further rock magnetic and chronostratigraphic results on reversal excursions during the last 50 ka as derived from northern high latitudes and discrepancies in precise ams 14c dating summary a total of five sediment cores from three sites the arctic ocean the fram strait and the greenland sea yielded evidence for geomagnetic reversal excursions and associated strong lows in relative palaeointensity during oxygen isotope stages 2 and 3 a general similarity of the obtained relative palaeointensity curves to reference data can be observed however in the very detail results from this high resolution study differ from published records in a way that the prominent laschamp excursion is clearly characterized by a significant field recovery when reaching the steepest negative inclinations whereas only the n r and r n transitions are associated with the lowest values two subsequent excursions also reach nearly reversed inclinations but without any field recovery at that state a total of 41 accelerator mass spectrometry ams 14 c ages appeared to allow a better age determination of these three directional excursions and related relative palaeointensity variations however although the three sites yielded more or less consistent chronological as well as palaeomagnetic results a comparison to another site ps2644 in the iceland sea revealed significant divergences in the ages of the geomagnetic field excursions of up to 4 ka even on basis of uncalibrated ams 14 c ages this shift to older 14 c ages cannot be explained by a time transgressive character of the excursions because the distance between the sites is small when compared with the size of and the distance to the geodynamo in the earth s outer core the most likely explanation is a difference of reservoir ages and or mixing with old 14 c depleted co2 from glacier ice expelled

late pleistocene chronology of sediments from the yermak plateau and uncertainty in dating based on geomagnetic excursions the yermak plateau is one of several regions in the arctic ocean where paleomagnetism yields controversial results despite low sedimentation rates late pleistocene paleomagnetic excursions have b

geochemical features of fe mn micronodules in deep sea sediments of the western north pacific ocean potential for co product metal extraction from rey rich mud abstract rare earth element and yttrium rey rich mud around minamitorishima island japan in the western north pacific ocean has received significant attention as a novel rey resource in rey rich muds industrially critical metals such as co ni and mo occur in relatively high concentrations we show that fe mn micronodules separated from rey rich muds are significantly enriched in these elements we measured co contents of almost 3000 ppm and ni contents that exceed 39 000 ppm through experiments we demonstrated that reductive chemical leaching can be used to extract major portions generally 80 of the metals associated with fe mn oxyhydr oxides from rey rich muds the fe mn micronodules were of an oxic diagenetic origin a simple mass balance calculation indicated that the contribution of the fe mn micronodules to the bulk fe mn oxyhydr oxides in the sediment can amount to 8 50 median 18 the other metals associated with fe mn oxyhydr oxides seem to be hosted in mn microparticles probably of a hydrogenetic origin we estimate that the most promising site for rey rich mud development contains 9 3 0 6 102 t 1 6 0 1 103 t and 2 8 0 2 102 t of leachable co ni and mo respectively in 1 km2 0 10 m below seafloor these amounts account for 0 66 0 04 0 061 0 004 and 0 097 0 007 of present annual global productions of co ni and mo respectively the feasibility of extracting these metals as co products during rey rich mud development depends on the cost efficiency of the recovery process which ultimately depends on their market price in the near future

osmium geochemistry of modern estuarine sediments from the tama and yasaka rivers in japan concentrations of re and os and 187 os 188 os ratios were obtained on the modern sediment samples from two estuarine areas the tama river in tokyo and the yasaka river in oita japan the shallow depth 25 cm intervals are 99 2 105 5 ppt os that are more than 3 times higher than ucc however all samples have 187 os 188 os ratios within a relatively narrow range of 0 3029 0 4035 much lower than that of ucc 1 0 1 3 indicating a similar source of os in both parts the lower 187 os 188 os ratios and high os concentrations of the sediments in the tama river suggest the impact from human activities the sudden enrichment of os at the deep interval may be related to the redox condition change in addition the os concentration is vertically constant in either the upper and lower intervals of the sediment profile suggesting constant burial fluxes of os in the sediment the os in the yasaka river estuary sediments 9 22 29 4 ppt are generally lower than that of the tama river either similar or much lower 1 3 than the average ucc os concentrations the samples with high os concentrations have lower 187 os 188 os ratios whereas the samples with lower os concentrations have relatively higher 187 os 188 os ratios probably indicating different os sources the relatively higher 187 os 188 os ratios and lower os concentrations in some yasaka river estuarine sediments than the tama river may also suggest less pollution from human activity to the yasaka river compared to the tama river there is a large decrease of re concentrations with depth in the yasaka river estuarine sediment whereas less variations of re in the tama river estuarine sediments the ratio of re os is also sharply different between the two estuarine sediments also indicating different sedimentary environments the tama river sediments may receive much more anthropogenic influence while the yasaka river sediments get strong impact from modern volcanic activity due to their different geographical and geological surroundings the tama river flows through a heavily industrial metropolitan area whereas the yasaka river flows through a volcanic active but less industrial area

re os geochronology of the hitachi volcanogenic massive sulfide deposit the oldest ore deposit in japan the hitachi volcanogenic massive sulfide vms deposit in the hitachi belt is one of the largest cu zn sulfide deposits in japan however its primary formation age has not been precisely determined because regional and contact metamorphism have disturbed some radiometric isotope systems e g k ar ages on wall rocks further metamorphism has greatly reduced the fossil record which has limited the use of biostratigraphy to establish the ore deposit age we applied re os isotope dating to samples from two representative sulfide deposits of the greater hitachi vms deposit the fudotaki and fujimi deposits re os isotope data from the fudotaki deposit yields a model 3 age of 533 13 ma with an initial 187 os 188 os ratio of 0 35 0 20 in contrast re os isotope data from the fujimi sulfide ore did not exhibit a linear correlation suggesting that the re os isotope system there has been disturbed by regional metamorphism of higher grade than the fudotaki deposit as well as contact metamorphism during intrusion of cretaceous granitic rocks although the fudotaki sulfide ores have been metamorphosed to lower epidote amphibolite facies the well defined re os isochron allowed us to interpret the timing of primary sulfide deposition on the paleoseafloor some orebodies of the greater hitachi vms deposit have been estimated to be early carboniferous based on the scarce fossil records and considered to be distributed in the daioin formation but our results revealed that the fudotaki deposit were formed during the cambrian and occurs in the upper akazawa formation which strongly supports the idea that the cambrian beds are widely distributed in the hitachi belt and that a significant unconformity exists between the cambrian and early carboniferous above the fudotaki deposit the cambrian re os date classifies the hitachi vms deposit as the oldest dated ore deposit in japan and in turn provides an insight to understand the geologic framework and genesis of the proto japanese islands and the east asian region

iron rich metalliferous sediments on the east pacific rise prototype of undifferentiated metalliferous sediments on divergent plate boundaries abstract sediments in a zone on the east pacific rise with an especially high spreading rate were studied chemically mineralogically and microscopically they consist of a mixture of metalliferous sediments and plankton tests the metalliferous sediments were formed by an acidic hydrothermal leaching of tholeiitic basalt with seawater and subsequent precipitation in contact with cold near bottom seawater we assume the precipitation from hydrothermal solutions in this part of the east pacific rise to be undifferentiated due to the high spreading rate and the resulting rapid flow on the water through the basalt thus these metalliferous sediments are an initial stage type that have not undergone differentiation mn mo la cu v ni fe zn co and y all of which are leachable in acidic hydrothermal solutions are enriched in the metalliferous sediments in comparison to the tholeiitic basalts zr al and ti on the other hand which under the same conditions are not easily leached are reduced in their concentrations all components of the metalliferous sediments precipitated as hydroxides or as adsorbed ions on the hydroxides of other elements this is due to the oxidizing conditions in the near bottom seawater the sedimentation rate is high the almost 3 m long cores reach only to the late pleistocene the only distinctly observable diagenetic process for this period of time is the formation of goethite from amorphous iron oxides only for na k and rb does it seem possible that a distinct enrichment in the sediments by adsorption from the seawater could have taken place ca sr pb and perhaps sc are primarily bound to the planktonic carbonate part of the sediments

marine os isotopic fluctuations in the early eocene greenhouse interval as recorded by metalliferous umbers from a tertiary ophiolite in japan abstract the mineoka umbers occur within the tertiary accretionary complex of central japan immediately overlying 53 7 ma tholeiitic basalts the associated tholeiitic basalts exhibit typical normal mid ocean ridge basalt n morb type geochemical signatures and are interpreted to be a remnant of tertiary oceanic crust centimeter resolution bulk rock chemical analyses were performed to cover the entire section of the 35 cm thick umber deposit there are striking similarities in major element trace element re and os contents between the umbers and modern metalliferous sediments along the east pacific rise these results demonstrate that the mineoka umbers are ancient counterparts of mor metalliferous sediments that are plume fall out ferromanganese precipitates scavenging various seawater derived elements including p v y rees and os and confirm that the umbers subaerially exposed in the accretionary complex generally preserve their primary geochemical signatures at the time of deposition the marine 187 os 188 os ratios inferred from the mineoka umbers gradually increase up section with moderate fluctuations the 187 os 188 os composition ranging from 0 47 to 0 54 is significantly higher than that of the prior period post paleocene eocene thermal maximum petm 187 os 188 os 0 38 this was probably the result of an increase in the chemical weathering rate of continental crust caused by the long duration of noticeably warm climate during the early eocene greenhouse interval several fluctuations observed in the marine 187 os 188 os record during this interval are most likely related to petm like brief hyperthermals supporting the suggestion that the intensity of continental crustal weathering controlled by climatic changes can fluctuate on timescales of 10 5 yr

the seawater osmium isotope record of south china sea implications on its history and evolution abstract the south china sea is the largest marginal basin in the world and is located in the confluence of three major tectonic plates pacific philippine sea indo australia eurasia its tectonic history and evolution throughout the cenozoic has been the subject of much discussion with regards to its mechanism timing and relationship to neighboring geological features we conducted the first re os isotope study of the south china sea cores recovered from ocean drilling odp ocean drilling program and iodp international ocean discovery program and from philippine oil exploration wells in order to investigate whether or not the basin s tectonic evolution will be reflected in the seawater os isotope record these cores represent the northern and southern conjugate margins of the south china sea and should have complementary records of the tectonic events in the basin we found three important negative anomalies in the south china sea s seawater os isotope record at 35 33 ma 26 23 ma and 13 6 ma which are temporally related to tectono magmatic events at the northern margin the record starts with the lowest 187os 188os i values of 0 37 and 0 32 for the oldest samples which then progresses to more radiogenic values for younger sediments the trend is consistent with the start of seafloor spreading at 33 ma that saw the peak in the flux of mantle derived material which later slowed down until the second peak between 26 and 23 ma however these unradiogenic values also mark the eocene oligocene transition and more likely implies south china sea connectivity to global ocean circulation since pre oligocene in both margins slight to marked decrease in 187os 188os i values deviate from the global trend and coincides with the ridge jump at 23 ma in the southern conjugate margin 187os 188os i show a general decreasing tendency opposite that of the northern margin and the global trend starting from mid to late miocene 13 6 ma mass balance modeling suggests that the two younger negative excursions may be accounted for by mantle and hydrothermal os inputs of 372 mol my at 23 ma and post 13 ma we suggest that the post 13 ma protracted decrease in 187os 188os i values for the southern margin reflects localized input of mantle derived lithogenic os from the luzon arc combined with post spreading magmatic intrusions and possibly gradual changes in paleoceanographic condition at the southern east sub basin

