coupled re os and u pb geochronology of the tonian chuar group grand canyon well preserved strata of the late tonian chuar group exposed in the grand canyon host fossil evidence for the development of eukaryotic predation the presence of unique biomarkers and large changes in c s and mo isotope chemostratigraphy despite the importance of this critical succession few radioisotopic age constraints are available to place these records into a global context here we couple high precision u pb chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims on zircon crystals with the rhenium osmium re os sedimentary and sulfide geochronometer to refine the temporal framework of this pivotal interval of earth history zircons recovered from a tuff within the uppermost walcott member of the kwagunt formation yield a weighted mean 206pb 238u age of 729 0 0 9 ma mean square of weighted deviates mswd 0 86 differing significantly from the previous air abrasion upper intercept age of 742 6 ma on zircons from this same horizon organic rich carbonates from the carbon canyon member of the galeros formation yield a model 1 re os age of 757 0 6 8 ma mswd 0 47 n 8 and an initial os isotope 187os 188os osi composition of 1 13 0 02 the radiogenic osi value from this horizon suggests that the basin was restricted from the open ocean during deposition of the carbon canyon member in agreement with sedimentological and stratigraphic data the re os geochronology of marcasite fes2 nodules from the awatubi member of the kwagunt formation yield a model 1 age of 751 0 7 6 ma mswd 0 37 n 5 with an osi of 0 44 0 01 this re os date is interpreted to constrain the growth of the marcasite nodules in the awatubi member during deposition the formation of sulfides and the less radiogenic osi value are consistent with an influx of sulfate laden seawater to the basin during deposition of the kwagunt formation attempts to apply the re os geochronometer to the walcott and tanner members of the chuar group failed to yield meaningful ages despite elevated re enrichments 20 ng g the re os data from these units yielded negative osi values which suggest disturbance to the re os system the low os abundances typically 100 pg g relative to the amount expected based on the elevated re abundances suggest leaching of os due to oxidative weathering on geologically recent time scales finally the carbon canyon member provides a useful case study for quantifying how input uncertainties in the re os geochronometer propagate into the resulting age uncertainty and we discuss the protocols that will yield the best improvement in age precision for future studies the u pb and re os geochronology presented here illustrates the power of coupling these systems and the importance of recent improvements in both methods our analysis suggests that for our data the most efficient way of reducing uncertainties in the presented re os dates is through improved precision of measured os values

organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

mid cretaceous sequence stratigraphy and sedimentary cyclicity in the western paris basin abstract cenomanian and turonian depositional patterns of the western paris basin are interpreted in terms of sequence stratigraphy a system tract analysis of the epicontinental normandie basin with pelagic chalks and of the maine platform covered by clastics provides evidence for relative changes in coastal onlap various minor uncomformities are related to these changes of sea level the four global cycles uza or zc 2 2 2 5 of haq et al 1987 1988 are recognised while an additional one is proposed for the geslinianum zone in addition periodic rhythmic cycles are commonly registered within the chalk expressed by the repitition of various facies enhanced both by biosedimentary processes and diagenetic alteration these elementary climatic cycles allow accurate lithostratigraphic correlations during this period when the sea level peaked on the tectonically passive border of the armorican block the paris basin appears to record a detailed set of events which can be correlated with those in the atlantic boreal and tethyan provinces

re os geochronology of the lacustrine green river formation insights into direct depositional dating of lacustrine successions re os systematics and paleocontinental weathering abstract lacustrine sedimentary successions provide exceptionally high resolution records of continental geological processes responding to tectonic climatic and magmatic influences these successions are therefore essential for correlating geological and climatic phenomena across continents and furthermore the globe producing accurate geochronological frameworks within lacustrine strata is challenging because the stratigraphy is often bereft of biostratigraphy and directly dateable tuff horizons the rhenium osmium re os geochronometer is a well established tool for determining precise and accurate depositional ages of marine organic rich rocks lake systems with stratified water columns are predisposed to the preservation of organic rich rocks and thus should permit direct re os geochronology of lacustrine strata we present re os systematics from one of the world s best documented lacustrine systems the eocene green river formation providing accurate re os depositional dates that are supported by ar ar and u pb ages of intercalated tuff horizons precision of the green river formation re os dates is controlled by the variation in initial 187 os 188 os and the range of 187 re 188 os ratios as also documented in marine systems controls on uptake and fractionation of re and os are considered to relate mainly to depositional setting and the type of organic matter deposited with the need to further understand the chelating precursors of re and os in organic matter highlighted in addition to geochronology the re os data records the 187 os 188 os composition of lake water 1 41 1 54 at the time of deposition giving an insight into continental runoff derived from weathering of the geological hinterland of the green river formation such insights enable us to evaluate fluctuations in continental climatic tectonic and magmatic processes and provide the ability for chemostratigraphic correlation combined with direct depositional dates furthermore initial 187 os 188 os values can be used as a diagnostic tool to distinguish between lacustrine and marine depositional settings when compared to known oceanic 187 os 188 os values

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

geochemical signatures of the namibian diatom belt perennial upwelling and intermittent anoxia 1 a gravity core from the nambian diatom belt 83 m water depth was analyzed for major al ca fe k mg p si ti and minor elements ag as ba bi cd co cr cu mn mo ni rb re se sr tl u v zn zr as well as c and s the major element geochemistry is dominated by the contribution of biogenic phases opal and minor amounts of carbonate and phosphate whereas terrigenous components of eolian and fluvial origin form only a minor admixture of 15 examination of the fe s c relationship reveals a completion of pyritization close to the sediment seawater interface higher than average shale fe al ratios reflect the presence of highly reactive iron oxides in terrigenous source material from the namibian desert and suggest little loss of fe within the omz the low total fe content likely represents an important factor responsible for sporadic h2s eruptions the upwelling system off namibia may be regarded as an intermediate system combining high productivity typical for upwelling areas with the sporadic presence of h2s in the water column by examining the source sink relationship of individual trace metals two different trends are discernible mo re and u accumulate following seawater availability whereas ag cd cu ni tl and zn require a biological preconcentration step trace metals like as ba cr se and v show an intermediate behavior metal enrichment is favored by high interstitial water sulfide concentrations close to the sediment seawater interface leading to slightly elevated co contents as opposed to extremely low mn al ratios reflecting the overall reducing character of the namibian system maximum contents of cu ni and zn are significantly lower than those reported previously this may in part be related to the absence of fecal material and a stronger dilution by biosiliceous material at this location compared to the seaward flank of the diatom belt

the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

controls on the geochemistry of rare earth elements along a groundwater flow path in the carrizo sand aquifer texas usa groundwater samples were collected along a groundwater flow path in the carrizo sand aquifer in south texas usa field measurements that included ph specific conductivity temperature dissolved oxygen do oxidation reduction potentials eh in mv alkalinity iron speciation and h2s concentrations were also conducted on site the geochemistry i e concentrations shale normalized patterns and speciation of dissolved rare element elements rees in the carrizo groundwaters are described as a function of distance along a flow path eh and other redox indicators i e do fe speciation h2s u and re indicate that redox conditions change along the flow path in the carrizo sand aquifer within the region of the aquifer proximal to the recharge zone groundwaters exhibit both highly oxidizing and localized mildly reducing conditions however from roughly 10 km to the discharge zone groundwaters are reducing and exhibit a progressive decrease in redox conditions dissolved ree geochemical behavior exhibits regular variations along the groundwater flow path in the carrizo sand aquifer the changes in ree concentrations shale normalized patterns and speciation indicate that rees are not conservative tracers with flow down gradient redox conditions ph and solution composite and adsorption modify groundwater ree concentrations fractionation patterns and speciation

dissolved osmium in bengal plain groundwater implications for the marine os budget abstract we report osmium concentrations and isotopic compositions of 40 groundwater samples from the bengal plain groundwaters have os concentrations 16 9 191 5 pg kg about 5 10 times higher than those published for most rivers or seawater 187 os 188 os varies widely from 0 96 to 2 79 and is related to the isotopic signatures of the sediments constituting local aquifers os contents are correlated with those of soluble elements such as sr mg and ca suggesting that differing extents of solid solution interaction explain most of the variation in measured os concentrations the covariation between os and sr allows us to estimate the mean os content of bengal groundwater 70 pg kg this concentration is too low to allow bengal groundwater to significantly influence the marine os isotopic composition if likely fresh groundwater discharge rates to the bay of bengal are assumed however if bengal groundwater os concentrations are typical the global os groundwater flux would be expected to be around 180 kg year making it the second largest input of os to the ocean after the river flux including this flux in the current os marine budget and assuming that this and other fluxes have remained constant with time would decrease the calculated residence time of os in the ocean by about 30

effects of black shale weathering on the mobility of rhenium and platinum group elements radiogenic os from the continents dominates the late cenozoic marine os budget a variety of proposed radiogenic sources includes organic rich sediments precambrian shields and re rich sulfides identifying the dominant sources of radiogenic os to the oceans has a strong impact on past climate models because weathering of silicates acts as a net sink of co 2 whereas weathering of organic matter acts as a source here we investigate the effects of black shale weathering on the integrity of the re os isotope system and release of re and platinum group elements time correlative pairs of fresh drill core and weathered outcrop black shales of late ordovician age utica shale magnafacies quebec were analyzed for re os ir pt and pd as well as total s n and c as c carb and c org the results indicate that 25 64 of the initial re budget 45 90 of the os budget 14 65 of the ir budget 60 77 of the pt budget 69 86 of the pd budget and 44 96 of the c org budget are lost during weathering we use positive correlations of os pt and pd with c org and n to calculate the respective platinum group element concentrations in the unweathered organic matter end member as 3 ng g os 9 ng g pt and 11 24 ng g pd although black shales make up

