26al in chondrules from unequilibrated l chondrites onset and duration of chondrule formation in the early solar system abstract al mg isotope records in sixteen ferromagnesian chondrules from five unequilibrated ordinary chondrites uocs four l chondrites with petrologic grades varying from 3 0 to 3 2 and one l ll chondrite with petrologic grade 3 1 were studied using an ion microprobe to look for presence of the now extinct nuclide 26 al at the time of their formation uocs of low petrologic grades were selected to avoid possible thermal perturbation of al mg isotope records in the analyzed chondrules the presence of resolved 26 mg excess due to decay of 26 al in al rich phases such as glassy mesostasis and plagioclase was found in all the chondrules barring a sole exception the inferred initial 26 al 27 al ratios in the chondrules range from 0 6 1 9 10 5 and most of them have values lying between 0 6 1 1 10 5 our data supports a late formation of chondrules relative to cais suggested in previous studies and indicates a time lag of at least 1 5 ma between cai formation and onset of an intense episode of chondrule formation in the early solar system that lasted less than a million years the paucity of chondrules 26 al 27 al 10 5 rules out active chondrule forming events at earlier epochs the presence of rare chondrules with initial 26 al 27 al 5 in uocs of low petrologic grades 3 0 to 3 2 analyzed by us and also reported previously in uocs of petrologic grade ranging up to 3 4 most probably represent parent body processes leading to disturbance of al mg isotope systematics in these cases an extended duration of chondrule formation lasting more than a couple of million years suggested in some earlier studies needs reassessment a long duration of chondrule formation is also difficult to reconcile with the problem of storage isolation mixing and assimilation of chondrules into their meteorite parent bodies

biodegradation and mixing of crude oils in eocene es3 reservoirs of the liaohe basin northeastern china a suite of heavy oils from a single eocene sandstone reservoir section in the liaohe basin northeastern china was analyzed to study the geological controls on oil viscosity which spans a range of almost three orders of magnitude the heaviest oils are biodegraded as determined from the absence of n alkanes and the low relative amount of isoprenoid alkanes the large variation in viscosity can be explained by mixing to various extents of heavy biodegraded oils with less degraded oils this is supported by a simple mixing model which reproduces the observed data excellently the model may assist in predicting the viscosity of reservoired oils before production by analyzing reservoir core extracts prior to deciding which intervals to steamflood

determination of the stable isotope composition and total dissolved solids of athabasca oil sands reservoir porewater part 1 a new tool for aqueous fluid characterization in oil sands reservoirs we present a new method to determine the total dissolved solids tds concentration and the stable isotope composition of drill core derived porewater in oil sands reservoirs of northeastern alberta canada the technique described here uses two end member mixing relationships between the stable isotope compositions of drilling fluids and formation waters from mechanically extracted porewater samples to calculate the formation water tds and values analysis of water samples extracted directly from mcmurray formation drill core provides an inexpensive and robust advance in the ability to characterize the properties of reservoir pore waters that can be widely deployed because of the ubiquity of drill core sampling porewater data from three oil sands wells from different locations within the athabasca region are presented in this study water derived from these wells had tds values of 860 to 45 000 mg l values of 172 to 149 and values of 22 4 to 19 3 these values are consistent with regional trends in formation water salinity and stable isotope compositions and illustrate the wide range of tds values that can be found in mcmurray formation waters the ability to characterize aqueous fluids within bitumen saturated reservoirs is a new development that enables measurement of aqueous fluid properties that is not easily obtained by other sampling means this methodology provides a tool to understand the origin and movement of reservoir water related to natural groundwater flow or to anthropogenic influence by steam injection novel in situ extraction technologies that use electromagnetic heating systems may also benefit from detailed characterization of aqueous reservoir fluids to accurately determine the properties of the reservoir porewater

evolution of protoplanetary disk inferred from 26 al chronology of individual chondrules abstract we review the 26al ages of chondrules in various type 3 0 chondrites the 26al ages of chondrules are 1 3 myr after calcium aluminum rich inclusion cai for ll3 0 co3 0 and acfer 094 ungrouped c 3 0 available data for chondrules in cr chondrites indicate that many chondrules are relatively younger 3 myr although data from chondrules in cr3 0 are not yet available to confirm their younger ages the total ranges for the 26al ages of chondrules in a single chondrite group are more than 0 5 1 myr however most chondrules show relatively narrow range of ages in a single chondrite group 0 2 0 4 myr 1 sd which might be short enough to preserve the group specific chemical and isotope signatures against radial diffusion of solid in the disk distinct oxygen isotope reservoirs might exist in the protoplanetary disk simultaneously which could be spatially separated

hf w chronometry of core formation in planetesimals inferred from weakly irradiated iron meteorites abstract the application of hf w chronometry to determine the timescales of core formation in the parent bodies of magmatic iron meteorites is severely hampered by 182w burnout during cosmic ray exposure of the parent meteoroids currently no direct method exists to correct for the effects of 182w burnout making the hf w ages for iron meteorites uncertain here we present noble gas and hf w isotope systematics of iron meteorite samples whose w isotopic compositions remained essentially unaffected by cosmic ray interactions most selected samples have concentrations of cosmogenic noble gases at or near the lowermost level observed in iron meteorites and for iron meteorite standards have very low noble gas and radionuclide based cosmic ray exposure ages

the age of the solar system redefined by the oldest pb pb age of a meteoritic inclusion the age of the solar system is defined by the formation of the first solid grains in the solar nebula pb pb age dating of these solids which were later trapped in a meteorite indicates that the solar system is 0 34 1 91 million years older than previously thought the age of the solar system can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto sun this age is estimated by dating calcium aluminium rich inclusions in meteorites these inclusions are considered as the earliest formed solids in the solar nebula their formation marks the beginning for several long and short lived radiogenic clocks that are used to precisely define the timescales of solar system events such as the formation and evolution of planetary bodies1 2 3 here we present the 207pb 206pb isotope systematics in a calcium aluminium rich inclusion from the northwest africa 2364 cv3 group chondritic meteorite which indicate that the inclusion formed 4 568 2 million years ago this age is between 0 3 refs 4 5 and 1 9 refs 1 6 million years older than previous estimates and is the oldest age obtained for any solar system object so far we also determined the 26al 26mg model age of this inclusion and find that it is identical to its absolute pb pb age implying that the short lived radionuclide 26al was homogeneously distributed in the nebular disc surrounding the proto sun from the consistently old ages in the studied inclusion we conclude that the proto sun and the nebular disc formed earlier than previously thought

26al in plagioclase rich chondrules in carbonaceous chondrites evidence for an extended duration of chondrule formation abstract the 26al 26mg isotope systematics in 33 petrographically and mineralogically characterized plagioclase rich chondrules prcs from 13 carbonaceous chondrites ccs one ungrouped acfer 094 six cr five cv and one co reveal large variations in the initial 26al 27al ratio 26al 27al 0 well resolved 26mg excesses 26mg from the in situ decay of the short lived nuclide 26al t1 2 0 72 ma were found in nine chondrules two from acfer 094 five from the cv chondrites allende and efremovka and one each from the paired cr chondrites eet 92147 and eet 92042 with 26al 27al 0 values ranging from 3 10 6 to 1 5 10 5 data for seven additional chondrules from three cv and two cr chondrites show evidence suggestive of the presence of 26al but do not yield well defined values for 26al 27al 0 while the remaining chondrules do not contain excess radiogenic 26mg and yield corresponding upper limits of 11 2 10 6 for 26al 27al 0 the observed range of 26al 27al 0 in prcs from ccs is similar to the range seen in chondrules from unequilibrated ordinary chondrites uocs of low metamorphic grade 3 0 3 4 however unlike the uoc chondrules there is no clear trend between the 26al 27al 0 values in prcs from ccs and the degree of thermal metamorphism experienced by the host meteorites high and low values of 26al 27al 0 are found equally in prcs from both ccs lacking evidence for thermal metamorphism e g crs and ccs where such evidence is abundant e g cvs the lower 26al 27al 0 values in prcs from ccs relative to most cais are consistent with a model in which 26al was distributed uniformly in the nebula when chondrule formation began approximately a million years after the formation of the majority of cais the observed range of 26al 27al 0 values in prcs from ccs is most plausibly explained in terms of an extended duration of 2 3 ma for the formation of cc chondrules this interval is in sharp contrast to most cais from ccs whose formation appears to be restricted to a narrow time interval of less than 105 years the active solar nebula appears to have persisted for a period approaching 4 ma encompassing the formation of both cais and chondrules present in ccs and raising important issues related to the storage assimilation and mixing of chondrules and cais in the early solar system

hf w chronometry of lunar metals and the age and early differentiation of the moon the use of hafnium tungsten chronometry to date the moon is hampered by cosmogenic tungsten 182 production mainly by neutron capture of tantalum 181 at the lunar surface we report tungsten isotope data for lunar metals which contain no 181 ta derived cosmogenic 182 w the data reveal differences in indigenous 182 w 184 w of lunar mantle reservoirs indicating crystallization of the lunar magma ocean 4 527 0 010 billion years ago this age is consistent with the giant impact hypothesis and defines the completion of the major stage of earth9s accretion

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

a review of prokaryotic populations and processes in sub seafloor sediments including biosphere geosphere interactions article i nfo sub seafloor biosphere marine microbiology prokaryotic diversity dark energy biosphere geosphere interactions a general review of the sub seafloor biosphere is presented this includes an update and assessment of prokary otic cell distributions within marine sediments current deepest 1922 m and the impact of this on global sub seafloor biomass estimates these global estimates appear relatively robust to different calculation approaches and our updated estimate is 5 39 10 29 cells taking into consideration new data from very low organic matter south pacific gyre sediments this is higher than other recent estimates which is justified as several sediments such as gas hydrate deposits and oil reservoirs can have elevated cell concentrations the proposed relationship between elevated cell concentrations and milankovitch cycles in sequential diatom rich layers at some sites demonstratesnotonlyadynamicdeepbiosphere butalsothatthedeepbiosphereisanintegralpartofearthsys tem processes over geological time scales cell depth distributions vary in different oceanographic provinces and this is also reflected in contrasting biodiversity despite this there are some clear common sub seafloor prokary otes for bacteria these are the phyla chloroflexi gammaproteobacteria planctomycetes and the candidate phylum js1 and for archaea uncultivated lineages within the phylum crenarchaeota miscellaneous crenarchaeotal group and marine benthic group b euryarchaeota sagmeg marine benthic group d thermoplasmatales associated groups and thaumarchaeota marine group i in addition spores viruses and fungi have been detected but their importance is not yet clear consistent with the direct demonstration of active prokaryotic cells prokaryotes have been enriched and isolated from deep sediments and these reflect a subset of the total diversity including spore formers that are rarely detected in dna analyses activities are generally low in deep marine sediments 10 000 times lower than in near surface sediments however depth integrated activity calculations demonstrate that sub surface sediments can be responsible for the majority of sediment activity up to 90 and hence are biogeochemically important unlike near surface sediments competitive metabolisms can occur together and metabolism per cell can be 1000 times lower than

