highly siderophile and chalcogen element constraints on the origin of components of the allende and murchison meteorites 187re 187os systematics abundances of highly siderophile elements hse re pge and au chalcogen elements te se and s and some major and minor elements were determined in physically separated components of the allende cv3 and murchison cm2 carbonaceous chondrites substantial differences exist in the absolute and relative abundances of elements in the components but the similarity of calculated and literature bulk rock abundances of hse and chalcogens indicate that chemical complementarity exists among the components with ci chondrite like ratios for many elements despite subsequent alteration and oxidation the overall cosmochemical behavior of most moderately to highly siderophile elements during high temperature processing has been preserved in components of allende at the sampling scale of the present study the 187re 187os systematics and element variations of allende are less disturbed compared with murchison which reflects different degrees of oxidation and alteration of these meteorites the hse systematics with the exception of au is controlled by two types of materials pd depleted condensates and ci chondrite like material enrichment and heterogeneous distribution of au among the components is likely the result of hydrothermal alteration chalcogen elements are depleted compared with hse in all components presumably due to their higher volatility small systematic variations of s se and te in components bear the signature of fractional condensation partial evaporation and metal sulfide silicate partitioning

187re 187os systematics highly siderophile element s se te abundances in the components of unequilibrated l chondrites abstract the 187re 187os systematics abundances of highly siderophile elements hse re platinum group elements and au te se and s as well as major and minor elements were determined in separated components of two unequilibrated l chondrites que 97008 l3 05 and ceniceros l3 7 the 187re 187os systematics are disturbed in the components of both meteorites most likely due to open system behavior of re during terrestrial weathering of que 97008 and alteration on the l chondrite parent body as indicated by an internal errorchron generated for components of ceniceros the hse abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members non magnetic fractions display lower re os and hse ir than ci chondrites chondrules metal troilite spherules and fine magnetic fractions are depleted in refractory hse and show higher rh ir pd ir and au ir than in ci chondrites the different hse compositions indicate the presence of unequilibrated alloys and loss of refractory hse rich carrier phases from the precursors of some l chondrite components gold is decoupled from other hse in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to s and se presumably inherited from preaccretionary processes tellurium is depleted in all components compared to other analysed siderophile elements and its abundance was most likely controlled by fractional condensation and different geochemical affinities the volatility dependent depletion of te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites tellurium also shows variable geochemical behavior siderophile in ceniceros predominantly chalcophile in que 97008 these differences may have been inherited from element partitioning during chondrule formation selenium and s on the other hand are almost unfractionated from each other and only show complementary s se in a few components presumably due to the effects of volatility or metal silicate partitioning during chondrule formation terrestrial weathering had negligible effects on the s se and te systematics

well preserved palaeogene and cretaceous biomarkers from the kilwa area tanzania we have investigated the biomarker composition of sediments ranging in age from 30 to 70 ma from the kilwa area of tanzania they are dominated by material of terrestrial n alkanols n alkanoic acids n alkanes and triterpenoids and bacterial hopanoids and a dipentadecyl glycerol diether dgd origin with only a minor contribution of marine origin crenarchaeol and some algal steroids this indicates a marine setting dominated by higher plant input which most likely stimulated sedimentary microbial activity including sulfate reduction the lipid composition specifically the presence of bacteriohopanepolyols bhps and the stereochemistry of hopanoids suggests a low degree of thermal maturity many biomarkers have still retained functionality even after 30 70 million years this is in good agreement with the exceptional preservation of foraminifera and nannofossils and can probably be attributed to the very low sediment permeability and burial depth there is a clear distinction in the biomarker distributions between the oligocene age sediments collected at the end of the peninsula near kilwa masoko and the older sediments collected from elsewhere indicating differences in depositional environment sediments from the end of the peninsula have higher branched and isoprenoid tetraether index values indicating a relatively higher terrestrial input they also contain two tentatively assigned c28 hopenes 28 30 dinorneohop 13 18 ene and 28 30 dinorhop 17 21 ene aromatic des a triterpenes des e hopenes aromatic pentacyclic triterpenoids c33 dgd archaeol and bhps which are absent from or only present in small amounts in the other sediments these differences likely reflect an evolution of the depositional area from a relative open shelf environment with substantial water depth to a shallower setting during the early oligocene

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

trace element abundances in hibonites from the murchison carbonaceous chondrite constraints on high temperature processes in the solar nebula abundances of trace elements including 14 rare earth elements ree and 8 other refractory trace elements rte have been measured in 33 hibonite and 3 perovskite bearing grains from the murchison carbonaceous chondrite the normalized abundance patterns show a good correlation with three morphological and chemical groups of hibonites sixteen platy hibonite crystals placs typically have patterns which are depleted in the relatively volatile trace elements v nb ba eu and yb group iii three placs also show large depletions in ce one plac is enriched in the ultrarefractory ree while two other placs have fractionated patterns enriched in the light ree with positive tm anomalies the placs commonly have a roll off in the abundances of the hree which is consistent with solid liquid partitioning three blue aggregates bags have patterns with low overall abundances and depletions in the ultrarefractory ree except tm group ii spinel hibonite grains shibs show a variety of patterns mainly of group ii but 4 shibs have relatively smooth patterns with anomalies in the volatile ree ce eu and yb the perovskites have patterns similar to group ii but with excesses in eu and yb the hree roll off in the placs and the igneous morphologies of the shibs indicate that these grains formed by the crystallization of melts distillation may be important for the bags and two of the placs which have large isotopic mass fractionation effects placs have the simplest trace element patterns and the largest ti isotopic anomalies and probably were the first hibonites to form in the early solar system the shibs have trace element signatures that require multiple processing episodes they are somewhat complementary to the placs in that they are enriched in the volatile elements which are depleted in the placs on average the shibs contain isotopically less anomalous ti than the placs however shibs contain 26mg excesses that are consistent with the in situ decay of 26al whereas placs generally have only small or no excesses of 26mg despite high 27al24mg while an overall relationship exists between the morphology chemistry and ti and mg isotopic systematics of meteoritic hibonites they do not as yet fit into a simple scenario for the formation of the solar system

