constraining diamond metasomatic growth using c and n stable isotopes examples from namibia the present paper provides c and n stable isotope characteristics n contents and n aggregation states for alluvial diamonds of known paragenesis from placers along the namibian coast the sample set includes diamonds with typical peridotitic and eclogitic inclusions and the recently reported undetermined suite of leost et al contrib mineral petrol 145 2003 15 which resulted from infiltration of high temperature carbonate rich melts 13c values range from 20 3 to 0 5 n 48 for peridotitic diamonds and from 38 5 to 1 6 n 45 for eclogitic diamonds diamonds belonging to the undetermined suite span a narrower range in 13c from 8 5 to 2 7 n 13 when compared with previous studies diamonds from namibia are characterised by unusually low proportions of n free i e type ii peridotitic and eclogitic diamonds 3 and 2 respectively and an unprecedented high proportion of n rich diamonds 15 and 73 respectively have n contents 600 ppm 15n values for diamonds of the peridotitic eclogitic and undetermined suites range from 10 to 13 without correlations with either n content or 13c the similarity in n isotopic composition and the n rich character of diamonds belonging to the eclogitic peridotitic and undetermined suites is striking and suggests a close genetic relationship we propose that a large part of the diamonds mined in namibia formed during metasomatic events of similar style that introduced carbon and nitrogen into a range of different host lithologies

bacterial magnetite produced in water column dominates lake sediment mineral magnetism lake ely usa summary environmental magnetic studies of annually laminated sediments from lake ely northeastern pennsylvania usa indicate that bacterial magnetite is the dominant magnetic mineral in the lake sediment in previous studies of lake ely sediment the dark organic rich layers in the annual laminae were interpreted to have high intensity saturation isothermal remanent magnetizations sirms while the light coloured silt rich layers have low intensity sirms to test the hypothesis that the magnetic grains in the sediments were an authigenic product of magnetotactic bacteria rather than detrital magnetic grains eroded from the watershed we analysed samples from the water column the lake sediment and a sediment trap installed near the lake bottom direct microscopic observation of the water column samples showed the presence of magnetotactic bacteria in and below the oxic anoxic transition zone oatz to characterize the magnetic minerals rock magnetic parameters were measured for material from the water column the sediment trap and the dark and light coloured lake sediments low temperature magnetic measurements tested for the presence of magnetosomes in separated dark and light coloured layer samples numeric unmixing of the low temperature results showed that biogenic magnetites were present in the lake sediment and contributed more significantly to the sirm in the dark organic rich layers than in the light coloured inorganic silt rich layers observations under the transmission electron microscope tem of magnetic extracts also show the abundance of magnetosomes in the lake sediment the presence of live magnetotactic bacteria in the water column and the predominance of bacterial magnetites in filtered particulate matter sediment traps and recent lake sediment all suggest that bacterial magnetites are the main magnetic minerals in lake ely sediment this finding suggests that changes in environmental factors that control the productivity of magnetic bacteria in the lake likely contribute to the variability of magnetic mineral concentrations observed in the lake sediments

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

most diamonds were created equal abstract diamonds crystallize deep in the mantle 150 km leaving their carbon sources and the mechanism of their crystallization debatable they can form from elemental carbon by oxidation of reduced species e g methane or reduction of oxidized ones e g carbonate bearing minerals or melts in response to decreasing carbon solubility in melts or fluids or due to changes in ph the mechanism of formation is clear for fibrous diamonds that grew from the carbonate bearing fluids trapped in their microinclusions however these diamonds look different and based on their lower level of nitrogen aggregation are much younger than most monocrystalline mc diamonds in the first systematic search for microinclusions in mc diamonds we examined twinned crystals macles assuming that during their growth microinclusions were trapped along the twinning plane visible mineral inclusions 10 m and nitrogen aggregation levels in these clear macles are similar to other mc diamonds we found 32 microinclusions along the twinning planes in eight out of 30 diamonds eight inclusions are orthopyroxene four contain 50 k2o probably as k2 mg ca co3 2 but the major element compositions of the remaining 20 are similar to those of carbonate bearing high density fluids hdfs found in fibrous diamonds we conclude that the source of carbon for these macles and for most diamonds is carbonate bearing hdfs similar to those found here and in fibrous diamonds combined with the old ages of mc diamonds up to 3 5 ga our new findings suggest that carbonates have been introduced into the reduced lithospheric mantle since the archaean and that the mechanism of diamond formation is the same for most diamonds

organic carbon flux controls the morphology of magnetofossils in marine sediments magnetotactic bacteria produce chains of magnetite crystals within a cell bacterial magnetites have characteristic morphologies and sizes that are strictly biologically controlled we examined morphologies of fossil bacterial magnetites magnetofossils preserved in pacific deep sea sediments and their relations to organic carbon fluxes isotropic crystals dominate magnetofossils in sediments in relatively oxidized conditions and anisotropic crystals predominate in more reduced conditions our finding has important implications for biomineralization processes and demonstrates the potential of magnetofossil morphology as a paleoenvironmental indicator

concretionary methane seep carbonates and associated microbial communities in black sea sediments abstract gas seeps in the euxinic northwestern black sea provide an excellent opportunity to study anaerobic methane based ecosystems with minimum interference from oxygen dependent processes an integrated approach using fluorescence and electron microscopy fluorescence in situ hybridization lipid biomarkers stable isotopes 13c and petrography revealed insight into the anatomy of concretionary methane derived carbonates currently forming within the sediment around seeps some of the carbonate concretions have been found to be surrounded by microbial mats the mats harbour colonies of sulphate reducing bacteria dss group and archaea anme 1 putative players in the anaerobic oxidation of methane isotopically depleted lipid biomarkers indicate an uptake of methane carbon into the biomass of the mat biota microbial metabolism sustains the precipitation of concretionary carbonates significantly depleted in 13c the concretions consist of rectangularly orientated rod to dumbbell shaped crystal aggregates made of fibrous high mg calcite the sulphate reducing bacteria exhibit intracellular storage inclusions and magnetosomes with greigite fe3s4 indicating that iron cycling is involved in the metabolism of the microbial population transfer of fe3 into the cells is apparently mediated by abundant extracellular vesicles resembling known bacterial siderophore vesicles marinobactine in size 20 to 100 nm and structure

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

fluid inclusions in ebelyakh diamonds evidence of co2 liberation in eclogite and the effect of h2o on diamond habit article i nfo fluidinclusionswerestudiedinsixoctahedrally grown eclogiticdiamondsfromtheebelyakhrivermine north ern russia using microthermometry and raman spectroscopy the fluids are co2 n2 mixtures with 40 4mol n2 whichare trappedalongfractures thathealedinthediamond stability field the co2 rich composition of the fluids provides the first empirical evidence that co2 can be liberated as a free phase in eclogite in the dia mond stability field of the lithospheric mantle as has been previously predicted from theory this finding means that the interpretation of carbon isotopes in eclogitic diamonds should not overlook isotopic fractionation due to co2 liberation from carbonatitic diamond forming media as it percolates through eclogites preferential nucle ation of co2 bubbles in eclogite compared to peridotite may lead to a rock type specific fracturing mechanism and sampling bias that would help explain the overabundance of eclogite xenoliths in kimberlites fluid inclusions in octahedrally grown non fibrous diamonds from both the studied ebelyakh diamonds and those from other cratons do not show detectable amounts of water in comparison fibrous diamond fluid inclu sions typically contain 10 25 wt water the absence of dry fluids in fibrous diamonds and the presence of these in octahedrally grown diamonds may indicate different compositions of fluids equilibrated with these two types of diamonds if there is variability in the water content in diamond forming fluids it should affect diamond growth morphology water could be responsible for causing fibrous diamond growth by inhibiting the advancement of growth steps within octahedral faces

experimental observation of magnetosome chain collapse in magnetotactic bacteria sedimentological paleomagnetic and evolutionary implications magnetotactic bacteria precipitate intracellular crystals of single domain magnetite fe3o4 and or greigite fe3s4 which have often been implicated in carrying the natural remanent magnetization nrm of freshwater and marine sediments in vivo the magnetic crystals are usually aligned in chains such that their moments add together generating net cellular moments high enough to rotate the cells passively to align with the geomagnetic field a magnetostatic biophysical analysis demonstrates that this arrangement is out of dynamic equilibrium and would collapse spontaneously without a support mechanism past rock magnetic analyses of shallow water marine carbonates suggest that partial collapse does occur during diagenesis and dolomitization to calibrate this effect we induced magnetosome chain collapse in magnetospirillum magnetotacticum strain ms 1 by progressive sonification and treatment with detergents and monitored the changes with rock magnetic analysis and tem although it has been speculated that the cell wall and associated membrane structures act to prevent magnetosome chain collapse our data indicate that magnetosome linearity persists long after cells are disrupted this is consistent with prior observations that in some magnetotcocci the magnetosome chains pass through the cell interior precluding continuous contact with the cell wall and implying additional support structures exist in some species using tem tomographic reconstructions prepared with a magnetic technique that prevents chain collapse we examined the three dimensional ultrastructure of magnetosomes without the problem of post mortem magnetosome motion this method revealed the presence of an intracellular organic sheath beyond that of actin like filaments reported recently that follows the chain of magnetosomes which we postulate evolved to hold the crystals in place and enhances their ability to preserve nrm in sediments as the genomes of two magnetotactic bacteria contain several apparent homologues of known eukaryotic cytoskeletal proteins natural selection for magnetotaxis may have played a role in the evolution of precursors to the eukaryotic cytoskeleton the presence of this sheath is also consistent with the observation of electron translucent material associated with putative magnetofossil chains in alh84001