geochemistry of metalliferous hydrothermal deposits in the aeolian arc tyrrhenian sea abstract in shallow water areas of the submerged volcanic complex around the island of panarea aeolian archipelago hydrothermal precipitation of both low temperature fe oxyhydroxide rich red muds and crusts and high temperature sediment hosted massive sulfides was discovered during an integrated high resolution survey iron rich crusts were also found on the bathymetric high of secca del capo north of salina island the exhalative iron rich sediments occur in small closed depressions or in proximity to faults and scarps at water depths ranging from 55 to 285 m the principal chemical characteristics of these deposits are high but variable fe content ranging from 12 2 to 45 and low contents of the transition elements mn cu zn ni and co the low contents of cu ni and co suggest a hydrothermal origin the fe oxyhydroxide deposits are enriched in light rare earth element ree 35 110 chondrite compared to heavy ree 10 25 chondrite their ree patterns are similar to those of associated calc alkaline volcanics negative slope of light ree and a horizontal distribution of the heavy ones this contrasts with the pattern for iron and manganese oxides of hydrogenous origin which have tilted trends of heavy ree paralleling that of seawater the mineralogy of the polymetallic sulfide deposits consists of galena sphalerite pyrite and barite in the form of silt sand grains and decimeter sized fragments disseminated in clay 30 cm below the seabed at a waterdepth of 80 m the chemistry of the aeolian iron rich low temperature deposits and of the high temperature ba rich pb and zn sulfides suggests that they are genetically analogous to respectively the kuroko type iron formation tetsusekiei and the black ore exposed in the miocene hokuroku district of japan

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

magnetostratigraphic data from late quaternary sediments from the yermak plateau arctic ocean evidence for four geomagnetic polarity events within the last 170 ka of the brunhes chron summary palaeomagnetic investigations of two sediment cores recovered from rv polarstern near the eastern slope of the yermak plateau sites ps 1533 and ps 2212 reveal convincing evidence for four polarity events of the earth s magnetic field during the last 170 ka a comprehensive rock magnetic study of the sediments proved that fine grained magnetite is the principal carrier of the remanent magnetization no changes in magneto mineralogy across the polarity transitions in the sediments investigated were found calcareous nannofossil biostratigraphy ams 14c accelerated mass spectrometry and oxygen isotope data and 10be and 230th stratigraphies yielded age ranges of 24 29 ka for the mono lake event 34 43 ka for the laschamp event 72 86 ka for the norwegian greenland sea event and 118 128 ka for the blake event two reverse polarity samples at the base of core ps 2212 3 kal are interpreted as the termination of the biwa i event 171 181 ka the events exhibit full inversion of inclination in both cores the data suggest that the transition process of the earth s magnetic field during such polarity events requires some 1 ka

re os isotopic records in pleistocene loess paleosol sequences from the yili basin northwestern china abstract the re os isotope system is a potentially powerful tool for obtaining information on source regions and transportation processes of aerosols such as mineral dust re os isotopic systematics were studied in two pleistocene loess paleosols exposed at kuerdenengbulake and zeketai in the yili basin northwestern china in the late pleistocene malan loess 187os 188os ratios 0 90 1 45 varied inversely with os abundances 28 61 pg g in the middle pleistocene lishi loess section fluctuations in os abundances 25 50 pg g were accompanied by a limited range of variation in 187os 188os ratios generally 1 21 1 40 four samples of malan loess from the kuerdenengbulake section had higher os concentrations and less radiogenic 187os 188os coupled with higher zoisite tourmaline ratios but uncorrelated with abundances of other minerals paleomagnetic parameters grain size characteristics major element composition or rb sr and sm nd isotopic systematics the correlation between os and zoisite tourmaline ratio suggests that the source material of the loess changed when these samples were deposited but this change was not evident in the other data in this study depth profiles show how re os isotopic compositions varied with age of deposition by characterizing os abundances and 187os 188os ratios of late pleistocene loess paleosol samples in the yili basin local paleoclimatic changes occurring over intervals of several thousand years could be identified that had not been found by traditional paleoclimatic proxies when the 143nd 144nd ratio alone cannot distinguish the provenance of global eolian sediments a combination of 143nd 144nd and 187os 188os can sometimes be effective however for the yili basin s loess paleosol the range of 187os 188os overlapped with ratios in eolian sediments from other areas offering no improvement over 143nd 144nd alone in this respect

high resolution magnetostratigraphy of four sediment cores from the greenland sea ii rock magnetic and relative palaeointensity data summary high resolution magnetostratigraphic analysis of three sediment cores from the base of the volcanic seamount vesteris banken in the greenland basin and one from the jan mayen fracture zone revealed records of three pronounced geomagnetic events the mono lake excursion 28 27 ka the laschamp event 37 33 ka and the biwa i jamaica event 189 179 ka rock magnetic investigations measurements of magnetic susceptibility and arm and irm acquisition demagnetization experiments show that only fine grained titano magnetite 0 5 m is the dominant magnetic carrier mineral in the hemipelagic muds there is no evidence for high amounts of high coercivity minerals like haematite or goethite volcanic basaltic ash layers in sediments around vesteris banken seamount are characterized by extremely high values of magnetic susceptibility reaching 16 000 times 10 6 si as well as by low median destructive fields of the anhysteretic remanent magnetization mdfarm indicating magnetite of larger grain sizes 1 m besides this no significant variation in rock magnetic parameters across intervals of intermediate to reversed chrm inclinations are observed therefore these are interpreted as true records of geomagnetic field variations the recovered sediments characterized by only moderate fluctuations in concentration as well as grain size related rock magnetic parameters provided good conditions for the reconstruction of the relative palaeointensity of the geomagnetic field the recorded geomagnetic events are clearly linked to a drastic reduction in the relative palaeointensity of the field the lowermost values were obtained for the time of the polarity transition with a trend to higher relative intensities in the course of the polarity events event ages and the relative palaeointensity variations based on different methods derived from the greenland sea sediments investigated are in good agreement with data published in the literature

evidence for a geomagnetic excursion recorded in the sediments of lac st front france a link with the laschamp excursion anomalous paleomagnetic directions accompanied by low intensities of natural remanent magnetization are recorded at 17 m depth in the sediments cored from lac st front massif central france the rock magnetic properties and the parameters characterizing anisotropy of susceptibility of samples taken from the sediment horizons carrying these anomalous directions spanning some 30 40 cm are identical to those of samples taken from the other stratigraphic intervals carrying a record of normal geomagnetic secular variation therefore the sequence of anomalous directions is interpreted as a geomagnetic excursion furthermore it is concluded that this excursion occurred at a time when the paleointensity field was low the excursion is dated at about 33 14c 37 ka b p by correlating the susceptibility and paleomagnetic logs from lac st front with the corresponding logs from the nearby lac du bouchet sedimentary sequence the excursional directions in lac st front can be averaged out with a triangular window of 20 cm these smoothed excursional directions resemble the directional variations observed in the corresponding lac du bouchet interval this finding indicates that the absence of this excursion in lac du bouchet may be due to a larger smoothing of the geomagnetic signal

chemostratigraphic evidence of deccan volcanism from the marine osmium isotope record continental flood basalt cfb volcanism is hypothesized to have played a causative role in global climate change and mass extinctions uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of cfb volcanism our results document a 25 decline in the marine 187 os 188 os record that predates the cretaceous tertiary boundary ktb and coincides with late maastrichtian warming we argue that this decline provides a chemostratigraphic marker of deccan volcanism and thus constitutes compelling evidence that the main environmental consequence of deccan volcanism was a transient global warming event of 3 to 5 c that is fully resolved from the ktb mass extinction

ocean wave scattering by natural sea ice transects 1 ocean waves propagate in continuous sea ice as flexural gravity waves so named because their dispersion is influenced by bending of the ice plate and by buoyancy such waves are scattered by topographic heterogeneity in the ice e g features like pressure ridges yet current models fail to account for the complexity that is symptomatic of sea ice here a two dimensional wave scattering model is described that allows real data from natural sea ice to be assimilated rather than synthetic ice terrain on the basis of linear wave theory and the elastic thin plate equation the model assumes an unbroken compliant sea ice cover with no free edges and uses green s functions to obtain an integral equation that is solved numerically while scattering in physical stretches of sea ice can vary greatly all transects behave as low pass filters and can display resonances that relate to how features are separated or to transect length the latter being an undesirable trait of the model in the paper an association is made between the statistical properties of the sea ice terrain and the nature of the scattering that results not unexpectedly sea ice with greater relative draft variation is more reflective it is proposed that this observation can be used to identify the draft variation for an unknown transect if its scattering response is known finally the progression of median energy density for ensembles of similarly sampled transects is examined at wave periods of less than 10 s and is found to decay exponentially with distance traveled in accord with the few observations available

geomagnetic paleointensity for the last 100 kyr from the sub antarctic south atlantic a tool for inter hemispheric correlation abstract we report relative paleointensity proxy records from four piston cores collected near the agulhas ridge and meteor rise south atlantic the mean sedimentation rate of the cores varies from 24 cm kyr to 11 cm kyr the two cores with mean sedimentation rates over 20 cm kyr record positive remanence inclinations at 40 41 ka coeval with the laschamp event age models are based on oxygen isotope data from three of the cores augmented by radiocarbon ages from nearby core rc11 83 and by correlation of paleointensity records for the one core with no oxygen isotope data the relative paleointensity proxy records are the first from the south atlantic and from the high to mid latitude southern hemisphere prominent paleointensity lows at 40 ka and 65 ka as well as many other features can be correlated to paleointensity records of comparable resolution from the northern hemisphere the records are attributable in large part to the global scale field and therefore have potential for inter hemispheric correlation at a resolution difficult to achieve with isotope data alone

origin of felsic volcanism in the izu arc intra arc rift an intra arc rift iar is developed behind the volcanic front in the izu arc japan bimodal volcanism represented by basalt and rhyolite lavas and hydrothermal activity is active in the iar the constituent minerals in the rhyolite lavas are mainly plagioclase and quartz whereas mafic minerals are rare and are mainly orthopyroxene without any hydrous minerals such as amphibole and biotite both the phenocryst and groundmass minerals have felsic affinities with a narrow compositional range the petrological and bulk chemical characteristics are similar to those of melts from some partial melting experiments that also yield dry rhyolite melts the hydrous mineral free narrow mineral compositions and low al2o3 affinities of the iar rhyolites are produced from basaltic middle crust under anhydrous low temperature melting conditions the iar basalt lavas display prominent across arc variation with depleted elemental compositions in the volcanic front side and enriched compositions in the rear arc side the across arc variation reflects gradual change in the slab derived components as demonstrated by decreasing ba zr and th zr values to the rear arc side rhyolite lavas exhibit different across arc variations in either the fluid mobile elements or the immobile elements such as nb zr la yb and chondrite normalized rare earth element patterns reflecting that the felsic magmas had different source the preexisting arc crust formed during an earlier stage of arc evolution most probably during the oligocene prior to spreading of the shikoku back arc basin the lack of systematic across arc variation in the iar rhyolites and their dry shallow crustal melting origin combines to suggest re melting of preexisting oligocene middle crust by heat from the young basaltic magmatism