archaeal lipid biomarkers and isotopic evidence of anaerobic methane oxidation associated with gas hydrates in the gulf of mexico abstract anaerobic oxidation of methane aom occurs in the gulf of mexico gas hydrate systems here we show lipid biomarker and isotopic evidence that archaea are involved in aom the estimated abundance of total archaeal lipids ranges from 44 8 to 60 4 g g dry sediment in hydrate bearing samples but is below detection limit in the hydrate free sample the 13c values of archaeal lipids range from 69 to 99 in hydrate bearing samples these results suggest that biomass of archaea is significantly enhanced through aom at the gas hydrate deposits these data also support a currently acknowledged mechanism of aom mediated by a consortium of sulfate reducing bacteria and archaea observed in a variety of methane rich marine settings anaerobic oxidation of oil hydrocarbons also occurs in the gulf of mexico gas hydrate systems as shown by degradation of n alkanes c15 in the anoxic sediments these processes convert hydrocarbons to carbon dioxide and increase pore water alkalinity which promote the precipitation of enormous volumes of authigenic carbonate rock depleted in 13c this long term geologic sequestration of carbon may affect models of global climate change

ch 4 consuming microorganisms and the formation of carbonate crusts at cold seeps to understand the role played by microorganisms in the formation of cold seep carbonates we conducted an integrated microbial mineralogical and organic geochemical study of methane related authigenic carbonate crusts formed on eastern mediterranean mud volcanoes we show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane combined lipid biomarker analysis and 16s rrna gene surveys identified a highly diversified methane consuming archaeal community possibly comprising novel species implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation moreover pore water sulphate gradients produced by co occurring methane based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation we propose that this may be the dominant mode of carbonate crust formation at cold seeps world wide in agreement with aquatic chemistry predictions and explaining carbonate mineralogy

carbon cycle in the coastal zone effects of global perturbations and change in the past three centuries abstract the coastal zone consisting of the continental shelves to 200 m including bays lagoons estuaries and near shore banks is an environment that is strongly affected by two much bigger environmental reservoirs adjacent to it the land and open ocean in the coastal zone as elsewhere in the earth system the biogeochemical cycle of carbon is coupled to and driven by the cycles of nitrogen and phosphorus through biological transfer processes human activities in the past 300 years have become an increasingly important geological factor with respect to the coastal zone through four major environmental perturbations 1 c n and s emissions from fossil fuel burning 2 changes in land use activities resulting in gaseous c emissions increased dissolved and particulate loads organic matter transport and feedbacks to biological production 3 application of inorganic nitrogen and phosphorus containing fertilizers and 4 discharges of sewage containing reactive organic c n and p in addition the mean global surface temperature of the planet has increased over this period of time by approximately 1 c perhaps also because of human activities starting with the year 1700 as a base for the industrial age perturbations on land we analyzed the consequences of these five perturbations to the carbon cycle in the coastal zone using the thirteen reservoir process driven model totem for the coupled c n p s biogeochemical cycles an indicator of the reliability of the model is the good agreement of its results showing the time course of increasing atmospheric co 2 concentrations since the year 1700 with the observational results reported in the literature during the past three centuries there has been a significant increase in the amount of organic carbon transported from land and stored in coastal zone sediments of the total transported about 65 was stored in sediments and the remaining 35 primarily recycled through exchange with the atmosphere and open ocean the imbalance between the amounts of organic carbon produced by gross photosynthesis and remineralized has apparently increased slightly in favor of remineralization corresponding to an increase in the degree of heterotrophy of the global coastal zone this process along with the release of co 2 from the formation of caco 3 counteracts the invasion of co 2 from the atmosphere to coastal waters that is driven by the rise in atmospheric co 2 concentrations an analysis of a possible reduction or full collapse of the oceanic thermohaline circulation as believed to have occurred in the past and a possibility for future centuries indicates that the co 2 transfer from the atmosphere to coastal waters would increase while that from the atmosphere to open ocean surface waters would decrease if such an event took place this is attributable to a reduced supply to the coastal zone of dissolved inorganic carbon by coastal upwelling from the deeper ocean a process linked to the global conveyor belt of the thermohaline circulation to date fossil fuel co 2 emissions to the atmosphere changes in land use practices and sewage discharges have been the three main factors affecting the carbon cycle in the global coastal zone the latter inputs from land have apparently produced a slight increase in the heterotrophy of the global coastal zone however increases in the inputs of nutrient nitrogen and phosphorus from land to the coastal zone in the future may drive its trophic state toward net production and storage autotrophy thereby also increasing its potential role as a sink for atmospheric co 2 the direction of future change in net ecosystem production in the coastal zone strongly depends on changes in the relative magnitudes of organic carbon and nutrient n and p fluxes to the coastal zone via rivers provided the upwelling fluxes remain constant

dark inclusions in allende leoville and vigarano evidence for nebular oxidation of cv3 constituents dark lithic inclusions are known to occur in several cv3 chondrites we report petrologic chemical and oxygen isotopic data on examples from allende leoville and vigarano the allende inclusions comprise a petrographic sequence ranging from a type which contains chondrules and refractory inclusions and resembles cv3 or co3 chondrites to a type which contains porous aggregates of iron rich olivine oxygen isotopic compositions correlate with the sequence chondrule rich inclusions have compositions similar to the host meteorite bulk values whereas olivine aggregate rich inclusions have more 16o depleted compositions chemical compositions on the other hand do not correlate with the petrographic sequence the dark inclusions are all systematically enriched in iron and depleted in potassium and sodium relative to their host meteorites the inclusions appear to be fragments of cv3 parent bodies which were processed to different degrees prior to their incorporation as clasts into allende leoville and vigarano the processing homogenized olivine compositions presumably through heating and also involved oxygen exchange with 16o poorer surroundings either parent body metamorphism or nebular heating might have produced the petrographic and isotopic sequences however the most 16o depleted inclusions also have layered silicate rims surrounding them which are better attributed to gas solid reactions than parent body processes in particular andradite is abundant in the rims which implies that the rims grew under conditions significantly more oxidizing than those likely to have occurred on a cv3 parent body at least part of the processing therefore appears to have taken place prior to final accumulation of the material when the fragments were dispersed in the nebula the evidence for coupled oxidation and 16o depletion in the nebula suggests that other features of the cv3 group such as the oxidized and reduced subgroups ferrous rims on forsteritic olivines and coarse grained rims on chondrules may have been established by similar gas solid reactions prior to the final assembly of the meteorites

