NEOPROTEROZOIC CHINGASAN GROUP IN THE YENISEI RIDGE: NEW DATA ON AGE AND DEPOSITION ENVIRONMENTS
A.D. Nozhkina, A.A. Postnikov b , K.E. Nagovitsin b , A.V. Travin a , A.M. Stanevich c , D.S. Yudin a
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3, prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
c Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Neoproterozoic; Chingasan Group; geochronology; paleontology; rifting; Yenisei Ridge
Pages: 1015-1025
Abstract
Trachybasalt-alkali trachyte volcanism in the Yenisei Ridge was found out to be synchronous with deposition of coarse tilloids and flysch of the Chivida Formation of the Neoproterozoic Chingasan Group. New 703 ± 4 Ma 40Ar/39Ar biotite and titan-augite ages of subalkaline basalts in the Chivida Formation indicated that they erupted in the Late Neoproterozoic. According to microfossil evidence, the Chingasan sediments correlate with Late Neoproterozoic strata in the type sections of the southern Siberian craton. The Chingasan deposition apparently lasted no longer than 30 Myr judging by the isotope ages obtained for the underlying Upper Vorogovka Group and subalkaline basalts in the Chivida Formation. The fault-parallel position of grabens and coarse grain sizes and variable thicknesses of their lithological complexes, as well as syndepositional trachybasalt-alkali trachyte volcanism provided evidence that the volcanosedimentary rocks of the Chingasan Group formed in an environment of active rifting.
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