the record of changing hematite and goethite accumulation over the past 22 myr on the chinese loess plateau from magnetic measurements and diffuse reflectance spectroscopy 1 high field isothermal remanence hirm and diffuse reflectance spectroscopy drs wereusedto characterize hematite and goethite in a suite of bulkand particle sized fractioned samples from the chinese loess plateau representing the main changes in magnetic mineralogy over the past 22 myr the record of drs defined hematite largely reflects variations in the pedogenic fraction 8 mm makes the main contribution to goethite concentrations in the bulk samples pedogenic goethite concentrations generally vary inversely with those of hematite the lack of consistent correlations between hirm inferred mineral content and drs measurements casts doubt on the validity of using hirm to characterize the concentrations and relative proportions of hematite and goethite in sediments representing a long time span or a wide grain size distribution the progressive decline in the coercivity of the antiferromagnetic minerals in bulk samples throughout the whole period is mainly an expression of changes in the detrital fraction reflecting changes in the source region possibly involving increased aluminum substitution the good correlation between drs defined hematite and frequency dependent magnetic susceptibility in several chronologically defined subgroups of samples is consistent with the hypothesis that maghemite forms a transitional phase in a weathering sequence from ferrihydrite to hematite the results shed new light on using hirm to characterize hematite and goethite in sediments and on the history of weathering and climate change over the past 22 myr in the dust source regions and on the loess plateau

particle size related mineral magnetic source sediment linkages in the rhode river catchment maryland usa characterization of both the source materials and the bottom sediments of an estuary by magnetic characters on a particle size basis allows the source of the bottom sediments to be determined and indicates a shift in sediment sources corresponding to changing land use patterns the major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines soil derived particulates from the uplands dominate the upper part of the cores this change in source occurred in the early part of the 19th century the magnetic character of the most recent sediments suggests a progressive depletion through time of the upland soils in the finest fractions

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

variations in relative abundances of goethite and hematite in bengal fan sediments climatic vs diagenetic signals abstract relative abundances of goethite and hematite in marine sediments have been increasingly used in reflectance spectrometry studies to infer the precipitation regime at the source area of detrital sediments this interpretation is contingent on the assumption that the ratio of these minerals is not modified by diagenetic processes our rock magnetic study of the 10 5 4 0 ma interval of the bengal fan sedimentary sequence indicates that this is not always the case we demonstrate that a statistical analysis of isothermal remanent magnetization acquisition curves provides an adequate estimate of the content of goethite and hematite in sediments we also identified distinctive biogenic and detrital components likely titano magnetite or maghemite in the studied samples the sediments of the bengal fan contain a significant change in relative abundance of goethite and hematite at 7 ma which is approximately coeval with a postulated climatic turnover in the sediment source region however systematic variations in the detrital and biogenic components as well as an increase in the total organic carbon content and the appearance of pyrite concretions at the same stratigraphic level suggest that this change in magnetic mineral content reflects a change in the degree of diagenetic alteration of the initial detrital assemblage rather than a climatic signal when assigning climatic interpretations to changes in the relative abundance of goethite and hematite in marine sediments in future studies the possibility of diagenetic modification should be evaluated with rock magnetic methods alteration of ancient sediments can be detected and the severity of alteration can be estimated based on the presence and grain size variation of the ferrimagnetic fraction magnetite maghemite which is more sensitive to early reductive dissolution than high coercivity minerals goethite and hematite