chlorine 36 evidence for the mono lake event in the summit grip ice core abstract a distinct peak has been discovered in the 36 cl data from the grip ice core between the dansgaard oeschger d o events 6 and 7 at approximately 32 kyr bp this peak can be attributed to a minimum of the geomagnetic dipole field associated with the mono lake event since the 36 cl peak reflects a higher production rate of all cosmogenic radionuclides it has an impact on the 14 c dating of the last ice age furthermore it provides an additional time marker similar to a peak found earlier corresponding to the laschamp event at approximately 39 kyr bp

magnetostratigraphic results from impact crater lake el gygytgyn northeastern siberia a 300 kyr long high resolution terrestrial palaeoclimatic record from the arctic summary a 12 7 m long sedimentary record recovered from lake el gygytgyn located in a meteorite impact crater created 3 6 ma in late cretaceous igneous rocks on chukotka peninsula northeast siberia has been analysed for its palaeo and rock magnetic properties continuous high resolution 1 mm measurements of magnetic susceptibility yielded successions of pronounced lows and highs analyses of the rock magnetic properties by low and high temperature runs of magnetic susceptibility determination of hysteresis parameters as well as irm acquisition experiments yielded a dominance of psd pseudo single domain magnetite in intervals of high magnetic susceptibility whereas due to selective magnetite dissolution associated with anoxic lake water and or pore water conditions during times of enhanced deposition of organic matter haematite dominates within low susceptibility intervals in terms of mass percentage here however magnetic properties are still dominated by magnetite five ams accelerator mass spectromentry 14 c ages eight irsl infrared stimulated luminescense ages together with preliminary pollen data suggest that variations in magnetite content reflect climatic variability of the last 300 ka with low high susceptibilities representing cold warm climates this pattern caused by a complex system of deposition preservation or decomposition of organic matter and or magnetic minerals in turn can be correlated in detail to global climate archives such as the oxygen isotope records from greenland ice cores and marine sediments respectively thus the sedimentary sequence recovered from lake el gygytgyn represents the longest continuous terrestrial climate record now available from the arctic

the early miocene 25 ma volcanism in the northern kyushu palau ridge enriched mantle source injection during rifting prior to the shikoku backarc basin opening the northern kyushu palau ridge kpr remnant conjugate arc of the izu ogasawara bonin mariana ibm active arc is dominated by basalt andesite except for the komahashi daini seamount where acidic plutonic rocks of 38 ma were recovered these mafic to intermediate volcanics are produced by the rifting volcanism in the proto ibm arc associated with spreading of the shikoku basin the hfse and hree contents and ratios of these volcanics indicate enriched source mantle composition compared to recent volcanic front the lile ratios exhibit similar characteristics to reararc volcanism of the recent izu arc and some enriched volcanics exhibit high abundance of sediment melt inputs based on these observations and compilations of the published data set the replacement event of the wedge mantle under the ibm arc occurred two times the first event occurred between 45 and 38 ma with pacific type mantle being replaced by depleted indian type mantle the second event occurred between 36 and 25 ma enriched mantle flowed from reararc side the slab component during the proto ibm arc rifting was a similar characteristic to recent reararc volcanism of the izu arc and sediment melt added in a local area

geochemistry of the margi umbers cyprus and the os isotope composition of cretaceous seawater the major element rare earth element and platinum group element chemistry of the margi umbers have been investigated in order to evaluate these sediments as recorders of past variations in the os isotopic composition of seawater because of the compositional similarity of the margi umbers to metalliferous sediments and hydrothermal plume particles from the modern ocean we conclude that these supraophiolite sediments record the os isotope composition of cretaceous seawater this conclusion requires that the margi umbers have in large part retained their compositional integrity throughout burial diagenesis and subsequent uplift that the 187 os 188 os ratio 0 52 0 55 of ca 90 ma seawater is similar to or more radiogenic than seawater throughout the paleogene provides evidence of decoupling of the marine sr and os isotope records beyond constraining the 187 os 188 os of cretaceous seawater these results are significant in that they provide a set of chemical criteria that can be used to evaluate the potential of other metalliferous sediment sequences as recorders of the 187 os 188 os ratio of ancient seawater establishing these criteria represents an important step toward extending the marine os isotope record into the mesozoic and paleozoic

paleoceanographic conditions on the sao paulo ridge sw atlantic ocean for the past 30 million years inferred from os and pb isotopes of a hydrogenous ferromanganese crust abstract hydrogenous ferromanganese fe mn crusts can provide records of long term environmental changes during the cenozoic to understand the paleoceanographic conditions in the southwestern atlantic ocean we investigated depth profiles of major and trace element concentrations as well as os and pb isotopic compositions in a fe mn crust collected from the southern flank of the sao paulo ridge in the southwestern atlantic major and trace element data plotted on ternary mn fe 10 ni co cu and rare earth element plus yttrium rey discrimination diagrams indicate that the analyzed sample is a typical hydrogenous fe mn crust the obtained 187 os 188 os data were matched to the cenozoic seawater os isotope evolution curve reconstructed from pelagic sediments the result suggests that the fe mn crust has accreted over 30 myr with growth rates of 0 5 3 mm myr although the sample likely grew in two directions during the early stage of its growth we found no evidence of growth hiatus in the sample which may contrast with the growth histories of many pacific fe mn crusts hence the conditions favorable for the accretion of hydrogenous fe mn crusts were likely to have developed on the sao paulo ridge over the past 30 myr the pb isotopic compositions show very limited ranges e g 206 pb 204 pb 18 80 18 85 and are similar to those of pre anthropogenic seawater in the southern ocean as the sao paulo ridge is located near the vema channel which is presently a major path of antarctic bottom water we suggest that a strong northward bottom current has continuously swept detrital and biogenic sediments from the ridge and played a vital role in the fe mn crust formation since 30 ma

enhanced cosmic ray production of 10be coincident with the mono lake and laschamp geomagnetic excursions the cosmogenic isotope 10 be total be and al were measured in partly varved sediments from the upper 50 m of core 480 leg 64 dsdp gulf of california the concentration of 10 be from 1 to 50 kyr is in general agreement with estimates of the geomagnetic dipole moment obtained from archaeomagnetic and marine core research 10 be anomalies were also found at 32 kyr and 43 kyr contemporaneous with the mono lake and laschamp excursions respectively the production of 10 be required to explain these anomalies is too high particularly for the mono lake excursion to be produced by a combination of decreased geomagnetic field and unprecedented long term solar activity we conclude that the cause is a change in the galactic cosmic ray flux consistent with a supernova event the coincidence with the two excursions remains a paradox

interelement relationships in ferromanganese crusts from the central pacific ocean their implications for crust genesis the fine scale chemical variations in ferromanganese fe mn crusts from the central pacific ocean were investigated using a variety of techniques in order to elucidate their genesis thirty seven major minor and trace elements were determined by icp oes and icp ms in sub samples collected at approximately 2 mm intervals throughout the crust sequences an inverse relationship is observed between the logarithm of the elemental distribution coefficients log cmncsw and the mean residence time tr of elements in seawater these associations provide evidence supporting the strong link between seawater and fe mn crust chemistry results of factor analysis reveal that elements in crusts can generally be partitioned into four major groups with selected elements displaying associations with several groups these statistical associations are interpreted to represent hydrogenetic mn ni co cu ce zn biogenic ba zn cu pt fe detrital al si fe and carbonate fluorapatite ca p ree groups a comparison between elemental associations in fine scale data from individual crust sequences and bulk compositional data from samples collected in separate locations reveals very similar elemental associations the similar elemental associations in bulk samples and in fine scale subsamples from individual crusts are consistent with the notions that hydrogenetic crusts exhibit no significant post depositional remobilization of elements and that elemental distributions within crusts reflect the chemistry of oceanic water during the period in which they accreted chemical paleotracks are proposed based on factor scores derived from chemical variations as a function of depth in individual crusts our results show that there is internal consistency between the chemical evolution previously proposed seamount paleotracks and nanofossil biostratigraphy dating results

variations of the187os 186os ratio of seawater over the past 28 million years as inferred from metalliferous carbonates abstract the os concentration and isotopic composition of metalliferous carbonates deposited on the east pacific rise over the past 28 ma are reported with complimentary sr isotope data variations in the os isotopic composition of these samples are interpreted as a record of past changes in the os isotopic composition of seawater these results are consistent with isotopic analyses of leachable os in pelagic clays which have also been interpreted as a record of the187os 186os ratio of seawater through time 1 the metalliferous carbonate record clearly shows that seawater os and sr isotope systems are partially decoupled from one another over the past 28 ma accelerated weathering of ancient organic rich sediments is suggested as a possible mechanism to account for this decoupling and the rapid increase in the187os 186os ratio of seawater over the past 15 ma this rapid increase suggests that the seawater os record can potentially be used as a stratigraphic tool in some neogene marine deposits

paleomagnetic constraints on sedimentation ratesin the eastern arctic ocean abstract deep sea sediments recovered from six sites visited during the international arctic ocean expedition of 1991 were examined to determine sedimentation rates in the eastern arctic ocean basin the dearth of age diagnostic biogenic material in these sediments precludes the application of biostratigraphic methods but ages can be deduced using paleomagnetism in conjunction with measurements of radiocarbon and carbonate concentration although no one of these techniques gives an unambiguous determination of age the interpretation most consistent with these diverse data implies that sedimentation rates in the eastern arctic are in general a few centimeters per thousand years such estimates of sedimentation rate are an order of magnitude greater than those previously determined from many sediment cores taken from the canada basin however one site examined on the morris jesup rise shows a relatively low rate of sediment accumulation less than 0 6 cm 103yr suggesting that although higher than in the canada basin sedimentation rates in the eastern arctic can be highly variable

chronology and correlation of quaternary magnetostratigraphy and nannofossil biostratigraphy in norwegian greenland sea sediments paleomagnetic analyses of a series of sediment cores from the norwegian greenland sea document the existence of seven short lived geomagnetic events during the last about 500 000 years calcareous nannofossil biostratigraphy correlated to oxygen isotope chronostratigraphy provides a time framework to infer age and duration of these periods of extreme divergence of the earth s magnetic paleofield from the regular normal polarity configuration of the brunhes chron the geomagnetic events typically extend over 5 to 10 kyr two events are observed within the oxygen isotope stage 2 4 interval a short event is recorded at the stage 4 5 boundary and another just below the stage 5 6 boundary additional three geomagnetic events are identified in oxygen isotope stage 6 at the stage 9 10 boundary and near the top of oxygen isotope stage 13 respectively