re os depositional ages and seawater os estimates for the frasnian famennian boundary implications for weathering rates land plant evolution and extinction mechanisms four toc rich shale intervals spanning the frasnian famennian f f boundary were recovered in a drillcore west valley nx 1 from western new york usa and radiometrically dated using re os two of the black shale intervals wvc785 from 2 9 m below and wvc754 from 6 4 m above the f f boundary respectively yielded statistically overlapping ages with uncertainties of 1 1 an interpolated age and associated graphically determined uncertainty of 372 4 3 8 ma provides new absolute age constraints on the f f boundary this date is 4 1 ma younger than the latest proposed f f boundary age of 376 1 ma obtained by interpolation of u pb dates from volcanic zircon kaufmann b 2006 calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy earth science reviews 76 175 190 and within uncertainty of the international commission on stratigraphy accepted date of 374 5 2 6 ma a third date from sample wvc802 8 2 m beneath the f f boundary yielded an imprecise age of 357 23 ma owing in part to a limited re os range the initial 187os 188os 0 45 to 0 47 reflecting contemporaneous seawater os values are low but similar to the value of 0 42 reported for the exshaw fm canada at the devonian mississippian boundary ca 361 ma selby d creaser r a 2005 direct radiometric dating of the devonian mississippian time scale boundary using the re os black shale geochronometer geology 33 545 548 this may suggest fairly constant and low global continental weathering rates during the late devonian although in view of the short residence time of os in seawater 1 4 104 yr further measurements are needed to assess potential short term variation in seawater os ratios owing to low os and re abundances at the f f boundary our data are inconsistent with long term volcanism and bolide impact as potential late devonian mass extinction mechanisms in addition the frasnian famennian ocean appears to have been depleted with respect to re possibly indicating an exhaustion of the re seawater reservoir owing to high burial rates of redox sensitive elements under dysoxic anoxic conditions leading up to the f f boundary

temporal record of osmium concentrations and 187os 188os in organic rich mudrocks implications for the osmium geochemical cycle and the use of osmium as a paleoceanographic tracer the final publication is available at elsevier via https doi org 10 1016 j gca 2017 06 046 2017 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

different crustal sources for au rich and au poor ores of the grasberg cu au porphyry deposit abstract the grasberg is a porphyry copper deposit that is crosscut by a second stage mineralization which is greatly enriched in gold sulfides from the porphyry type event yield a 2 9 0 3 ma re os isochron that agrees with published geochronology the initial 187os 188os ratio of the isochron is 0 56 0 02 and implies a significant crustal component for the source of os and by inference the other base metals the samples from the crosscutting secondary event do not form an isochron but form a mixing line with the older porphyry style mineralization as one of the end members and a very radiogenic end member possibly shale the initial 187os 188os ratios from samples of the second event range from 0 81 to 1 26 and correlate with gold content the most radiogenic samples have the highest gold the re os isotope data indicate different crustal sources for the ore forming elements at the grasberg cu au deposit and support a model in which gold is derived from sedimentary protoliths that may have been pre enriched by sedimentary processes the gold derived from these sources is concentrated by magmatic hydrothermal systems the requirement of a sedimentary source for gold to produce hydrothermal gold deposits has been debated for decades and this study provides strong support for the model

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

sequestration mechanisms and anthropogenic inputs of rhenium in sediments from eastern canada lakes abstract the concentrations of re as well as those of several other geochemical variables were measured in dated sediment cores and in porewater samples from four lacustrine basins in eastern canada one perennially oxic located 40 km from quebec city and three seasonally anoxic located within 25 km of non ferrous metal smelters the drainage basins of these lakes are uninhabited and have not been affected by human activity or wildfires all of the depth profiles of dissolved re indicate higher re concentrations in the water overlying the sediment than in the porewater diffusion of re across the sediment water interface a progressive decrease in porewater re concentrations to reach minimum values of 0 5 pm within a 10 cm sediment depth interval modeling of these re porewater profiles with a one dimensional transport reaction equation indicates that re is removed from porewater within this depth interval based on thermodynamic predictions of re speciation and of saturation states and on comparison of these predictions with sulfide porewater profiles we infer that re is removed from porewater by precipitation of rheniite res2 s the rate constant for the formation of res2 s in sediments is estimated from the modeling exercise to be 0 51 0 64 10 21 mol cm 3 s 1 accumulation of sedimentary re shows a strong authigenic component as in anoxic marine sediments sharp increases in solid phase re during the last century are attributed to atmospheric deposition of anthropogenic re deriving from coal burning and nearby smelter emissions

natural mass dependent variations in the isotopic composition of molybdenum we present the first observations of natural mass dependent fractionation of the isotopic composition of molybdenum mo using multi collector inductively coupled plasma mass spectrometry variations in the isotopic composition of mo are reported as 97 95mo 97mo 95mo sample 97mo 95mo standard 1 1000 external analytical precision of 97 95mo is 1 between sediments deposited under anoxic conditions 97 95mo 1 02 to 1 52 relative to our in house standard and ferromanganese nodules 97 95mo 0 63 to 0 42 97 95mo of pacific ocean seawater 97 95mo 1 48 lies within the range of values for anoxic sediments closest to modern black sea anoxic sediments molybdenites from continental ore deposits have intermediate 97 95mo ranging from 0 26 to 0 09 variations in the abundances of 92mo 95mo 96mo 97mo and 98mo are consistent with mass dependent fractionation a sporadic unidentified interference occurs at mass 94 and 100mo is not measured we hypothesize that the 97 95mo offset between anoxic sediments and ferromanganese nodules results from mo isotope fractionation during inefficient scavenging of mo from seawater by mn oxides under oxic conditions the similarity in 97 95mo of anoxic sediments and seawater is consistent with the very efficient removal of mo from seawater under anoxic conditions in the presence of h2s the data can be interpreted in terms of a steady state mass balance between the mo flux into the oceans from the continents and the mo flux out of the oceans into oxic and anoxic sediments such an interpretation is quantitatively consistent with existing estimates of the removal fluxes of mo to anoxic and oxic sediments these findings suggest that 97 95mo in seawater may co vary with changes in the relative proportions of anoxic and oxic sedimentation in the oceans and that this variation may be recorded in 97 95mo of anoxic sediments hence the mo isotope system may be useful in paleoredox investigations

calcareous nannofossil biostratigraphy and assemblages of the cenomanian turonian boundary interval implications for the origin and timing of oceanic anoxia a detailed nannofossil zonation has been derived for the cenomanian turonian boundary interval consisting of three zones two subzones and nine additional biohorizons this biostratigraphy based on the investigation of numerous sections from europe north america and africa allows accurate correlation of sections from shelf and deep sea environments the increased resolution helps solve several pertinent paleoceanographic and sedimentologic problems in this time period facies patterns are variable in this interval for numerous reasons a widespread hiatus occurred in the latest cenomanian and earliest turonian in much of northwest europe and may have been an indirect result of peak marine transgression in parts of the deep tethys dissolution of carbonate took place in undersaturated bottom waters or during early diagenesis only a few boundary sections mostly within the western interior united states are characterized by continuous carbonate deposition in many sections a 13c excursion which has been associated with the burial of large amounts of marine organic matter coincides with a facies change lower ratios of coccolith carbonate to micrite and poorer nannofossil preservation this excursion therefore may be strongly overprinted by diagenesis numerous nannofossil events indicate that the carbon excursion is slightly diachronous between sequences of the western interior and that the shift occurred distinctly later in this region than in northwest germany the data obtained do not invalidate the concept of a cenomanian turonian ocean wide anoxic event but show how local tectonic climatic and oceanographic perturbations have masked the global scenario in particular they indicate that carbon shifts may be basinal and not always oceanic phenomena a conclusion which can be rationalized with overall sluggish middle cretaceous circulation nannofossil assemblages in almost all sequences observed contain exceptionally high abundances of two dissolution resistant taxa in particular samples eprolithus floralis and broinsonia sp however the overall composition of assemblages does not change dramatically in the boundary interval in contrast to the macrofossils and foraminifera which suffered widespread extinctions

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

rhenium osmium and molybdenum isotope systematics of black shales from the lower cambrian niutitang formation sw china evidence of a well oxygenated ocean at ca 520 ma abstract the early cambrian was a key period in earth s history and the reconstruction of ancient ocean chemistry on spatial and temporal scales can contribute to a better understanding of events during that period new early cambrian data for re os and mo isotopic compositions and redox sensitive elements rse are reported here for the niutitang formation se chongqin sw china a re os age of 520 30 myr model 3 2 n 21 mswd 62 and a 187os 188os i ratio of 0 79 0 11 were obtained consistent with previously reported data for equivalent strata from other areas separate regression of samples with 187os 188os i of 0 72 0 79 and 0 81 0 89 produce more precise ages of 520 1 9 5 myr model1 2 n 7 mswd 1 0 and 513 10 myr model 1 2 n 8 mswd 0 96 respectively suggesting heterogeneity in the primary source of os as the dominant cause of scatter and uncertainty high initial 187os 188os of 0 79 0 11 may indicate a high os input from oxidative weathering of upper continental crust for early cambrian ocean based on rse data such as mo u v enrichment and ni co v cr v v ni moef uef re mo ratios two geochemically distinct zones upper and lower can be delineated in the sedimentary sequence as reflected in drillcore sections the upper section n 9 is characterized by low total organic carbon toc contents mean 1 8 1 5 wt low rse contents mo 0 008 0 006 10 3 g g v 0 22 0 15 10 3 g g u 0 008 0 004 10 3 g g and low v cr 2 0 1 7 ni co 5 9 3 5 moef uef 2 6 1 8 and mo toc 6 0 3 9 ratios in contrast the lower core section n 13 is characterized by high toc contents 4 4 2 2 wt high rse contents mo 0 10 0 08 10 3 g g v 1 0 1 0 10 3 g g u 0 05 0 04 10 3 g g high v cr 6 5 ni co 24 14 moef uef 6 3 2 2 and mo toc 21 9 ratios uncertainties are 1sd here significantly decreasing trends of those redox proxies from lower to upper sections suggest that the depositional conditions evolved from anoxic euxinic to oxic condition all samples display extremely low re mo ratios of 0 2 10 3 1 9 10 3 indicating the absence of intermediate reducing conditions possibly reflecting rapid ocean oxygenation the mo isotopic composition in the sedimentary succession of the yc9 core exhibits a large variation with 98 95mo values of 0 04 2 00 upper section 98 95mo values display an opposite trend to mn content and negative correlation with mo toc ratios indicating mo fractionation associated with adsorption on mn oxides or oxyhydroxides lower section 98 95mo values are positively correlated with mo toc ratios and negatively with re mo ratios suggesting incomplete conversion of molybdates to tetrathiomolybdates under weakly euxinic conditions high 98 95mo of 2 00 and high average mo toc ratios of 21 10 6 g g wt were observed in euxinic shales in the niutitang formation suggesting extensive ocean oxygenation may have taken place at ca 520 ma

