desert pavements and associated rock varnish in the mojave desert how old can they be desert pavements are common features of arid landscapes and have been widely used as a relative age indicator of the geomorphic surfaces upon which they are developed in this study i examined the patterns of pavement development as a function of elevation in the mojave desert as well as the causes for the gradual disappearance of pavement at high elevations pavement density as measured by percentage of pebble coverage decreases systematically with elevation gain by 3 per 100 m from 95 coverage below 500 m to less than 60 at 1700 m plants appear to be the main agent of pavement disruption plant density decreases as pavement density increases burrowing by rodents and crusting by cryptobiota also disrupt pavement development at higher elevation during the last glacial maximum plant communities were displaced 1000 1400 m downward in the mojave desert pavements today generally do not survive above the blackbush coleogyne ramossisma sagebrush artemisia tridentata zone evidence from packrat middens shows that these and other plants typical of high elevations today grew as low as 300 400 m during the last glacial maximum i suggest that during the last glacial maximum desert pavements were confined to the lowest alluvial fans of death valley and adjoining low valleys no alluvial desert pavements above 400 m in the region are older than the latest pleistocene by the same reasoning desert varnish on desert pavements above 400 m may all be holocene in age except where developed on stable boulders

origin of calcium in pedogenic carbonate nodules from silicate watersheds in the far north region of cameroon respective contribution of in situ weathering source and dust input significant amounts of pedogenic ca carbonate nodules have been observed in the far north region of cameroon in the carbonate free watershed of the mayo tsanaga thus a priori not favourable for carbonate nodules accumulations these nodules are associated with a clay rich parent material crpm covering either a granitic upstream or a greenstone bedrock downstream in this peculiar context the amount of pedogenic carbonate nodules represents large quantities of ca and c therefore determining the ca sources for pedogenic carbonate nodules is a key point regarding the mechanisms leading to carbonate nodule precipitation and their role in the biogeochemical cycle of ca three sites two on granite and one on greenstone were studied by combining sr et nd isotope systematics in order to assess the ca sources of carbonate nodules and the origin of the crpm associated with nodules carbonate nodules have a distinct sr isotopic composition in each profile pointing to the contribution of a local source for ca sr isotopic compositions of plagioclases and carbonate nodules display a concomitant variation in each profile indicating that plagioclases acted as a sr and thus ca source for the carbonate nodules nevertheless carbonate nodules have a higher sr isotopic signature than plagioclases implying the contribution of another more radiogenic sr source sr and nd isotope data from the crpm show that it is a mixture of weathered bedrock compounds and saharan dust this result highlights two other potential sr and ca sources biotite and saharan dust calculations of their respective contributions demonstrate that in situ weathering significantly adds to the ca source of nodules this result contrasts with many other studies from similar settings that highlight the importance of allochthonous marine aeolian inputs this conclusion points out that a substantial part of ca is transferred from the local bedrock to the carbonate nodules this mechanism seems to have been possible as peculiar edaphic conditions preserved the primary ca sources making in situ weathering a significant process for providing ca

carbon and oxygen isotope study of the active water carbonate system in a karstic mediterranean cave implications for paleoclimate research in semiarid regions abstract in a semiarid climatic zone such as the eastern mediterranean region annual rainfall variations and fractionation processes in the epikarst zone exert a profound influence on the isotopic compositions of waters seeping into a cave consequently the isotopic compositions of speleothems depositing from cave waters may show complex variations that need to be understood if they are to be exploited for paleoclimate studies this is confirmed by a four year study of the active carbonate water system in the soreq cave israel the 18o smow values of cave waters range from 6 3 to 3 5 the highest 18o values occur at the end of the dry season in waters dripping from stalactites and reflect evaporation processes in the epikarst zone whereas the lowest values occur in rapidly dripping fast drip waters at the peak of the rainy seasons however even fast drip waters are about 1 5 heavier than the rainfall above the cave which is taken to reflect the mixing of fresh with residual evaporated water in the epikarst zone 13c pdb values of dissolved inorganic carbon dic vary from 15 6 to 5 4 with fast drip waters having lower 13c values mostly 15 6 to 12 and higher dic concentrations relative to pool and stalactite drip water the low 13c values of fast drip waters and their supersaturation with respect to calcium carbonate indicates that the seepage waters have dissolved both soil co2 derived from overlying c3 type vegetation and marine dolomite host rock the 18o pdb values of various types of present day low magnesium calcite lmc speleothems range from 6 5 to 4 3 and 13c values from 13 to 5 5 and are not correlated with speleothem type an analysis of 18o values of present day calcite rafts and pool waters shows that they form in oxygen isotope equilibrium similarly the measured ranges of 13c and 18o values for all types of present day speleothems are consistent with equilibrium deposition at cave temperatures the 13c 18o range of contemporary lmc thus reflects the variations in temperatures and isotopic compositions of the presentday cave waters the 10 variation in the 13c values in waters can be modeled by a simple rayleigh calculation of the carbon isotope fractionation accompanying co2 degassing and carbonate precipitation these variations may obscure the differences in the carbon isotopic composition of speleothems that could arise when vegetation cover changes from c3 to c4 type plants this consideration emphasizes that it is necessary to characterize the full range of 13c values associated with contemporaneous speleothems in order to clarify the effects of degassing from those due to differing vegetation types isotopic studies of a number of different types of fossil lmc speleothems show many of them to exhibit isotopic trends that are similar to those of present day lmc but others show both higher and lower 18o ranges in particular the higher 18o range has been shown by independent age measurements to be associated with a period of drier conditions the results of the study thus indicate that it is necessary to work on a well calibrated cave system in semiarid climates and that the fossil speleothem record should be obtained from different types of contemporaneous deposit in order to fully characterize the 18o 13c range representative of any given climatic period

how fast does rock varnish grow rates of rock varnish accumulation have never been systematically documented owing to the difficulty in accurately determining both varnish thickness and age in this study we quantitatively assess varnish accumulation rates through thin sectioning and microscopic examination of rock varnish from radiometrically dated geomorphic features of late quaternary age in the western united states drylands our data indicate that rock varnish grows at rates ranging from 1 to 40 m k y on subaerially exposed rock surfaces and rarely reaches a thickness exceeding 200 m regardless of age our data also indicate that varnish accumulation rates vary greatly from sample to sample at a given site suggesting that varnish thickness does not correlate with the age of the associated geomorphic feature invalidating the potential use of varnish thickness as a relative age indicator in geomorphology and archaeology nevertheless being the slowest known accumulating terrestrial sedimentary deposit rock varnish constitutes a unique long term microscale sedimentary archive of past environmental changes in deserts

sulfate oxygen 17 anomaly in an oligocene ash bed in mid north america was it the dry fogs 1 the oxygen and sulfur isotope compositions of sulfate particularly the oxygen 17 anomaly provide clues to the origin of sulfate we report a variable oxygen 17 anomaly for water and acid leached sulfate from an oligocene volcanic ash bed in the northern high plains u s a we find no sulfate o 17 anomaly however in freshly collected ashes from recent eruptions around the world the oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the high plains thus a long term background atmospheric sulfate accumulation is less likely the origin combining sulfur isotope data we suggest that the anomalous sulfate was associated with volcanic eruptions in the west but was not directly carried by ash falls extreme dry fog sulfate haze events resulting from tropospheric oxidation of volcanic sulfur gases might provide a viable explanation for the sulfates in the ash bed that carry the oxygen 17 anomaly

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

abee and related eh chondrite impact melt breccias abstract the abee eh chondrite is an impact melt breccia about 80 90 of the chondrules were melted many of those that remain have been partly resorbed euhedral enstatite phenocrysts are abundant many have nucleated on the surfaces of relict chondrules and now protrude into kamacite globules euhedral laths of graphite essentially identical to those produced magmatically on earth occur throughout the rock abee experienced two episodes of impact melting with an intervening period of brecciation the first impact melting event produced a relatively homogeneous rock with abundant melt upon cooling the rock was shattered by bombarding meteoroids igneous oldhamite rich dark inclusions were introduced at this time a second impact event produced melt which engulfed the abee fragments and dark inclusions primarily digesting the small ones heat lost to the surrounding clastic debris caused the groundmass melt to quench previously described diamonds in abee containing typical solar system isotopic compositions of n and xe were probably produced from graphite by shock several other eh chondrites may also be impact melt breccias the most extensively melted of these is adhi kot which contains shocked but largely unmelted chondrule rich clasts as well as chondrule free sulfide and silica rich clasts that also appear to be impact products

presolar diamond sic and graphite in primitive chondrites abundances as a function of meteorite class and petrologic type abstract acid resistant residues were prepared for eighteen meteorites from seven chondrite classes using improved procedures designed to minimize loss of presolar grains noble gases were measured by stepped pyrolysis and the abundances of five exotic noble gas components were used to determine abundances of diamond sic and graphite diamond separates were prepared to check diamond abundances determined from noble gases diamond and sic were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in orgued ci and ll3 0 3 1 chondrites our data and noble gas and stable isotope data in the literature show that presolar grains were incorporated into all chondrite classes the grains are sited in the fine grained matrix and their abundances within the matrix reflect mainly the degree of metamorphism suffered by the host meteorite the pattern of metamorphic destruction differs from class to class in unequilibrated ordinary chondrites uocs graphite is most easily destroyed followed by sic and then diamond no presolar grains remain in uocs of petrologic type 3 8 whose matrices have been completely recrystallized in eh chondrites diamond and sic survive much more severe metamorphism than in uocs with sic apparently more stable than diamond presolar graphite was not detected in cv3 and c03 chondrites diamond appears to be more stable than sic and graphite again is missing inferred premetamorphic diamond abundances matrix normalized vary by a factor of 2 2 between classes with eh cv and co chondrites having higher initial abundances than orgueil similar diamond sic ratios are observed in most classes and differences in the ratio can be tied to secondary processing suggesting that all chondrite classes sampled the same solar system wide reservoir of presolar grains differences in initial abundances between classes appear to correlate with chemical and physical properties of the host meteorites these bulk properties and variations in presolar grain abundances both may be the result of thermal processing of presolar dust in the accretion disk

strontium in rainwater from israel sources isotopes and chemistry abstract eighteen rain samples from israel have been analyzed for their chemical composition and87sr 86sr ratios the sr isotopic ratios lie in the range 0 7078 and 0 7092 and the sr concentrations vary from 1 10 4 to 9 10 4 meq sr l soluble salts in rainwater are inherited from three major natural sources seaspray recent marine minerals and mineral dust eroded from rock outcrops and soil a mixing model is formulated to apply the chemical composition of rain cl and sr2 and its isotopic87sr 86sr ratio for the identification and estimation of the sr sources all the samples fall within the mixing space predicted by the model for the three end members mentioned above the data indicate that the most important non seaspray source contributing dissolved salts to the rains in israel comprises a mixture of senonian to eocene chalk and its weathering products and recent marine minerals from local and imported sources most of the samples 67 contain 50 or more non seaspray sr i e sr dissolved from dust or recent marine minerals whereas 56 of the samples display87sr 86sr ratios lower than 0 7090 the rest represent mixtures of seaspray and recent marine minerals

