Early Riphean Billyakh Group of the Anabar Uplift, North Siberia: C–O Isotopic Geochemistry and Pb–Pb Age of Dolomites

The U and Pb contents and C, O, and Pb isotopic compositions are determined for dolomites of the Billyakh Group (6 and 15 samples of the Kotuikan and Yusmastakh formations, respectively), which composes the upper part of the Riphean section of the Anabar Uplift of North Siberia. The δ 13 С and δ 18 O values of dolomites vary from –3.0 to +0.8‰ PDB and from 23.7 to 27.3‰ SMOW, respectively, and are in agreement with those of carbonate sediments 1600–1400 Ma in age. On the 206 Pb/ 204 Pb– 207 Pb/ 204 Pb plot, 18 data points of all samples of both formations occur along a straight line which corresponds to the age of 1513 ± 35 Ma. The Pb–Pb age of dolomites is a first direct geochronological characteristic of sedimentary rocks of the Anabar uplift cover and, along with the previously published Rb–Sr age of glauconite of the underlying Ust’-Il’ya Formation, allows us to ascribe the entire sedimentary sequence of the Billyakh Group to the Lower Riphean. These results indicate relatively fast (~10 m.y.) terrigenous-carbonate sedimentation of this group prior to intrusion of dolerites of the Kotui complex and origination of the Mesoproterozoic Kuonamka igneous province on the Siberian Craton. New data close a discussion on the age position of Riphean sediments of the Anabar Uplift.