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

quantitative extraction and analysis of carriers of magnetization in sediments we have applied an integrated procedure for quantitative magnetic mineral extraction based on the separation method of petersen von dobeneck vali 1986 to a range of sediment types to examine the efficiency and representative nature of the extraction process carriers of magnetization have been identified by rock magnetic measurements microscopy and x ray diffraction quantification of the extraction efficiencies is achieved by before and after extraction rock magnetic measurements susceptibility anhysteretic and isothermal remanences these magnetic measurements show that our modified extraction method extracts large proportions of the magnetization carriers in a range of sediment types e g over 75 per cent for magnetite dominated sediments the extraction efficiency is dependent on the sample magnetic mineralogy and whether the magnetic grains occur as discrete grains or as inclusions within host grains susceptibility extraction efficiencies are strongly dependent on whether the susceptibility is of paramagnetic or ferrimagnetic origin the amount of material recovered in the extract shows some inverse correlation with the density of the sediment suspension used during extraction in terms of the mineralogies extracted we identify a diverse and complex range of mineral assemblages all sizes of discrete grains of magnetite are extracted including single domain and superparamagnetic grains and chains of bacterial magnetite other commonly extracted iron and titanium oxides are haematite and ilmenite ferrimagnetic chromites and sulphides were also obtained from some samples considerable amounts of quartz and feldspar are extracted due to the presence of magnetic inclusions within these diamagnetic host grains in the deep sea sediments we examined feldspars constitute a large proportion of the extracts but are significantly less abundant in other sediments where quartz is dominant a wide variety of paramagnetic minerals was identified in the extracts including pyroxenes amphiboles chlorites micas mg cr spinels garnets ti oxides apatites tourmaline and zircon many of which contain ferrimagnetic inclusions possibly less than 0 1 m in grain size dissolution of ultrafine grains of magnetite during pre extraction carbonate dissolution as suggested by sun jackson 1994 does not occur in our samples

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

identifying goethite and hematite from rock magnetic measurements of soils and sediments we describe a sequence of experiments involving the acquisition of isothermal remanent magnetization irm in high 2 t fields followed by orthogonal demagnetization and the cooling and heating of remanent magnetization mr over the temperature range 196 c to 680 c the main aim of these experiments is to improve the basis for identifying the imperfect antiferromagnetic minerals contributing to the magnetic properties of natural soil and sediment samples which often contain complex mineral mixtures the procedures developed are first applied to a series of ore and synthetic samples of hematite and goethite each characterized by x ray diffraction xrd spectra and second to controlled mixtures of the two minerals the results confirm the mineral diagnostic nature of the experiments used they are subsequently used to identify goethite and hematite contributions to the rock magnetic properties of a variety of soils and recent sediments goethite can be unambiguously identified often accompanied by hematite in the majority of the samples studied despite indications from the synthetic mixtures that the ratio of goethite to hematite may have to exceed an order of magnitude before the goethite signatures are readily recognizable the rock magnetic tests are a much more sensitive basis for recognizing the presence of goethite in natural samples than are xrd analyses the results suggest that goethite s contribution to the rock magnetic properties of soil and sediment samples may often have been underestimated

importance of titanohematite in detrital remanent magnetizations of strata spanning the cretaceous paleogene boundary hell creek region montana intermediate composition titanohematite fe2 ytiyo3 with 0 5 y 0 7 is seldom the focus of paleomagnetic study and is commonly believed to be rare in nature while largely overlooked in magnetostratigraphic studies intermediate titanohematite has been identified as the dominant ferrimagnetic mineral in an array of late mesozoic and early cenozoic laramide clastic deposits throughout the central united states intermediate titanohematite is ferrimagnetic and has similar magnetic properties to titanomagnetite except its unique self reversing property due to these similarities and with detrital remanent magnetizations masking its self reversing nature intermediate titanohematite is often misidentified in sedimentary deposits past studies relied upon nonmagnetic techniques including x ray diffraction and electron microprobe analysis while these techniques can identify the presence of intermediate titanohematite they fail to test whether the mineral is the primary recorder to facilitate the identification of intermediate titanohematite in sedimentary deposits we characterize this mineral using low temperature magnetometry and high temperature susceptibility experiments and present a new identification technique based on titanohematite s self reversing property for sediments that span the cretaceous paleogene boundary hell creek region montana results from the self reversal test indicate that the majority of remanence is held by minerals that become magnetized parallel to an applied field but that intermediate self reversing titanohematite y 0 53 0 63 is an important ancillary carrier of remanence while earlier literature suggests that intermediate titanohematite is rare in nature reanalysis using specialized rock magnetic techniques may reveal that it is more abundant in the rock record particularly within depositional basins adjacent to calc alkaline volcanics than previously thought

