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Russian Geology and Geophysics

2001 year, number 7

STRATIGRAPHIC SCHEME OF THE CAMBRIAN DEPOSITS IN THE YENISEI REGION

E. A. Yolkin, V. A. Kashtanov, A. E. Kontorovich, I. V. Korovnikov, V. A. Krinin, V. A. Luchinina, S. V. Saraev, V. M. Tishchenko, Yu. F. Filippov, and A. V. Khomenko
Keywords: Stratigraphy, paleogeographic settings, Cambrian, West Siberia
Pages: 1015-1027

Abstract

A new Cambrian section has been exposed by Lemok BH-1, drilled on the left bank of the Yenisei River downstream from the mouth of the Angara River. Its lower part is saliferous, and the upper one is made up of variegated deposits. They are similar to the rocks of the Usol'e and Evenk Formations (Siberian Platform), respectively. These parts of the section are separated by a sequence of sulfate-carbonate and carbonate deposits containing shell debris and fragments of algal colonies. Trilobites Binodaspis cf. paula Suvorova and Bonnaria sp. as well as olenellids have been found in the depth range of 2804.4--2805.9 m. They indicate the Botomian age of the host rock.
We performed correlation of the sections of deep boreholes drilled on the left bank of the Yenisei River: Tyiskaya BH-1, Lemok BH-1, Eloguiskaya reference borehole, and Malokhetskaya BH-11. The correlation provides a basis for an independent scheme of Cambrian stratigraphy for the region under consideration. The Lower Cambrian includes four formations: Usol'e, Tyya, Averina, and Antsiferovka. The last three formations are proposed by us. They correspond to the Atdabanian, Botomian, and Toyonian, respectively. The Elogui Formation was formerly proposed for the lower Middle Cambrian (Amgaian). It is overlain by the Evenk Formation.
We have demonstrated that in the Early and early Middle Cambrian, the left bank of the Yeniser River was occupied by a vast carbonate platform (barrier reef). It separated the salt deposition basin of the Siberian Platform (continent) in the east from the oceanic water area open to the west. Volcanic rocks typical of back-arc basins have been found close to the margin of the Siberian continent in the Vezdekhodnaya area.