Elemental Abundance Data Research Articles

Platinum-rhenium-osmium isotope systematics of chromitite and native osmium from the Guli Massif (Maimecha-Kotui Province, Russia)

To gain insight into the source of ore material, this study presents the first Re-Os and Pt-Os isotopic and highly siderophile element (HSE) abundance data for chromitite and osmium minerals from the Guli massif of ultramafic, alkaline rocks and carbonatites located in the Maimecha-Kotui province, Polar Siberia. The study utilized a number of analytical techniques, including electron microprobe analysis, negative thermal ionization mass spectrometry (N-TIMS) and high pressure asher digestion and an isotope dilution-inductively coupled plasma-mass spectrometry. The HSE concentrations in chromitite samples range from 191 to 866 ppb with a predominance of Ir-group platinum-group elements (PGE) (Os, Ir and Ru) over Pt-group PGE (Rh, Pt and Pd) and Re, which is consistent with their platinum-group mineral control (i. e., Os-Ir alloys and laurite, RuS2) within the chromitite. The Re-Os and Pt-Os isotope data indicate that the HSE budget of the chromitite and osmium minerals from the Guli massif was largely controlled by that of the mantle source, which evolved with long-term near-chondritic Re/Os and Pt/Os ratios; this source is within the range of those for the majority of komatiite and abyssal peridotite sources.

Paleozoic Equatorial Records of Melting Ice Ages (PERMIA): calibrating the pace of paleotropical environmental and ecological change during Earth's previous icehouse

Abstract. The upper Paleozoic Cutler Group of southern Utah, USA, is a key sedimentary archive for understanding the Earth-life effects of the planet's last pre-Quaternary icehouse–hothouse state change: the Carboniferous–Permian (C–P) transition, between 304 and 290 million years ago. Within the near-paleoequatorial Cutler Group, this transition corresponds to a large-scale aridification trend, loss of aquatic habitats, and ecological shifts toward more terrestrial biota as recorded by its fossil assemblages. However, fundamental questions persist. (1) Did continental drift or shorter-term changes in glacio-eustasy, potentially driven by orbital (Milankovitch) cycles, influence environmental change at near-equatorial latitudes during the C–P climatic transition? (2) What influence did the C–P climatic transition have on the evolution of terrestrial ecosystems and on the diversity and trophic structures of terrestrial vertebrate communities? The Paleozoic Equatorial Records of Melting Ice Ages (PERMIA) project seeks to resolve these issues in part by studying the Elk Ridge no. 1 (ER-1) core, complemented by outcrop studies. This legacy core, collected in 1981 within what is now Bears Ears National Monument, recovered a significant portion of the Hermosa Group and the overlying lower Cutler Group, making it an ideal archive for studying paleoenvironmental change during the C–P transition. As part of this project, the uppermost ∼ 450 m of the core were temporarily transferred from the Austin Core Repository Center to the Continental Scientific Drilling Facility at the University of Minnesota for splitting, imaging, and scanning for geophysical properties and spectrophotometry. Here we (1) review the history of this legacy core, (2) introduce recently obtained geophysical and lithologic datasets based on newly split and imaged core segments to provide a sedimentological and stratigraphic overview of the Elk Ridge no. 1 core that aligns more accurately with the currently recognized regional lithostratigraphic framework, (3) establish the position of the boundary between the lower Cutler beds and the overlying Cedar Mesa Sandstone in the core, and (4) outline our ongoing research goals for the core. In-progress work on the core aims to refine biostratigraphic and chemostratigraphic age constraints, retrieve the polarity stratigraphy, interrogate preserved cyclostratigraphy, analyze sedimentary structures and paleosol facies, investigate stable isotope geochemistry, and evaluate elemental abundance data from X-ray fluorescence (XRF) scanning. Together with outcrop studies throughout Bears Ears National Monument and its vicinity, these cores will allow the rich paleontological and paleoenvironmental archives recorded in the continental Carboniferous–Permian transition of western North America to be confidently placed in a robust chronologic context that will help test hypotheses relating ecosystem evolution to the Carboniferous rainforest collapse, initial decline of the Late Paleozoic Ice Age, and long-wavelength astronomical cycles pacing global environmental change.

Expedient Bayesian prediction of subfossil bone protein content using portable ATR-FTIR data

Rapid and minimally destructive methods for estimating the endogenous organic content of subfossil bone save time, lab consumables, and valuable ancient materials. Fourier transform infrared (FTIR) spectroscopy is an established method to estimate bone protein content, and portable spectroscopes enable field applications. We review the ability of benchtop and portable FTIR indices to predict %N and %collagen from 137 bone specimens drawn from eight taxa. We also explore associations of these indices with the endogenous DNA content estimated for 105 specimens. Bulk bone elemental abundance and crystallinity index data reflect diagenetic alteration of these specimens, which come from a variety of depositional environments in four countries (Madagascar, Greece, Monaco, and Germany). Infrared (IR) indices from benchtop and portable units perform similarly well in predicting observed sample N content and collagen yields. Samples that include little collagen (0–5 wt%) tend to have similar IR index values, and we present a Bayesian approach for the prediction of collagen yields. Bone type best explains variation in target species DNA content (endogenous DNA being particularly abundant in petrosals), but low IR index values were consistently associated with minimal DNA content. We conclude that, although portable FTIR fails to distinguish collagen preservation among poorly preserved samples, a simple approach with minimal sample preparation can effectively screen bone from a variety of taxa, elements, and environments for the extraction of organics.

