The analysis of stable carbon and oxygen isotope composition is one of the most commonly used techniques in stratigraphic and diagenetic research of carbonate rocks. The wide-spread use and easy access of this long-established method has the side effect that little attention is paid to fundamental calibrations. Dolomite is often measured against a calcite standard (NBS19), and the acid fractionation factor used to calibrate is based on the one for calcite. To date, no reference material exists for dolomite.

In this study, which is part of dolomite research in the Qatar Carbonates and Carbon Storage Research Centre project, we focus on two main goals. First, we characterize a current standard of dolomite used for major and minor elemental geochemistry, and assess its suitability as a new dolomite standard for δ18O and δ 13C. Second, we attempt to better constrain the acid fractionation factor for dolomite and assess the influence of different dolomite types on this fractionation factor. As only two thirds of the total oxygen in the carbonate is released in the form of CO during acid reaction, a fractionation between the reacting carbonate and the resulting gas will occur. A recent study improved on the acid fractionation factors for calcite and aragonite. Often, the acid fractionation factor for dolomite is used to calculate δ18O and δ 13C from the values obtained by calibration with the calcite standard. Only two studies (from the 1980's) have attempted to constrain the acid fractionation factor for dolomite, of which only one did experiments not only at 25ºC, but also at 50 and 100ºC. The dataset of the latter experiment is, however, very limited and contains only two dolomite samples. We aim at improving the constraints on the acid fractionation factor of dolomite by reacting a wide range of different types of dolomite at a wide range of acid temperature, and compare this to the absolute isotopic composition of the samples measured on a fluorination line.


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  1. I.A. MacDonald, Improving stable carbon and oxygen isotope geochemical measurements in dolomite: reference material and acid fractionation factor, QFARF Proceedings, 2010, EEP22.
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