magnetostratigraphy in three arctic ocean sediment cores arguments for geomagnetic excursions within oxygen isotope stage 2 3 two zones with shallow to steep negative palaeomagnetic directions have been detected within similar lithological units in three high latitude gravity cores from the arctic ocean coinciding azimuthal distributions of declinations relative to arbitrary oriented sub sampling surfaces are attributed to the systematic acquisition of magnetic components by frictional deformation of the unconsolidated sediment during the sub sampling procedure alternating field demagnetization to 50 mt was only partly successful in obtaining stable single component directions magnetic polarity zones are deduced by extrapolation of directional trends of inclinations during progressive af demagnetization high delta 18o values in sinistrally coiled n pachyderma range between 4 30 4 68 pdb mean values reflecting sediment accumulation during continental glaciation amino acid ratios of n pachyderma suggest ages less than approximately 60 000 years ago when seen in conjunction these observations suggest that the sediments were deposited within oxygen isotope stages 2 3 the reversed palaeomagnetic polarity zones are concluded to represent two short duration excursions of the geomagnetic field which occurred less than 60 000 years ago likely known candidates are the lake mungo 28 000 30 000 years ago and laschamp olby 35 000 40 000 years ago excursions all confined within oxygen isotope stage 3 24 000 59 000 years ago

molybdenum isotopes in hydrothermal manganese crust from the ryukyu arc system implications for the source of molybdenum abstract a high concentration of molybdenum mo is a striking feature of modern marine hydrothermal manganese mn crusts from both low and high temperature hydrothermal systems however the origin of that mo is poorly constrained in this study we analyzed mo isotopic composition 98 95mo in a mn crust collected from the ryukyu arc system and assessed the possible use of 98 95mo to constrain the origin of mo in hydrothermal mn crusts along with mo isotope analysis we also measured the abundance of major and trace elements and the re os isotopic composition the mn crust sample had a high mn content 42 47 and was low in fe 0 2 0 5 among the manganophile elements co ni cu zn and mo only mo showed high concentrations 550 ppm we also found low contents of os 35 ppt with an isotopic composition of 187os 188os 1 00 these results are consistent with previously reported chemical compositions of hydrothermal mn crusts 98 95mo values in the sample ranged from 0 56 to 0 66 which are 2 7 lighter than the present day seawater 98 95mo but similar to those in modern hydrogenous fe mn crusts and mn nodules although current data do not preclude the possible contribution of hydrothermally derived mo the light 98 95mo values can be explained by isotope fractionation associated with a change in coordination number during the adsorption of mo from seawater onto mn oxides we suggest that the 98 95mo data are useful for constraining the source of mo in hydrothermal mn crusts

the importance of independent chronology in integrating records of past climate change for the 60 8 ka intimate time interval this paper provides a brief overview of the most common dating techniques applied in palaeoclimate and palaeoenvironmental studies including four radiometric and isotopic dating methods radiocarbon 230th disequilibrium luminescence cosmogenic nuclides and two incremental methods based on layer counting ice layer varves for each method concise background information about the fundamental principles and methodological approaches is provided we concentrate on the time interval of focus for the intimate integrating ice core marine and terrestrial records community 60 8 ka this dating guide addresses palaeoclimatologists who aim at interpretation of their often regional and local proxy time series in a wider spatial context and therefore have to rely on correlation with proxy records obtained from different archives from various regions for this reason we especially emphasise scientific approaches for harmonising chronologies for sophisticated and robust proxy data integration in this respect up to date age modelling techniques are presented as well as tools for linking records by age equivalence including tephrochronology cosmogenic 10be and palaeomagnetic variations finally to avoid inadequate documentation of chronologies and assure reliable correlation of proxy time series this paper provides recommendations for minimum standards of uncertainty and age datum reporting

post drilling changes in fluid discharge pattern mineral deposition and fluid chemistry in the iheya north hydrothermal field okinawa trough 1 the integrated ocean drilling program iodp expedition 331 investigated the iheya north hydrothermal field in the okinawa trough several post drilling underwater vehicle investigations were conducted over 2 years to identify post drilling changes in fluid discharge pattern mineral deposition and fluid chemistry drilling induced high temperature hydrothermal fluid vents were identified at deep holes not only near the naturally occurring nbc hydrothermal fluid vent site c0016 but also at the seafloor 450 m distal to the nbc vent site c0014 where no hydrothermal fluid discharge was observed prior to drilling a chimney structure at hole c0016a grew rapidly at the nbc mound crest where only small chimneys had been found before drilling a drilling induced diffuse hydrothermal flow region spread at site c0014 and this area was newly colonized by the galatheid crab from a fluid chemistry perspective the post drilling hydrothermal fluids were enriched in cl relative to seawater although this fluid chemistry was not observed during the 12 years prior to drilling the cl enriched fluid reservoir underlying the subseafloor impermeable layers observed by iodp expedition 331 is likely source for the cl enriched fluids discharging from the post drilling vents the drilling induced physical disturbance of subseafloor hydrogeological structures would release such fluids to the seafloor in turn the rapid chimney growth at the nbc mound crest may also be attributed to highly turbulent fluid flow with the enlarged artificial vent of hole c0016a which can contribute to the retention of the fluid seawater mixture for a sufficiently long period to precipitate sulfide sulfate minerals on the seafloor

deposition of osmium and other platinum group elements beneath the ultramafic hosted rainbow hydrothermal plume osmium and other platinum group elements pges have been measured in sediments accumulating directly under the rainbow hydrothermal plume at 36 deg n on the mid atlantic ridge 187os 188os and pge concentrations in the sediments of four cores taken 2 25 km from the active vent site reveal evidence of both radiogenic os scavenged from seawater and importantly unradiogenic os released by hydrothermal venting the majority of analyses n 16 yield 187os 188os ratios that fall in a narrow range 0 99 1 06 close to that of modern seawater in these samples os concentrations correlate linearly with hydrothermal v enrichments which are also derived from seawater scavenging a smaller subset of samples characterized by unusually high concentrations of ni and cr derived from ultramafic rock fragments exhibit distinctly lower 187os 188os ratios their ir content is also higher and their pge ratios are more similar to mantle material than the pge patterns of the larger set of samples dominated by seawater scavenged os although the two most proximal cores lack evidence for any similar ultramafic detritus in their surficial sediments 187os 188os ratios in these samples are also lower than that of ambient seawater suggesting they are likely to have been influenced by unradiogenic os from vent fluid incorporated into the plume samples from the most distal core by contrast exhibit 187os 188os ratios indistinguishable from that of seawater compared with background ne atlantic sediments os is enriched four fold in the seawater dominated samples while pd pt and ir are twice the background value burial fluxes of os scavenged by hydrothermal fe in these sediments are 200 400 pg cm 2 kyr 1 up to twice that found on the epr and several times the background bg of 50 pg cm 2 kyr 1 for pt burial fluxes are 1800 3000 pg cm 2 kyr 1 bg ca 1000 pg cm 2 kyr 1 and for pd 2700 4600 pg cm 2 kyr 1 bg ca 800 pg cm 2 kyr 1

geomagnetic field excursion recorded 17 ka at tianchi volcano china new 40ar 39ar age and significance new 40ar 39ar dating of a comenditic lava atop tianchi volcano china indicates eruption at 17 1 0 9 ka the flow interior records a pair of transitional virtual geomagnetic poles and a low paleointensity of 25 t thus it records a geomagnetic field excursion that is younger than the 41 ka laschamp or 32 ka auckland excursions implications are 1 following a repose of several tens of kyr tianchi volcano became highly active immediately following termination of the last glaciation maximum the flare up of silicic eruptions may reflect rapid deglaciation of the edifice 2 a 17 ka age for the tianchi excursion provides the first direct radioisotopic evidence that excursional behavior which is imprecisely dated and less well documented magnetically at several other sites is a global feature of geodynamo behavior 3 during the brunhes chron 13 well dated excursions cluster into two periods including seven between 17 and 212 ka and six between about 530 and 730 ka

the marine osmium isotope record over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research several analytical developments particularly in the past few years have significantly increased our ability to study the behaviour of osmium in the surficial environment the 187os 188os and osmium concentration of seawater river water rain and hydrothermal vent fluids have been measured directly recently the behaviour of osmium in estuaries critical for estimating the marine residence time of osmium has been studied our knowledge of the surficial osmium cycle has thus significantly improved in addition reconstructions of past variations in the marine 187os 188os recently have been extended back into the mesozoic this review attempts to summarize our current understanding of the marine osmium system present and past the 187os 188os of seawater during the cenozoic to first order mimics the marine 87sr 86sr record it is therefore tempting to interpret both records as reflecting increased input of radiogenic osmium and strontium resulting from enhanced continental weathering regulated by climatic tectonic processes however the marine osmium isotope system differs fundamentally from the marine strontium isotope system this review emphasizes three important differences first large impacts are capable of resetting the 187os 188os to unradiogenic values without significantly affecting the marine strontium system second organic rich sediments are characterized by high 187re 188os resulting 187os 188os ingrowth trajectories are similar to the average slope of the cenozoic 187os 188os seawater record trends towards more radiogenic 187os 188os seawater therefore can be caused by weathering of organic rich sediments at a constant rate third the marine residence time of osmium is sufficiently short to capture short periodic glacial interglacial fluctuations that are inaccessible to the buffered marine strontium isotope system this offers the opportunity to discriminate between high frequency climatic and low frequency tectonic forcing

approximations to wave scattering by an ice sheet of variable thickness over undulating bed topography an investigation is carried out into the effect on wave propagation of an ice sheet of varying thickness floating on water of varying depth in three dimensions by deriving a variational principle equivalent to the governing equations of linear theory and invoking the mild slope approximation in respect of the ice thickness and water depth variations a simplified form of the problem is obtained from which the vertical coordinate is absent two situations are considered the scattering of flexural gravity waves by variations in the thickness of an infinite ice sheet and by depth variations and the scattering of free surface gravity waves by an ice sheet of finite extent and varying thickness again incorporating arbitrary topography numerical methods are devised for the two dimensional versions of these problems and a selection of results is presented the variational approach that is developed can be used to implement more sophisticated approximations and is capable of producing the solution of full linear problems by taking a large enough basis in the rayleigh ritz method it is also applicable to other situations that involve wave scattering by a floating elastic sheet

major and trace element geochemistry and os isotopic composition of metalliferous umbers from the late cretaceous japanese accretionary complex 1 metalliferous umbers and red shales occur as unique products of the kula pacific ridge forearc collision in the late cretaceous shimanto supergroup an accretionary complex in japan these umbers are closely associated with greenstones of mid ocean ridge basalt morb origin and are regarded as hydrothermal metalliferous precipitates related to mor type volcanism the umbers and red shales were deposited in the trench area where both terrigenous detritus from land and hydrothermal metalliferous particulates from a mor were supplied simultaneously besides a predominance of fe and mn the umbers exhibit remarkable enrichments in p v co ni zn y mo rare earth elements rees and os relative to continental crustal abundances the x fe x mn p v co ni zn y and rees ratios and paas normalized ree patterns of the umbers are very similar to those of modern hydrothermal plume fallout precipitates deposited on flanks of mor this indicates that the umbers preserve primary geochemical signatures of hydrothermal metalliferous sediments that scavenged seawater derived elements and thus can be used as a proxy for late cretaceous seawater the marine 187os 188os ratios reconstructed from the late maastrichtian umbers range from 0 42 to 0 56 and are very consistent with recent data obtained from the pacific and atlantic pelagic carbonates that record an abrupt decline from 0 55 to 0 4 during the period between 67 0 ma and 65 7 ma

