indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

alteration of mesostasis in chondrules and aggregates from three c2 carbonaceous chondrites abstract microprobe analyses of mesostasis glass and phyllosilicate spinach in a variety of chondrules and aggregates from the c2 chondrites murchison essebi and renazzo suggest that a two stage alteration process acted on glass to produce the current range of spinach compositions the first stage was short but active coinciding both with a period of vigorous gardening of the c2 parent regolith and with the pervasive alteration that modified the proportion of matrix phyllosilicates in c2 meteorites during this stage mesostasis glass was hydrated and was mg enriched by limited reaction with chondrule and aggregate phenocrysts the second alteration stage involved slow but extensive reactions between mesostasis material and altered matrix resulting in a field of fe enriched spinach compositions that is distinctive for each meteorite

elephant moraine 96029 a very mildly aqueously altered and heated cm carbonaceous chondrite implications for the drivers of parent body processing elephant moraine eet 96029 is a cm carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration a later phase of heating and terrestrial weathering the presence of phyllosilicates and carbonates within chondrules and the fine grained matrix indicates that this meteorite was aqueously altered in its parent body features showing that water mediated processing was arrested at a very early stage include a matrix with a low magnesium iron ratio chondrules whose mesostasis contains glass and or quench crystallites and a gehlenite bearing calcium and aluminium rich inclusion eet 96029 is also rich in fe ni metal relative to other cm chondrites and more was present prior to its partial replacement by goethite during antarctic weathering in combination these properties indicate that eet 96029 is one of the least aqueously altered cms yet described cm2 7 and so provides new insights into the original composition of its parent body following aqueous alteration and whilst still in the parent body regolith the meteorite was heated to 400 600 c by impacts or solar radiation heating led to the amorphisation and dehydroxylation of serpentine replacement of tochilinite by magnetite loss of sulphur from the matrix and modification to the structure of organic matter that includes organic nanoglobules significant differences between samples in oxygen isotope compositions and water hydroxyl contents suggests that the meteorite contains lithologies that have undergone different intensities of heating eet 96029 may be more representative of the true nature of parent body regoliths than many other cm meteorites and as such can help interpret results from the forthcoming missions to study and return samples from c complex asteroids

new constraints on atmospheric co2 concentration for the phanerozoic earth s atmospheric co2 concentration ca for the phanerozoic eon is estimated from proxies and geochemical carbon cycle models most estimates come with large sometimes unbounded uncertainty here we calculate tightly constrained estimates of ca using a universal equation for leaf gas exchange with key variables obtained directly from the carbon isotope composition and stomatal anatomy of fossil leaves our new estimates validated against ice cores and direct measurements of ca are less than 1000 ppm for most of the phanerozoic from the devonian to the present coincident with the appearance and global proliferation of forests uncertainties obtained from monte carlo simulations are typically less than for ca estimates from other approaches these results provide critical new empirical support for the emerging view that large 2000 3000 ppm long term swings in ca do not characterize the post devonian and that earth s long term climate sensitivity to ca is greater than originally thought key points a novel co2 proxy calculates past atmospheric co2 with improved certainty co2 is unlikely to have exceeded 1000 ppm for extended periods post devonian earth s long term climate sensitivity to co2 is greater than originally thought

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

aqueous alteration in carbonaceous chondrites mass balance constraints on matrix mineralogy abstract bulk chemical compositions of matrix material in antarctic cm chondrites and other non antarctic cm and ci chondrites have been determined using microprobe defocused beam techniques these are used along with the results of previously published mineralogical studies to provide mass balance constraints on the relative proportions of intergrown and intermixed phyllosilicate phases in carbonaceous chondrite matrices results of these calculations indicate differing amounts of pcp a mixture of approximately 25 tochilinite and 75 cronstedtite and serpentines mg rich and fe rich varieties in varying proportions or intermediate compositional varieties additional sulfide phases are also probably necessary to account for excess ni and s fe si ratios for matrices of individual meteorites range from 1 21 to 2 77 corresponding to pcp pcp serf ratios of 0 16 to 0 58 progressive aqueous alteration of matrix appears to have occurred by formation of tochilinite then cronstedtite and mg rich serpentine and finally fe rich serpentine and sulfides cm matrix clearly did not behave as an isolated system during alteration ci chondrite matrices appear to contain little if any pcp this may be a natural consequence of the absence of chondrule associated metal from which pcp forms in the unaltered precursor material these data provide a more quantitative picture of low temperature aqueous alteration processes in carbonaceous chondrite parent bodies than has heretofore been possible from tem studies alone