Revisiting the Petrogenesis of Pyroclastic Glass Bead Deposits at the Apollo 15 and 17 Sites

Abstract The Apollo 15 low-titanium and Apollo 17 high-titanium pyroclastic glass beads are among the most primitive magmatically derived samples obtained from the Moon. Two key samples, the low-Ti Apollo 15426 green glass clod and the high-Ti Apollo 74220 orange glass are morphologically distinct, where the Apollo 15 beads are larger (~107 μm along maximum axis) and more fractured, and the Apollo 17 are smaller (~42 μm) and less fractured. In this study, holohyaline beads as well as crystallized beads were examined from both samples using petrography, electron microprobe analysis, and laser-ablation inductively coupled plasma mass spectrometry. Crystallized beads show compositional variability in major, minor, and trace elements and enable examination of magmatic mineral fractionation processes during cooling of both deposits. The Apollo 15426 beads experienced variable olivine crystallization, whereas the Apollo 74220 beads experienced both olivine and ilmenite crystallization. Holohyaline beads from both deposits show more limited major, minor, and trace element variability than their crystallized counterparts. Trace element abundance data for individual holohyaline beads show that in Apollo 74220, they are tightly clustered at ~30× Carbonaceous Ivuna chondrite [CI] with negative Eu anomalies and subchondritic Nb/Ta, interpreted to reflect the presence of late-stage magma ocean cumulates overturned into an otherwise primitive mantle source. Incompatible trace element abundances for holohyaline beads in 15426 are supra-chondritic from ~8× CI, to >80× CI, with pronounced relative depletions in Sr and Eu for the most incompatible element enriched beads, which represent a distinct bead group within the deposit. Apollo 15426 beads have elevated Ni and Co abundances at the edges of the beads compared to their centers. These data are interpreted to reflect a more complex magmatic evolution of the 15426 deposit, beginning with (i) initial magma generation, storage, and assimilation within shallower low- and high-Ca pyroxene bearing magma ocean cumulates (15B,C); (ii) mobilization of the earlier magmas by more recently generated primitive magmas (15A); (iii) eruption and crystallization of some beads (15D,E); and (iv) later jumbling of the deposit, possible impact contamination and addition of exotic basaltic bead components (J Group). In contrast, the 74220 data show no discernable difference between Ni and Co abundances at the edges and centers supporting prior observations for limited melt fractionation and an absence of meteoritic components. Both deposits are likely to have been formed in the presence of a transient atmosphere. Using 74220 melt compositions from this study, post-entrapment crystallization abundances range from 266 to 1130 μg/g for H2O, 36 to 68 μg/g for F, 441 to 832 μg/g for S, and 0 to 2.31 μg/g for Cl, consistent with prior studies and suggesting up to ~0.1 wt % H2O in the melt, with considerably less in the source. The role that late-stage magma ocean cumulates rich in ilmenite and high-Ca pyroxene might play in modifying this volatile element estimate, however, casts remaining doubt on the volatile element abundance and evolution of the primitive Moon.

Estuaries House Earth’s oldest known non-marine eukaryotes

Some of the oldest postulated non-marine eukaryotic microfossils occur in the 1.1–1.0 Ga Poll a’Mhuillt, Loch na Dal, and Diabaig formations in NW Scotland. These sedimentary strata have traditionally been interpreted as lacustrine. Here we report new trace element, sulfur isotope and metal abundance data and sedimentological observations for the latter two units. The geochemical data imply low salinity, oxic conditions whereas sedimentological features indicate marine tide and storm processes. Interpreting their depositional settings as estuaries, rather than lakes, with seawater-freshwater mixing fronts reconciles the contrasting datasets. Thus, whist these microbial habitats likely experienced frequent seawater input, they appear to have experienced the lowest salinity conditions of all known in situ fossil assemblages in the Precambrian. The Torridonian may in fact be representative of the low-salinity habitats predicted for ancestral eukaryotes based on phylogenetic reconstructions. Estuarine settings with gradients in water chemistry over space and time may have facilitated the transition of eukaryotic life from land to sea.