the behavior of natural and anthropogenic osmium in long island sound an urban estuary in the eastern u s abstract the os concentration and 187 os 186 os distributions in surface sediments of long island sound eastern u s provide a way of determining the sources and estuarine transport of os the contribution of anthropogenic os from sewer outfalls from the new york city region supplies a tracer with a characteristic 187 os 186 os of about 1 the os concentration of the bulk surface sediment increases steeply moving toward new york city in the westernmost sound and generally follows the concentration of organic carbon the 187 os 186 os ratio of bulk surface sediment increases from west to east in the westernmost part of the sound and is effectively constant in the central sound we interpret these results as indicating that the surface bulk sediments of the sound contain a low 187 os 186 os component perhaps as a reduced coating associated with organic remains from sewer outfalls the acid hydrogen peroxide leach fraction has an average 187 os 186 os of 9 5 in the central sound significantly higher than both the bulk sediment value and the probable sea water value of about 8 the leach fraction in the westernmost part of the traverse is less radiogenic than the central sound and follows the os wsotope trend of the bulk sediment liquid effluent from a new york city sewer outfall contains 30 pg l 1 of dissolved os with a 187 os 186 os of about 2 5 consistent with its being an end member of the west east sediment pattern recorded in the leach fractions of the westernmost cores the leachable os from the central sound predominantly reflects os in ferromanganese oxyhydroxide coatings from continentally derived sediments with 187 os 186 os ratios more radiogenic than seawater the distribution patterns of anthropogenic and natural os with their characteristic isotopic signatures in the sound and the insights gained from the behavior of other particle reactive species indicates that very little os in solution may pass through the estuarine gauntlet

the os isotopic composition of himalayan river bedloads and bedrocks importance of black shales re os data are presented for bedrocks and bedloads of selected rivers from the himalayan range in central nepal and bangladesh these data demonstrate that the os isotopic composition of most of the bedrocks is similar to that of the average continental crust notable exceptions to this are the black shales from the lesser himalaya lh which contain large quantities of radiogenic osmium in the black shales the os is not concentrated in the sulfides and may instead be associated with organic matter bedloads collected from rivers which include lh black shales in their catchment basins have notably high os ratios 187os 188os 3 this radiogenic signature persists into the ganga river in contrast the brahmaputra river is less radiogenic suggesting an ophiolite input in the headwater region simple physical mixtures of lh black shales with eroded products from the high range require unreasonably high proportions of black shale to explain the high os ratios observed at the outflow of the range assuming that our bedrock and bedload samples are representative of the source region and the eroded mixture respectively this observation suggests that erosion may not be occurring at steady state in addition mass balance calculations indicate that about 20 of the os and 60 of the re are carried in dissolved form implying that chemical erosion plays an important role in the osmium budget finally the contrast in os isotope ratio between ganga bedloads and bulk sediments in the bengal fan suggests that radiogenic os carried by particulate matter and later remobilized may significantly influence the os composition of seawater

sedimentary redox conditions in continental margin sediments n e pacific influence on the accumulation of redox sensitive trace metals redox conditions in near surface sediments from the continental margin off western canada were characterized to determine how they influence the accumulation of redox sensitive trace metals despite the development of suboxic conditions within millimeters of the sediment water interface there is little enrichment of re u cd or mo in the upper 10 to 15 cm of the sediment column this observation is consistent with the low extractible solid mn concentrations but high i corg ratios that imply that near surface sediment redox conditions are poised between mn and i reduction in contrast below 15 cm re and to a lesser extent cd and u are enriched e g up to 65 ng g re but only in those cores collected from within and below the oxygen minimum zone molybdenum concentrations remain low b1 5 g g in all cores indicating that these near surface sediments never became fully anoxic

foraminiferal changes and geochemical profiles across the cenomanian turonian boundary in central and south east poland two sections of the upper cenomanian and lower turonian in central and south east poland were investigated for foraminifers caco3content carbon content insoluble in hcl corg and in the carbonates ccarb carbon and oxygen isotopic composition of bulk rock carbonates and elemental abundances the cenomanian turonian boundary interval is characterized by the appearance of more marly facies a 13c and 18o stable isotope anomaly a considerable increase in corg content and decrease in ccarb content and substantial changes in the foraminiferal assemblages a major carbon stable isotope excursion with a shift of 2 pdb occurs in the lowermost whiteinella archaeocretacea zone the late cenomanian 13c anomaly is associated with heavy 18o values the peak value of 13c corresponds to the minima in p b ratio and in diversity of foraminiferal assemblages a late cenomanian anoxic event is thought to be responsible for changes in foraminiferal assemblages however elemental abundance analyses do not show changes in the concentrations of trace elements this may be explained by the long distance between studied area and a source of enrichment which was probably located in the western hemisphere

rhenium osmium geochronology of the toarcian posidonia shale sw germany abstract black shale samples from sedimentary layers below and between the unterer stein oberer stein inoceramus bank and nagelkalk horizons from the dormettingen quarry sw germany were analysed for their re and os isotope composition and content the 12 m thick sedimentary sequence of the posidonia shale formation composed of multiple layers of black shale and intercalated limestone beds was deposited during the early jurassic toarcian a time during which black shale sedimentation was ubiquitous in western europe during a widespread oceanic anoxic event both the marl and shale layers beneath the black shales and adjacent to the oberer stein limestone layer show signs of bioturbation the excellent biostratigraphic constraints and the high re and os contents 24 290 ppb and 290 1050 ppt respectively of the dormettingen shales thus make these samples ideal for testing the influence of bioturbation on the re os isotope system as well as refining age constraints for the toarcian oae and potential triggers for this event the calculated isochron age for the dormettingen shales is 183 0 2 0 ma with a low initial 187os 188osi of 0 377 0 065 indicating a pliensbachian to toarcian age this age is in agreement with published u pb and re os ages for other lower jurassic sites astronomical constraints and biostratigraphic correlations suggesting limited disturbance of the isotope system by minor degrees of biological activity the low 187os 188osi is consistent with significant influx of mantle derived material into the toarcian ocean likely from weathering of karoo ferrar large igneous province basalts

isotopic composition of osmium in terrestrial samples determined by accelerator mass spectrometry interest has revived in the rhenium osmium system due to significant advances in detection methods1 4 and because of its use for the identification of extraterrestrial material at the cretaceous tertiary boundary5 another perhaps more important application is its use as a tracer for the origin of crustal material this application is however severely restricted by the very low concentrations typical of crustal rocks we present here the first results for the isotopes 187os 188os and 189os measured in sub p p b parts per 109 level samples by accelerator mass spectrometry ams our first exploratory measurements on extraterrestrial and crustal material with os concentrations between 2 p p m parts per 106 and 0 006 p p b show a detection limit of 0 01 p p b and a precision of better than 10 the 187os 186os ratios measured for samples for the canyon diablo meteorite and from the east clearwater crater in quebec canada were close to 1 typical of extraterrestrial material in contrast ratios in samples from the ries crater in germany were around 10 which is evidence of predominantly crustal osmium in these rocks

molybdenum in the northeast pacific ocean1 the concentration of dissolved molybdenum has been determined in several profiles from the northeast pacific ocean the salinity normalized concentration is essentially constant in all open ocean samples 107 nm 1 2 5 nm the dissolved distribution is not significantly affected by biological cycling

osmium isotopes and silver as tracers of anthropogenic metals in sediments from massachusetts and cape cod bays high concentrations of osmium os and silver ag and low 187os 186os ratios in boston sewage make these elements sensitive tracers of the influence of sewage on marine sediments in massachusetts and cape cod bays pristine marine sediments have ag concentrations more than 200 times lower than sewage sludge os concentrations 10 40 times lower and 187os 186os ratios six times higher surface sediments from both massachusetts and cape cod bays exhibit both high ag concentrations and low 187os 186os ratios indicating the influence of sewage particles on marine sediments in this region extends some 70 km from the point of sewage release in detail the distribution of os and ag do not support a model of simple physical mixing of sewage particles with normal marine sediments deviations from the mixing model may be the result of fractionation of os and ag in the marine environment and or independent temporal variations in the os and ag content of the waste stream the results of this investigation suggest that osmium isotopes may be widely applicable as tracers of the influence of sewage on sediments in estuarine environments and that subtle variations in the isotopic composition of os in the waste stream may help constrain the sources of os and other metals delivered to the environment

