stable isotope composition of late pleistocene holocene eobania vermiculata muller 1774 pulmonata stylommatophora shells from the central mediterranean basin data from grotta d oriente favignana sicily abstract this paper presents stable isotopic results oxygen and carbon from both modern and late pleistocene holocene shells of the land snail eobania vermiculata muller 1774 from favignana island sicily it aims to contribute to the understanding of climate and vegetation history of this region during formation of upper palaeolithic mesolithic and meso neolithic deposits of grotta d oriente ort results from both an evaporative model fbm and an empirical regional isotopic model i e linear relation between oxygen isotopic composition of shells 18 os and those of local precipitation 18 op indicate that the 18 os values of modern specimens are mainly controlled by local temperature relative humidity and 18 op at the time of snail activity data also suggest that the modern snails are nocturnally active almost all year round in the study area the carbon isotopic compositions of shells 13 cs of the same specimens indicate a diet prevalently or exclusively composed of c3 vegetation the 18 os values of late pleistocene specimens suggest that climate conditions at 14 2 ka cal bp were similar to the present day in agreement with additional 18 os records from southern italy by contrast early middle holocene shells are notably 18 o depleted and suggest wetter conditions possibly combined with a decrease in isotopic composition of precipitation source compared to the present day when compared with regional palaeoclimatic records a large scale isotopic response to millennial scale changes in atmospheric and hydrological conditions e g enhanced rainfall in the central eastern mediterranean is observed during the early middle holocene the 13 cs of late pleistocene and holocene specimens are consistently higher than those of modern ones for the late pleistocene this could be reasonably explained in terms of water stressed vegetation on the other hand this seems to be less valid for holocene counterparts when the climate was wetter probably 13 cs values result from the combination of distinct competing factors involving atmospheric co 2 concentration seasonal water budget vegetation type cover and other carbon sources results reveal coherent relationships between regional 18 os and 13 cs demonstrating that late pleistocene holocene land snail shell remains from archaeological sites may provide useful snapshots of past seasonal climate conditions

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

the influence of diet on the δ13c of shell carbon in the pulmonate snail helix aspersa abstract the influence of diet and atmospheric co2 on the carbon isotope composition of shell aragonite and shell bound organic carbon in the pulmonate snail helix aspersa raised in the laboratory was investigated three separate groups of snails were raised on romaine lettuce c3 plant 13c 25 8 corn c4 plant 13c 10 5 and sour orange 12c enriched c3 plant 13c 39 1 the isotopic composition of body tissues closely tracked the isotopic composition of the snail diet as demonstrated previously however the isotopic composition of the acid insoluble organic matrix extracted from the aragonite shells does not track diet in all groups in snails that were fed corn the isotopic composition of the organic matrix was more negative than the body by as much as 5 whereas the matrix was approximately 1 heavier than the body tissues in snails fed a diet of c3 plant material these results indicate that isotopic composition of the organic matrix carbon cannot be used as an isotopic substrate for paleodietary reconstructions without first determining the source of the carbon and any associated fractionations the isotopic composition of the shell aragonite is offset from the body tissues by 12 3 in each of the culture groups this offset was not influenced by the consumption of carbonate and is not attributable to the diffusion of atmospheric co2 into the hemolymph the carbon isotopic composition of shell aragonite is best explained in terms of equilibrium fractionations associated with exchange between metabolic co2 and hco3 in the hemolymph and the fractionation associated with carbonate precipitation these results differ from previous studies based primarily on samples collected in the field that have suggested atmospheric carbon dioxide contributes significantly to the shell 13c the culture results indicate that the 13c of aragonite is a good recorder of the isotopic composition of the snail body tissue and therefore a better recorder of diet than is the insoluble shell organic carbon because the systematic fractionation of carbon isotopes within the snail is temperature dependent the 13c of the shell could provide an independent technique for estimating paleotemperature changes

limestone and the problem of radiocarbon dating of land snail shell carbonate in order to test the role of limestone in producing anomalously old radiocarbon ages in land snail shells 14 c analyses were performed on shell carbonate of modern land snails from limestone and nonlimestone areas of jamaica no anomaly was found in snails from the nonlimestone area implying that such material is suitable for radiocarbon dating snails from limestone areas produced variable anomalies of as much as 3 120 yr due to incorporation of 14 c free limestone into shell carbonate all rock scraping snails and most leaf litter feeding snails from limestone areas showed anomalous 14 c contents because of the variability in 14 c content even within species no standard correction factor for limestone anomaly can be applied however dating error can be minimized by selecting ecologically appropriate species or by comparison of analyses of several fossil species within a stratum to their modern counterparts

stable carbon isotope record of middle to late holocene climate changes from land snail shells at hinds cave texas abstract stable carbon isotope ratios of shell carbonate and shell organic matter from land snails rabdotus alternatus from hinds cave texas are used to reconstruct the climate history of the drier western part of the southern great plains present mean annual rainfall of 400 mm over the last ca 5000 yr ams radiocarbon analyses of four individual shells from each of two strata indicate that there are no problems of reworking or age mixtures within strata however burning is evident in many shells amino acid composition and racemization were used to identify shells that had been significantly heated and these were rejected for isotopic analysis because of possible alteration of the isotopic signal fourteen samples of snails from hinds cave each consisting of 2 6 individual shells from the same provenience were radiocarbon dated by ams and analyzed for stable carbon isotopes in addition a sample collected alive ca ad 1890 from a nearby site was analyzed to represent modern conditions the shells show no decrease in organic content with age indicating good preservation of shell organic matter both the organic and carbonate isotope values show similar temporal trends the oldest samples 4100 4600 cal yr bp are relatively depleted in 13 c maximum 13 c values are reached at ca 3500 cal yr bp thereafter there is a regular depletion in 13 c with the recent sample showing the lowest 13 c value the change in the isotopic values over time is quite large range of 4 5 for organic matter and indicates substantial climatic changes the variations in isotopic values are interpreted as resulting primarily from changes in moisture conditions affecting the abundance of drought adapted cam crassulacean acid metabolism plant species enriched in 13 c thus relatively moist mid holocene conditions are indicated with increasingly dry conditions reaching a maximum at ca 3500 cal yr bp followed by progressively moister conditions through the late holocene