empirical relationship between ph and the boron isotopic composition of globigerinoides sacculifer implications for the boron isotope paleo ph proxy culture experiments were carried out with the planktonic foraminifera globigerinoides sacculifer at three different ph values 7 6 0 05 8 20 0 05 8 60 0 05 in order to establish the ph dependence of the boron isotopic fractionation between the calcitic tests of g sacculifer and seawater additional objectives were to compare the ph dependences of boron isotopic composition of g sacculifer with that of orbulina universa and inorganic calcite in order to evaluate the robustness of the boron isotope paleo ph proxy the relationship between the boron isotopic composition of g sacculifer and the culture water ph shows heavier boron isotopic values at higher ph this empirical relationship is similar but slightly offset by 3 per mil from that of o universa indicating the presence of biogenic influence vital effect on the boron isotopic composition of foraminifera however comparison of the boron isotopic composition of o universa and g sacculifer with that of inorganic calcite grown over a common ph range shows that inorganic processes are the dominant control on the boron isotopic composition of foraminifera and the vital effects play a small but not insignificant role the results imply that in spite of a small biogenic influence the variation in boron isotopic composition of foraminiferal shells with ph at least for o universa and g sacculifer is consistent with that for inorganic calcite demonstrating the potential of this isotopic signature in foraminifera as a reliable paleo ph proxy

non nebular origin of dark mantles around chondrules and inclusions in cm chondrites abstract our examination of nine cm chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in cm chondrites are not discrete fine grained rims acquired in the solar nebula as modeled by metzler et al accretionary dust mantles in cm chondrites evidence for solar nebula processes geochim cosmochim acta 56 1992 2873 2897 nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles we infer that the mantles were produced from porous nebular materials on the cm parent asteroid by impact compaction a process that produces the lowest porosity adjacent to chondrules and inclusions compaction was followed by aqueous alteration that formed tochilinite serpentine ni bearing sulfide and other secondary products in voids in the interchondrule regions metzler et al reported a correlation between mantle thickness and the radius of the enclosed object in yamato 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation r2 0 44 if we limit consideration to central objects with radii 35 m a moderate correlation is also found in que 97990 we suggest that impact induced shear of a plum pudding like precursor produced the observed mantles these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions some mantles in cm chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity typically a gray uniform inner layer is surrounded by an outer layer consisting of darker silicates with bse bright speckles the cm chondrite objects characterized as primary accretionary rocks by metzler et al did not form in the nebula but rather on the parent body the absence of solar flare particle tracks and solar wind implanted rare gases in these clasts reflect their lithified nature and low surface volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles the clasts are analogous to the light colored metamorphosed clasts in ordinary chondrite regolith breccias which also lack solar flare particle tracks and solar wind gas

phyllosilicates in the matrix of the unique carbonaceous chondrite lewis cliff 85332 and possible implications for the aqueous alteration of ci chondrites abstract the fine grained matrix of the unique unequilibrated carbonaceous chondrite lewis cliff lew 85332 has been studied by scanning electron microscopy sem electron probe microanalysis epma and transmission electron microscopy tem compositionally lew 85332 has a matrix that is more fe rich than typical ci chondrites but has elemental abundance ratios that appear to be closer to ci matrices than to cm or cr chondrites the mineralogy of the matrix is dominated by phyllosilicate phases that are predominantly interlayered fe rich serpentine saponite anhydrous silicate phases such as olivine and pyroxene are rare minor magnetite troilite and ferrihydrite also occur associated with the phyllosilicates despite the high degree of weathering in lew 85332 the phyllosilicates appear to have an extraterrestrial origin but the highly variable mg fe ratios of saponite may be the result of partial terrestrial oxidation of fe rich saponite to a more mg rich saponite and ferrihydrite alternatively some of the ferrihydrite may have formed as a result of terrestrial weathering of fe ni metal the compositional and mineralogical data suggest that the matrix of lew 85332 may represent a very early stage in the type of aqueous alteration experienced by the ci chondrites although it is improbable that lew 85332 was a precursor to the ci chondrites because of its high abundance of chondrules the absence of carbonates the high fe content of the matrix and phyllosilicate phases and relatively low abundance of magnetite all indicate that the degree of oxidation and leaching of lew 85332 matrix was significantly less than that experienced by the ci chondrites the absence of clear evidence for alteration of chondrules suggests that either the formation of the hydrous phases in the matrix occurred prior to accretion or that alteration occurred on a parent body and involved limited amounts of fluid such that the reactions took place preferentially and exclusively within the fine grained anhydrous matrix materials