the late holocene history of gormire lake ne england and its catchment a multiproxy reconstruction of past human impact sedimentary evidence spanning the last 3500 years from cores taken from the centre of gormire lake cleveland northeast england points to two periods of deforestation and catchment erosion the first mainly late iron age romano british phase began c 200 bc and ended c ad 600 the second began c ad 1200 the time of early monastic activity and continued into the nineteenth century the chronology for the core rests on 137cs 210pb and 14c measurements and on the history of lead accumulation in the sediments the majority of the ams 14c dates are shown to be too old to varying degrees depending on the source of the organic matter in the sediments the record of vegetation change is derived from pollen analysis evidence for changes in sediment composition and source and for catchment erosion comes from magnetic measurements element analyses using xrf and organic biogeochemical analyses there is a high degree of coherence between all these lines of evidence interpretation of the magnetic record

high field remanence properties of synthetic and natural submicrometre haematites and goethites significance for environmental contexts haematite and goethite are significant magnetic components both of marine and terrestrial sediments variable magnetic behaviour in haematite and goethite has been reported reflecting variations in grain size crystal defects nonstoichiometry and mode of formation here we provide new data first for a range of synthetic haematite and goethite powders of known grain size and second for a variety of haematite and goethite bearing natural samples including red bed samples and modern and fossil soils based on the synthetic data we identify two high field parameters which may be of value in identifying and characterizing the high coercivity components of natural environmental samples even when these are dominated magnetically by the presence of trace concentrations of ferrimagnets h indicates the proportion of the room temperature rt remanence acquired in fields from 2 tesla t up to 7 t and hcool indicates the increase or decrease in high field remanence upon cooling in zero field to 77 k lt used in tandem these parameters can differentiate between goethite dominated and haematite dominated samples and indicate differences in haematite grain size h values for the synthetic haematites vary between 27 and 38 with some apparent grain size dependence and for the goethites between 84 and 92 hcool values range from 130 to 157 for the goethites and 75 to 95 for those haematites of grain size 100 nm

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

frank oldfield and his contributions to environmental change research frank oldfield s immense contribution to palaeoenvironmental science is summarized in relation to pollen analysis vegetation history and peat stratigraphy palaeolimnology and 210pb dating environmental magnetism catchment lake relationships and soil erosional history multiproxy approaches pages and editing the holocene the tribute includes an introduction to the 14 other papers in this special issue which were inspired in diverse ways by this remarkable scientist

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

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

the influence of particle size variations on the magnetic properties of sediments from the north eastern irish sea this paper considers the magnetic properties of a range of recent and contemporary sediments from the north eastern part of the irish sea principal component ordinations of the results show a close link between magnetic property variations and particle size the magnetic properties of a subset of samples particles sized by a combination of sieving and pipette analysis confirm that variations in ferrimagnetic magnetite grain size parallel those in particle size despite the fact that the magnetic grains in the fine grades have diameters 1 2 orders of magnitude smaller than those of the particle size fraction in which they occur this is best explained by postulating that the fine magnetic grains occur in the clay fraction but are present in declining concentrations in the coarser grades up to 4o as an artefact of the pipette method most samples have a biomodal distribution of magnetic minerals with a coarse mode associated with heavy minerals in the sands or coarse silts and a fine mode in the clays magnetic susceptibility x and saturation isothermal remanent magnetization sirm largely pick out the coarse mode where present anhysteretic remanent magnetization arm largely picks out the fine mode the results open up the possibility of normalizing samples from these environments for particle size and more specifically clay content by means of arm or arm x values the most likely source for the uniform and almost exclusive stable single domain magnetite which dominates the magnetic properties of the clays is thought to be bacterial magnetosomes the measurements as a whole do not appear to hold much promise for discriminating sediment source types

magnetostratigraphic dating of the proposed rhaetian gssp at steinbergkogel upper triassic austria implications for the late triassic time scale the global stratotype section and point gssp for the rhaetian stage has recently been proposed at steinbergkogel in austria we re sampled the steinbergkogel sections stk a and stk b c in high resolution to establish a robust magnetostratigraphy that allows global correlation the palaeomagnetic signal at steinbergkogel is composed of three components which can be separated by thermal demagnetization the highest temperature component revealed between 280 300 and maximum 600 c is of dual polarity and is interpreted as primary rock magnetic experiments showed that the signal is carried by magnetite our results allow correlation between the two individual steinbergkogel outcrops subsequently we correlate the two key biostratigraphic horizons for the base of the rhaetian the fo of m hernsteini and the fad of m post hernsteini to other sections of the tethys domain the correlation to the astronomically dated continental successions of the newark basin indicates that these positions for the base of the rhaetian are most likely determined in chrons e16n and e16r respectively this correlation is confirmed by cyclostratigraphic control on the marine pizzo mondello italy section where a combination of long period milankovitch cycles 175 myr and short eccentricity cycles 100 kyr provide additional correlation constraints respectively supporting a long duration of the rhaetian our study implies that the norian and rhaetian stages have durations of 17 and 9 myr

