C- AND Sr-ISOTOPE CHEMOSTRATIGRAPHY OF THE UPPER PROTEROZOIC-LOWER CAMBRIAN TRANSITIONAL DEPOSITS IN THE LENA-ANABAR TROUGH (NORTHEASTERN SIBERIAN PLATFORM)

. Studies have been made of the carbon and strontium isotope composition in carbonate sediments of the Khorbusuonka group and Kessyusa formation corresponding to the Upper Vendian in deep Khastakhskaya-930 and Burskaya-341-0 boreholes at the northeastern margin of the Siberian Platform. The maximum & delta;13C values in carbonates of the Turkut and Kessyusa formations in the Khastakhskaya-930 borehole are +7.0...+7.4 & PTSTHOUSND;, while the minimum 87Sr/86Sr ratios are as low as 0.7079. Such isotope-geochemical characteristics suggest that these formations are younger (Tommotian) or older (early Vendian) than it was supposed and allow for the possibility of alternatives to their regional correlation with the Burskaya-341-0 borehole and Olenek uplift sections. The deposition of sediments of the age considered, more intensive than in the adjacent regions, may be indicative of rift-related extension settings.

Automated summary

Studies were conducted on the carbon and strontium isotope composition of carbonate sediments from the Khorbusuonka group and Kessyusa formation in northeastern Siberia. The results showed that the maximum δ13C values of carbonate rocks from the Turkut and Kessyusa formations in the Khastakhskaya-930 borehole were +7.0...+7.4 ‰, while the lowest 87Sr/86Sr ratio was 0.7079. These isotope-geochemical characteristics suggest that these formations may be younger (Tommotian) or older (early Vendian) than previously thought, and provide alternative possibilities for their regional correlation with the Burskaya-341-0 borehole and Olenek uplift sections. The higher sediment deposition intensity during this period compared to adjacent regions may indicate rift-related extension settings.