Changes in the Provenance of the Holocene Deposits of the Oga and Tsivolki Bays (Novaya Zemlya Archipelago) according to Sr, Nd, and Pb Isotope Data

The paper considers Sr, Nd, and Pb isotope data obtained for two cores of bottom sediments taken in the Oga and Tsivolki bays of Severny Island of the Novaya Zemlya archipelago. The studied sequence of sediments from Oga Bay has accumulated over the last thousand years. The ⁸⁷Sr/⁸⁶Sr ratio decreases from top to bottom down the section from 0.72225 to 0.71995, the value of ε_Nd varies from –6.1 to –5.5. The Pb isotopic composition varies within narrow limits: the ²⁰⁶Pb/²⁰⁴Pb ratio from 19.107 to 19.139, the ²⁰⁷Pb/²⁰⁴Pb ratio from 15.632 to 15.635, and the ²⁰⁸Pb/²⁰⁴Pb ratio from 38.568 to 38.635. A rapid decrease in the ⁸⁷Sr/⁸⁶Sr ratio at a relatively stable neodymium and lead isotope composition indicates a change in the source of the clastic material. This can be explained by the fact that the material of the destruction of Permian clay shales, and then Devonian–Silurian sedimentary carbonates, first entered the area of glacier abrasion and further, respectively, into the sedimentation zone. The sediment column from Tsivolki Bay was formed over a little more than 10 000 years. Based on the Sr, Nd, and Pb isotope ratios, these bottom sediments are divided into lower and upper parts: before and after 150 cm (or ~3500 years). In the lower part of the column, the ⁸⁷Sr/⁸⁶Sr ratio increases from 0.72055 to 0.72580, the value of ε_Nd remains approximately the same and varies around –8.2. In the upper part, the ⁸⁷Sr/⁸⁶Sr ratio drops to 0.72049 in the near-surface layer; at the same time, the value of ε_Nd increases to –6.4. At the boundary of these two units, the ²⁰⁶Pb/²⁰⁴Pb ratio abruptly changes from about 18.0 in the lower part to 19.3 in the upper part and ²⁰⁸Pb/²⁰⁴Pb from about 36.5 in the lower part to 38.7 in the upper part of the section. The change in the Sr, Nd, and Pb isotope characteristics is likely a reflection of changes in the composition of the rocks in the area where the basin was removed, which is now being eroded by the glacier. Comparison with modern sources supplying clastic material to the Kara Sea showed that the material is supplied to the Oga and Tsivolki bays only from Novaya Zemlya.