source and genesis of sulphate and phosphate sulphate minerals in a quartz sandstone cave environment gypsum caso4 2h2o alunite kal3 so4 2 oh 6 and rare phosphate sulphate sanjuanite al2 po4 so4 oh 9 h2o and rossiantonite al3 po4 so4 2 oh 2 h2o 14 have recently been identified as secondary mineral deposits in different quartz sandstone caves in the gran sabana region venezuela due to the extended time scale required for speleogenesis in the hard and barely soluble quartz sandstone lithology these caves are considered to be as old as 20 to 30 my the study of these peculiar secondary mineral deposits potentially reveals important insights for understanding the interaction between deep superficial and atmospheric processes over thousands to perhaps millions of years in this study chemical and petrographic analyses of potential host rock sources sulphur and oxygen isotope ratios and meteorological hydrological and geographical data are used to investigate the origin of sulphates and phospho sulphates the results suggest that the deposition of sulphates in these caves is not linked to the quartz sandstone host rock rather these mineral deposits originate from an external atmospheric sulphate source with potential contributions of marine non sea salt sulphates terrestrial dimethyl sulphide and microbially reduced h2s from the forests or peatbogs within the watershed air currents within the caves are the most plausible means of transport for aerosols driving the accumulation of sulphates and other secondary minerals in specific locations moreover the studied sulphate minerals often co occur with silica speleothems of biological origin although this association would suggest a possible biogenic origin for the sulphates as well direct evidence proving that microbes are involved in their formation is absent nonetheless this study demonstrates that these quartz sandstone caves accumulate and preserve allogenic sulphates playing a yet unrecognized role in the sulphur cycle of tropical environments

structure composition and location of organic matter in the enstatite chondrite sahara 97096 eh3 the insoluble organic matter iom of an unequilibrated enstatite chondrite sahara sah 97096 has been investigated using a battery of analytical techniques as the enstatitechondrites are thought to have formed in a reduced environment at higher temperatures thancarbonaceous chondrites they constitute an interesting comparative material to test theheterogeneities of the iom in the solar system and to constrain the processes that could affectiom during solar system evolution the sah 97096 iom is found in situ as submicrometergrains in the network of fine grained matrix occurring mostly around chondrules and asinclusions in metallic nodules where the carbonaceous matter appears to be moregraphitized iom in these two settings has very similar d15n and d13c this supports the ideathat graphitized inclusions in metal could be formed by metal catalytic graphitization ofmatrix iom a detailed comparison between the iom extracted from a fresh part and aterrestrially weathered part of sah 97096 shows the similarity between both iom samples inspite of the high degree of mineral alteration in the latter the isolated iom exhibits aheterogeneous polyaromatic macromolecular structure sometimes highly graphitized withoutany detectable free radicals and deuterium heterogeneity and having mean h and n isotopiccompositions in the range of values observed for carbonaceous chondrites it contains somesubmicrometer sized areas highly enriched in 15n d15n up to 1600 these observationsreinforce the idea that the iom found in carbonaceous chondrites is a common componentwidespread in the solar system most of the features of sah 97096 iom could be explainedby the thermal modification of this main component

progressive aqueous alteration of cm carbonaceous chondrites abstract cm chondrites are aqueously altered rocks that contain 9 wt h 2 o i e indigenous water bound in phyllosilicates also present are clumps of serpentine tochilinite intergrowths previously called poorly characterized phases or pcp pentlandite and ni bearing pyrrhotite we studied 11 cm chondrites that span the known range from least altered to most altered we used various petrologic properties many previously identified that provide information regarding the degree of aqueous alteration there are no known unaltered or slightly altered cm chondrites e g rocks containing numerous chondrules with primary igneous glass some cm properties result from processes associated with early and intermediate stages of the alteration sequence i e hydration of matrix alteration of chondrule glass and production of large pcp clumps other petrologic properties reflect processes active throughout the alteration sequence these include oxidation of metallic fe ni alteration of chondrule phenocrysts changes in pcp composition reflecting an increase in the phyllosilicate sulfide ratio and changes in carbonate mineralogy reflecting the development of dolomite and complex carbonates at the expense of ca carbonate on the basis of these parameters we propose a numerical alteration sequence for cm chondrites because there are no known cm samples that display only incipient alteration the least altered sample was arbitrarily assigned to subtype 2 6 the most altered cm chondrites currently classified cm1 are assigned to subtype 2 0 these highly altered rocks have essentially no mafic silicates they contain chondrule pseudomorphs composed mainly of phyllosilicate however their bulk compositions are cm like and they are closer in texture to other c2 chondrites than to ci1 chondrites which lack chondrule pseudomorphs using several diagnostic criteria we assigned petrologic subtypes 0 1 to every cm chondrite in our study que 97990 cm2 6 murchison cm2 5 kivesvaara cm2 5 murray cm2 4 2 5 y 791198 cm2 4 que 99355 cm2 3 nogoya cm2 2 cold bokkeveld cm2 2 que 93005 cm2 1 lap 02277 cm2 0 met 01070 cm2 0 the proposed cm numerical alteration sequence improves upon the existing scheme of browning et al 1996 in that it does not require a complicated algorithm applied to electron microprobe data to determine the average matrix phyllosilicate composition the new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values new neutron activation analyses of que 97990 que 93005 met 01070 murchison and crescent together with literature data confirm the compositional uniformity of the cm group different degrees of alteration among cm chondrites do not lead to resolvable bulk compositional differences this suggests that the textural differences among individual cm chondrites reflect progressive alteration of similar hypothetical cm3 0 starting materials in different regions of the same parent body with minimal aqueous transport of materials over appreciable e g meters distances

multiple generations of carbonaceous material deposited in apex chert by basin scale pervasive hydrothermal fluid flow abstract the pilbara craton in western australia contains the best preserved and most complete record of archean rocks in the world as such they are some of the most studied rocks in the world paleontologists isotopic geochemists geologists and geobiologists have all investigated these rocks for clues about the early biosphere and atmosphere here we show using high resolution transmission electron microscopy that the carbonaceous material found in the apex chert and potentially in other associated units was formed by multiple processes such as abiotic catalytic synthesis and or biological synthesis we use these data as well as the geological history of the craton to demonstrate that when the rocks of the pilbara craton experienced a high degree of post depositional hydrothermal alteration carbonaceous material could have been remobilized and redeposited as the carbonaceous material within the apex chert samples was formed over nearly a billion years bulk chemistry even at the micron level will be unable to unambiguously delineate the presence of life in these ancient rocks although nanoscale observations may provide a way forward in the search for ancient life

organic geochemistry of precambrian shales and schists bohemian massif central europe abstract the composition and the structure of kerogens and subgraphitic materials from upper proteroic regionally metamorphosed black shales were investigated by different physico chemical method the isotopic composition of carbon changes with the intensity of the regional metamorphism kerogens from low grade metasediments have averaged 13 c values 35 kerogens from chlorite and biotite zones 31 samples display high diversity of primary sedimentary materialos details were obtained using transmission electron microscopy tem crystalline order improves with the intensity of the regional metamorophism turbostratic carbonacveous matter is described from low grade metasediments graphite occurs at the end of the biotite zone however both metallogenetic and contact metamorphic processes can be involved in some samples the second form of graphite has been identified probably of detrital origin inherited from some high grade metamorphic area existing at the time of sedimentation of primary rocks

micron scale d h heterogeneity in chondrite matrices a signature of the pristine solar system water abstract organic matter and hydrous silicates are intimately mixed in the matrix of chondrites and in situ determination of their individual d h ratios is therefore challenging nevertheless the d h ratio of each pure component in this mixture should yield a comprehensible signature of the origin and evolution of water and organic matter in our solar system we measured hydrogen isotope ratios of organic and hydrous silicates in the matrices of two carbonaceous chondrites orgueil ci1 and renazzo cr2 and one unequilibrated ordinary chondrite semarkona ll3 0 a novel protocol was adopted involving nanosims imaging of h isotopes of monoatomatic h and molecular oh secondary ions collected at the same location this allowed the most enriched component with respect to d to be identified in the mixture using this protocol we found that in carbonaceous chondrites the isotopically homogeneous hydrous silicates are mixed with d rich organic matter the opposite was observed in semarkona hydrous silicates in semarkona display highly heterogeneous d h ratios ranging from 150 to 1800 10 6 d smow 40 to 10 600 organic matter in semarkona does not show such large isotopic variations this suggests limited isotopic exchange between the two phases during aqueous alteration our study greatly expands the range of water isotopic values measured so far in solar system objects this d rich water reservoir was sampled by the ll ordinary chondrite parent body and an estimate 9 of its relative contribution to the d h ratio of water in oort cloud family comets is proposed

evidence for biogenic graphite in early archaean isua metasedimentary rocks the archaean rocks of isua west greenland contain graphite but its origins are debated geochemical and microscopic analyses suggest that the graphite was formed from biologically formed carbon that was deposited at least 3 7 billion years ago

oxygen 17 excesses of the central namib gypcretes spatial distribution abstract we present here sulfate oxygen isotopic data 72 samples with both 18o and 17o systematically collected from the central namib desert surface soils from two shore inland west east transects exhibit a gradual increase in the sulfate oxygen 17 excess 17o 17o 0 52 18o until at ca 70 km inland where no continuous gypcrete deposit is observed further east inland the oxygen isotopic compositions for water soluble sulfates extracted from soils and gypcretes range from 8 3 to 13 3 and 0 06 to 1 11 for 18o and 17o respectively the lateral pattern is similar to what has been seen in the cold deserts of the antarctic dry valleys however unlike the dry valleys no discernible correlation is found between 18o and 17o or between the depth of soil horizon and 17o in the namib possible explanations include a relatively smaller component of dimethylsulfide dms derived sulfate in the total gypsum deposits and or more active surface processes e g flooding and leaching in the central namib desert than in the antarctic cold deserts although current state of knowledge is insufficient to delineate quantitatively the sulfate contributions from different sources and reactions the measurement of sulfate 17o does identify an unmistakable atmospheric sulfate component and provides additional independent information regarding sources and reactions

volcanic sulfate aerosol formation in the troposphere the isotopic composition of volcanic sulfate provides insights into the atmospheric chemical processing of volcanic plumes first mass independent isotopic anomalies quantified by 17o and to a lesser extent 33s and 36s in sulfate depend on the relative importance of different oxidation mechanisms that generate sulfate aerosols second the isotopic composition of sulfate 34s and 18o could be an indicator of fractionation distillation condensation processes occurring in volcanic plumes here we present analyses of o and s isotopic compositions of volcanic sulfate absorbed on very fresh volcanic ash from nine moderate historical eruptions in the northern hemisphere most of our volcanic sulfate samples which are thought to have been generated in the troposphere or in the tropopause region do not exhibit any significant mass independent fractionation mif isotopic anomalies apart from those from an eruption of a mexican volcano coupled to simple chemistry model calculations representative of the background atmosphere our data set suggests that although h2o2 a mif carrying oxidant is thought to be by far the most efficient sulfur oxidant in the background atmosphere it is probably quickly consumed in large dense tropospheric volcanic plumes we estimate that in the troposphere at least more than 90 of volcanic secondary sulfate is not generated by mif processes volcanic s bearing gases mostly so2 appear to be oxidized through channels that do not generate significant isotopically mass independent sulfate possibly via oh in the gas phase and or transition metal ion catalysis in the aqueous phase it is also likely that some of the sulfates sampled were not entirely produced by atmospheric oxidation processes but came out directly from volcanoes without any mif anomalies

the origin of chondritic macromolecular organic matter a carbon and nitrogen isotope study the n and c abundances and isotopic compositions of acid insoluble carbonaceous material in thirteen primitive chondrites five unequilibrated ordinary chondrites three cm chondrites three enstatite chondrites a ci chondrite and a cr chondrite have been measured by stepped combustion while the range of c isotopic compositions observed is only delta 13c 30 the n isotopes range from delta 15n approximately 40 to 260 after correction for metamorphism presolar nanodiamonds appear to have made up a fairly constant 3 4 wt of the insoluble c in all the chondrites studied the apparently similar initial presolar nanodiamond to organic c ratios and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites suggest that the chondrites all accreted similar organic material this original material probably most closely resembles that now found in renazzo and semarkona these two meteorites have almost m shaped n isotope release profiles that can be explained most simply by the super position of two components one with a composition between delta 15n 20 and 40 and a narrow combustion interval the other having a broader release profile and a composition of delta 15n approximately 260 although isotopically more subdued the ci and the three cm chondrites all appear to show vestiges of this m shaped profile how and where the components in the acid insoluble organics formed remains poorly constrained the small variation in nanodiamond to organic c ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30 the most 15n rich material probably formed in the interstellar medium and the fraction of organic n in renazzo in this material ranges from 40 to 70 the isotopically light component may have formed in the solar system but the limited range in nanodiamond to total organic c ratios in the chondrite groups is consistent with most of the organic material being presolar

