Characterization of calcium isotopes in natural and synthetic barite

Griffith, Elizabeth M.; Schauble, E. A.; Bullen, Thomas D.; Paytan, Adina

doi:10.1016/j.gca.2008.08.010

Cited by 57 publications

(32 citation statements)

References 64 publications

(103 reference statements)

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“…Stable metal isotope effects have previously been described upon calcite (Ca and Mg isotopes) or barite (Ca isotopes) formation (e.g., Griffith et al, 2008;Tang et al, 2008;Immenhauser et al, 2010). As in the case of Ba, it was generally observed, that the lighter isotopes of Mg and Ca are enriched in the solid compared to the dissolved cations, and a rate dependence of isotope discrimination was found.…”

Section: Resultsmentioning

confidence: 90%

Barium isotope fractionation in the global barium cycle: First evidence from barium minerals and precipitation experiments

et al. 2010

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In this study, we present first results from an ongoing investigation on the stable barium (Ba) isotope fractionation in the natural barium cycle. Stable Ba isotope signatures of international IAEA reference materials (synthetic barium sulfate, IAEA-SO-5, -6, and barium carbonate, IAEA-CO-9), natural Ba minerals and experimental Ba precipitates have been analyzed as a first approach to evaluate potential discriminating processes in the global geochemical barium cycle. Ba = − 0.5‰ was found in a diagenetic barite sample from ODP Leg 207. The observed natural discriminations are clearly larger than the analytical uncertainty of the stable isotope measurements, indicating significant isotope discrimination in the natural barium cycle. Precipitation experiments from aqueous barium chloride solutions at temperatures of~21°C and 80°C indicate that the light Ba isotope is enriched in pure barium carbonate and barium sulfate compared to the aqueous solution. A maximum isotope fractionation of − 0.3‰ is observed for both barium carbonate and sulfate, that -in the case of BaCO 3 -seems to be influenced by precipitation rate and/or the aqueous speciation, but less by temperature.

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Section: Resultsmentioning

confidence: 90%

Barium isotope fractionation in the global barium cycle: First evidence from barium minerals and precipitation experiments

et al. 2010

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“…Barite was separated from these bulk sediment samples using a severe digestion process to dissolve all other solid phases except barite following Griffith et al (2008), including ashing to remove organics. Samples were examined under a FEI Quanta 200 Environmental Scanning Electron Microscope (ESEM) with EDS attachment to ensure that the purity of barite was N 80% in the residue prior to elemental and isotopic analyses.…”

Section: Barite Elemental Ratiosmentioning

confidence: 99%

“…Purified barite samples were dissolved in cation exchange resin (MCI Gel, CK08P) following the method outlined in Griffith et al (2008) and used in Widanagamage et al (2014). Strontium was isolated from other cations in the natural waters and dissolved barite solutions using extraction chromatography with Sr Spec resin (50-100 μm mesh, Eichrom Industries, Lisle, IL, U.S.A.) at the University of South Carolina (USC) following Scher et al (2014).…”

Section: Sample Preparationmentioning

confidence: 99%

Controls on stable Sr-isotope fractionation in continental barite

et al. 2015

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Barite precipitation typically occurs when barium rich fluids mix with sulfate rich fluids, however barite found in the modern continental environment suggests that biological activity can play an important role in barite formation by oxidizing sulfur and/or concentrating barium within microenvironments. These activities induce barite precipitation, and carry with them implications for studies of barite genesis. Strontium (Sr) is incorporated into the barite crystal structure during barite formation preserving a radiogenic and stable Sr-isotope signature in barite, providing information about its formation. Here we present Sr-isotope results from three artesian sulfidic springs with ongoing barite precipitation (Zodletone Spring, Oklahoma; Stinking Spring, Utah; and Doughty Springs, Colorado) to explore the controls on stable Sr-isotope fractionation during barite precipitation in a continental setting. Apparent stable Sr-isotope fractionation for all three sites ranged from −0.6‰ to~0.0‰ similar to previously published calculated values for equilibrium conditions and measured values of synthetic barite. However, clear relationships do not exist between water and barite chemistry in the natural systems, indicating that barite does not precipitate directly from solution, but heterogeneously within diverse microenvironments created by microbial biomass or on sediment surfaces. The dynamic microenvironments in a continental setting influence the apparent stable Sr-isotope fractionation during barite precipitation because of changing saturation conditions, Sr concentration and/or precipitation of different mineral phases (e.g., celestine). In order to better understand the geochemistry of barite deposits, future work is necessary to study the controls on radiogenic and stable Sr-isotope signatures of barite in the context of the temporally and spatially dynamic nature of the continental setting.

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“…A variety of isotopes and minerals have been investigated using first-principles methods based on density functional theory (DFT), such as stable isotopes O and C in carbonates (Schauble et al, 2006), and H, O and Si in silicates . Theoretical studies of calcium isotopic fractionation have also been conducted on sulfates (Griffith et al, 2008) and carbonates (Rustad et al, 2010;Wang et al, 2017). In addition, theoretical approaches make it possible to determine the isotopic fractionation properties of specific sites in the crystal structure (e.g.…”

Section: Introductionmentioning

confidence: 99%

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

Aufort

Ségalen

Gervais

et al. 2017

Geochimica et Cosmochimica Acta

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The stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates, biomineralization processes, dietary preferences and habitat of vertebrates. In this study, theoretical equilibrium isotopic fractionation of oxygen, carbon and calcium in hydroxyapatite and carbonate-bearing hydroxyapatite is investigated using first-principles methods based on density-functional theory and compared to the theoretical isotopic fractionation properties of calcite, CO 2 and H 2 O. Considering the variability of apatite crystal-chemistry, special attention is given to specific contributions of crystal sites to isotopic fractionation. Significant internal fractionation is calculated for oxygen and carbon isotopes in CO 3 between the different structural sites occupied by carbonate groups in apatite (typically 7‰ for both 18 O/ 16 O and 13 C/ 12 C fractionation at 37°C). Compared with calcite-water oxygen isotope fractionation, occurrence of A-type substitution in apatite structure, in addition to the main B-type substitution, could explain the larger temperature dependence of oxygen isotope fractionation measured at low temperature between carbonate in apatite and water. Theoretical internal fractionation of oxygen isotopes between carbonate and phosphate in B-type carbonated apatite ($8‰ at 37°C) is consistent with experimental values obtained from modern and well-preserved fossil bio-apatites. Concerning calcium, theoretical results suggest a small fractionation between apatite and calcite (À0.17‰ at 37°C). Internal fractionation reaching 0.8‰ at 37°C occurs between the two Ca sites in hydroxyapatite. Furthermore, the Ca isotopic fractionation properties of apatite are affected by the occurrence of carbonate groups, which could contribute to the variability observed on natural samples. Owing to the complexity of apatite crystal-chemistry and in light of the theoretical results, measurements of site-specific isotopic fractionation properties could improve our understanding and the interpretation of isotopic records in apatites.

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Characterization of calcium isotopes in natural and synthetic barite

Cited by 57 publications

References 64 publications

Barium isotope fractionation in the global barium cycle: First evidence from barium minerals and precipitation experiments

Barium isotope fractionation in the global barium cycle: First evidence from barium minerals and precipitation experiments

Controls on stable Sr-isotope fractionation in continental barite

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

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