NOVEL APPLICATIONS OF NON-TRADITIONAL STABLE ISOTOPES TO TEST THE FIDELITY OF BARITE PALEO-ENVIRONMENTAL PROXIES

In order to test the fidelity of paleo proxies in recording Earth and environmental history, we carried out multiple isotope exchange explements at 22, 50, and 80°C and 1 bar and concentrations of Ba2+ and SO4-2 at chemical equilibrium with barite. The experimental solutions were spiked with isotopes of barium, sulfur, and oxygen that differed from the natural barite reactant. The differences in isotopic compositions revealed continuous attachment and detachment of Ba2+ and SO4-2 ions to and from the surfaces of the barite crystal, a phenomenon that would have been otherwise imperceptible without isotope doping [1].

The experimental data unveiled several key findings: (1) the rates of isotope exchange between the aqueous solutions and the barite surfaces are identical for sulfur and barium isotopes, providing support for a reaction mechanism involving the simultaneous detachment and attachment of oppositely charged ions to and from the barite surfaces; (2) barium isotope exchange is reversible; and (3) multiple reaction stages occur after the contact of barite surfaces with aqueous solutions, indicating different types of reactions. The laboratory-measured isotope exchange rates are fast, and, when extrapolated to geological time scale, indicate that measurable diagenetic alteration of barite isotope signatures can occur within decades to thousands of years.

[1] Kang, J.T., J.N. Bracco, J.D. Rimstidt, G.H. Zhu, F. Huang, and C. Zhu. 2022. Ba attachment and detachment fluxes to and from barite surfaces in Ba-137-enriched solutions with variable Ba2+ / SO4-2 ratios near solubility equilibrium. Geochimica Et Cosmochimica Acta 317: 180-200.