formation timescales of cv chondrites from component specific hf w systematics abstract carbonaceous chondrites are an important meteorite group that closely resembles the bulk composition of the solar system we report the first elemental and isotope dataset for hf w in carbonaceous chondrites that includes chondrules matrix magnetic fractions as well as bulk compositions our study focuses on the three cv3 chondrites allende vigarano and bali compared to bulk chondrites matrix splits have low hf w ratios and e 182 w compositions whereas chondrule splits are characterized by high but more variable hf w ratios and e 182 w compositions thus hf w ratios behave complementary between chondrules and matrix in the analysed cv chondrites supporting the view that both components formed from the same parental reservoir strong nucleosynthetic effects were observed in most of the analysed cv3 components especially in matrices and chondrule splits that were found to have large e 183 w anomalies of several e units all separates define a rough correlation between initial 182 w 184 w and 183 w 184 w ratios in agreement with theoretical model trends based on calculations for stellar nucleosynthesis our results therefore indicate a heterogeneous distribution of s and r process w isotopes among the different cv3 chondrite components arguing for selective thermal processing of early solar system matter during chondrule formation after correcting for nucleosynthetic anomalies chondrules and matrix splits of reduced vigarano as well as oxidised allende cv3 chondrites define a linear correlation in e 182 w vs 180 hf 184 w space which is interpreted as an isochron covering an age interval within the first 2 6 ma after solar system formation as peak metamorphic temperatures for cv3 chondrites were well below the 182 hf 182 w closure temperature the resulting isochron within its error most likely defines a common formation interval for all components the calculated age interval is for the first time based on a combined chondrule matrix isochron a marked difference compared to previous studies where only chondrules were analysed notably our formation age interval covers previously reported chondrule formation ages determined using 26 al and pb pb chronometry illustrating that chondrule and matrix formation started contemporaneously with cai formation and lasted over a time interval of about 2 3 ma our results also corroborate previous models from ordinary chondrites in that chondrite parent bodies were not the first planetesimals to have formed in the early solar system

hf w chronology of ordinary chondrites abstract fifteen h l and ll ordinary chondrites of petrologic types 4 6 have been analyzed for hf w isotope systematics to constrain the chronology internal structure and thermal history of their parent bodies for most samples coarse grained metals plot below the isochrons defined by silicate dominated fractions which consist of variable mixtures of silicate minerals with tiny metal inclusions this offset results from an earlier hf w closure in the large metal grains and provides a new means for simultaneously determining cooling rates and hf w closure ages for individual samples for most type 5 and 6 samples cooling rates and hf w ages are inversely correlated indicating that these samples derive from concentrically zoned bodies in which more strongly metamorphosed samples derive from greater depth these data therefore provide strong evidence for a common onion shell structure for the h l and ll chondrite parent bodies the cooling rates and hf w ages of some type 5 and 6 chondrites overlap indicating that the hf w systematics provide a more robust measure of the thermal history and burial depth of a given sample than the simple petrographic distinction between types 5 and 6 two type 6 samples deviate from the correlation between cooling rates and hf w ages and cooled much faster than expected for their hf w age these samples likely were excavated by impacts that occurred during high temperature metamorphism and prior to complete closure of the hf w system at 10 ma after cai formation as these impacts would have disturbed the asteroid s cooling history these samples likely derive from different bodies than samples with undisturbed cooling histories implying that ordinary chondrites derive from more than just three parent bodies the hf w data reveal that metal silicate fractionation among the h l and ll groups occurred between 2 and 2 7 ma after cai formation and hence was about coeval to chondrule formation as both metal silicate fractionation and chondrule formation occurred prior to chondrite parent body accretion there should be no ordinary chondrite chondrules that are younger than 2 7 ma finally ordinary chondrite precursors had lower hf w ratios than carbonaceous chondrites suggesting that inner and outer solar system materials respectively were chemically distinct even for refractory elements

considerable methane fluxes to the atmosphere from hydrocarbon seeps in the gulf of mexico the flux of methane a greenhouse gas from submarine hydrocarbon seeps to the atmosphere is not well quantified direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep ocean sources could reach the surface ocean the fluxes of the greenhouse gas methane from many individual sources to the atmosphere are not well constrained1 marine geological sources may be significant2 but they are poorly quantified and are not included in the intergovernmental panel on climate change budget1 previous results based on traditional indirect sampling techniques and modelling suggested bubble plumes emitted from marine seeps at depths greater than 200 m do not reach the surface mixed layer because of bubble dissolution and methane oxidation3 4 5 here we report methane concentration and isotope depth profiles from direct submersible sampling of deepwater 550 600 m hydrocarbon plumes in the gulf of mexico we show that bubble size upwelling flows and the presence of surfactants inhibit bubble dissolution and that methane oxidation is negligible consequently methane concentrations in surface waters are up to 1 000 times saturation with respect to atmospheric equilibrium we estimate that diffusive atmospheric methane fluxes from individual plumes are one to three orders of magnitude greater than estimates from shallow water seeps6 7 8 greatly expanding the depth range from which methane seep emissions should be considered significant given the widespread occurrence of deepwater seeps we suggest that current estimates of the global oceanic methane flux to the atmosphere1 may be too low

dive site geology dsv alvin 2006 and rov jason ii 2007 dives to the middle lower continental slope northern gulf of mexico abstract use of dsv alvin 2006 and rov jason ii 2007 provided access to never observed or sampled sites of fluid gas expulsion from the little studied middle and lower continental slope of the northern gulf of mexico below water depths of 1000 m dives were focused on 15 locations selected by 3 d seismic surface attributes and shallow subsurface geologic analyses the linkage between highly positive seafloor reflectivity and hard bottoms proved to be an efficient indicator of potential sites of interest through observation and sampling of reflective sites starting in the mid 1980s it has become apparent that most hard bottoms on the northern gulf s continental slope are created by the precipitation of authigenic carbonates at hydrocarbon seep sites access to the bureau of ocean energy management regulation and enforcement s extraordinary archive of slope wide 3 d seismic data made efficient site selection possible from thousands of sites that display the characteristics of fluid gas expulsion 15 were observed and sampled during the 2006 and 2007 cruises water depths in which these 15 sites were located ranged from 2750 to 970 m all sites exhibited evidence of hydrocarbon seepage or more rapid venting chemosynthetic organisms authigenic carbonates barite gas hydrates highly anoxic surface sediments brine pools and hydrocarbon laced brine flows were identified and sampled high resolution acoustic autonomous underwater vehicle auv data including multibeam bathymetry side scan sonar swaths and chirp sonar subbottom profiles were collected at four locations ac601 wr269 gc852 and at340 data sets from the 2006 and 2007 dives resulted in a greatly improved understanding of both cross slope and along slope variability in the characteristics of fluid gas expulsion sites and associated habitats our studies confirmed the importance of fluid gas expulsion processes for sustaining chemosynthetic communities and impacting seabed geology on the middle and lower continental slope of the northern gulf of mexico

neutron capture on pt isotopes in iron meteorites and the hf w chronology of core formation in planetesimals the short lived 182hf 182w isotope system can provide powerful constraints on the timescales of planetary core formation but its application to iron meteorites is hampered by neutron capture reactions on w isotopes resulting from exposure to galactic cosmic rays here we show that pt isotopes in magmatic iron meteorites are also affected by capture of epi thermal neutrons and that the pt isotope variations are correlated with variations in 182w 184w this makes pt isotopes a sensitive neutron dosimeter for correcting cosmic ray induced w isotope shifts the pre exposure 182w 184w derived from the pt w isotope correlations of the iid iva and ivb iron meteorites are higher than most previous estimates and are more radiogenic than the initial 182w 184w of ca al rich inclusions cai the hf w model ages for core formation range from 1 6 1 0 million years ma for the iva irons to 2 7 1 3 ma after cai formation for the iid irons indicating that there was a time gap of at least 1 ma between cai formation and metal segregation in the parent bodies of some iron meteorites from the hf w ages a time limit of 1 5 2 ma after cai formation can be inferred for the accretion of the iid iva and ivb iron meteorite parent bodies consistent with earlier conclusions that the accretion of differentiated planetesimals predated that of most chondrite parent bodies

molybdenum isotope anomalies in meteorites constraints on solar nebula evolution and origin of the earth the early evolution of the solar nebula involved substantial transport of mass resulting in mixing and homogenization of isotopically diverse materials that were contributed to the solar system from multiple stellar nucleosynthetic sources the efficiency of this mixing as well as its timescale can be quantified by determining nucleosynthetic isotope variations among meteorites and terrestrial planets here we present mo isotopic data for a wide range of samples including ca al rich inclusions chondrites and differentiated meteorites as well as martian and terrestrial samples most meteorites are depleted in s process mo relative to the earth and only the iab iiicd irons angrites and martian meteorites have terrestrial mo isotopic compositions in contrast most ca al rich inclusions are enriched in r process mo but one inclusion is characterized by a large s process deficit molybdenum isotopic anomalies in the bulk meteorites correlate with those in ru exactly as predicted from nucleosynthetic theory but no obvious correlation is apparent between mo and ni anomalies therefore s process mo and ru seem to be hosted in the same carrier which must be distinct from the carrier responsible for isotopic anomalies in the fe group elements ni cr ti furthermore the isotopic heterogeneity in mo and other elements contrasts with the isotopic homogeneity for hf and os indicating that different s process carriers once existed in the early solar nebula and that only some of these were heterogeneously distributed the mo isotopic anomalies of meteorites and their components decrease over time and with increasing size of the parent bodies providing evidence for a progressive homogenization of the solar nebula however the carbonaceous chondrites exhibit larger mo anomalies than expected for their age indicating that they received a greater portion of material from the outer solar system where homogenization was slow than other meteorite parent bodies and terrestrial planets compared to the meteorites earth is enriched in s process mo and must have accreted from material distinct from the meteorites combined mo and o isotopic data show that the composition of the earth cannot be reconstructed by any known combination of meteorites implying that meteorites may be inappropriate proxies for the isotopic composition of the bulk earth this is exemplified by the covariation of 92mo and 142nd anomalies in chondrites showing that the 142nd deficit of chondrites compared to the accessible earth may not unequivocally be interpreted as a signature of an early differentiation of the earth however further high precision isotopic data are needed to evaluate the role of chondrites in defining the isotopic composition of the earth

subsurface biodegradation of crude oil in a fractured basement reservoir shropshire uk subsurface biodegradation of crude oil in current oil reservoirs is well established but there are few examples of ancient subsurface degradation biomarker compositions of viscous and solid oil residues bitumen in fractured precambrian and other basement rocks below the carboniferous cover in shropshire uk show that they are variably biodegraded high levels of 25 norhopanes imply that degradation occurred in the subsurface lower levels of 25 norhopanes occur in active seepages liquid oil trapped in fluid inclusions in mineral veins in the fractured basement confirms that the oil was emplaced fresh before subsurface degradation a triassic age for the veins implies a 200 myr history of hydrocarbon migration in the basement rocks the data record microbial biodegradation of hydrocarbons in a fractured basement reservoir and add to evidence in modern basement aquifers for microbial activity in deep fracture systems buried basement highs may be especially favourable to colonization through channelling fluid flow to shallow depths and relatively low temperatures and are therefore an important habitat within the deep biosphere

