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Russian Geology and Geophysics

2018 year, number 6

C AND Sr ISOTOPE CHEMOSTRATIGRAPHY OF VENDIAN-LOWER CAMBRIAN CARBONATE SEQUENCES IN THE CENTRAL SIBERIAN PLATFORM

B.B. Kochnev1,2, B.G. Pokrovsky3, A.B. Kuznetsov4, V.V. Marusin1,2
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Geological Institute, Russian Academy of Sciences, Pyzhevsky per. 7, Moscow, 119017, Russia
4Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034, Russia
Keywords: Венд, нижний кембрий, эдиакарий, изотопы углерода и стронция, карбонатные осадочные породы, изотопная хемостратиграфия, внутренние районы Сибирской платформы, Vendian, Lower Cambrian, Ediacaran, carbon and strontium isotope compositions, carbonate sediments, Оґ13C chemostratigraphy, craton interior

Abstract

We propose a detailed δ13С curve for the Vendian and Lower Cambrian (Tommotian) strata of the central Siberian Platform. Two positive carbon isotope excursions identified near the base of the Yuryakh Formation (up to 5.5‰) and in the lower Bilir Formation (up to 5 ‰) are assigned to the lowermost and middle Tommotian, respectively. This correlation is supported by paleontological data, specific 87Sr/86Sr values (0.70845-0.70856), and similar C isotope record in coeval Early Cambrian basins. The documented minor vertical oscillations (a few meters) of these isotope excursions relative to the formation boundaries in remote boreholes is presumably caused by the spatiotemporal migration of facies. A high-amplitude negative δ13С excursion (-8 to -11 ‰) in the upper Nepa Regional Stage putatively corresponds to the global Shuram-Wonoka negative carbon isotope excursion (Middle Ediacaran). Carbonates of the lower Nepa Regional Stage (Besyuryakh Formation) demonstrate positive δ13С values (up to 5 ‰) and minimum 87Sr/86Sr ratios of 0.70796-0.70832. The C and Sr isotope record of the Nepa Regional Stage provides its robust correlation with the Dal’nyaya Taiga and Zhuya Groups of the Patom Foredeep. Micropaleontological data herein reported and glacial diamictites documented at the base of the Vendian sedimentary cover both in the central Patom Foredeep and on its periphery suggest a full stratigraphic volume of the Ediacaran System in the most stratigraphically complete sections of the central Siberian Platform.