Stratigraphic scheme of the Cambrian deposits in the Yenisei region (West Siberia)

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. It s lower part is saliniferous, and the upper one is made up of variegated de posits. They are similar to the rocks of the Usol'e and Evenki 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 Suv orova and Bonnaria sp. as well as olenellids have been found in the depth r ange 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 l eft bank of the Yenisei River: Tyiskaya BH-1, Lemok BH-1, Eloguiskaya refer ence borehole, and Malokhetskaya BH-11. The correlation provides a basis fo r an independent scheme of Cambrian stratigraphy for the region under consi deration. The Lower Cambrian includes four formations: Usol'e, Tyya, Averin a, and Antsiferovka. The last three formations are proposed by,us. They cor respond to the Atdabanian, Botomian, and Toyonian, respectively. The Elogui Formation was formerly proposed for the lower Middle Cambrian (Amgaian). I t is overlain by the Evenki Formation. It has been demonstrated that in the Early and early Middle Cambrian, the l eft bank of the Yeniseri River was occupied by a vast carbonate platform (b arrier reef). It separated the salt deposition basin of the Siberian Platfo rm (continent) in the east from the oceanic water area open to the west. Vo lcanic rocks typical of back-arc basins have been found close to the margin of the Siberian continent in the Vezdekhodnaya area.