chondrules in the murray cm2 meteorite and compositional differences between cm co and ordinary chondrite chondrules abstract bulk compositions were determined by broad beam electron microprobe analysis for thirteen of the least aqueously altered chondrules in murray cm2 these and literature data reveal compositional differences between cm co and ordinary chondrite oc chondrules 1 a co chondrules are richer in refractory lithophiles and poorer in cr mn and volatile lithophiles than oc chondrules much lower refractory lithophile abundances in cm chondrules resulted from aqueous alteration 2 b in cm co chondrites abundances of refractory lithophiles are higher in nonporphyritic than porphyritic chondrules whereas in h l ll3 chondrites the converse is true 3 c cr ranges are greater and cr and mn correlate more strongly in chondrules in cm co than in h l ll3 chondrites we find evidence for two important lithophile precursor components of cm co chondrite chondrules 1 1 pyroxene and refractory rich feo poor 2 2 olivine rich refractory and feo poor the occurrence of a few feo rich chondrules attests to a third component similar to matrix olivine and feo rich refractories not characterized the first two components differ from those inferred for oc chondrules consistent with formation at different locations the pyroxene and refractory rich feo poor lithophile precursor component probably formed by an incomplete evaporation of presolar silicates that brought these materials into the enstatite stability field

boron and magnesium isotopic composition of seawater the isotopic systems of boron and magnesium are increasingly being used as proxies for a number of environmental variables and processes the isotopic composition of seawater for both systems plays a central role in these studies and is an important interlaboratory standard given the long residence times of both elements 10 7 years it is commonly assumed that seawater is isotopically homogenous for these systems yet no systematic studies currently exist here we present the b and mg isotopic composition of 26 28 seawater samples from a number of ocean basins that encompass a significant range in salinity 32 to 38 psu temperature 0 3 to 25 9c and water depth 0 to 1240 m we find no significant or systematic variation for either system in accordance with their long residence times we recommend that the mean values we report 11 b 39 61 0 04 2 s e n 28 25 mg 0 43 0 01 2 s e n 26 26 mg 0 82 0 01 2 s e n 26 be used in future studies involving mg and b isotopes copyright 2010 by the american geophysical union

yamato 86029 aqueously altered and thermally metamorphosed ci like chondrite with unusual textures we describe the petrologic and trace element characteristics of the yamato 86029 y 86029 meteorite y 86029 is a breccia consisting of a variety of clasts and abundant secondary minerals including coarse and fine grained phyllosilicates fe ni sulfides carbonates and magnetite there are no chondrules but a few anhydrous olivine rich grains are present within a very fine grained phyllosilicate rich matrix analyses of 14 thermally mobile trace elements suggest that y 86029 experienced moderate open system thermal metamorphism comparison with data for other heated carbonaceous chondrites suggests metamorphic temperatures of 500 600 oc for y 86029 this is apparent petrographically in partial dehydration of phyllosilicates to incompletely re crystallized olivine this transformation appears to proceed through intermediate highly disordered poorly crystalline phases consisting of newly formed olivine and residual desiccated phyllosilicate and their mixtures periclase is also present as a possible heating product of mg rich carbonate precursors y 86029 shows unusual textures rarely encountered in carbonaceous chondrites the periclase occurs as unusually large fe rich clasts 300 500 m fine grained carbonates with uniform texture are also present as small 10 15 m in diameter rounded to sub rounded shells of ankerite siderite enclosing magnetite these carbonates appear to have formed by low temperature aqueous alteration at specific thermal decomposition temperatures consistent with thermodynamic models of carbonate formation the fine and uniform texture suggests crystallization from a fluid circulating in interconnected spaces throughout entire growth one isolated aggregate in y 86029 also consists of a mosaic of polycrystalline olivine aggregates and sulfide blebs typical of shock induced melt re crystallization except for these unusual textures the isotopic petrologic and chemical characteristics of y 86029 are quite similar to those of y 82162 the only other heated ci like chondrite known they were probably derived from similar asteroids rather than one asteroid and hence may not necessarily be paired

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

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

formation and alteration of cais in cold bokkeveld cm2 abstract calcium aluminium rich inclusions cais from the carbonaceous chondrite cold bokkeveld cm2 have been located and characterised in situ the textural environment of cm2 cais has been studied for the first time based on their primary mineralogy 345 cais have been classified into four groups 1 1 spinel inclusions 2 2 a hibonite inclusion 3 3 spinel pyroxene sp py inclusions 4 4 spinel pyroxene olivine sp py ol inclusions in addition refractory spherules and spinel bearing isolated olivines are also recognised cais in cold bokkeveld underwent extensive aqueous alteration and contain secondary minerals including calcite and various phyllosilicates these assemblages are similar to those in the chondrules and matrix of the meteorite and it is concluded that all were altered more or less simultaneously within a parent body regolith as is common in cm2s most cais in cold bokkeveld have a rim sequence containing a prominent fe rich phyllosilicate layer this formed early in the alteration sequence by the dissolution of melilite and subsequent precipitation of fe rich phyllosilicates from fluids with a high fe mg ratio cais in cold bokkeveld experienced two stages of deformation an earlier nebula stage predated the formation of the dust mantles that surround most cais and a later stage occurred in an asteroidal regolith the cais in cm2s are smaller than those in cv3 chondrites because of the greater intensity of the earlier fragmentation episode that they experienced aqueous alteration of cais and regolith deformation appear to have been simultaneous phase relations and pyroxene compositional trends in sp py and sp py ol inclusions indicate that they crystallised from liquids most spinel bearing inclusions in cold bokkeveld have a normal mg isotopic composition so they could not have formed by the simultaneous melting and evaporation of primitive dust one inclusion is enriched in the heavy isotopes of mg and may have formed in this way two or more events are required to form most of the inclusions the first produced the refractory compositions either by vapour solid condensation or slow evaporation of primitive dust the second event melted the refractory precursors which later crystallised to form the observed textures and mineral assemblages it has been suggested that refractory spherules with inwardly radiating hibonites formed from molten droplets at temperatures as high as 2135 c however the crystallisation sequences of these inclusions inferred from textural evidence are incompatible with those derived from phase relations and estimates of bulk composition it is concluded that cm2 refractory spherules did not form by crystallisation of molten droplets but were derived by fragmentation of larger inclusions in which they formed by partial melting