three dimensional micromagnetic calculations for naturally shaped magnetite octahedra and magnetosomes abstract a three dimensional micromagnetic algorithm for modelling naturally shaped particles is presented it uses a fft accelerated calculation of the demagnetizing energy exchange energy calculation directly takes into account the micromagnetic boundary condition a rectangular grid enclosing the particle is chosen to economically fit the shape after verifying that the new program reliably reproduces previous calculations the program is used to determine room temperature magnetization structures and single domain to vortex transition sizes these calculations are performed for octahedral magnetite and magnetosomes of different elongations the least energy magnetization structures of octahedral particles are similar to the flower and vortex states found for cubic particles the critical size d 0 above which an inhomogeneous magnetization structure has lower energy than the homogeneous flower state as well as the grain size dependence of m rs m s closely resemble cubic particles however meta stable flower states persist up to much larger grain size in octahedral magnetite this explains previous observations of large trm arm peaks in hydrothermal magnetite in realistic magnetosome geometries the sd psd transition is shifted towards larger grain sizes as compared to previous estimates based on elongated rectangular grains for substantially elongated grains this is a result of the alignment of the particles long edge with the crystallographic easy axis for more equidimensional grains the rounded ends of magnetosomes reduce spin deflection at the top and bottom edges thereby the formation of nucleation centers is effectively inhibited even without additional stabilization by magnetostatic interaction within a magnetosome chain

paleomagnetic record of two successive miocene geomagnetic reversals in western crete abstract two geomagnetic reversals r n followed by n r have been recorded in a sequence of miocene marine clays of tortonian messinian age in western crete greece the time span of each transition is found to be of the order of 5000 10 000 years the transitional vgp paths are largely constrained in longitude either near the site longitude r n or opposite to it n r a normalized magnetization intensity record has also been obtained and its variations during reversals are found to be in excellent agreement with the predictions of hoffman s phenomenological model

glacial to interglacial mineral magnetic and palaeoceanographic changes at chatham rise sw pacific ocean core chat 1k from 3556 m depth east of new zealand shows marked changes in magnetic susceptibility correlating very well with 18o of foraminifera over the last 150 ka susceptibility is high during interglacial stages 1 and 5 and substages 5a to 5e are well marked the susceptibility is shown to be enhanced during interglacials and is neither an artefact of glacial carbonate dilution nor due to an interglacial increase of terrigenous material mineral magnetic property measurements arm sirm s ratio also show the same well defined glacial interglacial variability interpreted as an interglacial increase of single domain magnetite grains less than 0 1 m in size examination by tem of magnetic extracts reveals abundant cubic to octahedral grains of 0 02 0 2 m size often arranged in long chains characteristic of bacterial magnetite this material is much more abundant in interglacial than glacial samples it is suggested that during interglacials with lower productivity and organic carbon input to the bed the oxic zone in the sediments which can be colonised by magnetotactic bacteria is thicker and therefore is colonised for longer by magnetite producers this yields a climate controlled stratigraphy which leads that of infaunal benthic foraminifera by no more than a few centimetres

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

properties of intracellular magnetite crystals produced by desulfovibrio magneticus strain rs 1 desuffiovibrio magneticus strain rs 1 is an anaerobic sulfate reducing bacterium cells form intracellular nanocrystals of magnetite but are only weakly magnetotactic in order to understand the unusual magnetic response of this strain we studied magnetite crystals within cells grown with fumarate and sulfate many cells grown under either condition did not form magnetic crystals while others contained only i to 18 small similar to 40 nm magnetite containing magnetosomes bulk magnetic measurements of whole cells showed a superparamagnetic like behavior indicating that many of the magnetite crystals are too small to have a permanent magnetic moment at ambient temperature the temperature of the verwey transition is lower similar to 86 k than of magnetite from other magnetotactic strains likely indicating partial oxidation of magnetite into maghemite as a result of the small size and small number of magnetite magnetosomes the magnetic moments of most cells grown anaerobically with fumarate or sulfate are insufficient for magnetotaxis in addition to intracellular magnetite in some cultures another iron oxide hematite formed on the surfaces of cells the hematite grains are embedded in an extracellular polymeric material indicating that the crystals likely resulted from a biologically induced mineralization process although the hematite particles appear to consist of aggregations of many small 5 to 10 nm grains the grains have a consensus orientation and thus the whole particle diffracts as a single crystal the aligned arrangement of nanoparticles within larger clusters may reflect either a templated nucleation of hematite crystallites in an extracellular organic matrix or result from a self assembling process during the crystallization of hematite from ferric gels or ferrihydrite

mineral magnetic study of lacustrine sediments from lake pumoyum co southern tibet over the last 19 ka and paleoenvironmental significance abstract high resolution proxy records from tibetan plateau are essential to understand the past climatic and environmental changes in this work we conducted systematic environmental magnetic studies on lacustrine sediments from lake pumoyum co southern tibet spanning from the last deglaciation 19 ka to present we correlated the magnetic proxies in the lake core with environmental changes the magnetic proxies from the 3 units were studied both unit 3 19 13 2 ka and unit 2 13 2 8 4 ka contain evidences for an anoxic or sub anoxic environment fine grained greigite dominates the bulk magnetic properties of unit 3 while both magnetite and greigite coexist in unit 2 overall this reveals a transition from an anoxic environment to an oxic environment in contrast unit 1 8 4 ka present spans the holocene when the lake environment was oxic there is an increasing trend in the concentration of magnetic minerals which reflects an increasing transport of magnetic minerals from the catchment into the lake due to the increased post glacial melt water flow although different mechanisms affect the magnetic assemblage and associated magnetic properties in the different units our results suggest that the magnetic proxies of the local lake environment on southern tibet are sensitive to environmental changes

origin of stable remanent magnetization of siliceous sediments in the central equatorial pacific abstract siliceous sediments distributed in the central equatorial pacific have a stable remanent magnetization regardless of age or depth this is in contrast with the unstable remanence of unfossiliferous red clay defined as pelagic clay here which accumulates in the middle latitudes of the pacific we have conducted a rock magnetic study of the siliceous sediments to clarify the magnetic carriers of the stable remanence for this purpose we combined magnetic granulometry by the suspension method and observation of magnetic grains with a transmission electron microprobe tem the advantage of the former is that the magnetic extraction procedure is not required for obtaining size distribution of the magnetic grains in sediments the tem observations revealed that most of the magnetic extracts are identical in size and shape to bacterial magnetosomes the suspension method proved that the magnetic assemblages of the siliceous sediments of both quaternary and early miocene age have mean diameters of about 0 05 m which is within the single domain range of magnetite and have narrow size distributions compared with pelagic clay these characteristics can be explained if the magnetofossils observed by tem are the major constituent of the magnetic grains in the sediments and have been preserved for a long period of time the difference in the stability of the remanent magnetization between the siliceous sediments and the pelagic clay can be explained by the difference in the size distribution of magnetic grains which would reflect differences in their sources i e biogenic vs detrital eolian

the magnetostratigraphy of coniacian late campanian chalk sequences in southern england abstract magnetostratigraphic data are reported from the coniacian to early late campanian chalk sequences at culver cliff and scratchell s bay on the isle of wight and seaford head in east sussex uk mean natural remanent magnetisation nrm intensity values for individual sample sites range from 0 0013 to 1 6008 ma m with an overall mean of 0 0165 ma m reliable determination of the remanence of the very weakly magnetic units was achieved by carrying out replicate palaeomagnetic measurements on large volume samples using a 2 g wholecore cryogenic magnetometer palaeomagnetic measurements on other standard sized samples were made with a ccl discrete sample cryogenic magnetometer incremental thermal and af demagnetisation treatment was used to remove magnetic overprints and to isolate the characteristic remanent magnetisation chrm a reliability classification scheme has been developed and applied in this study to provide an objective assessment of the quality of the palaeomagnetic results irm acquisition experiments suggest that the dominant magnetic mineral in these sediments is magnetite but mixtures of hematite and magnetite occur also sem and tem studies of magnetic mineral extracts indicate the presence of magnetite and hematite preserved as inclusions within silicate grains together with abundant bacterial magnetite preserved as individual grains and chains in some samples samples containing the greatest proportions of bacterial magnetite generally have the highest nrm intensity the composite magnetic polarity sequence derived by combining the data from all three sections is characterised by three principal magnetic polarity zones which can be correlated with geomagnetic chrons c34n c33r and c33n respectively the positions of the chron boundaries have been tied to macrofossil and nannofossil biostratigraphic zones in these sections a series of previously undocumented short magnetic polarity sub chrons has been identified within the longer magnetochrons these have potential value for high resolution stratigraphic correlations and significance for theories of geodynamo behaviour

sedimentary iron cycling and the origin and preservation of magnetization in platform carbonate muds andros island bahamas carbonate muds deposited on continental shelves are abundant and well preserved throughout the geologic record because shelf strata are difficult to subduct and peritidal carbonate units often form thick rheologically strong units that resist penetrative deformation much of what we know about pre mesozoic ocean chemistry carbon cycling and global change is derived from isotope and trace element geochemistry of platform carbonates paleomagnetic data from the same sediments would be invaluable placing records of paleolatitude paleogeography and perturbations to the geomagnetic field in the context and relative chronology of chemostratigraphy to investigate the depositional and early diagenetic processes that contribute to magneitzation in carbonates we surveyed over 500 core and surface samples of peritidal often microbially bound carbonate muds spanning the last not vert similar 1000 yr and deposited on top of pleistocene aeolianites in the triple goose creek region of northwest andros island bahamas sedimentological geochemical magnetic and ferromagnetic resonance properties divide the sediment columns into three biogeochemical zones in the upper sediments the dominant magnetic mineral is magnetite produced by magnetotactic bacteria and dissimiliatory microbial iron metabolism at lower depths above or near mean tide level microbial iron reduction dissolves most of the magnetic particles in the sediment in some cores magnetic iron sulfides precipitate in a bottom zone of sulfate reduction likely coupled to the oxidation of decaying mangrove roots the remanent magnetization preserved in all oriented samples appears indistinguishable from the modern local geomagnetic field which reflects the post depositional origin of magnetic particles in the lower zone of the parasequence while we cannot comment on the effects of late stage diagenesis or metamorphism on remanence in carbonates we postulate that early cemented thin laminated parasequence tops in ancient peritidal carbonates are mostly likely to preserve syn depositional paleomagnetic directions and magnetofossil stratigraphies