tectonic implications of metamorphism and gravity field in the penokean orogen of northern michigan published geologic data together with new metamorphic pressure and temperature data and gravity data provide strong evidence for northward directed thrusting of lower proterozoic rocks in northern michigan and wisconsin metamorphic studies indicate pressures of 7 kbar at watersmeet node and 4 kbar at the peavy node the republic metamorphic node located 30 km to the north of peavy attained pressures of 2 3 kbar all three metamorphic highs reached temperatures in the range of 600 650 c and are correlated with areas of negative gravity anomalies relative to surrounding regions in the peavy high the center of the gravity anomaly lies on the sillimanite isograd and we suggest that the source of this negative anomaly may be remobilized underlying archean gneiss the highest grade rocks of the republic node lie well within a residual gravity anomaly which is interpreted to have a very shallow source and the watersmeet high lies above gneiss domes which show negative gravity anomalies a north south geologic cross section constructed from a two dimensional gravity model which extends northward from the dunbar dome in the magmatic arc terrane of wisconsin across a terrane boundary interpreted as a suture and marked by the niagara fault and across the peavy metamorphic node suggests that the dunbar dome was transported northward onto the continental foreland during the penokean orogenic event these north verging fold thrust sheets or nappes produced prominent tectonic thickening at the peavy and watersmeet as indicated by the relatively high metamorphic pressures there the thrust sheets evidently thinned to the north as suggested by the relatively low pressures at republic we suggest that the archean continental edge defined by the steep gradient in the regional northeast trending gravity high lies beneath the magmatic rocks of wisconsin and thus extends south of the niagara fault suture

stable isotope δ18o δ13c and δd signatures of recent terrestrial communities from a low latitude oceanic setting endemic land snails plants rain and carbonate sediments from the eastern canary islands abstract stable isotopes of oxygen and carbon extracted from fossil land snail shells have been used increasingly to interpret past environments to evaluate the utility of this approach for low latitude oceanic islands populations of the modern helicid land snail theba geminata a species also abundant in the quaternary fossil record of the region were sampled at ten low altitude d and 2 v smow for 18 o ranging from 11 to 2 v smow and from 2 6 to 0 7 v smow respectively the local vegetation is heterogeneous including c 3 c 4 and cam plants 13 c values vary from 13 0 to 29 0 v pdb across plant species of the 24 species five are c 4 15 are c 3 and four are cam plants the 18 o values for shells represent a narrow range of values from 0 3 to 2 5 v pdb which is consistent with the low climate seasonality typifying low latitude oceanic settings hypothetical model of the expected 18 o value for shell aragonite precipitated in equilibrium suggests that the most negative 18 o shell represent the closest estimate for 18 o rain water the 13 c values of shells range from 9 4 to 1 7 v pdb the most positive 13 c values are attributed to a diet based on c 4 plants the comparison of 13 c values of soft tissues and shells suggests that snails ingested notable amounts from 20 up to 40 of foreign carbonates consequently fossil shells with the most negative 13 c values should be selected for radiocarbon dating in future geochronological studies of the region the 13 c values of body tissues vary from 12 0 to 27 2 v pdb indicating that land snails consumed c 3 and c 4 plants indiscriminately the mean carbon isotopic composition averaged across multiple fossil specimens may thus provide a useful tool for reconstructing paleoclimates and paleoenvironments throughout the quaternary history of the canary islands and other comparable low latitude oceanic settings

a paleoclimate reconstruction for southwestern texas using oxalate residue from lichen as a paleoclimate proxy a calcium oxalate rock coating is ubiquitous on limestone surfaces inside dry rock shelters and under rock overhangs within the canyons of the southwestern edwards plateau in southwestern texas the oxalate was likely produced by epilithic lichens that ourished in these niches during dry climate regimes during wet climate conditions the productivity of the lichen would be severely reduced due to physiological response to moisture regime thus lichen productivity and the production of calcium oxalate may have changed through time in response to wet dry climate uctuations twenty ve ams radiocarbon ages of rock crust samples collected from 14 sites demonstrate that oxalate was produced episodically during the middle and late holocene the occurrence of oxalate is correlated with periods of dry climate whereas gaps in the record of oxalate deposition coincide with more mesic climate intervals the results of this study demonstrate the potential for obtaining paleoclimate data from biogenic residues on rock surfaces 2000 elsevier science ltd and inqua all rights reserved

the use of land snail shells in paleoenvironmental reconstruction fossil land snail shells constitute a valuable source of paleoenvironmental information for the quaternary they can be dated by a variety of methods including radiocarbon amino acid racemization and epimerization and perhaps also thu and esr the vast majority of paleoenvironmental studies based on land snail shells have examined the faunal composition of fossil assemblages from which a variety of paleoenvironmental characteristics such as biome temperature and moisture conditions have been reconstructed still there are a number of problems involved in using this approach and these are discussed shell morphology has occasionally been used to reconstruct such factors as rainfall and temperature stable isotope studies on quaternary land snails include analysis of 18o values of organic matter in the shells to reconstruct c4 plant distributions from which rainfall amounts can be inferred and analysis of 18o values of shell carbonate from which trends in the oxygen isotope composition of rainfall can be reconstructed stable carbon isotopes of shell carbonate have also been studied but their interpretation is not clear amino acid epimerization analysis dalloisoleucinel isoleucine ratios of land snail shells has been used for estimation of paleotemperatures some potential uses of land snail shells for paleoenvironmental reconstruction include the study of stable isotopes of h and n periodic growth lines and deposits of pedogenic carbonates on the shells

coherent changes in relative c4 plant productivity and climate during the late quaternary in the north american great plains evolution of the mixed and shortgrass prairie of the north american great plains is poorly understood because of limited proxies available for environmental interpretations buried soils in the great plains provide a solution to the problem because they are widespread both spatially and temporally with their organic reservoirs serving as a link to the plants than once grew on them through stable carbon isotopic analysis of soil organic carbon d

paleoclimatic implications of the spatial patterns of modern and lgm european land snail shell δ18o abstract the oxygen isotopic composition of land snail shells may provide insight into the source region and trajectory of precipitation last glacial maximum lgm gastropod shells were sampled from loess from belgium to serbia and modern land snail shells both record 18 o values between 0 and 5 there are significant differences in mean fossil shell 18 o between sites but not among genera at a single location therefore we group 18 o values from different genera together to map the spatial distribution of 18 o in shell carbonate shell 18 o values reflect the spatial variation in the isotopic composition of precipitation and incorporate the snails preferential sampling of precipitation during the warm season modern shell 18 o decreases in europe along a n s gradient from the north sea inland toward the alps modern observed data of isotopes in precipitation gnip demonstrate a similar trend for low altitude sites lgm shell 18 o data show a different gradient with 18 o declining toward the ene implying a mid atlantic source due to increased sea ice and a possible southern displacement of the westerly jet stream balkan lgm samples show the influence of a mediterranean source with 18 o values decreasing northward