petrologic study of the belgica 7904 carbonaceous chondrite hydrous alteration oxygen isotopes and relationship to cm and ci chondrites abstract seven components were separated from the belgica 7904 b7904 carbonaceous chondrite in order to learn more about the genetic relationships between the petrology hydration reactions and the oxygen isotopic compositions these components include two partially altered chondrules two phyllosilicate clasts two olivine fragments and one matrix sample the partially altered chondrules have a core rim structure cores have igneous textures and are unaltered and rims consist mainly of talc component bearing phyllosilicates and unaltered olivine clear textural evidence indicates that the phyllosilicates in the rims were produced by replacing pyroxene and plagioclase while the olivine remained unaltered during the process on the other hand the phyllosilicate clasts consist mainly of fine grained serpentine produced from olivine as well as the pyroxene and plagioclase the olivine fragments derived by disaggregation of large porphyritic olivine chondrules are unaltered the matrix sample consists mainly of fine grained phyllosilicates if the hydration reactions took place with liquid water in the parent body olivine would have produced talc component free phyllosilicates before pyroxene and plagioclase reacted this is not the case for the phyllosilicates in the chondrule rims therefore we suggest that the chondrule rims formed by hydration in the nebula prior to accretion rather than with liquid water in the parent body thermodynamic calculations show that the reactions of pyroxene and plagioclase with a gas would produce the talc component bearing phyllosilicates at temperatures higher than that at which olivine reacts to produce serpentine assuming that total gas pressure was 10 3 bars the chondrule rims may have been produced by reactions with a nebular gas having an h 2 o h 2 ratio of 0 052 at temperatures ranging from 560 to 330 k the phyllosilicate clasts where olivine also reacted may have been produced by reactions with this nebular gas at temperatures near 300 k and the matrix phyllosilicates may have been in equilibrium with the gas at temperatures higher than 250 k there is no evidence for liquid water interacting with the chondrite the cm mixing line in the three oxygen isotope plot mayeda et al 1991 which includes the separated components and whole rock composition of b7904 is explained by hydration in nebular gas ci chondrites may have formed from materials similar to the b7904 matrix by reactions with liquid water in a parent body cm chondrites have experienced two stage alteration including both hydrous reactions with a gas in the nebula and aqueous alteration with liquid water in their parent body

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

carbonates in cm chondrites complex formational histories and comparison to carbonates in ci chondrites cm chondrites are primitive solar system materials that have undergone high degrees of aqueous alteration resulting in the formation of secondary minerals including carbonates two different carbonate minerals calcite aragonite and dolomite together constitute 1 4 2 8 vol of cm chondrites in contrast ci chondrites contain four different carbonate minerals calcite aragonite dolomite breunnerite and siderite ci chondrites have abundant dolomite a mineral that seems to be absent in the most aqueously altered cm chondrites in this study carbonates in seven cm chondrites y 791198 lapaz icefield 04796 cold bokkeveld nogoya queen alexandra range 93005 allan hills 83100 and meteorite hills 01070 were studied petrographically and by electron microprobe the results indicate that carbonate formation in cm chondrites differs from that in ci chondrites and is more complex than previously recognized our studies of cm chondrites indicate that 1 carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition 2 at some stage ca and mg activities in the environment were high enough to form metastable dolomite and 3 dolomites disappeared in the most aqueously altered cm chondrites