nucleosynthetic w isotope anomalies and the hf w chronometry of ca al rich inclusions abstract ca al rich inclusions cai are the oldest dated objects formed in the solar system and are pivotal reference points in early solar system chronology knowledge of their initial 182hf 180hf and 182w 184w is essential not only for obtaining precise hf w ages relative to the start of the solar system but also to assess the distribution of short lived radionuclides in the early solar nebula however the interpretation of hf w data for cai is complicated by nucleosynthetic w isotope variations to explore their extent and nature and to better quantify the initial hf and w isotope compositions of the solar system we obtained hf w data for several fine and coarse grained cai from three cv3 chondrites the fine grained cai exhibit large and variable anomalies in e183w e i w equals 0 01 deviation from terrestrial values extending to much larger anomalies than previously observed in cai and reflecting variable abundances of s and r process w isotopes conversely the coarse grained mostly type b inclusions show only small if any nucleosynthetic w isotope anomalies the investigated cai define a precise correlation between initial e182w and e183w providing a direct empirical means to correct the e182w of any cai for nucleosynthetic isotope anomalies using their measured e183w after correction for nucleosynthetic w isotope variations the cai data define an initial 182hf 180hf of 1 018 0 043 10 4 and an initial e182w of 3 49 0 07 the hf w formation intervals of the angrites d orbigny and sahara 99555 relative to this cai initial is 4 8 0 6 ma in good agreement with al mg ages of these two angrites this renders a grossly heterogeneous distribution of 26al in the inner solar system unlikely at least in the region were cai and angrites formed

galactic cosmic ray produced 129xe and 131xe excesses in troilites of the cape york iron meteorite the flux of galactic cosmic rays gcr in the solar system appears to change with time based on the abundances in iron meteorites of cosmogenic nuclides of different half lives lavielle et al 1999 found that the gcr flux increased in recent times 100 ma by about 38 compared to average flux in the past 150 ma to 700 ma ago a promising technique for calibrating the gcr flux during the past 50 ma based on the 129i and 129xe pair of nuclides was discussed earlier marti 1986 murty and marti 1987 the 129i 129xen chronometer provides a shielding independent system as long as the exposure geometry remained fixed it is especially suitable for large iron meteorites te rich troilite because of the effects by the gcr secondary neutron component although gcr produced xe components were identified in troilites several issues require clarifications and improvements some are reported here we developed a procedure for achieving small xe extraction blanks which are required to measure indigenous xe in troilites the 129xe and 131xe excesses 129xen 131xen due to neutron reactions in te are correlated in a stepwise release run during the troilite decomposition our data show that indigenous xe in troilite of cape york has isotopic abundances consistent with ordinary chondritic xe oc xe in contrast to a terrestrial signature which was reported earlier two methods are discussed which assess and correct for an interfering radiogenic 129xer component from extinct 129i the corrected 129xen concentration in troilite d4 of cape york yields a cosmic ray exposure cre age of 82 7 ma consistent within uncertainties with reported data murty and marti 1987 marti et al 2004

distribution population structure reproduction and diet of ophiolimna antarctica lyman 1879 from kemp caldera in the southern ocean a new population of ophiolimna antarctica lyman 1879 was discovered at 1546 m in kemp caldera a topographic feature with active hydrothermal venting at the southern end of the south sandwich islands southern ocean the distribution population structure reproduction and diet of o antarctica were investigated o antarctica were found predominantly on basalt with an over dispersed distribution the mean density was 17 individuals m 2 with a range of 9 24 individuals m 2 there was a bimodal population structure with separate juvenile and adult peaks sexes were separate and the sex ratio was not significantly different from equality the maximum oocyte diameter was 520 m suggesting direct or lecithotrophic development whilst individual females reproduced asynchronously stomach contents included crustacean fragments flocculate material diatoms forams fish scales and ophiuroid tissues and spines which was indicative of omnivory there was no apparent influence of hydrothermal vents 500 m away on the diet of ophiolimna antarctica the ecology of ophiolimna antarctica is consistent with what is known for other antarctic and deep sea ophiuroid species

geochemistry and oxygen isotope composition of main group pallasites and olivine rich clasts in mesosiderites implications for the great dunite shortage and hed mesosiderite connection evidence from iron meteorites indicates that a large number of differentiated planetesimals formed early in solar system history these bodies should have had welldeveloped olivine rich mantles and consequentially such materials ought to be abundant both as asteroids and meteorites which they are not to investigate this great dunite shortage we have undertaken a geochemical and oxygen isotope study of main group pallasites and dunitic rocks from mesosiderites oxygen isotope analysis of 24 main group pallasites 103 replicates yielded a mean 17o value of 0 187 0 016 2 which is fully resolved from the hed 17o value of 0 246 0 014 2 obtained in our earlier study and demonstrates that both groups represent distinct populations and were derived from separate parent bodies our results show no evidence for 17o bimodality within the main group pallasites as suggested by a number of previous studies olivine rich materials from the vaca muerta mount padbury and lamont mesosiderites and from two related dunites nwa 2968 and nwa 3329 have 17o values within error of the mesosiderite average this indicates that these olivine rich materials are co genetic with other mesosiderite clasts and are not fragments from an isotopically distinct pallasite like impactor despite its extreme lithologic diversity the mesosiderite parent body was essentially homogeneous with respect to 17o a feature best explained by an early phase of large scale melting magma ocean followed by prolonged igneous differentiation based on the results of magma ocean modeling studies we infer that mg rich olivines in mesosiderites formed as cumulates in high level chambers and do not represent samples of the underlying mantle by analogy recently documented mg rich olivines in howardites may have a similar origin although the dawn mission did not detect mesosiderite like material on vesta evidence linking the mesosiderites and heds includes i their nearly identical oxygen isotope compositions ii the presence in both of coarse grained mg rich olivines iii both have synchronous lu hf and mn cr ages iv there are compositional similarities between the metal in both and v mesosiderite like material has been identified in a howardite breccia the source of the mesosiderites remains an outstanding question in meteorite science the underrepresentation of olivine rich materials amongst both asteroids and meteorites results from a range of factors however evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early catastrophic destruction of planetesimals in the terrestrial planet forming region and the subsequent preferential loss of their olivine rich mantles

contribution of neutron capture reactions to observed tungsten isotopic ratios to study whether tungsten isotopic ratios observed in terrestrial samples relative to w ratios in an iron meteorite could be made by neutron capture reactions in the iron meteorite the fluxes of thermal and epithermal neutrons in a large iron meteoroid toluca were calculated using monte carlo particle production and transport codes peak neutron capture rates on w isotopes were calculated to occur at depths of 30 34 cm the calculated changes in the 182w 183w due to neutrons are much less than those observed in terrestrial samples relative to iron meteorites indicating a non cosmogenic origin of the observed w isotopic ratios

planetesimal differentiation revealed by the hf w systematics of ureilites abstract determining the timescales of the accretion and chemical differentiation of meteorite parent bodies provides some of the most direct constraints on the formation of planetesimals and the earliest stages of planet formation we present high precision hf w isotope data for a comprehensive set of ureilites ultramafic mantle restites derived from a partially melted and incompletely differentiated asteroid all samples are characterized by strong 182w deficits indicating that silicate melt extraction on the ureilite parent body at 3 3 0 7 ma after cai formation postdated core formation in iron meteorite parent bodies by 2 3 ma thermal modeling of planetesimal heating by 26al decay combined with the new hf w data indicates that the ureilite parent body accreted at 1 6 ma after cai formation and therefore more than 1 ma later than iron meteorite parent bodies but more than 0 5 ma earlier that most chondrite parent bodies due to its relatively late accretion the ureilite parent body contained too little 26al to cause complete melting and therefore would have probably remained incompletely differentiated even without exhaustion of 26al by silicate melt segregation our results show that both in terms of degree of differentiation and accretion timescale the ureilite parent body is intermediate between fully differentiated and undifferentiated bodies implying that there is an inverse correlation between extent of melting and metal silicate separation versus time of accretion and differentiation

the tungsten isotopic composition of the earth s mantle before the terminal bombardment it has long been speculated that a late heavy bombardment of earth by meteoritic material replenished the mantle s budget of siderophile iron loving elements such as tungsten that were largely lost to the core during its segregation however evidence for this late veneer remains indirect and its influence has been much debated matthias willbold and colleagues present high precision tungsten isotope analyses of ancient greenland rocks and show that they have significantly higher 182w 184w ratios than modern terrestrial samples this finding is in good agreement with the expected influence of a meteoritic late heavy bombardment they speculate that both the tungsten isotope data and the observed decrease in 142nd 144nd neodymium ratios can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection many precious iron loving metals such as gold are surprisingly abundant in the accessible parts of the earth given the efficiency with which core formation should have removed them to the planet s deep interior1 one explanation of their over abundance is a late veneer a flux of meteorites added to the earth after core formation as a terminal bombardment that culminated in the cratering of the moon2 some 3 8 billion year old rocks from isua greenland are derived from sources that retain an isotopic memory of events pre dating this cataclysmic meteorite shower3 4 these isua samples thus provide a window on the composition of the earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet using high precision less than 6 parts per million 2 standard deviations tungsten isotope analyses of these rocks here we show that they have a isotopic tungsten ratio 182w 184w that is significantly higher about 13 parts per million than modern terrestrial samples this finding is in good agreement with the expected influence of a late veneer we also show that alternative interpretations such as partial remixing of a deep mantle reservoir formed in the hadean eon5 6 more than four billion years ago or core mantle interaction7 do not explain the w isotope data well the decrease in mantle 182w 184w occurs during the archean eon about four to three billion years ago potentially on the same timescale as a notable decrease in 142nd 144nd refs 3 and 6 we speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection

no 182w excess in the ontong java plateau source abstract small scale w isotope variations in ancient and modern terrestrial rocks provide insights into earth s accretion and early differentiation history as well as the long term evolution of the earth s mantle tungsten isotope studies on such rocks have exploited advances in mass spectrometry both ntims and mc icpms which now permit the determination of w isotope ratios at unprecedented precision while w isotope studies performed in different labs by mc icpms and ntims generally exhibit excellent agreement obtaining accurate w isotope data at this level of precision remains analytically challenging for example a recent ntims study reported a relatively large 24 ppm excess in 182w 184w for a phanerozoic sample from the ontong java plateau ojp but no such 182w 184w anomaly was found in another study by mc icpms the present study aims to resolve the discrepancy between these two previous studies and more generally to evaluate the agreement between different recent w isotope studies by ntims and mc icpms to this end we report new w isotope data for ojp drill core samples obtained by mc icpms the ojp samples analyzed here exhibit no resolvable 182w 184w excess relative to the standards and most terrestrial rocks moreover the ojp samples as well as the terrestrial rock standards analyzed here exhibit small but variable w isotope variations for ratios involving 183w producing coupled variations in both radiogenic i e 182w 183w and non radiogenic i e 183w 184w ratios these w isotope variations are analytical in origin induced during sample preparation and very likely caused by a nuclear field shift isotope fractionation affecting primarily the odd isotope 183w the recently reported 182w excess for an ojp sample may result from this nuclear field shift effect as the ntims analyses had to rely on a double normalization involving the 183w 184w ratio more generally these results demonstrate that using 183w data from any mc icpms or ntims study requires a careful quantification of any potential analytical 183w effect nevertheless once such effects are taken into account then both 182w 184w and 183w 184w can accurately be determined to a very high level of precision