carbon in howardite eucrite and diogenite basaltic achondrites the c contents and isotopic compositions of four eucrites four diogenites and two howardites have been determined stepped heating in an o atmosphere was employed to convert selectively different carbonaceous materials to co2 gas at various temperatures this technique successfully distinguishes between terrestrial contaminants and indigenous c with the exception of the kapoeta howardite the howardite eucrite and diogenite hed meteorites contain 10 30 ppm indigenous c with 13c between 29 and 19 kapoeta a regolith breccia has an elevated c content and 13c due to the presence of 13c enriched carbonate minerals 13c 20 in cm2 or cr2 like clasts the range in 13c displayed by hed samples is similar to that of other solar system basalts such as lunar rocks and martian meteorites but distinctly different from that of the terrestrial mantle the diogenites have a slightly lower total c yield and higher 13c than the eucrites which is a result of degassing of trapped co cc2 co2 3 from the silicate lattice during metamorphism or annealing however three out of the four diogenites studied appear to contain a discrete component possibly of graphitic c coating silicate grains that is seemingly unaffected by the extended annealing period experienced by the diogenites it is possible that this component might host the indigenous primitive xe recently identified in diogenites

characterizing and quantifying iron oxides in chinese loess paleosols implications for pedogenesis to accurately decode the paleoclimatic and paleoenvironmental significance of magnetic properties in chinese loess paleosols neoformation of magnetic iron oxides via pedogenesis as well as the relationship between ferrimagnetic maghemite and magnetite and antiferromagnetic minerals hematite and goethite of both detrital and pedogenic origins should be well determined to resolve this problem magnetic iron oxides from a contiguous loess paleosol sequence lower part of the loess unit l1 paleosol unit s1 and the upper part of l2 at luochuan center of the chinese loess plateau were well characterized and quantified by using an integrated approach including chemical dissolution diffuse reflectance spectroscopy and rock magnetism methods results showed that these magnetic minerals have distinct coercivity and dissolution behavior which is highly grain size dependent more specifically the paleosol is enriched with nano sized pedogenic hematites with a medium coercivity of 130 mt which are also preferentially dissolved in a weak reductive environment in contrast the coarse grained micro sized detrital hematites with a medium coercivity of 1 t are dominant in loess in addition these coarse grained detrital hematites are more stoichiometric than their pedogenic counterparts as evidenced by the higher band position on the diffuse reflectance spectrum goethite can be well distinguished from hematite by its higher coercivity 4 7 t at low temperature 10 k the consistent dissolution behavior of goethite for both loess and paleosol samples in citrate bicarbonate dithionite solution indicates that goethite could be less relevant to the pedogenic processes the reductive dissolution of pedogenic maghemite lags the dissolution of pedogenic hematite and fine grained goethite which suggests that average grain size of pedogenic maghemite is relatively larger than those of pedogenic hematite and fine grained goethite detrital magnetite is hard to dissolve and 50 of its initial remanence survived after dissolution on the basis of these contrasting behaviors pedogenic hematite fine grained goethite and maghemite content was further quantified our results suggest that single domain pedogenic hematite was produced after initial formation of pedogenic maghemite this provides direct evidence for the recently proposed pathway in which ferrihydrite is transformed into a transient maghemite like phase before its final transformation into hematite

