetic analysis abstract the loess palaeosol record on the island of susak in croatia is a unique archive of late glacial climate changes in the adriatic region possibly even in the wider area on susak up to 90 m of thick quaternary sediments were deposited and are accessible for detailed palaeoclimate reconstructions in this paper the results of a high resolution grain size and rock magnetic investigation on the last glacial upper pleniglacial sand pit section from susak are presented in spite of its significant thickness the sand pit section does not represent a continuous record it is a result of a very dynamic environment there the deposition of dust and formation of loess has been interrupted by pedogenesis periods of increased sand accumulation erosion due to slope wash and water activity redeposition and wildfires and all in the time period of about 10 000 years of the upper pleniglacial as seen from the irsl dating results the grain size data clearly show a shift towards coarser grain sizes which differs from typical loess regions such predominance of the coarser grained over the fine grained fraction very likely resulted from the predominance of deposition over pedogenesis increased wind activity and proximal source of material the rock magnetic signal preserved in the sediment also differs compared to loess palaeosol records from other regions the susceptibility values are several times higher than in the records from the pannonian basin and from typical eurasian loess both the increased susceptibility values and the grain size are very likely the result of a significant proximal material input from the po river plain

magnetic measurements used to identify paleoxidation fronts in deep sea sediments from the madeira abyssal plain we describe the results of rock magnetic measurements of a sediment core from the madeira abyssal plain which contains multiple turbidites previous studies of trace element e g u concentration and observations of sediment color changes have shown that turbidite emplacement has resulted in reductive diagenesis and the formation of paleoxidation fronts we show that variations in sediment lithology and postdepositional sedimentary processes can be characterized very sensitively using magnetic measurements low concentrations of magnetic minerals occur in turbidites with a high organic content reflecting the destruction of magnetic material via the process of reductive diagenesis in addition fossil redox fronts are readily identified by rock magnetic properties

a 580 kyr paleomagnetic record from the sub antarctic south atlantic ocean drilling program site 1089 1 we report geomagnetic directional paleosecular variation relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth mcd at south atlantic ocean drilling program odp site 1089 40 56 2 s 9 53 64 e 4620 m water depth the age model is provided by high resolution oxygen isotope stratigraphy augmented by radiocarbon dates from the upper 8 mcd of nearby piston core rc11 83 mean sedimentation rates at site 1089 are in the range of 15 to 20 cm kyr two intervals during the brunhes chron at 29 6 mcd 190 ka and at 48 mcd 335 ka have component magnetization directions with positive reverse polarity inclination however the excursional directions are heavily overprinted by the postexcursional field magnetite is the dominant carrier of magnetic remanence and occurs in the pseudosingle domain psd grain size an additional higher coercivity magnetic carrier characterized by low unblocking temperatures 350 c is assumed to be authigenic pyrrhotite a decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate indicating diagenetic reduction of magnetite despite down core changes in magnetic mineralogy normalized intensity records from site 1089 are comparable with high resolution paleointensity records from the north atlantic e g odp sites 983 and 984 sediment properties and sedimentation patterns within the cape site 1089 and iceland sites 983 and 984 basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation variations in normalized intensity from site 1089 therefore appear to reflect changes in global scale geomagnetic field intensity

magnetic properties derived from a loess section at the northern piedmont of tianshan mountains xinjiang china and their paleoenvironmental significance

experimental deformation of synthetic magnetite bearing calcite sandstones effects on remanence bulk magnetic properties and magnetic anisotropy we have quantified effects of experimental deformation on the magnetic properties of a set of synthetic calcite sandstone samples containing magnetite the deformation was carried out in a microcomputer controlled apparatus that adjusted the applied differential stress as needed to maintain a constant strain rate of 10 5 s 1 most samples were deformed under dry conditions but a few were deformed with a pore fluid present the samples deformed under dry conditions required substantially higher differential stresses macroscopically ductile shortening strains of up to 25 produced the following irreversible changes in magnetic properties 1 increased bulk coercivity remanence coercivity and mean anhysteretic remanence susceptibility 2 decreased mean low field susceptibility 3 decreases in the component of remanence parallel to shortening 4 smaller decreases for most samples in the component normal to shortening resulting in a net rotation of the remanence away from the shortening axis 5 larger decreases in the normal component in a few samples resulting in a net rotation of the remanence towards the shortening axis 6 increased magnetic anisotropy and 7 increased deformation of initial magnetic ellipsoids a comparison of data for samples deformed under dry and wet conditions higher and lower differential stresses respectively indicates that remanence reorientation and susceptibility anisotropy are controlled primarily by bulk strain i e rotation and displacement of particles whereas coercivity and anhysteretic anisotropy are controlled dominantly by microstrain or intragranular stress