diamonds through time diamonds form in the upper mantle during episodic events and have been transported to the earth s surface from at least the archean to the phanerozoic small diamonds occur as inclusions in robust minerals in tectonically activated ultrahigh pressure metamorphosed crustal rock establishing an association with subduction processes and recycled carbon but providing no economic deposits diamonds in economic deposits are estimated to be mainly 99 derived from subcontinental lithospheric mantle and rarely approx 1 from the asthenosphere harzburgite and eclogite are of roughly equal importance as source rocks followed by lherzolite and websterite diamonds which provide evidence of extensive residence time in the mantle are with minimal exceptions smooth surfaced crystalline diamonds scd with potential commercial value the oldest prolific scd formation event documented on the world s major diamond producing cratons occurs in archean lithospheric mantle harzburgite metasomatized by likely subduction related potassic carbonatitic fluids disaggregation of the diamondiferous carbonated peridotite on decompression during volcanic transit gives rise to the association between diamonds g10 garnets and diamond inclusion type chromites well used in diamond exploration within the mantle domains of diamond stability there have been repeated episodes of further diamond crystallization and or growth these are associated with old often proterozoic subduction related melt generation metasomatic fluid migration and reaction with preexisting mantle eclogite websterite and peridotite using improved methods of isotope analysis diamond formation ages can be correlated with specific major processes such as craton accretion craton edge subduction and magmatic mantle refertilization fibrous cuboid diamond and fibrous coats on scd are rough surfaced diamonds with abundant fluid inclusions they have low mantle residence time forming rapidly from late stage metasomatic fluids in diamond stable domains that may already contain scd the symbiotic relationship between formation of fibrous diamond and magmatic sampling and transport of diamonds into the crust suggest that the associated fluids contribute diamond friendly volatile loading of the deep lithospheric mantle shortly before the triggering of a volcanic eruption continuing a process of volatile enrichment in the lithospheric mantle already identified in the archean harzburgite diamond event mantle derived scd commonly shows evidence of resorption illustrating that diamond unfriendly processes including lamproite and kimberlite generation are also active and may have a substantial negative effect in extreme cases on scd crystal size exposure of scd to a long period of changing conditions during mantle residence contributes to the difficulty of assigning specific parageneses and ages to individual inclusion free diamonds with our current state of knowledge

magnetofossils in the sediment of lake baikal siberia abstract a multidisciplinary approach involving rock magnetics transmission electron microscopy and x ray diffraction was used to identify a biogenic magnetite component in the lake baikal siberia sedimentary magnetic record the distinctive biogenic component to the magnetic record occurs as chains of single domain elongate hexagonal and tear drop cone shaped magnetite particles these magnetofossils are inferred to be magnetosomes produced by magnetotactic bacteria living in the surficial sediment throughout lake baikal postdepositional reduction diagenesis results in the loss of the fine grained magnetofossils at depth in addition this study shows that the fine grained magnetofossils are removed by the process of storage diagenesis during long periods 21 months of core storage which results in a change to a coarser grained slightly higher coercivity bulk magnetic mineral assemblage although the lake baikal sedimentary magnetic record has several distinct and complex components by determining their origin this study has shown that the sediments are well suited for environmental magnetic study

sulfur and iron diagenesis in temperate unsteady sediments of the east china sea inner shelf and a comparison with tropical mobile mud belts mmbs redox cycling of iron fe and sulfur s exerts profound influences on fates of numerous elements in coastal marine sediments in this study s and fe cycling and its geochemical expressions in the east china sea ecs inner shelf a representative of temperate mobile mud belts mmbs were characterized and compared with tropical counterparts the amazon shelf and the gulf of papua fe and s speciation consistently points to the dominance of authigenic nonsulfidized fe ii phases i e poorly crystalline clays pccs and carbonates and the prevalence of fe redox cycling in the suboxic or weakly sulfidic regimes of the ecs mmbs high contents of authigenic magnetite may be a common diagenetic expression in all mmbs compared to the tropical mmbs three main differences of diagenetic expressions in the ecs mmbs are i light 34spyrite in the ecs mmb vs characteristically heavy 34spyrite in the amazon shelf mmbs ii lower total reactive fe fetr total diagenetic fe ii and ratio of fetr to total fe in the ecs mmbs iii fe ii carbonates and pccs are equally important sinks for nonsulfidized fe ii in the ecs mmbs whereas pccs are the predominant sink in the tropical counterparts these differences are ascribable to factors including low degradability of organic matter small diffusion scales less intense chemical weathering in the drainage basin and or weaker reverse weathering in the ecs mmbs despite the differences above fe and s diagenetic expressions that characterize the prevalence of fe redox cycling in the unsteady suboxic regimes are shared by the ecs and tropical mmbs

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

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

evidence for exclusively inorganic formation of magnetite in martian meteorite alh84001 magnetite crystals produced by terrestrial magnetotactic bacterium mv 1 are elongated on a 111 crystallographic axis in a so called truncated hexa octahedral shape this morphology has been proposed to constitute a biomarker i e formed only in biogenic processes a subpopulation of magnetite crystals associated with carbonate globules in martian meteorite alh84001 is reported to have this morphology and the observation has been taken as evidence for biological activity on mars in this study we present evidence for the exclusively inorganic origin of 111 elongated magnetite crystals in alh84001 we report three dimensional 3 d morphologies for 1000 magnetite crystals extracted from 1 thermal decomposition products of fe rich carbonate produced by inorganic hydrothermal precipitation in laboratory experiments 2 carbonate globules in martian meteorite alh84001 and 3 cells of magnetotactic bacterial strain mv 1 the 3 d morphologies were derived by fitting 3 d shape models to two dimensional bright field transmission electron microscope tem images obtained at a series of viewing angles the view down the 110 axes closest to the 111 elongation axis of magnetite crystals 111 110 0 provides a 2 d projection that uniquely discriminates among the three 111 elongated magnetite morphologies found in these samples 111 elongated truncated hexa octahedron 111 tho 111 elongated cubo octahedron 111 eco and 111 elongated simple octahedron 111 eso all 111 elongated morphologies are present in the three types of sample but in different proportions in the alh84001 martian meteorite and in our inorganic laboratory products the most common 111 elongated magnetite crystal morphology is 111 eco in contrast the most common morphology for magnetotactic bacterial strain mv 1 is 111 tho these results show that 1 the morphology of 111 elongated magnetite crystals associated with the carbonate globules in martian meteorite alh84001 is replicated by an inorganic process and 2 the most common crystal morphology for biogenic mv 1 magnetite is distinctly different from that in both alh84001 and our inorganic laboratory products therefore 111 elongated magnetite crystals in alh84001 do not constitute as previously claimed a robust biosignature and in fact an exclusively inorganic origin for the magnetite is fully consistent with our results furthermore the inorganic synthesis method i e the thermal decomposition of hydrothermally precipitated fe rich carbonate is a process analogue for formation of the magnetite on mars namely precipitation of carbonate globules from carbonate rich hydrothermal solutions followed at some later time by a thermal pulse perhaps in association with meteoritic impact or volcanic processes on the martian surface

diagenetic dissolution of biogenic magnetite in surface sediments of the benguela upwelling system intense primary biologic productivity in the surface waters of the benguela upwelling system provides a high supply of organic matter to the sea floor at the continental slope off namibia and sustains extreme concentrations of magnetite producing bacteria in the top sediment layers biogenic magnetite is thus by far the dominant carrier of the magnetic signal in these deposits also because of a very minor input of terrigenous ferrimagnetic minerals reducing conditions in the sediment column cause a selective dissolution of the bacterial magnetite fraction just a few centimeters below the main mineralization horizon this diagenetic process is documented in detail by high resolution rock magnetic analyses and transmission electron microscopy concentration dependent and grain size sensitive magnetic parameters such as susceptibility laboratory imparted remanences and hysteresis data reveal a significant drop in ferrimagnetic mineral content within the upper 10 cm of the sediments accompanied by a gradual downward coarsening of the ferrimagnetic mineral assemblage from primarily magnetic single domain particles in the top centimeters to multi domain grains in deeper strata electron microscope observations enable both an unequivocal identification of bacterial magnetite on the basis of shape and grain size and to trace dissolution effects on the biogenic magnetic mineral component to depth

nature and origin of magnetic minerals within the middle jurassic shallow water carbonate rocks of the paris basin france implications for magnetostratigraphic dating summary the middle and upper jurassic bathonian oxfordian shallow water carbonate rocks from the paris basin france consist mainly of oolitic and bioclastic limestones that are hydrocarbon reservoirs in the subsurface despite a preliminary positive study these deposits have been considered to be largely remagnetized rochette private communication and hence not amenable to palaeomagnetic dating to establish their magnetic mineralogy and test this remagnetization hypothesis we have used an integrated investigation combining petrographic geochemical rock magnetic and palaeomagnetic measurements on samples extracted from five cores from the paris basin and from outcrops in burgundy magnetic minerals in the bathonian oxfordian carbonates include 1 primary biogenic single domain magnetite and detrital multi domain ti magnetite and their oxidized form maghemite 2 authigenic spheres of magnetite probably related to hydrocarbons and 3 goethite either restricted to ferruginous ooid layers or resulting from surficial alteration notably replacement of pyrite framboids rock magnetic experiments carried out on 68 samples reveal hcr hc and mrs ms ratios ranging from 1 88 to 5 58 and 0 017 to 0 314 respectively these values are clearly distinct from diagnostic values for a chemical remagnetization pyrrhotite was not identified within these sediments moreover the average hcr hc ratio of 3 14 is significantly different from the value of 1 333 for natural pyrrhotite dekkers 1988 these results have a direct implication for the preservation of the primary magnetization consequently these deposits are selectively amenable for magnetostratigraphic dating and possible regional correlations

