Carboniferous-Lower Permian Carbonate Reservoirs of the Timan-Pechora Basin

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Abstract
The Carboniferous-Lower Permian carbonate succession of the Timan-Pechora basin is a major hydrocarbonbearing complex, hosting about half of the oil and nearly a third of the gas reserves of the basin. The succession represents the last episode of carbonate deposition on the northeastern margin of the Russian platform before the closure of the Ural seaway in the mid- Permian. The lower part of the succession (upper Visean-Moscovian) contains three major transgressive-regressive sequences. Depositional facies ranged from nearshore carbonate-shale-evaporite through shallow shelf detrital carbonates to outer-shelf carbonate-siliceous shale. The most pronounced regression during this interval occurred during the Serpukhovian, when marine sabkhas covered vast portions of the carbonate platform. Late Carboniferous-Early Permian sedimentation was complicated by the onset of Uralian tectonism. Flysch from the encroaching orogen accumulated initially in the east, advanced westward across the passive margin, and finally covered the carbonate platform in Artinskian- Kungurian time. Simultaneously, structural inversion along the Pechora-Kolva aulacogen and elsewhere provided sites for bioherm growth, in addition to exposing parts of the lower succession to erosion and karstification. Overall polarity of the basin switched as the eastern margin was elevated in the frontal thrusts of the Urals. The carbonate succession was terminated by increased clastic input from the advancing Ural orogen.

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