Carbon isotope stratigraphy of the Precambrian-Cambrian Sukharikha River section, northwestern Siberian platform

A high-resolution carbon isotope profile through the uppermost Neoproterozoic-Lower Cambrian part of the Sukharikha section at the northwestern margin of the Siberian platform shows prominent secular oscillations of delta C-13 with peak-to-peak range of 6-10 parts per thousand. There are six minima, In-6n, and seven maxima 1p-7p, in the Sukharikha Formation and a rising trend of VC from the minimum In of - 8.6 parts per thousand to maximum 6p of + 6.4 parts per thousand. The trough In probably coincides with the isotopic minimum at the Precambrian-Cambrian boundary worldwide. Highly positive delta C-13 values of peaks 5p and 6p are typical of the upper portion of the Precambrian-Cambrian transitional beds just beneath the Tommotian Stage in Siberia. A second rising trend of VC is observed through the Kxasnoporog and lower Shumny formations. It consists of four excursions with four major maxima that can be correlated with Tommotian-Botomian peaks II, IV, V, and VII of the reference profile from the southeastern Siberian platform. According to the chemostratigraphic correlation, the first appearances of the index forms of archaeocyaths are earlier in the Sukharikha section than in the Lena-Aldan reuion.