constraining the internal variability of the stable isotopes of carbon and nitrogen within mantle diamonds the carbon and nitrogen isotope values of mantle xenoliths and xenocrysts are used to trace the cycling of volatiles in the deep earth for example to place empirical constraints on the origin of diamond forming carbon in the mantle the global database for diamond shows that the 13c value of peridotitic diamonds is very narrow typically around 5 whereas eclogitic diamonds can show positive and very negative 13c values resembling crustal carbonates and crustal organic carbon 2 commonly interpreted to reflect a relationship between eclogitic diamond formation and subduction zone planet tectonics curiously diamonds from both parageneses can show positive crust like and negative mantle like 15n values from 20 most of these data are derived from single stage combustion gas sourced mass spectrometry which produces simplistic datasets by fragmenting single diamonds or using in situ ion beam techniques it is known that single diamonds can show large scale heterogeneity for their carbon isotope values and nitrogen abundances sometimes as large as entire populations of diamond across a few hundred micrometres what is less well known is the scale of nitrogen isotope heterogeneity within single diamonds and if the nitrogen isotope heterogeneity of single diamonds can provide an insight into why diamonds that show very restricted 13c values show a much large range of 15n values to investigate the scale and to determine the origin of the nitrogen isotope heterogeneity source vs fractionation during diamond formation shown for populations of mantle diamonds we have determined multiple 13c 15n values and nitrogen abundances from 14 monocrystalline mcds and 25 polycrystalline diamonds pcds using step wise oxidation gas sourced mass spectrometry these data show that the heterogeneity shown for carbon and nitrogen isotope values from single diamond samples presented here is typically 5 and 8 respectively both of which are comparable to the standard deviation for the mean mantle 13c and 15n values 3 and 4 however there are samples that show much larger heterogeneities for 13c and 15n values 23 and 33 respectively which cannot be generated by equilibrium stable isotope fractionation during or prior to diamond formation these data suggest that isotopic heterogeneity may be present within the diamond forming fluid on sub mm scale or that these diamonds formed during multiple diamond formation events from isotopically distinct sources from these 39 samples there are only 5 pcds that show a larger range of carbon isotopes relative to nitrogen isotopes but of these 5 samples only 2 show a range of 13c values outside of analytical uncertainty the remaining 34 samples show a greater isotopic heterogeneity for 15n relative to 13c values the samples with the largest carbon and nitrogen isotopic heterogeneity are also the samples with low bulk 13c values 10 whilst there is no relationship between the ranges of nitrogen isotope values for a given sample and the corresponding bulk 15n value or nitrogen content these data show that 15n values recorded in mantle diamonds are relatively heterogeneous and can show both mantle like negative and crustal sedimentary like positive 15n values within the same sample we conclude that the large range of nitrogen isotope values seen within individual diamonds means that the observation of negative mantle like nitrogen in mantle diamonds acquired by single stage bulk combustion isotope ratio mass spectrometry cannot be used as a conclusive indicator for a mantle origin for the entirety of the diamond forming carbon and vice versa also the behaviour of 15n 14n is not coupled with the behaviour of 14n 12c during diamond formation instead it appears that diamond forming fluids can have positive and negative 15n values irrespective of their 13c value s these data suggest that subduction induced nitrogen isotope heterogeneity may not be coupled with subduction induced carbon isotope heterogeneity in diamond forming fluids

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

quaternary climatic control of biogenic magnetite production and eolian dust input in cores from the mediterranean sea we report high resolution magnetic measurements from two mediterranean piston cores lc07 sicily strait and lc10 ionian sea magnetostratigraphic results and 18o data provide age constraints for core lc07 where we investigate magnetic property variations for two age intervals 0 600 kyr and 660 1020 kyr for core lc10 rock magnetic parameters appear to be climatically controlled and are used to derive an astronomically tuned age model for the interval between 780 and 1200 kyr in core lc07 the dominant control on the magnetic properties appears to be glacial interglacial variations in the concentration of biogenic magnetite in addition an increased contribution from high coercivity minerals e g hematite and or goethite probably reflects an enhanced eolian input during glacial periods climatic control of magnetotactic bacterial populations has been previously suggested in other environments but this is the first such report from the mediterranean in contrast the rock magnetic response to quaternary climatic variability in core lc10 seems to be better expressed by variations in the concentration of high coercivity magnetic minerals the contrast between a dominantly detrital eolian flux and a dominantly biogenic flux at the same time for the two mediterranean settings might relate to the presence of an active current regime in the sicily strait which might decrease delivery of an eolian component to the seafloor compared to the deep ionian sea

biogenic magnetite as a primary remanence carrier in limestone deposits abstract studies on the microbial communities and magnetic phases of samples collected from carbonate oozes at sugarloaf key fl u s a and calcareous laminated sediments from laguna figueroa baja california mexico have revealed the existence of magnetotactic bacteria and ultrafine grained single domain magnetite in both environments magnetotactic bacteria were identified by light and electron microscopy the single domain magnetite was detected by coercivity spectra analysis with a squid magnetometer and examined under the transmission electron microscope the similarity in terms of size and shape between the single domain magnetite found in these sediments and the magnetite observed in the bacterial magnetosome from enriched cultures indicates the ultrafine grained magnetite in these two marine environments was biologically formed these results combined with the common occurrences of ultrafine grained magnetite in limestone deposits detected rock magnetically suggest biogenic magnetite may be present and contribute to the magnetic remanence in these rocks several cambrian limestone samples separately collected from siberia china and kazakhstan were examined for the presence of bacterial magnetite samples from the lower cambrian sinskian formation at siberia platform were found to contain both a large amount of apparently bacterial magnetite particles and a very stable primary magnetic component post cambrian diagenesis does not seem to affect the microgranulometry of these apparently bacterial magnetite crystals or the magnetic remanence carried by them assessing the potential role of biogenic magnetite as a primary remanence carrier in other phanerozoic limestone deposits ought to be further pursued

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

new chronology for the late paleocene thermal maximum and its environmental implications the late paleocene thermal maximum lptm is associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle we have developed a new orbital chronology for ocean drilling program odp site 690 weddell sea southern ocean by using spectral analysis of high resolution geochemical records the lptm interval spans 11 precessional cycles yielding a duration of 210 to 220 k y the 13 c anomaly associated with the lptm has a magnitude of about 2 5 to 3 we show that about 2 of the excursion occurs within two steps that each were less than 1000 yr in duration the remainder developed through a series of steps over 52 k y the timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial further we are able to correlate the records between odp sites 690 and 1051 western north atlantic on the scale of 21 k y cycles which demonstrates that the details of the 13 c excursion are recognizable between distant sites comparison of cycle records at sites 690 and 1051 suggests that sediment representing the interval 30 k y just prior to and at the onset of the lptm are missing in the latter location this unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k y of the start of the lptm

environmental rock magnetism of pelagic clay implications for asian eolian input to the north pacific since the pliocene we conducted a rock magnetic study of pelagic sediments in order to document variations of asian eolian input to the north pacific since the pliocene the materials studied consist of five pelagic clay red clay cores of several meters long taken from the central north pacific and surface sediments of box cores obtained at 40 sites along two lines a n s line along 175 e and an e w line along 20 n the magnetic susceptibility concentration of magnetic minerals and s ratio relative abundance of low coercivity magnetic minerals of the five pelagic clay cores have decreased synchronously since about 2 5 ma this age coincides with the onset of the northern hemisphere glaciation and chinese loess deposition geographical distribution of s ratios measured on the surface sediments revealed that they are remarkably low in the central north pacific these facts suggest that s ratio can be used as a proxy for asian eolian dust mossbauer spectroscopy showed that hematite dominates the high coercivity minerals observation with a transmission electron microscope suggests two sources of magnetic minerals in the pelagic clay biogenic magnetite produced in situ and detrital magnetite and hematite the variations of s ratio and magnetic susceptibility with time and region can be explained by a model that asian eolian dust has higher lower hematite magnetite concentration than other sources of magnetic minerals and that its input to the central north pacific has increased since 2 5 ma we recognized subtle s ratio fluctuations of about 400 kyr in recurring intervals superimposed on the decreasing trend since 2 5 ma rock magnetic parameters diagnostic of magnetic grain size on the other hand showed small or no variations with age although eolian grain size is generally thought to have increased significantly since the pliocene based on sedimentological studies