molybdenum isotope multiple sulfur isotope and redox sensitive element behavior in early pleistocene mediterranean sapropels abstract organic rich sediments sapropels deposited in the mediterranean are presumed to have formed during periods of increased productivity and or deep water oxygen depletion possibly including the development of sulfidic conditions euxinia geochemical redox proxies re mo mo isotopes v fe al and multiple s isotopes in 8 sapropels from the pleistocene confirm water column euxinic conditions of varying intensity during sapropel deposition these same proxies indicate an oxic origin for hemipelagic sediments deposited between sapropel forming episodes in one intensively sampled sapropel deposited between 1 450 and 1 458 ma changing concentrations of organic carbon ba re mo v and fe al track one another closely reflecting coupling between water column euxinia and biological productivity multiple s isotope data from this sapropel suggest that the redox interface where oxidative sulfur cycling occurred was present in the sediments during hemipelagic sedimentation but moved into the water column during sapropel deposition molybdenum isotopes of these 8 sapropels encompass a range of values 98mo 0 2 to 1 7 but are all 98mo depleted relative to seawater 98mo 2 3 suggesting that quantitative removal of mo did not occur this finding contrasts with modern black sea sediments in general re mo ratios in sapropels are greater than in modern seawater implying that the water column was not sufficiently sulfidic during sapropel forming episodes to induce complete removal of both these elements surprisingly the heaviest 98mo values are found within hemipelagic sediments very few of the hemipelagic samples preserve the negative 98mo values commonly associated with modern oxic marine sediments many of the hemipelagic samples also contained higher concentrations of re and mo than are common in oxic sediments these features may be attributable to diffusion from the sapropels of a 98mo enriched component into the hemipelagic sediments

impure marbles of the lesser himalaya another source of continental radiogenic osmium abstract the marked rise of the 187 os 188 os ratio of seawater over the cenozoic era is generally attributed to increased continental input and particularly to increased erosion of black shales thus os isotopes are thought to trace the weathering of organic carbon here we present evidence that impure marbles lacking organic carbon provide an important source of radiogenic os to the bedload of himalayan rivers these marbles provide a critical component necessary for balancing the os isotopic budget of the bedloads the analyzed marbles have 187 os 188 os ratios as high as 194 and often contain as much 187 os as typical black shales most of this radiogenic os is not contained in the carbonate itself but rather in associated phases these phases are often of hydrothermal origin and their os may ultimately be provided by fluids circulating through black shales while these results complicate the relationship between the os isotopic ratio of seawater and erosion of organic rich rocks they also provide new information necessary for understanding the marine os isotopic record

re os system of black schist from the mesoproterozoic bayan obo group central inner mongolia china and its geological implications abstract the mesoproterozoic bayan obo group in central inner mongolia china represents a sedimentary sequence deposited in the bayan obo rift basin new re os dates are reported here for the black shale schist from the group re os geochronology of the black schist provides an age of 1447 42 ma which is consistent with the previous work from the literature and provides a direct and new constraint for the age of the group the dating indicates that the re os isotopes for the black schist have remained undisturbed during lower amphibolite facies metamorphism the ca 250 ma age for gold bearing sulfides also indicates that the re os isotopes for the schist have not been affected by hydrothermal overprinting of reduced fluid the initial 187 os 188 os value of 0 93 0 14 for the schist is interpreted to represent the os isotopic composition of the seawater during deposition of the group which indicates that the os composition of mesoprotozoic seawater fluctuated during the mesoproterozoic and was temporary very radiogenic similar to present day seawater the re os data suggests that rifting of the bayan obo basin peaked during ca 1447 ma and the bilute formation in the bayan obo group may have been deposited in the bayan obo sea in a restricted or semi restricted depositional environment

intensification of the oxygen minimum zone in the northeast pacific off vancouver island during the last deglaciation ventilation and or export production 1 the oxygen minimum zone omz off vancouver island was more oxygen depleted relative to modern conditions during the allerod 13 5 to 12 6 calendar kyr and again from 11 to 10 kyr the timing of omz intensification is similar to that seen throughout the north pacific although the onset appears to have been delayed by 1500 years off vancouver island radiocarbon dating of coeval benthic and planktonic foraminifera shows that between 16 0 and 12 6 kyr the age contrast between surface and intermediate waters 920 m depth off vancouver island was similar to or slightly less than that today there is no evidence of an increased age difference i e decreased ventilation during the deglaciation particularly during the allerod however sedimentary marine organic carbon concentration and mass accumulation rate increased substantially in the allerod suggesting that increased organic matter export was the principal cause of late pleistocene omz intensification off vancouver island

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

enhanced recycling of organic matter and os isotopic evidence for multiple magmatic or meteoritic inputs to the late permian panthalassic ocean opal creek canada abstract the geochemical record for the permian triassic boundary in northern latitudes is essential to evaluation of global changes associated with the most profound extinction of life on earth we present inorganic and organic geochemical data and re os isotope systematics in a critical stratigraphic interval of pre and post extinction upper permian lower triassic sediments from opal creek western canada paleolatitude of 30 n we document significant and long lived changes in panthalassa seawater chemistry that were initiated during the first of four magmatic or meteoritic inputs to late permian seawater evidenced by notable decreases of os isotopic ratios upsection geochemical signals indicate establishment of anoxic bottom waters shortly after regional transgression reinitiated sedimentation in the late permian euxinic signals are most prominent in the upper permian sediments with low organic carbon and high sulfur contents and gradually wane in the lower triassic the observed features may have been generated in a strongly euxinic ocean in which high bacterioplankton productivity sustained prolific microbial sulfate reduction in the sediment and or water column providing hydrogen sulfide to form pyrite this scenario requires nearly complete anaerobic decomposition of predominantly labile marine organic matter om without the necessity for a complete collapse of primary marine productivity similar geochemical variations could have been achieved by widespread oxidation of methane by sulfate reducers after a methanogenic burst in the late permian both scenarios could have provided similar kill mechanisms for the latest permian mass extinction despite the moderate thermal maturity of the section om in all studied samples is dominantly terrestrial and or continentally derived recycled and refractory ancient om we argue that as such the quantity of the om in the section mainly reflects changes in terrestrial vegetation and or weathering and not in marine productivity at opal creek a pyrite layer and

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

sources and sinks of unradiogenic osmium runoff from papua new guinea the fly and sepik are two of the largest rivers draining the island of new guinea and among the world s large rivers in discharge and sediment yield sediment from the upper fly river and its delta have low 187os 188os of 0 511 0 560 and sediments from the upper and lower sepik river have even lower ratios of 0 294 0 418 filtered waters 1 2 burial of os of both seawater and riverine derivation occurs in conjunction with organic carbon burial in the gulf of papua there is a negative correlation between the os isotopic composition of the bulk sediment and the fraction of organic matter of terrestrial origin based on c isotopes the systematic relationship between c and os isotopic compositions in these samples indicates that organic matter is the major host of os in tropical estuarine sediments the os corg of gulf of papua surface sediments is intermediate between that of other modern and ancient sediments approximately 1011 mol yr of corg and 20 57 mol yr of os are buried in the inner shelf 50 m depth of the gulf of papua over an area of only 21 000 km2 corresponding to 1 3 of the global marine os burial flux in 0 006 of the total sea surface area these results suggest that a large proportion of the global burial flux of os may take place in conjunction with the deposition of low corg sediments lowering of the os isotopic composition of ambient seawater due to a large flux of unradiogenic riverine os may be indicated by the os isotopic composition of water from the coral sea 187os 188os 0 844 and marine sediments within the gulf of papua the island of new guinea is estimated to provide 4 5 of the global riverine os flux given the very large particulate and dissolved flux to the oceans from rivers in the wet tropics the effect of the weathering of young arc related crust in the sw pacific is an important source of unradiogenic os to modern seawater

geochemical and palaeontological studies of the δ13c anomaly in boreal and north tethyan cenomanian turonian sediments in germany and adjacent areas in two sections of the upper cenomanian and lower turonian of northwest germany boreal realm north sea basin and southeast germany north tethys regensburg area stable isotopes 13c 18o acid soluble manganese carbonate contents and foraminifera were investigated in addition other sections across norttwest and middle europe are reviewed with respect to the detailed stratigraphy of a positive 13c anomaly which was found earlier to be of global importance in the archaeocretacea foraminiferal zone cenomanian turonian transition the 13c excursion was found to be isochronous with the lower limit marked by the extinction of the foraminiferal genus rotalipora the upper limit is found immediately above the entry of the foraminiferal praeglobotruncana helvetica bolli in the macrofossil zonation the base is marked by the occurrence of the belemnite actinocamax plenus blainville in the upper part the metoicoceras geslinianum ammonite zone the upper limit falls in the watinoceras coloradoense ammonite zone just above the entry of the inoceramid genus mytiloides in some cases the 13c excursion refers to a maximum of a more or less well expressed oscillation of the 13c values with minima in the lowermost cenomanian and the upper turonian in other cases 13c is constant with a marked spike at the position of the anomaly the locally different structures of the 13c trends point to incomplete mixing of water masses between basins in northwest europe a manganese anomaly associated with the 13c excursion in the anglo paris basin was found at a higher position in northwest germany and is apparently absent from the german north tethys in both cases high mn contents appear to be associated with a markedly increased terrigenous input expressed by an increase in grainsize of the acid insoluble residue the stratigraphical value of the mn anomaly is therefore limited the palaeoecological conditions are discussed in terms of foraminiferal diversity and the occurrences of macrofossils a shift to higher 18o values coincident with the 13c excursion is possibly a response to cooling of ocean water for which evidence is provided by a low diversity globular planktonic assemblage the correlation of 18o and foraminiferal diversity is suggested to provide a tool for bathymetric interpretations of sections but needs further investigations