late holocene changes in precipitation and hydrography recorded in marine sediments from the northeastern caribbean sea abstract we present a record of climate variability spanning the last 2000 years obtained from sediment cores retrieved south and west of puerto rico in the northeastern caribbean sea the records include lithological and mineral magnetic parameters as well as planktonic foraminifer data for chronostratigraphic control ams 14 c and 210 pb 137 cs measurements were made harmonic analysis of the values of the mineral magnetic parameters saturation isothermal remanent magnetization sirm anhysteric remanent magnetization divided by magnetic susceptibility arm and saturation isothermal remanent magnetization divided by magnetic susceptibility sirm indicate the existence of a 200 year long climate cycle in the northeastern caribbean during the last 2000 years the detected cycle may reflect changes in precipitation patterns over the low latitude north atlantic ocean and surrounding continental areas higher organic carbon contents appear in the sediments both off southern and western puerto rico before and at the onset of the little ice age around a d 1300 to 1500 this is indicative of increased run off and or enhanced surface productivity possibly associated with more intense wind induced upwelling major changes in the geochemical and mineral magnetic records around a d 850 1000 concur with changes in other records from the caribbean and north african regions indicating a shift toward a more humid climate over the low latitude north atlantic

thermally activated viscous remanence in some magnetite and hematite bearing dolomites a brunhes age viscous remanent magnetization vrm carried by magnetite and hematite in the el paso and montoya dolomite formations has unblocking temperatures significantly higher than those predicted by single domain theory the samples appear to contain a substantial fraction of pseudo single domain magnetite suggesting transdomain processes may be responsible for the stable vrm a strong inverse correlation between the occurrence of high unblocking temperatures and high isothermal remanence fractions acquired above 0 3 tesla suggests that the hematite grain size may also be important in determining the range of observed temperatures larger grains are inferred to have lower coercivities but higher unblocking temperatures an older reverse polarity component is also observed and appears to be a record of late cretaceous tertiary tectonic activity

magnetotactic bacterial response to antarctic dust supply during the palaeocene eocene thermal maximum distinct magnetic properties of marine sediments that record the palaeocene eocene thermal maximum petm have been suggested to be due to a bacterial magnetofossil signal that is linked to enhanced weathering conditions during the petm we document the dominance of bacterial magnetite in deep sea sediments from southern kerguelen plateau ocean drilling program hole 738c southern ocean not only during the petm but also before and after the thermal event this occurrence of magnetofossils throughout the petm indicates that the occurrence of bacterial magnetosomes is not due to a preservation effect instead we suggest that it is due to sustained mild iron reducing conditions that dissolved the most labile aeolian derived iron which favoured continued magnetotactic bacterial activity without being strong enough to dissolve the less reactive magnetite and haematite enhanced aeolian haematite abundances at the beginning of the petm indicate drier conditions on the neighbouring antarctic continent at those times our results provide evidence that iron fertilisation by aeolian dust was the main limiting factor that conditioned proliferation of magnetotactic bacteria in the deep sea at the southern kerguelen plateau with the exception of two short periods of rapidly changing palaeoenvironmental conditions at the onset and termination of the petm increased iron supply from aeolian dust that enhanced oceanic primary productivity and subsequent delivery of organic carbon to the seafloor along with mild iron reducing diagenetic conditions seem to have been necessary to provide the iron needed for magnetite biomineralization by magnetotactic bacteria to drive their marked increase in abundance in the studied petm record from southern kerguelen plateau our analyses of a deep sea petm record from hole 1051b at blake nose atlantic ocean failed to identify magnetofossils despite evidence for the occurrence of magnetite and haematite of probable aeolian origin contrasting magnetic properties at these petm sections indicate that further work is needed to understand the palaeoenvironmental and diagenetic factors whose interactions lead to production and preservation of magnetofossils in deep sea sediments

past environmental and circulation changes in the south china sea input from the magnetic properties of deep sea sediments abstract the south china sea located at the transition between the pacific and the indian ocean receives every year mainly during the rain season enormous amounts of river sediments originating from the erosion weathering of rocks in the catchment basins at sea these sediments are carried by different water masses to their deposition site and they constitute a unique archive for past environmental studies in this region the magnetic fraction of deep sea sediments though forming a minority in volume provides incredibly valuable information for paleoceanographic reconstructions as long as its provenance and source to sink processes are well constrained after a brief description of the climatic sedimentological and oceanographic context of the south china sea scs a review of the information available so far in the literature about the magnetic properties of scs sediments is presented it shows a large variety of interpretations conclusions that finally results in a rather unclear picture because in such a context the characterization of the sediment at the source is critical the magnetic properties recently obtained from a set of samples from rivers and marine surface sediments are summarized to describe the present day situation they are then used to interpret paleorecords from a set of seven marine cores distributed from the southern to the northern basins at different water depths and all covering at least the last climatic cycle the results reported here for the first time suggest that the magnetic mineralogy remains rather stable in time on land and that its time and spatial distribution at sea is an interplay of changes in sea level and deep sea circulation during low sea level periods bottom deep sea circulation is weak and the deposited sediment originates from the proximal rivers on the contrary during high sea level the circulation is enhanced transporting more sediment most likely from taiwan and luzon to the northwestern part of the scs and also in smaller proportion to the southern basin where it mixes with the local river borne sediment by comparing the two longest records we observe that this pattern is repeated over the last 900 ka superimposed to the 100 kyr cyclicity we also observe a longer term evolution with a maximum in the bottom current strength around 500 ka coinciding with global changes in the deep ocean circulation and carbon cycle these new results based on a wide spectrum of magnetic properties of numerous marine sedimentary cores from the scs show that the magnetic fraction yields important insights into past changes of the sedimentary pathways in particular the dynamic of the deep sea circulation depending on the global climatic context