accretionary rims on inclusions in the allende meteorite abstract many inclusions in allende particularly those with irregular shapes are surrounded by a sequence of thin layers which differ from one another in texture mineralogy and mineral chemistry the layer underlying all others contains either ia pyroxene needles olivine clumps of hedenbergite and andradite ib olivine doughnuts or ic rectangular olivine crystals the next layer outward ii contains tiny

are c1 chondrites chemically fractionated a trace element study abstract six c1 chondrite samples and a c2 xenolith from the plainview h5 chondrite were analyzed by radiochemical neutron activation for the elements ag au bi br cd ce cs eu ge in ir lu nd ni os pd pt rb re sb se sn tb te tl yb and zn the data were combined with 9 earlier analyses from this laboratory and examined for evidence of chemical fractionation in c1 chondrites a number of elements br rb cs au re os ni pd sb bi in te show small but correlated variations those of the first 8 probably reflect hydrothermal alteration in the meteorite parent body whereas those of sb bi in and te may at least in part involve nebular processes br and au show systematic abundance differences from meteorite to meteorite which suggests hydrothermal transport on a kilometer scale the remaining elements vary from sample to sample suggesting transport on a centimeter scale there is no conclusive evidence for nebular fractionation affecting c1 s though c1 chondrites have lower zr hf and ir re ratios than do other chondrite classes these ratios vary in other classes suggesting that those classes rather than c1 s are fractionated three fractionation prone ree ce eu and yb have essentially the same relative abundances in c1 s and all other chondrite classes and hence apparently are not fractionated in c1 s we did not confirm the large tb and yb variations in c1 s reported by other workers we present revised mean c1 abundances for 35 elements based on the new data and a critical selection of literature data changes are generally less than 10 except for br rb ag sb te au and the ree the plainview c2 xenolith has normal trace element abundances except for 3 elements falling appreciably above the c2 range rb cs and bi hydrothermal alteration may be the reason for all 3 though nebular fractionation remains a possibility for bi

rhodium gold and other highly siderophile element abundances in chondritic meteorites abstract the abundances of the highly siderophile elements hse re os ir ru pt rh pd and au and 187os 188os isotope ratios have been determined for a set of carbonaceous ordinary enstatite and rumuruti chondrites using an analytical technique that permits the precise and accurate measurement of all hse from the same digestion aliquot concentrations of re os ir ru pt and pd were determined by isotope dilution icp ms and n tims analysis the monoisotopic elements rh and au were quantified relative to the abundance of ir differences in hse abundances and ratios such as re os 187os 188os pd ir and au ir between different chondrite classes are further substantiated with new data and additional rh and au data including new data for ci chondrites systematically different relative abundances of rh between different chondrite classes are reminiscent of the behaviour of re carbonaceous chondrites are characterized by low average rh ir of 0 27 0 03 1s which is about 20 lower than the ratio for ordinary 0 34 0 02 and enstatite chondrites eh 0 33 0 01 el 0 32 0 01 r chondrites show higher and somewhat variable rh ir of 0 37 0 07 well defined linear correlations of hse in particular for bulk samples of ordinary and el chondrites are explained by binary mixing and or dilution by silicates the hse carriers responsible for these correlations have a uniform chemical composition indicating efficient homogenization of local nebular heterogeneities during or prior to the formation of the host minerals in chondrite components excepting rumuruti chondrites and au in carbonaceous chondrites these correlations also suggest that metamorphism alteration and igneous processes had negligible influence on the hse distribution on the bulk sample scale depletion patterns for rh pd and au in carbonaceous chondrites other than ci are smoothly related to condensation temperatures and therefore consistent with the general depletion of moderately volatile elements in carbonaceous chondrites fractionated hse abundance patterns of ordinary enstatite and rumuruti chondrites however are more difficult to explain fractional condensation combined with the removal of metal phases at various times and later mixing of early and late formed metal phases may provide a viable explanation planetary fractionation processes that may have affected precursor material of chondrite components cannot explain the hse abundance patterns of chondrite groups hse abundances of some but not all rumuruti chondrites may be consistent with solid sulphide liquid sulphide fractionation processes during impact induced melting

