Stratigraphic Structure of the Vendian Oil and Gas Complex of the Southern Oil and Gas Regions of the Lena–Tunguska Province of the Siberian Platform

Abstract

—The Vendian oil and gas complex (OGC) consists of the Vilyuchan, Nepa, and Tira stratigraphic horizons. The horizons are divided into correlation layers, stratigraphic charts are refined, cyclometric stratigraphic charts of oil and gas-bearing areas of the southern part of the Lena–Tunguska province are constructed. The lower boundary of the Vendian oil and gas complex and the base of the Vendian system are established in the Nuj zone of the Nepa–Botuoba and Irkutsk zones of the Angara–Lena oil and gas region (OGR) at the end of the pre-Vendian break in sedimentation. In the Angara–Lena OGR, the Typta Formation lies after a break both on different formations of the Baikalian system, and on the basement, and it is covered by sandstones of the Vendian Nepa horizon. The Typta Formation is assigned to the Vendian system, to the Vilyuchan horizon. In the Nepa–Botuoba OGR, a long pre-Vendian break divided the Talakan Formation into an upper Vendian and a lower Riphean parts. The name Talakan is left for the Vendian strata, the lower part is divided into three strata of the Baikalian system. The cyclometric stratigraphic scale is based on repetitions of cyclically constructed sections of horizons and their parts. Repetitions are considered as the result of oscillatory movements of the Earth, which take place at different intervals of time. The ranks of movements are planetary (40 Myr), long-period (20 Myr), and regional. In these ranks of time, nexacylites, horizons and regocyclites were formed. The horizons linked the regional and cyclometric stratigraphic scales. Breaks in the sedimentation of the Vendian OGC are divided by duration into short-term separating regocyclites, long-term separating horizons and two breaks – pre-Vendian and pre-Danilovo, the duration of which reaches 10–20 Myr.