varying responses to indian monsoons during the past 220 kyr recorded in deep sea sediments in inner and outer regions of the gulf of aden although the climate in the arabian sea is controlled primarily by the southwest monsoon the southwest monsoon has little influence in the gulf of aden to examine the different responses to monsoons between the gulf of aden and areas outside the gulf a comprehensive data set of bulk organic and inorganic geochemistry sea surface temperature and 15n of pheopigments was obtained from deep sea sediment cores recovered from inner and outer regions of the gulf the results indicated that during the past 220 kyr the influence of the southwest monsoon was stronger in the outer region of the gulf than in the inner region which implies that the southwest monsoon trajectory has not changed substantially during that time period furthermore influxes of o2 depleted water from the southern ocean and the lateral advection of upwelled seawater also had limited influence in the inner region in contrast concentrations of lithogenic materials transported by the southwest monsoon were similar in the two regions 15n of pheopigments indicated that during the last glacial maximum the southwest monsoon was weaker and the northeast monsoon was stronger than at present a stronger southwest monsoon during interglacials enhanced primary productivity and may have caused anoxic conditions to develop in the arabian sea as indicated by redox proxies in the outer region anoxic conditions also formed during mis 3 but no increase in the primary productivity is indicated therefore another mechanism such as an influx of o2 depleted water from the southern ocean may have been the cause

hydrothermal scavenging at the mid atlantic ridge modification of trace element dissolved fluxes abstract we have carried out an icp ms study of the distributions of trace elements fe ca mg al mn cu zn v as cr co pb y mo ag sn cd and be in particulate material collected from the tag hydrothermal plume 26 n mid atlantic ridge to examine the extent to which fluxes of dissolved trace elements emitted from hydrothermal vent fluids are balanced by the precipitation of associated particulate phases comparison of particulate trace element distributions with particulate fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes i co precipitation from vent fluids ii scavenging from seawater and iii preferential settling from the plume and oxidative dissolution within the water column for y and be continuous scavenging from seawater appears to be important whereas for v as and cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume from a comparison of trace element fe ratios in the particles and associated mid atlantic ridge vent fluids it appears that for many elements e g cu co ag pb al cd be and zn the flux of dissolved material from vent fluids is matched closely by the precipitation of hydrothermal particulate phases of the various elements studied here hydrothermal activity only appears to act as a significant source for dissolved ca and dissolved mn

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

redox conditions in the atmosphere and shallow marine environments during the first huronian deglaciation insights from os isotopes and redox sensitive elements article history the paleoproterozoic 2 5 2 0 ga is one of the most important periods in earth s history and was characterized by a rise in atmospheric oxygen levels and repeated at least three severe glaciations the huronian glaciations in this study we investigate redox conditions in the atmosphere and in shallow marine environments immediately after the first huronian glaciation based on the isotopic composition of os and the abundance of redox sensitive elements os re and mo in sedimentary rocks from the huronian supergroup canada we found no significant authigenic enrichment of os in the sedimentary rocks deposited during the first huronian deglaciation the initial isotopic composition of os in the sediments was close to that of chondrite at the time of deposition 187 os

re os geochronology of the iimori besshi type massive sulfide deposit in the sanbagawa metamorphic belt japan abstract besshi type cu deposits are strata bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents although there are numerous besshi type deposits in the sanbagawa metamorphic belt japan their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints we report re os data for the iimori deposit one of the largest besshi type deposits in western kii peninsula in order to examine the robustness of the re os isotope system for dating sulfide minerals in the high p t metamorphic belt and to elucidate the primary depositional environment of the iimori sulfide ores an 11 point re os isochron plot yields an age of 156 8 3 6 ma as this re os isochron age is significantly older than the timing of the sanbagawa peak metamorphism 110 120 or 90 ma and a well defined isochron was obtained the re os age determined here is most likely the primary depositional age despite high grade metamorphism at up to 520 25 c and 8 9 5 kbar the re os isotope system of the iimori sulfides was not disturbed hence we consider that the whole rock re os closure temperature for the iimori sulfide ores was probably higher than 500 c as the accretion age of the sanbagawa metamorphic belt is considered to be 120 130 or 65 90 ma on the basis of radiolarian and radiometric ages we estimated the time from the iimori sulfide deposition on the paleo seafloor to its accretion at the convergent plate boundary to be greater than 25 myr consequently the depositional environment of the iimori sulfide ores was not in the marginal sea but was truly pelagic

geomagnetic intensity and inclination variations at hawaii for the past 98 kyr from core soh 4 big island a new study and a comparison with existing contemporary data abstract reliable thellier thellier paleointensity determinations were obtained from 321 out of 766 examined samples from the upper 200 units 675 m of core soh 4 drilled in the kilauea volcano the main trend of the soh 4 record is a marked decrease from values higher than present in the last 4 kyr to values about 40 smaller from about 20 kyr to the bottom of the sampled interval three main lows coinciding with shallow or negative inclinations observed in the record were identified with an excursion previously documented in hawaii and the mono lake and laschamps events for the last 15 kyr the soh 4 intensities are largely in agreement with the worldwide distribution of volcanic data in the 15 75 kyr interval the general lack of volcanic data makes comparison with the soh 4 data difficult the soh 4 record is similar to a composite record of paleointensity largely based on a recent north atlantic sedimentary paleointensity stack napis 75 the soh 4 record is also generally consistent with a record of geomagnetic field intensity obtained from a study of 36 cl in the grip ice core calculated with the assumption that the production rate of 36 cl is controlled only by the geomagnetic field one pronounced discrepancy between the different records is observed around 50 kyr bp when the sedimentary and cosmogenic based records document high intensities which are not observed in soh 4 these high intensities are also absent in a recent record based on the analyses of sea floor magnetic anomalies the histogram of vadms obtained from soh 4 is different from that obtained from the sedimentary or 36 cl based records and is more skewed than the distribution given by kono and tanaka for the last 2 5 million years

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

uptake and fractionation of rare earth elements on hydrothermal plume particles at 9 45 n east pacific rise abstract particulate samples 0 45 m from a neutrally buoyant hydrothermal plume at 9 45 n on the northern east pacific rise were collected using large volume in situ filtration and analyzed for fe al mn ni and fourteen rare earth elements ree the sm fe ratio a proxy for overall ree fe and nd er light heavy ree fractionation increased moderately with decreasing particulate fe chemically the sense of these relationships matched that documented previously in the tag plume on the mid atlantic ridge german et al 1990 although particulate fe was about 10 fold lower at 9 45 n spatial trends relative to the vent source however were opposite of expectation because slow fe ii oxidation and fe iii colloid aggregation over this interval led to increased particulate fe 10 26 nm with distance from source field and sherrell submitted after subtraction of non plume background particle composition plume particles at 9 45 n and tag had indistinguishable ranges of light ree enriched fractionation relative to ambient seawater and had very similar sm fe therefore kd for fe oxyhydroxides demonstrating that plume particles in both oceans reflect to a first degree the local seawater ree composition within plume ree variations at 9 45 n were investigated using a simple mixing model which accounts for the bulk fe al mn variations in the plume using two endmembers fresh hydrothermal oxyhydroxide precipitates and ridge crest background particles composed largely of locally resuspended sediment sm fe and nd er plot linearly with mixing ratio r 0 96 implying that the observed ree trends result from mixing of these two endmembers extrapolation to the composition of pure hydrothermal precipitates suggests that nd er is fractionated relative to seawater by a factor of 1 8 during adsorption onto fresh fe oxyhydroxide particles the ridge crest background particles are 5 fold higher in sm fe and nd er is 2 49 relative to seawater partly a result of enriched terrigenous component in the resuspended matter a reinterpretation of ree at tag reveals that positive curvature in ree vs fe plots argued previously to reflect continuous ree uptake i e increasing kd german et al 1990 may result from local depletion of the dissolved ree pool by partitioning onto fe particles at fe 100 nm similar drawdown effects could contribute to the variable degrees of curvature observed for all seawater source particle reactive species in plumes that are sampled at high particulate fe concentration in sum ree behavior in hydrothermal plumes is more consistent with equilibrium adsorption and mixing of distinct particle types than with kinetic uptake control precise measurements of rees in modern ridge crest metalliferous sediments could be compared to the endmember composition calculated from the plume data to evaluate long term changes in ree of the hydrothermal component

uranium in iron formations and the rise of atmospheric oxygen abstract the concept of the great oxidation event goe during which atmospheric oxygen rose precipitously and perhaps to near modern levels around 2 4 2 1 billion years ago ga has become entrenched in our views on secular atmospheric evolution multiple proxies confirm a permanent shift towards more oxygenated conditions at some time near the archean proterozoic boundary however it remains unclear precisely when this transition occurred due in part to the likely temporal variability in those early levels and different sensitivities of the proxies utilized to track atmospheric oxygen partial pressures here we provide a new look at the timing and magnitude of early atmospheric oxygenation through the record of uranium u concentrations in iron formations if just as if are important archives of the redox state of seawater concentrations of redox sensitive u in if are faithful proxies for oxidative continental weathering and associated delivery of dissolved u to seawater our dataset suggests that there was an increase in u redox cycling and transport at ca 2 47 ga just before the permanent loss of mass independent sedimentary sulfur isotope anomalies traditionally used to define the onset of the goe further there is significant temporal variability in the if u record that we propose reflects dynamic precambrian redox conditions we provide additional support for earlier suggestions that the goe was a protracted event marked by vacillating oxygen levels