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

temporal trends of magnetic dissolution in the pelagic realm gauging paleoproductivity abstract magnetic hysteresis data from the western equatorial pacific suggest that the preservation of magnetic remanence in pelagic carbonates is controlled by paleoproductivity hysteresis excursions 100 k y intervals are linked here to greater magnetic dissolution associated with increased glacial organic carbon supply changes in the redox boundary coupled to glacial terminations result in anomalous magnetic features which are preserved in the sedimentary record these high frequency variations are superimposed on a longer term signal of magnetic dissolution which may reflect decreased productivity since the miocene

mechanisms of diamond oxidation and their bearing on the fluid composition in kimberlite magmas diamond oxidation experiments were undertaken in a piston cylinder apparatus at 1150 to 1500 c and 1 gpa to understand the mechanism of diamond oxidation in kimberlite melts and to determine the main rate controlling parameters for this process only surface graphitization and no diamond resorption occurs in melts that are fluid undersaturated synthetic kimberlite carbonate melt alkaline basalt cao mgo sio 2 h 2 o co 2 melts in contrast fluid oversaturated conditions as evidenced by the presence of bubbles produce resorption features commonly seen in natural diamonds recovered from kimberlites the diamond oxidation rate is the same in the melts with a free fluid phase in a pure h 2 o or co 2 fluid suggesting that the process of diamond oxidation is its reaction with the fluid and not with the melt both co 2 and h 2 o oxidize diamonds at a similar rate but produce very different surface features therefore the surface features of natural kimberlite hosted diamonds may provide information on the relative proportion of h 2 0 and co 2 in the kimberlitic fluid the common diamond morphologies imply significant amount of h 2 o the absence of diamonds with surface graphitization and the abundance of resorbed diamonds in kimberlites suggest the presence of a free fluid phase in kimberlite magmas for hours or days we found no correlation between the rate and character of diamond oxidation and the physical properties of diamonds nitrogen content color

paleomagnetic evidence for fossil biogenic magnetite in western crete abstract previous paleomagnetic research has shown that the concentration of fine grained magnetite preserved in miocene marine clays of western crete drops during two successive geomagnetic transitions although the mechanism responsible for this effect was not known magnetite precipitation by magnetotactic bacteria offers a straightforward explanation for this decrease reduced field strengths during a reversal will strain the competitive advantage of having intracellular magnetite and will force bacteria to precipitate correspondingly more magnetite if they are to maintain the same alignment in the geomagnetic field their ability to do this is limited by several magnetophysical constraints which should act to reduce the numbers of magnetite precipitating cells particularly in fields of less than about 12 of the present level this would lead to a decrease in the supply of bacterial magnitude to the sediments recovery of intact magnetotactic bacterial fossils may lead to a new method for estimating paleointensities from sedimentary rocks

biogenic magnetite in stromatolites i occurrence in modern sedimentary environments abstract in this paper we report the occurrence of biogenic ultra fine grained single domain magnetite in both marine and non marine modern stromatolitic environments magnetotactic bacteria were found associated with the microbial communities involved in the deposition of laminated sediments at laguna figueroa baja california mexico and carbonate stromatolitic nodules at sugarloaf key fl u s a these bacteria and the ultra fine grained magnetite they produce have a profound effect on the magnetic properties of the sediments the presence of this single domain magnetite was detected using rock magnetic methods while the morphology was identified by transmission electron microscopy examination by rock magnetic methods of microbial mats and laminated sediments from solar lake sinai guerrero negro baja california mexico and shark bay australia as well as stromatolites from shark bay and clifton lake australia bacalar lake and cuatro cienegas mexico and walker lake u s a indicate these localities contain single domain magnetite biogenic magnetites of presumed bacterial origin have been extracted from shark bay mats walker lake stromatolites and bahama carbonates these findings suggest that bacterial magnetites can be recognized as the tiniest trace fossil and may be found preserved in fossil stromatolites and laminated sediments

calibrating the duration and timing of the messinian salinity crisis in the mediterranean linked tectonoclimatic signals in thrust top basins of sicily the messinian 9salinity crisis9 which affected the mediterranean represents one of the most dramatic examples of base level fluctuation known in the geological record an amplitude of perhaps 2 km within a stage with a duration of less than 2 ma deposits within the caltanissetta basin of central sicily are used to calibrate the duration and timing of these fluctuations two successions of evaporites termed 9first cycle9 and 9second cycle9 are separated by an inter regional unconformity the first cycle is regionally regressive while the second is transgressive chronostratigraphic calibration of these deposits has been provided by a linked magnetostratigraphic structural and sedimentological study the regression was protracted the earliest evaporites in our study accumulated early in chron c3ar pre 6 88 ma and the youngest accumulated late in chron c3an post 6 0 ma during this interval the basinward shift in coastline was 70 km and in vertical section implies a relative fall in sea level at 0 3 0 4 m ka 1 lowstand probably finally occurred at 5 8 5 5 ma transgression marked by accumulation of the 9second cycle9 deposits which all record reversed magnetizations c3r apparently occurred far more rapidly 200 ka prior to the return to 9normal9 marine conditions in the central mediterranean late in chron c3r local rates of tectonic deformation are relatively slow within the thrust belt which underlies the caltanissetta basin therefore it is likely that the timing and rates of the messinian 9salinity crisis9 on sicily are generally applicable to other basins in the region and help to underpin rates of climate change within this part of the neogene

magnetostratigraphic dating of shallow water carbonates from mururoa atoll french polynesia implications for global eustasy magnetostratigraphic results are reported from a core penetrating the top 100 m of mururoa atoll french polynesia the sequence of polarity reversals based on relative up down direction in the unoriented core is correlated to the geomagnetic polarity time scale from the gauss early pliocene through the brunhes chron late pleistocene holocene the polarity sequence is matched with the help of an early brunhes radiometric date in a nearby core and the projected level of gephyrocapsa oceanica mid brunhes from an adjacent inclined core rock magnetic tests and extraction of magnetic components suggest a mixture of single and multi domain magnetite or maghemite carries the magnetic remanence newly refined atoll chronostratigraphy indicates a punctuated growth history and variable sedimentation rate of the reefal rim magnetostratigraphically dated periods of low accumulation correspond well with the increased frequency of subaerial exposure horizons these new data suggest that third order scale 1 m y sea level events are recorded in reefal deposits on moderate to slowly subsiding atolls mururoa and the bahamian island of san salvador have similar accumulation curves suggesting a global eustatic control

magnetotactic bacteria and single domain magnetite in hemipelagic sediments remanent magnetism in marine sediments has been used extensively over the past twenty years to calibrate the geological time scale study geomagnetic reversals and secular variation and measure the rates of seafloor spreading although these sediments may contain different magnetic minerals magnetite is the most commonly observed and magnetically stable phase and its size shape and post depositional fate affect the magnetic remanence of the sediments biogenic magnetites are single domain with a high natural magnetic remanence nrm and have been suggested as a significant source of magnetic remanence in marine sediments we have studied surface sediments from the santa barbara basin and report the occurrence of living magnetotactic bacteria and the deposition of biogenic ultra fine grained single domain magnetite using a novel extraction technique transmission electron microscopy and squid magnetometry we show that these bacteria and the magnetite they produce are the major source of stable remanent magnetism in these sediments

nanoinclusions in microdiamonds from neogenic sands of the ukraine samotkan placer a tem study abstract mineral and fluid inclusions in seven microdiamonds ca 0 2 mm in diameter from the neogene samotkan placer of the ukrainian shield were investigated by tem various types of submicron or nanometre sized inclusions such as olivine and orthopyroxene fe sn oxide and assemblages of mineral multi phases were observed in an octahedral microdiamond crystal numerous olivine and enstatite micro and nanocrystals were observed their composition is close to that of other olivine and enstatite inclusions found in kimberlitic diamonds worldwide an unusual feature of these minerals in the samples studied however is a relatively high nio content 0 50 0 80 wt in olivine fo 91 3 92 1 and 0 40 0 70 wt in enstatite fo 94 1 95 4 these peridotitic mineral associations represent the host possibly lherzolitic mantle in which the diamonds grew the mean mg values of olivine and enstatite inclusions in samotkan s microdiamond are respectively 91 43 and 94 83 which are closer to mg values of these minerals in lherzolite rather than in harzburgite assemblages included in diamond in addition enstatite clinoenstatite k richterite graphite and fe sn oxide were also identified as nanoinclusions in samotkan diamond the fe sn oxides and magnetite were found in two microdiamonds of the transitional 111 110 form the k richterite and graphite have been attributed to epigenetic inclusions the origin of fe sn oxide is not clear assemblages of multi phase minerals were observed in four microdiamonds of variable morphology octahedron transitional 111 110 form cube and cube coated diamond these phases belong to fluid bearing inclusions and are enclosed in cavities which as a rule are not filled completely by the solid phases the remainder of the volume is occupied by a fluid that for the most part has been released during sample preparation in the majority of cases the multi phase assemblages consist of carbonate mica rutile ilmenite apatite and sylvite carbonates are the most abundant phases in the fluid inclusions they are calcium rich carbonates frequently with admixtures of fe mg and sr the mica inclusions are enriched in silicon with si varying from ca 6 7 to 7 0 a p f u the multi phase mineral assemblages present in samotkan s microdiamond are similar to fluid bearing microinclusions found previously in other diamond types e g fibrous diamonds the fibrous coat of coated diamonds or the internal clouds of octahedral diamonds from kimberlites of different provinces worldwide they represent the carbonate alkali and chlorine rich mantle fluid composition present during crystallisation of the samotkan s microdiamond judging from the composition of the multi phase assemblages it may be assumed that the samotkan s microdiamond grew from a carbonatitic to a slightly silicic melt rich in alkali and volatile components

a case for a comet impact trigger for the paleocene eocene thermal maximum and carbon isotope excursion abstract we hypothesize that the rapid onset of the carbon isotope excursion cie at the paleocene eocene boundary 55 ma may have resulted from the accretion of a significant amount of 12c enriched carbon from the impact of a 10 km comet an event that would also trigger greenhouse warming leading to the paleocene eocene thermal maximum and possibly thermal dissociation of seafloor methane hydrate indirect evidence of an impact is the unusual abundance of magnetic nanoparticles in kaolinite rich shelf sediments that closely coincide with the onset and nadir of the cie at three drill sites on the atlantic coastal plain after considering various alternative mechanisms that could have produced the magnetic nanoparticle assemblage and by analogy with the reported detection of iron rich nanophase material at the cretaceous tertiary boundary we suggest that the cie occurrence was derived from an impact plume condensate the sudden increase in kaolinite is thus thought to represent the redeposition on the marine shelf of a rapidly weathered impact ejecta dust blanket published reports of a small but significant iridium anomaly at or close to the paleocene eocene boundary provide supportive evidence for an impact

