The Sr isotopic characterization and Pb-Pb age of carbonate rocks from the Satka formation, the Lower Riphean Burzyan Group of the southern Urals

• Published in: Stratigraphy and geological correlation 2008-04, Vol.16 (2), p.120-137
• Main Authors: Kuznetsov, A. B., Ovchinnikova, G. V., Semikhatov, M. A., Gorokhov, I. M., Kaurova, O. K., Krupenin, M. T., Vasil’eva, I. M., Gorokhovskii, B. M., Maslov, A. V.
• Format: Article
• Language: English
• Subjects: Archaeology; Basins; Carbonate rocks; Carbonates; Earth and Environmental Science; Earth Sciences; Geology; Geophysics/Geodesy; Historical Geology; Leaching; Rocks; Sedimentary basins; Sedimentology; Sediments; Structural Geology; Studies; Systematics
• ISSN: 0869-5938; 1555-6263
• DOI: 10.1134/S0869593808020020

The Rb-Sr and U-Pb systematics are studied in carbonate deposits of the Satka and Suran formations corresponding to middle horizons of the Lower Riphean Burzyan Group in the Taratash and Yamantau anticlinoria, respectively, the southern Urals. The least altered rock samples retaining the 87 Sr/ 86 Sr ratio of sedimentation basin have been selected for analysis using the original method of leaching the secondary carbonate phases and based on strict geochemical criteria of the retentivity (Mn/Sr < 0.2, Fe/Sr < 5 and Mg/Ca < 0.024). The stepwise dissolution in 0.5 N HBr has been used to enrich samples in the primary carbonate phase before the Pb-Pb dating. Three (L-4 to L-6) of seven consecutive carbonate fractions obtained by the step-wise leaching are most enriched in the primary carbonate (in terms of the U-Pb systematics). In the 206 Pb/ 204 Pb- 207 Pb/ 204 Pb diagram, data points of these fractions plot along an isochron determining age of 1550 ± 30 Ma (MSWD = 0.7) for the upper member of the Satka Formation. The initial 87 Sr/ 86 Sr ratio in the least altered limestones of this formation is within the range of 0.70460–0.70480. Generalization of the Sr isotopic data published for the Riphean carbonates from different continents showed that 1650–1350 Ma ago the 87 Sr/ 86 Sr ratio in the world ocean was low, slightly ranging from 0.70456 to 0.70494 and suggesting the prevalent impact of mantle flux.