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Chemical geology
Elsevier
Chemical geology

Elsevier

0009-2541

Chemical geology/Journal Chemical geologySCIISTPAHCIEI
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    Disentangling diagenetic and biogenic trace elements and Sr radiogenic isotopes in fossil dental enamel using laser ablation analysis

    Léonie ReyThéo TacailFrédéric SantosStéphane Rottier...
    10页
    查看更多>>摘要：The reconstruction of life histories traits such as the ontogenic evolution of diet or sequences of mobility can be achieved for fossil mammals thanks to laser ablation analysis of trace elements concentration and radiogenic Sr isotope composition in dental enamel. However, a major limitation for the use of laser ablation to study fossil tooth enamel is that the analysis must be carried out on bulk sample hence prohibiting any ad hoc leaching step to remove diagenetic compounds. Biogenic and diagenetic trace elements along with the ~(87)Sr/~(86)Sr ratio must be monitored and post hoc correlation tests processed to isolate areas free of diagenesis. The present study combines a unique combination of biogenic (Sr and Ba), diagenetic (Mn and U) trace elements, major elements (Mg and Ca) and ~(87)Sr/~(86)Sr ratio time series obtained by means of laser ablation ICPMS and MC-ICPMS on a large number (n = 94) of fossil tooth enamel samples of humans and animals from a set of neighboring Neolithic sites in France. Bone fragments sampled from the same specimens are also analyzed for comparison. Trends between diagenetic and biogenic trace and major elements are first identified using inclusive data analysis. The trends are then validated at the scale of the laser ablation raster, and a protocol of data cleaning is developed to identify areas free of diagenesis. Non-significantly altered Sr/Ca, Ba/Ca and ~(87)Sr/~(86)Sr average values are thus gathered for each cleaned tooth enamel samples and are discussed, along with previously measured bone collagen δ~(13)C and δ~(15)N values, in terms of diet and mobility in the context of the Neolithic revolution.
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    A model for the solubility of anhydrite in H_2O-NaCl fluids from 25 to 800 ?C, 0.1 to 1400 MPa, and 0 to 60 wt% NaCl: Applications to hydrothermal ore-forming systems

    Emily C. CreaserMatthew Steele-MacInnisBenjamin M. Tutolo
    12页
    查看更多>>摘要：Anhydrite (CaSO_4) is a common gangue mineral in hydrothermal ore-forming systems, but currently there is no comprehensive numerical model for the solubility of anhydrite in H_2O-NaCl hydrothermal fluids over wide ranges of pressure, temperature and fluid salinity (P, T and X). Here, we present a new thermodynamic model for the solubility of anhydrite in saline aqueous fluids throughout a wide range of P-T-X conditions relevant to crustal hydrothermal settings. A database of experimentally determined solubility of anhydrite was used to calibrate the model, and the experimental data covers P-T-X ranges of 0.1-1400 MPa, 25-800 ?C, and 0-60 wt% NaCl. The model is successful at reproducing solubility values and overall trends from the experimental dataset within error, and also reproduces results for experimental solubility data that were not included in the calibration. We demonstrate that the model can perform well over a wide-range of P-T-X conditions, including conditions of liquid + vapor coexistence. We also provide examples of applications of the solubility model to predict the precipitation and/or dissolution of anhydrite along fluid flow paths representative of hydrothermal systems.
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    • NSTL
    • Elsevier