relative paleointensity of the geomagnetic field during the brunhes chron abstract we conducted a paleomagnetic study of four sediment cores taken from different regions in the low latitudes of the pacific ocean in order to recover relative paleointensity variations during the brunhes chron three cores have good age control from oxygen isotope stratigraphy we extensively examined rock magnetic uniformity by the iso thermal remanent magnetization irm acquisition and the alternating field demagnetization of the anhysteretic remanent magnetization arm and the irm only rock magnetically homogeneous sediments were used biogenic magnetites were found in all but one core and their dissolution in early diagenesis was not significant the four cores showed coherent variations of the remanent intensity normalized by the arm implying that these variations represent the behavior of the geomagnetic field long term paleointensity variations during the brunhes chron are characterized by an asymmetric pattern rapid increases in the intensity occurred just after the brunhes matuyama transition in the mid brunhes from about 500 to 400 ka and during the last 100 ka and gradual decreases between them the first one supports the idea of rapid regeneration of the geomagnetic field after polarity reversals 1 the other two may have been triggered by very short polarity reversals

morava river floodplain development during the last millennium stražnicke pomoravi czech republic floodplain sediments deposited along the lower course of the morava river eastern czech 206 pb 207 pb and pop ddt pcb analysis and 137 cs activity data thecu trienmethodwasusedforstratigraphicallycorrelatingthesedepositsbasedonthevariationofexpand able clay minerals in the sediments the resulting stratigraphic pattern reveals the alluvial history of the cur rently active river channel system since the end of the first millennium ad fine overbank clayey sediments deposited during the mediaeval warm period were eroded from cultivated fields newly formed during mediaeval colonization between 1250 and 1450 these fine deposits are overlain by coarser floodplain sedi mentsofthe littleiceage indicatingachangeinthesedimentsourcesincethesixteenthcentury ad anda substantial increase in the sediment load in the second half of twentieth century the straunicke pomoravi floodplaindepositsrepresentavaluablepalaeoenvironmentalarchiveofthelastmillennium containingrecords offluvialprocessesconsiderablyalteredbyhumanactivities

environmental magnetism of pleistocene sediments in the north pacific and ontong java plateau temporal variations of detrital and biogenic components 1 an environmental magnetic study was conducted to investigate temporal variations of the sources of magnetic minerals in the pacific ocean using sediment cores of pleistocene age the proportion of interacting i to noninteracting n i single domain components was estimated from first order reversal curve diagrams and the proportion of middle m to low l coercivity components was determined from decomposition of isothermal remanent magnetization irm acquisition curves the i and m components are interpreted to be carried by terrigenous maghemite while the n i and l components represent biogenic magnetite an inverse correlation between the ratio of anhysteretic remanent magnetization susceptibility arm to saturation irm sirm and the i n i ratio was confirmed for sediments across wide expanses in the pacific ocean this implies that arm sirm can be used to estimate the relative abundances of biogenic and terrigenous components in sediments in the north pacific the relative abundance of the i and m components increases in glacial periods variations of arm sirm and s ratio s 0 1t resemble each other and decrease in the same time intervals these variations reflect increases of terrigenous input in glacial periods as eolian dust on the ontong java plateau in the western equatorial pacific on the other hand minima in arm sirm and s 0 1t occur at glacial to interglacial transitions and the relative abundance of the i and m components increases in these periods terrigenous material in this region is considered to be transported mainly from the new guinea and solomon islands by the equatorial undercurrent the higher proportion of the terrigenous component at glacial to interglacial transitions is coeval with carbonate preservation maxima reported from the ontong java plateau suggesting a linkage between the two