stable isotope trophic patterns in echinoderm megafauna in close proximity to and remote from gulf of mexico lower slope hydrocarbon seeps abstract hydrocarbon seep communities in the gulf of mexico have a high biomass that is exploited as a food source to varying degrees by the photosynthesis dependent fauna inhabiting the surrounding mud bottom a decline concurrent with ocean depth in detritus influx to that background habitat results in a much lower background biomass the biomass contrast between population rich seeps and depauperate mud bottom leads to the prediction that seep utilization by the background fauna should be extensive at all depths and should increase with depth species depth zonation makes like species comparisons over the full depth of the gulf of mexico impossible seeps and normal bottom above 1000 m have different fauna from those below 1000 m lower slope seeps are surrounded by a fauna rich in echinoderm species especially asteroids ophiuroids and holothuroids all three taxa have species that are abundant within seeps and are probably endemic to them they also contain species found only in mud background or within mud and seeps backgrounds tissue analyses of 13 c and 15 n of echinoderms collected by rov within seeps and trawling away from seeps indicate a pattern of utilization similar to that found in upper slope seeps exploited by different taxa seastar and ophiuroid species abundant in or endemic to seeps have tissue isotope values reflecting seep chemosynthetic input via a free living microbial detritus or predation a single seep endemic deposit feeding holothuroid showed distinct seep tissue values background deposit feeding holothuroids collected within seeps showed either no or only minor incorporation of seep carbon indicating either a lack of access to seep detritus or short feeding times within the seep a predicted extensive utilization of seep productivity at the deeper seeps was not found seeps may be relatively closed systems that require special adaptations of species in order for them to enter exploit and survive alternately the surrounding deep benthos may not be as food poor as assumed from biomass measurements and flux estimates

the early differentiation of mars inferred from hf w chronometry abstract mars probably accreted within the first 10 million years of solar system formation and likely underwent magma ocean crystallization and crust formation soon thereafter to assess the nature and timescales of these large scale mantle differentiation processes we applied the short lived 182 hf 182 w and 146 sm 142 nd chronometers to a comprehensive suite of martian meteorites including several shergottites augite basalt nwa 8159 orthopyroxenite alh 84001 and polymict breccia nwa 7034 compared to previous studies the 182 w data are significantly more precise and have been obtained for a more diverse suite of martian meteorites ranging from samples from highly depleted to highly enriched mantle and crustal sources our results show that martian meteorites exhibit widespread 182 w 184 w variations that are broadly correlated with 142 nd 144 nd implying that silicate differentiation and not core formation is the main cause of the observed 182 w 184 w differences the combined 182 w 142 nd systematics are best explained by magma ocean crystallization on mars within 20 25 million years after solar system formation followed by crust formation 15 million years later these ages are indistinguishable from the i pu xe age for the formation of mars atmosphere indicating that the major differentiation of mars into mantle crust and atmosphere occurred between 20 and 40 million years after solar system formation and hence earlier than previously inferred based on sm nd chronometry alone

the complex exposure histories of the pitts and horse creek iron meteorites implications for meteorite delivery models the concentrations of cosmogenic radionuclides and noble gases in pitts iab and horse creek ungrouped provide unambiguous evidence that both irons have a complex exposure history with a first stage irradiation of 100 600 myr under high shielding followed by a second stage exposure of 1 myr as small objects the first stage exposure ages of 100 myr for horse creek and 600 myr for pitts are similar to cosmic ray exposure ages of other iron meteorites and most likely represent the yarkovsky orbital drift times of irons from their parent bodies in the main asteroid belt to one of the nearby chaotic resonance zones the short second stage exposure ages indicate that collisional debris from recent impact events on their precursor objects was quickly delivered to earth the short delivery times suggests that the recent collision events occurred while the precursor objects of horse creek and pitts were either very close to the chaotic resonance zones or already in earthcrossing orbits since the cosmogenic noble gas records of horse creek and pitts indicate a minimum radius of a few meters for the precursor objects but do not exclude km sized objects we conclude that these irons may represent fragments of two near earth asteroids 3103 eger and 1986 da respectively finally we used the cosmogenic nuclide concentrations in horse creek which contains 2 5 wt si to test current model calculations for the production of cosmogenic 10be 26al and neonisotopes from iron nickel and silicon

182w and 187re 187os systematics of iron meteorites chronology for melting differentiation and crystallization in asteroids w isotopic compositions measured by n tims in five iron meteorite groups are used in conjunction with 187re 187os isotopic data to constrain the timing of metal segregation and crystallization respectively in the iron meteorite parent bodies fractionation of the parent isotope 182hf half life 9 2 ma from the daughter 182w likely occurred during segregation of metal from silicate in the iron meteorite parent bodies if w isotopic equilibrium was achieved between silicate and metal during metal segregation then the w isotopic compositions in the irons should record the timing of this event samples were taken from the five largest iron meteorite groups including the four magmatic groups iiab iiiab iva and ivb and the nonmagmatic iab iiicd group together these groups comprise approximately 90 by weight of iron meteorites classified so far with the exception of the iva group the groups have well defined 187re 187os isochron ages which are interpreted as the time of crystallization of the metal of their parent bodies within each magmatic group samples that crystallized both early and late in the sequence of each core were analyzed to evaluate possible evolution of the w isotopic composition during crystallization all the samples examined display very similar w values within a narrow range of compositions between 5 1 and 3 1 witzation began less than a few percent of additional metal was segregated to the cores moreover the average w values for the five groups have no resolvable difference ranging from 4 08 0 69 iva to 3 30 0 15 iab iiicd these data indicate that all of the iron meteorite parent bodies underwent metal segregation within 5 ma of each other apparently independent of their composition size and time of crystallization of the metal in all groups except the iiiab group there is a resolvable time interval between the timing of metal segregation as constrained by the w isotopic data and the initiation of core crystallization as given by the re os isotopic systematics

initial 26al 27al in carbonaceous chondrite chondrules too little 26al to melt asteroids we report 26mg excesses correlated with al mg ratios in five chondrules from the primitive co3 0 chondrite yamato 81020 that yield a mean initial 26al 27al ratio of only 3 8 0 7 10 6 about half that of ordinary chondrite oc chondrules even if asteroids formed immediately after chondrule formation this ratio and the mean al content of co chondrites is only capable of raising the temperature of a well insulated co asteroid to 940 k which is more than 560 k too low to produce differentiation the same ratio combined with the higher al content of cv chondrites results in a cv asteroid temperature of 1100 k we calculate that the mean initial 26al 27al ratio of about 7 4 10 6 found in ll chondrules is only able to produce small amounts of melting too little to produce differentiation these results cast serious doubt on the viability of 26al as the heat source responsible for asteroid differentiation inclusion of 60fe raises temperatures about 160 k but this increment is not enough to cause differentiation even of an ll chondrite asteroid

correlated helium 3 and tungsten isotopes in iron meteorites quantitative cosmogenic corrections and planetesimal formation times abstract core formation in planetesimals can in principle be dated using the short lived 182 hf 182 w chronometer however it has been predicted that burnout and production of w isotopes by nuclear reactions can substantially modify the compositions in iron meteorites when exposed for several hundred million years myr to galactic cosmic rays this may severely limit the use of the hf w system for determining chronologies of metal segregation as recorded in iron meteorites here we present the first experimental evidence of cosmogenic effects on w isotopes in two magmatic iron meteorites carbo iid and grant iiiab the 182 w 184 w ratio near the pre atmospheric centre of the meteorites is lower by 0 5 epsilon compared to values near the pre atmospheric surface the 182 w 184 w ratio displays excellent correlations with the 3 he concentration which in turn provides a proxy for the fluence of the relevant cosmic ray particles using new nuclear physics parameters a first order correction for cosmic ray effects on w isotopes is proposed based on the 3 he concentration and on an independent exposure age of the meteorite this method is then applied to other magmatic iron meteorites negrillos cape of good hope navajo and arispe when corrected for cosmogenic effects the w isotopic compositions of carbo grant negrillos cape of good hope and navajo are similar to the initial composition recorded in allende cais this shows that at least some magmatic meteorites from groups iiab iid iiiab and ivb segregated within less than 1 2 myr of the hf w system closure in allende cais the isotopic variations among the samples indicate that the iron meteorites studied in this paper segregated over a time interval of 4 myr carbo being the oldest iron meteorites of this study

the impact of severe biodegradation on the molecular and stable c h n s isotopic compositions of oils in the alberta basin canada abstract although the effects of biodegradation on the composition and physical properties of crude oil have been well studied effects of in reservoir petroleum biodegradation on molecular and isotopic compositions of crude oils are not yet clearly understood the alberta basin in western canada is one of the world s largest petroleum accumulations and constitutes an ideal example of a natural suite of sequentially biodegraded oils the basin hosts moderately to severely biodegraded petroleum regionally distributed and in single more or less continuous oil columns in this study a series of oil samples from the alberta heavy oil and oil sands provinces with varying degrees of biodegradation were analyzed to assess the impact of progressive biodegradation on the molecular and c h n and s isotopic compositions of oils the results of the molecular characterization of the hydrocarbon fraction of the studied oils show that the oils have suffered biodegradation levels from 2 to 10 toward the alberta saskatchewan border on the peters and moldowan scale of biodegradation abbreviated pm 2 to pm 10 and from tens to hundreds on the manco scale within single reservoirs increasing biodegradation was observed from top to bottom of the oil columns at all sites studied the whole oil stable isotopic compositions of the samples varied in the ranges 13 c 31 2 to 29 0 2 h 147 to 133 15 n 0 3 4 7 and 34 s 0 4 6 4 the maximum differences between values of samples within single oil columns were 13 c 1 4 2 h 7 15 n 1 7 and 34 s 1 0 regional variations in the isotopic compositions of oil samples from different wells averaged values from top to bottom were 1 2 for 13 c 12 for 2 h 4 1 for 15 n and 5 5 for 34 s and hence generally significantly larger variations were seen than variations observed within single oil columns especially for n and s it appears that even severe levels of biodegradation do not cause observable systematic variations in carbon nitrogen or sulfur isotope composition of whole oils this indicates that sulfur and nitrogen isotopic compositions may be used in very degraded oils as indicators for oil charge from different source rock facies

alpha decay of 184os revealed by radiogenic 180w in meteorites half life determination and viability as geochronometer abstract the decay of the rare nuclide 184os by alpha emission to 180w has been theoretically predicted but was previously never observed in experiments variable excesses of 180w were recently observed for iron meteorites but the contribution to these excesses by 184os decay was regarded as insignificant here we present combined 180w and os w concentration data for meteorites and terrestrial rocks now indicating that the 180w heterogeneities can be explained by decay of 184os a combined 184os 180w isochron for iron meteorites and chondrites yields a decay constant value of 184 os of 6 49 1 34 10 14 a 1 half life 1 12 0 23 10 13 yr in good agreement with theoretical estimates the 184os 180w decay system may constitute a viable tracer and chronometer for important geological processes like core formation silicate differentiation or late accretion processes this is illustrated by a measured 180w deficit in terrestrial basalts relative to chondrites by 1 16 0 69 parts in 10 000 consistent with core formation 4 5 ga ago