    Effect of barite-bound Sr on detrital Sr isotope systematics in marine sediments

    Gert J. de LangeJiawang WuZhifei LiuAnnie Michard...
    19页
    查看更多>>摘要：In marine sediments, the Sr content and isotope composition (~(87)Sr/~(86)Sr) of the terrigenous detrital component are widely used to track changes in provenance and related transport and weathering processes. Accurately separating detrital-Sr from other sedimentary Sr-phases is a prerequisite for such studies. Conventionally, it is assumed that Sr in the carbonate-free residue corresponds to detrital Sr alone. However, the decarbonated residue may contain barite with significant Sr content and a non-detrital ~(87)Sr/~(86)Sr composition; this may substantially affect the measured Sr signal. To examine this chronically overlooked phenomenon, the Mediterranean Sea is an ideal area because 1) detailed provenance studies have been done using Sr and ~(87)Sr/~(86)Sr of the residual fraction, and 2) enhanced levels of barite repeatedly occurred in association with distinct, organic-rich sapropel sediments. Here, we use the most-recent sapropel S1 interval to evaluate the effect of barite-bound Sr in the residual fraction after decarbonation. A total of 130 samples were taken from 10 cores in the eastern Mediterranean Sea (EMS) and 1 core in the western Mediterranean Sea. This selection represents a geographic and bathymetric coverage of the EMS and permits the basin-wide comparison between organic-rich and -lean sediments. After decarbonation using 1 M HCl solution, the residual sediments were subject to NH_4Cl extraction (2 M, pH 7), known to selectively dissolve barite. Our results demonstrate the presence of Sr-bearing barite after traditional carbonate removal and its effect on the derived "detrital" Sr signature. This barite-Sr effect is considerable for samples with barite-Ba >400 μg/g in bulk sediment. The impact of barite is prominent if accompanied by a detrital provenance background of high ~(87)Sr/~(86)Sr (>0.713) or low Sr/Al (<1.0 mg/g). In such cases, removal of remaining barite is required to obtain an unbiased detrital Sr signal. We recommend an improved
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    • NSTL
    • Elsevier

    Ni partitioning between olivine and highly alkaline melts: An experimental study

    Alina N. KoshlyakovaAlexander V. SobolevStepan P. KrasheninnikovValentina G. Batanova...
    12页
    查看更多>>摘要：Here, we present the results of 55 one atmosphere experiments conducted to determine the effects of Na_2O and K_2O on Ni-Mg partitioning between olivine and highly alkaline melts. The experiments were performed in the temperature range of 1250-1450 ?C at Ni/NiO buffer conditions using a crucible-supported loop technique, which allowed the alkali content to be kept constant in melts containing up to 12 wt% K_2O and up to 8 wt% Na_2O. Based on the obtained experimental data combined with 169 olivine-melt pairs from the literature, and using the Ni-Mg olivine-melt exchange reaction, we calibrated an equation to predict the Ni partitioning coefficient: The effects of Na_2O and K_2O on the Ni-Mg partitioning were found to be significant. Both K and Na along with Ti and Ca decrease the exchange equilibrium constant value, whereas Si increases it. The effect of K is more significant, than the effect of Na.
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    • NSTL
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    A strontium isoscape of Italy for provenance studies

    Federico LugliAnna CiprianiLuigi BrunoFrancesco Ronchetti...
    10页
    查看更多>>摘要：We present a novel database of biological and geological ~(87)Sr/~(86)Sr values (n = 1920) from Italy, using literature data and newly analysed samples, for provenance purposes. We collected both bioavailable and non-bioavailable (i.e. rocks and bulk soils) data to attain a broader view of the Sr isotope variability of the Italian territory. These data were used to build isotope variability maps, namely isoscapes, through Kriging interpolations. We employed two different Kriging models, namely Ordinary Kriging and Universal Kriging, with a geolithological map of Italy categorized in isotope classes as external predictor. Model performances were evaluated through a 10-fold cross validation, yielding accurate ~(87)Sr/~(86)Sr predictions with root mean squared errors (RMSE) ranging between 0.0020 and 0.0024, dependent on the Kriging model and the sample class. Overall, the produced maps highlight a heterogeneous distribution of the ~(87)Sr/~(86)Sr across Italy, with the highest radiogenic values (>0.71) mainly localized in three areas, namely the Alps (Northern Italy), the Tuscany/Latium (Central Italy) and Calabria/Sicily (Southern Italy) magmatic/metamorphic terrains. The rest of the peninsula is characterized by values ranging between 0.707 and 0.710, mostly linked to sedimentary geological units of mixed nature. Finally, we took advantage of the case study of Fratta Polesine, to underscore the importance of choosing appropriate samples when building the local isoscape and of exploring different end-members when interpreting the local Sr isotope variability in mobility and provenance studies. Our user-friendly maps and database are freely accessible through the Geonode platform and will be updated over time to offer a state-of-the-art reference in mobility and provenance studies across the Italian landscape.
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    • NSTL
    • Elsevier

    Strontium isotope fractionation during precipitation of strontianite in aqueous solutions as a function of temperature and reaction rate