early diagenesis in an organic rich turbidite and pelagic clay sequence from the cape verde abyssal plain ne atlantic magnetic and geochemical signals abstract processes of early diagenesis in sediments from the cape verde abyssal plain are investigated using the complimentary techniques of environmental magnetism and solid phase geochemistry the sequence captured by a 2 m long box core comprises an organic rich turbidite derived from the nw african continental margin emplaced ca 330 ka bp overlain by brown pelagic clay diagenesis in the pelagic clay mainly involves slow in situ oxidation of the iron oxide phases present which mossbauer effect data suggest are detrital haematite and magnetite possibly maghaemitised in the turbidite diagenesis has proceeded in two stages the first involving suboxic reductive processes following depletion of porewater o2 and the second involving oxidative processes associated with the slow descent of an oxidation front through the bed due to diffusion of o2 from the overlying seawater carbonate free magnetic parameters interparametric quotients and remanence acquisition demagnetisation and coercivity measurements of the core reveal that significant depletion of detrital ferrimagnetic iron fe2 fe3 oxide grains like titano magnetite has occurred within the turbidite during suboxic diagenesis and confirm previous suggestions that reductive dissolution of such components is a grain size selective process however the higher oxidation state fe3 canted antiferromagnetic iron oxide grains like haematite and goethite are much less susceptible to reductive diagenesis remobilisation of transition metal ions from below the oxidation front in the turbidite has led to authigenic precipitation of ferrimagnetic fe mn micronodules in a distinct layer immediately overlying the front and above this a further interval of mn enriched diagenetic laminae however within the suboxic organic rich zone of the turbidite well below the oxidation front there is clear evidence for the presence of a significant concentration of fine single domain ferrimagnetic iron oxide grains which are most probably associated with a population of live magnetotactic bacteria between this zone and the oxidation front there is a transitional interval in which the number of live magnetotactic bacteria declines rapidly and fossil magnetosomes in the sediment are being reductively dissolved progressively up sequence these results are broadly similar though differing in some respects to magnetic and geochemical studies of hemipelagic and high productivity pelagic sediments in which mn and fe redox boundaries have been recognised and further illustrate the value of environmental magnetic parameters for characterising early diagenetic processes in sediments of this kind

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

the upper olduvai geomagnetic field reversal from death valley california a fold test of transitional directions high resolution records of the upper olduvai geomagnetic field reversal were obtained from two localities within steeply dipping lacustrine sediments of the confidence hills southern death valley california the difference in bedding attitude between the two localities allowed us to perform a fold test of both transitional and non transitional paleomagnetic directions this is the first positive fold test obtained for transitional directions from any geomagnetic field reversal in addition variations in lithology allowed a comparison of transitional records from different sedimentary environments alternating field and thermal demagnetization reveals that most samples have either single or simple two component magnetizations the low coercivity low blocking temperature component is most likely held by large multidomain grains of magnetite and aligns with the present day field when uncorrected for bedding orientation the high coercivity component is held primarily by single and pseudo single domain titanomagnetite as determined from standard magnetic studies and electron microscopy this component is interpreted as a primary magnetic signature based on the presence of stratigraphically bound reversals in the tilt corrected data and positive reversal tests short term field variations can be correlated between the two records and differences are readily explained by the recording process inherent to the two sedimentary environments the sampling site is located within one of the preferred bands of transitional virtual geomagnetic poles vgp s 1 3 yet the transitional vgp paths from both localities are clustered within two primary longitudinal bands which are approximately 90 away from the sampling site longitude one lies over the atlantic ocean 10 50 w and the other antipodal to this 130 170 e these bands are also inconsistent with eight previous studies of the upper olduvai transition 4 9 3 10 when all reported studies of this reversal are examined however no global consistency exists instead the transitional vgp s are better grouped in a sampling site reference frame

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

historical climatic record from flood sediments deposited in the interior of spiralka cave czech republic abstract magnetic susceptibility was measured on more than four hundred samples collected from a 5 m high section of fine grained sediments deposited during flood events in the interior of spiralka cave spiralka cave is located in the northeastern portion of the moravian karst czech republic in the upper 1 5 m of this profile mineral magnetic fe arm sirm s ratio t and other non magnetic measurements heavy mineral concentration loss on ignition and particle grain size indicate that variations are controlled by the concentration of magnetite and by magnetic grain size i e increased magnetic susceptibility results from increased concentration of coarse grained magnetite a positive correlation with ti and zr concentrations in this part of the profile with our magnetic susceptibility record is a detrital signal responding to changing environmental conditions in the catchment area furthermore a comparison of our susceptibility record to the record of winter temperature anomalies constructed from both instrumental and historical records collected at the klementinum observatory in prague shows a remarkable correlation the most probable explanation of these correlations is that during years with warmer winters positive winter temperature anomalies and less snow cover the floods were less intensive but probably had access to larger tracts of cultivated land as agriculture tended to expand during these warmer periods cultivation of the land provided flood waters with greater access to coarser grained magnetite like materials exposed by tilling of soils lower in the profile interpreting the environmental significance of magnetic susceptibility variations is more complex as remobilization of iron has occurred nevertheless the magnetic susceptibility record when coupled with non magnetic measurements can be shown to correlate to known environmental conditions present in central europe during the deposition of the lower portion of the profile

