Regional Late Paleozoic Tectono-Stratigraphic Settings and Perspectives for Discoveries at the Pricaspian Basin's North-Western Margin, Russia

Dolson, John¹, Yuri Nikitin², Sergei Ostapenko³ (1) TNK-BP, Moscow, Qatar (2) Tyumen Petroleum Research Center, Tyumen, Russia (3) TNK-BP, Moscow, Saba

Yuri Nikitin, Tyumen Petroleum Research Center, Russia Tyumen, West Siberia +7 (3452) 792-544 , [email protected] 67 Lenina Street, Tyumen, Russia Sergei Ostapenko, TNK-BP Management Arbat-1, Moscow, Russia +74951068822, [email protected]

The northwestern margin of the Pricaspian Basin intersects the Ryazano-Saratov Trough to the west and to the southeast, platform carbonate and clastic deposits grade to deep water. This trough has created strong controls on deposition in the deep basin. Carbonate platform slopes change from several degrees in the Devonian to up to 45o in the lower Permian. Unlike the southeastern portion of the Pricaspian basin where the giant Tengiz and Kashagan carbonate buildups overlie older basement highs, steady, strong tectonic subsidence in the north did not favor development of isolated carbonate platforms. During sea level lowstands, clastics by-passed the shelf into the deep basin. Fluvial and deltaic systems entered the basin during Early Visean and Middle Carboniferous along the Ryazano-Saratov Trough, feeding shelf edge deltas and deep water deposits to the east. The largest Middle Carboniferous deltaic deposits cover more then 2500 km2 and reach thickness of 1.5-1.7 km. Seismic anomalies at the base of the basinal clinoforms are probably submarine fans. In the late Carboniferous, major unconformities associated with at least one sea level lowering or tectonic uplift created paleo- relief in excess of 600 meters. The Upper Carboniferous carbonate platform was exposed and karsted. Along the shelf margin and around isolated carbonate banks, waves created additional erosion. In contrast, mud and shale deposits were transported into deep water from south to north from the Karpinsky fold belt. Only a few wells penetrate these deep water sands and shales in the interior of Pricaspian Basin. This deep-water clastic play may hold promising commercial oil-gas deposits at depths between 5200 and 5800 meters.