    Mahmoud AlkhatibMutaz QutobSamia AlkhatibAnton Eisenhauer...
    7页
    查看更多>>摘要：In order to study Strontium (Sr) isotope fractionation during the precipitation of strontianite (SrCO_3) as a function of the specific precipitation rate (R*) and temperature (T), strontianite was precipitated at 12.5, 25.0 and 37.5 ?C by diffusing NH_3 and CO_2 gases into aqueous solutions. The specific precipitation rate R* (mol/ cm~2·h) for every sample was determined by applying the initial rate method. The mean isotope difference between bulk solution and precipitate (Δ~(88/86)Sr_(strontianite-solution)) was found to be-0.279 ± 0.005‰ (2σ_(mean)) independent of both rate and temperature. Hence, Sr isotope fractionation in strontianite is completely different from that in calcite and aragonite, where a strong dependency from both rate and temperature can be observed. The latter is interpreted to reflect the competition between Sr~(2+) and Ca~(2+) ions for incorporation into the calcium carbonate crystal lattice, which is absent during the precipitation of pure strontianite. The isotope difference between strontianite and bulk solution then simply reflects the intermolecular forces in the aqueous solutions as well as the kinetic effect. The difference in the (Δ~(88/86)Sr_(strontianite-solution) between experiments then reflects the dehydration energy of Sr ions in the adsorption layer of SrCO_3.
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    • NSTL
    • Elsevier

    Mantle sources of ocean islands basalts revealed from noble gas isotope systematics

    James M.D. DayTim D. JonesRobert W. Nicklas
    17页
    查看更多>>摘要：Noble gas isotope systematics, particular those of He, have been fundamental in showing that some ocean island basalts (OIB) were sourced from deep mantle plumes. Relationships between He, W, Os, Sr, Nd and Pb isotopes in Hawaiian, Samoan, Galapagos, and Icelandic lavas have been suggested to reflect contributions from less degassed lower mantle sources, and perhaps even materials advected from the core-mantle boundary. This study reviews the noble gas (He-Ne-Ar-Xe) isotope systematics of major OIB suites. Important in this evaluation are considerations of spatial and temporal variations, including the sample media (glass, minerals, hydrothermal gases and fluids) used for analyzing noble gases, as well as the degree of partial melting experienced to produce OIB. Limited availability of gas-rich samples means patchy coverage in definition of OIB Ne, Ar, Xe isotope compositions. Additionally, low-degree partial melting will lead to preferential sampling of more fusible, generally more enriched components which could affect noble gas isotope systematics. OIB with low- (<8R_A) to MORB-like ~~3He/~~4He (8 ± 2R_A) dominantly sample convecting mantle domains and can also contain some relatively undegassed (solar) components. Their range in Sr-Nd-Os-Pb isotope compositions reflect a strongly recycled crustal and/or lithospheric heritage. Intermediate (>10R_A) to high-~~3He/~~4He (>25R_A) OIB (Loihi, Hawaii; Iceland; Fernandina, Galapagos; Ofu, Samoa) sample a reservoir that has been relatively isolated since ~4.5 billion years as shown by noble gases (He, Ne, Ar, Xe), and by W isotopes. However, this reservoir is not pristine and these OIB show evidence for containing depleted and enriched recycled components from Xe isotopes as well as lithophile-siderophile radiogenic isotope systematics. Linking the highest-~~3He/~~4He OIB to a putative Focus Zone (FOZO) reservoir is also problematic; FOZO is not a reservoir least affected by recycling of crust, rather a mantle reservoi
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    Fate and availability of dust-borne phosphorus in a sub-humid temperate forest

    Zhuojun ZhangHairuo MaoZhi-Qi ZhaoShilu Wang...
    13页
    查看更多>>摘要：Aeolian dust deposition is an important phosphorus (P) input to terrestrial ecosystems, but it lacks evidence of how dust inputs supply available P and affect P geochemistry and dynamics in soils of sub-humid ecosystems. We determined soil P speciation using P K-edge X-ray absorption near edge spectroscopy and P availability using modified Hedley sequential chemical extractions in a weakly acidic soil profile (2.5 m thick) in a sub-humid temperate forest ecosystem. The soil profile receives substantial dust inputs that account for 34.8% - 53.5% of the soil mass at depths based on a Sr isotope analysis. The acidic topsoils (5 < pH < 5.5) contain Ca-bound P (Ca- P) that accounts for 4%-18% of total soil P. Since Ca-P compounds are unstable and transform to other forms at pH < 5.5, continuous inputs of dust materials rich in Ca-P must occur to sustain the considerable Ca-P in the topsoils. Across all depths, soil Ca-P positively correlates with soil labile Pi (both resin and NaHCO_3 extracted) in proportion, suggesting that dissolution of dust-borne Ca-P compounds replenishes the labile Pi pool. On the other hand, weathering of the Fe-rich dusts leads to formation of abundant iron oxides that in turn favors formation of occluded P (44-85%) and Fe (and Al)-bound P (57-83%), which may fix released P from the dust-borne Ca-P dissolution and reduce soil P availability in a long term. Interestingly, the saprolite layer has an unexpectedly high weathering degree with nearly depleted Ca-P, likely caused by dust inputs that increase soil moisture and microbial activities and accordingly weathering. Our study identifies that continuous deposition and subsequent dissolution of dust-borne Ca-P compounds in acidic soils sustain soil P availability. The study also highlights that aeolian dust inputs affect soil P availability and dynamics in a sub-humid forest ecosystem not only by acting as a bioavailable P source but also altering soil chemistry and weathering.
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    • NSTL
    • Elsevier

