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UDC 551.733.3.022:551.24(571.5-16)
SILURIAN LITHOSTRATIGRAPHY OF THE NORTHWEST SIBERIAN PLATFORM
N. V. Melnikov, T. V. Lopushinskaya, T. A. Divina, V. A. Krinin, L. D. Doroshenko
The article considers stratigraphy of Silurian formations of the northwestern Siberian Platform. Stratigraphic columns were prepared based on well (logging and core) data and description of Silurian outcrops on the margins. Typical cross-sections and lithofacies zones of the Turukhan-Bakhta, Tura, Norilka and Moyero lithofacies regions are described. Since 1979 in the Turukhan-Bakhta region based on core and well logging data the Silurian succession has been found to include the Graptolite, Chalbysheva, Mogokta, Velek, and Dyavolskaya formations in the Lower Silurian and the Nimda Formation in the Upper Silurian. In the region there are six lithofacies zones: the Sukhaya Tunguska, Fatyanikha, Chalbysheva, Tutonchana, Moktakon zones in the south of the region and the Pyasina zone in the north, west of the Norilsk City. In the Pyasina zone between the Dyavolskaya and Nimda Formations there is the Imangda Formation in the uppermost Lower Silurian. In the Tura region the Silurian succession is composed of the Chalbysheva, Mogokta, Orlovskaya formations in its lower part and the Nimda and Miroshko formations in its upper part. The regressive Miroshko Formation is a possible analog of the Devonian Khrebtovaya Formation in the Norilka region. In the Norilka region the data on core and fauna acquired in 1979 revealed (bottom up) in the Lower Silurian the Chamba and Talikit formation composed of mudstone and marl, the Omnutakh Formation containing marl and limestone, the Khyukta Formation that consists of limestone, dolomite and marl and in the Upper Silurian the Makus and Postna formations composed of marls. Analysis of logs has revealed that the boundaries, quantity and lithology of formations shall be refined. Based on core and well logging data the Graptolite and Mogokta formations were distinguished in the Norilka region. The Omnutakh Formation remains above in the section. The Khyukta Formation is bounded by the coralstromatolithic carbonaceous strata. In the top of the Lower Silurian there is the Imangda Formation, and in the uppermost Upper Silurian there is the Nimda Formation. The boundary between the Devonian and Silurian systems was drawn in the bottom of the Khrebtovaya Formation. In equal position is the boundary drawn along the break and erosion in the bottom of the Zub Formation. The Silurian succession of the Ledyanskaya zone is composed of the same formations as the Moyero region.
Key words: Silurian, Devonian, formations, wells, lithofacies regions, zones.
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