first evidence of hydrous silicic fluid films around solid inclusions in gem quality diamonds abstract diamonds form from fluids or melts circulating at depth in the earth s mantle analysis of these fluids is possible if they remain entrapped in the diamond during its growth but this is rarely observed in gem quality stones we provide the first evidence that typical mineral inclusions in gem quality diamonds from the siberian and kaapvaal cratons are surrounded by a thin film of hydrous silicic fluid of maximum thickness 1 5 m the fluid contains si 2 o oh 6 si oh 4 and molecular h 2 o and was identified using confocal micro raman spectroscopy and synchrotron based x ray tomographic microscopy as the solid mineral inclusions have both peridotitic and eclogitic affinities and occur in two cratonic regions our results demonstrate the strong connection between water rich fluids and the growth of gem quality lithospheric diamonds the presence of the fluid films should be taken into account for a proper evaluation of h 2 o contents in the mantle based on h 2 o contents in solid inclusions and for a robust assessment of diamond formation pressures based on the residual pressures of the inclusions

raman microspectrometry of fluid inclusions abstract for many kinds of fluid inclusions the coupling of microthermometry and raman microspectrometry is still the only viable option to obtain compositions of single fluid inclusions a review is given on the basis of 16 years of experience and helped with about 120 references of the instrumentation analytical conditions and methodology of the application of raman microspectrometry to gaseous aqueous and hydrocarbon inclusions and their daughter minerals

biogenic magnetite from surface holocene carbonate sediments great bahama bank magnetic separates and rock magnetic tests from holocene carbonate surface sediments of the bahamas indicate that fine grained magnetite maghemite is common at or near the sediment water interface and forms a major portion of the magnetic fraction magnetite crystals range from 400 to 1000 a in diameter as observed under the transmission electron microscope tem and often occur as elongate chains or multi grain clusters crystals are very similar in dimension and grain habit to those of known biogenic origin mainly bacteria all measured grains are within the single domain stability field for magnetite based on crystal dimensions coercivity distributions are fairly broad 5 100 mt or greater likely the result of partial oxidation of the magnetic minerals no large multidomain grains were observed in the tem study individual grains occur in several shapes in the microscope image mainly hexagonal and cuboidal prismatic widespread occurrence of single domain magnetite in this isolated carbonate setting suggests that biogenic precipitation is a major contributor of early in situ depositional magnetization a contribution of magnetite from authigenic precipitation during burial has not been documented in these near surface environments

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

the detection of bacterial magnetite in recent sediments of lake chiemsee southern germany the sediments of lake chiemsee located in the alpine foreland in southern germany host a variety of magnetotactic bacteria mtb which contain intracellular crystals of magnetite arranged in linear chains to detect bacterial magnetite in the carbonate dominated surface sediments and further quantify its contribution to the magnetic signal of the sediments we conducted detailed rock magnetic measurements as well as complimentary non magnetic analyses electron microscopy powder x ray diffraction and sediment pore water analysis our results demonstrate that biogenic single domain magnetite characterized by bullet and truncated hexagonal prismatic shapes is the dominant ferrimagnetic component in the topmost few centimetres of the sediment the changes of magnetic properties with depth are due to the occurrence of live mtb and the downward increasing dissolution of biogenic magnetite moreover the ratios of remanence loss on warming through the verwey transition after field cooling and zero field cooling of saturation isothermal remanence dfc dzfc were determined as 1 47 and 1 25 for freeze dried and air dried sediment samples containing mtb respectively these low ratios suggest that the bacterial magnetite chains were disrupted to a large extent and or that the bacterial magnetosomes might have undergone partial

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

carbonatitic mineralogy of natural diamond forming fluids a suite of 20 cuboid fibrous diamonds from the democratic republic of congo was studied to determine mineral phases crystallized from diamond forming fluids that were trapped as inclusions in diamonds we identified minerals and non crystalline components using their compositional trends in the electron microprobe analyses of inclusions an innovative bulk x ray diffraction analysis and characteristic ftir and raman peaks the drc diamonds contain fluid inclusions of the ca carbonatitic silicic composition most common phases precipitated from the fluid are found to be high si micas 90 30 of the solids volume complex non crystalline na ca mg fe carbonate matter and apatite together 5 70 leaving a residual aqueous solution of k cl and carbonate ions and gaseous co2 a notable absence of carbonate minerals in bulk x ray diffraction patterns combined with the vibrational spectroscopy observations on the c o bonds indicates that c may be included in dissolved or amorphous carbonate matter the modes of the most abundant phases are controlled by chemical trends of the bulk fluid compositions other relatively rare 30 minerals including various minerals with structural and coordinated h2o are detected by the vibrational spectroscopic and x ray analyses the fluid also contains some hydrocarbons associated with the carbonate material the presence of some rare minerals and exotic compositions of solid solution minerals in the fluid suggest crystallization from a closed system with high salinity high ah2o high aco2 composition that persisted to relatively low temperatures and pressures the bulk of the fluid crystallized in the diamond stability field p 7 gpa t 950 c but continued to form hydrocarbons accessory and deuteric phases down to 200 c and 0 2 gpa overall the mineralogy of the fluid resembles carbonatite

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

ferromagnetic resonance characterization of greigite fe3s4 monoclinic pyrrhotite fe7s8 and non interacting titanomagnetite fe3 xtixo4 ferromagnetic resonance fmr spectroscopy has become an increasingly useful tool for studying the magnetic properties of natural samples magnetite fe3o4 is the only magnetic mineral that has been well characterized using fmr this limits the wider use of fmr in rock magnetism and paleomagnetism in this study we applied fmr analysis to a range of magnetic minerals including greigite fe3s4 monoclinic pyrrhotite fe7s8 magnetically non interacting titanomagnetite fe3 xtixo4 and synthetic magnetite chains to constrain interpretation of fmr analysis of natural samples and to explore applications of fmr spectroscopy we measured the fmr signatures of a wide range of well characterized samples at the x and q bands fmr spectra were also simulated numerically to compare with experimental results the effects of magnetic anisotropy mineralogy domain state and magnetostatic interactions on the fmr spectra are discussed for all studied minerals our experimental and theoretical analyses of magnetically non interacting tuff samples and magnetically interacting chains enable quantitative assessment of contributions of magnetostatic interactions and magnetic anisotropy to the fmr spectra our results also indicate that intact magnetosomes are a unique system with distinct fmr signatures while fmr analysis is useful for characterizing magnetic properties of natural samples care is needed when making interpretations because of overlaps in a range of fmr signatures of different magnetic minerals with different magnetic properties our analyses will help to constrain such interpretations in rock magnetic studies

the origin and formation of metamorphic microdiamonds from the kokchetav massif kazakhstan a nitrogen and carbon isotopic study abstract this study reports 13c 15n and n content values for microdiamonds from ultrahigh pressure metamorphic rocks of the kokchetav massif in kazakhstan both alluvial diamonds and in situ diamonds from a garnet clinopyroxene rock and a marble i e a garnet pyroxene dolomitic rock were investigated in situ diamonds were analysed in batches because of their small size average 40 m whereas the larger alluvial diamonds were analysed individually the latter group has 13c values ranging from 15 92 to 10 57 15n from 1 8 to 1 1 and n contents from 2300 to 3650 ppm diamonds from the garnet clinopyroxene rock yield mean values of 10 50 for 13c 5 9 for 15n and a high average nitrogen content of 11 150 ppm values for diamonds in marble are 10 19 8 5 and 2650 ppm respectively for diamonds from garnet clinopyroxene rock and marble there is more nitrogen released by bulk combustion than estimated by infrared ir spectroscopy the differences being of about 7000 and 1500 ppm respectively these differences suggest that a significant quantity of nitrogen is ir inactive and may be present as fluid inclusions their carbon and nitrogen isotopic compositions are compatible with an in situ crystallisation of diamond from dominantly metasedimentary sources suggesting that sedimentary nitrogen can be subducted to very high pressures carbon isotopic fractionation between coexisting carbonate and diamond suggests crystallisation temperatures before the peak of metamorphism at temperatures probably below 700 c and deduced pressures of 3 gpa relative to the isotopic data reported for sediments metasediments and in situ diamonds the slightly 15n depleted compositions of alluvial diamonds is striking these values suggest that the contribution of any metasedimentary source is unlikely and may point toward a mafic ultramafic protolith

elongated prismatic magnetite crystals in alh84001 carbonate globules potential martian magnetofossils using transmission electron microscopy tem we have analyzed magnetite fe 3o 4 crystals acid extracted from carbonate globules in martian meteorite alh84001 we studied 594 magnetites from alh84001 and grouped them into three populations on the basis of morphology 389 were irregularly shaped 164 were elongated prisms and 41 were whisker like as a possible terrestrial analog for the alh84001 elongated prisms we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain mv 1 by tem again we examined 206 magnetites recovered from strain mv 1 cells natural darwinian selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment in this study we describe six properties of magnetite produced by biologically controlled mechanisms e g magnetotactic bacteria properties that collectively are not observed in any known population of inorganic magnetites these criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories of the alh84001 magnetites that we have examined the elongated prismatic magnetite particles 27 of the total are indistinguishable from the mv 1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals

synthesis of diamonds with mineral fluid and melt inclusions abstract experiments on the synthesis of inclusions bearing diamond were performed in the sio 2 mg ca co 3 fe ni s system at 6 3 gpa and 1650 1750 c using a multi anvil high pressure apparatus of the split sphere type diamond synthesis was realized in the sandwich type experiments where the carbonate oxide mixture acted as a source of both co 2 dominated fluid and carbonate silicate melt and fe ni sulfide played a role of reducing agent as a result of redox reactions in the carbonate oxide sulfide system diamond was formed in association with graphite and mg fe silicates coexisting with co 2 rich fluid carbonate silicate and sulfide melts the synthesized diamonds are predominantly colorless or light yellow monocrystals with octahedral habit 20 200 m and polycrystalline aggregates 300 400 m photoluminescence spectroscopy revealed defects related to nickel impurity s3 optical centers which are characteristic of many diamonds in nature the density of diamond crystallization centers over the entire reaction volume was 3 10 2 10 3 cm 3 the overwhelming majority of diamonds synthesized were inclusions bearing according to raman spectroscopy data diamond trapped a wide variety of inclusions both mono and polyphase including orthopyroxene olivine carbonate silicate melt sulfide melt co 2 fluid graphite and diamond the raman spectral pattern of carbonate silicate melt inclusions have bands characteristic of magnesite and orthopyroxene sio 2 the spectra of sulfide melt displayed marcasite and pyrrhotite peaks we found that compositions of sulfide silicate and carbonate phases are in good agreement not only with diamond crystallization media in experiments but with data on natural diamond inclusions of peridotitic and eclogitic parageneses the proposed methodological approach of diamond synthesis can be used for experimental simulation of the formation of several types of mineral fluid and melt inclusions observed in natural diamonds