a magnetic signature of bottom current erosion abstract to characterize the magnetic signal associated with bottom current erosion we have conducted downcore measurements of magnetic texture and fabric in three cores containing known erosional hiatuses using biostratigraphic and magnetostratigraphic analysis erosional hiatuses were identified for three cores from two current dominated environments the northern bermuda rise and the south indian basin the cores were contiguously subsampled and the magnetic susceptibility k the anisotropy of magnetic susceptibility ams and the anhysteretic susceptibility k arm were measured the ams parameters h and q were used to describe the relative magnitude and the shape respectively of the representative susceptibility ellipsoid the concentration independent and dimensionless ratio k arm k was used to indicate relative changes in magnetic grain size hiatuses in the three cores were marked by unusually high values of h and q indicating a greater development of internal fabric with a more linear fabric representation depressed values of k arm k indicated a coarser mean magnetic grain size the magnitude of this signal however did not have a simple relationship with hiatus duration t test results statistically confirmed the existence of an erosional signature to enhance the applicability of this technique a quantitative discriminant model was constructed and calibrated using the magnetic characteristics of erosion since this model was constructed from samples of known erosional and non erosional character the discriminant functions could then be used as reference equations to identify erosion in other cores biostratigraphic and oxygen isotopic data from a 14 m core from the northern bermuda rise extending back to isotopic stage 8 250 ka bp indicate two short intervals of low accumulation rate which for this region are most probably attributable to bottom current erosion magnetic data for this core were entered into the reference discriminant model and the two zones of suspected erosion were classified by the functions as being highly crosional in character zones of probable erosion were identified at several other levels in the core the timing of these short term crosional events was found to coincide closely with glacial intervals suggesting that bottom currents active on the northern bermuda rise were invigorated periodically during glacial maxima at c 18 58 64 85 130 140 165 180 225 and 250 ka bp

magnetic characterization of distinct soil layers and its implications for environmental changes in the coastal soils from the yellow river delta abstract the soils in the yellow river delta yrd were formed through the deposition of the yellow river sediments under complicated hydrodynamic conditions resulting in large variability in soil properties in this study environmental magnetic analyses were conducted on four typical soil profiles and one high resolution soil profile with distinct soil layers to examine the soil formation process and to track the environmental changes the results showed that the red clay layer rcl in the yrd soil profiles had unique magnetic properties which could be clearly separated from the yellow silt layer ysl at frequency dependent susceptibility fd 6 susceptibility of anhysteretic remanent magnetization arm 250 10 8 m3 kg 1 arm magnetic susceptibility lf 5 arm saturated isothermal remanent magnetization sirm 45 10 5 m a 1 and sirm lf

decay rate dependence of anhysteretic remanence fundamental origin and paleomagnetic applications 1 we have measured the intensity of anhysteretic remanent magnetization arm as a function of alternating field af decay rate for synthetic and natural single domain sd and pseudo single domain psd magnetites arm intensity increases as decay rate decreases multidomain md magnetites have the opposite response arm increasing as the decay rate increases these are identical to the sd psd and md dependences of thermoremanent magnetization on cooling rate for all grain sizes and domain structures arm intensity increases as the af decay rate used to achieve an initial demagnetized state decreases decay rate differences in arm intensity are a property of low and medium coercivity grains as shown by annealing and by stepwise af demagnetizing samples we interpret the sd results to mean that increased af exposure time permits a closer approach to equilibrium magnetization an approximate thermal activation theory based on neel 1949 and an exact theory by egli and lowrie 2002 predict 6 11 increases in arm for an order of magnitude decrease in decay rate in reasonable accord with the observed 12 increase for 0 065 m sd grains for md grains we hypothesize that increased exposure time slower decay permits more efficient self demagnetization reducing arm low coercivity grains experience the largest self demagnetizing fields and therefore have the largest decay rate response initial state decay rate response is attributed to longer exposure times leaving domain walls more strongly pinned in deeper potential wells the net self demagnetizing field is zero in the demagnetized state acquisition decay rate annealing and initial state responses of psd grains are a blend of sd and md responses because arm is the most frequently used normalizer in relative paleointensity determination it is important either to use a standard decay rate or else to remove the decay rate dependence by demagnetizing the arm to 30 of its initial value arm0 3 a standard demagnetization level for the normalizing arm is particularly important when comparing paleointensity records from different laboratories

behavior of u channels during acquisition and demagnetization of remanence implications for paleomagnetic and rock magnetic measurements abstract we have examined the effects of translation speed on the acquisition and demagnetization of remanence in u channels the speed at which the u channel moves through alternating and steady fields has a significant effect on the efficiency of remanence acquisition and demagnetization anhysteretic remanence arm acquisition and alternating field af demagnetization efficiency are inversely correlated with translation speed arm acquisition is most efficient at a track speed of 1 cm s whereas at higher speeds arm reaches an apparent saturation at low peak fields and has a soft coercivity spectrum during subsequent af demagnetization the dependence of magnetization acquired or removed on translation speed through alternating or steady fields is explained by the number of alternating field half cycles experienced as the sample is translated through the applied field and on the alternating field decay rate at slow translation speeds a u channel experiences a comparable number of alternating field cycles to that experienced by a stationary discrete sample at fast translation speeds the u channel experiences a factor of 100 fewer alternating field cycles and the conditions experienced by the u channel sample can be comparable to the natural reorganization time of the magnetic moments within the sediment particles during remanence acquisition and demagnetization at low decay rates the sample has more time in the blocking field and thus a more complete approach to equilibrium

