Print this pageUpper Carboniferous - Lower Permian Kozhim Carbonate Bank, Polar Urals, Russia: Outcrop Analog for Some Timan-Pechora Basin Reservoirs
WAHLMAN, GREGORY P., and M. V. KONOVOLOVA
The Kozhim "Reef", a 380 m thick, massive carbonate buildup of Gzhelian- Sakmarian age exposed along the Kozhim River, NE Komi Republic, Russia, grew on a topographic high near the margin of the Ural Trough. It is composed of intermixed small bioherms and associated skeletal wackestones-packstones grainstones, with common and diverse brachiopods, and rather sparse fusulinids. Traditionally the buildup has been referred to as a reef, but recent studies suggest that it should be considered a carbonate bank.
Through most of the bank section, there are common small bioherms composed of Tubiphytes - fenestrate bryozoan - radiaxial calcite cement boundstone/cementstone, which is considered a relatively cool water boundstone type. In the upper bank, plate-like bioherm-building Palaeoaplysina become more common, and palaeoaplysinid boundstones are dominant near the top of the buildup. Sparse calcareous sponges are also present. The gradual transition in the upper bank from a cooler water Tubiphytes - fenestrate bryozoan biohermal community to a relatively warmer water palaeoaplysinid biohermal community suggests upward bank growth into shallower and warmer water, and/or a period of seawater warming during upper bank growth.
The upper Kozhim bank is a potential outcrop analog for some Upper Carboniferous - Lower Permian hydrocarbon reservoirs in the adjacent Timan- Pechora Basin that are composed of similar carbonate bank and palaeoaplysinid bioherm facies. More systematic sampling and detailed microfacies analysis are needed in order to reconstruct internal stratigraphic relationships within the bank.