Atmospheric record in the Hadean Eon from multiple sulfur isotope measurements in Nuvvuagittuq Greenstone Belt (Nunavik, Quebec)

Emilie A Thomassot (1, 2) , Jonathan O'Neil (2) , Don Francis (2) , Pierre A Cartigny (3) , Boswell A Wing (2)

1 GeoRessources
2 EPS - Department of Earth and Planetary Sciences [Montréal]
3 IPGP - Institut de Physique du Globe de Paris

The hydrous magnesiumcarbonate minerals dypingite (Mg-5(CO3)(4)(OH)(2)center dot 5H(2)O) and nesquehonite (MgCO3 center dot 3H(2)O) were precipitated in the presence and absence of Gloeocapsa sp. and Synechococcus sp. cyanobacteria in batch reactors. The Delta C-13(mineral-DIC) is similar in both biotic and abiotic systems. Stable carbon isotope analyses of the precipitated minerals and co-existing fluids indicated that the delta C-13 values of the precipitated carbonates co-vary over time with the delta C-13(DIC) of the fluid phase, even after the precipitation of the carbonate is complete. This observation indicates the continuous isotopic exchange between the carbonates and the fluid, a process that efficiently resets the original delta C-13 values of the solids. Therefore although cyanobacterial-induced Mg carbonates are 10 +/- 5% enriched in C-13 compared to inorganic carbonates, the delta C-13 values of natural hydrousMg carbonates may reflect post precipitation processes and may not be reliable for paleo-environmental reconstructions.

Keywords: Hydrous magnesium carbonates; Cyanobacteria; Carbon isotopes; Isotope re-equilibration

Domains: Geochemistry

Emilie A Thomassot, Jonathan O'Neil, Don Francis, Pierre A Cartigny, Boswell A Wing. Atmospheric record in the Hadean Eon from multiple sulfur isotope measurements in Nuvvuagittuq Greenstone Belt (Nunavik, Quebec). Proceedings of the National Academy of Sciences of the United States of America, 2015, 112 (3), pp.707 - 712. ⟨10.1073/pnas.1419681112⟩. ⟨insu-01453065⟩