use of magnetic and radiometric measurements to investigate erosion and sedimentation in a british upland catchment in response to the potential shortcomings of single technique strategies in the investigation of erosion and sedimentation a combined magnetic and radiometric 13cs and 210pb approach has been undertaken in the upland watershed lake system of howden reservoir derbyshire by combining these techniques some assessment of sediment sources and the erosion status of the catchment has been achieved alone each approach would have been unable to determine unequivocally sediment provenance furthermore the parallel use of these measurements has highlighted limitations and or uncertainties in both the magnetic and 137cs techniques these problems reflect the particular soil characteristics and drainage conditions of this upland catchment despite the documented severity of peat erosion in the region howden reservoir has a mixture of sediment sources and a relatively moderate rate of sedimentation sediment yields total 127 7 t km 2 yr 1 including organic fraction 31 3 t km 2 yr 1 are however higher than in other british upland areas

the magnetic record of particulate pollution in a saltmarsh dee estuary uk in the sediments of a rapidly accreting salt marsh at the head of the dee estuary northwest england magnetic measurements reveal a strong and persistent signal which can be related to the historical effluent discharges of a large iron and steel works the iron oxide content of the pipeline emissions from the works permits their detection by rapid and simple measurements of the weak remanent magnetization of sediments the spatial extent of contamination of the saltings has been determined a clear distance decay effect from the point source has been observed in those parts of the saltings which accumulated during the period of strongest emissions from the plant furthermore down core a marked and spatially consistent spiked magnetic profile has been recorded this distinctive pattern of changes in magnetic concentration and grain size mirrors the past activities and discharges of the works this supposition is corroborated by a supporting chronology based on the record of 137cs emissions from the se

geomagnetic paleointensity variation with a 100 kyr quasi period abstract we analyzed records of geomagnetic field intensity paleointensity during the last 700 kyr in five sediment cores from a wide region of the pacific ocean a global paleointensity variation with a 100 kyr quasi period was successfully extracted using the wavelet transform because the variation does not correlate with that of magnetic properties of the sediments it originated from a change in the geomagnetic field the 100 kyr quasi period of the geomagnetic field is close to the timescales of eccentricity one of the earth s orbital elements and of the glacial interglacial cycle of the late quaternary paleoclimate in particular there is a correlation between the variations of the geomagnetic field intensity and climate with an 18 kyr time lag while the geodynamo has widely been thought to be a self sustained system our results support the possibility of an external energy supply of the variation through orbital forcing or climate change

origin of magnetic mineral concentration variation in the southern ocean 1 in the southern ocean magnetic mineral concentration increases in glacial periods the variation pattern closely resembles eolian dust flux records from antarctic ice cores but the cause of the linkage remains unclear as the dust flux is too small for the source of terrigenous materials in the southern ocean we have conducted an environmental magnetic study of late pleistocene sediments from the south indian ocean to investigate the origin of the magnetic concentration changes biogenic magnetites can be detected using the characteristics of almost no magnetostatic interactions and narrow coercivity distribution reflecting occurrence of single domain magnetites in a chain we interpret that a non interacting component on first order reversal curve diagrams and low coercivity components with small dispersion from isothermal remanent magnetization irm component analyses represent biogenic magnetites and that the interacting and middle coercivity components represent terrigenous maghemites the ratio of anhysteretic remanent magnetization susceptibility to saturation irm reflects relative abundance of the biogenic and terrigenous components it was revealed that biogenic magnetites are a dominant constituent of the magnetic minerals in glacials the abundance of both biogenic and terrigenous components increased with increased proportions of the latter increased ocean productivity in glacials is suggested from increased proportions of biogenic magnetites with elongated morphologies indicative of less oxic conditions and increased sedimentation rates these observations suggest that the increased magnetic concentration in glacials in the southern ocean may be explained by iron fertilization the production of biogenic magnetites was enhanced associated with increased ocean productivity which was fueled by increased eolian dust flux

parameters in the use of pxrf for archaeological site prospection a case study at the reaume fort site central minnesota abstract field portable hand held x ray fluorescence pxrf analyzers have been characterized as potentially useful for archaeological site prospection but little has been published on the parameters of their use in this manner the purpose of this study is to explore whether the variability of surface geochemistry as characterized with a pxrf analyzer corresponds with subsurface archaeological features at a site subsequently excavated and what conditions influence the success of this endeavor including feature depths soil moisture and sample processing a 520 m 2 within site area was systematically surveyed on a 2 m interval within which several types of archaeological features were excavated chimney bases wall trenches and a bonebed of faunal waste taking readings in situ and collecting samples for ex situ testing undried dried but not powdered and dried powdered the four different tests of each grid location analyzed through univariate and multivariate tests showed that the pxrf surface data does correspond with some types of subsurface features when those features are very shallow within 5 cm of surface level and are associated with clayey fills further the data from the subsurface samples provides excellent distinction of feature fills from other sediments regardless of sample preparation in situ surface survey with pxrf analyzers may however be adequate for sites with a thorough baseline geochemical database