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

chondritic lithic clasts in the cb ch like meteorite isheyevo fragments of previously unsampled parent bodies the cb ch like chondrite isheyevo is characterized by the absence of fine grained interchondrule matrix material the only present fine grained material is found as chondritic lithic clasts in contrast to the pristine high temperature components of isheyevo these clasts experienced extensive aqueous alteration in an asteroidal setting hence the clasts are foreign objects that either accreted together with the high temperature components or were added later to the final isheyevo parent body during regolith gardening in order to constrain the origin and secondary alteration of the clasts in isheyevo we studied their mineralogy petrography structural order of the polyaromatic carbonaceous matter and oxygen isotopic compositions of carbonates three main groups of clasts were defined based on mineralogy and petrology group i clasts consist of phyllosilicates carbonates magnetite and lath shaped fe ni sulfides group ii clasts contain different abundances of anhydrous silicates embedded in a hydrated matrix sulfides magnetite and carbonates are rare with only a few exceptions groups i and ii clasts did not experienced significant thermal metamorphism group iii clasts are characterized by the absence of magnetite and the presence of fe ni metal in addition to aqueous alteration they experienced thermal metamorphism as reflected by the structure of their polyaromatic carbonaceous matter while there are some similarities between the isheyevo clasts ci chondrites and the matrices of cm and cr chondrites on the whole the characteristics of the clasts do not match those of any of these aqueously altered meteorite classes nor do they match those of similar material in various types of chondritic clasts present in other meteorite groups we conclude that the isheyevo clasts represent fragments of previously unsampled parent bodies

recognition and implications of eocene tufas and travertines in the chadron formation white river group badlands of south dakota there are few descriptions of pre quaternary tufa or travertine yet these deposits have important climatic hydrological and tectonic implications in the badlands of south dakota the late eocene chadron formation contains a variety of tufa fluvial lacustrine paludal and perched springline types travertine and calcrete pedogenic and non pedogenic types in fluvial channels tufas and tufa barrages oncolites tufa lithoclast conglomerates and phytoherms are transitional to travertines pseudostromatolitic boundstone gravels and small pinnacle resurgences with rimstone edges and pools lacustrine tufas formed in small ponds adjacent to other types of tufas and are similar to the low energy bench margin facies types observed in modern groundwater fed temperate zone hardwater lakes paludal tufas are laterally discontinuous sheets of pisoid intraclast wackestone that fill palaeotopography distal perched springline tufas are mounds of numerous sloping tufa sheets concretions and rhizoliths associated with palaeosols are recognized as pedogenic calcretes whereas non pedogenic calcretes are variably cemented vertically oriented conduits for palaeogroundwater discharge that are located in fault zones these deposits resulted from palaeogroundwater discharge along faults during the late eocene coeval unroofing of the black hills uplift created a regional groundwater flow system through karsted palaeozoic limestones exposed in the black hills the chadron formation is an avulsion dominated siliciclastic unit yet important bodies of carbonate accumulated in it as a result of groundwater processes

graphitization in a high pressure low temperature metamorphic gradient a raman microspectroscopy and hrtem study the graphitization of carbonaceous material cm in a high pressure metamorphic gradient is characterized along a cross section in the schistes lustres formation western alps along this 25 km cross section both the cm precursor and the host rock lithology are homogeneous and the prograde evolution of the pressure temperature metamorphic conditions from the lower blueschist facies 13 kbar 330 c to the eclogite facies 20 kbar 500 c is tightly constrained by literature data raman microspectroscopy shows that at the micrometre scale this process is progressive and continuous with increasing metamorphic grade and that the structure of cm is very sensitive to temperature variations at the nanometre scale hrtem the cm is composed of a mixture of a microporous phase and an onion ring like phase both known as non graphitizing under the effect of temperature at ambient pressure the hp lt graphitization produces structurally and microtexturally heterogeneous cm with increasing metamorphic grade the graphitization of the two types of cm proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of cm the microporous material is progressively transformed into graphite through a macroporous transitional stage in this case graphitization mainly occurs on the pore walls as a result of pore growth in the case of concentric onion ring like material graphitization occurs in the regions with the largest radius of curvature i e on the outer part of the ring in comparison with 1 bar experiments pressure seems to induce microtextural changes which allows the subsequent structural modifications of the starting material

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

anomalous 17o compositions in massive sulphate deposits on the earth the variation of 18o that results from nearly all physical biological and chemical processes on the earth is approximately twice as large as the variation of 17o this so called mass dependent fractionation is well documented in terrestrial minerals1 2 evidence for mass independent fractionation 17o 17o 0 52 18o where deviation from this tight relationship occurs has so far been found only in meteoritic material and a few terrestrial atmospheric substances3 in the rock record it is thought that oxygen isotopes have followed a mass dependent relationship for at least the past 3 7 billion years ref 4 and no exception to this has been encountered for terrestrial solids5 here however we report oxygen isotope values of two massive sulphate mineral deposits which formed in surface environments on the earth but show large isotopic anomalies 17o up to 4 6 these massive sulphate deposits are gypcretes from the central namib desert and the sulphate bearing miocene volcanic ash beds in north america the source of this isotope anomaly might be related to sulphur oxidation reactions in the atmosphere and therefore enable tracing of such oxidation these findings also support the possibility of a chemical origin of variable isotope anomalies on other planets such as mars6

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

fall recovery and characterization of the novato l6 chondrite breccia the novato l6 chondrite fragmental breccia fell in california on 17 october 2012 and was recovered after the cameras for allsky meteor surveillance cams project determined the meteor s trajectory between 95 and 46 km altitude the final fragmentation from 42 to 22 km altitude was exceptionally well documented by digital photographs the first sample was recovered before rain hit the area first results from a consortium study of the meteorite s characterization cosmogenic and radiogenic nuclides origin and conditions of the fall are presented some meteorites did not retain fusion crust and show evidence of spallation before entry the meteoroid was 35 5 cm in diameter mass 80 35 kg with a cosmic ray exposure age of 9 1 ma if it had a one stage exposure history a two stage exposure history is more likely with lower shielding in the last few ma thermoluminescence data suggest a collision event within the last similar to 0 1 ma novato probably belonged to the class of shocked l chondrites that have a common shock age of 470 ma based on the u th he age of 420 220 ma the measured orbits of novato jesenice and innisfree are consistent with a proposed origin of these shocked l chondrites in the gefion asteroid family perhaps directly via the 5 2 mean motion resonance with jupiter novato experienced a stronger compaction than did other l6 chondrites of shock stage s4 despite this a freshly broken surface shows a wide range of organic compounds less

the origin and evolution of chondrites recorded in the elemental and isotopic compositions of their macromolecular organic matter extraterrestrial organic matter in meteorites potentially retains a unique record of synthesis and chemical thermal modification by parent body nebular and even presolar processes in a survey of the elemental and isotopic compositions of insoluble organic matter iom from 75 carbonaceous ordinary and enstatite chondrites we find dramatic variations within and between chondrite classes there is no evidence that these variations correlate with the time and or location of chondrite formation or with any primary petrologic or bulk compositional features that are associated with nebular processes e g chondrule and volatile trace element abundances nor is there evidence for the formation of the iom by fischer tropsch type synthesis in the nebula or in the parent bodies the elemental variations are consistent with thermal maturation and or oxidation of a common precursor for reasons that are unclear there are large variations in isotopic composition within and between chondrite classes that do not correlate in a simple way with elemental composition or petrologic type nevertheless because of the pattern of elemental variations with petrologic type and the lack of any correlation with the primary features of the chondrite classes at present the most likely explanation is that all iom compositional variations are the result of parent body processing of a common precursor if correct the range of isotopic compositions within and between chondrite classes implies that the iom is composed of several isotopically distinct components whose relative stability varied with parent body conditions the most primitive iom is found in the cr chondrites and bells cm2 isotopically the iom from these meteorites resembles the iom in interplanetary dust particles chemically their iom resembles the chon particles of comet halley despite the large isotopic anomalies in the iom from these meteorites it is uncertain whether the iom formed in the interstellar medium or the outer solar system although the former is preferred here

lake elji and a geological perspective on the evolution of petra jordan abstract the draining of the herein introduced ancient lake elji and the subsequent erosion of its lacustrine sediments were necessary precursors to the late epipalaeolithic natufian and later settlement of petra this study investigates this geological history and relates it to human occupation of the broader region widespread carbonates consisting of algal mat deposits beach rocks and rhizoliths are consistently present at the 1060 m contour line of what is believed to be the shoreline of lake elji in the petra basin well sorted siliciclastic fluvio lacustrine sediments at lower elevations and human settlement patterns all indicate that a standing body of water once existed in the area stable isotopes of carbon and oxygen as well as the fossil assemblages and the textures of the carbonate deposits suggest that the body of water was an open lake with regular outflows a sill has been identified at ras btahi indicating a southward outflow direction as opposed to the current drainage pattern towards the west the lack of a basin closure towards the west at the time as evidenced by thick low energy sediment accumulations suggest that tectonic movements were responsible for breaching the lake and establishing the current hydrological pattern results obtained from the optical stimulated luminiscence osl in the palaeolake sediments indicate that the basin was closed from at least 100 ka up to approximately 9 ky this timeline is also supported by the distribution of archaeological sites in the area and a previously documented massive erosional event at the end of this period subsequent gradual denudation of the basin sediments allowed for the settlement in the center of petra during the early nabatean period

precursor and metamorphic condition effects on raman spectra of poorly ordered carbonaceous matter in chondrites and coals abstract geothermometers based on raman spectrometry of carbonaceous matter and covering a wide range of temperatures 100 650 c have been developed over recent years while raman data have been largely interpreted in terms of temperature they are also the fingerprint of certain metamorphic conditions especially in the low temperature range relevant to poorly ordered carbonaceous matter this study investigates the raman spectra of two series of chondritic carbonaceous matter and coal samples formed from different precursors and under different metamorphic conditions the raman spectra of polyaromatic carbonaceous matter pcm from 42 chondrites and 27 coal samples measured with visible 514 nm and ultra violet 244 nm excitation wavelengths are analyzed the raman spectra of low rank coals and chondrites of petrologic types 1 and 2 which contain the more disordered pcm reflect the distinct carbon structures of their precursors the 514 nm raman spectra of high rank coals and chondrites of petrologic type 3 exhibit continuous and systematic spectral differences reflecting different carbon structures present during the metamorphism event they result from differences in the chemical structures of the precursors concerning for instance the reticulation of polyaromatic units or an abundance of ether functional groups or possibly from a lack of carbonization processes to efficiently expel oxygen heteroatoms due to weak lithostatic pressure and confinement these results suggest that the use of low temperature carbon thermometers should be restricted to a given geological context at the same time the sensitivity of raman spectra to precursors and certain metamorphic conditions could be used to obtain information other than temperature the analysis also provides evidence of the accretion of relatively homogeneous pcm precursors among ordinary co and cv carbonaceous chondrite parent bodies given that the 514 nm raman spectra of pcm efficiently trace the metamorphism grades looking closer however the 514 nm raman data are more scattered in chondrites than in coals and the maturity tracers are less sensitive and miscorrelate with the atomic h c ratio suggesting slight compositional and structural differences among the pcm precursors accreted