aqueous alteration of chondrules in the cm carbonaceous chondrite allan hills 81002 implications for parent body alteration abstract alh 81002 is a cm carbonaceous chondrite that has petrographic characteristics suggesting that it experienced a high degree of aqueous alteration but has entirely escaped parent body brecciation in this study we report the results of a systematic investigation of the alteration of more than 35 chondrules in alh 81002 that belong to specific well defined chondrule types our results show that the extent of chondrule alteration is almost exclusively controlled by the properties of the chondrule phases although these chondrules taken as a group show highly variable degrees of alteration no evidence for differences in the alteration histories of chondrules has been found instead the widely varying rates of alteration of chondrule phases such as forsteritic and fayalitic olivine clinoenstatite orthopyroxene and augite are sufficient to explain the diversity of chondrule alteration in alh 81002 chondrules with similar primary textural and mineralogical characteristics e g type ia type iia etc show remarkably similar degrees of alteration detailed studies of the alteration products of chondrules show that they retain a detailed record of the alteration history of the chondrules from the earliest to last stages and provide strong evidence for the compositional evolution of the altering fluid contrary to what might be expected the fluid composition appears to be the dominant controlling factor on the composition of serpentines that replace olivines pyroxenes and mesostasis the consistent degree of alteration observed in chondrules of the same type in alh 81002 indicates that they were altered under the same conditions for similar lengths of time such conditions are most consistent with alteration in a parent body environment in addition the compositional and textural uniformity of rim material chondrule alteration phases and vein fillings in chondrule components throughout alh 81002 also argue strongly that alteration occurred after accretion several observations on alh 81002 provide additional constraints and modifications on existing models of in situ parent body alteration for example inferences on the degree of alteration of cm chondrites based on the extent of brecciation as a parameter of the alteration degree appear to be compromised in addition models which suggest that tochilinite serpentine pcp rich objects have resulted from the break up of chondrules during brecciation are also inconsistent with our observations on alh 81002

a unique omphacite amphibole and graphite bearing clast in queen alexandra range que 99177 a metamorphosed xenolith in a pristine cr3 chondrite abstract a metamorphosed unshocked chondritic clast containing approximately equal volumes of matrix and chondrules has been identified in the primitive cr3 chondrite que 99177 the most striking features of this clast are the presence of ferroan omphacitic pyroxenes amphiboles pargasite and pargasitic hornblende and coarse grained up to 70 m graphite laths the clast also contains relatively equilibrated feo rich olivine low ca pyroxene and sulfides pentlandite and troilite the clast s matrix contains coarse interlocking crystals the chondrules are extensively recrystallized contain no mesostasis or metal and present poorly defined boundaries based on its compositional and crystallographic features omphacite appears to have formed at high pressures 6 gpa amphibole formation probably postdated graphite formation and occurred by reaction of olivine clinopyroxene and omphacite in the presence of an oxidizing na rich fluid at high temperatures 700 c the absence of metal suggests that this fluid was also rich in s

mineralogy of carbonaceous chondritic microclasts in howardites identification of c2 fossil micrometeorites abstract seventy one carbonaceous chondritic microclasts of average size 150 m have been found in three howardites yamato 793497 jodzie kapoeta all carbonaceous chondritic microclasts are made of a fine grained phyllosilicate rich matrix supporting a variety of minerals such as olivine pyroxene spinel iron oxides iron nickel sulfides and calcium carbonates such a mineralogy is typical of chondritic c2 matter half of the carbonaceous chondritic microclasts are tochilinite rich and have been tentatively called cm2 microclasts the other half are magnetite rich and have been tentatively called cr2 microclasts the absence of a correlation between the cm2 cr2 ratio in carbonaceous chondritic microclasts and in numerous millimeter sized clasts found in the same sections argues for carbonaceous chondritic microclasts being true micrometeorites rather than fragments of larger objects dynamical simulations show that it is possible for asteroidal dust to encounter vesta the howardite s putative parent asteroid at velocity low enough 1 to prevent fragmentation because the micrometeorite flux in the inner solar system has been decreasing with time we argue that carbonaceous chondritic microclasts have been trapped in vesta s regolith early in the history of the solar system and are fossil micrometeorites because both microclasts and clasts found in howardites are related to c2 chondritic matter we propose that c2 matter represents the bulk or at least a significant fraction of the primordial howardite parent asteroid considering the abundance of c2 matter among fossil micrometeorites we speculate that the c2 fossil micrometorites are the so far unidentified agent of the late chondritic veneer that endowed the earth s mantle with an excess of siderophile elements relative to the contents predicted by the core mantle separation models the discovery that c2 fossil micrometeorites are similar to c2 modern antarctic micrometeorites supports recent models proposing a micrometeoritic origin for the earth s oceans and volatile species