rockmagnetic properties of fine grained natural low temperature haematite with reference to remanence acquisition mechanisms in red beds summary grain size dependence of some remanent magnetic properties of a natural low temperature haematite is reported the haematite was obtained from a gossan in montarnu france and upgraded by magnetic separation seven grain size fractions were prepared ranging from 10 down to 0 25 m by means of microprecision sieving and centrifuging the haematite has an average crystallite size of 60 nm and contains minor contents of si al and h2o its unit cell dimensions are very close to those of ideal haematite the magnetic properties of the haematite are strongly dependent on its thermal history for the original unheated haematite fractions the isothermal saturation remanence jrs decreases with grain size the remanent coercive force hcr remanent acquisition coercive force hcr and median destructive field of the saturation remanence h1 2i are maximal in the 1 0 0 5 m fraction this grain size range can be understood as the sd threshold size in analogy with ferrimagnetic minerals jrs hcr x xin is a useful grain size indicator lowtemperature cycling of jrs shows identical behaviour for all fractions the remanence decreases slightly and shows no sharp morin transition after annealing the haematite fractions at 700 c jrs is considerably reduced relative to the original haematite predominantly due to removal of the defect moment both hcr and hcr have increased and their maximal values are shifted to the 2 1 1 0 m fraction all fractions show a much sharper morin transition during low temperature cycling of jrs due to crystallite enlargement trm decreases with grain size the different rock magnetic properties before and after annealing might provide a basis for the discrimination in sediments between a haematite drm with a high temperature origin and a haematite crm which has a low temperature origin two natural red beds one with a crm and one with a drm associated with high temperature haematite broadly show the expected differences in coercivity and in annealing behaviour although a full account of all aspects of the observed behaviour can not yet be given

astrochronology of the mediterranean langhian between 15 29 and 14 17 ma an integrated high resolution magnetobiocyclostratigraphy including radioisotopic dating and astronomical tuning is presented for the interval between 15 29 and 14 17 ma in the marine la vedova section in northern italy the natural remanent magnetization is carried by the iron sulphide greigite and the resultant magnetostratigraphy can be correlated straightforwardly to the interval ranging from c5bn 2n to c5adn in the astronomically tuned neogene time scale atnts2004 spectral analysis on high resolution magnetic susceptibility and geochemical proxy records in the depth domain and using our magnetobiostratigraphic age model in the time domain demonstrate that the various scales of cyclicity in the section are related to astronomical climate forcing starting from our initial age model larger scale cycles were first tuned to eccentricity this first order tuning was followed by tuning the basic cycle to precession and boreal summer insolation using inferred phase relations between maxima in ca al redox sensitive elements and ba and minima in magnetic susceptibility and maxima in precession and minima in obliquity and boreal summer insolation our astronomical ages for reversal boundaries are supported by analysis of sea floor spreading rates and should replace the existing ages in the atnts2004 lacking direct astronomical control two major steps in the geochemical proxy records astronomically dated at 15 074 and 14 489 ma coincide with abrupt changes in sedimentation rate and are the result of the combined effect of the 400 kyr eccentricity cycle superimposed upon a longer term climatic or tectonic induced trend

diagenetic formation of bedded chert implications from a rock magnetic study of siliceous precursor sediments abstract bedded chert is a distinctive rock type characterized by a rhythmic alternation of quartz rich chert beds and clay rich interbeds the origin of the lithologic variations is not well understood a rock magnetic study of a sequence of alternating bands of radiolarian rich and clay rich bands recovered by odp leg 129 which is considered to be the best known analog for the bedded chert precursor sediments shows that the relative abundances and characteristics of magnetic phases are similar in both sediment types with only a minor 1 5 times on average increase in bulk concentration in clay rich bands comparison with magnetic properties of the diagenetically mature chert shale couplets suggests that siliceous precursor sediments undergo strong differential diagenetic modification a simple silica transfer model with dissolution of silica in proto shale donor beds and deposition in proto chert receiver beds indicate that the known features of the bedded chert sequences such as the difference in thickness cosmic dust content between chert and shale can be reproduced in case of donor beds having initially lower clay higher biogenic silica content compared to receiver beds while contrary to the current depositional model explaining chert beds formation by episodic radiolarian bloom on a background of slow accumulation of clays an association of proto shale beds with high productivity episodes is supported by an independent paleoproductivity proxy their higher al ti values and is in full agreement with the known silica diagenesis trends particularly with the retarding influence of detrital minerals on silica transformations the impetus for diagenetic silica segregation is provided by initial variability in clay content within a siliceous sedimentary succession silica dissolution starts in clay poor intervals when diffusing silica encounters clay rich beds adsorption to clay lowers dissolved silica content below the saturation level of the higher solubility phases and leads to deposition of low solubility quartz early deposition of quartz cement prevents significant compaction of chert layers while the loss of silica in donor beds leads to their compaction and concomitant increase in non reactive clay and cosmic dust particles severe distortion of primary environmental signals during differential diagenesis questions the use of bedded chert sequences for cyclostratigraphic studies