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

exploring former subglacial hodgson lake antarctica paper ii palaeolimnology direct exploration of subglacial lakes buried deep under the antarctic ice sheet has yet to be achieved however at retreating margins of the ice sheet there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered one of these lakes hodgson lake 72 00 549 s 068 27 708 w has emerged from under more than 297 465 m of glacial ice during the last few thousand years this paper presents data from a multidisciplinary investigation of the palaeolimnology of this lake through a study of a 3 8 m sediment core extracted at a depth of 93 4 m below the ice surface the core was dated using a combination of radiocarbon optically stimulated luminescence and relative palaeomagnetic intensity dating incorporated into a chronological model stratigraphic analyses included magnetic susceptibility clast provenance organic content carbonate composition siliceous microfossils isotope and biogeochemical markers based on the chronological model we provisionally assign a well defined magnetic polarity reversal event at ca 165 cm in the lake sediments to the mono lake excursion ca 30 34 ka whilst osl measurements suggest that material incorporated into the basal sediments might date to 93 9 ka four stratigraphic zones a d were identified in the sedimentological data the chronological model suggests that zones a c were deposited between marine isotope stages 5 2 and zone a during stage 1 the holocene the palaeolimnological record tracks changes in the subglacial depositional environment linked principally to changing glacier dynamics and mass transport and indirectly to climate change the sediment composition in zones a c consists of fine grained sediments together with sands gravels and small clasts there is no evidence of overriding glaciers being in contact with the bed reworking the stratigraphy or removing this sediment this suggests that the lake existed in a subglacial cavity beneath overriding lgm ice in zone d there is a transition to finer grained sediments characteristic of lower energy delivery coupled with a minor increase in the organic content attributed either to increases in allochthonous organic material being delivered from the deglaciating catchment a minor increase in within lake production or to an analytical artefact associated with an increase in the clay fraction evidence of biological activity is sparse total organic carbon varies from 0 2 to 0 6 and cannot be unequivocally linked to in situ biological activity as comparisons of 13c and c n values with local reference data suggest that much of it is derived from the incorporation of carbon in catchment soils and gravels and possibly old co2 in meteoric ice we use the data from this study to provide guidelines for the study of deep continental subglacial lakes including establishing sediment geochronologies determining the extent to which subglacial sediments might provide a record of glaciological and environmental change and a brief review of methods to use in the search for life

a three dimensional model of wave attenuation in the marginal ice zone 1 a three dimensional model of wave scattering by a large array of floating thin elastic plates is used to predict the rate of ocean wave attenuation in the marginal ice zone in terms of the properties of the ice cover and the incoming wavefield this is regarded as a small step toward assimilating interactions of ocean waves with areas of sea ice into oceanic general circulation models numerical results confirm previous findings that attenuation is predominantly affected by wave period and by the average thickness of the ice cover it is found that the shape and distribution of the floes and the inclusion of an archimedean draft has little impact on the attenuation produced the model demonstrates a linear relationship between ice cover concentration and attenuation an additional study is conducted into the directional evolvement of the wavefield where collimation and spreading can both occur depending on the physical circumstances finally the attenuation predicted by the new three dimensional model is compared with an existing two dimensional model and with two sets of experimental data with the latter producing convincing agreement

a new and prospective resource for scandium evidence from the geochemistry of deep sea sediment in the western north pacific ocean abstract scandium is a critical element in state of the art green technologies however it is also extremely expensive due to its scarcity recently some deep sea sediments that contain significant amounts of rare earth elements that are indispensable to modern industries have been discovered in the western north pacific ocean and the concentration of sc in these sediments is comparable with that of land based mines a simple leaching experiment has demonstrated that up to 70 of sc in these sediments contained within biogenic calcium phosphate particles can be recovered in 5 min using dilute acids on the basis of available core samples we propose that a promising target area to mine sc is along a west east transect between longitudes 153 30 e and 154 00 e at an approximate latitude of 21 58 n depending on the depth of the most enriched sediment layer just 1 km2 of the sediment could potentially yield 3 3 6 6 times the current global annual consumption of sc because these sediments contain an unusually high concentration at commercial quantities of industrially important heavy rare earth elements apart from sc they could be a productive source for the long term extraction of these critical metals

os pb and nd isotope geochemistry of the permian emeishan continental flood basalts insights into the source of a large igneous province abstract the nature of the source of continental flood basalts cfb is a highly debated topic proposed mantle sources for cfbs including both high and low ti basalts include subcontinental lithospheric mantle sclm asthenospheric mantle and deep plume related mantle re os isotope systematics can offer important constraints on the sources of both ocean island basalts oib and cfb and may be applied to distinguish different possible melt sources this paper reports the first re os isotope data for the late permian emeishan large igneous province lip in southwest china twenty one cfb samples including both low and high ti basalts from five representative sites within the emeishan lip have been analyzed for os nd and pb isotopic compositions the obtained os data demonstrate that crustal assimilation affected os isotopic compositions of some emeishan basalt samples with low os concentrations but not all of the samples and the emeishan basalts with high os contents likely experienced the least crustal contamination the low and high ti basalts yield distinct os signatures in terms of 187os 188os and os content the low ti basalt with the highest os concentration 400 ppt has a radiogenic os isotopic composition os t 6 5 similar to that of plume derived oib because the os isotopic composition of basalts with relatively high os concentrations typically 50 ppt likely represents that of their mantle source this result implies a plume derived origin for the low ti basalts on the other hand the high ti basalts with high os concentration over 50 ppt have unradiogenic os isotopic signatures os t values range from 0 8 to 1 4 suggesting that a subcontinental lithosphere mantle sclm component most likely contributed to the generation of these magmas combining pb and nd isotopic tracers with the os data we demonstrate that the low ti basaltic magmas in the emeishan cfb were mainly sourced from a mantle plume reservoir whereas the high ti basaltic magmas were most likely derived from a sclm reservoir or were contaminated by a significant amount of lithospheric mantle material during plume related magma ascent through the sclm

a multiproxy approach to reconstruct the environmental changes along the eurasian continental margin over the last 150 000 years abstract sediment cores located along the eurasian continental margin arctic ocean have been studied to reconstruct the environmental changes in terms of waxing and waning of the barents kara sea ice sheets atlantic water inflow and sea ice distribution over the last 150 kyr the stratigraphy of the cores is based on stable oxygen isotopes ams 14 c and paleomagnetic data we studied variations in marine and terrigenous input by a multiproxy approach involving direct comparison of sedimentological and organo geochemical data extensive episodes of northern barents sea ice sheet growth during marine isotope stages mis 6 and 2 have been supported by at least subsurface atlantic water inflow moisture bearing storms low summer insolation and minimal calving of ice ice advance during mis 4 was probably restricted to the shallow shelf between mis 4 and mis 2 large ice sheet fluctuations correspond to contemporary laurentide surging events and indicate short term climatic changes in the arctic ocean as has been recorded in lower latitudes in contrast in low precipitation areas in eastern eurasia glacial activity was rather limited only distinct ice rafted debris ird input during termination ii and early mis 3 reflects severe glaciations on the northern severnaya semlya margin during mis 6 and mis 4 we conclude that 1 oscillations of ice sheets are less frequent along the eastern eurasian margin than in areas with continuous moisture supply like the western eurasian margins and that 2 major fluctuations of the kara sea ice sheet during the last 150 kyr apparently followed the major interglacial glacial mis 5 4 and mis 7 6 transitions rather than the precession 23 kyr and the tilt 41 kyr cyclicity of the earth s orbit as observed for the scandinavian sis and the svalbard ice sheets respectively mangerud j jansen e landvik j y 1996 late cenozoic history of the scandinavian and barents sea ice sheets in solheim a riis f elverhoi a faleide j j jensen l n cloetingh s eds impact of glaciations on basin evolution data and models from the norwegian margins and adjacent basins global and planetary chance special issue 12 pp 11 26 surface and or subsurface atlantic water masses coupled with seasonally ice free conditions penetrated continuously to at least the franz victoria trough during the last 150 kyr however sustained periods of open water were largely restricted to substages 5 5 5 1 and the holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter mom signals of periodic open water conditions along the northern margin of severnaya semlya are of less importance higher production of foraminifera probably due to atlantic water inflow occurred between 38 and 12 14 c kyr and corresponds to periodic atlantic water advection penetrating into the arctic ocean however marine organic proxies indicate a continuous decrease of surface water productivity from the western to the eastern eurasian continental margin due to a more extensive sea ice cover over the last 150 kyr

late pleistocene geomagnetic excursion in icelandic lavas confirmation of the laschamp excursion in 1980 kristjansson and gudmundsson 1 reported a late glacial geomagnetic excursion in three hills in the reykjanes peninsula iceland with shallow negative inclinations and westerly declinations they named it the skalamaelifell excursion more extensive field work has identified the same excursional paleomagnetic direction declination 258 inclination 15 at four additional outcrops in a 10 10 km area in the reykjanes peninsula the excursion lavas are olivine tholeiites with similar petrography and chemical compositions paleointensity determinations by the thellier method average 4 2 0 2 t for 8 samples more than an order of magnitude weaker than the present geomagnetic field in iceland together these results suggest extrusion of the excursion lavas in a very brief span of time probably less than a few hundred years kar dating of the excursion lavas gives a mean age for 19 determinations of 42 9 7 8ka 2 compilation of thirty kar ages of the laschamp and olby flows by three laboratories yield a new age for the laschamp excursion in france of 46 6 2 4ka 2 the age of the excursion in southwestern iceland is statistically indistinguishable from the laschamp excursion at the 95 confidence level and both have very low paleointensities therefore we suggest that the laschamp and olby flows in france and the skalamaelifell units of iceland recorded essentially the same geomagnetic excursion differences in the virtual paleomagnetic poles vgps of these excursions may be due to 1 the probable non dipole character of the geomagnetic field during the excursion 2 rapid geomagnetic secular variation and possible small age differences of the extrusive rocks in france and iceland and or 3 crustal magnetic anomalies which might dominate the local geomagnetic field during the excursion at either or both locations

sedimentation rates in the makarov basin central arctic ocean a paleomagnetic and rock magnetic approach three long sediment cores from the makarov basin have been subjected to detailed paleomagnetic and rock magnetic analyses investigated sediments are dominated by normal polarity including short reversal excursions indicating that most of the sediments are of brunhes age in general the recovered sediments show only low to moderate variability in concentration and grain size of the remanence carrying minerals estimations of relative paleointensity variations yielded a well documented succession of pronounced lows and highs that could be correlated to published reference curves however together with five accelerator mass spectrometry c 14 ages and an incomplete be 10 record still two different interpretations of the paleomagnetic data are possible with long term sedimentation rates of either 1 3 or 4 cm kyr 1 however both models implicate highly variable sedimentation rates of up to 10 cm kyr 1 and abrupt changes in rock magnetic parameters might even indicate several hiatuses

high resolution paleomagnetic secular variations and relative paleointensity since the late pleistocene in southern south america abstract paleomagnetic inclination declination and relative paleointensity were reconstructed from the sediments of laguna potrok aike in the framework of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado here we present the u channel based full vector paleomagnetic field reconstruction since 51 2 ka cal bp the relative paleointensity proxy rpi was built by normalising the natural remanent magnetisation with the anhysteretic remanent magnetisation using the average ratio at 4 demagnetisation steps part of the chrm interval nrm arm 10 40 mt a grain size influence on the rpi was removed using a correction based on the linear relationship between the rpi and the median destructive field of the natural remanent magnetisation mdf nrm the new record is compared with other lacustrine and marine records and stacks from the mid to high latitudes of the southern hemisphere revealing consistent millennial scale variability the identification of the laschamp and possibly the mono lake geomagnetic excursions and a direction swing possibly associated to the hilina pali excursion at 20 ka cal bp nonetheless a global scale comparison with other high resolution records located on the opposite side of the earth and with various dipole field references hint at a different behaviour of the geomagnetic field around southern south america at 46 ka cal bp