tetrad effects in ree abundance patterns of chondrules from cm meteorites implications for aqueous alteration on the cm parent asteroid abstract lanthanide tetrad effect in bulk chondrules from two moderately altered cm chondrites murchison and yamato 793321 y 793321 are reported for the first time twenty three chondrules were petrographically characterized and analyzed for 10 rare earth elements ree and other trace and major elements ba sr rb k ca mg and fe using the precise isotope dilution technique the results indicate systematic depletion several times of alkali and alkaline earths compared to cv and co chondrules most of the porphyritic olivine 8 po and olivine pyroxene 4 pop porphyritic and radial pyroxene 2 pp 1 rp and granular olivine 1 go chondrules show a light ree l ree depleted heavy ree h ree smoothly fractionated pattern composed of four upward convex segments possessing a relatively large negative eu anomaly ci normalized la sm lu er and eu eu ratios 0 3 1 eu normal value on the other hand all barred olivine 5 bo chondrules a few po and pop indicate almost a flat l ree pattern in addition regardless of their textural types nearly half of the chondrules have a variable degree of ce and yb anomalies and or l h ree discontinuity which is similar to cv and co chondrules the observed l and h convex ree patterns accompanied with the negative eu anomaly is the first known case for chondrules as well as meteoritic materials but have been previously reported for geological samples such as sedimentary rocks late stage igneous and metamorphic rocks and are explained as the lanthanide tetrad effect which plausibly results from fluid rock interaction we suggest that the marked ree fractionations occurred by the selective incorporation of l h rees and eu into alteration products in the matrix during alteration processes on the cm parent body but that the gas solid ree fractionation characteristics established in the nebula have basically remained unchanged we suggest that the tetrad effects observed here represent a new index of physico chemical conditions of fluid rock interactions prevalent on the cm parent body

aqueous alteration of chondrules from the murchison cm carbonaceous chondrite replacement pore filling and the genesis of polyhedral serpentine forsterite and clinoenstatite in type iab chondrules from the murchison cm carbonaceous chondrite have been partially serpentinized and the mechanisms of their alteration reveal crystallographic and microstructural controls on the reaction of silicate minerals with parent body aqueous solutions grains of forsterite were altered in two stages narrow veinlets of fe rich serpentine formed first and by the filling of sheet pores most of these pores were oriented parallel to 010 and 001 and had been produced by earlier fracturing and or congruent dissolution in the second stage the subset of veinlets that were oriented parallel to 001 was widened accompanying the replacement of forsterite by mg fe serpentine this reaction proceeded most rapidly parallel to 001 and crystallographic controls on the trajectory of retreating vein walls created fine scale serrations murchison clinoenstatite grains have a skeletal appearance due to the presence of abundant veinlets and patches of phyllosilicate two alteration stages can again be recognized with initial water mineral interaction producing tochilinite rich veinlets by the filling of 001 parallel contraction cracks pores then formed by congruent dissolution that was guided principally by orthopyroxene lamellae and they were subsequently filled by submicrometer sized crystals of polyhedral serpentine this finding that murchison forsterite and clinoenstatite grains have been altered demonstrates that aqueous processing of magnesium silicate minerals started much earlier in cm parent body history than previously believed our results also show that the occurrence of polyhedral serpentine can be used to locate former pore spaces within the parent body

modelling the oxygen isotope distribution of ancient seawater using a coupled ocean atmosphere gcm implications for reconstructing early eocene climate one of the motivations for studying warm climates of the past such as the early eocene is the enhanced understanding this brings of possible future greenhouse conditions traditionally climate information deduced from biological or chemical proxies have been used to test computer model simulations of past climatic conditions and hence establish some of the uncertainties associated with model based predictions however extracting climate information from proxies is itself an interpretative process and discrepancies between climate information inferred from different types of proxy undermines the assumption that model data conflicts automatically mean that the model is inherently flawed a new approach which both acknowledges and reduces the uncertainties associated with both model and data is required although the oxygen isotopic ratio 18o preserved in calcareous marine fossils has been used to reconstruct past seawater temperature for several decades significant uncertainties associated with this method persist these include assumptions about past seawater 18o for which no proxy exists and which is a key control on the temperature inferred from fossil carbonate here we present the results of an early eocene simulation made using a state of the art general circulation model gcm hadcm3 with co2 set at six times pre industrial values and which has oxygen isotopes incorporated into the full hydrological cycle and hence simulates the 18o of past seawater this allows us to explore the implications of the different seawater 18o correction factors commonly used for 18o based temperature reconstruction it also allows us to focus model data comparison on 18o rather than interpret ocean temperature an approach that reduces uncertainties in model data comparison since the effects of both the temperature and the isotopic composition of ocean water on 18o of carbonate are accounted for the good agreement between model and data for both modern and well preserved early eocene carbonate increases confidence in climate reconstructions of this time