nanosized carbon rich grains in carbonaceous chondrite meteorites abstract macromolecular carbonaceous material is common in primitive meteorites little information exists on its form and composition and there are no published data on nanometer scale chemical and structural variations transmission electron microscopy tem studies of cm meteorites reveal abundant previously unrecognized nanosized carbonaceous grains they have a high aromatic component as revealed by electron energy loss spectroscopy eels with up to 20 at substituted by s n and o they occur as discrete hollow and solid nanospheres and sparse nanotubes the grains exhibit considerable variations in composition size morphology and abundance among meteorites and may represent materials from multiple reservoirs

taming the torrents the hydrological impacts of ancient terracing practices in jordan extensive terracing was an important component of the water and agricultural management regime of nabatean petra the exact function s of these terraces qualitatively and quantitatively is herein investigated field studies and computer modeling for two sites within the drainage basin of petra show that these terraces were highly effective at reducing surface runoff different design features seem to have been adapted in order to achieve different objectives at varying sites for example the beidha site in the lower reaches of the catchment area falls within the higher relief ordovician disi sandstone formation area here the terrace system was designed to slow water flow and trap sediments the terracing greatly reduced surface water flow through the entrapment of sandy loam sediments behind it on the other hand the baqa a site falls in the upper reaches of the drainage basin within the upper cretaceous amman silicified limestone formation the effect of the terrace system here on runoff is significant but less than that seen at beidha this system was more suited for soil conservation and agriculture as the soil here in its natural state already had a high infiltration rate neglect and abandonment of these terraces at both sites have led to increased runoff as evidenced by the development of gullies and by periodic flooding downstream in the core of the ancient city based on the six modeled cases terraces can minimize the surface flow by an average of 28 with values as high as 90 when 2010 precipitation data were used conducting an intensive survey within the catchment area surrounding the ancient city of petra mapping the ancient terraces and reviving their function may produce significant results in flood mitigation and control there

the oxygen isotopic composition of water from tagish lake its relationship to low temperature phases and to other carbonaceous chondrites the fall and recovery of the tagish lake meteorite in british columbia in january 2000 provided a unique opportunity to study relatively pristine samples of carbonaceous chondrite material measurements of the oxygen isotopic composition of water extracted under stepped pyrolysis from a bulk sample of this meteorite have allowed us to make comparisons with similar data obtained from ci and cm chondrites and so further investigate any relationships that may exist between these meteorites the much lower yield of water bearing a terrestrial signature in tagish lake is indicative of the pristine nature of the meteorite the relationship between the isotopic composition of this water and reported isotopic values for carbonates bulk matrix and whole rock have been used to infer the extent and conditions under which parent body aqueous alteration occurred in tagish lake the difference in 17o isotopic composition between the water and other phases is greater than that found in either cms or cis suggesting that reaction and isotopic exchange between components was more limited this in turn suggests that in the case of tagish lake conditions during the processes of aqueous alteration on the parent body which ultimately controlled the formation of new minerals were distinct from those on both ci and cm parent bodies

high resolution tem of chondritic carbonaceous matter metamorphic evolution and heterogeneity the insoluble carbonaceous matter from 12 chondrites ci cm co cv eh and uoc was characterized by high resolution transmission electron microscopy hrtem besides ubiquitous nanoglobules the insoluble organic matter from petrologic type 1 and 2 chondrites and semarkona ll 3 0 is composed of a highly disordered polyaromatic component no structural differences were observed between these ioms in agreement with the limited thermal metamorphism they all experienced in chondrites of petrologic type 3 0 the evolution of the iom is controlled by the extent of thermal metamorphism the polyaromatic layers shorter than 1 nm in petrologic type 3 0 chondrites grow up to sizes between 5 and 10 nm in petrologic type 3 6 chondrites contributing to the increase of the degree of structural order in addition we find rare but ubiquitous onion like carbons which may be the product of nanodiamond graphitization the insoluble carbonaceous matter of the enstatite chondrite sahara 97096 eh 3 is different from the other meteorites studied here it is more heterogeneous and displays a high abundance of graphitized particles this may be the result of a mixture between 1 the disordered carbon located in the matrix and 2 catalytic graphitized phases associated with metal potentially originating from partial melting events the structural and nanostructural evolution are similar in all ioms this suggests that the structure of the accreted precursors and the parent body conditions of their secondary thermal modifications temperature duration and pressure were similar the limited degree of organization of the most metamorphosed ioms compared with terrestrial rocks submitted to similar temperature suggests that the conditions are not favorable to graphitization processes due to the chemical nature of the precursor or the lack of confinement pressure

isotope geochemistry of caliche developed on basalt enormous variations in oxygen and carbon isotopes occur in caliche developed on 3 ma basalts in 3 volcanic fields in arizona significantly extending the range of 18o and 13c observed in terrestrial caliche within each volcanic field 18o is broadly co variant with 13c and increases as 13c increases the most 18o and 13c enriched samples are for subaerial calcite developed on pinnacles knobs and flow lobes that protrude above tephra and soil the most 18o and 13c depleted samples are for pedogenic carbonate developed in soil atmospheres the pedogenic caliche has 18o fixed by normal precipitation in local meteoric waters at ambient temperatures and has low 13c characteristic of microbial soil co2 subaerial caliche has formed from 18o rich evapoconcentrated meteoric waters that dried out on surfaces after local rains the associated 13c enrichment is due either to removal of 12c by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over layered during burial by calcite carrying the isotopic signature of the soil environment the large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if mars had a warm wet early period and photosynthesizing microbes were present in the early soils the approach can be similarly applied to terrestrial precambrian paleocaliche in the search for the earliest record of life on land large variations reported for 18o of carbonate in martian meteorite alh84001 do not necessarily require high temperatures playa lakes or flood runoff if the carbonate is an example of altered martian caliche

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

stable isotope records of late quaternary climate and hydrology from mediterranean lakes the isomed synthesis lake isotope records can be used to assess the spatial coherency of late quaternary climate change across the circum mediterranean region we place modern and palaeo data within a simple conceptual lake response model to show that the isotope hydrology of most mediterranean lakes has been influenced strongly by water balance even in those systems that are chemically dilute i e freshwater 18o data on biogenic and endogenic carbonates from 24 lake basins are used to reconstruct multi millennial scale trends since the lgm while it is difficult to make direct comparisons between lake records in terms of single climatic parameters coherent regional isotopic trends can be identified during glacial times mediterranean lakes deposited carbonates isotopically heavier in 18o compared to the holocene partly due to source area effects isotopic enrichment was most marked during intervals corresponding to the h1 and younger dryas events confirming that late pleistocene cold stages in the north atlantic region were marked by aridity around much of the mediterranean almost all mediterranean lake records shifted to more depleted isotopic values during the last glacial interglacial transition lgit this shift is the reverse of the trend which characterised the same transition in lakes from northern and central europe and suggests that temperature changes were not an important direct driver of mediterranean lake isotopic records over glacial interglacial timescales in the early holocene many lakes in the eastern part of the region were more depleted isotopically than in recent millennia this corresponds with marine sapropel formation both chronologically and geographically and implies that increases in local rainfall contributed significantly to the creation of a freshwater lid and anoxia in the east mediterranean sea in contrast no such pattern is currently apparent from lake isotope records from the west mediterranean suggesting a possible nw se contrast in climate history during the holocene

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

revised model calculations for the thermal histories of ordinary chondrite parent bodies recent measurements of ordinary chondrite physical and thermal properties along with new geothermometry studies have provided the necessary parameters for updating a previously proposed model miyamoto et al 1981 for the thermal evolution and internal structure of ordinary chondrite parent bodies model calculations assumed a heat source term derived from the decay of 26al justification is provided differences from the previous model include varying the thermal diffusivity parameter with increasing temperature and decreasing porosity using variable physical and thermal parameters to provide end member models and incorporating a shortened thermal history of 60 ma obtained from new pb pb chronology of phosphates rather than 100 ma times of isotopic closure in chondrite phosphates overlap the thermal model estimates and postmetamorphic cooling rates from the model approximately coincide in both trend and magnitude with metallographic and fission track cooling rate data model calculations attempt to match peak metamorphic conditions in the central portions of these bodies and yield accretion ages between 1 4 to 3 1 ma after calcium aluminum inclusion cai formation model calculations also predict that both the h and the l chondrite parent asteroids consisted of 80 equilibrated and 20 unequilibrated chondritic material and that their original radii ranged from 80 to 95 km

tectonic evolution of the gulf of aqaba dead sea transform fault system abstract neogene tectonic phases related to stresses which created the gulf of aqaba dead sea transform fault system were recorded from evidence in the central part of the wadi araba the chronological sequence of deformation stages is as follows 1 1 epeirogeny latest late eocene oligocene 2 2 faulting and warping oligocene middle miocene 3 3 folding striking between north northeast and northeast e w trending and n s shear faulting and nw se normal faulting miocene 4 4 uplift and faulting pliocene pleistocene 5 5 faulting with volcanic activity pleistocene 6 6 sinistral movement along the major shear fault in the wadi araba indications are that this phase is still active pleistocene recent the re strain phases recognised are clues for the investigated area and the entire region to the understanding of the tectonic evolution of the gulf of aqaba dead sea transform structural features contributing to evidence of strike slip movement are drag folds reverse and normal flower structures alternation of the downthrown side along the fault trace gently waved vertical fault planes horizontal slickensides transpressive and transtensional pressure ridges and rhombs linear fault traces without marked vertical throw and fault plane ridges a sinistral offset of 40 km along the n s al quweira fault was deduced from the displacement of distinctive andesitic rocks found on both sides of the fault for the e w salawan fault a dextral movement of at least 7 km was determined from the offset of formation boundaries north northeast striking deformed belts containing monoclinal to recumbent en echelon folds can be seen in the gulf of aqaba dead sea transform fault zone the axial planes of the folds dip southeast and face northwest these structural elements indicate local se nw compressional stress

multiple oxygen and sulfur isotopic analyses on water soluble sulfate in bulk atmospheric deposition from the southwestern united states 1 sulfate is a major component of bulk atmospheric deposition including dust aerosol fog and rain we analyzed sulfur and oxygen isotopic compositions of water soluble sulfate from 40 sites where year round dust traps collect bulk atmospheric deposition in the southwestern united states average sulfur and oxygen isotopic compositions 34s and 18o are 5 8 1 4 cdt and 11 2 1 9 smow n 47 respectively samples have an oxygen 17 anomaly 17o with an average value of 1 0 0 6 except for a weak positive correlation between 18o and 17o values r2 0 4 no correlation exists for 18o versus 34s 17o versus 34s or any of the three isotopic compositions versus elevation of the sample site exceptional positive 17o values up to 4 23 are found in samples from sites in the vicinity of large cities or major highways and near zero 17o values are found in samples close to dry lakes comparison of isotopic values of dust trap sulfate and desert varnish sulfate from the region reveals that varnish sulfate has average isotopic values that are 4 8 lower for 18o 2 1 higher for 34s and 0 3 lower for 17o than those of the present day bulk deposition sulfate although other factors could cause the disparity this observation suggests a possibility that varnish sulfate may have recorded a long term atmospheric sulfate deposition during the holocene or pleistocene as well as the differences between sulfur and oxygen isotopic compositions of the preindustrial bulk deposition sulfate and those of the industrial era

human induced calcretisation in anthropogenic soils and sediments field observations and micromorphology in a mediterranean climatic zone israel abstract for over a century the study of pedogenic calcrete and its formation focuses on natural processes disregarding the possible role of humans in its formation here we present field and micromorphological evidence from archaeological and modern sites in the eastern mediterranean region israel that indicate that some specific calcretes are human induced we demonstrate that anthropogenic affected calcrete differs from natural non human induced calcrete we show that the occurrence of the human induced calcrete is spatially limited and is associated with both macro and micro scale remnants and occasionally high content of organic material we propose an operative definition for anthropogenic calcretisation as the interference of humans with a component s that influence the formation of calcrete we assume that if present day calcretised environments will retain their calcretisation prone conditions for the next 5 10 millennia a distinct calcretic morphology could become a significant terrestrial formation this discovery can be particularly useful for evaluating past human impact on the environment adding a new archaeological set of research tools that should further be developed