anoxic sediments an important environment for pge an overview anoxic sediments and metasediments have been recently recognized as important host environments for the platinum group elements pge economically significant pge concentrations have been reported from marine metal rich black shales in china yukon canada and poland these ore bearing horizons are characterized by extremely restricted vertical and sometimes larger horizontal extents they are associated with the evolution of intracontinental rifting structures without any magmatic activity suggesting a possible driving mechanism for mineralization processes complex pge associations including a significant relationship of pd and pt with ni bi se y and also with sb cu co au u and f are suggested using the results of a new statistical evaluation of available geochemical data these occurrences show more common features with other hydrothermal pge deposits the rift volcanic related marine metal rich black shales of the czech republic and finland however display lower pge values the mineralized layers are much thicker with a typically limited horizontal extent showing a close association with volcanic centres pd reveals a strong correlation with ni zn au and v pt exhibits a highly significant link with the cu and mo phases low average nicu ratios and pge au chondrite normalized patterns are similar to those of some magmatic pge deposits hosted in mafic and ultramafic rocks it is very likely that organic matter played an important role in the genesis of pge accumulations in metal rich black shales in both rift and rift volcanic related environments

petrography mineral chemistry fluid inclusion microthermometry and re os geochronology of the kure volcanogenic massive sulfide deposit central pontides northern turkey the re os isotopic system is applied for the first time to the sulfide ores and the overlying black shales at the kure volcanogenic massive sulfide deposit of the central pontides northern turkey the ore samples collected include predominantly pyrite accompanied by chalcopyrite sphalerite and other species massive ore is almost free of gangues whereas the stockwork ore includes quartz and calcite gangue the composition of sphalerite is similar to ancient and modern massive sulfide mineralizations globally microthermometric studies from quartz from the stockwork ore has shown two populations of two phase fluid inclusions with vapor liquid ratios between 4 to 28 low to intermediate th 161 5 317 0 c and low salinities 0 9 5 wt nacl equiv which are mostly in good agreement with the ranges for volcanogenic massive sulfide mineralizations these studies also suggest a h2o cacl2 kcl mgcl2 ore forming fluid system in a shallower subsurface near the seafloor vents the re os dating of the llhr sulfides yield a nominal depositional age of upper toarcian for the massive sulfide mineralization two largely different model ages obtained are attributed to other pyrite crystallization events prior to and postdating the main sulfide deposition some lower homogenization temperatures 200 c from the quartz of the stockwork may also similarly be related to the post vms events it is concluded that a submarine volcanic extrusion episode has continued until upper toarcian in the kure basin when it has entered a stagnation period that allowed the discharge of hydrothermally circulated sulfide laden fluids from the seafloor vents this age data promotes the palaeotectonic models interpreting the kure basin as a permian early jurassic marginal back arc basin of the devonian triassic karakaya ocean the re os data from the overlying black shale provide a glimpse to the initial os isotope ratio of the water column at the time of the sedimentation 0 45 0 46 for 180 ma the lack of common os from the sulfides does not let us to infer a source of os and initial 187os 188os ratios from the black shale are not statistically robust to make a significant deduction a further detailed study on the isotopic composition of the black shale strata may help us to make an apporach to the os source s in the deposition environment of the kure vms deposit

sediment accumulation in the central western black sea over the past 5100 years the postdepositional particle flux accumulation rate over the last 5100 years was studied in the anoxic sediment units i and ii from the central western black sea deposition of unit ii sapropel in the deep black sea basin was divided further into two subunits the beginning of the deposition of the sapropel in the black sea 5100 3100 years b p subunit iib was characterized by higher organic carbon accumulation rates due largely to higher primary production accumulation rates of lithogenic matter were at a minimum compared to younger units during the subsequent 2100 years 3100 1000 years b p subunit iia organic carbon accumulation rates decreased considerably while accumulation rates of lithogenic matter increased to the present level at 1000 years b p unit i total mass accumulation rates increased by a factor of 3 this increase was largely a result of an increase in carbonate accumulation rates by a factor of 11 which was caused by the rapid appearance of emiliania huxleyi in the black sea higher carbonate accumulation rates in unit i are mainly the cause for the considerably lower organic carbon content compared to unit ii since the organic carbon accumulation rate in unit i did not decrease general correspondence of accumulation rates of lithogenic matter in different cores through time suggests overregional long term 100 year scale climatic effects on the terrigenous particle supply to the black sea

osmium isotopic variations in metalliferous sediments from the east pacific rise and the bauer basin the osmium concentration and isotopic composition of metalliferous sediments from the east pacific rise epr and bauer basin have been determined 187os186os ratios range from 7 9 to 8 6 with epr samples between 8 4 and 8 6 and bauer basin samples between 7 9 and 8 2 the osmium isotopic composition of epr samples is indistinguishable from the inferred osmium isotopic composition of seawater requiring that nearly all the osmium in these sediments is hydrogenous in origin this result is used to place broad constraints on the behavior of osmium in ridge crest hydrothermal systems while bauer basin samples also contain predominantly hydrogenous osmium an additional source of osmium with low 187os186os is required to account for the lower measured ratios calculation of total osmium burial fluxes in the bauer basin show that the background flux of cosmic osmium is adequate to produce the observed depression in bauer basin 187os186os ratios burial flux calculations also suggest that metalliferous sediment deposition is a significant sink in the marine osmium cycle

spectral properties and aster based alteration mapping of masahim volcano facies se iran abstract this study applies advanced spaceborne thermal emission and reflection radiometer aster data and the mixture tuned matched filtering mtmf algorithm to map the sub pixel distribution of alteration minerals associated with the masahim volcano se iran for understanding the spatial relationship between alteration minerals and volcano facies investigations of the alteration mineralogy were conducted using field spectroscopy x ray diffraction xrd analysis and aster short wave infrared swir spectral data in order to spectrally characterize the stratovolcano deposits lithological units and alteration minerals the volcano was divided into three facies the central proximal and medial distal facies the reflectance spectra of rock samples show absorption features of a number of minerals including white mica kaolinite montmorillonite illite goethite hematite jarosite opal and chlorite the end members of key alteration minerals including sericite phyllic zone kaolinite argillic zone and chlorite propylitic zone were extracted from imagery using the pixel purity index ppi method and were used to map alteration minerals accuracy assessment through field observations was used to verify the fraction maps the results showed that most prominent altered rocks situated at the central facies of volcano the alteration minerals were discriminated with the coefficient of determination r2 of 0 74 0 81 and 0 68 for kaolinite sericite and chlorite respectively the results of this study have the potential to refine the map of alteration zones in the masahim volcano

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

a model for the oceanic mass balance of rhenium and implications for the extent of proterozoic ocean anoxia the final publication is available at elsevier via https doi org 10 1016 j gca 2018 01 036 2018 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

sea level changes and geochemical anomalies across the cenomanian turonian boundary pecinov quarry bohemia relationships between geochemical anomalies sea level change and other events were studied in the cenomanian turonian boundary interval in the pecinov quarry in southwestern part of the bohemian cretaceous basin czech republic a major 3rd order sea level rise at the base of the late cenomanian m geslinianum zone was followed by deposition of organic enriched mudstones in a succession of parasequences deposited in response to high frequency 4th order sea level fluctuations and recording a stepwise decrease in bottom oxygenation towards intensely dysaerobic conditions a complex 13c excursion occurs in total organic matter of the late cenomanian deposits a sequence boundary of latest cenomanian age in the pecinov section is correlated to a global sea level fall during the n juddii zone a renewed sea level rise occurred during the early turonian w coloradoense zone and reached maximum flooding during the m nodosoides zone during the early turonian bottom waters were generally aerobic and the positive 13c excursion waned early in the w coloradoense zone the magnitude of the 13c excursion more than 4 is approximately the same as in north america and northern africa confirming that it was controlled by a global paleoceanographic mechanism the absence of anoxia and a 13c anomaly during the peak flooding of early turonian age suggests that widespread deposition of organic enriched deposits as well as the positive shift in 13c generally did not depend on the absolute elevation of sea level but rather on the area of newly flooded land during transgression abrupt small scale shifts in 13c towards higher values coincide with the flooding surfaces of parasequences and may reflect either regional changes in the proportion of marine and terrestrial organic matter or rapid global changes in isotopic composition of marine organic matter related to high frequency sea level changes abundances of ir sc cr v and other elements previously reported as forming anomalous concentrations in the boundary interval showed no enrichment in the bohemian section this is most probably due to the large distance of the depositional site from the presumed volcanic source of element enriched deep waters in the proto caribbean region anomalous concentration of mn at the base of the turonian deposits was caused by diagenetic incorporation of mn into siderite

osmium isotope geochemistry of a tropical estuary abstract fundamental aspects of the estuarine geochemistry of os were investigated by analysis of the os isotope composition and concentration variations in filtered water samples from a salinity transect taken in the estuary of the tropical fly river of new guinea 187os 188os of the waters in the salinity transect increase with salinity from 0 6165 in the river endmember 0 1 salinity to a maximum of 0 913 in the most saline water 33 these values are distinctly lower than the 187os 188os of 1 06 reported for open ocean waters from the indian and pacific oceans sharma et al 1997 levasseur et al 1998 woodhouse et al 1999 the os concentrations in the waters range from a minimum of 4 59 pg os g in the river to a maximum of 5 66 pg os kg at 12 salinity these concentrations are all significantly lower than the open ocean range of 6 6 to 10 86 pg os kg levasseur et al 1998 woodhouse et al 1999 the isotopic results indicate that the rivers draining the new guinea landmass provide unradiogenic dissolved os to the oceans and led to a lowering of the 187os 188os of the local seawater the os concentration salinity relationship indicates that the mixing process is not conservative and that removal of os from the dissolved state has taken place the proportion of os lost from solution increases with salinity resulting in removal of a large proportion of seawater os in the estuary high concentrations of os in marine sediments within the gulf of papua were previously interpreted to be due to incorporation of seawater derived os into organic matter martin et al 2000 earth planet sci lett 183 261 274 and are the likely complement to the processes observed in the dissolved state enhanced removal of seawater os in estuaries could help to resolve the differences in estimates of os residence time made on the basis of oceanic deposits versus those based on measured river water concentrations