gold bearing iron formation in a granulite terrane of the canadian shield a possible deep level expression of an archean gold mineralizing system gold occurs in metamorphosed iron formation within a migmatized paragneiss terrane in the eastern superior province of the canadian shield the main gold prospect which is located 100 m from a tonalite pluton has undergone skarn like metamorphism that occurred late during the granulite grade metamorphism despite its occurrence in a high grade metamorphic host rock the mineralization shares many of the characteristics of lowergrade archean greenstone belt gold mineralization such as 1 enrichment in au as s sb w u and feo 2 a low base metal gold ratio 3 the inclusion of gold in arsenopyrite 4 the proximity to a felsic pluton 5 an iron rich fractured host rock and 6 a similar mineralization time around 2650 ma this gold occurrence occurs near the metamorphic peak and represents a deep level expression of the widespread crustal scale mineralizing system documented for the late archean the main conclusion of this work is that the principal characteristics of archean gold mineralization are present in the deep crust and do not come from the leaching of upper level rock piles such as greenstone belts

oxygen isotope composition of living land snail shells data from italy sixty seven shells of living land snails were selected from 31 different localities across italy to investigate the relationships between their oxygen isotopic composition 18os and the mean value of local rainfall 18op despite the difficulty for some localities to correctly estimate the oxygen isotopic composition of local rainfall a good relationship was found this indicates that the oxygen isotopic composition of environmental water used by the snails is in italy strictly related to that of the local meteoric precipitation however the relationship found is substantially different from that previous established for central europe indicating that regional climatic conditions are important in defining the final isotopic composition of land snail shells moreover these equations may not hold for different climatic conditions existing during for instance glacial and interglacial periods the data also show that isotopic differences among species are relatively narrow and that they may depend on ecological factors i e style of life rather than any clearly identifiable different vital offset

stable isotope composition of land snail body water and its relation to environmental waters and shell carbonate abstract day to day and within day diel variations in d and 18 o of the body water of the land snail theba pisana were studied at a site in the southern coastal plain of israel three phases of variation which relate to isotopic changes in atmospheric water vapor were distinguished 1 on rain days snail water becomes isotopically depleted approximately in the direction of the rain isotope values but always less depleted in d as is atmospheric water vapor 2 during the 1 3 days following a rain the snail water becomes isotopically enriched along a line with slope 18 o space this relates to an increasing influence of humidity derived from the mediterranean sea 3 a period of relative stability of the isotopic composition persists until the next rain event the isotopic variations can be explained by isotopic equilibration with atmospheric water vapor and or uptake of dew derived therefrom during the winter when the snails are active there is only very minor enrichment in 18 o relative to equilibrium with water vapor or dew apparently as a result of metabolic activity but this enrichment becomes pronounced after long periods of inactivity within day variation in body water isotopic composition is minor on non rain days shell carbonate is enriched in 18 o by ca 1 2 relative to equilibrium with body water in most regions the isotopic composition of atmospheric water vapor or dew is a direct function of that of rain because the isotopic composition of snail body water is related to that of atmospheric water vapor and the isotopic composition of shell carbonate in turn is related to that of body water land snail shell carbonate 18 o should provide a reliable indication of rainfall 18 o however local environmental conditions and the ecological properties of the snail species must be taken into account

on the origin of early proterozoic gneiss domes and metamorphic nodes northern michigan biotite 40 r 39 r cooling ages from medium pressure 500 600 mpa rocks in the watersmeet district northern michigan suggest significant cooling uplift and concomitant deformation during gneiss dome formation at 1755 ma well after the close of the 1870 1830 ma penokean orogeny however an 1822 ma hornblende plateau date indicates that the isograds surrounding the dome are penokean in age we attribute gneiss dome formation and doming of penokean aged isograds to an episode of orogenic collapse superimposed on an earlier history of crustal shortening this contrasts with the compressional origin for gneiss domes preserved in the low pressure 200 300 mpa republic district the different origins may reflect the fact that collapse was localized along the overthickened region of the orogenic belt in contrast to the watersmeet area hornblende and biotite 40ar 39ar ages obtained from the republic area are 1720 1680 ma given the relatively shallow depth of this region it is unlikely that temperatures re

stable isotopic evidence for latest pleistocene and holocene climatic change in north central texas abstract a paleoclimatic record for a southern great plains locality the aubrey clovis site in north central texas has been established using stable carbon and oxygen isotopes detailed composite stratigraphic sections constrained by 14 c ages place the age of these deposits between 14 200 and 1600 yr b p calcium carbonate samples of lacustrine and pedogenic origin were analyzed oxygen isotopic compositions of most of these in situ carbonates reflect equilibrium precipitation from local meteoric waters oxygen isotope values reflect changes in the composition of meteoric waters tied to changes in the isotopic composition of moisture derived from the gulf of mexico oxygen isotopic variability at the aubrey site is coincident with marine isotopic records from the gulf that vary due to changes in laurentide ice sheet volume and meltwater influx the stable carbon isotopic record reflecting changing biomass through time corroborates humid versus arid interpretations based on sedimentology and rates of alluviation a middle holocene arid period was in contrast to moist early and late holocene climate affirming interpretations of other workers studying southern great plains holocene climate history

late quaternary vegetation and climate changes in central texas based on the isotopic composition of organic carbon stable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central texas reveals significant shifts in the ratio of c3 to c4 plant biomass production during the past 15 000 yr these temporal changes in vegetation appear to be in response to changes in climate during the late pleistocene c4 plants comprised only about 45 to 50 of the vegetative biomass in this area suggesting that conditions were cooler and wetter than at any time during the past 15 000 yr the time between 11 000 and 8000 yr b p is interpreted as transitional between late pleistocene conditions and warmer and drier holocene conditions based on a slight increase in the abundance of c4 plant biomass during the middle holocene between approximately 6000 and 5000 yr b p mixed c3 c4 plant communities were replaced almost completely by c4 dominated communities indicating prairie expansion and warmer and drier climatic conditions by 4000 yr b p the abundance of c4 plant biomass decreased to levels similar to the early holocene transitional period suggesting a return to cooler and wetter climatic conditions no significant shift in the ratio of c3 to c4 productivity has occurred during the last 4000 yr except for a slight increase in the abundance of c4 plant biomass around 2000 yr b p the results of this investigation correlate well with other regional late quaternary climatic interpretations for central and north texas the southern plains region and with other portions of the great plains