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

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

archaeo and paleosecular variation and long term asymmetries of the geomagnetic field this report summarizes progress made during the last four years in i obtaining records of the geomagnetic secular variation using paleomagnetic techniques ii analysis and modelling of the secular variation and iii the study of asymmetries in the time averaged field seen both as departures from the geocentric axial dipole model and as statistical differences between polarity states

magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern mediterranean sea summary magnetic properties irm arm xin s ratio at 0 3 t room temperature rt hysteresis and thermomagnetic curves and geochemical data fe s mn al ti organic c were studied in two eastern mediterranean boxcores abc26 and bc19 at a resolution of 3 5 mm the boxcores contain sapropel s1 9 6 kyr bp at a few decimetres below seafloor the magnetic fraction consists predominantly of single domain sd to pseudo singledomain psd magnetite in the entire cores the original input of magnetic grains comes from two sources aeolian dust both cores and volcanic ash from the minoan eruption of santorini core bc19 only non steady state diagenesis has changed the magnetic mineralogy considerably in these alternating organic rich organic poor sediments during deposition of sapropel s1 reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities coarser magnetic grain sizes and partial maghemitization in thermomagnetic curves two types of pyrite can be identified one oxidizes below 450 uc and the other above 450 uc the higher oxidation temperature is predominantly found below the sapropel this may be related to the microtexture of pyrite which is euhedral below sapropels and mainly framboidal within sapropels since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half c 5 cm of the sapropel the oxidized part of the sapropel is enriched in diagenetically formed fe oxides with relatively high coercivity and arm the maximum coercivity is found in a distinct layer between the present day mn and fe redox boundaries at the top of the unoxidized sapropel the freshly precipitated fe oxides in this centimetre thick layer contain a mixture of superparamagnetic sp grains and high coercivity sd magnetite higher in the oxidized zone the freshly precipitated fe oxides have aged into generally slightly lower coercivity sd grains with relatively high arm in addition to the diagenetic formation of fe oxides at the top of the sapropel formation of a ferrimagnetic fe monosulphide may have occurred within the sapropel during later stages of diagenesis which may have enhanced the arm signal in the organic rich interval in particular

metal residence sites in lavas and tuffs from volcan popocatepetl mexico implications for metal mobility in the environment volcan popocatepetl is a quaternary stratovolcano located 60 km southeast of mexico city the summit crater is the site of recent ash eruptions excess degassing and dacite dome growth the modern cone comprises mainly pyroclastic flow deposits airfall tephras debris flows and reworked deposits of andesitic composition it is flanked by more mafic monogenetic vents in least degassed fallout tuffs and mafic scoria transition metals are concentrated in phases formed before eruption during eruption and after eruption preeruptive minerals occur in both lavas and tephra and include oxides and sulfides in glass and phenocrysts the magmatic oxides consist of magnetite ilmenite and chromite the sulfides consist of both fe ni 1 xs mss and cu fe sulfide iss syn and posteruptive phases occur in vesicles in both lavas and tephra and on surfaces of ash and along fractures the mineral assemblages in lavas include cu fe sulfide and fe ti oxide in vesicles and fe sulfide and cu fe sulfide in segregation vesicles assemblages in vesicles in scoria include fe ti oxide and rare fe cu sn sulfide vesicle fillings of fe ti oxide ni rich chromite fe sulfide cu sulfide and barite are common to two pumice samples the most coarse grained of the vesicle fillings are cu fe sulfide and cu sulfide which are as large as 50 in diameter the youngest plinian pumice also contains zn fe sulfide as well as rare ag cu sulfide ag fe sulfide ag bromide ag chloride and au cu telluride the assemblage is similar to those typically observed in high sulfidation epithermal mineralization the fine grained nature and abundance of syn and or posteruptive phases in porous rocks makes metals susceptible to mobilization by percolating fluids the abundance of metal compounds in vesicles indicates that volatile exsolution prior to and or during eruption played an important role in releasing metals to the atmosphere

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

holocene break up and reestablishment of the petermann ice tongue northwest greenland abstract over the last decade two major calving events of the petermann ice tongue in northwest greenland have led to speculation on its future stability and contribution to further greenland ice sheet mass loss however it has been unclear if these events are anomalous or typical within the context of limited historical observations we extend the historical record of the floating ice tongue using the stratigraphy of petermann fjord sediments to provide a longer term perspective computed tomography ct scans x ray fluorescence xrf scans ice rafted debris ird counts and the magnetic properties of specific particle size fractions constrain changes in depositional processes and sediment sources at our core sites allowing for reconstructions of past behavior of the petermann ice tongue radiocarbon dating of foraminifera 210pb and paleomagnetic secular variation psv provide age control and help to address uncertainties in radiocarbon reservoir ages a floating ice tongue in petermann fjord formed in late glacial time as petermann glacier retreated from an advanced grounded position this paleo ice tongue broke up during the early holocene when high northern latitude summer insolation was higher than present after gradual regrowth of the ice tongue associated with regional cooling the ice tongue reached its historical extent only within the last millennium little or no ice tongue was present for nearly 5000 years during the middle holocene when decadal mean regional temperatures are estimated to be 0 8 2 9 c higher than preindustrial 1750 ce and seasonal sea ice in the lincoln sea was reduced this pre historical behavior shows that recent anthropogenic warming may already be in the range of ice tongue instability and future projected warming increases the risk of ice tongue break up by the mid 21st century

