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| Titel |
Magnesium incorporation in calcite in the presence of organic ligands |
| VerfasserIn |
Vasileios Mavromatis, Andre Baldermann, Bettina Purgstaller, Martin Dietzel |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105291
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| Publikation (Nr.) |
 EGU/EGU2015-4788.pdf |
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| Zusammenfassung |
| The formation of authigenic Mg-calcites in marine early diagenetic environments is
commonly driven by a bio-induced process, the anaerobic oxidation of methane (AOM),
which provides inorganic carbon required for the precipitation of such authigenic carbonates.
In such settings the availability of major and/or trace divalent metal cations (Me2+)
incorporated in calcite and their aqueous speciation are controlled by the presence of aqueous
organic molecules that are produced either as (by-)products of biological activity (i.e.
exopolymeric substances) or during degradation of allochthonous organic matter in the
sediments. Despite the fact that the presence of aqueous organic ligands strongly affects the
growth rates and the mineralogy of precipitating CaCO3 polymorphs, till now no study
addresses the role of Me2+-ligand aqueous complexes on the extent of Mg and/or other trace
element content of Mg-calcites. In order to shed light on this process, relevant to authigenic
calcite formation in organic-rich marine sediments and continental soils, we precipitated
calcite in the presence of aqueous Mg and a variety of low molecular weight carboxylic- and
aminoacids. Our experimental data indicate that the presence of organic ligands augments
significantly the saturation state of calcite in the parent fluid during its precipitation.
Moreover, they suggest that the higher the ligand concentration, the higher the obtained
distribution coefficient of Mg in calcite. The latter is directly proportional to the ratio of
Mg2+/Ca2+ aqueous ions for all ligands used. Hydrogeochemical modelling of the
aqueous fluids indicate that the observed correlation can be explained by the stronger
complexation of Ca2+ with organic ligands compared to Mg2+, which results in
higher availability of Mg2+ vs. Ca2+ aqueous ions. Overall the obtained results
suggest that the higher the organic ligand aqueous concentration the higher the Mg
content of calcite forming from this fluid. These findings are of great importance
for the understanding of the mechanisms controlling impurities and trace element
incorporation in carbonates forming in marine diagenetic and soil environments. |
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