thermal and impact history of the h chondrite parent asteroid during metamorphism constraints from metallic fe ni abstract we have studied cloudy taenite metallographic cooling rates and shock effects in 30 h3 6 chondrites to elucidate the thermal and early impact history of the h chondrite parent body we focused on h chondrites with old ar ar ages 4 4 gyr and unshocked and mildly shocked h chondrites as strongly shocked chondrites with such old ages are very rare cooling rates for most h chondrites at 500 c are 10 50 c myr and do not decrease systematically with increasing petrologic type as predicted by the onion shell model in which types 3 5 are arranged in concentric layers around a type 6 core some type 4 chondrites cooled slower than some type 6 chondrites and type 3 chondrites did not cool faster than other types contrary to the onion shell model cloudy taenite particle sizes which range from 40 to 120 nm are inversely correlated with metallographic cooling rates and show that the latter were not compromised by shock heating the three h4 chondrites that were used to develop the onion shell model ste marguerite beaver creek and forest vale cooled through 500 c at 5000 c myr our thermal modeling shows that these rates are 50 higher than could be achieved in a body that was heated by 26al and cooled without disturbance by impact published ar ar ages do not decrease systematically with increasing petrologic type but do correlate inversely with cloudy taenite particle size suggesting that impact mixing decreased during metamorphism metal and silicate compositions in regolith breccias show that impacts mixed material after metamorphism without causing significant heating impacts during metamorphism created portales valley and two other h6 chondrites with large metallic veins excavated the fast cooled h4 chondrites around 3 4 myr after accretion and mixed petrologic types metallographic data do not require catastrophic disruption by impact during cooling

stable carbon and nitrogen isotope compositions of hydrocarbon seep bivalves on the gulf of mexico lower continental slope abstract stable isotope compositions of cold seep bivalves can illuminate processes that affect the chemical and isotopic compositions of seeping fluids along the continental slope of the gulf of mexico as well as provide insight into the physiological ecology of these species carbon and nitrogen isotope compositions were analyzed in mussels and clams from 14 seep sites spanning a depth range of 1000 to 2800 m along the lower louisiana slope of the gulf of mexico mussels of three species found on the lower slope bathymodiolus childressi b brooksi and b heckerae showed site specific differences in tissue 13c reflecting differences in the local methane pool mussels from sites on the lower slope sitting atop the contiguous salt sheet generally had tissue 13c values that reflected a stronger biogenic methane signal 70 8 to 58 8 than mussels on the upper slope or seaward of the sigsbee escarpment 67 3 to 40 4 clams calyptogena ponderosa and calyptogena sp nov had a narrow range of 13c values between 37 0 and 34 4 indicating that their thiotrophic symbionts are fixing primarily seawater dissolved organic carbon the most depleted tissue 15n values yet published for both mussels and clams are reported in this study at 23 7 and 9 2 respectively these depleted values have implications for the assimilation of inorganic nitrogen by these symbioses and the concentrations of particular inorganic nitrogen sources in the local environment

tungsten stable isotope compositions of terrestrial samples and meteorites determined by double spike mc icpms abstract tungsten stable isotopes hold great potential to examine a variety of physical and chemical processes operating during the accretion and differentiation of asteroids and terrestrial planets such as core formation and mantle crust differentiation to assess the magnitude and origin of w isotope fractionations we determined the w stable isotopic compositions of six usgs geological reference materials a nist steel and 24 iron meteorites and chondrites the w isotope data were obtained using multi collector inductively coupled plasma mass spectrometry mc icpms and using a 180 w 183 w double spike chondrites and iron meteorites exhibit a very narrow range in w stable isotope compositions resulting in a mean 184 183 w 0 027 0 007 95 conf relative to the nist 3163 w standard this value represents a good estimate for the w stable isotope composition of bulk planetary bodies from the inner solar system the 184 183 w of some iron meteorites slightly deviates from this value most likely due to w isotope fractionations induced during crystallization of the metal cores of iron meteorite parent bodies the investigated terrestrial silicate rocks exhibit a narrow range in 184 183 w which for most samples is indistinguishable from the mean value of chondrites and iron meteorites however felsic samples tend to be isotopically lighter than mafic samples indicating that magmatic processes on earth induced w isotope fractionations these fractionations are possibly related to the fluid mobility of w in subduction zones but more data are needed to test this hypothesis given that most terrestrial igneous rocks are isotopically indistinguishable from chondrites and iron meteorites core formation on earth does not seem to have induced a measurable isotopic fractionation for w however more data are needed to firmly arrive at this conclusion

cosmogenic tungsten and the origin and earliest differentiation of the moon the decay of formerly live 182hf with a half life of 9 myr results in variations in the abundance of 182w in early solar system objects here we demonstrate that major excesses in 182w in some lunar samples are the results of cosmogenic additions apollo 17 high ti mare basalts yield high 182w 184w of up to w 11 1 even more extreme variations of up to w 22 1 are found for mineral separates although these lavas were erupted more than 500 myr after the start of the solar system the measured 182w excess in the separated minerals is correlated with their ta w confirming theoretical models that implicate the 181ta n 182ta 182w reaction from cosmic irradiation as the most likely cause in contrast olivine basalt 15555 which has a low cosmic ray exposure age displays no internal 182w variations and defines an w of 1 3 0 4 this is consistent with earlier conclusions that the moon formed about 50 myr after the start of the solar system the high ti mare basalt source with very high hf w has a w isotopic composition that is not grossly different from which a time limit of 70 myr after the start of the solar system can be inferred for the formation of ilmenite rich layers in the final stages of the lunar magma ocean

a novel microbial hydrocarbon degradation pathway revealed by hopane demethylation in a petroleum reservoir abstract the origin of 25 norhopanes is controversial despite their abundance in many biodegraded oils in a biodegraded oil reservoir we found concomitant and directionally opposite changes with depth in the concentrations of certain 17 hopanes and their 17 25 norhopane counterparts demonstrating microbially induced demethylation of hopanes these observations suggest a hitherto unknown biodegradation mechanism and provide insight into the poorly understood process of natural petroleum biodegradation

biodegradation scales applications and limitations abstract biodegradation schemes based on the sequential removal of hydrocarbons are commonly applied to indicate the level of degradation that a petroleum accumulation may have experienced but inconsistent patterns of degradation are typically seen if large data sets are examined and oil mixing greatly complicates any attempt at seeking a globally consistent biodegradation scheme in the athabasca oil sands province degradation of steranes diasteranes and hopanes can occur simultaneously along with the formation of 25 norhopanes highlighting the difficulties towards assigning a degradation level to reflect the degree of compositional alteration experienced by a heavy oil or bitumen in addition the aromatic hydrocarbons such as the methyl phenanthrene isomers show differential susceptibility to degradation whilst the 9 methylphenanthrene 9 mp may show selective resistance to degradation compared to 1 methylphenanthrene 1 mp we have also seen that 9 mp may be removed prior to 1 mp in some cases both 9 mp and 1 mp may be strongly removed in comparison with the 3 and 2 methylphenanthrenes the complex interplay of charge history reservoir environment e g presence absence of water legs and extent and mass transport mechanics of the basal biodegradation reaction zone are most likely to have led to the many and varied petroleum compositions that are a feature of the athabasca tar sands and many other degraded oil provinces

the effect of biodegradation and water washing on the occurrence of alkylphenols in crude oils abstract biodegraded oils from california and nigeria were analysed to assess the impact of biodegradation upon alkylphenol occurrence in crude oils the extent of biodegradation in the 13 californian samples ranged from very mild full n alkane distribution present to moderate complete degradation of c 15 n alkanes and significant reduction of acyclic isoprenoids corresponding to a range of n alkanes and acyclic isoprenoids stage 5 the data from the naturally degraded sample suites were compared to the results of an in vitro aerobic biodegradation experiment conducted with a north sea oil biodegradation resulted in significant reduction in total alkylphenol abundance and preferential depletion of c 3 and c 2 alkylated compounds in the nigerian and laboratory degraded samples these effects were most pronounced in oils in which the methylated naphthalenes had been biodegraded biodegradation stage 4 or 5 there was no clear relationship between alkylphenol abundance or molecular distributions and the extent of biodegradation in the californian samples although alkylphenol distributions in the biodegraded samples were generally dominated by the c 3 compounds simple oil water partition calculations showed that these distributions were consistent with the effects of water washing

lack of late accreted material as the origin of 182w excesses in the archean mantle evidence from the pilbara craton western australia abstract we report 182w and 142nd isotopic compositions 187re 187os systematics and abundances of highly siderophile elements hse re os ir ru rh pt pd and au for a suite of komatiites and basalts from the 3 3 ga ruth well formation and the 3 45 ga warrawoona group of the pilbara craton western australia the 182w compositions from all samples are indistinguishable from each other and more radiogenic than modern bulk silicate earth with a mean 182w value of 9 1 4 2 2sd by contrast the 142nd values for all samples are indistinguishable from each other and terrestrial standards with a mean 142nd value of 1 6 3 2 2sd the 146sm 142nd and 187re 187os systematics are consistent with chondritic sm nd and re os ratios in the mantle source during the lifetime of 182hf and the observed 182w excesses therefore cannot be accounted for by early hf w fractionation by magma ocean processes neither by silicate liquid crystal fractionation nor by high p t metal silicate equilibration the estimated abundances of hse in the mantle source however are significantly lower than modern bulk silicate earth with only 51 9 1sd of modern bulk silicate earth abundances these results are consistent with a partial lack of late accreted material within the pilbara source at 3 3 ga to account for the 182w excesses further widespread 182w excesses of similar magnitude in other archean mantle derived rocks worldwide strongly suggests that a common process most likely incomplete addition of late accreted material was responsible the apparent mismatch between late accreted 182w hse systematics for some other localities likely reflects either the inherent difficulties associated with estimating source hse abundances and or dissociation of w and hse by mantle processes finally the combined average 182w hse systematics of archean samples indicate that the pre late accretion bse likely had a 182w value similar to that of the lunar mantle which strongly suggests post giant impact earth moon equilibration and indicates that the moon formed after 182hf extinction

hf w evidence for rapid differentiation of iron meteorite parent bodies abstract new high precision w isotope data on iron meteorites are presented that provide important constraints on the timing of silicate metal segregation in planetesimals magmatic iron meteorites all have e 182 w within error or less radiogenic than initial e 182 w estimated by studies of chondritic meteorites at face value this implies that iron meteorites are as old and older than refractory calcium aluminium rich inclusions cai which are widely thought to be the oldest solar system objects moreover different meteorites from the same magmatic groups believed to be derived from the same planetissimal core display a range of e 182 w we suggest that the paradoxical e 182 w values more negative than initial solar system initial ssi are most readily explained as a result of secondary spallation reactions with cosmic rays during transit between parent body and the earth this is supported by the most negative e 182 w being found in meteorites with the oldest exposure ages and the magnitude of the effect is shown to be consistent with known nuclear reactions on the other hand it is also striking that none of the magmatic iron group meteorites have e 182 w analyses outside error more radiogenic than the estimated solar system initial ratio this suggests that core formation in parent bodies of magmatic iron meteorites occurred 1 5 myr after the formation age of cai y amelin a n krot i d hutcheon and a a ulyanov lead isotopic ages of chondrules and calcium aluminum inclusions science 297 1678 1683 2002 this extremely early metal silicate differentiation is coeval with the first chondrules m bizzarro j a baker and h haack mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions nature 431 275 278 2004 a n krot y amelin p cassen and a meibom young chondrules in cb chondrites from a giant impact in the early solar system nature 436 989 992 2005 formation of later chondrules and hence the parent bodies of some chondritic meteorites must therefore have occurred in the presence of planetesimals large enough to possess iron cores we conclude that early planetary accretion and differentiation was sufficiently fast for 26 al decay to be an important heat source non magmatic iron meteorites however display more radiogenic and varied w isotope signatures this is in keeping with them being generated later by impact melting during which the metal partially re equilibrated with the then more radiogenic silicate fraction