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

climatological signals of the paleogroundwater in jordan abstract isotopic data on paleowaters from various groundwater basins in jordan have been compiled in order to document the various types in terms of age and 18 o d relationships the data indicate that the various types of water can be correlated with the various climatic pluvial phases which have affected the area since the beginning of the wurm period thus the oldest waters 30 ka have d values d d 8 18 o which range from 0 5 to 9 middle to late wurm waters from 8 6 to 17 middle holocene from 13 to 18 and modern precipitation from 21 to 30 moreover the slopes of the regression lines which describe the various suites of data have been decreasing from 9 3 for the oldest waters 8 1 for middle to late wurm waters 6 4 for middle holocene water and 6 2 for modern precipitation the trends of the groundwater isotopic contents with time suggest that although pluvials are part of the climatic cycles in the region there seems to be a significant change in the climatic conditions at the source of the moisture from one pluvial period to the next this change suggests lower relative humidity over the water masses i e the mediterranean sea through time moreover the slopes of the regression lines suggest increasing re evaporation before recharge through time also suggesting lower relative humidity in the areas of precipitation the data suggest that the timing of recharge of waters in the area can be roughly estimated based on the oxygen and deuterium isotopic signature

sulfate oxygen 17 anomalies in desert varnishes rock varnishes are ubiquitous in arid regions on earth and are believed to be commonly present on mars here we report high water soluble sulfate and nitrate contents in desert varnishes from the death valley region of southwestern u s a and that sulfate in varnishes possess 17o 18o ratios that do not fall on terrestrial mass dependent fractionation line sulfate from wet and dry atmospheric deposition is probably the source of the 17o anomalies the anomalies are only moderately lower than that of aerosol sulfates collected from the greater los angeles area indicating probably more than half of the sulfate in desert varnish is supplied by atmospheric deposition this finding suggests that earth surface environments are constantly accumulating 17o anomalous sulfate from the atmosphere arid and stable conditions facilitate the preservation of these atmospheric signatures this finding also indicates that different 17o 18o ratios found in different components in the martian meteorites may result from atmospheric chemical processes

oxygen isotope constraints on the alteration temperatures of cm chondrites abstract we report a systematic oxygen isotopic survey of ca carbonates in nine different cm chondrites characterized by different degrees of alteration from the least altered known to date paris 2 7 2 8 to the most altered alh 88045 cm1 our data define a continuous trend that crosses the terrestrial fractionation line tfl with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk o isotopic compositions of cm chondrites this bulk matrix carbonate bmc trend does not correspond to a mass dependent fractionation i e slope 0 52 as it would be expected during fluid circulation along a temperature gradient it is instead a direct proxy of the degree of o isotopic equilibration between 17 18 o rich fluids and 16 o rich anhydrous minerals our o isotopic survey revealed that for a given cm no carbonate is in o isotopic equilibrium with its respective surrounding matrix this precludes direct calculation of the temperature of carbonate precipitation however the o isotopic compositions of alteration water in different cms inferred from isotopic mass balance calculation and direct measurements define another trend cmw for cm water parallel to bmc but with a different intercept the distance between the bmc and cmw trends is directly related to the temperature of cm alteration and corresponds to average carbonates and serpentine formation temperatures of 110 c and 75 c respectively however carbonate o isotopic variations around the bmc trend indicate that they formed at various temperatures ranging between 50 and 300 c with 50 of the carbonates studied here showing precipitation temperature higher than 100 c the average 17 o and the average carbonate precipitation temperature per chondrite are correlated revealing that all cms underwent similar maximum temperature peaks but that altered cms experienced protracted carbonate precipitation event s at lower temperatures than the least altered cms our data suggest that the 17 o value of ca carbonates could be a reliable proxy of the degree of alteration experienced by cm chondrites

multiple oxygen 16o 17o and 18o and sulfur 32s 33s 34s and 36s isotope signatures of the dissolved sulfate from deception island antarctic peninsula implications on sulfate formation transportation and deposition in the antarctic region abstract oxygen 16 o 17 o and 18 o and sulfur 32 s 33 s 34 s and 36 s isotope ratios of and major ion na ca 2 cl no 3 and so 4 2 concentrations in lakes ponds and creeks from deception island antarctic peninsula were analyzed to study the sources of sulfate its oxidation and the surficial processes of the dissolved sulfate the positive relationship between the 34 s sulfate 8 1 to 17 3 and the cl so 4 2 molar ratio suggests mixing of sulfate from atmospheric deposition and from oxidation of sulfide minerals the average sea salt fraction 28 and 34 s nss values from 5 6 to 15 9 indicate that a combination of sea salt and marine biogenic sulfide provide the high 34 s end member of the dissolved sulfates the relatively low 18 o sulfate from 4 6 to 0 7 of deception island water suggests a role of local water in the formation of sulfate slightly negative but mass dependent 17 o sulfate values imply that atmospheric oxidation by o 3 and h 2 o 2 are negligible while these values might suggest a significant role of oxidation by molecular oxygen and oh the distinctly low 34 s sulfate value of two samples dcw 2 and dcw 3 suggests the input of sulfate from sulfide oxidation slight elevation of 34 s sulfate values up to 17 3 compared to a typical atmospheric value indicates a minimal role for dissimilatory microbial sulfate reduction of deception island water and sediments both 33 s sulfate and 36 s sulfate values are homogeneous and near zero implying that the dominant atmospheric oxidation process is tropospheric and that there are minimal to no contributions of stratospheric sulfate to deception island water

carbide magnetite assemblages in type 3 ordinary chondrites abundant carbide magnetite assemblages occur in matrix chondrules and chondrule rims in several h3 l3 and ll3 chondrites carbides cohenite fe ni 3c and haxonite fe ni 23c6 show compositional variations between different meteorites and appreciable ranges within meteorites carbides in h chondrites have lower co contents 0 0 6 wt than those in l and ll chondrites 0 3 1 2 wt metal associated with carbides and magnetite consists of high ni 50 70 wt taenite and in l and ll chondrites co rich up to 35 wt kamacite minor element contents of troilite and magnetite are very low textural observations indicate that carbide magnetite assemblages formed by replacement of metal sulfide nodules the high co contents of residual kamacite in association with carbides indicates that co is not incorporated into carbides i e fe co is much higher in the carbides than in kamacite because ni in carbides and magnetite is low the ni contents of residual taenite tend to be high ni rich sulfides were found only in ll3 chondrites possibly indicating their more extensive oxidation and or aqueous alteration we suggest that carbide magnetite assemblages in type 3 ordinary chondrites formed as the result of hydrothermal alteration of metallic fe in metal troilite nodules by a coh bearing fluid on their parent bodies this alteration resulted in carbidization of feni metal probably by co gas e g 15 fe s 4 co g fe3c s fe3o4 s or 3 fe s 2 co g fe3c s co2 g and oxidation probably by h2o gas e g 3fe s 4h2o g fe3o4 s 4h2 g the coh bearing fluids which were possibly released during metamorphism and transported through zones of high permeability may have been derived from ices adsorbed gases or hydrated minerals the co may be the result of the reaction of carbon compounds e g hydrocarbons with water vapor or magnetite

palustrine carbonates and pedogenic calcretes in the cal basin of sw anatolia implications for the plio pleistocene regional climatic pattern in the eastern mediterranean abstract sedimentologic and stable isotopic studies in the cal basin fill provide new insights on the late neogene quaternary climatic pattern in the eastern mediterranean long term subsidence and terrestrial sedimentation in the basin beginning in the late miocene are recorded in alluvial fan and fluvial deposits overlain by pliocene palustrine carbonates an erosional unconformity separates the pleistocene siliciclastic and calcrete deposits above as a single sedimentary unit resting on top of floodplain fines and restricted to the basin center the stable isotopic analysis of the palustrine carbonates and pedogenic calcretes displays a wide range of values 7 98

a contamination assessment of the ci carbonaceous meteorite orgueil using a dna directed approach the orgueil meteorite has become one of the most well studied carbonaceous meteorites after it fell in france 150 yr ago extraterrestrial organic compounds such as amino acids and nucleobases in the parts per billion ranges were identified in orgueil samples with supporting isotopic analyses however speculations of terrestrial contamination such as organic inclusions in the form of microbes and seeds accompanied the analyses of the orgueil meteorite ever since its fall by using molecular analysis we performed dna extractions and spiking experiments combined with 16s and 18s rrna gene targeted pcr amplification to quantify the level of terrestrial biocontamination our results indicate that terrestrial contamination with dna was insignificant in the investigated meteorite fraction we also remeasured and confirmed concentrations of amino acids found in previous studies and conclude that their rather high concentrations and distribution cannot be explained by terrestrial contamination with microorganisms alone these results represent the first analysis using dna directed tools in the analysis of the orgueil meteorite to determine trace levels of biomarkers

provenance of the various grain size fractions in the negev loess and potential changes in major dust sources to the eastern mediterranean abstract the isotopic composition of sr and nd and elemental concentrations e g na k ca mg al of three primary negev loess sequences trace the relative contributions of desert dust sources over the past 180 000 yr to the southeastern mediterranean we focused on the geochemical signature of the fine 20 m grain size modes of the loess to identify their respective provenances the isotopic composition of the coarse fraction falls on a mixing line of sources feeding the nile and its delta the chemical compositions of the coarse fraction and the sinai negev sand dunes are similar indicating that this fraction is the product of aeolian abrasion of the adjacent sinai negev sands in turn these sands are derived from the nile delta and transported inland the fine fraction has less negative end values and slightly deviates from the mixing line indicating an additional end member the higher end values and mg al ratios of the fine fraction are relatively well correlated r2 0 64 and point to arabian dust as an additional source temporal changes in the geochemical composition of loess over time reflect changes in climates of source areas and the eastern mediterranean shifts from saharan to arabian fine dust dominated intervals indicate wetter conditions in the southern sahara that weaken dust fluxes from this source relative to the arabian fluxes

organic thermometry for chondritic parent bodies abstract a unique spectroscopic feature has been identified in a study of twenty five different samples of meteoritic insoluble organic matter iom spanning multiple chemical classes groups and petrologic types using carbon x ray absorption near edge structure xanes spectroscopy the intensity of this feature a 1s exciton appears to provide a precise measure of parent body metamorphism the intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state 13c nmr experiments reveal that upon heating primitive iom is transformed into material that is indistinguishable from that in thermally processed chondrites including the development of the 1s exciton a thermo kinetic expression is derived from the experimental data that allows the intensity of the 1s exciton to be used to estimated the effective temperature integrated over time a good correlation is observed between the intensity of the 1s exciton and previously published microraman spectral data these data provide a self consistent organic derived temperature scale for the purpose of calibrating raman based thermometric expressions

