ORCID Profile
0000-0002-8094-6036
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Publisher: Wiley
Date: 28-02-2023
DOI: 10.1111/SED.13087
Abstract: Carbonate concretions collected from the Dominican Republic present a valuable opportunity to evaluate the internal isotopic variations within concretions that have never been exposed to deep burial or structural deformation. Here, three concretions from the Neogene (Late Miocene–Early Pliocene) Cibao Basin are investigated, utilizing a multi‐isotope (δ 13 C, δ 18 O, δ 34 S CAS and ∆ 47 values) high‐resolution approach, to constrain the microenvironmental conditions associated with multiple stages of concretion growth. Isotopic variability and potential disequilibrium effects, which can influence geological interpretations utilizing concretions, are also considered. The petrographic characteristics and geochemical profiles indicate internal differences relating to concretion growth mechanisms and environmental changes, driven by sea‐level fluctuations. The δ 34 S values of carbonate‐associated sulphate indicate a closed system environment however, the overall values are influenced by sulphide oxidation within the sediments, resulting in a complex signal. The ∆ 47 ‐derived temperatures of the concretions range between 29 to 55°C, indicating significantly warmer temperatures than are measured from the host sediments, which average 24°C. This indicates that carbonate concretion ∆ 47 values are in disequilibrium with their environments of formation, likely related to ion diffusion in the pore fluids or isotopic fractionation associated with microbial processes. Here geochemical variations within concretions are utilized to assess the environmental conditions and microbial interactions after sediment deposition. However, for future studies, caution should be taken when using concretions for making environmental assessments as the signals can be influenced by a multitude of processes, even prior to diagenetic alteration.
Publisher: Wiley
Date: 07-07-2021
DOI: 10.1002/RCM.9147
Abstract: Information on the temperature of formation or alteration of carbonate minerals can be obtained by measuring the abundance of the isotopologues 47 and 48 (Δ 47 and Δ 48 values) of CO 2 released during acid dissolution. The combination of these two proxies can potentially provide a greater insight into the temperature of formation, particularly if the carbonate minerals form by non‐equilibrium processes. We have precipitated calcium carbonates at seven temperatures between 5 and 65°C and measured their δ 48 values using a Thermo‐253 plus isotope ratio mass spectrometer. The values were transformed to Δ 48 values in the conventional manner and then converted to the carbon dioxide equilibrium scale. Using the Δ 48 values, we have established an empirical calibration between temperature and Δ 48 values: urn:x-wiley:09514198:media:rcm9147:rcm9147-math-0001 The calibration line produced allows the determination of the temperature of natural carbonates using the Δ 48 values and agrees with the measurements of the Δ 47 and Δ 48 values of some carbonates assumed to have formed under equilibrium conditions.
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