holocene paleoenvironment 7200 4000 cal bp of the los castillejos archaeological site se spain inferred from the stable isotopes of land snail shells abstract neolithic copper age and modern land snail shells from the los castillejos archeological site 37 20 n se iberian peninsula were analyzed for 13 c 12 c and 18 o 16 o ratios to estimate the paleoenvironmental conditions during shell deposition modern and ancient 13 c values ranged from 9 2 to 7 7 and from 13 6 to 5 7 respectively and they differed among taxa 13 c values were similar for neolithic 13 c 8 1 2 3 copper age 13 c 8 4 0 6 and modern 13 c 8 4 0 5 herbivorous cernuella specimens alternatively fossil shells of the herbivorous ferussacia folliculum 13 c 9 9 1 2 and the omnivorous rumina decollata 13 c 11 1 2 showed substantially lower 13 c values than modern specimens which may suggest lower water stress during the early to mid holocene than today the 18 o values from modern specimens ranged from 1 1 to 0 6 while the 18 o values from fossil specimens ranged from 6 7 to 0 and they differed among species cernuella exhibited shell 18 o values that increased from the neolithic 18 o 2 3 1 8 and copper age 18 o 1 7 0 6 to the present 18 o 0 3 0 5 the 18 o values of fossil shells of f folliculum 18 o 3 7 1 0 and r decollata 18 o 4 0 1 6 were also lower than modern shells calculations of a published snail flux balance mixing model for 18 o values indicate that early to mid holocene shells precipitated during times when relative humidity was greater than today the se iberian peninsula was noticeably wetter 7200 cal bp and experienced drier conditions thereafter the results are consistent with other regional paleoclimatic proxies and reinforce the potential use of land snail shells as paleoenvironmental archives

archaean gneisses amphibolites and banded iron formations from the anshan area of liaoning province ne china their geochemistry metamorphism and petrogenesis an investigation of the trace element geochemistry and geothermobarometry of amphibolites and banded iron formations bif of the anshan group and of associated amphibolite facies orthogneisses in the anshan area of liaoning province of ne china has been carried out with a view to understanding the petrogenesis and evolution of this archaean high grade terrain which is unique for its abundance of bif the anshan supracrustal group which has a sm nd isochron age of 2 79 ga comprises bif metavolcanic amphibolites quartzites phyllites and schists the bif actinolite cummingtonite magnetite quartz stilpnomelane occurs in kilometre long beds up to 80 m thick which contain very low contents of total ree co2 s cu pb zn mn ni p ti v and cr s34 is near chondritic and o18 approximates the calculated primary o18 of sio2 deposited from archaean sea water the amphibolites hornblende plagioclase quartz epidote tourmaline form beds up to 1 km thick range from quartz to olivine and hyperthene normative and have low zr and ti abundances and trace element patterns that are most similar to those of basalts derived from sub continental mantle or to those of modern island arc tholeiites metasediments are muscovite tourmaline quartzites quartz muscovite chlorite phyllites quartz biotite muscovite garnet staurolite schists quartz garnet biotite schists quartz garnet cumming tonite gedite rocks and quartz k feldspar plagioclase biotite sillimanite gneisses the tiejiashan orthogneisses which have rb sr and pb pb isotopic ages of 2 83 2 86 ga probably represent basement to the anshan group they range from granites to trondhjemites and consist of quartz plagioclase biotite and microcline the anshan orthogneisses have a sm nd isochron age of 2 53 ga and range in composition from granites to tonalites they intruded the anshan supracrustals with the result that the bif and associated supracrustal rocks now form lenses of up to several kilometres in the gneisses the most common assemblage is quartz k feldsparplagioclase biotite both the tiejiashan and anshan gneisses have high sr rb and k sr and low ca and thus are similar to amphibolite facies gneisses in many high grade terrains and to modern volcanic arc granites geothermometry of metasediments suggests that t increased from 500 550 c in the south to 600 c in the north of the area these temperatures are consistent with the presence of amphibolites sillimanite in gneisses and staurolite in schists no assemblages are suitable for estimating pressure combined geological geochronological and geochemical data suggest to us that the anshan group was deposited in a shallow water basin on or against a continental margin or basement and close to a magmatic arc during the accretion events associated with the 2 5 ga anshan orogeny arc driven granitic rocks intruded the basin and engulfed the supracrustal rocks leaving the bif etc as enclaves in ductile orthogneisses

c4 plant productivity and climate co2 variations in south central texas during the late quaternary abstract a continuous record of organic carbon 13c from a buried soil sequence in south central texas demonstrates 1 strong coupling between marine and adjacent continental ecosystems in the late pleistocene as a result of glacial meltwater entering the gulf of mexico and 2 ecosystem decoupling in the holocene associated with a reduction of meltwater and a shift in global circulation patterns in the late pleistocene reduction in c4 plant productivity correlates with two well documented glacial meltwater pulses 15 000 and 12 000 14c yr b p indicating a cooler than present adjacent continental environment increased c4 production between 11 000 and 10 000 14c yr b p suggests that the younger dryas was a warm interval responding to the diversion of glacial meltwater away from the mississippi river with waning meltwater flow c4 productivity generally increased throughout the holocene culminating in peak warm intervals at 5000 and 2000 14c yr b p shifts in the abundances of c3 c4 plants through the late quaternary show no correlation to ecophysiological responses to atmospheric co2 concentration

reconstruction of late pleistocene climate in the valsequillo basin central mexico through isotopic analysis of terrestrial and freshwater snails we aim to reconstruct the climatic and environmental conditions in the valsequillo basin during the deposition of the valsequillo gravels between c 40 000 and 8000 years ago when large mega fauna and potentially humans occupied the basin fossil freshwater fossaria sp and sphaeriidae family and terrestrial polygyra couloni holospira sp and cerionidae family snail shells from sections within the barranca caulapan were collected for oxygen and carbon stable isotope analysis oxygen and carbon isotopes in terrestrial and freshwater snail shells relate to local climatic parameters and environmental conditions prevailing during the lifetime of the snail whole shell isotope analysis showed that c 35 000 years ago climate in the valsequillo basin was similar to the present day between c 35 000 and 20 000 bp conditions became increasingly dry after which conditions became wetter again although this record is truncated intra shell isotopic analyses show that the amount of precipitation varied seasonally during the late pleistocene if people did reach this part of the americas in the late pleistocene they would have experienced changing long term and seasonal climatic conditions and would have had to adapt their life strategies accordingly

