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Research Article |
1 Geological Survey of Norway, Leiv Eirikssons vei 39, N-4791, Trondheim, Norway
2 Centre for Geobiology, University of Bergen, PO Box 7803, N-5020 Bergen, Norway
3 Geological Institute, Russian Academy of Sciences, Pyzhevsky 7, 119017 Moscow, Russia
4 Scottish Universities Environmental Research Centre, East Kilbride, Glasgow G75 0QF, UK
5 Institute of Precambrian Geology and Geochronology, nab. Makarova, 2, 199034 St. Petersburg, Russia
*Corresponding author (e-mail: victor.melezhik{at}ngu.no)
Supplementary material: XRF and ICP-AES analysis, C, O and Sr isotopic data are available at http://www.geolsoc.org.uk/SUP18324.
In SE Siberia, carbonate formations with 
13Ccarb values ranging between –12
and –7 (V-PDB) and Sr concentrations of up to 2.5% occupy an area of 40 000 km2. Several successions exceed 1000 m in thickness and represent the world's largest known exposures of sedimentary carbonates exhibiting extreme depletion in 13C. 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 13Ccarb 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 87Sr/86Sr from 0.70802 to 0.70862 in several sections of limestones, containing 4400 µg g–1 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 87Sr/86Sr observed in the Cenozoic is applied to the Siberian sections, the calculated minimum duration for the Suram–Wonoka event is 10 Ma.