signatures and significance of aeolian fluvial bacterial and diagenetic magnetic mineral fractions in late quaternary marine sediments off gambia nw africa 1 two gravity cores retrieved off nw africa at the border of arid and subtropical environments geob 13602 1 and geob 13601 4 were analyzed to extract records of late quaternary climate change and sediment export we apply end member em unmixing to 350 acquisition curves of isothermal remanent magnetization irm our approach enables to discriminate rock magnetic signatures of aeolian and fluvial material to determine biomineralization and reductive diagenesis based on the occurrence of pedogenically formed magnetic minerals in the fluvial and aeolian ems we can infer that goethite formed in favor to hematite in more humid climate zones the diagenetic em dominates in the lower parts of the cores and within a thin near surface layer probably representing the modern fe2 fe3 redox boundary up to 60 of the irm signal is allocated to a biogenic em underlining the importance of bacterial magnetite even in siliciclastic sediments magnetosomes are found well preserved over most of the record indicating suboxic conditions temporal variations of the aeolian and fluvial ems appear to faithfully reproduce and support trends of dry and humid conditions on the continent the proportion of aeolian to fluvial material was dramatically higher during heinrich stadials especially during heinrich stadial 1 dust export from the arabian asian corridor appears to vary contemporaneous to increased dust fluxes at the continental margin of nw africa emphasizing that meltwater discharge in the north atlantic had an enormous impact on atmospheric dynamics

siliciclastic prelude to elatina nuccaleena deglaciation lithostratigraphy and rock magnetism of the base of the ediacaran system

heavy metal release by peat erosion in the peak district southern pennines uk upper north grain ung is a heavily eroding blanket peat catchment in the peak district southern pennines uk concentrations of lead in the near surface peat layer at ung are in excess of 1000 mg kg 1 for peatland environments these lead concentrations are some of the highest globally high concentrations of industrially derived atmospherically transported magnetic spherules are also stored in the near surface peat layer samples of suspended sediment taken during a storm event that occurred on 1 november 2002 at ung and of the potential catchment sources for suspended sediments were analysed for lead content and the environmental magnetic properties of anhysteretic remanent magnetization arm and saturation isothermal remanent magnetization sirm at the beginning of the storm event there is a peak in both suspended sediment and associated lead concentration sirm arm values for suspended sediment samples throughout the storm reveal that the initial lead flush is associated with a specific sediment source namely that of organic sediment eroded from the upper peat layer using the magnetic fingerprinting approach to discrimination of sediment sources this study reveals that erosion of the upper peat layer at ung is releasing high concentrations of industrially derived lead and by inference other toxic heavy metals associated with industrial particulates into the fluvial systems of the southern pennines climate change scenarios for the uk involving higher summer temperatures and stormier winters may result in an increased flux both of sediment associated and dissolved heavy metals from eroding peatland catchments in the southern pennines adversely affecting the quality of sediment and water entering reservoirs of the region copyright 2005 john wiley sons ltd

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

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

sea ice switches and abrupt climate change we propose that past abrupt climate changes were probably a result of rapid and extensive variations in sea ice cover we explain why this seems a perhaps more likely explanation than a purely thermohaline circulation mechanism we emphasize that because of the significant influence of sea ice on the climate system it seems that high priority should be given to developing ways for reconstructing high resolution in space and time sea ice extent for past climate change events if proxy data can confirm that sea ice was indeed the major player in past abrupt climate change events it seems less likely that such dramatic abrupt changes will occur due to global warming when extensive sea ice cover will not be present