Describing geochemical backgrounds of lithium in rock-soil-sediment systems

An empirical equation has been proposed to describe geochemical backgrounds of trace elements during rock weathering on weathering and lithological indices. However, with respect to lithium, the equation was derived on only 9 regolith profiles in China and was not applicable to carbonate-bearing materials with WIG (weathering index of granite) larger than 120. To derive a robust and widely used equation on geochemical backgrounds of lithium, 851 elemental abundance data including 379, 280, and 192 records of rocks, soils, and stream sediments, respectively, were used to fit the new equation.lgc = −0.02630xy2z + 0.03000xyz2 + 0.03540xy + 0.6425y + 3.288 for WIG<20 （1）lgc = 0.00001579x2yz + 0.001141y2xz - 0.9445y + 0.3650z for 20≤WIG<120 （2）lgc = 0.1849xy2z + 0.03382xyz2 + 0.6839xyz - 09414x - 1.471y + 1.070z for WIG≥120 （3）where c is the calculated geochemical background of Li in μg/g. WIG is the weathering index of granite. The x in Eq. (1) and Eq. (2) is WIG and is lg(WIG) in Eq. (3). The y is lg(Al2O3/Ti) where Al2O3 and Ti represent their contents with units of wt% and μg/g respectively. The z is lg(K2O/SiO2) where K2O and SiO2 represent their contents in wt%. The fitting data of Li, WIG, Al2O3/Ti, and K2O/SiO2 are 3.5–70 μg/g, 6.9–9400, 0.0003–0.0356, and 0.0006–0.1410, respectively. By comparison with the previous equation in a linear fitting, the newly presented equation in a nonlinear fitting is applicable to geological materials without WIG limitations. However, to the materials with WIG ranging from 0 to 120, the fitted results between the previous and the newly presented equations are generally similar. In summary, the new equation works well to describe lithium geochemical backgrounds of geological materials and could play an important role in environmental and exploration geochemistry. In mineral exploration, the method of seven levels' classification of geochemical anomaly can be improved on this newly presented equation and has been validated in the Tieshanlong tungsten deposit area in Southeastern China.

Comment on Mints not Mines: a macroscale investigation of Roman silver coinage by J.R. Wood, M. Ponting, and K. Butcher

Wood et al. (2023), hereinafter WPB, unveils a number of historical issues relevant to Roman economy and metallurgy based on trace element and Pb isotope abundance data on a large set of important coins minted during the Roman Empire (Ponting and Butcher 2015). Here, we discuss several points which, in our view, misrepresent the work of other groups, ours included, and bias the overall interpretation of the WPB data set.

Pristinity and petrogenesis of eucrites

AbstractNew petrography, mineral chemistry, and whole rock major, minor, and trace element abundance data are reported for 29 dominantly unbrecciated basaltic (noncumulate) eucrites and one cumulate eucrite. Among unbrecciated samples, several exhibit shock darkening and impact melt veins, with incomplete preservation of primary textures. There is extensive thermal metamorphism of some eucrites, consistent with prior work. A “pristinity filter” of textural information, siderophile element abundances, and Ni/Co ratios of bulk rocks is used to address whether eucrite samples preserve endogenous refractory geochemical signatures of their asteroid parent body (i.e., Vesta), or could have experienced exogenous impact contamination. Based on these criteria, Cumulus Hills 04049, Elephant Moraine 90020, Grosvenor Range 95533, Pecora Escarpment 91245, and possibly Queen Alexander Range 97053 and Northwest Africa 1923 are pristine eucrites. Eucrite major element compositions and refractory incompatible trace element abundances are minimally affected by metamorphism or impact contamination. Eucrite petrogenesis examined through the lens of these elements is consistent with partial melting of a silicate mantle that experienced prior metal–silicate equilibrium, rather than as melts associated with cumulate diogenites. In the absence of the requirement of a large‐scale magma ocean to explain eucrite petrogenesis, the interior structure of Vesta could be more heterogeneous than for larger planetary bodies.

Metal production in the early Universe: what chemical abundances in old stellar populations in the Milky Way tell us

AbstractOld stellar populations in our Galaxy provide fossil records of the metal enrichment in the first few billion years of the cosmic history. Growing elemental abundance data of individual stars combined with stellar ages and kinematics allow us to make constraints on characteristic properties of the metal-enrichment sources in the early Universe, such as the first stars. In order to interpret observed chemical abundances in the oldest stellar populations in terms of metal-enrichment sources, stellar and supernova yield models are crucial. In this article, we review how we can interpret observed chemical abundances in old stars in terms of the nature of metal enrichment sources. We discuss the limitations and the prospects of empirically constraining supernova yield models based on a large sample of extremely metal-poor stars. At the same time, we emphasize the importance of hunting old stars beyond the Solar neighborhood, which can be achieved with the next-generation multi-object spectrographs at large telescopes.