a biogenic origin for anomalous fine grained magnetic material at the paleocene eocene boundary at wilson lake new jersey 1 the paleocene eocene thermal maximum which occurred 55 5 ma was caused by a massive release of carbon as indicated by an 3 negative carbon isotope excursion recorded in the marine atmospheric and terrestrial reservoirs one suggested source for the carbon a cometary impactor is based on the sudden appearance and high concentration of single domain sd magnetite in paleocene eocene p e boundary cores from the north atlantic continental margin we evaluate the potential sources of sd magnetite at the p e boundary by presenting new magnetic hysteresis low temperature magnetic remanence and transmission electron microscopy data from the north atlantic coastal ocean our results show a similar increase in sd material but demonstrate that the magnetic material has a biogenic origin these findings indicate that the high concentrations of sd magnetite immediately above the p e boundary are the result of unusual accumulations and or preservation of magnetotactic bacteria such bacteria typically occupy the oxic anoxic transition zone near the sediment water interface or in the water column the high abundances of sd magnetite in sediments from across the shelf may be an artifact of nonsteady state redox conditions and exceptional preservation of sd magnetite it may also indicate that the oxic anoxic redox boundary shifted into the water column the latter explanation implies transient eutrophy of the coastal ocean in this region most likely due to seasonally enhanced runoff and increased stratification and nutrient loading

low temperature remanence in stable single domain magnetite 1 a numerical model is developed in order to simulate the loss of low temperature remanence while warming through the verwey transition we concentrate on the amount of remanence lost fc and zfc during field cooled and zero field cooled low temperature demagnetization curves for stable single domain ssd particles of 1 inorganic magnetite and 2 biogenic magnetite in the form of magnetosome chains the model predicts that delta ratios fc zfc for inorganic ssd magnetite increase from 1 to 1 6 with increasing aspect ratio and that magnetosome chains have elevated delta ratios of at least 2 0 disaggregated magnetosomes are predicted to behave similarly to inorganic acicular ssd magnetite the numerical results agree with experimental results

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

magnetofossil dissolution in a palaeomagnetically unstable deep sea sediment magnetofossils1 the fossil remains of bacterial magneto somes2 are found in various deep sea sediments and have been linked to the preservation of stable natural remanent magnetization in many of them1 3 5 they have also been extracted and identified from lithified carbonates of jurassic5 and precambrian6 age showing that magnetotactic bacteria have been a sedimentary source of fine grained magnetite for much of geological time some clay rich deep sea sediments however do not record a stable remanent magnetization for unknown reasons here we report results from a high resolution transmission electron microscope study on samples of this type collected by the deep sea drilling project dsdp the material contains a complex mixture of single domain magnetic minerals well preserved magnetofossils show the same crystal structures as those found in magnetosomes from recent bacteria7 10 whereas others in these same preparations display a wide range of dissolution corrosion and aggregation effects rock magnetic measurements are consistent with the presence of these alterations in many dsdp sediments including those that preserve reliable palaeomagnetic directions as we were unable to fina authigenic magnetic minerals in our sample and as the magnetic fraction is dominated by well preserved magnetofossils we suggest that the poor preservation of the magnetization is a result of diagenetic interactions between the magnetofossils and the clay minerals in the matrix

brine mobilization during lithospheric heating on europa implications for formation of chaos terrain lenticula texture and color variations the background lineated plains on europa are locally highly modified and destroyed in regions known as chaos and lenticulae produced there are 1 isolated fragments and polygons of background material which rotate and translate 2 matrix which fills in the areas between the fragments and polygons and 3 surface discolorations using observations and constraints from high resolution galileo images we find that a model for the formation of these terrains which involves mobilization and migration of brines and a possible percolation phase transition as the europan lithosphere is warmed can readily explain the vast majority of their characteristics in addition the presence of melt fractions of a few percent in the adjacent ice framework may enhance the creep rate and the accompanying deformation rates the characteristics and distribution of lenticulae suggest that among the strong candidates for heat sources for brine migration and ice mobilization processes is diapirism linked to solid state convection in a layer underlying a brittle lid and possibly overlying a liquid water layer

evaluating iron as a biomarker of rhythmites an example from the last paleozoic ice age of gondwana abstract microorganisms play a significant role in mineral precipitation but detecting them in the fossil record is still a challenge here we offer an example of how the detection of biological activity in the sedimentary environment can modify a classical depositional model this study describes the activity of microorganisms in sedimentary structures and the iron mineral formation during the last paleozoic ice age in southwestern gondwana recorded by the itu rhythmites parana basin brazil the itu rhythmites have been considered to be varve type deposits that present alternating dark laminae clay silt size sediments and light layers sand gravel size sediments of varied thickness forming couplets earlier studies focused on abiotic processes of these structures we applied different techniques and analytical approaches were used such as synchrotron based techniques and rock magnetic techniques in order to test the biogenicity of iron minerals contained in putative microbially induced sedimentary structures by detecting biominerals in this rock succession the depositional model had to be reconsidered taking into account the biological activity the limitations on the specific conditions for bacterial growth and for mineral precipitation therefore we offer a new depositional model that considers the role of microorganisms in formation of these laminae and this model can be considered for other iron rich rhythmic deposits in other places of the world considering the effects of temperature and other factors in the bacterial productivity the deposition of the latest couplets in the outcrop occurred in different seasons and by different depositional processes corroborating with the non periodicity of 1 year per lithological couplet

magnetofossils the magnetization of sediments and the evolution of magnetite biomineralization magnetite fe 3o 4 is one of the most stable carriers of natural remanent magnetization nrm in sedimentary rocks and paleomagnetic studies of magnetite bearing sediments such as deep sea cores and pelagic limestones have provided a detailed calibration between the biostratigraphic and magnetic polarity time scales despite this important role there is as yet a very poor understanding of how ultrafine grained 0 1 m magnetite is formed transported and preserved in marine environments a major conceptual advance in our understanding of these processes is the recent discovery that biogenic magnetite formed by magnetotactic bacteria and or other magnetite precipitating organisms is responsible for much of the stable magnetic remanence in many marine sediments and sedimentary rocks since these magnetite particles are of biogenic origin they are termed properly magnetofossils kirschvink chang 1984

evidence for bacterial palaeoecological origin of mineral magnetic cycles in oxic and sub oxic tasman sea sediments abstract sediments from the tasman basin in the southwest pacific ocean show a cyclic pattern of variation in mineral magnetic properties including susceptibility and remanence over the brunhes chron the magnetic pattern is dominated by fluctuations in the concentration of a single domain ferrimagnetic component identified as bacterial magnetofossils by tem investigation of the magnetic fraction the intervals of low bacterial magnetite concentration occurring in glacial periods are accompanied by a change of the bacterial magnetosome morphology assemblage interpreted as recording a change in bacterial species assemblage there is no evidence of iron or sulphate reducing conditions during low bacterial magnetite intervals concentrations of bacterial magnetite are low when oxygen concentrations in surface sediment pore waters dropped either as the result of variation in bottom water oxygen concentration or sedimentation rate the variations in the magnetic signal are therefore interpreted as resulting primarily from bacterial palaeoecological control rather than dissolution or alteration the bacteria in this deep sea environment are apparently aerophilic and grow near the sediment surface within the oxic zone implying that magnetic remanence is also acquired near the surface but up to tens of centimetres below where the oxic zone is very thick

magnetostratigraphic dating of shallow water carbonates from san salvador bahamas magnetostratigraphic results are reported here from a sequence of late neogene quaternary shallow water carbonate sediments from a continuous core drilled on the island of san salvador bahamas on the basis of the remanent magnetism of 136 samples from a 91 m measured section of core the polarity sequence can be correlated with the magnetic polarity time scale from the gilbert chron early pliocene through the late brunhes chron late pleistocene holocene magnetic polarities were determined on the basis of relative up down direction in the unoriented core extraction studies of the magnetic particles reveal the presence of single domain crystals of magnetite resembling those produced by the magnetotactic bacteria and algae the sequence of reversals provides a minimum of six new major chronostratigraphic markers for the pliocene pleistocene of the bahamas it confirms and refines the local timing of both the lithologic change from skeletal to nonskeletal sediments and the disappearance of coral and molluscan species from the bahamas as upper late pliocene between 2 6 and 2 7 ma that the primary magnetic remanence is preserved in shallow water carbonates including replacement dolomites suggests that this technique could be used to date similar tertiary and possibly even older carbonate sequences the establishment of a reliable magnetostratigraphy provides refined dating of shallow water carbonates and regional faunal appearances or disappearances sediment accumulation rates subsidence and depositional events

diamond formation in the system mgo sio2 h2o c at 7 5 gpa and 1 600 c diamond crystallization has been studied in the sio2 h2o mg2sio4 h2o and h2o subsystems at 7 5 gpa and 1 600 c we found that dissolution of initial graphite is followed by spontaneous nucleation of diamond and growth of diamond on seed crystals in 15 h runs the degree of graphite to diamond transformation mdm mdm mgr 100 where mdm is mass of obtained diamond and mgr mass of residual graphite reached 100 in h2o rich fluids but was only 35 50 in water saturated silicate melts in 40 h runs an abrupt decrease of has been established at the weight ratio h2o h2o sio2 0 16 or h2o h2o mg2sio4 0 15 our results indicate that is a function of the concentration of water which controls both the kinetics of diamond nucleation and the intensity of carbon mass transfer in the systems the most favorable conditions for diamond crystallization in the mantle silicate environment at reliable pt parameters occur in the fluid phase with low concentration of silicates solute in h2o poor silicate melts diamond formation is questionable

