Constraints on <sup>87</sup>Sr/<sup>86</sup>Sr of Late Ediacaran seawater: insight from Siberian high-Sr limestones

<p>In SE Siberia, carbonate formations with δ<sup>13</sup>C<sub>carb</sub> values ranging between −12‰ and −7‰ (V-PDB) and Sr concentrations of up to 2.5% occupy an area of 40 000 km<sup>2</sup>. Several successions exceed 1000 m in thickness and represent the world's largest known exposures of sedimentary carbonates exhibiting extreme depletion in <sup>13</sup>C. The carbonates were deposited on a carbonate platform evolving from a mixed carbonate–siliciclastic ramp to a carbonate ramp, and then from a peritidal rimmed shelf to a deep-water open shelf. All sequences reveal a facies-independent, upward rise in marine δ<sup>13</sup>C<sub>carb</sub> from −12‰ to −7‰. The trend and magnitude of the values mimic those that are characteristic of the 600–550 Ma Shuram–Wonoka isotope event. A coincident stratigraphic rise in <sup>87</sup>Sr/<sup>86</sup>Sr from 0.70802 to 0.70862 in several sections of limestones, containing 4400 μg g<sup>−1</sup> Sr on average, is considered to be by far the best available constraint on a temporal variation of seawater isotopic composition through the Late Ediacaran. If the greatest temporal rate of change in seawater <sup>87</sup>Sr/<sup>86</sup>Sr observed in the Cenozoic is applied to the Siberian sections, the calculated minimum duration for the Suram–Wonoka event is 10 Ma. </p>