Lithology, organic geochemistry, and petroleum potential of the northern areas of the Kureika syneclise

We present results of lithological and geochemical studies of Paleozoic deposits stripped by drilling within the Ledyanskaya area in the north of the Tunguska syneclise. The studied section has a terrigenous sulfate-carbonate composition and is complicated by trap intrusions. We have established that the Ordovician-Devonian sedimentation proceeded within an epicontinental basin, with its depth varying from supralittoral to lower sublittoral zones. In the Carboniferous and Permian, coastal-continental sedimentation was predominant; in the Late Permian it was accompanied by volcanic activity. Analysis of the poroperm properties of rocks has distinguished three potential oil reservoirs: Silurian reef carbonate deposits and Ordovician and Carboniferous sand horizons. The Lower Silurian argillaceous-carbonate rocks and Devonian carbonate-sulfate-clay members, halite beds, dolerite bodies, and tuffaceous rocks are probably confining beds of these reservoirs. Geochemical study of organic matter has shown several possible sources of hydrocarbons: Upper Proterozoic deposits, Lower and Middle Cambrian Kuonamka complex, Middle Devonian Yukta Formation, and Upper Paleozoic coal-bearing deposits.