Is manganese the key? Lowering the dolomite kinetic barrier via redox-driven templating

Daniel A. Petrash, Or M. Bialik , Yihang Fang, Maartje Hamers, Travis B. Meador, Tomaso R.R. Bontognali, Michael Boettcher, Oliver Plümper

Fabric-preserving and strata-bound dolostones in deep-time successions defy high temperature burial models, implying an elusive low-temperature, syndepositional formation pathway. Here, we demonstrate a kinetically facile route to disordered dolomite nucleation driven by the synergy of manganese redox cycling and carboxyl functionalization. Using a bio-inspired electrochemical reactor, we show that electrochemical valence state manganese modulation accelerates Mn sequestration into authigenic carbonate by 61% (vs. <25% in non-electrochemical control) and enhances Mg2+ and Ca2+ co-incorporation in polycrystalline precursor by ~52% relative to control. The crystallization route generates reactive, electrode surface-confined Mn(III) intermediates where carboxyl ligand stabilization suppresses oxide precipitation, enabling the rapid nucleation of spheroidal magnesian kutnahorite. Nanostructural characterization reveals a core-shell architecture where this isostructural precursor templates the epitaxial growth of substitutionally disordered dolomite cortices on the spheroidal aggregates. Mechanistically, localized acidity from redox cycling triggers a "proton-driven cation pump," actively mobilizing Mg2+ from the functionalized hydrogel reservoir to the mineralization front near the electrode interface. Mg2+ incorporates into lattice-distorted sites previously occupied by Mn2+ in the templating phase. This electrochemical mechanism can be extrapolated to explain the paragenesis of delicate fabric-retentive dolomite in deep time.