A partial isotopic decomposition for the sculptor dSph

Abstract All stellar evolution models require an initial isotopic abundance set as input, but these abundances are well known only for the Sun. Yet, input compositions can be estimated by scaling solar abundances using a previously constructed isotopic history model based on astrophysical processes in the Milky Way (MW). This method, however, may not work for obtaining inputs for compositions that have distinct chemical histories from the MW. We thus present a partial isotopic history model for the Sculptor dwarf spheroidal galaxy based on astrophysical processes, which can be used to estimate input isotopic abundances in future nucleosynthesis studies. The model is fitted to observational data, and follows the methodology of the previously constructed MW isotopic history model. First, we estimate the isotopic composition of Sculptor’s late-stage evolution (LSE) using the OMEGA chemical evolution code, and then decompose that composition into contributions from various astrophysical sources. Each contribution is then assumed to scale as a function of metallicity. The isotopic abundances are summed into elemental abundances and fit to available observational elemental abundance data to tune the model’s free parameters. The result is an average isotopic history model of Sculptor for massive star, Type Ia SNe, s-process, and r-process contributions that uses elemental data to constrain the isotopic abundances. As an example, our model finds that Type Ia SNe contribute ≈ 87 percent to the LSE Fe abundance, and neutron star mergers contribute ≈ 36 percent to the LSE Eu abundance, in agreement with previous studies.

Evidence for Seawater Retreat With Advent of Meghalayan Era (∼4200 a BP) in a Coastal Harappan Settlement

AbstractThe transformation of mature (urbanized) phase of the ancient Indus civilisation between ∼4200 and 3800 years Before Present (yr BP) overlaps with the beginning of the Meghalayan Age (∼4200 ± 100 yr BP). Though exact cause(s) for decline of urbanized Indus phase are not yet clear, researchers continue to debate whether monsoonal dryness was the sole cause or several other regional factors manifested in a compounding manner. Here, we show a regional relative sea level fall in the downstream area of Indus habitation (south‐western Gujarat region) which initiated at 4150 ± 230 and continued up to 3625 ± 200 yr BP. We provide a multi‐proxy (chronological, sedimentological, mineralogical, isotopic and elemental abundance) data set from a well‐dated vertical sediment trench from Lothal (ancient dockyard area of Indus era) to support this inference. Chief proxies used for inferring the relative sea level fall were bulk sediment carbon and sulfur contents along with their stable isotopes (δ13C and δ34S) and foraminiferal assemblage. The conspicuous shifts in majority of proxies hint at a lowering of sea stand at the regional level that likely dried this ancient Harappan dockyard (used for sea trade). Findings of our study possess implications for Holocene climate changes and their plausible impact(s) on Harappan trade and culture. Additionally, it invites evidences for large scale geological changes at ∼4200 yr BP distinct to the Meghalayan era.

Early global mantle chemical and isotope heterogeneity revealed by the komatiite-basalt record: The Western Australia connection

Although the heterogeneous nature of the chemical composition of Earth's mantle is now well established, the origin and longevity of the heterogeneities continue to be debated. In order to further study early-Earth heterogeneities, we present a set of Sm-Nd, Lu-Hf, Re-Os, and Hf-W isotope and lithophile and siderophile element abundance data for komatiites and basalts from the ∼3.53 Ga Coonterunah, ∼3.34 Ga Kelly, and ∼3.18 Ga Ruth Well and Regal systems of the Pilbara Craton in Western Australia. The Sm-Nd, Lu-Hf, and Re-Os isotope data yield isochrons consistent with the accepted emplacement ages of the respective komatiite-basalt lavas. The mantle sources evolved with long-term 147Sm/144Nd = 0.200 to 0.214 and 176Lu/177Hf = 0.0355 to 0.0395, spanning the entire range of the time-integrated Sm/Nd and Lu/Hf measured in the Archean and Proterozoic komatiite-basalt systems to-date. Unlike with the other early Archean komatiites and basalts, the coupled 143Nd-176Hf isotope systematics of the Pilbara lavas provide no evidence for the involvement of early magma ocean processes in the evolution of their mantle sources. Episodes of variable degrees of partial mantle melting and melt extraction can account for the observed large variations in the time-integrated Sm/Nd and Lu/Hf ratios in the early Archean mantle domains.In contrast to the highly variable Nd-Hf systematics, the initial γ187Os values vary within a narrow range from +0.9 to −0.4 indicating that the Pilbara mantle sources evolved with chondritic time-integrated Re/Os. The apparent discrepancy between the depletions in incompatible lithophile trace elements and near-chondritic Re/Os observed globally is reconciled via a model whereby early low-degree mantle melting events fractionated Sm from Nd and Lu from Hf, but had little effect on the Re/Os ratio. This in turn would imply early formation and long-term isolation of a basaltic crust highly enriched in incompatible lithophile trace elements.The calculated total HSE abundances in the komatiite mantle sources range from ∼30% in the Coonterunah to ∼70% in the Regal system, of those in the estimates for the modern BSE, indicative of a 2.4× increase in HSE abundances from 3.53 to 3.18 Ga.All four komatiite-basalt systems exhibit positive 182W anomalies ranging between +11.4 and +7.7 ppm. The 182W/184W compositions and calculated HSE abundances in the Pilbara komatiite-basalt sources are inversely correlated and are most consistent with grainy late accretion of large differentiated planetesimals. Regression of the combined 182W-HSE data for the komatiite systems allows an estimate of the W isotopic composition of the pre-late accretion BSE of +17 ± 7. This estimate is similar to that of the Moon of +25 ± 5 and lends further support to the notion regarding an initially common W isotopic composition in the Earth-Moon system.Regression of the available HSE abundance data for komatiite mantle sources worldwide provides an estimate for the time of complete homogenization of late accreted materials within the mantle by 2.5 ± 0.2 Ga. Calculations indicate an average survival time of late accreted planetesimals in the Earth's mantle of 1.9 ± 0.2 Ga, which constrains the average mantle stirring rates for the HSE in the Hadean and Archean.

