Calcium isotopic evidence for rapid recrystallization of bulk marine carbonates and implications for geochemical proxies

Fantle, Matthew S.

doi:10.1016/j.gca.2014.10.005

Cited by 71 publications

(84 citation statements)

References 36 publications

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“…However, based on studies of carbonate and pore-fluid Sr, O, Ca, and Mg concentrations and isotopic compositions as well as scanning electron microscopy, it has been demonstrated that deep-sea carbonates can undergo extensive recrystallization (10s of percent) during burial and lithification over tens of millions of years DePaolo, 1987, 1988;Richter and Liang, 1993;Schrag et al, 1995;Pearson et al, 2001;Fantle andDePaolo, 2006, 2007;Higgins and Schrag, 2012;Fantle, 2015). We use the term 'recrystallization' to indicate the reactions that dissolve and reprecipitate minerals with no net change in the overall mass of carbonate mineral (other than removal or addition of trace constituents such as Mg or rare isotopes); i.e., recrystallization is used to discuss diagenetic reactions in which dissolution and reprecipitation rates are equal.…”

Section: Use Of mentioning

confidence: 99%

Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings

Stolper

Eiler

Higgins

2018

Geochimica et Cosmochimica Acta

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. O values provides new constraints on both the diagenetic history of deep-sea settings as well as past equatorial sea-surface temperatures. Specifically, the combination of the diagenetic model and data support previous work that indicates equatorial sea-surface temperatures were warmer in the Paleogene as compared to today. We then explore whether the model is applicable to shallow-water settings commonly preserved in the rock record. Using a previously published dataset from the Bahamas, we demonstrate that the model captures the main trends of the data as a function of burial depth and thus appears applicable to a range of depositional settings.

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Section: Use Of mentioning

confidence: 99%

Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings

Stolper

Eiler

Higgins

2018

Geochimica et Cosmochimica Acta

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“…However, the relatively low MgO content and the similar δ 26 Mg of continental crust (Rudnick & Gao, 2003;Teng et al, 2013;Workman & Hart, 2005;Yang et al, 2016) can hardly modify the δ 26 Mg of the mantle. On the other hand, δ 44/40 Ca of modern carbonates (0.9‰; e.g., Fantle, 2015;Griffith et al, 2015) cannot affect the mantle's composition significantly due to the small difference in Ca isotopic compositions between them. Thus, the carbonates are most likely derived from the oceanic crust.…”

Section: Geodynamic Implicationsmentioning

confidence: 99%

Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

Liu

Wang

et al. 2017

JGR Solid Earth

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Tracing and identifying recycled carbonates is a key issue to reconstruct the deep carbon cycle. To better understand carbonate subduction and recycling beneath the southeastern Tibetan Plateau, high‐K cal‐alkaline volcanic rocks including trachy‐basalts and trachy‐andesites from Tengchong were studied using Mg and Ca isotopes. The low δ26Mg (−0.31 ± 0.03‰ to −0.38 ± 0.03‰) and δ44/40Ca (0.67 ± 0.07‰ to 0.80 ± 0.04‰) values of these volcanic rocks compared to those of the mantle (−0.25 ± 0.07‰ and 0.94 ± 0.05‰, respectively) indicate the incorporation of isotopically light materials into the mantle source, which may be carbonate‐bearing sediments with low δ26Mg and δ44/40Ca values. In addition, no correlations of δ26Mg and δ44/40Ca with either SiO2 contents or trace element abundance ratios (e.g., Sm/Yb and Ba/Y) were observed, suggesting that limited Mg and Ca isotopic fractionation occurred during cal‐alkaline magmatic differentiation. A binary mixing model using Mg–Ca isotopes shows that 5–8% carbonates dominated primarily by dolostone were recycled back into the mantle. Since Tengchong volcanism is still active and probably related to ongoing plate tectonic movement, we propose that the recycled carbonates are derived from oceanic crust related to the ongoing subduction of the Indian plate.