concentration of gold during retrograde metamorphism of archean banded iron formations slave province canada gold bearing iron formations are widely distributed within extensive metasedimentary terranes of the archean slave province situated in the northwestern canadian precambrian shield mineralized iron formations occur within thick turbidite sequences overprinted by a protracted history of deformation metamorphism and plutonism economically significant gold prospects are specifically sited at structural culminations characterized by polyphase folding based on garnet biotite geothermometry on the stable prograde metamorphic assemblage of enveloping metapelites peak metamorphic conditions are approximated to be 570 c and 4 kbar 1 kbar 100 mpa diagnostic prograde mineralogy reveals that two facies of silicate iron formation are represented at the five gold occurrences investigated 1 amphibolitic iron formation aif characterized by quartz grunerite hornblende pyrrhotite garnet f graphite ilmenite and 2 pelitic iron formation pif consisting of quartz biotite garnet ilmenite f grunerite hornblende textures reveal that grunerite crystallization preceded hornblende and garnet within aif banded pyrrhotite is in textural equilibrium with prograde metamorphic minerals retrograde hornblende garnet zoisite apatite carbonate ferroactinolite and gold bearing sulphide minerals replace the prograde mineral assemblages on the margins of quartz veins that intensify at aif fold hinges it is hypothesized that the iron formation hosted gold deposits of the slave province are a result of multistage processes gold concentrated at high background levels within pyrrhotite bearing aif was remobilized during fluid migration into brittle aif fold hinges in subsequent metamorphic and deformational events metamorphic fluid ponded in fractured aif hinge domains caused retrogressive replacement quartz veining and gold bearing sulphide precipitation during waning temperature although the mineralized hinge zones commonly display evidence of late chloritization this alteration did not further affect gold distribution the gold precipitated with destabilization of thio complexes due to sulphidation prior to lowtemperature hydrothermal activity

chemical sedimentary protoliths in the 3 75 ga nuvvuagittuq supracrustal belt quebec canada abstract analyses of chemical sedimentary precipitates such as banded iron formation bif provide a direct means to explore the nature and composition of the early hydrosphere the recently discovered 3750 myr old nuvvuagittuq supracrustal belt nsb in the northeast superior province quebec canada hosts a suite of iron oxide rich pyroxene and amphibole units that are interpreted to be the metamorphosed equivalents of fe oxide facies bif and a collection of bif like ca fe mg silicate rocks the nsb rocks provide a rare glimpse of trace metal availability in eoarchean ca 3800 ma seawater as they may be contemporaneous with the relatively well studied isua supracrustal belt of southern west greenland their comparison provides an opportunity to enhance our basic understanding of the eoarchean oceans at a global scale work since the initial discovery of the nsb in 2001 has established the basic lithological geochemical and petrographic characteristics of these bif and bif like rocks here we review the current state of knowledge of nsb rocks of probable chemical sedimentary origin including aspects of their geology likely origin and age we conclude by examining the implications of results thus far for our understanding of early seawater compositions and for the emergence of life in the context of early metallo enzyme evolution

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

thermodynamics of the amphiboles ca mg fe2 quadrilateral a thermodynamic model has been developed and calibrated for monoclinic and orthorhombic amphiboles compositionally contained within the ca mg fe 2 amphibole quadrilateral the model incorporates the energetic consequences of cation ordering of fe 2 and mg over nonequivalent sites in the crystal structure and accounts for the temperature pressure and compositional dependence of the orthorhombic monoclinic phase transition calibration is based on previously published work on the thermodynamic properties of fe 2 mg amphiboles and tremolite and experimental cation ordering data along with solvus width and tieline orientations of natural coexisting amphiboles in the quadrilateral among derived parameters is the enthalpy of formation of end member ferroactinolite 10534 966 kj mol a calculated femg 1 isopotential solvus at mid composition in the quadrangle agrees well with a revised calibration of experimental data from cameron 1975 the solvus is not strongly asymmetric and narrows with increasing fe mg ratio and temperature phase relations along the mg and fe sides of the quadrilateral are compared and contrasted cummingtonite anthophyllite phase relations are shown in the t x f e plane with and without coexisting calcic amphibole the breakdown reactions of quadrilateral amphiboles to assemblages of two pyroxenes olivine quartz and h 2 o are depicted as functions of temperature pressure composition h 2 o activity and oxygen fugacity some highlights of their relevance to metamorphic and igneous systems are discussed

paleoenvironment of the folsom archaeological site new mexico usa approximately 10 500 14c yr b p as inferred from the stable isotope composition of fossil land snail shells abstract well preserved aragonitic land snail shells vallonia from late pleistocene eolian sediment in the folsom archaeological site in new mexico exhibit an overall decrease of 18opdb from maximum values of 2 7 more positive than modern to younger samples with lower average values of about 3 6 within the modern range the age of the samples approximately 10 500 14c yr b p suggests that the decrease in 18o may manifest climatic changes associated with the younger dryas some combination of increased relative humidity and cooler temperatures with decreased 18o of precipitation during the times of snail activity can explain the decrease in shell 18o a well known paleoindian bison kill occurred at the folsom site during this inferred environmental transition average 13c values of the aragonite shells of the fossil vallonia range from 7 3 to 6 0 among different archaeological levels and are not as negative as modern values this suggests that the proportion of c4 vegetation at the folsom site approximately 10 500 14c yr b p was greater than at present a result which is consistent with other evidence for higher proportions of c4 plants in the region at that time

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

differentiation of pedogenic and lithogenic carbonate forms in texas abstract sixteen pedons representing soils developed from limestone and fluvial deltaic sediments were sampled in central and western texas 300 800 mm annual precipitation to differentiate pedogenic secondary and lithogenic inherited carbonate forms by field and laboratory techniques lithogenic carbonate forms identified in the field included indurated limestone bedrock and coarse limestone fragments lithorelicts field identified pedogenic forms included petrocalcic horizons thin laminar cappings on indurated limestone carbonate joint seams pendants on pebbles and carbonate films and threads on ped faces small