an early solar system magnetic field recorded in cm chondrites abstract we present a paleomagnetic study of seven cm carbonaceous chondrites cm chondrites are believed to be some of the most chemically primitive materials available in our solar system and may sample the continuum of transitional objects between asteroids and comets formed in the outer solar system as such cm chondrites can help us to understand primordial aspects of the history of the early solar system including protoplanetary disk and planetesimal magnetism the ferromagnetic assemblage of cm chondrites is composed of a mixture of primary metallic iron pyrrhotite and magnetite the remanent properties are usually dominated by secondary pyrrhotite paleomagnetic analyses using thermal and alternating field demagnetization identified a stable origin trending component of magnetization in the seven studied cm chondrites in each meteorite this component is homogeneous in direction at least at the cm scale and is therefore post accretional we interpret this stable component as a pre terrestrial chemical remanent magnetization acquired during crystallization of magnetite and pyrrhotite during parent body aqueous alteration in a field of at least a few t 2 1 5 t considering the timescale and intensities of primordial magnetic fields both internally generated fields from a putative dynamo and external fields generated in the protoplanetary disk may have been recorded by cm chondrites it is presently difficult to discriminate between the two hypotheses regardless cm chondrites likely contain the oldest paleomagnetic record yet identified

the controls on the composition of biodegraded oils in the deep subsurface part 1 biodegradation rates in petroleum reservoirs abstract biodegradation rates in oilfields have been assessed conservatively using whole oil column minimum rate estimates diffusion controlled oil column compositional gradient modelling and mixed oil kinetic models biodegradation rate constants first order are around 10 6 10 7 yr 1 for hydrocarbons in the degradation zones these corresponding well with zero order field wide minimum rate estimates of about 10 8 kg hydrocarbons kg oil year for the whole oil column with biodegradation induction times of around 1 2 ma to perturb an entire oil column for light oil reservoirs and 10 20 ma for heavy oil reservoir degradation the results indicate that where we see continuous gradients in the oil columns degradation must have been occurring episodically for many millions of years to remove the n alkanes from an oil i e about 10 of an oil around ca 15 ma is needed for a heavy oil ca 5 ma for a light n sea oil the timescales of oilfield degradation and filling are thus very similar and consequently the degree of biodegradation will be substantially controlled by oilfield charge history assessment of mixed degraded non degraded oil occurrence provides an independent confirmation that these rates are realistic and that timescales of degradation and field charging are similar the maximum effective rate constant of degradation ultimately controlled by the limiting effect of diffusion of alkanes to the oil water contact owc ca 10 4 yr 1 for a 130 m thick oil column first order rate constant is well above the estimated rate constants indicating oil biodegradation rate is not limited by electron donor supply i e hydrocarbons but by supply of nutrients or oxidants this suggests that diffusive transport of nutrients and electron acceptors in the aquifer to the site of biodegradation may be adequate to maintain the low rate biosphere

fractionation of benzocarbazoles between source rocks and petroleums the concentrations of the a and c isomers of benzocarbazoles in a number of crude oils and source rock bitumens were obtained by in house methods and from reported published data the changes in benzocarbazole concentrations and the benzocarbazole a a c ratio relating to source maturity facies and migration are described with increasing source maturity in north sea oils and source rocks up to 0 85 vitrinite reflectance equivalent benzocarbazole concentrations increase due to generation followed by a decrease above 0 85 vitrinite reflectance equivalent due to expulsion dilution by newly generated hydrocarbons comparison of benzocarbazole concentrations between reservoired petroleum and related source petroleum revealed a concentration bias in favour of source petroleum where concentrations of benzocarbazoles reached up to 10 times that found in equivalent reservoired petroleum the differences in benzocarbazole concentrations between related oils and source rocks indicate that the major fractionation is introduced during primary migration and expulsion because when secondary migration is limited as in the miller field we see extensive benzocarbazole fractionation between reservoired petroleum and associated source petroleum the relationships between source rock toc content and petroleum benzocarbazole concentrations and a a c ratios indicate that source organic matter exerts a strong influence on benzocarbazole distributions the introduction of a reservoir source fractionation parameter rsfp defined as the ratio between the concentrations of benzo a benzo c carbazole in reservoired petroleum versus the concentration of benzo a benzo c carbazole in source petroleum enables description of the relationship between reservoired petroleum and source petroleum from different petroleum systems petroleum deriving from clastic source rocks demonstrated high levels of benzocarbazole fractionation between reservoired petroleum and source petroleum during primary and secondary migration compared to petroleum deriving from carbonate systems the rsfp parameter may also be used to examine fractionation effects during migration between different compound types the more polar benzocarbazoles are fractionated more strongly than dibenzothiophene and phenanthrene between reservoired petroleum and source petroleum whereas sometimes source maturity signals do dominate the benzocarbazole signals in migrated oils in other circumstances often associated with clastic source rocks no clear maturity signal is transferred to migrated oils

pd ag chronometry of iron meteorites correction of neutron capture effects and application to the cooling history of differentiated protoplanets abstract the short lived 107 pd 107 ag system is a versatile tool for dating iron meteorites but neutron capture reactions during cosmic ray exposure might have modified ag isotope compositions these cosmic ray induced effects would vary depending on the exposure time of a sample and its location within the parent meteoroid and therefore could bias the age information inferred from pd ag isotope systematics our new combined pd ag and pt isotope data for iron meteorites in conjunction with model calculations reveal large cosmic ray induced downward shifts of 107 ag 109 ag which preclude the determination of pd ag isochrons based on measured ag isotope compositions for the strongly irradiated iron meteorites ainsworth iiab and carbo iid these shifts are similar to or even larger than the effects from radiogenic ingrowth resulting from 107 pd decay for the less strongly irradiated iiiab iron meteorites boxhole grant and henbury the cosmic ray induced shifts are smaller than the radiogenic 107 ag excesses but are nevertheless significant we have developed a method to quantify the cosmic ray induced ag isotope shifts using a neutron capture model and pt isotope compositions as the neutron dose monitor after correction pd ag isochrons are obtained for all investigated iron meteorites even for the most strongly irradiated samples the pd ag ages inferred from the isochrons are in good agreement with other chronological data for iron meteorites indicating that our neutron capture model provides a reliable correction method for quantifying cosmic ray induced shifts on measured ag isotope compositions the pd ag ages for iron meteorites obtained in this and previous studies indicate rapid crystallization and cooling of the parental metal cores within a few ma after core formation and solar system formation such rapid cooling can be attributed to either small parent body sizes or collisional erosion of the insulating silicate mantle from larger bodies the collisions would have facilitated rapid cooling below pd ag isotopic closure and so in this case the pd ag ages would effectively date the time of the collisions

a practical biodegradation scale for use in reservoir geochemical studies of biodegraded oils existing scales widely used to describe the extent of biodegradation of petroleum have insufficient resolution to usefully characterize many heavy oil and bitumen occurrences including the volumetrically dominant heavily and severely biodegraded oil accumulations in the foreland basins of western canada and venezuela in these and other deposits existing classifications or descriptions of the biodegradation level may vary only slightly yet oil may vary in viscosity by orders of magnitude the manco biodegradation scale proposed here is based on integrating the extent of degradation of various members of compound classes not included in previous biodegradation scales they include alkyl aromatic and alkyl thiophenic compounds that show variable extent of alteration in samples degraded to uniform levels on standard scales but which may show variation in local degradation systematics related to biodegradation mechanisms and extent of oil mixing the manco scale uses a combination of a consideration of the extent of alteration within a compound class together with a consideration of biodegradation across a range of compound classes it can be reliably used as a basis for interpreting geochemical changes in heavily biodegraded oil suites and can also be used to differentiate biodegraded oil samples likely to be amenable to cold production from those requiring production strategies such as steam or chemical flooding as with other biodegradation scales the scale may also provide evidence for the influx of later higher quality oil into a reservoir fluid that had been previously biodegraded

from shale oil to biogenic shale gas retracing organic inorganic interactions in the alum shale furongian lower ordovician in southern sweden methane rich gas occurs in the total organic carbon rich alum shale furongian to lower ordovician in southern sweden the lower part of the thermally immature alum shale was impregnated by bitumen locally generated by heating from magmatic intrusions from the carboniferous to the permian organic geochemical data indicate that the migrated bitumen is slightly degraded in the upper alum shale where methane is the main hydrocarbon in thermovaporization experiments centimeter size calcite crystals occur that contain fluid inclusions filled with oil gas or water the alum shale is thus considered a mixed shale oil biogenic shale gas play the presented working hypothesis to explain the biogenic methane occurrence considers that water soluble bitumen components of the alum shale were converted to methane a hydrogeochemical modeling approach allows the quantitative retracing of inorganic reactions triggered by oil degradation the modeling results reproduce the present day gas and mineralogical composition the conceptual model applied to explain the methane occurrence in the alum shale in southern sweden resembles the formation of biogenic methane in the antrim shale michigan basin united states in both models melting water after the pleistocene glaciation and modern meteoric water may have diluted the contents of total dissolved solids tds in basinal brines such pore waters with low tds contents create a subsurface aqueous environment favorable for microbes that have the potential to form biogenic methane today biogenic methane production rates with shale as the substrate using different hydrocarbon degrading microbial enrichment cultures in incubation experiments range from 10 to 620 nmol per gram and per day

noble gases in the xinjiang armanty iron meteorite a big object with a short cosmic ray exposure age abstract we measured the concentrations and isotopic ratios of the cosmogenic noble gases he ne and ar in the very large iron meteorite xinjiang iiie the 3he and 4he data indicate that a significant portion of the cosmogenic produced helium has been lost via diffusion or in a recent impact event high 22ne 21ne ratios indicate that contributions to the cosmogenic 21ne from sulfur and or phosphorous are significant by combining the measured nuclide concentrations with model calculations for iron meteorites we were able to determine the preatmospheric diameter of xinjiang to 260 320 cm which corresponds to a total mass of about 70 135 tons the cosmic ray exposure age of xinjiang is 62 16 ma i e relatively short compared to most of the other iron meteorites with the current database we cannot firmly determine whether xinjiang experienced a complex irradiation history the finding of 3he and 4he losses might argue for a recent impact event and therefore for a complex exposure

tungsten isotopes and the origin of the moon abstract the giant impact model of lunar origin predicts that the moon mainly consists of impactor material as a result the moon is expected to be isotopically distinct from the earth but it is not to account for this unexpected isotopic similarity of the earth and moon several solutions have been proposed including i post giant impact earth moon equilibration ii alternative models that make the moon predominantly out of proto earth mantle and iii formation of the earth and moon from an isotopically homogeneous disk reservoir here we use w isotope systematics of lunar samples to distinguish between these scenarios we report high precision 182w data for several low ti and high ti mare basalts as well as for mg suite sample 77215 and lunar meteorite kalahari 009 which complement data previously obtained for kreep rich samples in addition we utilize high precision hf isotope and ta w ratio measurements to empirically quantify the superimposed effects of secondary neutron capture on measured 182w compositions our results demonstrate that there are no resolvable radiogenic 182w variations within the moon implying that the moon differentiated later than 70 ma after solar system formation in addition we find that samples derived from different lunar sources have indistinguishable 182w excesses confirming that the moon is characterized by a small uniform 26 parts per million excess in 182w over the present day bulk silicate earth this 182w excess is most likely caused by disproportional late accretion to the earth and moon and after considering this effect the pre late veneer bulk silicate earth and the moon have indistinguishable 182w compositions mixing calculations demonstrate that this earth moon 182w similarity is an unlikely outcome of the giant impact which regardless of the amount of impactor material incorporated into the moon should have generated a significant 182w excess in the moon consequently our results imply that post giant impact processes might have modified 182w leading to the similar 182w compositions of the pre late veneer earth s mantle and the moon

a dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the liaohe basin ne china abstract a suite of petroleum reservoir extracts from the liaohe basin ne china was analyzed to investigate the effects and controls of biodegradation on petroleum composition systematic changes seen as marked gradients in petroleum bulk composition component concentrations and molecular indicators have been observed in two biodegraded oil columns in the es3 column 1700 1850 m biodegradation has removed substantial amounts of normal and isoprenoid alkanes more severe biodegradation occurs in the shallower es1 column 1500 1650 m with both steranes and hopanes being partially removed temperature has an overall control on biodegradation in the two columns a lower reservoir temperature leading to a higher degree of biodegradation however observed variation in the degree of biodegradation in the es3 column at different sites is controlled by water leg size with a higher level of degradation being associated with a thicker water leg the supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation in addition to water leg size nutrient supply the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed a biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column the stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil water contact owc and diffusion of biodegradation products such as 25 norhopanes and other metabolites away from the reaction site the mixing of continuously charged oil with residential biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process the conceptual model illustrates all of these processes and opens the possibility of model driven prediction of oil properties and sweetspot location in reservoirs

a reversed compositional pseudo gradient in biodegraded oil column from liaohe basin ne china abstract most heavy oils or tar sands are formed by microbial biodegradation and show a compositional gradient toward the base of oil column however a reversed pseudo gradient has been observed from the fourth member of the shahejie formation in shuguang oilfield liaohe basin ne china on the basis of bulk and molecular compositions in a series core extracts from well k037 the bulk compositions show systematic depletion of saturated hydrocarbons and enrichment of polars resins asphaltenes toward the top of the oil column molecular compositions illustrate that these extracts have similar source input depositional environment and thermal maturity and their compositional differences are mainly caused by varying degrees of biodegradation biodegradation removes all n alkanes most isoprenoid alkanes partial alkylnaphthalenes and alkylphenanthrenes at the top of oil column whereas only n alkanes are affected at the bottom reservoir temperature has no crucial impact on biodegradation levels as the whole oil column in the temperature range of 41 44 c is ideal for microbial activities the studied reservoir is not a continuous oil column which is separated by a few barriers and baffles the occurrence of locally high water saturation layers caused multiple small gradients in the mid and lower part of oil column with a normal biodegradation gradient in the lowermost compartmentalized interval the overall reversed compositional pseudo gradient is controlled by a generally upward coarsening sedimentary sequence and the existence of top water situated at a lithology change boundary from coarse sandstones and conglomerates to fine grained sandstones this study provides a new perspective to assess the reservoir fluid heterogeneity and sheds the light on sweet spots identification for heavy oil exploration and development

food web structure of seep sediment macrobenthos from the gulf of mexico abstract the slope environment of the gulf of mexico gom supports dense communities of seep megafaunal invertebrates that rely on endosymbiotic bacteria for nutrition seep sediments also contain smaller macrofaunal invertebrates whose nutritional pathways are not well understood using stable isotope analysis we investigate the utilization of chemosynthetically fixed and methane derived organic matter by macrofauna biological sampling was conducted in three lower slope gom seep environs green canyon gc852 1428 m atwater valley at340 2230 m and alaminos canyon ac601 2384 m infaunal 13 c and 15 n exhibited a broad range of values most infauna appeared to be heterotrophic although several taxa had very light 15 n and 13 c values indicating possible reliance on chemoautotrophic symbioses the lightest 13 c and 15 n values were observed in nematodes 13 c 54 6 0 1 15 n 6 1 0 2 and one gastropod 13 c 54 1 15 n 1 1 from green canyon mixing model results indicated that sulfur oxidizing beggiatoa may be an important food source for seep infauna the rate of utilization ranged from 60 to 100 at green canyon and atwater valley the overall range in isotope values was similar across the three sites suggesting that biogeochemical processes may be very similar in these geographically distinct areas

global distribution of microbial abundance and biomass in subseafloor sediment the global geographic distribution of subseafloor sedimentary microbes and the cause s of that distribution are largely unexplored here we show that total microbial cell abundance in subseafloor sediment varies between sites by ca five orders of magnitude this variation is strongly correlated with mean sedimentation rate and distance from land based on these correlations we estimate global subseafloor sedimentary microbial abundance to be 2 9 1029 cells corresponding to 4 1 petagram pg c and 0 6 of earth s total living biomass this estimate of subseafloor sedimentary microbial abundance is roughly equal to previous estimates of total microbial abundance in seawater and total microbial abundance in soil it is much lower than previous estimates of subseafloor sedimentary microbial abundance in consequence we estimate earth s total number of microbes and total living biomass to be respectively 50 78 and 10 45 lower than previous estimates

new w isotope evidence for rapid terrestrial accretion and very early core formation the short lived hf 182 w 182 isotope system is an ideal clock to trace core formation and accretion processes of planets planetary accretion and metal silicate fractionation chronologies are calculated relative to the chondritic hf 182 w 182 isotope evolution here we report new high precision w isotope data for the carbonaceous chondrite allende that are much less radiogenic than previously reported and are in good agreement with published internal hf w chronometry of enstatite chondrites if the w isotope composition of terrestrial rocks representing the bulk silicate earth is homogeneous and 2 24 epsilon 182w units more radiogenic than that of the bulk earth metal silicate differentiation of the earth occurred very early the new w isotope data constrain the mean time of terrestrial core formation to 34 million years after the start of solar system accretion early terrestrial core formation implies rapid terrestrial accretion thus permitting formation of the moon by giant impact while hf 182 was still alive this could explain why lunar w isotopes are more radiogenic than the terrestrial value copyright c 2002 elsevier science ltd

the controls on the composition of biodegraded oils in the deep subsurface part 3 the impact of microorganism distribution on petroleum geochemical gradients in biodegraded petroleum reservoirs abstract a combined geochemical geological and microbiological analysis of an actively biodegrading 24 5 m thick oil column in a canadian heavy oil reservoir has been carried out the reservoir properties associated with the cored vertical well are characterised by a 15 75 m thick oil column and an 8 75 m zone of steadily decreasing oil saturation below the oil column referred to as the oil water transition zone owtz grading down into a thin water leg the oil column exhibits systematic gradients in oil physical properties and hydrocarbon composition and shows variations in biodegradation level throughout the reservoir consistent with the notion that the biodegradation of oil is focussed in a bioreactor zone at the base of the oil column through the oil column the dead oil viscosity measured at 20 c ranged from 50 000 cp 0 05 mcp at the top of the oil column to 1 4 mcp at the oil owtz contact and continued to increase to 10 5 mcp within the owtz the saturated and aromatic hydrocarbons are characterised by systematically decreasing bulk fraction and component concentrations down through the oil column different compound classes decreased to levels below their detection limit at different depths within the owtz defining a likely bioreactor extent of over 5 m in depth with for example n alkanes being reduced to their detection limit concentration at the bottom of the oil column top of the owtz while branched isoprenoid alkanes were not completely degraded until well into the owtz core samples from the oil column and the lower part of the owtz were estimated to contain ca 104 105 bacterial cells g based on qpcr of bacterial 16s rrna genes while samples from a narrow interval in the owtz immediately below the oil column contained on the order of 106 107 cells g of sediment interestingly these latter numbers are typical of those observed in active deep subsurface biosphere systems with the notion that microbial activity and abundance in the deep subsurface is elevated at geochemical interfaces the numbers of organisms are not constant throughout the owtz the highest bacterial abundance and geochemical gradients of for example methylphenanthrene biodegradation define a zone near the oil water contact as likely the most active in terms of biodegradation the largest bacterial abundances in the upper part of the owtz are in line with the trend of bacterial abundance with depth that has emerged from extensive analysis of microbial cells in deep subsurface sediments implying that in terms of deep biosphere cell abundance oil reservoirs are similar to other deep subsurface microbial environments this is puzzling given the atypical abundance of organic carbon in petroleum reservoirs and may imply a common large scale control on microbial abundance and activity in the deep biosphere including in oilfields

investigations of cosmic ray produced nuclides in iron meteorites 6 the signer nier model and the history of the cosmic radiation about thirty years ago a simple model was proposed by martin and by ebert and wanke to describe the interaction of cosmic rays with meteoritic iron the model was later used by signer and nier to calculate the spatial distribution of cosmogenic noble gas nuclides in spherical meteoroids a rigorous mathematical evaluation of the model known as the signer nier model is presented the model is broadly compatible with data on noble gas nuclides and on41k 40k exposure ages 1 in the framework of the model the abundance ratio of any two of the cosmogenic nuclides3he 4he 21ne and38ar is correlated with the ratio of any other pair of these nuclides these ratios depend only on the effective irradiation hardness in the sample analysis of these nuclides in a single sample doesnot permit determination of radiation dosage of size of the meteoroid and of location of the sample within the meteoroid the model derived correlations agree with the corresponding experimental correlations except for samples from relatively large depths 2 the model makes it possible to derive ap21 4he21ne diagram predicting how21ne production ratep21 and4he 21ne ratio depend on meteoroid size and sample depth possible combinations of values forp21 and4he 21ne are restricted they define the allowed field of the diagram each location in this field is associated with a distinct combination of values for meteoroid size and sample depth the diagram is a tool to determine model dependent values for sizes and depths values ofp21 and4he 21ne from previous noble gas analyses and from41k 40k age determinations fall into or close to the allowed field the model represents therefore a reasonable description of the cosmic ray interaction with iron meteoroids analysis of age size and depth distributions indicates that space erosion was probably effective with a rate of the order of 1 cm per 100 ma an investigation of the compatibility of noble gas potassium and radionuclide data reveals the following 1 the traditional age scale of the41k 40k method is correct 2 the intensity of the cosmic radiation was essentially constant in the course of the last 1 2 ga 3 the intensity exceeded its long term average by 50 during the last few million years

influence of seep emission on the non symbiont bearing fauna and vagrant species at an active giant pockmark in the gulf of guinea congo angola margin detailed surveying with an rov found that a dense and diverse cold seep community colonises a giant pockmark located at 3200 m depth 8 km north from the deep congo channel several types of assemblages either dominated by mytilidae and vesicomyidae bivalves or siboglinidae polychaetes are distributed on the 800 m diameter active area the site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high density clusters of mussels and siboglinids dominate in contrast the peripheral zones display large fields of dead and live vesicomyids on soft sediment with a lower mean density and lower methane concentration in seawater the associated megafauna includes alvinocarididae shrimps echinoids holothurians of the family synaptidae several species of gastropods two species of galatheids and zoarcidae and ophidiidae fishes multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission occurrence of hydrates substratum variability and by the presence of large symbiont bearing species several assemblages dominated either by mytilids vesicomyids or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements 13c and 15n of dominant species and food sources the highest estimates of megafauna densities have been obtained in mytilid beds according to their stable isotopes values non symbiont bearing species mainly rely on chemosynthesis originated carbon either as primary consumers of chemoautotrophic microorganisms or at higher trophic level recycling organic matter or relying on bivalve and tubeworm production most of them likely feed on different sources like shrimps but differences according to habitat have been evidenced carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis originated carbon in their diet from 15 to 38 according to the species captured as far as 4 km to the site

