CLUMPED ISOTOPE REORDERING RATES IN CARBONATE MINERALS AND APPLICATIONS TO PALEOCLIMATE AND BASIN ANALYSIS

Carbonate clumped isotopes are a promising thermometry technique, with applications in a diverse range of fields. Recently, it has been shown that clumped isotope signals reequilibrate under burial temperature conditions over timescales of millions to hundreds of millions of years. This has negative impacts for paleoclimatology studies, but has proved useful for basin analysis and sedimentology, where reordered clumped isotope signals can be used to determine the extent of burial and burial heating. To investigate reordering kinetics in carbonate minerals, we conducted heating experiments at 485 °C on natural calcite (CaCO₃) and dolomite (CaMg(CO₃)₂ samples, as well as synthetically grown witherite (BaCO₃) and strontianite (SrCO₃). Using data from a variety of heating durations between 1 hour and 64 hours, we fit our data to a two-step paired-diffusion model, which considers isotopic exchange between neighboring carbonate ions as well as the migration of carbonate ions (and associated isotopes) through the crystal lattice. Preliminary results show that carbonate minerals reorder at different rates, with orthorhombic minerals reordering faster than trigonal minerals. This implies that some minerals (such as dolomite) are more resistant to burial heating and more likely to record a primary clumped temperature signal for paleoclimate applications. For basin analysis, analyzing multiple mineralogies (when present) that reorder at different rates allows a construction of past geothermal gradients and cooling rates, and serves as an indicator of the temperature and duration of burial for a target carbonate layer.