Precise kinetic parameters for thermal resetting of clumped-isotope signatures in biogenic and abiogenic calcites

Carbonate clumped-isotope (∆47) thermometry is a powerful tool to reconstruct paleotemperatures. However, episodes of heating or cooling can alter original ∆47 values through diffusive C-O bond reordering by isotopic exchange between neighboring carbonate groups within the mineral lattice and/or oxygen isotope exchange between carbonate groups and water (collectively termed "thermal resetting"). Nevertheless, if precise kinetic constraints are available, altered ∆47 values can be utilized to reconstruct thermal burial histories of sedimentary basins or to restore primary ∆47 values from carbonates which experienced thermal resetting in their geological history. Here we present new high-resolution heating experiments on optical (abiogenic) and belemnite (biogenic) calcite. By capturing early signals, we derive new precise disordered kinetic parameters for both materials [optical calcite: µE = 216.47 ± 6.95 kJ mol-1, sE = 14.51 ± 1.22 kJ mol-1, and v0 = 28.61 ± 1.12 ln(min)-1; belemnite calcite: µE = 180.15 ± 7.94 kJ mol-1, sE = 22.24 ± 2.62 kJ mol-1, and v0 = 27.76 ± 1.43 ln(min)-1]. We present new FTIR data confirming the importance of intracrystalline water and organic matter on the faster thermal resetting observed for belemnite calcite. Complementary "snapshot" experiments on a diverse suite of materials reveal a systematic difference in reordering behavior between biogenic and abiogenic calcites, highlighting the importance of structural and compositional characteristics in controlling reordering kinetics. These snapshot experiments can complement petrographic and geochemical methods in assessing the pristine nature of calcite samples and provide guidance for selecting the appropriate kinetic parameters for thermal modeling of different calcites.