Rb-Sr Systematics and U-Pb Age of Carbonate Rocks of the Staraya Rechka Formation, the Vendian of the Anabar Uplift, Northern Siberia

The results of Sr-chemostratigraphic study of carbonates of the Staraya Rechka and Nemakit-Daldyn formations which make up the upper part of the Precambrian cover of the Anabar Uplift in Northern Siberia are presented. A Pb-Pb age of the Staraya Rechka Formation dolostone has been obtained (549 +/- 25 Ma, MSWD = 1.4) for the first time. An improved stepwise dissolution procedure was used to determine the Sr-87/Sr-86, Pb-206/Pb-204 and Pb-207/Pb-204 isotopic ratios in carbonates rocks. The methodology for studying the Rb-Sr systematics included the chemical removal of about a third of the crushed sample [fraction L(Rb-Sr)(1)] by preliminary acid leaching in 0.2N CH3COOH and subsequent partial dissolution [fraction L(Rb-Sr)(2)] of the remaining part of the sample in CH3COOH of the same concentration. The Pb-Pb isotopic systematics of dolostones was studied by six to nine-step dissolution in 0.5N HBr. Chemical procedures resulted in the removal of secondary epigenetic carbonate material, which improved the quality of Sr-chemostratigraphic and U-Pb geochronological information. The initial Sr-87/Sr-86 ratios in the least altered carbonate material [fraction L(Rb-Sr)2] of the Staraya Rechka Formation dolostone are 0.70822-0.70836, and in the Nemakit-Daldyn Formation limestone, 0.70854-0.70856. The Pb-Pb age of early diagenesis of dolostones of the Staraya Rechka Formation (549 +/- 25 Ma) was calculated from fractions [L(U-Pb)(2)-L(U-Pb)(n)], where n for different samples varied in the range from 6 to 9. Epigenetic carbonate fractions L(U-Pb)(1) are characterized by a Pb-Pb age of 360 +/- 190 Ma (MSWD = 0.8). The obtained results prove that the Staraya Rechka Formation of the Anabar Uplift belong to the Late Vendian (Late Ediacaran), allowing them to be confidently correlated with the carbonate rocks of the upper part of the Yudoma Group of the Uchur-Maya region and to include the named strata into a single Yudoma Complex of Siberia.