isotopic composition of sulfur in size resolved marine aerosols above the atlantic ocean sulfur isotope measurements were performed on size segregated aerosols collected during the albatross oceanographic campaign from 61 n to 35 s above the atlantic ocean in october and november 1996 results obviously showed the dependence of the sulfur isotope ratio upon particle size the finest particles being depleted in 34s compared to coarse particles suggesting a heavier continental influence in the fine mode in the coarse mode 50 90 of the excess sulfate in both hemispheres was found to be of biogenic origin in the fine mode a different picture was obtained in the northern hemisphere the contribution of biogenic sulfur was found to be less than 35 of the excess sulfur even in relatively clean air masses on the other hand in the southern hemisphere the participation of biogenic sulfur was about 60 of the excess sulfur in purely marine air the contribution of continental sulfur to the fine fraction in the southern hemisphere was up to 40 25 even under pure oceanic conditions and far more in the northern hemisphere these results attest to the possible importance of long range transport of fine sulfate particles or so2 possibly through the free troposphere or the importance of anthropogenic emissions due to shipping

direct major and trace element analyses of rock varnish by high resolution laser ablation inductively coupled plasma mass spectrometry la icpms laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine major and trace element concentrations in rock varnish samples from the lahontan range near fallon nv and from a remote wilderness area near the san juan river in southeastern utah the data indicate that rapid la icpms analyses provide ample analytical resolution for semi quantitative compositional determinations of both trace and major elements in the varnish despite the presence of a rock substrate component in most analyses the overall major element contents of rock varnish from the two localities are grossly similar to rock varnish from other locations analyzed by solution icpms electron microprobe and energy dispersive scanning electron microscopy sem differences between microprobe and la icpms analyses may stem from different sampling scales and different degrees of substrate involvement it was possible to detect significant variations in trace element contents in the rock varnish samples the lahontan range is situated within a belt of w mineralization and varnish from that locality contained significantly higher w and mo contents than varnish from localities outside the w belt lead tl bi cd and as contents of varnish coated pebbles from near the san juan river in southeastern utah varied by an order of magnitude as a function of the position of the sampling site on the pebble elevated heavy element contents on the skyward facing varnish surfaces indicate that heavy elements may be preferentially scavenged at the locations most likely to receive direct inputs of atmospherically deposited airborne particulates the source of metal rich airborne particulates in this case is probably any one of several large coal fired power plants in the four corners region proximal to the san juan study area these patterns indicate that rock varnish chemistry is influenced by atmospherically derived fluxes of both dissolved and particulate constituents and that rock varnish can be used as a passive environmental indicator for a wide variety of elements in much the same manner as moss and lichens

development distribution and palaeoenvironmental significance of terrestrial carbonates in the petra region southern jordan abstract terrestrial carbonate deposits are common in both natural and human modified landscapes in petra and its surroundings three broad genetic categories are recognized cementations of pre existing clastics veins crusts cemented cobbles free water deposits massive laminated deposits mld rhizoliths carbonate blisters coatings on archaeological water delivery systems and pedogenic deposits nodules calcrete the oxygen isotopic composition of carbonates suggests mainly precipitation from stored water that reflects the weighted isotopic average of rainfall in the area oxygen and carbon isotope data indicate that a combination of evaporation and co2 degassing are the mechanisms for precipitation depending on the setting and climate at the time of deposition strontium isotopes of carbonates point to an aeolian source from adjacent sources for the calcium the cementations of pre existing clasts are both markers of previous base levels in the case of cemented cobbles and the presence of soil above impermeable bedrock in the case of crusts and veins these types of deposits help to discover previously terraced sites the open water deposits reflect humid pleistocene conditions and their presence inform on the extent and distribution of water resources that may have been available in the late pleistocene and early holocene

morphological study of insoluble organic matter from carbonaceous chondrites correlation with petrologic grade abstract the major form of organic material delivered to earth from an extraterrestrial origin is insoluble organic matter iom a morphological study of iom in the cr renazzo type and cm mighei type carbonaceous chondrites was performed in order to constrain its origins and processing history iom residues from the following cr chondrites gro 95577 cr1 al rais cr1 2 eet 92042 cr2 que 99177 cr3 and the cm chondrites met 01070 cm2 2 cold bokkeveld cm2 3 murchison cm2 4 and que 97990 cm2 5 were studied using annular dark field stem imaging characteristic features of the iom organic nanoglobules were manually identified and measured for their abundances and size distributions the iom residues were also compared holistically for their degree of average roughness or coarsening using fractal image analysis manually identified nanoglobules have abundances making up less than 10 of the total iom which is consistent with previous studies their measured abundances do not correlate with petrologic grade thus parent body processing did not systematically deplete their abundances the iom is however on average smoother or coarser in the more altered chondrites demonstrated by a lower fractal dimension using fractal box counting db the db values for the iom in the cr chondrites are distinctive que 99177 has the largest db value average 1 54 0 004 and gro 99577 has the lowest average 1 45 0 011 al rais and eet 92042 have iom with average db values within this range average 1 46 0 009 and 1 50 0 006 the cms record a similar but less distinctive trend in db with que 97990 having the largest value 1 52 0 004 met 01070 the lowest 1 45 0 019 and cold bokkeveld 1 50 0 011 and murchison 1 49 0 017 equivalent to one another within error the identified nanoglobules in the iom of the cm chondrites are on average larger than those in the cr chondrites the coarsening or smoother texture of the iom lower db in the more altered chondrites coupled with a tentative increase in the size of large features identified nanoglobules demonstrates that the aqueous processes leading to the lower petrologic types also formed the overall iom morphology in addition observations of fluid like textures more frequently found in the more altered carbonaceous chondrite residues suggests that organic and aqueous fluids determined at least some of these morphologies the polymerization of organic solutions is consistent with these morphologies their formation conditions are more favorable under the containment of carbonaceous chondrite parent bodies

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

origin of chondrule rims and interchondrule matrices in unequilibrated ordinary chondrites optical microscopy electron probe microanalysis scanning electron microscopy and analytical transmission electron microscopy were used to study the interchondrule matrix and opaque chondrule rims in bishunpur krymka semarkona chainpur all ll3 tieschitz and sharps both h3 the size distribution of grains in matrix in bishunpur obeys a power law rims around chondrules tend to be finer grained than matrix and may be layered all rims and matrices studied contain clasts of forsteritic olivine and low ca pyroxene in bishunpur the clasts may be cemented by amorphous glue rich in normative albite and partly altered to smectite rims in krymka sharps chainpur and tieschitz have a densely packed olivine groundmass with a grain size of about 0 1 m in krymka groundmass olivine is fo20 30 and forms interlocking dendrites various fe oxides are present in rims and matrices grain size distribution and chemical data indicate that clastic olivines and pyroxenes are derived from chondrules from analyses matrices rims in the ll group apparently are enriched in a feldspathic component tieschitz rims are slightly enriched but here the feldspathic component is present as white matrix sharps rims are not enriched in a feldspathic component opaque interchondrule matrices and chondrule rims probably formed from the products of fragmentation of chondrules partly induced by contraction of protopyroxene on inversion to clinopyroxene fragmented silica rich chondrule mesostases reacted with fe oxides and na to form the groundmass of fayalitic olivine and feldspathic glue a low temperature nebular or pre solar component is limited to 3 vol of each meteorite so equilibrium condensate was not the carrier of volatiles such as tl and bi

a reappraisal of the metamorphic history of eh3 and el3 enstatite chondrites abstract the thermal history of a series of eh3 and el3 chondrites has been investigated by studying the degree of structural order of the organic matter om located and characterized in matrix areas by raman micro spectroscopy by comparison with unequilibrated ordinary chondrites uocs and co and cv carbonaceous chondrites the following petrologic types have been assigned to various e chondrites sahara 97096 and allan hills 84206 3 1 3 4 allan hills 85170 and parsa 3 5 allan hills 85119 3 7 qingzhen macalpine hills 88136 and macalpine hills 88184 3 6 3 7 the petrologic type of qingzhen is consistent with the abundance of the p3 noble gas component a sensitive tracer of the grade of thermal metamorphism the petrologic types are qualitatively consistent with the abundance of fine grained matrix for the whole series no significant effects of shock processes on the structure of om were observed however such processes certainly compete with thermal metamorphism and the possibility of an effect cannot be fully discarded in particular in the less metamorphosed objects the om precursors accreted by the eh3 and el3 parent bodies appear to be fairly similar to those of uocs and co and cv carbonaceous chondrites raman data however show some slight structural differences that could be partly accounted for by shock processes the metamorphic history of eh3 and el3 chondrites has often been described as complex in particular regarding the combined action of shock and thermal metamorphism because om maturity is mostly controlled by the temperature of peak metamorphism it is possible to distinguish between the contributions of long duration thermal processes and that of shock processes comparison of the petrologic types with the closure temperatures previously derived from opaque mineral assemblages has revealed that the thermal history of eh3 and el3 chondrites is consistent with a simple asteroidal onion shell model thermal metamorphism in enstatite chondrites appears to be fairly similar to that which takes place in other chondrite classes the complex features recorded by mineralogy and petrology and widely reported in the literature appear to be mostly controlled by shock processes

widespread oxidized and hydrated amorphous silicates in cr chondrites matrices implications for alteration conditions and h2 degassing of asteroids abstract the cr chondrites carry one of the most pristine records of the solar nebula materials that accreted to form planetesimals they have experienced very variable degrees of aqueous alteration ranging from incipient alteration in their matrices to the complete hydration of all of their components in order to constrain their chemical alteration pathways and the conditions of alteration we have investigated the mineralogy and fe oxidation state of silicates in the matrices of 8 cr chondrites from type 3 to type 1 fe l edge x ray absorption near edge structure xanes was performed on matrix fib sections using synchrotron based scanning transmission x ray microscopy stxm the fe 3 fe ratio of submicron silicate particles was obtained and coordinated with tem observations in all the least altered cr chondrites que 99177 eet 87770 eet 92042 lap 02342 gra 95229 and renazzo we find that the matrices consist of abundant submicron fe rich hydrated amorphous silicate grains mixed with nanometer sized phyllosilicates the fe 3 fe ratios of both amorphous and nanocrystalline regions are very high with values ranging from 68 to 78 in the most altered samples al rais and gro 95577 fine grained phyllosilicates also have a high fe 3 fe ratio around 70 whereas the coarse micrometer sized phyllosilicates are less oxidized down to 55 and have a lower iron content these observations suggest the following sequence submicron fe2 amorphous silicate particles were the building blocks of cr matrices after accretion they were quickly hydrated and oxidized leading to a metastable amorphous gel like phase nucleation and growth of crystalline phyllosilicates was kinetically limited in most type 3 and 2 crs but increased as alteration became more extensive in al rais and gro 95577 the decreasing fe 3 fe ratio is interpreted as a result of the transfer of fe3 from silicates to oxides during growth while aqueous alteration progressed higher temperature longer duration change of fluid composition in a fully closed system equilibrium thermodynamics suggest that the water to rock ratios typically assumed to be low fe 3 fe ratio such a high fe 3 fe value could be accounted for however if the system was partially open at least with respect to h2 and other gases as well rapid degassing of the fluid would have favored more oxidizing fluid conditions recently proposed scenarios involving some degree of water d h increase through rayleigh isotopic fractionation are supported by these results