changing atmospheric co2 concentration was the primary driver of early cenozoic climate the early eocene climate optimum eeco which occurred about 51 to 53 million years ago was the warmest interval of the past 65 million years with mean annual surface air temperature over ten degrees celsius warmer than during the pre industrial period subsequent global cooling in the middle and late eocene epoch especially at high latitudes eventually led to continental ice sheet development in antarctica in the early oligocene epoch about 33 6 million years ago however existing estimates place atmospheric carbon dioxide co2 levels during the eocene at 500 3 000 parts per million and in the absence of tighter constraints carbon climate interactions over this interval remain uncertain here we use recent analytical and methodological developments to generate a new high fidelity record of co2 concentrations using the boron isotope 11 b composition of well preserved planktonic foraminifera from the tanzania drilling project revising previous estimates although species level uncertainties make absolute values difficult to constrain co2 concentrations during the eeco were around 1 400 parts per million the relative decline in co2 concentration through the eocene is more robustly constrained at about fifty per cent with a further decline into the oligocene provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the eocene was similar to that of the late quaternary period this co2 decline was sufficient to drive the well documented high and low latitude cooling that occurred through the eocene once the change in global temperature between the pre industrial period and the eocene caused by the action of all known slow feedbacks apart from those associated with the carbon cycle is removed both the eeco and the late eocene exhibit an equilibrium climate sensitivity relative to the pre industrial period of 2 1 to 4 6 degrees celsius per co2 doubling 66 per cent confidence which is similar to the canonical range 1 5 to 4 5 degrees celsius indicating that a large fraction of the warmth of the early eocene greenhouse was driven by increased co2 concentrations and that climate sensitivity was relatively constant throughout this period

deformation and mantle flow beneath the sangihe subduction zone from seismic anisotropy abstract subduction of oceanic lithosphere is the most direct feedback between the earth s surface and deep interior however the detail of its interaction with the broader convecting mantle is still unclear mantle flow around subduction zones can be constrained using seismic anisotropy but despite many such studies a simple global picture is lacking the sangihe subduction zone where the molucca sea microplate is subducting westward beneath the eurasian plate is part of the tectonically complex sulawesi philippine region and an ideal natural laboratory to study complex subduction processes we investigate the anisotropic structure of the sangihe subduction zone with shear wave splitting measurements of local s and sks phases at two stations mni in sulawesi dav in the philippines as well as downgoing s phases at five stations at teleseismic distances combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase the broad depth distribution of local events 60 630 km allows us to observe a change in splitting behaviour at 380 km depth above fast directions are trench parallel and delay times t are 0 34 0 53 s with no increase with depth we suggest this anisotropy is caused by aligned cracks possibly melt filled beneath the volcanic arc and fossil anisotropy in the overriding plate below 380 km is predominantly trench normal and t are slightly higher 0 53 0 65 s as no correlation is observed with inferred distance travelled inside the slab we attribute this anisotropy to shear layers atop the slab which are coherent from 200 to 400 km depth and perhaps extend into the transition zone sks and source side measurements show larger t 1 53 and 1 33 s respectively and trench parallel since these phases predominantly sample sub slab mantle we consider along strike lateral flow associated with the double sided subduction of the molucca sea microplate to be the most likely explanation we thus infer three dominant regions of anisotropy at the sangihe subduction zone one within the overriding lithosphere one along the slab wedge interface and one below the subducting molucca sea slab the mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy this study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex subduction systems

the paradox between low shock stage and evidence for compaction in cm carbonaceous chondrites explained by multiple low intensity impacts abstract petrographic analysis of eight cm carbonaceous chondrites eet 96029 lap 031166 lon 94101 met 01072 murchison murray sco 06043 que 93005 by electron imaging and diffraction and x ray computed tomography reveals that six of them have a petrofabric defined by shock flattened chondrules with the exception of murchison those cms that have a strong petrofabric also contain open or mineralized fractures indicating that tensional stresses accompanying the impacts were sufficient to locally exceed the yield strength of the meteorite matrix the cms studied span a wide range of petrologic subtypes and in common with rubin 2012 we find that the strength of their petrofabrics increases with their degree of aqueous alteration this correspondence suggests that impacts were responsible for enhancing alteration probably because the fracture networks they formed tapped fluid reservoirs elsewhere in the parent body two meteorites that do not fit this pattern are met 01072 and murchison both have a strong petrofabric but are relatively unaltered in the case of met 01072 impact deformation is likely to have postdated parent body aqueous activity the same may also be true for murchison but as this meteorite also lacks fractures and veins its chondrules were most likely flattened by multiple low intensity impacts multiphase deformation of murchison is also revealed by the microstructures of calcite grains and chondrule defined petrofabrics as revealed by x ray computed tomography the contradiction between the commonplace evidence for impact deformation of cms and their low shock stages most belong to s1 can be explained by most if not all having been exposed to multiple low intensity i e