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

rhenium osmium systematics of calcium aluminium rich inclusions in carbonaceous chondrites the re os isotopic systematics of calcium aluminium rich inclusions cais in chondrites were investigated in order to shed light on the behavior of the re os system in bulk chondrites and to constrain the timing of chemical fractionation in primitive chondrites cais with relatively unfractionated rare earth element ree patterns groups i iii v vi define a narrow range of 187 re 188 os 0 3764 0 4443 and 187 os 188 os 0 12599 0 12717 and high but variable re and os abundances 3209 41 820 ppb os in contrast cais that show depletions in highly refractory elements and strongly fractionated ree patterns group ii also show a much larger range in 187 re 188 os 0 409 0 535 and 187 os 188 os 0 12695 0 13770 and greater than an order of magnitude lower re and os abundances than other groups e g 75 7 680 2 ppb os sixteen bulk cais and cai splits plot within analytical uncertainty of a 4558 ga reference isochron as is expected for materials of this antiquity eight samples however plot off the isochron several possible reasons for these deviations are discussed data for multiple splits of one cai indicate that the nonisochronous behavior for at least this cai is the result of re os reequilibration at approximately 1 6 ga thus the most likely explanation for the deviations of most of the nonisochronous cais is late stage open system behavior of re and os in the asteroidal environment the 187 os 188 os os systematics of cais are consistent with previous models that indicate group ii cais are mixtures of components that lost the bulk of their highly refractory elements in a previous condensation event and a minor second component that provided refractory elements at chondritic relative proportions the high re os of group ii cais relative to other cais and chondrite bulk rocks may have been caused by variable mobilization of re and os during medium to low temperature parent body alteration 4 5 ga ago this model is favored over nebular models which pose several difficulties the narrow range of 187 os 188 os in group i iii v and vi bulk cais and the agreement with 187 os 188 os of whole rock carbonaceous chondrites suggest that on a bulk inclusion scale secondary alteration only modestly fractionated re os in these cais the average of 187 os 188 os for group i iii v and vi cais is indistinguishable from average ci chondrites indicating a modern solar system value for 187 os 188 os of 0 12650 corresponding to a 187 re 188 os of 0 3964 copyright 2001 elsevier science ltd

compositional continuity of enstatite chondrites and implications for heterogeneous accretion of the enstatite chondrite parent body abstract chemical compositions of eleven enstatite chondrites 1 eh5 4 eh3 3 el3 i el5 and 2 el6 and their metal and nonmagnetic fractions determined by instrumental neutron activation analysis are reported the abundances of nonvolatile lithophile elements such as al sc and mg increase from eh to el while those of siderophile and moderately volatile elements decrease in the sequence of eh5 to eh3 el3 and el5 6 the continuity in compositions of enstatite chondrites and in particular the inverse variations of moderately volatile element abundances with petrographic type between eh and el groups demonstrate that enstatite chondrites have been derived from a common parent body the enstatite chondrite parent body formed by heterogeneous accretion of materials available in the accretional region metal was effectively accreted into the core where eh5 chondrites were derived and the abundances of metal decreased as accretion proceeded in complement silicate abundances gradually increased in the layers that accreted later the lack of correlation between volatile element abundances and metamorphic degree demonstrates that losses of moderately volatile elements from enstatite chondrites cannot have resulted from parent body processes furthermore it is expected that during accretion various components would mix and thus erase any early fractionation of moderately volatile elements of a single parent body variations of ambient gas temperatures during accretion are also impossible to produce the volatile element pattern of enstatite chondrites it is suggested that moderately volatile elements in the enstatite chondrites were lost during local heating the chondrule formation process formation of chondrules appears to have proceeded during the accretion of the enstatite chondrite parent body and lasted for a certain period the mineralogical and textural features of enstatite chondrites can be explained in terms of two stages of metamorphism the metamorphic trend from eh3 to eh5 resulted from internal heating whereas the trend from el3 to el6 was due to an external heat source it seems very likely that the eh chondrites were metamorphosed during accretion thus cooled rather rapidly activities of the early sun could serve as an energy source for the external heating

complementary element relationships between chondrules and matrix in rumuruti chondrites abstract the complimentary chemical composition of chondrules and matrix has so far only been studied in carbonaceous chondrites we have extended these studies to the matrix rich rumurutis we have determined the chemical composition of 27 bulk chondrules and 100 matrix spots in unequilibrated fragments of three different rumuruti r chondrites nwa 2446 nwa 753 hughes 030 also the bulk chemical composition of nwa 753 was determined bulk r chondrites have about ci chondritic solar ratios of fe mg 1 89 al ti 18 62 and al ca 0 94 while chondrules and matrix are complementary to each other mean fe mg ratios in chondrules are 0 43 nwa 2446 0 36 nwa 753 and 0 34 hughes chondrules are depleted in fe while matrices are enriched in fe with respective values of 2 59 2 45 and 2 39 bulk fe mg ratio of nwa 753 the only sample which is unaffected by terrestrial weathering is reproduced by careful mass balance calculations using compositions and abundances of chondrules matrix and sulphides from the same thin section refractory element ratios are also complementary al ti and al ca are sub chondritic in chondrules al ti 10 43 in nwa 753 12 24 in nwa 2446 and 11 47 in hughes 030 al ca 0 66 in nwa 2446 0 53 in nwa 753 and 0 46 in hughes 030 while matrices generally have super chondritic al ca and al ti ratios al ti 28 00 in nwa 2446 23 20 in nwa 753 and 19 00 in hughes 030 al ca 2 30 in nwa 2446 1 90 in nwa 753 and 0 41 in hughes 030 calcium is enriched in the hughes 030 matrix due to terrestrial weathering these complementary element ratios and the ci chondritic bulk strongly suggest a common reservoir from which all r chondrite components formed similar to carbonaceous chondrites further super chondritic si mg and ci chondritic fe mg ratios in bulk r chondrites require addition of si to their reservoir most probably before chondrule formation

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

the paleocene eocene transition in the marginal northeastern tethys kazakhstan and uzbekistan we studied two sections that accumulated during the paleocene eocene transition in shelf waters in the northeastern tethys stable carbon isotopic compositions of marine and terrestrial biomarkers are consistent with a 13c depletion in the oceanic and atmospheric carbon dioxide pools during the late paleocene thermal maximum lptm subzone p5b the 2 3 negative 13c excursion in planktic foraminifera coincides with minimum 18o values an incursion of transient subtropical planktic foraminiferal fauna and the occurrence of an organic rich sapropelite unit in uzbekistan which accumulated at the onset of a transgressive event biomarker distributions and hydrogen indices indicate that marine algae and bacteria were the major organic matter sources during the late paleocene subzones p4 and p5a the marginal northeastern tethys experienced a temperate to warm climate with wet and arid seasons most likely warm and humid climate initiated during the lptm subzone p5b and subsequently extended during the eocene zone p6 onto adjacent land areas of the marginal northeastern tethys