formation and preservation of pedogenic carbonates in south india links with paleo monsoon and pedological conditions clues from sr isotopes u th series and rees the influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the western ghats karnataka plateau south west india has been studied along the climosequence the current mean annual rainfall mar varies within a 80 km transect from 6000 mm at the edge of the plateau to 500 mm inland pedogenic carbonates occur in the mar range of 500 1200 mm in the semi arid zone mar 500 900 mm carbonates occur i as rhick hardpan calcretes on pediment slopes and ii as nodular horizons in polygenic black soils i e vertisols in the sub humid zone mar 900 1500 mm pedogenic carbonates are disseminated in the black soil matrices either as loose irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size they also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate cemented lumps of centimetric to decimetric size chemical and isotopic sr 87 sr 86 compositions of the carbonate fraction were determined after leaching with 0 25 n hcl the corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed the trend defined by the sr 87 sr 86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition considering the residual fraction of each sample as the most likely lithogenic source of ca in carbonates it is estimated that from 24 to 82 55 on average of ca is derived from local bedrock weathering leading to a consumption of an equivalent proportion of atmospheric co2 these values indicate that climatic conditions were humid enough to allow silicate weathering mar at the time of carbonate formation likely ranged from 400 to 700 mm which is 2 to 3 fold less than the current mar at these locations the sr u and mg contents and the u 234 u 238 activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation the relatively high concentrations of sr u and mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite possibly due to a better confinement of the pore waters which is supported by their high u 234 u 238 signatures and or to higher content of dissolved carbonates in the pore waters the occurrence of ce mn and fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation the carbonate ages determined by the u th method range from 1 33 0 84 kyr to 7 5 2 7 kyr and to a cluster of five ages around 20 kyr i e the last glacial maximum period the young occurrences are only located in the black soils which therefore constitute sensitive environments for trapping and retaining atmospheric co2 even on short time scales the maximum age of carbonates depends on their location in the climatic gradient from about 20 kyr for centimetric nodules at mule hole mar 1100 mm yr to 200 kyr for the calcrete at gundlupet mar 700 mm yr durand et al 2007 the intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils c 2010 elsevier ltd all rights reserved

modal mineralogy of cm2 chondrites by x ray diffraction psd xrd part 1 total phyllosilicate abundance and the degree of aqueous alteration abstract cm carbonaceous chondrites are samples of incompletely serpentinized primitive asteroids using position sensitive detector x ray diffraction psd xrd and a pattern stripping technique we quantify the modal mineralogy of cm2 chondrites mighei murray murchison nogoya and cold bokkeveld there is a narrow range in the combined modal volume vol of the most abundant phases mg serpentine 25 33 and fe cronstedtite 43 50 cold bokkeveld is anomalous in containing more mg serpentine 49 59 than fe cronstedtite 19 27 even including cold bokkeveld the range in modal total phyllosilicate is 73 79 average 75 total phyllosilicate abundance provides a non ambiguous measure of the degree of aqueous alteration and indicates that these meteorites have all experienced essentially the same degree of aqueous alteration this reflects pervasive hydration of matrix across cm2 samples apparent differences in the alteration of chondrules observed in petrographic studies represent various stages in the progression towards complete hydration of all components but are not manifest in significant differences in modal mineralogy for all samples there is a limited range in olivine 6 9 and pyroxene 5 abundances modal abundances of the remaining identified phases also show a limited range calcite 0 1 3 gypsum 0 1 6 magnetite 1 1 2 4 pentlandite 0 2 1 and pyrrhotite 1 3 8 as expected we observe a strong negative correlation in the modal abundance of anhydrous fe mg silicates olivine pyroxene and total phyllosilicate mg serpentine fe cronstedtite consistent with the idea that phyllosilicate is forming by aqueous alteration of the anhydrous components the negative correlation in the modal abundance between mg serpentine and fe cronstedtite indicates a mineralogic transformation of fe cronstedtite to mg serpentine by fluid driven recrystallisation or b that these meteorites had different initial abundances of olivine and pyroxene the observed positive correlation in the relative proportion of mg serpentine with increasing total phyllosilicate abundance reflects the evolution of increasingly mg rich phyllosilicate during aqueous alteration fe cronstedtite is the dominant phyllosilicate while cm chondrule olivines are forsteritic and will form mg serpentine during aqueous alteration this implies that matrix olivine was more fe rich than chondrule olivine prior to aqueous alteration

organic matter and metamorphic history of co chondrites abstract the metamorphic grades of a series of eight co3 chondrites alha77307 colony kainsaz felix lance ornans warrenton and isna have been quantified the method used was based on the structural grade of the organic matter trapped in the matrix which is irreversibly transformed by thermal metamorphism the maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration this metamorphic tracer is thus valid whatever the chemical class of chondrites moreover it is sensitive to the peak metamorphic temperature the structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals fa and fs silicate composition in type i chondrules presolar grains and noble gas p3 component abundance the deduced metamorphic hierarchy and the attributed petrographic types are the following alha77307 3 03 for most metamorphosed objects the peak metamorphic temperature can be estimated using a geothermometer calibrated with terrestrial metasediments beyssac o goffe b chopin c and rouzaud j n 2002 raman spectrum of carbonaceous material in metasediments a new geothermometer j metamorph geol 20 859 871 a value of 330 c was obtained for allende cv chondrite warrenton and isna consistent with temperatures estimated from fe diffusion weinbruch s armstrong j and palme h 1994 constraints on the thermal history of the allende parent body as derive from olivine spinel thermometry and fe mg interdiffusion in olivine geochim cosmochim acta 58 2 1019 1030 from the ni content in sulfide metal assemblages zanda b bourot denise m and hewins r 1995 condensate sulfide and its metamorphic transformations in primitive chondrites meteorit planet sci 30 a605 and from the d002 interlayer spacing in poorly graphitized carbon rietmeijer f and mackinnon i 1985 poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials nature 315 733 736 the trapped noble gas and c content appear to be sensitive but not precise metamorphic tracers indicating that the ornans paradox does not exist major problems with the current petrologic types derived from induced thermoluminescence are pointed out

cause and implications of rock varnish microchemical laminations rock varnish is a dark coating composed mostly of clays and manganese and iron oxides1 that accretes on rock surfaces in all terrestrial environments2 perry and adams3 first observed micron scale manganese rich and manganese poor relatively iron rich layers in varnish and proposed that these may be related to unspecified environmental changes electron microprobe analyses reported here suggest that mn fe ratios vary systematically with depth in varnishes on k ar dated volcanic rocks from the coso and cima volcanic fields eastern california and on talus flatirons in the negev desert israel these microchemical laminations probably reflect past fluctuations in the level of aeolian alkalinity and possibly climatic change this new indicator of terrestrial environmental change may be of importance to research on geomorphology archaeology palaeoclimatology and quaternary studies in arid environments

characteristics evolution and distribution of quaternary channel calcretes southern jordan cemented and calcretized conglomerates of quaternary age are found within ancient river channels exposed at various heights between 1 and 125 m above the current bed of the wadi dana in southern jordan in cross section the calcrete deposits are typically lensoid in shape and are found in lling palaeochannels cut into the bedrock the fossilized channel sediments preserve evidence of past river conditions sediment loads source areas phases of river down cutting and sediment accretion as well as post depositional alteration processes samples have been analysed in thin section and under the scanning electron microscope in order to determine the calcrete micromorphology cement types and crystal sizes the results show that the river deposits have undergone signi cant displacement and replacement of the detrital grains by caco3 and this has resulted in the cementation in places of over 4 m of river material the cements display an alpha type fabric with no evidence of biogenic activity the nature of the cement fabric within and between deposits differs as a function of two key variables i the speci c location within the channel and ii height above the modern wadi oor firstly in many of the deposits cement crystal size varies with sparite dominating at depth within impermeable palaeowadi channels whereas on the anks of the channels and near the top of the channels micrite is the main type of cement these variations are thought to be a result of differences in the length of residence time of calcium carbonate rich uids in different parts of the channel and the spatially varying in uence of evaporation secondly distinct changes in cement fabric can be seen in channels of different ages with a reduction in the amount of micrite and an increase in the amount of secondary recrystallized pore lling spar over time copyright 2004 john wiley sons ltd

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

relationships between organics water and early stages of aqueous alteration in the pristine cr3 0 chondrite met 00426 abstract in order to investigate the nature of organics at the time of their accretion into chondrite parent bodies as well as their subsequent evolution with aqueous alteration we have conducted a study of the morphologies spatial distribution and relationships between organic particles and the surrounding matrix phases in one of the most pristine carbonaceous chondrites currently known met 00426 cr which is therefore likely to contain the best preserved record of pre accretion features focused ion beam sections were extracted for transmission electron microscope observations from its matrix organic matter om shows a heterogeneous population of grains most of them smaller than 1 m diverse morphologies are observed such as compact rounded aggregates individual and aggregated nanoglobules and micron to nanometer sized veins a common feature is the systematic presence of cracks connected to the grains and filled with om the surrounding matrix groundmass consists of amorphous iron rich silicate particles intimately mixed with phyllosilicates sulfides and occasional tochilinite with sizes ranging from several hundreds of nanometers to below 10 nm a close spatial relationship is commonly observed between some of the organic matter particles and alteration phases such as tochilinite and phyllosilicates phyllosilicates sometimes occur intimately intercalated with organic matter at a scale below 10 nm we used tem eds techniques to quantify the water concentration in the matrix amorphous silicate material and the phyllosilicates the water contents of both materials are identical at 10 6 wt h 2 o and demonstrate that the amorphous silicate material in this meteorite is hydrated therefore even though these cr3 0 chondrites are the least altered objects from a mineralogical point of view their matrices contain significant amounts of water in the amorphous silicate this coupled in situ study of organics and aqueous alteration suggests that a significant population of the om accreted as a mixture of soluble and insoluble molecules together with water ice grains and that the om was mobile at the micrometer scale the spatial distribution of the om grains can therefore in part be attributed to parent body processes we suggest that as accreted ice melted hydration of the amorphous silicates and formation of tochilinite and phyllosilicates occurred in the immediate vicinity of the composite water ice organic matter grains the water soluble component of the organics was likely transported and redistributed in the surrounding porosity cracks grain boundaries as water circulated the textural settings suggest that some of the om material could have been polymerized during aqueous alteration and transformed into insoluble molecules perhaps during the last stages of alteration as water was consumed by silicate hydration reactions

evidence of past environmental conditions during the evolution of a calcretised wadi system in southern jordan using stable isotopes abstract a stratigraphically and temporally ordered sequence of channel calcretes preserved along the wadi dana southern jordan records the quaternary evolution of the formation and infilling of rock cut channels and their subsequent incision in a tectonically subsiding basin it is currently unknown under what palaeoenvironmental conditions these non pedogenic calcretes formed stable isotope analyses have been used to investigate whether any past topographical hydrological vegetational diagenetic and or temporal signatures can be identified from the channel calcretes the results of this research indicate that channel calcrete development is influenced by altitudinal variation affecting vegetation and hydrology within the landscape as well as location within individual wadi channels which has an affect on diagenetic processes the lack of calcretisation of a terrace that is between 1 and 1 5 m above the modern wadi floor supports the idea that the environment is currently too arid for calcrete to develop thus the presence of older wadi dana channel duricrusts suggests wetter conditions when they formed the 18o data of the calcrete implies cooler conditions than today as there is little evidence of a strong evaporative effect any temporal control is limited and mainly a function of stratigraphic position with some numeric dating