rhenium in indian rivers sources fluxes and contribution to oceanic budget 1 the abundance and distribution of dissolved and particulate rhenium re has been measured in several rivers draining the himalaya and peninsular india from their origin to outflow into the bay of bengal and the arabian sea the large data set resulting from this study on rivers flowing through a variety of lithologies e g the crystallines and sediments of the himalaya deccan basalts vindhyan sediments and the indian shield significantly enhances our understanding of the aqueous geochemistry of re and also constrains its sources to rivers and fluxes to the sea the concentration of dissolved re in rivers of the himalaya and the peninsular india shows wide range 1 4 to 72 7 pmol kg mean 7 8 pmol kg and 0 5 to 122 pmol kg mean 15 pmol kg respectively the discharge weighted average annual flux of dissolved re transported by the rivers from these regions are 5800 and 15 700 mol year respectively the major source of dissolved re as determined from inter element associations is black shales for the himalayan rivers and pyrites in basalts for the east flowing deccan rivers in addition there are evidences of considerable anthropogenic supply of re to some of the rivers that have very high re concentrations estimates of anthropogenic supply based on their re k ratios suggest that this source accounts for most of the re in the peninsular rivers particularly the godavari the annual flux of anthropogenic re transported by the peninsular rivers is 14 600 mol most of which is from the godavari this anthropogenic flux accounts for 70 of the total re supply by the indian rivers to the adjacent seas and 3 4 of the global riverine flux to the oceans the global average pre anthropogenic natural concentration of dissolved re in rivers is estimated to be 3 pmol kg based on re k correlation this value is much lower than the contemporary average determined from the measured concentrations and earlier estimate of natural re based on re so4 link

precipitation of molybdenum from euxinic waters and the role of organic matter abstract molybdenum preserved in organic rich shales is a key archive employed in studying earth s past oxygenation and life s evolution in these shales positive correlations between mo and corg are common and have been attributed to mo scavenging from seawater by organic shuttles here we argue that known organic ligands are too weak or too scarce to capture more than minor amounts of mo from seawater especially in competition with sulfide alternatively we demonstrate that mo corg correlations can arise simply from microbially mediated oxidation of corg by so42 this process produces sulfide and lowers ph triggering precipitation of femos4 which soon transforms irreversibly to femos2 s2 in euxinic basins the extent of sulfate reduction progress increases with depth and can be modeled as an empirical function of biological productivity and water replacement time the response of dissolved mo to sulfate reduction progress occurs in three stages identified by a thermodynamic model in stage i progress is too small to precipitate mo from waters that are only mildly sulfidic in stage ii the flux of mo to sediments is promoted by sulfate reduction progress giving rise to positive mo corg correlations in sediments due to fluctuations in biological productivity in some cases precipitation in this stage begins before mos42 becomes the predominant dissolved mo species in which case femos4 with negative 98mo can be produced in stage iii the flux of mo becomes independent of further sulfate reduction progress and mo corg correlations degrade as reported in extremely corg rich shales even though the model omits a number of potentially important processes its predicted mo profiles in waters of several modern euxinic basins are qualitatively reasonable and are consistent with observed reduction of movi in water to moiv in sediments according to the model spikes in atmospheric pco2 will markedly increase mo accumulation and lower 98mo in euxinic basin sediments this appears to have occurred repeatedly during the phanerozoic and may be commencing now as a result of fossil fuel combustion minimal deposition of mo in organic rich shales during the archean has been attributed to low moo42 in seawater but seems more likely to be due to low so42

further evaluation of the re os geochronometer in organic rich sedimentary rocks a test of hydrocarbon maturation effects in the exshaw formation western canada sedimentary basin abstract re os isotopic analyses of a single organic rich sedimentary rock unit ors of known depositional age and at three levels of regional hydrocarbon maturity show that hydrocarbon maturation does not affect the ability the 187re 187os chronometer to yield a depositional age for such rocks we present re os isotope analyses from the late devonian exshaw formation in the subsurface of the western canada sedimentary basin alberta and obtain a re os isochron age of 358 10 ma 2 model 3 1 666 10 11 a 1 for samples ranging from hydrocarbon immature to overmature this age is within uncertainty of the established absolute age for the exshaw formation hydrocarbon immature and mature plus overmature samples show no significant age differences if regressed individually indicating that hydrocarbon maturation did not greatly disturb the re os isotope system in the exshaw formation as such we propose that the re os geochronometer may be used as a reliable tool for measuring the depositional ages of ors regardless of their level of hydrocarbon maturity we find that minimizing natural variation in the initial 187os 188os ratio is more important than avoiding hydrocarbon maturation in obtaining precise re os ages in particular the exshaw formation appears to contain a nonhydrogenous component of unradiogenic os in addition to the hydrogenous os load a subset of exshaw formation samples with 5 total organic carbon toc which should best reflect the hydrogenous os load alone yields a very well fitted isochron having a depositional age of 358 9 ma 2 1 666 10 11 a 1 with an initial 187os 188os ratio of 0 59 0 05 model 3 mean square of weighted deviates mswd 1 8 the initial 187os 188os ratio of this regression may provide an estimate of the os isotopic composition of local seawater at the time of deposition

co variation of nitrogen isotopes and redox states through glacial interglacial cycles in the black sea abstract in all aquatic environments nitrogen cycling within the water column is strongly influenced by oxygen we hypothesize that the nitrogen isotopic composition 15 n of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition we tested the hypothesis by measuring the bulk sedimentary 15 n values in a drill core from the black sea a basin that alternates between oxic less saline conditions and anoxic marine conditions on glacial interglacial time scales we reconstructed these changes in black sea redox conditions using sedimentary 15 n total organic carbon toc total nitrogen tn redox sensitive metals and micropaleontological data from a deep sea core dsdp site 380 the sedimentary data reveal that during the transitions between oxic and anoxic conditions 15 n values increased relative to the preceding and succeeding quasi steady state oxic and anoxic periods the results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification during the quasi stable oxic and anoxic states characterized by glacial fresh water and interglacial marine conditions nitrification and complete nitrate utilization respectively dominate the nitrogen cycle while other factors may influence the 15 n record our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the black sea subphotic zone on glacial interglacial time scales and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems our model suggests that the nitrogen isotopic composition of marine sediments on geological time scales can be used to reconstruct the redox state of the overlying water column

re os sm nd and pb isotopic constraints on mantle and crustal contributions to magmatic sulfide mineralization in the duluth complex abstract previous petrologic and stable isotopic studies of sulfide mineralization in the duluth complex have led to the premise that sulfide genesis is strongly linked to the interaction between mantle derived magmas and sedimentary country rocks in a rift zone environment in order to more fully evaluate the nature of this interaction and to gain an insight into the possible importance of externally derived metals in the ore forming process pb sm nd and re os isotopic studies of the babbitt cu ni deposit were initiated rock types examined include low sulfide troctolite that show very little petrologic evidence for contamination disseminated sulfide bearing troctolitic to gabbroic rocks that occur close to the basal contact with country rocks and contain metasedimentary xenoliths and massive sulfide lead isotopic values of whole rocks plagioclase mineral separates and massive sulfides show only subtle differences and are compatible with 3 to 5 contamination of a mantle derived melt with a proterozoic crustal contaminant e nd 1 1 ga values of the troctolite and gabbro samples are chondritic and only the massive sulfides show strong evidence for contamination based on sm nd isotopic values massive sulfides tend to be more sensitive indicators of contamination in the sm nd system because of late stage incorporation of a light rare earth element rich fluid into a ca po 4 apatite component of the immiscible sulfide liquid os 1 1 ga values are also strongly anomalous and range from 500 to 1200 in disseminated sulfide bearing troctolites and massive sulfides these values are also consistent with from 1 to 3 contamination by c rich and strongly radiogenic proterozoic sedimentary rocks elemental and isotopic mass balance calculations suggest that up to 50 of the pb and at least 35 of the os in the sulfide mineralization have been derived from external sources a corollary is that other metals may also be in part derived from external sources which would aid in explaining the compositional diversity of the sulfide mineralization selective assimilation of country rocks by mantle derived magmas may occur in crustal staging chambers during ascent to shallower levels or in situ as a result of devolatilization reactions and partial melting

re os isotope systematics in black shales from the lesser himalaya their chronology and role in the 187os 188os evolution of seawater abstract re and os abundances and os isotope systematics have been measured in a number of black shales sampled from outcrops and two underground phosphorite mines maldeota and durmala in the lesser himalaya the re and os concentrations in these samples exhibit wide range 0 2 to 264 ng g and 0 02 to 13 5 ng g respectively with a mean re os of 25 the 187 os 188 os of these samples also show a broad range 1 02 to 11 6 with many of them far more radiogenic than the currently eroding continental crust the black shales from the maldeota and durmala mines collected a few meters above the krol tal pc c boundary and occurring in the same stratigraphic horizon yield 187 re 187 os isochron ages of 554 16 and 552 22 ma respectively consistent with fossil evidences and those assigned for the pc c boundary at various other locations these results indicate closed system behaviour of re and os in these mine samples and reaffirm the validity of 187 re 187 os pair to date organic rich sediments the age of these mine samples from the outer belt seems to be a few hundred millions of years younger than the preliminary re os age of 839 138 ma for black shales from theog collected from the inner belt these initial results lean toward the hypothesis that the inner belt sediments were deposited earlier than the outer belt however more analyses of black shales are needed to confirm this the role of weathering black shales from the himalaya in contributing to the os isotope evolution of seawater over the past 25 ma was assessed using a simple budget model for seawater os and assuming values for os fluxes and 187 os 188 os based on the available limited data on os concentration and its 187 os 188 os in rivers and oceans these calculations indicate that the required contributions from black shale weathering to account for the entire increase in oceanic 187 os 188 os over the past 16 ma is difficult to satisfy by varying only the os flux from htp rivers 187 os 188 os kept constant at 1 324 or their 187 os 188 os 188 os flux constant at today s value 131 moles yr the requirements to balance os isotope budget in ocean through weathering of black shales however is easier to accommodate if both the os flux from htp himalayan tibetan plateau rivers and their 187 os 188 os are allowed to vary measurements of os abundance in htp rivers and its isotopic composition are needed to test the validity of the model results