First record of the early Toarcian Oceanic Anoxic Event in the Hebrides Basin (UK) and implications for redox and weathering changes

The early Toarcian (~183 Ma) was characterized by a prominent volcanism-induced warming event associated with a massive addition of 12 C-enriched carbon to the ocean-atmosphere system. This warming likely contributed to marked ocean deoxygenation during this time, giving the event its name: the early Toarcian Oceanic Anoxic Event (T-OAE). Although the T-OAE has been recognized globally, clear geographic differences in the character of the event and its environmental effects have been noted. Here we present new carbon isotope, element abundance and organic geochemical data from a lower Toarcian succession on the Isle of Raasay, Scotland (Hebrides Basin, Northwest European Shelf). These data provide the first evidence of the T-OAE in Scotland. The succession is generally enriched in organic matter through the T-OAE interval, though redox-sensitive trace element data indicate that oxic-suboxic bottom water conditions prevailed, potentially interspersed with ephemeral anoxic episodes. Our elemental data contrast with evidence for persistent anoxia/euxinia in nearby basins, and emphasize how deoxygenation was spatially variable and dependent on water depth and basin hydrography. Similarly, the data emphasize how anoxia was not a prerequisite for the deposition of organic-rich lithologies during the T-OAE. Sedimentological evidence, coupled with inorganic geochemical data, indicates increased coarse-grained detrital flux and enhanced chemical weathering during the T-OAE. Our findings support emerging evidence for a marked strengthening of hydrological cycling and increased storminess at tropical and subtropical latitudes globally in response to global warming during the T-OAE. • Toarcian Oceanic Anoxic Event described from Hebrides Basin (sub-Boreal realm) for the first time. • Negative organic carbon isotope excursion (~-2.7‰) during the early Toarcian • Oxic to suboxic conditions through the T-OAE, in contrast to strong anoxia in nearby basins • Significant strengthening of continental weathering through T-OAE at sub-tropical latitudes

Interstellar Extinction and Elemental Abundances: Individual Sight Lines

Abstract While it is well recognized that both the Galactic interstellar extinction curves and the gas-phase abundances of dust-forming elements exhibit considerable variations from one sight line to another, as yet most of the dust extinction modeling efforts have been directed to the Galactic average extinction curve, which is obtained by averaging over many clouds of different gas and dust properties. Therefore, any details concerning the relationship between the dust properties and the interstellar environments are lost. Here we utilize the wealth of extinction and elemental abundance data obtained by space telescopes and explore the dust properties of a large number of individual sight lines. We model the observed extinction curve of each sight line and derive the abundances of the major dust-forming elements (i.e., C, O, Si, Mg, and Fe) required to be tied up in dust (i.e., dust depletion). We then confront the derived dust depletions with the observed gas-phase abundances of these elements and investigate the environmental effects on the dust properties and elemental depletions. It is found that for the majority of the sight lines the interstellar oxygen atoms are fully accommodated by gas and dust and therefore there does not appear to be a “missing oxygen” problem. For those sight lines with an extinction-to-hydrogen column density A V /N H ≳ 4.8 × 10−22 mag cm2 H−1 there are shortages of C, Si, Mg, and Fe elements for making dust to account for the observed extinction, even if the interstellar C/H, Si/H, Mg/H, and Fe/H abundances are assumed to be protosolar abundances augmented by Galactic chemical evolution.