geochemical and mineralogic effects of contact metamorphism on banded iron formation an example from the transvaal basin south africa intrusion of a diabase sill into the paleoproterozoic kuruman iron formation transvaal basin south africa makes it possible to distinguish between effects of contact and regional metamorphism on mineralogic elemental and isotopic compositions of banded iron formation bif lithofacies temperatures within the aureole of contact metamorphism likely did not significantly exceed 450 c as suggested by the presence of early diagenetic carbonates greenalite and stilpnomelane formed prior to intrusion in chert rich facies as close as 4 m from the sill in sediments 32 m away from the intrusion a temperature of 280 c is indicated by the magnitude of 18o fractionation between successive chert and siderite microbands in unmetamorphosed equivalents similar isotopic analyses on whole rock samples yield temperature estimates between 150 and 230 c in comparison with samples of similar lithofacies from the underlying campbellrand kuruman transition zone carbonates from within the metamorphic aureole are depleted in 13c and 18o the abundance and c isotopic composition of total organic c toc in whole rock samples is lower and more enriched in 13c than those in samples outside of the zone of contact metamorphism within 5 m of the diabase sill the abundance of fe increases dramatically and the oxidation state of the sediments fluctuates considerably more than in sediments outside of the metamorphic aureole isotopic and mineralogic systematics in the zone of contact metamorphism in the kuruman iron formation are similar to those in siliceous dolomites and limestones altered by similar thermal processes as the most distinct isotopic and elemental variations occur within 10 m of the diabase sill it is suggested that volatilization and fluid infiltration associated with the intrusion were the main processes of alteration consideration of the effects of metamorphism both contact and regional as well as early diagenesis on the mineralogy and isotopic chemistry of bif sediments may be a key to our understanding of primary mineralogies and oxidation state of these enigmatic deposits

metamorphic alteration mineral paragenesis and geochemical re equilibration of early archean quartz amphibole pyroxene gneiss from akilia southwest greenland quartz amphibole pyroxene gneiss from the island of akilia southwest greenland has been claimed to contain the earliest traces of life on earth in the form of biogenic carbonaceous matter encapsulated as inclusions in apatite crystals various lines of evidence including petrography geochronology field relations and geochemistry have however been presented that challenge this interpretation textural relationships and geochemical signatures in this controversial gneiss presented here manifest a complex spatially variable metamorphic history that includes granulite and amphibolite facies overprints and metasomatism a peak metamorphic granulite facies quartz orthopyroxene clinopyroxene amphibole magnetite assemblage is preserved in only a few centimeter scale layers within the 5 m thick quartz amphibole pyroxene gneiss unit calcite veinlets that appear to postdate the peak metamorphism occur in pyroxene the quartz amphibole pyroxene gneiss unit has subsequently experienced isochemical except hydration amphibolite facies alteration during which pyroxenes were retrogressed to amphiboles and magnetite and calcite was consumed parts of the quartz amphibole pyroxene gneiss that contain texturally late hornblende have experienced metasomatic alteration by al carrying fluids these fluids controlled the alteration of pyroxenes and amphiboles to hornblende and modified the trace element composition by remobilizing lree and eu apatite has variable ree composition and 87sr 86sr in the quartz amphibole pyroxene gneiss but on the local scale cm is in equilibrium with co existing silicates effective recrystallization of apatite crystals as well as co existing silicates during several stages of the metamorphic history makes the intact preservation of diagenetic apatite with encapsulated primary carbonaceous matter implausible hence it is highly unlikely that akilia apatite could serve as repository of the earliest traces of life on earth

metasomatic rocks with greisenization associated with the ore bearing zones in the iron mountains železne hory mountains eastern bohemia czechoslovakia in the central iron mountains the ore mineralized deformation zones represent deep reaching faults which possibly reach the upper mantle during geological history they were used by ascending magmas fluids and barren and ore hydrothermal solutions it can be shown that the metasomatism provoked by acid fluids bears the character of greisenization the type of the original greisenized rocks here can be determined on the basis of elements that were immobile during greisenization especially si ti sc and ree after or even during greisenization the metasomatic rocks were affected by shearing metamorphism corresponding in its pt conditions to the middle zone of the almandine amphibolite facies it was possibly in this period that the enigmatic skarn body of sama ov originated owing to its similarity to the dyke skarn of kraskov its similar origin could be assumed the deposition of skarn minerals from circulating fluids which were perhaps released during greisenization

metamorphic petrology of the negaunee iron formation marquette district northern michigan mineralogy metamorphic reactions and phase equilibria progressive regional metamorphism of the negaunee iron formation in the marquette district from chlorite to sillimanite grade has resulted in the development of three metamorphic zones and two subzones the diagnostic zone assemblages are in order of increasing grade 1 siderite quartz or ankerite or minnesotaite or stilpnomelane or magnetite 2 grunerite or quartz or ankerite or magnetite and grunerite or siderite or ankerite or magnetite 3a grunerite or garnet or quartz or magnetite and grunerite or ca amphibole or quartz or calcite or magnetite 3b grunerite or olivine or clinopyroxene or quartz or calcite or magnetite and grunerite or ca amphibole or olivine or magnetite the grunerite garnet and ca amphibole and olivine and clinopyroxene isograds define the boundaries between the respective zones and subzones temperature estimates are approximately 300 degrees c for zone 1 and approximately 600 degrees c for subzone 3b pressure is estimated at between 200 to 300 mpa microprobe analyses of coexisting minerals indicate general attainment of exchange equilibrium and a strong localized influence of bulk composition on mineral chemistry theoretical analysis of phase relations on isobaric t x sub co 2 diagrams leads to the following conclusions 1 throughout zone 1 minnesotaitc bearing assemblages are diagnostic of low x sub co 2 values stilpnomelane bearing assemblages represent low to medium values and chlorite bearing assemblages represent medium to high x sub co 2 values juxtaposition of these three assemblages at one locality indicates that fluid phase compositional gradients most likely existed 2 throughout zone 3 actinolite hornblende and garnet bearing assemblages reflect similar low to high x sub co 2 values the continued juxtaposition of these various assemblages suggests the continued presence of fluid phase compositional gradients into the highest grade metamorphic zones 3 metamorphic reactions caused substantial localized co 2 enrichment in the coexisting fluid phase a diversity of t x sub co 2 paths was followed typically differing on the scale of individual mesobands

