Fingerprinting kinetic isotope effects and diagenetic exchange reactions using fluid inclusion and dual‐clumped isotope analysis

Geochemical analyses of carbonate minerals yield multiple parameters which can be used to estimate the temperature and water composition at which they formed. Analysis of fluid trapped in minerals is a potentially powerful tool to reconstruct paleotemperatures as well as diagenetic and hydrothermal processes, as these could represent the parent fluid. Internal fluids play important roles during the alteration of carbonate fossils, lowering energetic barriers associated with resetting of clumped isotopes, as well as mediating the transport of elements during diagenesis. Here, we explore the behavior of the Delta(47)-Delta(48) "dual-clumped" isotope thermometer during fluid-carbonate interaction and demonstrate that it is highly sensitive to the water/carbonate ratio, behaving as a linear system in "rock buffered" alteration, and as a decoupled system in water-dominated systems due to non-linear mixing effects in Delta(48). Dry heating experiments show that the extrapolated heated end-member is indistinguishable from the predicted Delta(47) and Delta(48) value expected for the experimental temperature. Furthermore, we evaluate two common laboratory sampling methods for their ability to thermally alter samples. We find that the temperature of the commonly used crushing cells used to vapourize water for fluid inclusion delta O-18 analyses is insufficient to cause fluid-carbonate oxygen isotope exchange, demonstrating its suitability for analyses of fluid inclusions in carbonates. We also find that belemnites sampled with a hand-drill yield significantly warmer paleotemperatures than those sampled with mortar and pestle. We conclude that thermally-driven internal fluid-carbonate exchange occurs indistinguishably from isotopic equilibrium, limited by the extent to which internal water and carbonate can react. Plain Language Summary Carbonate minerals contain multiple, independent, chemical and isotopic parameters which can be used to calculate the temperature at which the mineral formed. If these proxies agree with one another, it has been confidently assumed that the temperature is indeed genuine. Here, we investigate three such parameters and show how they record kinetic processes during mineral formation, as well as thermally-driven processes which may alter a climate record. We find that this method could potentially be used to study the kinetic factors at play during biomineralization, even if the "true" temperature is unknown. We also find that some thermal processes result in all three parameters agreeing with one another. Because thermal alteration poses a potential dilemma for climate researchers, we investigate two common laboratory preparation techniques that involve heating a sample before analysis: drilling and heating sample for fluid inclusion analysis. We find that the heat of a drill is sufficient to facilitate these reactions, and potentially imparts a warm bias onto paleotemperatures, however the apparatus used for analyzing fluid inclusions does not appear to significantly alter the material. We conclude our approach using fluid inclusion analysis and dual-clumped isotopes has the potential to resolve many ambiguities in interpreting climate records.