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“…The long residence time of Mg in seawater (~13 to 20 Ma; Broecker and Peng, 1982) and resulting homogeneity of seawater δ 26 Mg (-0.84 ± 0.06 ‰) suggests that diagenesis can be studied over million-year time scales while making well-grounded assumptions regarding initial pore fluid chemistry. Work aimed at quantifying diagenetic effects (dδ s ) is necessarily involved, and requires knowledge of the recrystallization rate (R) of the solid, the isotopic disequilibrium between the solid and coexisting pore fluids ( ) and the duration of the reaction (dt; e.g., Fantle and DePaolo, 2007;Fantle et al, 2010;Fantle, 2015):…”

Section: Introductionmentioning

confidence: 99%

Quantifying the effect of diagenetic recrystallization on the Mg isotopic composition of marine carbonates

Chanda

Fantle

2017

Geochimica et Cosmochimica Acta

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The Mg and Sr isotopic compositions (δ 26 Mg and 87 Sr/ 86 Sr) of pore fluids and bulk carbonates from Ocean Drilling Project Site 1171 (South Tasman Rise; 2148.2 m water depth) are reported, in order to evaluate the potential of diagenesis to alter carbonate-based geochemical proxies in an open marine system. Given the trace amounts of Mg in marine carbonates relative to coexisting pore fluids, diagenesis can alter carbonate δ 26 Mg, a promising proxy for seawater δ 26 Mg that may help elucidate long-term changes in the global Mg cycle. Constraints on the effect of diagenetic recrystallization on carbonate δ 26 Mg are therefore critical for accurate proxy interpretations. This study provides context for assessing the fidelity of geochemical proxyreconstructions using the primary components (i.e., foraminiferal tests and nannofossils) of bulk carbonate sediments.We find that pore fluid δ 26 Mg values (on the DSM3 scale) at Site 1171 increase systematically with depth (from -0.72‰ to -0.39‰ in the upper ~260 m), while the δ 26 Mg of bulk carbonates decrease systematically with depth (from -2.23‰ to -5.00‰ in the upper ~260 m). This variability is ascribed primarily to carbonate recrystallization, with a small proportion of the variability due to down-hole changes in nannofossil and foraminiferal species composition. The inferred effect of diagenesis on bulk carbonate δ 26 Mg correlates with downcore changes in Mg/Ca, Sr/Ca, Na/Ca, and 87 Sr/ 86 Sr. A depositional reactive-transport model is employed to validate the hypothesis that calcite recrystallization in this system can generate sizeable shifts in carbonate δ 26 Mg. Model fits to the data suggest a fractionation factor and a partition coefficient that are consistent with previous work, assuming calcite recrystallization rates of ≤7%/Ma constrained by Sr geochemistry. In addition, either partial dissolution or a distinctly different previous diagenetic regime must be invoked in order to explain aspects of the elemental chemistry and 87 Sr/ 86 Sr of relatively deep sediments from Holes A and C. This study indicates that the dynamics of a given sedimentary system can significantly alter bulk carbonate geochemistry, and presents a framework for considering the potential impact of such alteration on picked archives such as foraminiferal tests and nannofossils. Ultimately, this study contributes to the development of δ 26 Mg as a proxy for seawater δ 26 Mg by quantifying the susceptibility of carbonate δ 26 Mg to diagenetic alteration, particularly in sediments in open marine systems. This study suggests that because of the sensitivity of carbonate δ 26 Mg to diagenetic recrystallization, it can, in certain systems, be used to quantify the impact of diagenesis on carbonate-based geochemical proxies.

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Calcium isotopic evidence for rapid recrystallization of bulk marine carbonates and implications for geochemical proxies

Cited by 71 publications

References 36 publications

Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings

Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings

Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

Quantifying the effect of diagenetic recrystallization on the Mg isotopic composition of marine carbonates

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