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New Experimental Constraints on Clumped Isotope Bond Reordering in Dolomite
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  • Paul Petschnig,
  • Nathan Looser,
  • Jordon Hemingway,
  • Max W. Schmidt,
  • Stefano M. Bernasconi
Paul Petschnig
ETH Zurich
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Nathan Looser
Department of Earth Sciences, ETH Zurich
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Jordon Hemingway
ETH Zurich
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Max W. Schmidt
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Stefano M. Bernasconi

Corresponding Author:[email protected]

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The conditions controlling the formation of sedimentary dolomite are still poorly understood despite decades of research. Reconstructing formation temperatures and δ18O of fluids from which dolomite has precipitated is fundamental to constrain dolomitization models. Carbonate clumped isotopes are a very reliable technique to acquire such information if the original composition at the time of precipitation is preserved. Sedimentary dolomite first mostly forms as a poorly-ordered metastable phase (protodolomite) and subsequently transform to the more stable ordered phase. Due to this conversion its important to determine if the original clumped isotope composition of the disordered phase is preserved during diagenetic conversion to ordered dolomite, and how resistant clumped isotope signatures are against bond reordering at elevated temperatures during burial diagenesis. Here, we present a series of heating experiments at temperatures between 360 and 480 °C with durations between 0.125 and 426 hours. We uses fine-grained sedimentary dolomites to test the influence of grains size, and cation ordering on bond reordering kinetics. We analyzed a lacustrine dolomite with poor cation ordering and well ordered a replacement dolomite, both being almost stoichiometric. The poorly ordered dolomite shows a very rapid alteration of its bulk isotope composition and higher susceptibility to solid state bond reordering, whereas the well-ordered dolomite behaves like a previously studied coarse-grained hydrothermal dolomite. We derive dolomite-specific reordering kinetic parameters for ordered dolomitea and show that ∆47 reordering in dolomite is material specific. Our results call for further temperature-time series experiments to constrain dolomite ∆47 reordering over geologic timescales.
21 Oct 2023Submitted to ESS Open Archive
08 Nov 2023Published in ESS Open Archive