determination of the petrologic type of cv3 chondrites by raman spectroscopy of included organic matter abstract this paper reports the first reliable quantitative determination of the thermal metamorphism grade of a series of nine cv3 chondrites allende axtell bali mokoia grosnaja efremovka vigarano leoville and kaba the maturity of the organic matter in matrix determined by raman spectroscopy has been used as a powerful metamorphic tracer independent of the mineralogical context and extent of aqueous alteration this tracer has been used along with other metamorphic tracers such as fe zoning in type i chondrules of olivine phenocrysts presolar grain abundance and noble gas abundance bulk and p3 component the study shows that the petrologic types determined earlier by induced thermoluminescence were underestimated and suggests the following values pt allende axtell 3 6 pt bali mokoia grosnaja 3 6 pt efremovka leoville vigarano 3 1 3 4 pt kaba 3 1 the most commonly studied cv3 allende is also the most metamorphosed bali is a breccia containing clasts of different petrologic types the attribution suggested by this study is that of clasts of the highest petrologic types as pointed out by iom maturity and noble gas bulk abundance cv3 chondrites have complex asteroidal backgrounds with various degrees of aqueous alteration and or thermal metamorphism leading to complex mineralogical and petrologic patterns fe mg chemical zoning in olivine phenocrysts on the borders of type i chondrules of porphyritic olivine and pyroxene rich textural types has been found to correlate with the metamorphism grade this suggests that chemical zoning in some chondrules often interpreted as exchanges between chondrules and nebular gas may well have an asteroidal origin furthermore the compositional range of olivine matrix is controlled both by thermal metamorphism and aqueous alteration this does not support evidence of a nebular origin and does not necessarily mirror the metamorphism grade through fe mg equilibration on the other hand it may provide clues on the degree of aqueous alteration vs thermal metamorphism and on the timing of both processes in particular mokoia experienced significant aqueous alteration after the metamorphism peak whereas grosnaja which has similar metamorphism grade did not

solid state cp mas 13 c nmr of the insoluble organic matter of the orgueil and murchison meteorites quantitative study solid state cp mas 13c nuclear magnetic resonance nmr study of the insoluble organic fraction isolated by hf hcl treatment under an inert atmosphere from the orgueil and murchison carbonaceous meteorites is reported based on these spectra eight different types of carbons aro and ali linked ch3 ch2 aliphatic c linked to heteroelements protonated and non protonated aromatic c carboxyls and carbonyls were identified their relative amounts were determined and theoretical nmr derived h c atomic ratios were calculated comparison of these h c ratios with those obtained from elemental analysis revealed that a large part of the carbons of the insoluble fraction of both meteorites are not detected by cp mas 13c nmr taking into account these undetected carbons the relative abundance of aromatic carbons as of the total carbons was calculated as between 69 and 78 in orgueil and 61 and 67 in murchison and thus shown to be much higher than previously thought in addition the nmr data allowed to calculate the ratio of non protonated and protonated aromatic carbons based on previous studies on chemical and thermal degradation the present nmr data were interpreted as reflecting the occurrence of highly substituted rather small aromatic moieties in these insoluble organic materials along with ftir data nmr results also pointed to a relatively high branching level in the aliphatic chains especially for murchison according to the above results the insoluble organic matter in these meteorites did not suffer a marked thermal maturation during the late hydrothermalism of the parent body its synthesis involved a statistical combination of all the possible bonds between ch3 ch2 and ch radicals producing both the aliphatic and the aromatic moieties this model explains not only the chemical features of the chondritic insoluble organic material but also the typical ftir signature of the interstellar medium therefore organic material found in the interstellar medium and that incorporated in the most primitive objects of the solar system seem to share a common organosynthesis

different sulfate sources and their post depositional migration in atacama soils abstract sulfate is one of the major salts accumulated in the hyperarid atacama desert chile its origin has been attributed to local weathering volcanic source sea salt and atmosphere deposition previous studies concluded that atmospheric sulfate is present in the desert but this term was poorly defined in terms of chemical origin and its contribution to the total sulfate budget in soil is debated the contribution of each potential sulfate source is expected to vary geographically due to different source locations efforts to quantify the contribution from each source have been hampered by the lack of well defined isotopic compositions for its end members in this study we discard the vague term of atmospheric sulfate by recognizing two major sulfate sources on the basis of their formation pathways primary and secondary sulfate primary sulfate including those from rock weathering sea salt and volcanic ash leachates do not have an 17o anomaly secondary sulfate derived from the oxidation of reduced sulfur gases biological or volcanic emissions by atmospheric ozone or hydrogen peroxide however has an 17o anomaly we developed a method to extract water soluble anions sequentially or entirely from bulk soil samples and analyzed the sulfate concentrations and 17o anomalies for four geographically representative soil profiles in the central atacama desert 23 s to 25 5 s we found that sequential sulfate extractions on the same soil sample produce sulfate with decreasing 17o values except for a positive bulge at 20 to 50 cm in depth there is a general increase in the 17o value for total sulfate with soil depth for all the four soil profiles that we examined these findings are consistent with the hypothesis that secondary sulfates 17o anomalous sulfates are more soluble and thus preferentially leached in liquid water than primary sulfate the finding also warns that incomplete sulfate extraction from sulfate rich soils yields unpredictable results we infer a 17o value of 4 6 for secondary sulfate based on data from partial sulfate extraction experiments total contribution of secondary sulfate in the central atacama desert is estimated to range from 9 to 24 with the highest percentage in the central depression

first sulfur isotope measurements in central greenland ice cores along the preindustrial and industrial periods 1 sulfur isotopes of sulfate have been measured in a discontinuous set of polar ice core samples from summit central greenland covering the preindustrial from the fourteenth to the eighteenth century and industrial from 1872 to 1969 a d periods results have been used to estimate the different source contributions to the deposited sulfate and their evolution along the last centuries they indicate that the preindustrial background sulfate budget is slightly dominated on a year round average by marine biogenic emissions amounting to close to half of the non sea salt sulfate 49 the second contribution is provided by continental sources of secondary sulfate including background volcanism and to a lesser extent continental biota 44 of the non sea salt sulfate sulfur emitted by relatively weak eruptions is found to be largely depleted in 34s compared to bulk volcanic s suggesting an efficient washout of the heavier isotope during the tropospheric transport the impact of human driven emissions on the sulfate deposited in central greenland ice is visible in isotope data as early as 1870 a d the isotopic signature of anthropogenic sulfur deposited during the twentieth century is found to be constant 34s 3 0 1 5 regardless of the changes of dominant source regions and emission processes this signature is slightly but measurably lighter than the one reported for arctic haze pollution events

investigating the variations in carbon and nitrogen isotopes in carbonaceous chondrites the carbonaceous chondrites contain significant amounts of carbon and nitrogen bearing components the most abundant of which is organic matter stepped combustion data of whole rock and hf hcl residues of carbonaceous chondrites reveal that the organic material can be subdivided operationally into three components 1 free organic matter fom which is readily extractable from whole rock meteorites and is enriched in 13c and 15n 2 labile organic matter lom which has a macromolecular structure but is liberated by hydrous pyrolysis lom is the parent structure for some fom and is also enriched in 13c and 15n and 3 refractory organic matter rom which is also macromolecular but is virtually unaffected by hydrous pyrolysis and is relatively depleted in 13c and 15n the macromolecular entities lom and rom are by far the most abundant organic components present and as such the relative abundances of the 13c and 15n enriched lom and the 13c and 15n depleted rom will have a major influence on the overall isotopic composition of the whole rock meteorite laboratory experiments designed to simulate the effects of parent body aqueous alteration indicate that this form of processing removes lom from the macromolecular material allowing rom to exert a stronger influence on the overall isotopic compositions hence aqueous alteration of macromolecular materials on the meteorite parent body may have a significant control on the stable isotopic compositions of whole rock carbonaceous chondrites the enstatite chondrites are also carbon rich but have been subjected to high levels of thermal metamorphism on their parent body stepped combustion data of hf hcl residues of enstatite chondrites indicate that if they and carbonaceous chondrites inherited a common organic progenitor metamorphism under reducing conditions appears to incorporate and preserve some of the 13c enrichments in lom during graphitisation however when metamorphism is at its most extreme the 15n enrichments in lom are lost

insight into factors controlling formation rates of pedogenic carbonates a combined geochemical and isotopic approach in dryland soils of the us southwest abstract natural accumulation of pedogenic carbonates has been well documented but few studies have focused on carbonate formation in agricultural drylands this study aims to determine accumulation rates of pedogenic carbonates in intensively irrigated soils and to define key linkages between flood irrigation salt loading and soil atmosphere co 2 exchange in cultivated drylands of the southwestern united states we used a combination of elemental chemistry cao soil organic and inorganic carbon contents mineralogy and u series 238 u 234 u 230 th disequilibrium dating technique to investigate calcium sources ages and formation rates of pedogenic carbonates study sites include an irrigated alfalfa field near el paso in western texas and a non irrigated natural dryland site on the usda jornada experimental range of southern new mexico our results showed that large amounts of dissolved calcium and inorganic carbon along with other soluble elements were loaded onto agricultural fields through irrigation waters in el paso tx while dust and rainfall were important for salt loading in natural soils of the jornada u series activity ratios 234 u 238 u and 230 th 238 u in bulk soils suggested eolian deposits added u and modified u isotopes in shallow soils at both the irrigated and natural sites mobility of 234 u within the soil profile is related to leaching of u and by inference other soluble ions and carbonate accumulation at depth the u series dating technique in pedogenic carbonates revealed the presence of much younger carbonates at the irrigated site compared to the natural site pedogenic carbonate formation rates in the irrigated soils were also much higher than those in the non irrigated soils likely a result of influxes from dissolved ca and inorganic carbon in water used for irrigation this study demonstrates the potential for agricultural expansion and land use change in drylands to increase rate of pedogenic carbonate accumulation such changes may have important implications to global carbon cycling since drylands are forecast to become the most expansive terrestrial biome by mid century and dryland agriculture is expanding quickly

mass independent isotopic signatures of volcanic sulfate from three supereruption ash deposits in lake tecopa california abstract hundreds to thousands of megatons of sulfur dioxide released by supereruptions can change chemical and physical properties of the atmosphere and thus induce climate perturbations we present oxygen and sulfur isotope analyses of sulfate in 48 volcanic ash samples and 26 sediment samples from dry lake beds in the tecopa basin california usa these ash layers represent three supereruptions including the 0 64 ma lava creek tuff 2 04 ma huckleberry ridge tuff and 0 76 ma bishop tuff mass independent oxygen signatures 17o up to 2 26 that are present in these ash units and not in associated sediments indicate oxidation of volcanic so2 by mass independent ozone and its products in this study we consider the formation deposition preservation and dilution of mass independent volcanic sulfate mivs using the isotopic compositions of the sulfates we construct a mixing model that demonstrates that the main source of sulfate in lake tecopa is mass dependent sediment derived sulfate mdsds 77 however ash beds still preserve up to 23 of mivs that initially had undiluted 17o value around 8 and 33s as low as 0 35 and 36s up to 1 08 therefore despite potential dilution by mdsds the mivs signatures can be preserved in the geologic record for few million years if deposited as gypsum in arid environments alkaline or saline lake the oxygen and sulfur mass independent signatures of the volcanic sulfates indicate that photolysis and oxidation of volcanic so2 has been achieved in the upper atmosphere since only supervolcanic eruptions were shown to generate massive amount of mass independent sulfate it requires that up to 20 60 of the global ozone layer is consumed as a result of supervolcanic so2 released this may occur as a result of a strong physical and chemical degradation of the tropopause we speculate that the distinction between the high troposphere and the low stratosphere at least locally could be erased by supereruptions and recorded by mivs