rock magnetic characteristics of surficial marine sediments from the california continental borderland abstract the rock magnetic variability of surficial marine sediments from the california continental borderland adjacent to southern california is described the data were derived from measurement of the natural nrm anhysteretic arm and isothermal irm remanent magnetization and magnetic susceptibility of 385 samples from 230 cores magnetic mineralogy studies carried out on selected samples indicate that detrital magnetite predominates throughout the borderland but there are also locally important contributions from detrital and authigenic hematite altered glauconite and biogenic magnetite maps of the distributions of various rock magnetic parameters show that 1 the proportion of magnetic material decreases outward from the coastline through dilution by organic material and carbonate 2 the magnetic grain size distribution shifts to finer average grain size outward from the coastline 3 important local contributions to the sediment magnetic material can come from erosion of submerged bank tops or ridges 4 glauconite rich zones on bank tops can be altered to remanent magnetic material that is anomalously strong in intensity and coercivity and 5 that diagenetic processes occur ubiquitously within the deep basins causing large scale dissolution of the magnetic material comparisons of arm and sirm saturation irm indicate that arm is very sensitive to grain size changes and that both the quantity arm 2 2 0 5 and sirm are good indicators of volume of remanent magnetic material in the borderland

magnetic effects of maghemitization of plio pleistocene marine sediments northern california a magnetic study conducted on reversed polarity plio pleistocene marine sediments from the rio dell formation suggests that maghemitization occurring in the source area may have enhanced their paleomagnetic reliability in a section characterized by variable amounts of magnetic overprinting some of the reliable horizons had natural remanent magnetization nrm intensities nearly 1 order of magnitude greater than other reliable and all the unreliable horizons from the rio dell these high nrm horizons had high anhysteretic remanent magnetization arm and saturation isothermal remanent magnetization sirm intensities suggesting a greater concentration of magnetic minerals thermal demagnetization data indicate that maghemite is the magnetic carrier in the high nrm horizons arm versus and lowrie fuller tests show that these horizons have magnetic grains dramatically smaller than magnetite bearing horizons contraction cracking during maghemitization may have reduced the effective grain size of the maghemite bearing horizons the small magnetic grain size of the maghemite increases these horizons coercivity and viscous acquisition coefficient but not their jvrb sediment grain size analyses show that the magnemite bearing horizons have the smallest sediment grains and unreliable magnetite bearing horizons have the largest grains assuming hydrodynamic sorting of the magnetic oxides these data suggest that the finest grained magnetic minerals are the most susceptible to oxidation maghemite occurs in horizons 1 5 0 9 m y old reduced chemical and increased mechanical weathering during the pleistocene glaciations could have increased the concentration of magnetic iron oxides in these sediments and caused their maghemitization in the provenance area

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

inverse to normal magnetic fabric transition in an upper miocene marly sequence from tuscany italy the magnetic susceptibility fabric of an upper miocene marly sequence exposed along the morra creek tuscany italy changes from inverse maximum susceptibility axis sub perpendicular to bedding to normal from the bottom to the top of the section the change is gradual with the presence of anomalous magnetic susceptibility fabrics at some levels the anhysteretic remanence anisotropy is always normal throughout the sequence the changes in the magnetic fabric seem to be controlled by sedimentological variations with the inverse susceptibility fabric related to the abundance of iron bearing carbonates in the lower part of the section in the upper part of the section subtle changes in the detrital inputs in the basin and particularly a larger contribution of clayey and ferrimagnetic particles turned the susceptibility fabric to a normal type

environmental factors as complicating influences in the recovery of quantitative geomagnetic field paleointensity estimates from sediments we have recently recovered replicate records of the earth s magnetic field relative paleointensity for 12 71 000 years bp from marine sediments of the western north atlantic ocean our records are remarkably similar to two other recently published relative paleointensity records from marine and lacustrine sediments in europe this suggests to us that even over this wide region sediments may serve as reasonable correlatable recorders of fluctuations in the strength of the earth s magnetic field if this is true then similar records from around the globe could eventually provide valuable information about the deep earth processes which create the field we note however that our intensity record is significantly correlated with the down core ratio of magnetic susceptibility to anhysteretic remanent magnetism arm this ratio is a measure of the relative grain size of magnetite the primary magnetic mineral in these sediments and as such is a sediment magnetic property which is controlled only by the local depositional environment and indirectly by global climate we are concerned that the european records may be similarly biased by climatic or other environmental factors possibly synchronous with ours we caution that extreme care must be taken to understand and remove any such magnetic influences from sediment relative paleointensity records before they are used as quantitative estimators of the past intensity of the earth s magnetic field