high density co2 n2 inclusions in eclogite facies metasediments of the munchberg gneiss complex se germany the eclogite facies metasedimentary rocks in the munchberg gneiss complex t 630 30 c p 17 24 kbar locally contain co2 n2 rich fluid inclusions of extremely low molar volumes 32 cm3 mol in quartz these fluid compositions are mainly found in rocks intercalated with calcsilicate bands densities were determined from low temperature phase transitions like stable or metastable homogenization l v l partial homogenization s l v s l and the transition s l l l liquid v vapour s solid the high fluid densities are in agreement with eclogite facies pressure and temperature and subsequent amphibolite facies co2 n2 inclusions were not observed in adjacent eclogites nor in non calcareous metasediments these rock types contain predominantly h2o rich inclusions correlating with amphibolite facies conditions the variation of fluid composition with lithological differences indicates local fluid gradients and speaks against a pervasive fluid flow during eclogite facies metamorphism

biogenic magnetite in stromatolites ii occurrence in ancient sedimentary environments abstract in this paper we report the discovery of fossil bacterial single domain magnetite particles in ancient stromatolites the biogenicity of the crystals was determined by the following criteria 1 distinctive morphology and habit 2 composition and 3 environment of deposition stromatolites ranging in age from the middle archean to pleistocene composed of both carbonate and chert were analyzed for the presence of single domain magnetite using rock magnetic methods the granulometry and composition of the ultra fine grained magnetite crystals extracted were determined by transmission electron microscopy and electron diffraction the oldest magnetofossils were extracted from stromatolitic chert of the gunflint iron formation which is approximately 2000 ma old the implications of these findings and the potential uses of fossil bacterial magnetite in studies of the evolution of biomineralization and prokaryotic metabolic processes paleomagnetism and as an indicator of ancient oxygen levels are discussed bacterial magnetite represents the oldest evidence of biomineralization yet discovered in the fossil record

the nama group revisited summary the nama group of southern namibia is a candidate for the terminal proterozoic global stratotype section and point gssp desirable characteridics of a gssp include a well preserved index fossil assemblage little deformation or metamorphism well constrained isotopic ages stable isotope records and magnetostratigraphic control the age of the nama group sediments is now constrained to between 570 and 510 ma assuming the gondwana assembly was nearly complete at this same time there is a discrepancy between the previously published nama poles a revised 55cl510 ma apparent polar wander path for gondwana and the preceding supercontinental assemblages of rodinia and panottia for these reasons the nama group sediments were resampled in an effort to evaluate the potential of detailing the magnetostratigraphy of the nama group and resolving the discrepancy between the nama poles and the apwp of gondwana collectively both the previous studies of the nama group and this one show a complex series of overprints and no easily discernible primary direction of magnetization we therefore urge caution in using the nama group poles in any tectonic models of the neoproterozoic early palaeozoic specifically the n1 component of magnetization previously identified as a primary magnetization was discovered in a younger suite of samples therefore previous tectonic models that used the n1 magnetization direction as representative of the time of nama deposition should be revised in light of these recent findings

ultrafine grained magnetite in deep sea sediments possible bacterial magnetofossils a new extraction technique now permits ultrafine magnetite crystals to be separated from a variety of deep sea sediments morphologic characterization of these particles with transmission electron microscopy reveals the presence of several distinct crystal types some of which closely resemble those formed by the magnetotactic bacteria the apparently biogenic magnetite particles are of single domain size and dominate the population in calcareous deep sea sediments bacterially precipitated magnetite may therefore be a major source of the stable magnetic remanence in some marine sediments these objects possibly constitute the smallest mineral fossils yet recovered from the sedimentary record

co existing fluid and silicate inclusions in mantle diamond we document the compositions of co existing silicate macro inclusions and fluid micro inclusions in the fibrous coats of eight coated diamonds from the panda kimberlite canada the mineral inclusions in the diamond coats come from either the peridotite suite cr pyrope orthopyroxene olivine and cr diopside or the eclogite suite omphacite therefore fibrous diamonds grow in the same paragenetic environments as octahedral diamonds the inclusions document a more fertile source composition lower mg and higher cao than for equivalent phases in octahedral diamonds from panda and worldwide however moderate to high cr2o3 contents in garnet and clinopyroxene inclusions suggest that this apparent fertility is due to a secondary process geothermometry of the silicate inclusions yields low equilibration temperatures of 930 to 1010 c the co existing fluid micro inclusions are dominated by h2o carbonate and kcl fluid inclusions in both the peridotitic and eclogitic samples fall along linear arrays between fe ca mg carbonate and kcl inclusions in the one eclogitic sample also contain quartz we suggest that the diamonds have trapped both metasomatised minerals and the metasomatic fluid and so provide a snap shot of a metasomatic event in the mantle

crystal size and shape distributions of magnetite from uncultured magnetotactic bacteria as a potential biomarker we studied the sizes and shapes of magnetite nanocrystals produced by several types of uncultured magnetotactic bacteria to understand whether their size distributions can be used for identifying the biogenic origin of magnetite crystals in geological samples the two dimensional projections of the crystals were measured on transmission electron microscope tem images and features of crystal size and shape factor distributions csd and sfd respectively were analyzed in agreement with previous results most magnetite csd curves are asymmetric and negatively skewed however one magnetotactic strain produced particles that have a normal size distribution a statistical analysis of csds and sfds both from this and previous studies reveals similarities among magnetite from magnetotactic strains from various locations in particular crystals in a cultured marine strain mc 2 were indistinguishable from magnetite from a freshwater strain we tested whether csds of distinct magnetosome types can be recovered from the shape and size data of all particles combined in samples that contain several types of magnetosomes such samples can be used as models for rocks that contain magnetite nanocrystals of unknown and presumably various origins if the sfds of the distinct magnetosome types occurring in the same sample differ the csds of individual magnetosome types can be retrieved from bulk data in such cases the characteristic shape of the size distribution can be used for identifying magnetite as originating from magnetotactic bacteria

iron sulfides from magnetotactic bacteria structure composition and phase transitions using transmission electron microscopy we studied the structures and compositions of fe sulfides within cells of magnetotactic bacteria that were collected from natural habitats ferrimagnetic greigite fe3s4 occurred in all types of sulfide producing magnetotactic bacteria examined mackinawite tetragonal fes and tentatively sphalerite type cubic fes were also identified in contrast to earlier reports we did not find pyrite fes 2 or pyrrhotite fe12xs mackinawite converted to greigite over time within the bacteria that were deposited on electron microscope grids and stored in air orientation relationships between the two minerals indicate that the cubic close packed s substructure remains unchanged during the transformation only the fe atoms rearrange neither mackinawite nor cubic fes are magnetic and yet they are aligned in chains such that when converted to magnetic greigite the probable easy axis of magnetization 100 is parallel to the chain direction the resulting chains of greigite are ultimately responsible for the magnetic dipole moment of the cell both greigite and mackinawite magnetosomes can contain cu depending on the sampling locality because bacterial mackinawite and cubic fes are unstable over time only greigite crystals are potentially useful as geological biomarkers

chains clumps and strings magnetofossil taphonomy with ferromagnetic resonance spectroscopy magnetotactic bacteria produce intracellular crystals of magnetite or greigite the properties of which have been shaped by evolution to maximize the magnetic moment per atom of iron intracellular bacterial magnetite therefore possesses traits amenable to detection by physical techniques typically narrow size and shape distributions single domain size and arrangement in linear chains and often crystal elongation past strategies for searching for bacterial magnetofossils using physical techniques have focused on identifying samples containing significant amounts of single domain magnetite or with narrow coercivity distributions searching for additional of traits would however increase the likelihood that candidate magnetofossils are truly of biological origin ferromagnetic resonance spectroscopy fmr is in theory capable of detecting the distinctive magnetic anisotropy produced by chain arrangement and crystal elongation here we present analyses of intact and lysed magnetotactic bacteria dilutions of synthetic magnetite and sedimentary samples of modern carbonates from the great bahama bank oligocene miocene deep sea muds from the south atlantic and pleistocene lacustrine deposits from mono basin california we demonstrate that fmr can distinguish between intact bacterial magnetite chains collapsed chains and linear strings of magnetite formed by physical processes we also show that sediments in which the magnetization is likely carried by bacterial magnetite have fmr spectra resembling those of intact or altered bacterial magnetite chains

nitrogen bearing aqueous fluid inclusions in some eclogites from the western gneiss region of the norwegian caledonides minerals in eclogites from different localities in the western gneiss region of the norwegian caledonides age 425 ma contain a variety of fluid inclusions the earliest inclusions recognized are contained in undeformed quartz grains protected by garnet and consist of h2o n2 with x text h text 2 text o geqslant 0 8 the reconstructed p v t x properties of these fluid inclusions are compatible with peak or early retrograde metamorphic conditions matrix minerals quartz garnet apatite plagioclase contain a complex pattern of mostly truly secondary inclusions dominated by co2 and n2 the textural patterns and p v t x properties of these inclusions are incompatible with the high pressures of the eclogite forming metamorphic event but suggest that they were formed during uplift by a combination of remobilization of preexisting inclusions and influx of external fluids the fluid introduced at a late stage was dominated by co2 and did not contain n2 the present data agree with theoretical predictions of eclogite fluids from mineral equilibria and highlight the differences between granulite co2 and eclogite h2o n2 fluid regimes the provenance of the nitrogen in the eclogite fluid inclusions represents an important but unsolved question in the petrology of high pressure metamorphic rocks