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

coupled greenhouse warming and deep sea acidification in the middle eocene 1 the middle eocene climatic optimum meco is an enigmatic warming event that represents an abrupt reversal in long term cooling through the eocene in order to further assess the timing and nature of this event we have assembled stable isotope and calcium carbonate concentration records from multiple deep sea drilling project and ocean drilling program sites for the time interval between 43 and 38 ma revised stratigraphy at several sites and compilation of 18o records place peak warming during the meco event at 40 0 ma chron c18n 2n the identification of the 18o excursion at sites in different geographic regions indicates that the climatic effects of this event were globally extensive the total duration of the meco event is estimated at 500 ka with peak warming lasting 100 ka assuming minimal glaciation in the late middle eocene 4 6 c total warming of both surface and deep waters is estimated during the meco at the study sites the interval of peak warming at 40 0 ma also coincided with a worldwide decline in carbonate accumulation at sites below 3000 m depth reflecting a temporary shoaling of the calcite compensation depth the synchroneity of deep water acidification and globally extensive warming makes a persuasive argument that the meco event was linked to a transient increase in atmospheric pco2 the results of this study confirm previous reports of significant climatic instability during the middle eocene furthermore the direct link between warming and changes in the carbonate chemistry of the deep ocean provides strong evidence that changes in greenhouse gas concentrations exerted a primary control on short term climate variability during this critical period of eocene climate evolution

the leoville cv3 accretionary breccia leoville is a cv3 chondrite that contains a large variety of inclusions besides refractory inclusions resembling those in allende fine grained dark inclusions are especially prominent same of these are xenoliths of material very similar to cm chondrites in texture bulk composition and oxygen isotopes however they show an unusually large range in the degree of hydrous alteration other dark inclusions are similar to host matrix the cv3 host of this breccia is similar to other cv chondrites although less metamorphosed than allende we suggest that leoville is a typical accretionary breccia whose parent body accreted after the cm like material represented by the xenoliths had formed and undergone alteration after accretion leoville suffered severe deformation leading to foliation stronger than in any other chondrite but the nature of the event that caused this remains unclear

fine grained dust rims in the tagish lake carbonaceous chondrite evidence for parent body alteration the tagish lake carbonaceous chondrite consists of heavily aqueously altered chondrules cais and larger mineral fragments in a fine grained phyllosilicate dominated matrix the vast majority of the coarse grained components in this meteorite are surrounded by continuous 1 5 to 200 m wide fine grained accretionary rims which are well known from meteorites belonging to petrological types 2 and 3 and whose origin and modification is still a matter of debate texturally the fine grained rims in tagish lake are very similar throughout the entire meteorite and independent of the nature of the enclosed object they typically display sharp boundaries to the core object and more gradational contacts to the meteorite matrix compared to the matrix the rims are much more finegrained and characterized by a significantly lower porosity the rims consist of an unequilibrated assemblage of phyllosilicates fe ni sulfides magnetites low ca pyroxenes and forsteritic olivines and are except for a much lower abundance of carbonates very similar to the tagish lake matrix electron microprobe and synchrotron x ray microprobe analyses show that matrix and rims are also very similar in composition and that the rims differ significantly from matrix and bulk meteorite only by being depleted in ca x ray elemental mapping and mineralogical observations indicate that ca was lost during aqueous alteration from the enclosed objects and preferentially crystallized as carbonates in the porous matrix the analyses also show that ca is strongly fractionated from al in the rims whereas there is no fractionation of the ti al ratios our data suggest that the fine grained rims in tagish lake initially formed by accretion in the solar nebula and were subsequently modified by in situ alteration on the parent body this pervasive alteration removed any potential evidence for preaccretionary alteration but did not change the overall texture of the tagish lake meteorite

ground truthing the boron isotope paleo ph proxy in planktonic foraminifera shells partial dissolution and shell size effects 1 sediment samples from the ontong java plateau in the pacific and the 90 east ridge in the indian ocean were used to investigate whether shell size and early diagenesis affect 11b of the symbiont bearing planktonic foraminifer globigerinoides sacculifer in pristine shells from both study locations we found a systematic increase of 11b and mg ca with shell size shells in the sieve size class 515 865 m revealed 11b values 2 1 to 2 3 higher than shells in the 250 380 m class this pattern is most likely due to differences in symbiont photosynthetic activity and its integrated effect on the ph of the foraminiferal microenvironment we therefore suggest smaller individuals must live at approximately 50 100 m water depth where ambient light levels are lower using the empirical calibration curve for 11b in g sacculifer only shells larger than 425 m reflect surface seawater ph partial dissolution of shells derived from deeper sediment cores was determined by shell weight analyses and investigation of the shell surface microstructure by scanning electron microscopy the 11b in partially dissolved shells is up to 2 lower relative to pristine shells of the same size class in agreement with a relatively higher weight loss in smaller shells samples from the ontong java plateau show a more pronounced dissolution effect than larger shells on the basis of the primary size effect and potential postdepositional dissolution effects we recommend the use of shells that are visually pristine and in the case of g sacculifer larger than 500 m for paleoreconstructions