high coercivity remanence in baked clay materials used in archeomagnetism a study of the high coercivity remanence in archeological baked clays has been carried out more than 150 specimens from 46 sites across europe have been analyzed selected on the basis of the presence of a fraction of their natural remanence that was resistant to alternating field demagnetization to 100 mt the study was based on the stability of isothermal remanence to alternating field and thermal demagnetization and its variation on cooling to liquid nitrogen temperature results indicate that the high coercivity remanence may be carried by magnetite hematite and in isolated cases partially oxidized magnetite and goethite in addition a high coercivity thermally stable low unblocking temperature phase has been identified the unblocking temperatures of both the isothermal remanence and the alternating field resistant natural remanence exhibit similar unblocking temperatures suggesting that the same phases carry both signals the high coercivity low unblocking temperature phase contributes to the natural remanence sometimes carrying a stable direction and behaving ideally during palaeointensity experiments and sometimes not an unambiguous mineralogical identification of this phase is lacking although likely candidates include hemoilmentite related to clay source lithology and substituted hematite or magnetic ferri cristabolite both possible products of thermal transformation of iron bearing clays

annual laminations in the sediments of loe pool cornwall annually laminated freshwater lacustrine sediments have been recorded at several sites in central europe1 5 north america6 13 and fennoscandia14 24 the presence of laminations may reflect either 1 regular changes within the lake ecosystem itself or 2 variation in the intensity of erosion and transport of material from the catchment particularly where instability in the lake watershed system has occurred as a result of human activities22 the principal cause of lamination is therefore seasonal variation of environmental conditions particularly climate lakes with laminated sediments tend to be physically deep exhibit a strong seasonal stratification and be situated in areas of continental climate we describe here what we believe to be the first reported instance of a long sequence of laminated lake sediments from great britain unlike most of the previous examples these have been formed in a shallow polymictic lake in an oceanic climate

field and temperature behavior of remanence in synthetic goethite paleomagnetic implications synthetic powders of pure goethite exhibit an antiferromagnetic behavior and negligible isothermal remanent magnetization up to 4 tesla however thermoremanence up to 0 3 am kg 1 can be imparted to the samples high field measurements show median acquisition field of 9 13 t and suggest saturation fields of the order of 10 t large increase in remanence at low temperature is an intrinsic feature of goethite the weak ferromagnetism observed is linked to a bulk origin for spin imbalance rather than to an effect of very fine grain size or surface defects the results are compared with properties of rocks bearing goethite and hematite

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

multiproxy record of monsoon variability from the ganga plain during 400 1200 a d abstract understanding on the indian summer monsoon ism variability is chiefly based upon the marine proxies and a few continental records the ganga plain one of the most densely populated regions of the world marked by intensive cultivation of monsoon dependent crops and a rich cultural history is not yet well understood in the context of monsoon variability we present here a 400 1200 a d ams radiocarbon dated record of ropan chhapra tal in the central ganga plain using sedimentology environmental magnetism and stable isotope of oxygen for ism variability the environmental magnetic parameters lf arm sirm lf s ratio b 0 cr and hirm inferred antiferromagnetic mineralogy hematite and or goethite independent of grain size variation during 400 900 a d depicting climate variability within warm humid to warm arid conditions favouring stronger ism seasonality prevalence of ferrimagnetic mineralogy under less oxygenated conditions intermittently demonstrates an altered catchment regime or possibly in response to stronger winter monsoon the higher 18 o values around 500 580 and 740 a d indicate warm and arid conditions under weak ism the lower 18 o values around 480 540 and 700 a d and from 900 to 1200 a d occur during warm and humid conditions indicating maximum intensity of the ism increased silt content from 800 a d onwards is due to increased surface runoff in response to enhanced precipitation and the higher clay percentage around 500 580 and 740 indicates low energy ponding conditions under weak ism the well sorted nature of sediment indicates consistency of the lacustrine environments under fairly uniform energy and constant bottom water conditions under varied monsoonal intensity combinations of sediment textures and stable isotope indicate intense ism at 480 and 540 a d with flooding around 700 a d and a weak monsoon at 580 and 740 a d with drought at 500 a d during 900 1200 a d the multiproxy record suggests strong summer monsoon synchronous with medieval warm period mwp whereas after 1200 a d the weak monsoon phase coincides with the onset of the little ice age lia