detailed study on the anisotropy of magnetic susceptibility of arctic marine sediments summary five sediment cores from three different areas the jan mayen fracture zone in the greenland sea the fram strait and the makarov basin in the arctic ocean have been subjected to a detailed analysis of the magnetic fabric by analysing their anisotropy of magnetic susceptibility ams as a supplementary parameter to already existing palaeo and rock magnetic data sets intervals of reversed inclinations documented within the five cores can be interpreted as geomagnetic excursions because all the investigated sediments are characterized by an undisturbed magnetic fabric as expected for layered sediments that is an oblate anisotropy ellipsoid with its short principal axis oriented vertically excursional directions are also not associated with significant changes in rock magnetic parameters however cores from the arctic ocean in particular exhibit a strong cyclicity in their anisotropy parameters here sand rich layers are characterized by a low anisotropy whereas clay rich layers yielded highest anisotropy degrees of up to 9 per cent indicating an ams mainly controlled by the matrix properties of the sediment a simple three axis determination of the anisotropy of anhysteretic remanent magnetization aarm on one of these cores surprisingly yielded an even higher degree of anisotropy of the ferrimagnetic fraction of up to 18 per cent i e twice as high as determined for the susceptibility which is also influenced by the paramagnetic fraction this implies a strong contribution of this sediment fraction to the overall magnetic susceptibility of the investigated arctic ocean deposits

high resolution magnetostratigraphy of four sediment cores from the greenland sea i identification of the mono lake excursion laschamp and biwa i jamaica geomagnetic polarity events summary high resolution magnetostratigraphic analysis of three sediment cores from the base of the volcanic seamount vesteris banken in the greenland basin and one core from the jan mayen fracture zone revealed records of three pronounced geomagnetic events within the last 200 ka dating by stable carbon and oxygen isotope analysis ams14c measurements and biostratigraphic data foraminifera abundances yielded ages of 28 27 ka for the mono lake excursion 37 33 ka for the laschamp event and 189179 ka for the biwa i event in at least one of the cores the laschamp event exhibits a full reversal of the local geomagnetic field vector the same is true of the biwa i event documented in one of the cores

geomagnetic events and relative palaeointensity variations during the past 300 ka as recorded in kolbeinsey ridge sediments iceland sea indication for a strongly variable geomagnetic field magnetostratigraphic analyses of five sediment cores recovered from the kolbeinsey ridge area revealed consistent records of several geomagnetic events linked with low relative palaeointensities within the past 300 ka interpretation of various rock magnetic parameters clearly rule out the possibility that the recorded non normal polarity directions are linked to a deviating magnetomineralogical fraction or a distorted magnetic fabric therefore these directions are interpreted as true recordings of geomagnetic field variations hysteresis parameters and thermomagnetic measurements revealed pure pseudo single domain psd magnetite with curie temperatures of 580 c as the dominant remanence carrier mineral due to the homogeneity of the rock magnetic parameters the sediments are also suitable for relative palaeointensity determinations oxygen isotope stratigraphies for two of the cores provided a time frame to estimate the age ranges for the recorded geomagnetic field variations the obtained record of ten events of up to 12 ka duration during the past 300 ka and the related record of relative palaeointensity indicate a fairly dynamic character of the earth s magnetic field which is in clear contrast to published polarity time scales

relative geomagnetic paleointensity and δ18o at odp site 983 gardar drift north atlantic since 350 ka abstract at odp site 983 relative geomagnetic paleointensity and planktic and benthic 18o records have been acquired for the last 350 kyr the mean sedimentation rate in this interval is 11 3 cm kyr magnetic properties and hysteresis ratios indicate that pseudo single domain magnetite is the remanence carrier volume susceptibility k anhysteretic arm and isothermal irm remanence values vary by a factor of 3 4 well within the criteria usually cited for paleointensity studies natural remanent magnetization nrm is normalized by arm and irm to acquire the paleointensity proxy arithmetic means of nrm arm and nrm irm calculated for five demagnetization steps in the 25 45 mt range constitute the relative paleointensity estimates some paleointensity lows particularly those at 40 120 and 188 ka are associated with directional excursions of the field especially the event at 188 ka referred to here as the iceland basin event that constitutes a short lived polarity reversal for the last 200 kyr the records can be correlated with other high resolution paleointensity records such as those from the labrador sea mediterranean somali basin and sulu sea implying that the millennial scale features are globally synchronous a labeling system for paleointensity features is proposed that ties prominent highs and lows to oxygen isotope stages

possible manifestations of slab window magmatisms in cretaceous southwest japan abstract the slab window system related to ridge subduction is studied to explain the conspicuous activity and the along arc migration of the magmatisms in the eastern margin of eurasian continent in the late mesozoic the trend of the granite ages is scrutinized with systems approach and analyzed by the statistical method in cretaceous southwest japan a reference field of the eurasian eastern margin the magmatic distribution of simultaneous activity was determined to be the v shape of the slab window excluding dating errors from the located age data the slab window magmatism has the most dominant zone of the acidic rocks at or near the centerline of the window the spreading center of two plates and also has the subdominant zone of the acidic to intermediate rocks on either side of the window as the slab window opens due to the plate motions the upwelling current is adiabatically induced in the asthenosphere to fill the window gap the partial melt is generated in the upwelling flux and transports heat to the lower crust to make greater granitic magma chambers by heat conduction to and assimilation with the crustal matter the younger and hotter slabs outside the window also play a role in partial slab melting and or dehydration to the asthenosphere and generate the subdominant granodioritic and adakitic and or high magnesian andesitic magmatisms as the pre and post activities of the main granite genesis the slab window formed by the subducted ridge between the kula and pacific plates was the strong heat source of the active magmatisms and migrated at the rate of 2 8 cm year from southwest to northeast about 8000 km along the continental margin the growth of the continent associated with the active acidic to intermediate magmatisms including the adakitic and or high magnesian andesitic activities is modeled by the slab window system

re os isotope systematics of the taklimakan desert sands moraines and river sediments around the taklimakan desert and of tibetan soils abstract reported here are the first 187os 188os ratios and abundances of os and re for taklimakan desert sands and glacial moraines from the kunlun mountains osmium isotopic data are also reported for river sediments around the taklimakan desert river sediments from the kunlun and tianshan mountains tibetan soils and loesses from the loess plateau as well as sr and nd isotopic data for these samples the taklimakan desert sands from various regions show surprisingly homogeneous os isotopic ratios 187os 188os 1 29 0 08 and abundances os 11 ppt with some variations in re abundances re 130 to 260 ppt and 187re 188os ratios 60 to 140 the 187os 188os ratios for the taklimakan desert sands are close to the average for kunlun moraines river sediments around the taklimakan desert sands and the tibetan soils supporting the idea that the taklimakan desert sands are derived from moraines and river sediments around the desert or from tibetan soils and are homogenized by aeolian activity in the desert furthermore the os isotopic data for the sediments studied here are compared with those 187os 188os 1 04 os 32 ppt re 206 ppt 187re 188os 35 of loesses from the loess plateau reported elsewhere and it is concluded that the re os data for the loess can be used as proxy for the upper continental crust

os isotopes as tracers in seafloor hydrothermal systems metalliferous deposits from the tag hydrothermal area 26 n mid atlantic ridge abstract os isotopic analyses of a suite of samples from the tag hydrothermal area 26 n on the mid atlantic ridge reveal evidence of release of ocean crust derived os to seawater and removal of seawater derived os to the seafloor 187 os 186 os ratios of sulfide samples from the active tag mound vary between 8 7 and 1 3 the highest ratios are indistinguishable from the inferred 187 os 186 os ratio of seawater the incorporation of seawater derived os in these samples is interpreted as evidence of both entrainment of seawater into hydrothermal fluids and the addition of seawater os to samples during sulfide oxidation several sulfide samples from the active tag mound have 187 os 186 os ratios lower than the inferred seawater value with the lowest ratio approaching values expected for pristine oceanic crust these low 187 os 186 os ratios indicate that os derived from alteration of the oceanic crust is released to seawater in association with venting of high temperature hydrothermal fluids precipitates from low temperature hydrothermal fluids fe and mn oxide deposits from the east wall of the axial rift valley also have low 187 os 186 os ratios 4 2 6 8 relative to seawater these data suggest os isotopes may be sensitive tracers of low temperature hydrothermal circulation on the seafloor and that supply of ocean crust derived os to seawater is not strictly limited to high temperature hydrothermal vents the os concentration and isotopic composition of metalliferous sediment samples from a push core collected 125 m from the base of the active tag mound are also reported in this core metalliferous sediment horizons derived from mass wasting of altered sulfides exhibit variable 187 os 186 os ratios 4 8 8 7 reflecting mixing of seawater derived and ocean crust derived os in contrast sediments in which the metalliferous component is derived from fall out of hydrothermal material from the neutrally buoyant hydrothermal plume have 187 os 186 os ratios which vary over a narrow range 8 6 8 7 and appear to accurately record the os isotopic composition of seawater

deep sea mud in the pacific ocean as a potential resource for rare earth elements world demand for rare earth elements and the metal yttrium is rapidly increasing an analysis of more than 2 000 seafloor sediment samples suggests that deep sea mud constitutes a highly promising giant resource for these elements

geochemistry and mineralogy of rey rich mud in the eastern indian ocean abstract deep sea sediments in parts of the pacific ocean were recently found to contain remarkably high concentrations of rare earth elements and yttrium rey of possible economic significance here we report similar rey rich mud in a core section from deep sea drilling project site 213 in the eastern indian ocean the sediments consist mainly of siliceous ooze with subordinate zeolitic clay that contains relatively high rey concentrations the maximum and average total rey rey contents of this material are 1113 and 629 ppm respectively which are comparable to those reported from the pacific ocean the rey rich mud at site 213 shows enrichment in heavy rare earth elements negative ce anomalies and relatively low fe2o3 rey ratios similar to those in the pacific ocean in addition the major element composition of the indian ocean rey rich mud indicates slight enrichment in lithogenic components which probably reflects a contribution from southern african eolian dust a volcaniclastic component from neighboring mid ocean ridges or intraplate volcanoes is also apparent elemental compositions and x ray diffraction patterns for bulk sediment and microscopic observation and elemental mapping of a polished thin section demonstrate the presence of phillipsite and biogenic apatite such as fish debris in the rey rich mud the strong correlation between total rey content and apatite abundance implies that apatite plays an important role as a host phase of rey in the present deep sea sediment column however positive correlations between rey and elements not present in apatite e g fe2o3 mno and tio2 imply that the rey rich mud is not formed by a simple mixture of rey enriched apatite and other components

paleomagnetism of quaternary sediments from lomonosov ridge and yermak plateau implications for age models in the arctic ocean abstract inclination patterns of natural remanent magnetization nrm in quaternary sediment cores from the arctic ocean have been widely used for stratigraphic correlation and the construction of age models however shallow and negative nrm inclinations in sediments deposited during the brunhes chron in the arctic ocean appear to have a partly diagenetic origin rock magnetic and mineralogical studies demonstrate the presence of titanomagnetite and titanomaghemite thermal demagnetization of the nrm indicates that shallow and negative inclination components are largely unblocked below 300 c consistent with a titanomaghemite remanence carrier following earlier studies on the mendeleev alpha ridge shallow and negative nrm inclination intervals in cores from the lomonosov ridge and yermak plateau are attributed to partial self reversed chemical remanent magnetization crm carried by titanomaghemite formed during seafloor oxidation of host detrital titanomagnetite grains distortion of paleomagnetic records due to seafloor maghemitization appears to be especially important in the perennially ice covered western mendeleev alpha ridge and central arctic ocean lomonosov ridge and to a lesser extent near the ice edge yermak plateau on the yermak plateau magnetic grain size parameters mimic the global benthic oxygen isotope record back to at least marine isotope stage 6 implying that magnetic grain size is sensitive to glacial interglacial changes in bottom current velocity and or detrital provenance