non nucleosynthetic heterogeneity in non radiogenic stable hf isotopes implications for early solar system chronology abstract nucleosynthetic heterogeneity and secondary neutron capture reactions may have important implications for 176 lu 176 hf chronology and modelling of early planetary evolution so far the relevance of these phenomena for the lu hf system has not been explored we therefore have analyzed the non radiogenic stable hf isotope composition 177 hf 178 hf 179 hf and 180 hf of meteorites meteorite components and terrestrial rock samples to identify nucleosynthetic or neutron capture induced variations all analyzed chondrites have uniform 178 hf 177 hf and 180 hf 177 hf values that cannot be resolved from the average terrestrial composition thus there is no evidence for nucleosynthetic heterogeneity in chondrites or earth and these data support the use of a chondritic reference value for the hf isotope composition of the bulk silicate earth this homogeneity contrasts with nucleosynthetic heterogeneities found in lighter elements and provides evidence for a separate synthesis of light and heavy r process nuclei various mesosiderite samples and one lunar meteorite display coupled 178 hf 177 hf and 180 hf 177 hf anomalies that are associated with neutron capture induced deviations in 149 sm 154 sm and 150 sm 154 sm however the analyzed chondrites and an aubrite show only sm isotope anomalies and these are the result of neutron capture the hf isotope anomalies require substantial capture of epithermal neutrons whereas sm anomalies result primarily from thermal neutron capture the non radiogenic stable isotope composition of hf is thus a suitable monitor for epithermal neutron capture reactions the data reveal distinct neutron energy spectra mesosiderites are characterized by high epithermal to thermal neutron fluence ratios whereas the remaining samples show low epithermal to thermal ratios secondary neutron capture may significantly increase the measured 176 hf 177 hf in whole rock meteorite samples without causing a resolvable shift in 176 lu 177 hf thus it could potentially induce scatter in lu hf whole rock isochrons and produce spurious initial 176 hf 177 hf values however the slopes of internal i e mineral isochrons cannot be increased significantly by secondary neutron capture this process therefore cannot account for the unrealistically old 176 lu 176 hf ages e g 4 75 ga of some meteorites

the oxygen isotope composition of diogenites evidence for early global melting on a single compositionally diverse hed parent body oxygen isotope measurements of a suite of 22 diogenites demonstrate that they have a restricted range of 17o values 0 246 0 014 2 these results indicate that the diogenites form a single population consistent with a single parent body source rather than multiple sources as has recently been suggested our previously published analysis of eucrites and cumulate eucrites n 34 give very similar results to the diogenites with o17 0 241 0 016 2 and confirm that diogenites and eucrites are from the same parent asteroid the isotopic homogeneity displayed by diogenites eucrites and cumulate eucrites provides strong evidence for an early large scale melting event on the hed parent body possibly resulting in the formation of a magma ocean the paradox whereby diogenites show isotopic evidence in favor of global melting but also geochemical features indicative of late stage interaction with eucritic crust may reflect a rapid transition from global to serial magmatism on their parent body the fact that all the lithologically varied hed units have an isotopically homogeneous composition supports the proposal that they are derived from a single large diverse asteroid most likely 4 vesta the recent suggestion that the heds are not from vesta but instead represent material from the same asteroidal source as the main group pallasites and iiiab irons can be excluded by our oxygen isotope data

comment on cosmogenic 180w variations in meteorites and re assessment of a possible 184os 180w decay system by cook d l kruijer t leya i kleine t

correlated cosmogenic w and os isotopic variations in carbo and implications for hf w chronology an obstacle for establishing the chronology of iron meteorite formation using 182hf 182w systematics t1 2 8 9 myr is to find proper neutron fluence monitors to correct for cosmic ray modification of w isotopic composition recent studies showed that siderophile elements such as pt and os could serve such a purpose to test and calibrate these neutron dosimeters the isotopic compositions of w and os were measured in a slab of the iid iron meteorite carbo this slab has a well characterized noble gas depth profile reflecting different degrees of shielding to cosmic rays the results show that w and os isotopic ratios correlate with distance from the pre atmospheric center negative correlations barely resolved within error were found between epsilo190os epsilo189os and epsilo186os epsilo189os with slopes of 0 64 0 45 and 1 8 1 9 2 1 respectively these os isotope correlations broadly agree with model predictions for capture of secondary neutrons produced by cosmic ray irradiation and results reported previously for other groups of iron meteorites correlations were also found between epsilo182w epsilo189os slope 1 02 0 37 and epsilo182w epsilo190os slope 1 38 0 58 intercepts of these two correlations yield pre exposure epsilo182w values of 3 32 0 51 and 3 62 0 23 respectively weighted average epsilo182w 3 57 0 21 this value relies on a large extrapolation leading to a large uncertainty but gives a metal silicate segregation age of 0 5 2 4 myr after formation of the solar system combining the iron meteorite measurements with simulations of cosmogenic effects in iron meteorites equations are presented to calculate and correct for cosmogenic effects on 182w using os isotopes

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous

26al 26mg systematics of chondrules in a primitive co chondrite abstract we have conducted systematic investigations of formation age chemical compositions and mineralogical characteristics of ferromagnesian chondrules in yamato 81020 co3 05 one of the most primitive carbonaceous chondrites to get better understanding of the origin of chemical groups of chondrites the 26 al 26 mg isotopic system were measured in fourteen feo poor type i six feo rich type ii and two aluminum rich al rich chondrules using a secondary ion mass spectrometer excesses of 26 mg in plagioclase 1 0 13 5 are resolved with sufficient precision mostly 0 4 6 6 at 2 level in all the chondrules studied except one chemical zoning of mg and na in plagioclase were investigated in detail in order to evaluate the applicability of 26 al 26 mg chronometer we conclude that the al mg isotope system of the chondrules in y 81020 have not been disturbed by parent body metamorphism and can be used as chronometer assuming homogeneous distribution of 26 al assuming an initial 26 al 27 al ratio of 5 10 5 in the early solar system 26 al 26 mg ages were found to be 1 7 2 5 ma after cai formation for type i 2 0 3 0 ma for type ii and 1 9 and 2 6 ma for al rich chondrules the formation ages of ferromagnesian chondrules in y 81020 are in good agreement with those of l and ll type 3 0 3 1 chondrites in the literature which indicates that common chondrules in the co chondrite were formed contemporaneously with those in l and ll chondrites the concurrent formation of chondrules of co and l ll chondrites suggests that the chemical differences between co and l ll chondrites might be caused by spatial separation of chondrule formation environments in the protoplanetary disk

si isotope fractionation between si poor metal and silicate melt at pressure temperature conditions relevant to metal segregation in small planetary bodies abstract experimental investigations of si isotope fractionation between si bearing metal alloy and silicate phases have to date been limited to high pressure 1 7 gpa and high temperature 1800 2200 c conditions at highly reducing conditions to optimize applicability of results to early core formation processes in the earth here we assess the extent and mechanism of si isotopic fractionation at conditions relevant to metal segregation in small km scale planetary bodies using samples obtained from an industrial scale blast furnace of tata steel ijmuiden the netherlands during the low pressure high temperature process of steelmaking inhomogeneous blast furnace burden consisting of pre and untreated iron ore iron silicates and coke is reduced to oxygen fugacities near the c co buffer resulting in the segregation of a metal phase containing only 0 3 wt si seven sample sets each comprising a metal alloy and a silicate slag were taken during tapping of the blast furnace at tapping temperatures between 1400 c and 1600 c we find large isotopic mass fractionation between metal and silicate with 30sisilicate metal varying between 0 7 and 1 6 values that are as high as previously obtained in high pressure highly reduced experiments a model for metal silicate si isotope fractionation in blast furnaces can explain both the sense and magnitude of fractionation if the presence of sio bearing vapour is explicitly taken into account our data indicate that significant si isotope fractionation can occur between metal and silicate at low pressure high temperature and only mildly reducing conditions for which si solubility in molten fe rich metal is low this suggests an important role for sio at low confining pressures our data can be applied to models of aubrite meteorite formation through high temperature differentiation of an enstatite chondrite parent body our calculations suggest a far larger degree of rehomogenisation during differentiation than previously thought on the basis of metal silicate si isotopic fractionation measured in natural meteorites that re equilibrated at low temperature

the controls on the composition of biodegraded oils in the deep subsurface part ii geological controls on subsurface biodegradation fluxes and constraints on reservoir fluid property prediction the principal controls on the fluid properties of biodegraded oil systems have been determined by a combination of petroleum geochemistry numerical modeling of oil biodegradation in reservoirs and analysis of oil property data sets from a variety of geological settings petroleum biodegradation proceeds under anaerobic conditions in any reservoir that has a water leg and has not been heated to temperatures more than 80c in most reservoirs with low concentrations of aqueous sulfate methanogenic degradation is a primary mechanism of petroleum degradation whereas in waters containing abundant sulfate sulfate reduction and sulfide production may dominate net degradation of petroleum fractions in reservoirs is primarily controlled by the reservoir temperature the chemical compounds being degraded and relationships between the oil water contact owc area and oil volume the relative volumes of water leg to oil leg prior level of oil biodegradation and reservoir water salinity act as second order controls on the process typically degradation fluxes kilograms of petroleum destroyed per square meter of oil water contact area per year or kg petroleum m2 owc yr1 for fresh petroleum in clastic reservoirs are in the range of 103 104 kg petroleum m2 owc yr1 and increase with decreasing reservoir temperature from zero near 80c to a maximum flux at the owc of less than 103 kg petroleum m2 owc yr1 at a temperature less than 40c at very low reservoir temperatures and with severely degraded oils such as are seen in the near surface canadian tar sands at the present day the net degradation fluxes are much less than maximum values nutrient supply from the aquifer and adjacent shales mostly buffered by mineral dissolution probably provides the ultimate control on the range of degradation flux values oil compositional gradients and resulting oil viscosity variations are common on both reservoir thickness and field scales in biodegraded oil reservoirs and are a defining characteristic of heavy oil fields produced by crude oil biodegradation continuous vertical gradients in the oil columns document episodic degradation for many millions of years suggesting that the time scales of oil field degradation and petroleum charging are similar the flux temperature relationship we have derived coupled with typical reservoir charge histories defines the range of variation of fluid properties seen in many biodegraded oil provinces and identifies oil charge mixing of biodegraded and fresh oils and reservoir temperature history as the primary controls on fluid properties these flux temperature relationships are easily integrated into prospect charge modeling procedures sensitivity analyses show that the limiting factor in fluid property predictions using even this first level approach are ultimately constrained by the accuracy of current oil charge modeling estimates the absence today of any functional geochemical proxies for assessing oil residence time in oil fields and the substantial uncertainty in petroleum charging times estimated by forward basin modeling is a major obstacle to more accurate fluid property predictions that needs to be addressed