SCaspienne4

Caspian Sea

On this regional cross--section, from North to South, three main basins can be individualized: (i) North Caspian Depression ; (ii) Middle Caspian Geographic Basin and (iii) South Caspian geographic basin. Three fold-belts, created by the closing of marginal seas (collision between continental crust), are underlined by three structural highs: a) Buzachi High ; b) Karatau High and Kopet Dag High. These structural highs are the geological relics of the Proto-Tethys, Paleo-Tethys and Neo-Tethys, which closures took place at end Paleozoic (Permo-Trias), Mesozoic (Middle Jurassic) and Cenozoic (beginning of closure starting in Eocene). The Buzachi high limits the North Caspian Depression from the Middle Caspian Geographic Basin. The South Caspian Geographic Basin is, conventionally, limited between the Kopet Dag and the Kara Bogaz arch. Northward of the Buzachi high, a large salt basin was developed during the Devonian (Kungurian). Below the evaporites, an organic shale interval, the Artinskian shales, is the responsible of the majority of the hydrocarbons generated in the area (Peri-Caspian basin). The potential reservoir rocks are associated with a huge Devonian-Carboniferous limestone platform (Kasahgan, in offshore), in which reefal build-ups are possible (Tengiz, in onshore). These potential reservoir rocks are, generally, well sealed either by the overlying Artinskian shales or by the Kungurian evaporites. In Middle and South Caspian Geographic Basins, the petroleum system is completely different. It is not a Paleozoic petroleum system but Cenozoic. The potential source rocks are assumed to be Oligocene organic shales (Maykop formation). The main potential reservoir rocks are the sandstones horizons of the Pereryva formation, which is considered as Plio-Pleistocene in age. If that is so, it is important to notice that, in South Caspian Geographic Basin, the so called “Maykop formation” is not well recognized and studied. This organic rich shaly formation has nothing to see with the “Maykop formation” of the Black Sea. Probably, both formations seem to have the same age and both are very good potential source rocks. However, their depositional systems and their geologic contexts are questionable.