highly siderophile elements and 187re 187os isotopic systematics of the allende meteorite evidence for primary nebular processes and late stage alteration abstract the abundances of highly siderophile elements hse re os ir ru pt and pd as well as 187 re 187 os isotopic systematics were determined for calcium aluminum rich inclusions cais chondrules and matrix separated from the cv3 carbonaceous chondrite allende consistent with prior studies cais are characterized by significant depletions in pd relative to the other hse while the other hse are in generally bulk chondritic relative abundances the depletions in pd can be linked with initial formation of cais via condensation or subsequent processing by evaporative processes chondrules generally have relative hse patterns similar to cais although they have lower absolute abundances palladium depletions in chondrules may reflect solid metal liquid metal fractionation at the time of formation or alternatively be the result of processes that acted on precursor materials matrix samples have nearly chondritic absolute abundances of all hse measured consequently matrix is the only major chondritic component examined here that shows no relative depletion in pd mass balance suggests the existence of an unidentified pd rich carrier although it is possible that the dataset presented here is too limited to represent typical hse abundances of some chondritic components e g chondrules the 187 re 187 os isotopic systematics of only six out of twenty four allende chondritic components analyzed plot within uncertainties of a 4568 ma primordial reference isochron the deviations from the expected isochron most likely reflect late stage open system behavior within the last 2 billion years and in some cases could even have resulted from terrestrial alteration the open system behavior is most readily observed in small millimeter size sub samples of allende consistent with re and or os mobility on that scale

biomarker indicators for anaerobic oxidizers of methane in brackish marine sediments with diffusive methane fluxes the anaerobic oxidation of methane aom is a major methane sink in marine sediments and plays a crucial role in mitigating methane fluxes to the overlying water column we investigated biomarker distributions and compound specific isotopic signatures in sediments from sites on the northern european continental margin that are characterized by a diffusive flux of methane at all sites the organic matter om is predominantly derived from terrestrial higher plants with subordinate abundances of algal biomarkers but biomarkers for archaea and bacteria are also present the co occurrence of the archaeal lipids archaeol sn 2 hydroxyarchaeol and 2 6 10 15 19 pentamethylicosane pmi with non isoprenoidal glycerol diethers inferred to derive from sulfate reducing bacteria srb is similar to microbial biomarker assemblages observed at cold seeps the archaeal and inferred srb biomarker concentrations typically reach maxima close to the sulfate methane transition zone smtz where archaeal biomarkers are depleted in 13c the 16s rrna gene sequences from the smtz of the aarhus bay sediment core indicate the occurrence of anme 1 archaea consistent with inferences derived from biomarker distributions the observations suggest that aom in these diffusive settings is mediated by consortia of archaea and bacteria similar to those found at many seep and methane hydrate sites around the world

comparison of the trace element composition of tagish lake with other primitive carbonaceous chondrites a meteorite fall on 18 january 2000 was detected by u s defense department satellites which established its pre impact orbit fresh samples were collected from frozen tagish lake in british columbia a week later and some properties of these samples reveal it to be a unique meteorite we characterized tagish lake and 8 other samples using icpms and rnaa data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the orgueil normalized plateaus expected for members of such types trends evident in tagish lake differ from all other carbonaceous chondrites including ci and cm samples of tagish lake collected later show similar patterns affected by weathering

algal and archaeal polyisoprenoids in a recent marine sediment molecular isotopic evidence for anaerobic oxidation of methane 1 analyses of 13c contents of individual organic molecules in a marine sediment show that crocetane 2 6 11 15 tetramethylhexadecane an isomer of phytane is produced by microorganisms that use methane as their main source of carbon the sediments lie at a water depth of 68 m in the kattegat the strait between denmark and sweden crocetane appears first 185 cm below the sediment water interface in the zone marking the transition from sulfate reduction to methanogenesis its 13c value is 90 10 versus vienna pee dee belemnite vpdb its structure which includes four isoprene units arranged symmetrically around a tail to tail linkage suggests that it is produced by a member of the archaea growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters the source organism apparently functions as a methane consuming member of the microbial consortium responsible for the anaerobic oxidation of methane hoehler et al 1994 in which as first demonstrated quantitatively in these sediments iversen and jorgensen 1985 electrons are transferred from methane to sulfate the presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2 6 10 15 19 pentamethylicosane pmi and of ether bound phytane and biphytane the pmi reaches a minimum value of 47 well below the transition zone its isotopic depletion could reflect either methanogenic or methanotrophic sources the ether bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane

lipid biomarkers preserved in hydrate associated authigenic carbonate rocks of the gulf of mexico anaerobic oxidation of methane aom is common in ocean margin sediments where it is mediated by consortia of archaea and bacteria and can result in the formation of authigenic carbonate including extensive carbonate crusts previous work indicates that aom is associated with gulf of mexico hydrocarbon seeps and is mediated by similar organisms as identified in other settings however biological investigations have not been done on the associated 13c depleted carbonates here we show that 13c depleted archaeal and bacterial biomarkers are abundant in gulf of mexico authigenic carbonate rocks revealing that aom mediating organisms are closely associated with carbonate authigenesis moreover the rocks share general characteristics of the background soft sedimentary archaeal and bacterial community inferred from biomarker analysis suggesting that the organisms associated with carbonate authigenesis are the same as those that live elsewhere in the hydrocarbon seep environment this provides further evidence that aom by archaea and sulfate reducing bacteria can result in the sequestration of significant quantities of methane derived carbon in carbonate rocks