re os age and depositional environment for black shales from the cambrian ordovician boundary green point western newfoundland chemical and isotopic signatures for black shales serve as potential proxies for reconstruction of paleoenvironmental conditions here we bring rock eval major and trace element and re os isotopic data together to examine the environmental record at the cambrian ordovician global stratotype section and point gssp at green point in western newfoundland canada the green point shales are oil mature and contain type ii organic material of marine origin a re os isochron for the shales provides the first radiometric age for shale deposition at the gssp at 484 16 ma with an initial 187os 188os ratio of 0 74 0 05 model 3 age mswd 21 n 13 2 uncertainties factor analysis of the geochemical data set shows association of most trace elements with total organic carbon toc and s contents ensuring an authigenic origin for most elements and hence their validity for evaluating the paleo redox state relatively high enrichment factors for redox sensitive elements e g re u and mo compared to average shale but comparatively low enrichment compared to modern black sea sediments suggest deposition in anoxic but not euxinic waters comparison of lower ordovician shale geochemistry data sets at a global scale leads us to suggest that anoxic conditions and warm oceanic regimes were restricted to the margins of laurentia and baltica whereas depositional basins with colder waters e g avalonia and gondwana were less reducing these outcomes underscore the important role of paleogeography in regulating oceanic conditions and marine life

stable isotope evidence for foraminiferal habitats during the during of the cenomanian turonian ocean anoxic event oxygen and carbon isotope analyses of several species of size controlled planktonic and benthic foraminifera from the plenus marls of dover kent england show a clear separation in oxygen and carbon isotope ratios consistent with different habitats the analyses indicate the existence of vertical gradients of temperature and 13 c in dissolved co 2 in the chalk sea whereas sequential ontogenetic stages of planktonic foraminifera do not show systematic variations in 18 o or 13 c values implying no systematic change in depth habitat during the growth of individual species species of the genera hedbergella and dicarinella are interpreted to have lived nearer to the surface than rotalipora because vertical 13 c gradients in the chalk sea remained stable during the late cenomanian the oxygen minimum zone is unlikely to have impinged on this area

an osmium based method for assessing the source of dissolved rhenium and molybdenum to archean seawater abstract authigenic enrichments of re and mo in 2 7 2 5 ga organic rich mudrocks orm indicate that dissolved re and mo were present in late archean seawater however it can be difficult to determine if the dissolved re and mo were sourced from oxidative crustal weathering or magmatic hydrothermal extraterrestrial mhe inputs comparison of re mo and 192 os non radiogenic os isotope concentrations and initial 187 os 188 os isotope compositions from re os isochron regressions of orm can shed insight on the source of re and mo to archean seawater seawater 187 os 188 os reflects the relative contributions of radiogenic crustal versus unradiogenic mhe os inputs to seawater during the phanerozoic transient increases in magmatic hydrothermal activity marked by unradiogenic 187 os 188 os excursions and higher 192 os concentrations in orm are accompanied in some cases by higher re concentrations these unradiogenic os sources could thus have played a greater role in the archean marine re and possibly mo budget given that the riverine re and mo flux at that time was likely smaller than the phanerozoic flux hence a positive correlation between re mo and 192 os concentrations in archean orm that yields unradiogenic initial 187 os 188 os may reflect a mhe origin for dissolved re and mo in the overlying paleo seawater local oxidative weathering in the presence of photosynthetic o 2 of mafic ultramafic rocks and crustal sulfide minerals with low re os ratios is an alternative explanation but the two scenarios cannot be readily distinguished on the basis of initial 187 os 188 os by contrast an initial 187 os 188 os from archean orm that is statistically higher than the mhe baseline of 0 10 0 11 points to oxidative mobilization of re os and mo from crustal sulfide minerals rhenium and mo concentrations that are negatively correlated with 192 os concentrations in archean orm yielding unradiogenic initial 187 os 188 os suggests that some re and mo were derived from oxidative weathering such negative correlations may reflect an increased marine os sink adsorption to oxide minerals during a mild increase in local environmental o 2 levels these concepts may help trace the onset of photosynthetic o 2 production and accumulation along archean ocean margins

pge re os and mo isotope systematics in archean and early proterozoic sedimentary systems as proxies for redox conditions of the early earth abstract re os data and pge concentrations as well as mo concentrations and isotope data are reported for suites of fine clastic sediments and black shales from the barberton greenstone belt south africa fig tree and moodies groups 3 25 3 15 ga the belingwe greenstone belt zimbabwe manjeri formation ca 2 7 ga and shales from the witwatersrand ventersdorp and transvaal supergroups south africa ranging from 2 95 to 2 2 ga moderately oxidizing conditions are required to mobilize re and mo in the environment mo fractionation only occurs in solution and these parameters thus have potential use as paleoredox proxies for the early earth pge re abundance patterns of barberton greenstone belt sediments are uniform and very similar in shape to those of komatiites this indicates 1 that the pge came from a source of predominantly ultramafic composition and 2 that pge were transported and deposited essentially in particulate form sediments from the younger belingwe greenstone belt show more fractionated pge re patterns and have re os ratios 10 to 100 higher than those of barberton sediments their pge abundance patterns and re os ratios are intermediate between those of the mid archean shales and neoproterozoic to recent black shales they reflect scavenging of re from solution in the sedimentary environment 98 95 mo values of black shales of all ages correlate with their concentrations the barberton greenstone belt samples have 1 3 ppm mo similar to a granitoid basaltic source this mo has 98 95 mo between 1 9 and 2 4 relative to present day mean ocean water molybdenum momo and is thus not isotopically fractionated relative to such a source similar to the pge this indicates transport in solid form sediments from the belingwe greenstone belt show in part enhanced mo concentrations up to 6 ppm and mo isotope fractionation 98 95 mo up to 1 4 relative to momo the combined pge re and mo data show mainly reducing conditions in the mid archean and suggest that by 2 7 ga the atmosphere and oceans had become more oxidizing substantially younger samples from the transvaal supergroup to ca 2 2 ga surprisingly have mainly low mo concentrations around 1 ppm and show no significant mo isotope fractionation relative to the continental source among possible explanations for this are a return to reducing atmospheric conditions after 2 7 ga reservoir effects or mo removal by sulfide precipitation following sulfate reduction in early proterozoic oceans

osmium in marine sediments osmium is enriched in ferromanganese minerals and its concentrations follow those of other pt group metals except pd oxidative capture during solid formation is the probable mechanism for uptake in some sediments forming under reducing conditions phosphorites and anoxic coastal deposits there is also an enrichment this may relate to reductive capture although deposits also formed under reducing conditions from hydrothermal areas are depleted in osmium

hot acidic late permian seas stifle life in record time abstract the end of permian time 252 251 ma hosts the largest mass extinction in earth history yet events heralding this global catastrophe remain intensely disputed we present a chemostratigraphic marker the 187re 188os ratio which soars to unprecedented levels approaching the permo triassic boundary these ratios are tied to profound trace element changes and a precise re os time record at 252 ma preserved in black shales from east greenland and the mid norwegian shelf within a 36 meter shale section an 80 fold increase in re concentrations two fold for os signals seawater conditions that became increasingly inhospitable to life unwavering initial 187os 188os ratios of 0 6 preclude mafic volcanism and meteorite impact as the direct cause of late permian anoxia we argue that extraordinarily high 187re 188os ratios are the hallmark of simultaneously rising ocean temperature and acidity leading to loss of oxygen and the stifling of life in latest permian time

sources of osmium isotopes in manganese nodules abstract we have measured the 187 os 186 os and os concentrations of ferromanganese crusts forming on serpentinized peridotites from the atlantic ocean and also report major element data for these samples and six manganese nodules previously analyzed for os variations in the 187 os 186 os ratios of manganese nodules are the result of two processes operating on different spatial scales the large scale variations result from the impression of intense local os inputs from continental and oceanic sources on a generally homogeneous oceanic 187 os 186 os ratio fine scale variations may be understood as the result of the mixing of a constant fine grained debris flux of meteoritic os imposed on varying amounts of os precipitated from seawater