Meter-Scale Chemical and Isotopic Heterogeneities in the Oceanic Mantle, Leka Ophiolite Complex, Norway

AbstractMantle peridotites from three 3 × 3-meter grids sampled at kilometer distances from one another in the ca. 497 Ma Leka Ophiolite Complex (LOC), Norway, are examined to investigate the chemical and isotopic nature of oceanic mantle domains at the centimeter to kilometer scale. The lithology of each grid locality is predominantly harzburgite, but includes layers and lenses of dunite and pyroxenite. Major and lithophile trace element compositions indicate a history of prior melting at pressures at or slightly below the garnet stability field. The common presence of orthopyroxenite veins likely reflects infiltration of silicic melts associated with supra-subduction zone processes. Osmium isotopes and highly siderophile element (HSE) abundance data for centimeter-scale sampling of traverses from the pyroxenites into the harzburgites reveal that the formation of the veins had little effect on Os isotopic compositions, and Os, Ir, Ru and Re abundances in the harzburgites. Adjacent to one of the orthopyroxenite veins studied, however, Pt and Pd abundances appear to have been strongly modified by interactions with vein-forming melts or fluids at distances of as much as 4–6 cm from the pyroxenite-harzburgite contact. Leka harzburgites have initial γOs values (% deviation from a chondritic reference) that range from −4.7 to +2.2 (6.9% variation), with individual uncertainties of ±0.2 units. Averaged initial Os isotopic compositions for harzburgites from the three grid sites separated by as much as 6 km, by contrast, differ by only a maximum of 2.6%. Isotopic heterogeneity on the centimeter to meter scale is, therefore, larger than kilometer-scale heterogeneity, indicating that at least some of the Os isotopic heterogeneity commonly observed globally among mantle peridotites is the result of processes that acted on a local scale. The general uniformity of these isotopic compositions among the three grid sites suggests that the portion of the oceanic mantle sampled by the LOC was homogenous at the kilometer scale with respect to the long-term Re/Os ratio. The long-term projected Re/Os for LOC harzburgites is similar to the average required for modern abyssal peridotites. This observation strengthens previous interpretations, based largely on data for abyssal peridotites, that state the Os isotopic evolution of oceanic mantle is consistent with a long-term 187Re/188Os of ∼0.38. The present ∼3 to 4% difference between the Os isotopic composition of the modern oceanic mantle and estimates for primitive mantle suggests that at least ∼6% of the mass of the oceanic mantle has been removed from it in the form of Re-enriched, mafic oceanic crust. Despite the recycling of this crust back into the mantle, most of it has evidently not been mixed back into accessible portions of the upper oceanic peridotite mantle. Compared to composition estimates for the primitive mantle, the median HSE compositions for the three grid sites are moderately to strongly depleted in Pd and Re, consistent with the corresponding lithophile element evidence for 20–30% melt depletion. As with initial γOs values, most harzburgites from a given grid are characterized by greater variations in absolute and relative HSE abundances than the differences between the median abundances of the three grid sampling locales. This observation indicates that as with Os isotopes, the HSE abundance heterogeneity among the harzburgites most strongly reflects centimeter- to meter-scale melting and remobilization effects. Except for Ru, median HSE abundances for grid harzburgites are similar to median abundances for abyssal peridotites. The ∼30% lower median Ru/Ir in the LOC compared to the median ratio for abyssal peridotites suggests that the abundance of Ru in the oceanic mantle may be more variable than generally thought.

Elemental abundances of major elements in the solar wind as measured in Genesis targets and implications on solar wind fractionation.

We present elemental abundance data of C, N, O, Na, Mg, Al, Ca, and Cr in Genesis silicon targets. For Na, Mg, Al, and Ca, data from three different SW regimes are also presented. Data were obtained by backside depth profiling using Secondary Ion Mass Spectrometry. The accuracy of these measurements exceeds those obtained by in-situ observations; therefore the Genesis data provide new insights into elemental fractionation between Sun and solar wind, including differences between solar wind regimes. We integrate previously published noble gas and hydrogen elemental abundances from Genesis targets, as well as preliminary values for K and Fe. The abundances of the solar wind elements measured display the well-known fractionation pattern that correlates with each elements' First Ionization Potential (FIP). When normalized either to spectroscopic photospheric solar abundances or to those derived from CI-chondritic meteorites, the fractionation factors of low-FIP elements (K, Na, Al, Ca, Cr, Mg, Fe) are essentially identical within uncertainties, but the data are equally consistent with an increasing fractionation with decreasing FIP. The elements with higher FIPs between ~11 and ~16 eV (C, N, O, H, Ar, Kr, Xe) display a relatively well-defined trend of increasing fractionation with decreasing FIP, if normalized to modern 3D photospheric model abundances. Among the three Genesis regimes, the Fast SW displays the least elemental fractionation for almost all elements (including the noble gases) but differences are modest: for low-FIP elements the precisely measured Fast-Slow SW variations are less than 3%.

