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Mediterranean deep basins are surrounded by oil and gas producing areas, either onshore or beneath the continental shelf. The main zones are the Ebro delta and the Valencia Gulf (Spain); the Pelagian Sea off Tunisia, western Libya; Sicily; the Adriatic Sea; the Prinou basin in the Greek Aegean Sea; and the Nile delta. In other areas, as in the Adana basin (Turkey), offshore Cyprus (DSDP Leg 42A), and west of Sardinia (DSDP Leg 13), oil and gas shows were present in boreholes.
In general, the Mediterranean basins have relatively flat and uniform bottoms with water depths of the order of 2,800-3,000 m (9,200-9,850 ft). Several major exceptions are the Tyrrhenian Sea and the Aegean Sea, which are internal parts of the Alpine orogenies with a stretched structure of a back-arc type. The Ionian Sea has gradual northward slopes. The Eastern basin occupies a typical external position with the front of the Hellenic and Tauric nappes and the external overthrust zone known as the "Mediterranean ridge."
In terms of the crust, the problem can be approached with the aid of geophysical studies (gravimetry, magnetism, and seismic) and variations in heat flow. The superposition of these varied data thus enables us to schematize the nature of crust of the Mediterranean basins.
The western Mediterranean has a high heat flow that is surpassed only at certain points in the Tyrrhenian Sea. In contrast, the eastern Mediterranean in general has a very low heat flow, even in the Ionian Sea where a very considerable positive gravimetric anomaly is known to exist. Without reaching the high Tyrrhenian levels, the Aegean Sea has relatively high heat values. This is normal because of the area's volcanic activity.
The main potential oil and gas objectives are the Oligocene and Miocene Series, deposited after and during the main orogenic phases, and covered by thick Messinian evaporites and Pliocene-Pleistocene marine sediments. Underlying the Ionian Sea, the Mediterranean ridge, and the eastern basins, Mesozoic and Paleogene rocks may be possible targets. The zone at the shelf limit of the African platform and the alpine chains resembles many of the productive areas around the globe.
In conclusion, the deep Mediterranean basins could hide large targets. The exploration effort will require various improvements (excluding that of the price of crude oil): a better comprehension of the deep structure, seismic techniques capable of obtaining reflection beneath the evaporites and in the overthrust sectors, and technology that allows drilling in 3,000-4,000 m (10,000-13,000 ft) of water with the requisite security safeguards.
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