Carbon and oxygen isotope ratios, and geochemistry of the Precambrian-Cambrian Sukharikha River section, northwestern Siberian platform

There are six minima, 1n-6n, and seven maxima 1p-7p, in the Sukharikha Formation and a rising trend of d13C from the minimum 1n of -8.6 ‰ to maximum 6p of +6.4 ‰. The trough 1n probably coincides with the isotopic minimum at the Precambrian-Cambrian boundary worldwide.

Highly positive d13C 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 d13C is observed through the Krasnoporog and lower Shumny formations. It consists of four excursions with four major maxima that can be cor related with Tommotian-Botomian peaks II, IV, V, and VII of the reference profile from the southeastern Siberian platform.