Early riphean billyakh group, Anabar Uplift, Northern Siberia: isotope C–O geochemistry and Pb–Pb age of dolostones

Abstract

U and Pb contents and C, O and Pb isotope composition have been determined in dolostones of the Billyakh Group (in 6 samples of the Kotuikan Formation and 15 samples of the Yusmastakh formation) which comprises the upper part of the Riphean section of the Anabar Uplift. The δ 13 С and δ 18 O values in the Billyakh dolostones vary respectively from –3.0 to +0.8‰ PDB and from 23.7 to 27.3‰ SMOW and conform with those in carbonate deposits precipitated 1600–1400 m.y. ago. In the 206 Pb/ 204 Pb– 207 Pb/ 204 Pb diagram, 18 data points of all the dolostone samples of the Kotuikan and Yusmastakh formations are arranged along the straight line which corresponds to the age of 1513 ± 35 Ma. This age for the first time provides immediate geochronological description of the sedimentary rocks from the cover of the Anabar Uplift. Coupled with previously published Rb–Sr glauconite age of the subjacent Ust’-Il’ya formation, this date allows to place all the sedimentary succession of the Billyakh Group into the Early Riphean. These results are indicative of the relatively fast (within ~10 m.y.) accumulation of terrigenous-carbonate deposits of the Billyakh Group preceding injection of dolerites of the Kotui Complex and emplacement of Mesoproterozoic Kuonamka Igneous Province on Siberian Craton. The new data put a full stop in discussions about age position of the Riphean deposits exposed on the Anabar Uplift.