Home – Home – Jornals – Russian Geology and Geophysics 2005 number 8

The Talakan-Upper Chona zone of petroleum accumulation lies at the top of the Nepa arch. The largest Talakanskoe petroleum deposit has been discovered there, in carbonates of the Lower Cambrian Osa Horizon.
The structure of the Talakan petroleum field and data of prospecting drilling for oil and gas in the Irkutsk Region and in the Republic of Sakha (Yakutia) have shown that within the Talakan-Upper Chona zone a sublatitudinal Talakan-Ignyali marginal reef formed in Osa time. It extends along the southern margin of the Botuobiya-Talakan carbonate platform of Osa age. Also within the platform, there were bioherms and separating basins.
Analysis of the distribution and thicknesses of halite beds overlying the Osa Horizon shows that the lower beds of halites successively overlapped the surfaces of the Osa bioherms. Zones of thin deposits distinctly outline the Talakan-Ignyali marginal reef and bands of bioherms. The geomorphology of the Talakan-Upper Chona zone in late Osa-early Late Usol'ye time has been reconstructed from the distribution and thickness of the lower beds of halite. The sublatitudinal Talakan ridge no less than 20 m above sea level has been recognized there. North of the ridge lies the Upper Nyuya lowland flooded occasionally by sea waters. In the northeast and south of the Talakan-Upper Chona zone, there are margins of a halmeic sea basin. On the land, the most likely processes were karsting and destruction of carbonates of the Osa Horizon, which led to the formation of reservoirs of porous and cavernous types. The sublatitudinal position of the Talakan-Ignyali reef was not reflected in paleotectonic reconstructions of the zone.