a 35 000 year record of terrigenous and marine lipids in amazon fan sediments elemental and lipid analyses were carried out on sediments recovered from ocean drilling program odp site 942 to provide a 35 kyr record of organic matter input to amazon fan sediments total organic carbon toc and higher plant biomarker mass accumulation rates were an order of magnitude greater during the last glacial period compared to the current interglacial due to sea level controlled variations in amazon river sediment supply large maxima were also seen at similar to 12 ka which are most likely due to discharge events higher plant n alkane average chain lengths did not change throughout the record suggesting consistency in the source vegetation type the abundance of taraxerol relative to other plant biomarkers increased at similar to 12 ka indicating increased mangrove input due to either higher mangrove productivity or increased erosion of mangrove deposits the mass accumulation rates mars of some bacterial and eustigmatophyte biomarkers varied closely with those of higher plant biomarkers and so seem to have a non marine source long chain alkenones were present in some of the sediments generally in very low concentration indicating dilution of the marine signal with terrestrial organic matter c 2005 elsevier ltd all rights reserved

archaeal and bacterial lipids in authigenic carbonate crusts from eastern mediterranean mud volcanoes abstract we investigated the distributions and 13 c values of lipid biomarkers in authigenic methane related carbonate crusts formed on eastern mediterranean mud volcanoes a highly diverse suite of microbial membrane lipids was detected strongly 13 c depleted lipids diagnostic for archaea include isoprenoid glycerol diethers isoprenoid glycerol dialkyl glycerol tetraethers and several c 20 c 35 isoprenoid hydrocarbons bacterial lipids mainly consist of dialkyl glycerol diethers branched fatty acids and hopanoids showing important 13 c depletions albeit less than archaeal lipids the data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane aom and in the sequestration of methane derived carbon in authigenic carbonate crusts varying distributions and isotopic compositions of 13 c depleted lipids argue for heterogeneous aom related microbial consortia expanding on existing work at cold seeps distinctive biomarker features and inferred microbial assemblages are observed in these crusts in agreement with available phylogenetic data for the samples our results support the potential of lipids for distinguishing methanotrophic communities despite the observed variances conservative features in the abundances and isotopic offsets of microbial biomarkers occur likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them

sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation south east atlantic off namibia abstract sulfate reduction rates srr and concentrations of so 4 2 h 2 s pyrite sulfur total sulfur ch 4 and organic carbon were measured with high depth resolution through the entire length of the so 4 2 zone and well into the ch 4 zone at two continental slope stations in the eastern south atlantic benguela upwelling area the sediments were characterized by a high organic carbon content of approx 7 5 at geob 3703 and 3 7 at geob 3714 at geob 3703 so 4 2 concentrations decreased linearly with depth to about 40 m at the sulfate methane transition zone smt at 3 5 m while at geob 3714 so 4 2 remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 m at the smt at 6 m direct rate measurements of srr 35 so 4 2 showed that the highest srr occurred within the surface 3 5 cm with peak rates of up to 20 and 7 nmol so 4 2 cm 3 day 1 at geob 3703 and geob 3714 respectively srr decreased quasi exponentially with depth at geob 3703 and the cumulative srr over the length of the so 4 2 zone resulted in an areal srr srr area of 1114 3493 mol m 2 day 1 median value 2221 mol m 2 day 1 at geob 3703 with more than 80 of the total sulfate reduction proceeding in the top 30 cm sediment at geob 3714 srr exhibited more scatter with a cumulative srr area of 398 1983 mol m 2 day 1 median value 1251 mol m 2 day 1 and with 60 of the total sulfate reduction occurring below a depth of 30 cm due partially to a deeply buried zone of sulfate reduction located between 3 and 5 m depths srr peaks were also observed in smt of both cores ostensibly associated with methane oxidation but with rates about 10 times lower than at the surface modeled srr balanced both methane oxidation rates and measured srr within the smt but severely underestimated by up to 89 the total srr area that were obtained from direct measurements modeled and measured srr were reconciled by including solute transport by irrigation described by a non local pore water exchange function which had values of up to 0 3 year 1 in the top sediment and decreased exponentially to zero i e no irrigation at 2 3 meters i e above smt these results suggested that co existing sulfate reduction processes and linear so 4 2 gradients can be maintained by a non local transport mechanism such as irrigation by which pore water in tubes or burrows is exchanged with bottom waters by activities of tube dwelling animals or some similar physical transport phenomenon i e bubble ebullition further support for an irrigation mechanism was found in the observations of open tubes of up to 8 mm id at depths down to 6 m which also contained fecal pellets indicating that these tubes were or had been inhabited

fractionation of highly siderophile and chalcogen elements in components of eh3 chondrites abstract abundances of highly siderophile elements hse re platinum group elements and au chalcogens te se and s 187os 188os and the major and minor elements mg ca mn fe ni and co were determined in the components of sahara 97072 eh3 find and kota kota eh3 find in order to understand the element fractionation processes in a 187re 187os isochron diagram most magnetic components lie close to the 4 56 ga iiia iron meteorite isochron whereas most other components show deviations from the isochron caused by late redistribution of re presumably during terrestrial weathering metal and sulfide rich magnetic fractions and metal sulfide nodules are responsible for the higher 187os 188os in bulk rocks of eh chondrites compared to ci chondrites the hse and chalcogens are enriched in magnetic fractions relative to slightly magnetic and nonmagnetic fractions and bulk compositions indicating that fe ni metal is the main host phase of the hse in enstatite chondrites hse abundance patterns indicate mixing of two components a ci chondrite like end member and an au enriched end member because of the decoupled variations of au from those of pd or the chalcogens the enrichment of au in eh metal cannot be due to metal sulfide silicate partitioning processes metal and sulfide rich nodules may have formed by melting and reaction of pre existing refractory element rich material with volatile rich gas a complex condensation and evaporation history is required to account for the depletion of elements having very different volatility than au in eh chondrites the depletions of te relative to hse se and s in bulk eh chondrites are mainly caused by the depletion of te in metal s se and s mn are lower than in ci chondrites in almost all components and predominantly reflect volatility controlled loss of sulfur the latter most likely occurred during thermal processing of dust in the solar nebula e g during chondrule formation followed by the non systematic loss of s during terrestrial weathering

