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Earliest marine diagenetic sabkha type dolomites are widespread in Earth's geological record. Potentially, these carbonates may act as archives of past seawater magnesium isotope (δ26Mg) ratios. At present, however, the fractionation of magnesium isotopes (Δ26Mg) between seawater – here evaporated marine porewater – and sabkha dolomite is not constrained. In order to explore Δ26Mgdol-Mg(porewater), we make use of actualistic sabkha type dolomite precipitation in the Gulf region (Trucial coast, United Arab Emirates). This paper documents and discusses the first detailed sabkha δ26Mg data set of Mg-bearing solids including stoichiometric dolomites (degree of ordering > 0.9; mean δ26Mgdol = − 0.79‰ ± 0.41 2σ, n = 17) and related marine pore waters. The presence of dolomite crystals with a broad range of ordering in shallow cores is documented using X-ray diffraction and scanning electron microscopy, but individual crystals are too small ( |
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