oxygen and carbon stable isotopes of modern land snail shells as environmental indicators from a low latitude oceanic island abstract land snails provide a unique opportunity to study terrestrial paleoenvironments because their shells which are generally highly abundant and well preserved in the fossil record contain a temporal record of environmental change in the form of isotope codes to evaluate the utility of this approach for a low latitude oceanic setting 207 modern shells of 18 species of land snail were analyzed for their oxygen and carbon isotope composition along a north and south facing altitudinal gradient 10 2160 m a s l in tenerife island 28 n of the canary archipelago shells collected at each locality showed a relatively large range in isotope composition which was greater along the south facing transect drier and hotter suggesting that the variance in shell isotope values may be related to water stress although pooled isotope values did not generally show strong relationships with environmental variables i e altitude temperature and precipitation mean isotope values were strongly associated with some climatic factors when grouped by site the mean 18o value of the shell 18oshell by site displayed a negative correlation with elevation which is consistent with the positive relationship observed between temperature and the 18o value of rain 18orain calculated 18o values of the snail body water 18obody derived from observed temperatures and 18oshell values using the equation of grossman and ku grossman e l and ku t l 1986 oxygen and carbon isotope fractionation in biogenic aragonite chem geol isotope geosci sec 59 59 74 displayed a trend with respect to altitude that was similar to measured and hypothetical 18o values for local rain water the calculated 18obody values from the shell declined 0 17 vsmow per 100 m which is consistent with the altitude effect observed for tropical rains in western africa and it correlated negatively with rainfall amount accordingly lower 18oshell values indicate lower temperatures lower 18orain values and possibly higher rainfall totals a positive correlation between the mean 13c values of shells 13cshell and plants by site suggests that shells potentially record information about the surrounding vegetation the 13cshell values varied between 15 7 and 0 6 vpdb indicating that snails consumed c3 and c4 cam plants where more negative 13cshell values probably reflects the preferential consumption of c3 plants which are favored under wetter conditions individuals with more positive 13cshell values consumed a larger percentage of c4 plants other potential factors such as carbonate ingestion or atmospheric co2 contribution were unlikely that were more common at lower elevations of the hotter and drier south facing transect the relatively wide range of shell isotope values within a single site requires the analysis of numerous shells for meaningful paleoclimatic studies although small differences were observed in isotope composition among snail species collected at a single sampling site they were not significant suggesting that isotope signatures extracted from multi taxa snail data sets may be used to infer environmental conditions over a broad range of habitats

radiocarbon and δ13c depth profiles of soil organic carbon in the u s great plains a possible spatial record of paleoenvironment and paleovegetation abstract soil profiles from undisturbed grassland sites around the great plains of the usa were sampled for analysis of soil organic carbon soc content radiocarbon age and stable carbon isotope composition 13 c with the exception of a few pronounced dating anomalies soc radiocarbon age generally increases steadily with depth back to 10 15 000 cal yr bp the deepest soil intervals in 9 of the 12 sites the radiocarbon ages were used to establish the chronology of changes in past plant distribution over time and space based on soc 13 c as an indicator of c 3 and c 4 plant abundance changes were referenced to an soc 13 c value of 20 which is the approximate mid point between c 3 and c 4 carbon isotope composition i e an equal mixture of c 3 and c 4 carbon prior to 10 000 cal yr bp the region was dominated by c 3 plants with the exception of the southernmost texas sites from 10 000 to 2000 cal yr bp c 4 plants expanded their range initially as a peninsula of c 4 predominant grasses extending northeastward and ultimately dominating all but the northernmost border of the region finally the c 3 predominant region re expanded after 1000 cal yr bp perhaps as a response to the little ice age cooling despite uncertainties associated with using radiocarbon dated soc depth profiles as a proxy the past c 3 and c 4 plant distribution inferred from soc 13 c conforms well to results from other paleoclimate proxies and differences may be helpful in targeting future research

implications for late holocene climate from stable carbon and oxygen isotopic variability in soil and land snail shells from archaeological site 41km69 in texas usa abstract well preserved fossil land snail shell collected in a 115 cm soil profile from archaeological site 41km69 in texas usa minimally span the past 2200 years and provide an opportunity to explore the paleoclimate implications of isotopic variability in shell carbonates bulk soil carbonates and soil organic matter carbon isotopic compositions 13 c values of modern and archaeological adult snail shell carbonates suggest significant 60 dietary input of c 3 plants during all periods oxygen isotopic compositions of shells suggest that the isotopic composition of environmental water available at the time of shell growth has changed little over the period of the profile a linearly decreasing trend in 13 c of soil organic matter from 22 8 at the bottom of the profile 115 cm below surface to 25 6 for modern surface samples indicate an overall 20 increase in abundance of c 3 plants this implies a progressively wetter climate and less severe water stress conditions or decreasing summer rainfall that is in agreement with other studies on late holocene climate change in the southern great plains usa these results strongly suggest a stable climate that favored c 3 vegetation in this portion of texas during this period

tethyan to boreal correlation in the kimmeridgian using high resolution sequence stratigraphy vocontian basin swiss jura boulonnais dorset ammonite biostratigraphy plays a central role in the definition of jurassic stratigraphy nevertheless the strong provincialism of european ammonite species during the kimmeridgian is a long standing problem in correlation attempts between the boreal and tethyan faunal realms moreover the sequence stratigraphic interpretations for northern and southern europe given in the jurassic chronostratigraphic chart of hardenbol et al in sepm publ 60 chart 1998 are different the present study aims to resolve this correlation problem in order to better understand the connections between the boreal and the tethyan realms during the kimmeridgian a sedimentological and high resolution sequence stratigraphic interpretation is presented for two unpublished sections cras d hermont and roche de mars in the northern swiss jura where recently discovered ammonites display both boreal and tethyan influences then these sections are correlated with the same time interval in the central swiss jura and vocontian basin which belong to the tethyan realm lastly a long distance transect is constructed between the vocontian basin swiss jura northern france and southern england the last two areas being part of the sub boreal realm the main results of this work are that 1 third order depositional sequences and also higher frequency sequences can be correlated from the tethyan to the boreal realm 2 the sequence stratigraphic interpretation given by hardenbol et al in sepm publ 60 chart 1998 for northern europe seems to be accurate and agrees with the sequence stratigraphic framework established in the swiss jura 3 the late kimmeridgian of the swiss jura displays boreal influences 4 integrated high resolution sequence stratigraphic and cyclostratigraphic studies are a valuable approach for bridging the correlation gap between northern and southern europe

sedimentary and metamorphic lithofacies of the lower negaunee iron formation marquette district michigan usa the base of the proterozoic negaunee iron formation is exposed in the open pit at tilden mine marquette michigan juxtaposed against the archean aged palmer gneiss it is bounded by the regional scale southern shear zone and cut by two sets of dykes an older chloritic and schistose set and a younger 1 1 ga keweenawan set tilden mine is dominated by a 100 m scale plunging northwest anticline and is cut by a growth fault locally termed the tower hill fault that intersects the southern shear zone the base of the exposed iron formation is composed of three lithofacies including lower clastics that grade into the overlying banded iron formation that in turn grades upward into granular iron formation this succession is capped by chloritic metadiabases locally termed the summit hill sill and pillar intrusive petrographic and mineral chemical investigations document primary or early diagenetic hematite siderite and possibly ferri hydrite metamorphic and related hydrothermal magnetite chlorite late mar