scattering of ice coupled waves by variable sea ice terrain the reflection and transmission of ice coupled waves under a sea ice sheet is re examined in this work recent theory can account for inhomogeneities in ice sheets such as the sails of pressure ridges and cracks or leads but has only examined small numbers of features here the scattering coefficients can be obtained for an ice sheet containing a region of arbitrarily varying thickness that more closely approximates a real ice sheet and consequently models wave scattering more effectively we explore the consequences of inverting ridge keels placing the mass above the ice sheet as a technique by which the keel can be partially accounted for it is found that the ridge sails themselves can reasonably be neglected upward looking submarine sonar data are used to demonstrate the use of the model noting that there are choices as to how to interpret such data the model is tested to establish its sensitivity to these choices

hydroelastic wave diffraction by a vertical cylinder a linear three dimensional problem of hydroelastic wave diffraction by a bottom mounted circular cylinder is analysed the fluid is of finite depth and is covered by an ice sheet which is clamped to the cylinder surface the ice stretches from the cylinder to infinity in all lateral directions the hydroelastic behaviour of the ice sheet is described by linear elastic plate theory and the fluid flow by a potential flow model the two dimensional incident wave is regular and has small amplitude an analytical solution of the coupled problem of hydroelasticity is found by using a weber transform we determine the ice deflection and the vertical and horizontal forces acting on the cylinder and analyse the strain in the ice sheet caused by the incident wave

the marine187os 186os record of the past 80 million years we report new187os 186os data and re and os concentrations in metalliferous sediments from the pacific to construct a composite os isotope seawater evolution curve over the past 80 m y analyses of four samples of upper cretaceous age yield187os 186os values of between 3 and 6 5 and187re 186os values below 55 mass balance calculations indicate that the pronounced minimum of about 2 in the os isotope ratio of seawater at the k t boundary probably reflects the enormous input of cosmogenic material into the oceans by the k t impactor s following a rapid recovery to187os 186os of 3 5 at 63 ma data for the early and middle part of the cenozoic show an increase in187os 186os to about 6 at 15 ma variations in the isotopic composition of leachable os from slowly accumulating metalliferous sediments show large fluctuations over short time spans in contrast analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data these results together with sediment leaching experiments indicate that dissolution of non hydrogenous os can occur during the hydrogen peroxide leach and demonstrate that os data from pelagic clay leachates do not always reflect the os isotopic composition of seawater new data for the late cenozoic further substantiate the rapid increase in the187os 186os of seawater during the past 15 ma we interpret the correlation between the marine sr and os isotope records during this time period as evidence that weathering within the drainage basin of the ganges brahmaputra river system is responsible for driving seawater sr and os toward more radiogenic isotopic compositions the positive correlation between87sr 86sr and u concentration the covariation of u and re concentrations and the high dissolved re u and sr concentrations found in the ganges brahmaputra river waters supports this interpretation accelerating uplift of many orogens worldwide over the past 15 ma especially during the last 5 ma could have contributed to the rapid increase in187os 186os from 6 to 8 5 over the past 15 ma prior to 15 ma the marine sr and os record are not tightly coupled the heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic os and sr to the oceans and account for the periods of decoupling of the marine sr and os isotope records

magnetostratigraphic results from the eastern arctic ocean ams 14c ages and relative palaeointensity data of the mono lake and laschamp geomagnetic reversal excursions summary a new high resolution magnetostratigraphic record from the eastern arctic ocean has yielded further evidence for the existence of the laschamp excursion 37 35 ka the mono lake excursion 27 25 5 ka and possibly another very short excursion 22 ka inferred from steep negative inclinations ages are based on nine ams accelerator mass spectrometry 14c dates oxygen isotope stratigraphy and correlation with odp site 983 estimates of relative palaeointensity variations for the time interval from 80 to 10 ka have revealed that the documented geomagnetic excursions are linked to large fluctuations of the relative palaeointensity the lowest values were obtained for the two excursions and the normal reversed n r and reversed normal r n transitions of the laschamp polarity excursion which itself is characterized by a slight increase of relative palaeointensity during its reversed state the results are in general agreement with palaeointensity studies from other regions indicating that these fluctuations could be global phenomena and that the geomagnetic field of the brunhes chron was very variable in amplitude as well as in geometry the new result is one of the rare records comprising large directional as well as large relative palaeointensity variations

hematite formation by oxygenated groundwater more than 2 76 billion years ago geoscientific drilling in the marble bar area of the pilbara craton western australia resulted in the discovery of locally abundant hematite in archean basalts 200 m below the present land surface the hematized basalts occurring along a bedding parallel shear zone are cross cut by pyrite veinlets 3 mm in width and contain euhedral pyrite grains 10 500 m in diameter with sharp crystal edges indicating that the hematite formed before the pyrite we have dated the pyrite in the veinlets at 2 763 0 016 ga using the re os method therefore the hematite formed prior to 2 763 ga the basalts containing the hematite belong to the apex basalt of the warrawoona group and were erupted onto the archean seafloor at 3 46 ga due to 2 9 ga orogenic deformation and subsequent deep erosion the apex basalt was exposed at the surface of a continental landmass prior to 2 77 ga sometime in the period between 2 9 ga and 2 77 ga the basalt section we describe was less than 200 m below the late archean land surface and within range of groundwater percolation through the shear zone in the basalts geological mineralogical and geochemical lines of evidence strongly suggest that the infiltration of o2 rich groundwater through the bedding parallel shear in the basalts formed hematite prior to 2 76 ga and hence oxygenated surface environments at least localized and or short lived emerged more than 300 million years before the widely accepted great oxidation event during 2 45 and 2 32 ga

re os isotope and platinum group element geochemistry of the pobei ni cu sulfide bearing mafic ultramafic complex in the northeastern part of the tarim craton a number of mafic ultramafic intrusions that host ni cu sulfide mineralization occur in the northeastern tarim craton and the eastern tianshan orogenic belt nw china the sulfide mineralized pobei mafic ultramafic complex is located in the northeastern part of the tarim craton the complex is composed of gabbro and olivine gabbro cut by dunite wehrlite and melatroctolite of the poyi and poshi intrusions disseminated ni cu sulfide mineralization is present towards the base of the ultramafic bodies the sulfide mineralization is typically low grade 4 wt samples from the pobei complex have end at 280 ma values up to 8 1 consistent with the derivation of the magma from an asthenospheric mantle source fo 89 5 mol olivine from the ultramafic bodies is consistent with a primitive parental magma sulfide bearing dunite and wehrlite have high cu pd ratios ranging from 24 000 to 218 000 indicating a magma that evolved under conditions of sulfide saturation the grades of ni cu and pge in 100 sulfide show a strong positive correlation a model for these variations is proposed where the mantle source of the pobei magma retained 0 033 wt sulfide during the production of a pge depleted parental magma the parental magma migrated from the mantle to the crust and underwent further s saturation to generate the observed mineralization along with its high cu pd ratio at an r factor varying from 100 to 1 200 the mineralization at poshi and poyi has very high os at 280 ma values 30 to 292 that are negatively correlated with the abundance of os in 100 sulfide 5 81 271 ppb and positively correlated with the re os ratios this indicates that sulfide saturation was triggered by the assimilation of crustal sulfide with both high os and re os ratios when compared to other permian mafic ultramafic intrusions with sulfide mineralization in the east tianshan the poyi and poshi ultramafic bodies were formed from more primitive magmas and this helps to explain why the sulfide mineralization has high ni tenor

manganese formations in the accretionary belts of japan implications for subduction accretion process in an active convergent margin abstract in the accretionary complexes of japan many bedded manganese and iron manganese ore deposits occur especially in the jurassic complexes such as the chichibu tamba mino ashio and northern kitakami belts the manganese ores in these jurassic accretionary complexes probably formed from manganese nodule crust bearing siliceous sediments on deep sea floor and were subsequently converted to the manganese ores by metamorphism during the subduction accretion process some of the deposits also show the signatures of younger granitic intrusions the manganese formations now incorporated within these belts are marker beds of accretionary tectonics associated with plate tectonic processes in convergent margins

re os geochronology of organic rich sediments an evaluation of organic matter analysis methods rhenium and osmium in organic rich sedimentary rocks are dominantly hydrogenous but any nonhydrogenous component will influence the accuracy and precision of the re os date obtained to minimize the influence of any nonhydrogenous re and os we evaluate analysis of isolated organic matter from the whole rock together with whole rock analysis using a cro3 h2so4 digestion medium instead of inverse aqua regia for a black shale unit of the exshaw formation canada this unit previously returned a whole rock re os date of 358 10 ma model 3 geochim cosmochim acta 2002 using inverse aqua regia dissolution organic matter isolated from the whole rock matrix using the hf bf3 technique org geochem 20 1993 249 yields scattered data and a re os date of 449 220 ma model 3 mswd 616 the organic matter analyses show similar 187os 188os values but significantly lower 187re 188os values in comparison to the whole rock analyses we show that the re os systematics of organic matter are altered during chemical isolation and as such we suggest that the hf bf3 method should not be used for re os analysis of organic matter whole rock re os analysis using a cro3 h2so4 digestion medium yields significantly better regression analysis compared with the inverse aqua regia method and the re os data identify two distinct initial 187os 188os values for the sample set separate regressions of these data yield precise dates 366 1 9 6 mswd 2 2 and 363 4 5 6 ma mswd 1 6 model 3 which are indistinguishable from the age constraints for this formation 363 4 0 4 ma u pb monazite comparison of the re os dates obtained from aqua regia and cro3 h2so4 methods suggests that the former may contain nonhydrogenous re and os whereas the cro3 h2so4 method dominantly liberates hydrogenous re os from organic matter allowing for better stratigraphic age determinations and evaluation of the os isotope composition of seawater

variations in the osmium isotope composition of sea water over the past 200 000 years the first osmium isotope data are presented for marine sediments spanning the past 200 000 years two full glacial cycles and establish that there have been ocean wide variations in sea water osmium isotope composition over this time while the osmium isotope composition of sea water has been relatively invariant over much of this interval 187os 186os of 8 5 to 8 6 excursions to lower isotope ratios 187os 186os 8 1 occur late in the last two glacial periods at 20 ka and 160 ka these are times of high global aridity low global temperature and maximum ice extent while various interpretations are possible a likely explanation is that the low sea water ratios reflect reduced chemical weathering of the continents during times of extreme cold and aridity there is no evidence that there is a net enhancement of chemical weathering during periods of continental glaciation the response of ocean composition to changes in input flux constrain the oceanic residence time of osmium to be less than 12 000 years