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

ARTEM KOUCHINSKY^*,, STEFAN BENGTSON^*, VLADIMIR PAVLOV, BRUCE RUNNEGAR, PETER TORSSANDER^¶, EDWARD YOUNG^|| and KAREN ZIEGLER^||

^* Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
Institute of Physics of the Earth, Bol’shaya Gruzinskaya 10, Moscow 123995, Russia
NASA Astrobiology Institute, MS 240–1, Ames Research Center, Moffett Field, California 94035, USA
^¶ Department of Geology and Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden
^|| Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, California 90095-1567, USA

Author for correspondence: artem.kouchinsky{at}nrm.se

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 ¹³C with peak-to-peak range of 6–10 . There are six minima, 1n–6n, and seven maxima 1p–7p, in the Sukharikha Formation and a rising trend of ¹³C 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 ¹³C 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 ¹³C is observed through the Krasnoporog 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 region.

Key Words: Cambrian • carbon • isotope ratios • stratigraphy