dissolved rhenium in the yamuna river system and the ganga in the himalaya role of black shale weathering on the budgets of re os and u in rivers and co 2 in the atmosphere extensive measurements of dissolved re and major ion abundances in the yamuna river system yrs a major tributary of the ganga have been performed along its entire stretch in the himalaya from its source near the yamunotri glacier to its outflow at the foothills of the himalaya at saharanpur in addition re analysis has been made in granites and precambrian carbonates some of the major lithologies of the drainage basin these data coupled with those available for black shales in the lesser himalaya allow an assessment of these lithologies contributions to the re budget of the yrs the re concentrations in the yrs range from 0 5 to 35 7 pm with a mean of 9 4 pm a factor of 4 higher than that reported for its global average concentration in rivers dissolved re and cations na k ca mg are strongly correlated in the yrs indicating that they are released to these waters in roughly the same proportion throughout their course the re cations in most of these rivers are one to two orders of magnitude higher than the re na k mg ca measured in granites of the yamuna basin this leads to the conclusion that on average granites crystallines make only minor contributions to the dissolved re budget of the yrs on a basin wide scale though they may be important for rivers with low dissolved re similarly precambrian carbonates of the lesser himalaya do not seem to be a major contributor to dissolved re in these rivers as their re ca mg is much less than those in the rivers the observation that re concentrations in rivers flowing through black shales and in groundwaters percolating through phosphorite black shale carbonate layers in phosphorite mines are high and that re and so4 are significantly correlated in yrs seems to suggest that the bulk of the dissolved re is derived from black shale carbonaceous sediments material balance considerations based on average re of 30 ng g 1 in black shales from the lesser himalaya require that its abundance in the drainage basin of the yrs needs to be a few percent to yield average re of 9 4 pm furthermore the positive correlation between re and cations would require that these re rich sediments e g black shales and re poor lithologies e g crystallines precambrian carbonates contribute re and cations in roughly the same proportion throughout the drainage basin the available data on the abundance and distribution of black shales in the basin are not adequate to test if these requirements can be met the annual fluxes of dissolved re at the base of the himalaya from the yamuna are 150 mol at batamandi and 100 mol at saharanpur compared to 120 mol from the ganga at rishikesh the total flux from the yamuna and the ganga account for 0 4 of the global riverine re flux much higher than their contribution to global water discharge this is also borne out from the mobilization rate of re 1 to 3 g km 2 y 1 in the ganga and yamuna basins in the himalaya compared to the global average of 0 1 g km 2 y 1 black shale weathering can also significantly influence the budgets of os and u in rivers and co2 in rivers and the atmosphere using dissolved re in rivers as a proxy it is estimated that 6 9 108 kg y 1 of black shales are being weathered in the ganga and yamuna basins in the himalaya weathering of such amounts of black shales can account for the reported concentrations of os and u in these rivers furthermore if the weathering results in the conversion of organic carbon in the black shales to co2 it would release 2 105 mol of co2 km 2 y 1 in the yamuna and ganga basins in the himalaya comparable to the co2 consumption from silicate weathering

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

evaluating re os systematics in organic rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments abstract successful application of the 187re 187os geochronometer has enabled the determination of accurate and precise depositional ages for organic rich sedimentary rocks ors as well as establishing timing constraints of petroleum generation however we do not fully understand the systematics and transfer behaviour of re and os between ors and petroleum products e g bitumen and oil to more fully understand the behaviour of re os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks the permian phosphoria formation toc 17 4 type ii s kerogen and the jurassic staffin formation toc 2 5 type iii kerogen the laboratory based hydrous pyrolysis experiments were carried out for 72 h at 250 300 325 and 350 c these experiments provided us with whole rock extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of re os isotopic and elemental abundance the data from these experiments demonstrate that the majority 95 of re and os are housed within extracted rock and that thermal maturation does not result in significant transfer of re or os from the extracted rock into organic phases based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of re and os than sulphides across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187re 188os ratios show small variations 3 3 and 4 7 for staffin respectively and 6 3 and 4 9 for phosphoria respectively similarly the 187os 188os ratios show only minor variations for the staffin and phosphoria whole rock and extracted rock samples 0 6 and 1 4 and 1 3 and 2 2 these isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the re os systematics in ors as supported by various studies on natural systems the elemental abundance data reveal limited transfer of re and os into the bitumen from a type iii kerogen in comparison to type ii s kerogen 0 02 vs 3 7 suggesting that these metals are very tightly bound in type iii kerogen structure the 187os 188os data from the pyrolysis generated phosphoria bitumens display minor variation 4 across the experimental temperatures with values similar to that of the source rock this indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation these data further support the premise that the os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of re or os 120 and 3 ppt respectively in contrast to natural oils 2 50 ppb and 34 288 ppt for re and os respectively which may suggest that kinetic parameters are fundamental to the transfer of re and os from source rocks to oils from this we hypothesise that at the temperatures employed in hydrous pyrolysis re and os are assimilated into the extracted rock as a result of cross linking reactions

the geochemistry of the plenus marls at dover england evidence of fluctuating oceanographic conditions and of glacial control during the development of the cenomanian turonian δ13c anomaly

raman spectroscopy and biomarker analysis reveal multiple carbon inputs to a precambrian glacial sediment extractable biomarkers can help elucidate the environment and biota of ancient glaciations although the method must be applied with care as glacial sediments have a potential for incorporation of older detrital carbon in phanerozoic glacial sediments the distinct elemental molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter however as the proterozoic biosphere was largely microbial and marine biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter here we report the combined application of raman spectroscopy and biomarker analysis to precambrian glacial sediments which together allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening precambrian sediments for immature organic matter amenable to biomarker analysis

the importance of organic rich shales to the geochemical cycles of rhenium and osmium abstract the role that marine organic rich sediments play in the surficial osmium and rhenium cycles has been assumed to be important due to the high re os ratios and high concentrations of these elements in such reducing sediments compared to the average continental crust the high re os leads to rapidly increasing 187os 188os ratios we determine how large a role these sediments play in the surficial osmium and rhenium budgets by compiling a geochemical database to quantify the mean 187re 188os and 187os 188os ratios of organic rich sediments we then utilize estimates of the abundance of organic rich sediments in the geologic record of different ages to estimate an average 187os 188os for these sediments we find that the calculated 187os 188os value of organic rich sediments varies between 2 22 and 2 27 depending on the volume age model used with error estimates of 2 07 to 2 42 and 2 12 to 2 48 respectively despite the fact that these sediments constitute a relatively small proportion of the upper continental crust they contribute a disproportionately large amount 50 to the upper continental crustal rhenium and to a lesser extent 5 10 osmium inventories owing to their high concentrations of these elements

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

sedimentary and geochemical indicators of productivity and oxygen contents in modern and ancient basins the holocene black sea as the type anoxic basin data on the accumulation rates of organic carbon total phosphorus and reduced sulfur over the past 7000 yr from modern abyssal black sea sediments are examined as geochemical monitors of variations in biologic productivity and the development of deep water masses variations in organic carbon accumulation rates at both intermediate and deep water sites are believed to be controlled by the combined effects of enhanced preservation of organic matter under anoxic bottom conditions and the regulation of primary productivity in surface waters by nutrient availability estimates of variations in water column and pore water organic carbon consumption by sulfate reducing bacteria can be made using average carbon and sulfur accumulation rates for various depositional episodes and are examined in the light of changes in the thickness of the h2s zone in the water column the amount of available sulfate within this zone and the reactiveness of particulate organic matter sulfur and phosphorus accumulation rates are used to estimate the maximum amount of phosphorus regenerated from organic matter during bacterial sulfate reduction processes total phosphorus accumulation rates are found to markedly increase over the part 1000 yr and are not proportionally paralled by organic carbon accumulation rates these accelerated phosphorus accumulation rates appear to stem from organic matter degradation adsorption on surfaces of caco3 and perhaps diffusion into sediments from bottom waters and authigenic precipitation of phosphate minerals accumulation rates of organic carbon and phosphorus in black sea sediments are low in comparison to those typical of modern highly productive upwelling zones peru south west africa namibia accumulation rates of reduced sulfur and the ratios of reduced sulfur to organic carbon burial may be higher in anoxic basins than in oxic ones knowledge of accumulation rates therefore rather than concentrations alone may help to differentiate black shales which resulted from enhanced organic matter preservation under anoxic conditions from those resulting from high biologic productivity with or without accompanying oxygen deficiencies

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

correlation of sturtian diamictite successions in southern australia and northwestern tasmania by re os black shale geochronology and the ambiguity of sturtian type diamictite cap carbonate pairs as chronostratigraphic marker horizons recent geochronological studies have raised concerns regarding the accuracy of regional and global correlations of neoproterozoic sedimentary successions using relative dating methods such as carbon isotope chemostratigraphy and glaciogenic diamictite cap carbonate lithological and geochemical characteristics precise and accurate radio isotopic age constraints for neoproterozoic sedimentary rocks thus remain a high priority for establishing a reliable neoproterozoic chronostratigraphy here we present a new re os age of 640 7 4 7 ma from black shales of the upper black river dolomite togari group northwestern tasmania that represents a minimum age for deposition of the immediately underlying diamictite bearing julius river member the upper black river dolomite re os age is statistically identical to a re os age of 643 0 2 4 ma previously determined for the sturtian post glacial tindelpina shale member umberatana group adelaide rift complex southern australia consistent with previous lithostratigraphic and stromatolite biostratigraphic evidence the re os ages suggest broadly coeval deposition of the julius river member and sturtian diamictites and overlying organic rich marine shales consideration of the neoproterozoic geochronological database suggests that sturtian type diamictite cap carbonate pairs cannot be used as chronostratigraphic marker horizons for global correlation of the neoproterozoic rock record

a possible link between the seawater osmium isotope record and weathering of ancient sedimentary organic matter the os isotopic composition of leachable os from a north pacific pelagic clay sequence pegram et al 1992 and bulk sediment samples of metalliferous carbonates deposited near the east pacific rise ravizza 1993 display similar patterns of temporal variation fig 1 this similarity indicates that the composite record of t87os 186os ratio variations reflects changes in the os isotopic composition of seawater temporal changes in the sr isotopic composition of seawater record changes in the relative rates of continental weathering and oceanic crustal alteration the os isotopic composition of seawater should be influenced by similar processes in both the rb sr and re os systems the continental crust is characterized by large time integrated parent daughter ratios compared to the deep earth imparting relatively radiogenic sr and os signatures to continental material however the seawater sr and os records are decoupled from one another over the past 27 ma from 27 to 15 ma 87sr 86sr increased rapidly while the 18vos 186os ratio of seawater remained nearly constant at 15 ma the 87os ts6os ratio of seawater began to increase rapidly but the rate