archaea mediating anaerobic methane oxidation in deep sea sediments at cold seeps of the eastern aleutian subduction zone cold seeps in the aleutian deep sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation this process is active in the anaerobic sediments at the sulfate reduction methane production boundary and is probably performed by archaea working in syntrophic co operation with sulfate reducing bacteria diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi as well as the glycerol ether lipid archaeol 2 3 di o phytanyl sn glycerol these biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates carbon isotopic compositions of the biomarkers are strongly depleted in 13c with values of 13c as low as 130 3 pdb the process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with 13c values of 39 2 and 41 8 and of the carbonate precipitates with values of 45 4 and 48 7 this suggests that methane oxidizing archaea have accumulated within the microbial community which is active at the cold seep sites the dominance of crocetane in sediments at one station indicates that probably due to decreased methane venting archaea might no longer be growing whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane the assemblages are apparently dependent on specific conditions found at each cold seep environment selective conditions probably include water depth temperature degree of anoxia and supply of free methane

chemical compositions of siderophile element rich opaque assemblages in an allende inclusion abstract ten opaque assemblages or fremdlinge weighing 0 17 19 g from an allende type b ca al rich coarse grained inclusion were analyzed by inaa for ca na mn sc ta ti v cr fe ni co w re os ir mo ru pt rh au as sb and se refractory siderophiles are usually enriched by factors of 103 104 relative to cl chondrites but not uniformly from sample to sample c1 chondrite normalized re os ir pt os ru and pt rh ratios vary from 0 81 1 03 0 70 2 25 0 67 3 32 and 0 45 1 43 respectively attempts to model the abundances of refractory siderophiles by condensation from the solar nebula into a single phase assuming ideal solution fail to match the observed combination of subchondritic re os and ir pt ratios even allowing for fractionation of the highest temperature condensates a different model in which all metals whose high temperature crystal structures are hcp condense into one alloy bcc into another and fcc into a third is capable of matching virtually all refractory siderophile fractionations in these fremdlinge in this model all isostructural metals are assumed to form ideal solutions with one another and metals of different structure are assumed to be insoluble in one another after fractionation of high temperature hcp and fcc alloys individual proto fremdlinge formed by mixing of high and low temperature varieties of each of the three alloys either in the nebula before and during cai accretion or during later partial melting of the silicate oxide and metal components of cais

nonlinear strong ground motion in the ml 5 4 chittenden earthquake evidence that preexisting damage increases susceptibility to further damage 1 we use 55 repeating earthquake sequences located near the 1989 mw 6 9 loma prieta earthquake to identify time dependent velocity changes in the shallow crust in addition to large delays caused by the loma prieta mainshock the ml 5 4 chittenden earthquake an aftershock of loma prieta caused direct s wave delays of up to 6ms and s coda delays exceeding 15ms we attribute the delays to cracks formed or opened during the strong shaking of the chittenden earthquake the same mechanism believed responsible for the delays observed following loma prieta the magnitude of the delays caused by chittenden strongly correlate with those caused by loma prieta this suggests that rocks recently damaged by nonlinear strong ground motion are particularly susceptible to further damage until they are completely healed therefore we expect that the onset of nonlinearity will occur at substantially lower ground motion for large aftershocks than would otherwise be anticipated

biomarker and 16s rdna evidence for anaerobic oxidation of methane and related carbonate precipitation in deep sea mud volcanoes of the sorokin trough black sea many mud volcanoes were recently discovered in the euxinic bottom waters of the sorokin trough ne black sea three of them i e nioz odessa and kazakov were selected for a detailed biogeochemical investigation four methane related carbonate crusts covered with microbial mats and sediments dmud brecciat from these mud volcanoes were collected during the 11th training through research cruise ttr 11 in 2001 the first finding of methanotrophic microbial mats associated with authigenic carbonates in the deep black sea we measured the concentrations and 13c values of methane and specific archaeal and bacterial lipids and determined archaeal and bacterial 16s rrna gene sequences the 13c of the microbial lipids reflected the carbon isotopic values of the methane indicating that methane was the main carbon source for microorganisms inducing carbonate formation anaerobic oxidation of methane aom in these settings was performed by archaea affiliated with the so called anme 1 group none of the identified archaeal sequences were closely related to known methanogens the combined 16s rrna gene sequence and biomarker data revealed a distinct difference in archaeal assemblage between the carbonate crusts and mud breccias besides gene sequences of sulfate reducing bacteria dna analysis of bacterial communities revealed a diversity of bacteria with apparent contrasting metabolic properties the methane utilization via aom processes was detected in the uppermost sediments where it subsequently induces authigenic carbonate precipitation most probably below seafloor the results of integrated biomarker and 16s rrna gene study reveal a crucial role of aom processes in formation of authigenic carbonates in methane seep environments

brecciation and chemical heterogeneities of ci chondrites abstract fragments in the size range from 40 m to several hundred m in the ci chondrites orgueil ivuna alais and tonk show a wide range of chemical compositions with variations in major elements such as iron 10 4 42 4 wt feo silicon 12 7 42 2 wt sio 2 and sulfur 1 01 15 8 wt so 3 but also important minor elements such as phosphorous up to 5 2 wt p 2 o 5 or calcium up to 6 6 wt cao these variations are the result of the varying mineralogical compositions of these fragments the distribution of phyllosilicates magnetites and possibly ferrihydrite in particular control the abundances of these elements high ree contents up to 150 times the solar abundances were observed in phosphates while matrix and sulfates are ree depleted the studied 113 fragments were subdivided into eight lithologies with similar mineralogical and thus chemical properties the most common is the cga lithology consisting of a groundmass of mg rich coarse grained phyllosilicates and varying abundances of inclusions such as magnetite the second most abundant lithology is the fga lithology consisting of a groundmass of fine grained fe rich phyllosilicates a rare but important lithology consists of fragments with high contents of phosphates and other minerals the proposed model for the evolution of these lithologies is based on a closed system alteration where mineralogical differences in the lithologies reflect heterogeneities in the starting material comparison of our results with literature data indicates a general similarity of the four ci chondrites analyzed further comparison of bulk analyses suggests that the mass threshold for chemical heterogeneities in ci chondrite samples is smaller than 1 2 g