Highly siderophile elements in shergottite sulfides and the sulfur content of the martian mantle

Shergottite meteorites are ultramafic to mafic igneous rocks derived from partial melting of distinct regions of the martian mantle. As such, they trace magmatic processes, including fractional crystallization and mixing processes in Mars. New chalcophile (Cu, Se, Zn, Pb), siderophile (Ni, Co, W), and highly siderophile element (HSE: Au, Re, Pd, Rh, Pt, Ru, Ir, Os) abundance data are reported for sulfide assemblages in a suite of thirteen incompatible trace-element depleted, intermediate and enriched shergottites, along with new whole-rock HSE abundance and 187Os/188Os data for seven shergottites. Sulfide grains in depleted and intermediate shergottites typically have the highest absolute abundances of HSE, with broadly flat CI-chondrite normalized patterns. Enriched shergottite sulfide grains typically have highly variable Au, elevated Pd and Rh and are relatively depleted in Zn, Ir and Os. The new HSE whole-rock data for enriched (Northwest Africa [NWA] 7397, NWA 7755, NWA 11043), and intermediate shergottites (NWA 10961, NWA 11065, NWA 12241, and NWA 12536) are generally consistent with existing 187Os/188Os and HSE abundance data for these geochemical groupings. Enriched shergottites with >1 ppb bulk rock Os have measured 187Os/188Os ranging between 0.1296 and 0.1471, with variable Pd and Pt contents. Intermediate shergottites with >1 ppb bulk rock Os have chondrite-relative proportions of the HSE at ∼0.01 to 0.001 × CI chondrites and 187Os/188Os from 0.1284 and 0.1295. Sulfides are the major host of the HSE, and they control the behavior of the HSE during petrogenetic processes in shergottite magmas, enabling the determination of HSE compatibility for martian magmatism in the order: Os > Ir ≥ Ru ≥≥ Rh ≥ Pd ≥ Re ≥ Pt ≥ Au. Fractionation models of removal of an olivine-dominated cumulate recreate HSE patterns for the whole-rock shergottites. Enriched shergottites are best reproduced by 25 to 30% of fractionation from a degassed parent melt (250 ± 50 ppm of S), whereas depleted and intermediate shergottites can be explained by slightly lower fractionation (10 to 15%) from higher S content parent melts (350 ± 100 ppm of S). Sulfur contents in the melt that are ∼50% higher than these estimates yield earlier S-saturation during fractional crystallization, leading to an abrupt decrease of the more compatible HSE (Ru, Ir, Os), which is not observed. These results indicate that the martian mantle and partial melts derived from it, are probably not anomalously enriched in S, and instead are similar to slightly higher than those of the terrestrial mantle and its partial melts.

High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2)

Oceanic Anoxic Event 2 (OAE-2) occurred at the Cenomanian-Turonian boundary (∼94.1 Ma) and was a time of profound global changes in ocean chemistry and the carbon cycle. This event was characterized by a positive carbon isotope excursion (CIE) caused by massive organic carbon burial, global greenhouse temperatures, ocean deoxygenation, and changes in ocean life driven by large igneous province (LIP) activity. LIPs throughout the Phanerozoic have had dynamic magma flux, with episodes of major eruptions interspersed with periods of relatively less intense eruptions. A possible trigger for LIP activity throughout the Phanerozoic has been attributed to extraterrestrial impacts because there are multiple contemporaneous occurrences of large craters, LIP activity, and mass extinctions in the geologic record. At the Cenomanian-Turonian boundary, there is a 25 km diameter (rim-to-rim) complex crater in NW Alberta, Canada known as the Steen River impact structure dated at 91 ± 7 Ma (Carrigy and Short, 1968). An alternative explanation for those craters found contemporaneous with LIP activity and mass extinctions is that they were created by large explosive events related to LIP activity. Explosive events associated with mantle plume incubation beneath cratonic lithosphere have been suggested to create geologic features commonly attributed to impacts (e.g., shocked quartz, microspherules, etc.). Currently, the trigger for LIP activity during OAE-2, as well as the duration of LIP activity and the temporal variation and magnitude of eruption rates are not well constrained.To address the issue of LIP eruption rates and the trigger for LIP activity, we examined osmium (Os) abundances and isotopes as well as highly siderophile element (HSE; for this study: Re, Ru, Pd, Os, Ir, Pt) abundance data from a continuous sedimentary section spanning OAE-2. The section is from the Eagle Ford Group in the Iona-1 core, deposited in the Cretaceous Western Interior Seaway (KWIS). We found three high Os concentration intervals with mantle-like initial Osi isotope (initial 187Os/188Os) values of ∼0.16. These intervals are interpreted to reflect high-flux LIP magmatic pulses. Between the pulses, lower Os abundances with more radiogenic Osi values of ∼0.20 are observed, which we interpret as low-flux LIP activity between the high-flux periods. This trend of high-and-low flux Os concentration pulses with mantle-like Osi values during the high flux periods is found in another KWIS core (USGS Portland #1) deposited to the north of Iona-1, and in core Deep Sea Drilling Project (DSDP) Site 530 Hole A (hereafter DSDP 530A; drilled off-shore Namibia in the Angola Basin) deposited in the Southern Hemisphere. Before and throughout the Iona-1 core OAE-2 interval, HSE abundance patterns indicate a mantle source for the unradiogenic Os, and are not consistent with an extraterrestrial impact trigger or contribution to LIP activity during OAE-2.This evidence for multiple high-flux pulses of LIP activity driving ocean deoxygenation has implications for the modern ocean, which is currently experiencing deoxygenation. These results provide new constraints on subsequent high-flux periods that extended the event. The first high-flux period started ∼60 Kyr after our selection of the onset of the CIE. The second and third high-flux periods started ∼270 and ∼400 Kyr after the onset of the CIE, respectively. After the third high-flux period, δ13Corg and Os isotope ratios shifted back to pre-excursion values over ∼585 kyr. In the Iona-1 core, OAE-2 lasted for 1.04 ± 0.12 Myr based on our selection of the CIE.