magnetic mineral inventory of equatorial atlantic ocean marine sediments off senegal glacial and interglacial contrast summary in complex sedimentary environments with different sources of the magnetic particles it is vital that all factors contributing to and affecting the magnetic signals be well understood for a better constrained interpretation of palaeomagnetic and climatic data palaeoclimatically driven signals may be convolved with volcanic and cosmogenic sources and diagenesis may alter the primary magnetic mineral assemblage rock magnetic methods and electron microscopy provide suitable means to characterize magnetic assemblages in this study of core retrieved sediments from the last 150 kyr off the coast of senegal nw africa the occurrence of magnetic spherules of volcanic origin and cosmogenic particles appeared to be insignificant in glacial stages ferrimagnetic iron and iron titanium oxides magnetically dominate with few signs of a diagenetic overprint low and room temperature magnetic results reveal evidence for haematite and goethite while haemoilmenite and titanomagnetite were identified from low temperature ac susceptibility measurements and sem observations in contrast the interglacial samples appeared to have been severely affected by diagenesis with pyrite making up over 50 per cent of the iron bearing phases the verwey transition observed at 110 k confirms the presence of magnetite the glacial and interglacial contrast reveals the close link between northwest african climate and the magnetic mineralogy of the sediments

mid to late holocene climate response from the triloknath palaeolake lahaul himalaya based on multiproxy data abstract a 2 13 m thick palaeolake sequence deposited between the right lateral moraine and the valley wall of triloknath glacier has been studied at high resolution to understand the past climatic changes in lahaul himalaya the osl and ams 14c chronology suggests that the lake building activity was initiated post cooling phase since 6484 cal ybp the combination of sedimentological geochemical and environmental magnetic parameters helped to infer five first order climatic zones the influx of magnetic minerals along with a notable increase in antiferromagnetic mineralogy appearance of hematite and higher chemical index of alteration cia values during 5925 cal ybp to 5676 cal ybp suggests warm and wet conditions owing to enhanced indian summer monsoon ism precipitation corresponding to the mid holocene warming further reduction in the magnetic mineral concentration with few peaks of antiferromagnetic mineralogy and higher cia values suggests warmer episodes within an overall cold climate and the finer ferrimagnetic grain size suggests intermittent low energy and ponding conditions during 3904 cal ybp to 2365 cal ybp this was followed by fluctuating cold arid conditions in response to reduced ism precipitation during 2365 cal ybp and 1758 cal ybp further between 1758 cal ybp to the present episodic warming pedogenic enhancement and increased monsoon precipitation have been recorded a major warm episode medieval warm period as depicted from enhanced antiferromagnetic mineralogy and higher cia values has been recorded between 742 cal yrs bp and 593 cal ybp the sudden drop in the magnetic mineral concentration as well as the cia value around 300 cal ybp 1650 ce is likely because of colder conditions prevailing during the little ice age lia the study illustrates high sensitivity of the lake sediment sequence to witness the climatic episodes experienced in the glaciated regime of the triloknath glacier

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

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

magnetostratigraphic correlation of the oxfordian kimmeridgian boundary a magnetic polarity pattern for boreal and sub boreal ammonite zones of the upper oxfordian to lower kimmeridgian was established and confirmed in four british sections including the proposed global boundary stratotype section and point gssp on the isle of skye scotland to define the base of the international kimmeridgian stage a coeval pattern for sub mediterranean ammonite zones was compiled from seven sections in poland one german section and multi section composites from france and spain the mean paleopole for the european craton excluding spain at the oxfordian kimmeridgian boundary is 74 2 n 181 3 e 95 3 8 the common magnetic polarity scale enables inter correlation of ammonite subzones among these three faunal provinces and to the marine magnetic anomaly m sequence the proposed gssp at the base of the pictonia baylei zone is near the base of an extended interval dominated by reversed polarity which is interpreted to be chron m26r this gssp level projects to the lower to middle part of the epipeltoceras bimammatum subzone which is the middle subzone of this e bimammatum zone in the sub mediterranean standard zonation in contrast the traditional placement of the oxfordian kimmeridgian boundary in that sub mediterranean standard zonation base of sutneria platynota zone is at the base of chron m25r or nearly 1 million years younger