stable carbon and oxygen isotopic variations in modern rabdotus land snail shells in the southern great plains usa and their relation to environment abstract variations of stable isotopic ratios of carbon 13c 12c and oxygen 18o 16o were investigated in modern shells of two species of rabdotus land snails r dealbatus and r alternatus in the southern great plains geographic variation in relation to climate and vegetation microgeographic variation variability among individuals and detailed records of seasonal variations within individual shells were studied stable carbon isotopic ratios in shell carbonate are primarily a function of the isotopic composition of the diet of the snails as represented by the isotopic composition of shell organic matter this in turn reflects the presence or absence of cam crassulacean acid metabolism or c4 plants vegetation density may have a small effect on the carbon isotope ratios microgeographic variation samples within 25 to 300 m is greater than that seen across different climatic regions and points to very local control of isotopic variations predominantly related to vegetation seasonal variations as assessed through serial analysis of individual shells up to 35 samples per shell may provide a means for distinguishing between isotopic influences of perennial cam vs annual c4 plants carbon isotopic variations in time series of shells from a site provide a means of reconstructing temporal changes in environment and climate oxygen isotopic values of shell carbonate are uniform across the region and also show no significant microgeographic variation the oxygen isotopic composition appears to be mainly a function of the rainwater isotopic composition with no direct influence of rainfall amount or evaporative effects the 18o values are only 2 enriched relative to estimated equilibrium with rainwater variability is low sd of 0 8 among sites so the isotopic composition of fossil rabdotus shells can provide a precise record of changes in the isotopic composition of rain over time

environmental significance of 13c 12c and 18o 16o ratios of modern land snail shells from the southern great plains of north america c 12 c and 18 o 16 o ratios of aragonite shells of modern land snails from the southern great plains of north america were measured for samples from twelve localities in a narrow east west corridor that extended from the flint hills in north central oklahoma to the foothills of the sangre de cristo mountains in northern new mexico usa across the study area shell y 18 o values pdb scale ranged from 4 1x to 1 2x while y 13 c values ranged from 13 2x to 0 0x y 18 o values of the shell aragonite were predicted with a published steady state evaporative flux balance model the predicted values differed with one exception by less than 1x from locality averages of measured y 18 o values this similarity suggests that relative humidity at the time of snail activity is an important control on the y 18 o values of the aragonite and emphasizes the seasonal nature of the climatic information preserved in the shells correlated y 13 c values of coexisting vallonia and gastrocopta suggest similar feeding habits and imply that these genera can provide information on variations in southern great plains plant ecology although there is considerable scatter multispecies transect average y 13 c values of the modern aragonite shells are related to variations in the type of photosynthesis i e c3 c 4 in the local plant communities the results of this study emphasize the desirability of obtaining isotope ratios representing averages of many shells in a locale to reduce possible biases associated with local variations among individuals species etc and thus better represent the bneighborhoodq scale temporal and or spatial environmental variations of interest in studies of modern and ancient systems d 2004 university of washington all rights reserved

stable isotope composition of middle to late holocene land snail shells from the marroquies archeological site jaen southern spain paleoenvironmental implications abstract the marroquies archeological site located in the metropolitan area of jaen 37 46 southern spain contains land snail shells which have been preserved jointly with other human and zooarcheological remains new radiocarbon analyses carried out on pristine domestic animal and human bones confirmed that these remains belong to the copper age interval 4470 3880 cal bp n 8 land snail entire shells of two species one herbivorous and one omnivorous were analyzed for 13 c 12 c and 18 o 16 o ratios to estimate the paleoenvironmental conditions prevailing during the middle to late holocene in the southernmost part of europe the 13 c values of fossil shells ranged from 13 8 to 8 1 n 15 whereas modern specimens ranged from 10 8 to 8 6 n 20 the fact that ancient and modern shells generally exhibited similar 13 c values suggests that the 13 c values of the vegetation have remained relatively stable during 4470 3880 cal bp and the present snail species did not differ in 13 c values despite their differing dietary habits the 18 o values of fossil shells ranged from 4 9 to 1 2 n 15 whereas modern specimens ranged from 2 8 to 0 9 n 20 fossil shells were on average 2 lower in 18 o values than modern shells calculations from a snail evaporative steady state flux balance model suggest that shells at 4470 3880 cal bp precipitated under appreciably higher relative humidity conditions than today whereas rain 18 o values and air temperatures at the soil air interface during snail active period were possibly similar although samples from this study represent a time period in which the well documented late holocene aridification trend in southern spain already started snails suggest conditions at 4470 3880 cal bp were yet noticeably wetter than at present this study shows that land snail shells preserved in holocene archeological sites offer valuable paleoenvironmental information in their isotope codes

phase equilibria in the system k 2 o feo mgo al 2 o 3 sio 2 h 2 o co 2 and the stability limit of stilpnomelane in metamorphosed precambrian iron formations the phase relations of al and fe bearing silicates in the system k2o feo mgo al2o3 sio2 h2o co2 in the presence of quartz and magnetite are discussed on the basis of mineralogic and petrologic data from precambrian iron formations and blueschist facies meta ironstone from the franciscan formation california these relations allow an estimation of the physiochemical conditions during low grade metamorphism of iron formations petrologic data together with available experimental and predicted thermodynamic data on the associated minerals place the upper stability limit of stilpnomelane in iron formations at about 430 470 c and 5 6 kilobars fe end member stilpnomelane can persist to a maximum temperature of 500 c and pressures up to 6 7 kilobars although it is unlikely to occur in metamorphosed iron formations in iron formation occurrences the stilpnomelane stability field is bordered by four equilibrium reactions with the assemblages stilpnomelane zussmanite chlorite minnesotaite stilpnomelane zussmanite chlorite grunerite stilpnomelane biotite chlorite grunerite and stilpnomelane biotite almandine grunerite the stability field is reduced by increasing x co2 and xmgstil and is also a function of a k a h in the metamorphic fluid if the value of a k a h is smaller than that defined by the above assemblages stilpnomelane decomposes to chlorite but if larger it is replaced by biotite at pressures less than 4 kilobars the zussmanite field is restricted to a very high value of a k a h 5 0 in log units at 1 0 kilobar where iron formation assemblages are not stable