    Persistence of old soil carbon under changing climate: The role of mineral-organic matter interactions

    Katherine E. GrantValier V. GalyNegar HaghipourTimothy I. Eglinton...
    14页
    查看更多>>摘要：Globally, soils store between 1500 and 2800 Pg of organic carbon (OC). The physical and chemical stability of these terrestrial soil carbon stores under plausible climate change scenarios is unclear. Soil organic carbon (SOC), especially in volcanic soils, is stabilized through mineral matrix interactions. How susceptible are these mineralorganic matter interactions to environmental change? Here we present a study of SOC age along a climate gradient of andisols from Kohala volcano on the Island of Hawai'i. We measure carbon isotope composition (~(14)C/~(12)C, ~(13)C/~(12)C) in bulk samples and extracted biomarkers for 4-8 horizons of 15 soil profiles to understand variability in SOC age and persistence across incremental differences in mean annual precipitation. Bulk OC in the subsoil has radiocarbon fraction modern (Fm) values as low as 0.28 to 0.16 (~10,160 to ~14,630 conventional radiocarbon years). Coexisting plant-derived long chain fatty acids (LCFAs) are older, over 22,500 yrs. (Fm = 0.060), implying that these are among the most stable compounds in the soil, while corresponding shorterchain (C16) fatty acids are much younger, consistent with an origin from active microbial communities assimilating young OC percolating from surface horizons. There is significant Fe loss at higher mean annual precipitation (MAP) (>2200 mm yr~(-1)) sites associated with episodic soil saturation and microbial Fe reduction. %OC is higher at these sites, consistent with the expectation that saturated conditions promote SOC storage. However, in these higher MAP sites iron depletion is associated with much younger bulk SOC and LCFAs ~(14)C ages (~2900 ~(14)C years) than at equivalent sample depths in sites that retain most Fe (~14,200 ~(14)C years). The remaining mineral matrix consists primarily of Si, Al, and Ti as SRO minerals. The data imply that modest increases in precipitation resulting from environmental change at locations near a potential saturation or redox threshold coul
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    Geochemical evidence for secondary microbial gas in deep hot reservoirs of the Tarim Basin

    Daowei WangChunfang CaiLu YunZicheng Cao...
    12页
    查看更多>>摘要：It is hard to determine secondary microbial gas from deep burial reservoirs with multiple generations of petroleum charge. Herein, oils at depths from 5000 m to 6500 m in the Ordovician carbonate reservoirs, Tarim basin, are found to have been biodegraded to secondary microbial gas. These oils experienced severe biodegradation and thus contain abundant 25-norhopanes and 17-nortricyclic terpanes. The associated gases have methane δ~(13)C_1 from -51.9‰ to -47.3‰ and δ~2H_1 from -327.8‰ to -192.4‰, and CO_2 δ~(13)C_(CO_2) from -0.7‰ to +15.3‰. These features suggest that the gases are secondary microbial gas, generated predominantly via CO_2 reduction with preferential reduction of ~(13)C-depleted CO_2 and contribution of methane hydrogen from formation water in closed environments. The secondary microbial gas may have generated from biodegradation of oils at reservoir temperatures of about <75?C during the Late Permian, and has subsequently mixed with a later charge of non-biodegraded oils and wet gas during the Late Cretaceous. Consequently, the present gas shows relatively low dryness (C_1/ΣC_(1-4) < 0.87) and has varied δ~(13)C_1 and δ~2H_1 values in methane. The study implies that the signatures of secondary microbial gas can easily be masked by thermogenic gas and thus more secondary microbial gas has yet to be identified.
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    • Elsevier