Noble gas elemental abundances in three solar wind regimes as recorded by the Genesis mission

We discuss elemental abundances of noble gases in targets exposed to the solar wind (SW) onboard the “Genesis” mission during the three different SW “regimes”: “Slow” (interstream, IS) wind, “Fast” (coronal hole, CH) wind and solar wind related to coronal mass ejections (CME). To this end we first present new Ar, Kr, and Xe elemental abundance data in Si targets sampling the different regimes. We also discuss He, Ne, and Ar elemental and isotopic abundances obtained on Genesis regime targets partly published previously. Average Kr/Ar ratios for all three regimes are identical to each other within their uncertainties of about 1% with one exception: the Fast SW has a 12% lower Xe/Ar ratio than do the other two regimes. In contrast, the He/Ar and Ne/Ar ratios in the CME targets are higher by more than 20% and 10%, respectively, than the corresponding Fast and Slow SW values, which among themselves vary by no more than 2–4%. Earlier observations on lunar samples and Genesis targets sampling bulk SW wind had shown that Xe, with a first ionisation potential (FIP) of ∼12 eV, is enriched by about a factor of two in the bulk solar wind over Ar and Kr compared to photospheric abundances, similar to many “low FIP” elements with a FIP less than ∼10 eV. This behaviour of the “high FIP” element Xe was not easily explained, also because it has a Coulomb drag factor suggesting a relatively inefficient feeding into the SW acceleration region and hence a depletion relative to other high FIP elements such as Kr and Ar. The about 12% lower enrichment of Xe in Genesis’ Fast SW regime observed here is, however, in line with the hypothesis that the depletion of Xe in the SW due to the Coulomb drag effect is overcompensated as a result of the relatively short ionisation time of Xe in the ion-neutral separation region in the solar chromosphere. We will also discuss the rather surprising fact that He and Ne in CME targets are quite substantially enriched (by 20% and 10%, respectively) relative to the other solar wind regimes, but that this enrichment is not accompanied by an isotopic fractionation. The Ne isotopic data in CMEs are consistent with a previous hypothesis that isotopic fractionation in the solar wind is mass-dependent.

Climate impact on fluvial-lake system evolution, Eocene Green River Formation, Uinta Basin, Utah, USA

AbstractIn light of a modern understanding of early Eocene greenhouse climate fluctuations and new highly seasonal fluvial system faces models, the role of climate in the evolution of one classically-cited continental, terminal lake system is re-examined. Detailed stratigraphic description and elemental abundance data from fifteen cores and seven outcrop regions of the Green River Formation were used to construct a ∼150 km cross section across the Uinta Basin, Utah, USA. Lake Uinta in the Uinta Basin is divided into five lake phases: (1) post-Paleocene Eocene Thermal Maximum, (2) peak Eocene hyperthermal, (3) waning hyperthermal, Early Eocene Climatic Optimum (EECO), (4) post-hyperthermal, and (5) post-EECO regimes, based primarily on climatically driven changes in fluvial style in combination with sedimentary indicators of lacustrine carbonate deposition, organic matter preservation, salinity, and lake depth. Basinwide siliciclastic dominated intervals were deposited by highly seasonal fluvial systems and record negative organic carbon isotope excursions associated with early Eocene abrupt, transient global warming (hyperthermal) events. Carbonate dominated or organic rich intervals record stable, less seasonal climate periods between hyperthermals, with lower siliciclastic sediment supply allowing the development of carbonate and organic matter preservation. The stratigraphic progression from alternating organic rich and lean zones to the overlying organic rich Mahogany and R8 zones represents the global transition out of the pulsed early Eocene hyperthermal climate regime to a time of sediment starvation and lake stratification, sequestering sedimentary organic carbon. This study provides a novel approach to terrestrial paleoclimate reconstruction that relies largely on unique sedimentary indicators and secondarily on isotopic proxy records within the context of a large basin-wide sedimentologic and stratigraphic data set, thus setting the stage for future detailed geochemical terrestrial paleoclimate proxy development.