gas hydrate destabilization and methane release events in the krishna godavari basin bay of bengal abstract methane release events have been linked to global warming alteration of the carbon cycle and influence on biota however unequivocal evidence of paleomethane release events are limited we report several negative carbon stable isotope excursions in planktic and benthic foraminifera in a core md161 8 from the krishna godavari k g basin bay of bengal the most negative 13 c spikes are recorded during the marine isotope stages mis 4 and at the transition of mis 5 to 4 occurrence of highly 13 c depleted average 13 c 48 2 4 vpdb authigenic high magnesian calcite are also reported within this time window from the core md161 8 in the present work an unequivocal explanation for the observed 13 c depletion in the marine planktic and benthic foraminifera is difficult to achieve solely from the optical electron microscopy or c o stable isotope ratio analyses due to possible influence of diagenetic alteration we attribute the observed episodic methane expulsion events as inferred from the negative 13 c excursions and earlier reports on the occurrence chemosynthetic bivalves and mo concentration anomaly to the destabilization of the base of gas hydrate stability zone bghsz sea level drop and shale tectonics induced focused fluid flow are the two possible causes of hydrate destabilization discussed here shale tectonics were possibly responsible for creating fault systems which acted as the conduit for gas flow through the sediment column and subsequent seepage shale and salt tectonics in the passive continental margins being a globally observed phenomenon its role as an important driving force for enhanced methane emission needs detailed investigation to understand the climatic perturbations through geologic time additional evidence of methane emission from site md161 15 further supports the link between shale tectonics and methane emission

molecular and isotopic analysis of anaerobic methane oxidizing communities in marine sediments convergent lines of molecular carbon isotopic and phylogenetic evidence have previously indicated hinrichs k u hayes j m sylva s p brewer p g delong e f 1999 methane consuming archaebacteria in marine sediments nature 398 802 805 that archaea are involved in the anaerobic oxidation of methane in sediments from the eel river basin offshore northern california now further studies of those same sediments and of sediments from a methane seep in the santa barbara basin have confirmed and extended those results mass spectrometric and chromatographic analyses of an authentic standard of sn 2 hydroxyarchaeol hydroxylated at c 3 in the sn 2 phytanyl moiety have confirmed our previous tentative identification of this compound but shown that the previously examined product was the mono tms rather than di tms derivative further analyses of 13 c depleted lipids appreciably more abundant in samples from the santa barbara basin have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in 13 c these are additional glycerol ethers and fatty acids the alkyl substituents in the ethers mostly monoethers with some diethers are non isoprenoidal the carbon number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar suggesting strongly that they are produced by the same organisms their structures n alkyl and methyl branched n alkyl require a bacterial rather than archaeal source the non isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic sulfate and nitrate reducing organisms which lie near the base of the rrna based phylogenetic tree based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate it appears likely that the non archaeal 13 c depleted lipids are products of one or more previously unknown sulfate reducing bacteria which grow syntrophically with the methane utilizing archaea their products account for 50 of the fatty acids in the sample from the santa barbara basin at all methane seep sites examined the preservation of aquatic products is apparently enhanced because the methane oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column

geo and cosmochemistry of the twin elements yttrium and holmium we have analyzed the y ho ratios in bulk chondrites chondrules and four ca and al rich inclusions cais from carbonaceous and unequilibrated ordinary and enstatite chondrites ec by laser ablation inductively coupled mass spectrometry la icpms we demonstrate that bulk rock sample preparation by containerless melting is a suitable method for preparation of bulk rock samples for high precision la icpms bulk chondrites have variable y ho ratios carbonaceous chondrites ci1 cm2 cv3 and ck4 have a common y ho ratio 25 94 0 08 2 that is regarded as the solar system y ho ratio the y ho ratio increases from carbonaceous through ordinary ll l h to enstatite chondrites el6 which show the highest y ho ratio of 27 25 we discuss the result with respect to the origin of fractionation of re and os between chondrite groups within analytical error y and ho show a good correlation in oc and cv3 chondrules and define an y ho ratio of 26 22 0 40 2 y ho fractionation in ca and al rich inclusions is related to differences in volatility the bulk silicate earth is suggested to have a solar y ho ratio and links the earth with carbonaceous chondrites y ho variations in primitive and differentiated terrestrial igneous rocks are discussed in framework of incompatibility of y and ho during partial melting applicability of y ho as tracer for or against a sedimentary origin of the putative host rock of the earth s oldest traces of life from the island of akilia is briefly discussed

mixed sources contribute to the molecular isotopic signature of methane rich mud breccia sediments of kazan mud volcano eastern mediterranean abstract we have investigated the molecular carbon isotopic signature of mud breccia sediments from a methane seep environment on kazan mud volcano in the eastern mediterranean many different classes of lipids have been identified and attributed to methane oxidizing archaea sulfate reducing bacteria methane oxidizing bacteria and sulfide oxidizing bacteria as well as older organic matter associated with the ascending mud diapirs in the region of particular interest is the record of glycerol dialkyl glycerol tetraethers gdgts derived from various types of archaea a geochemical depth profile of the upper 30 cm of sediment allows the assessment of vertical variability in the microbial community which proves to be diverse based on molecular isotopic analyses and the importance of present day microbes relative to paleo organic matter in this environment it seems that anaerobic oxidation of methane aom has progressed at relatively low rates or for a shorter time compared with other seep sites based on the high relative abundance of organic matter associated with the ascending mud matrix rather than with aom and the carbon isotopic composition of gdgt derived biphytanes the presence of many different biomarkers of aom related microbes with varying depth trends in both concentration and carbon isotope composition suggests substantial variability in the microbial community on a small vertical scale 30 cm