EVOLUTION OF NATURAL ENVIRONMENT OF THE KERCH STRAIT AREA DURING RECENT 25 THOUSAND YEARS

Evolution scheme of the natural environment of the Kerch Strait for recent 25,000 years has been proposed basing on the results of paleogeographic investigation (lithology-facial, malacofaunistic, radiocarbon analyzes) of the cores of four boreholes drilled on the Tuzla spit (island) during engineering and exploration work for the construction of the Crimean bridge. The principal stages are as follows: 1 – the New Euxinian regression, which corresponded to the Late Valdaj glacial period. The Azov Sea was lowland, the Don River estuary was situated within the modern Black Sea shelf zone and freshwater fauna inhabited the Kerch Strait; 2 – the New Euxinian transgression, which corresponded to the beginning of degradation of the Late Valdaj glaciation. The Kerch Strait was a lagoon-type basin with freshwater and slightly brackish-water mollusks indicating the discharge of the Caspian Sea (Khvalynian) waters into the New Euxinian basin. The lagoon-type basin in the area of the modern Kerch Strait existed about 10,110±330 years ago; 3 – the New Euxinian basin level decrease as a result of discharge of its water to the Mediterranean Sea when it reached the Bosphorus threshold. The extension of the Don River delta and the dispersal of freshwater mollusks; 4 – The Black Sea transgression characterized by the access and dispersal of the Mediterranean species, from euryhaline to moderately euryhaline and moderately stenohaline. Unstable sea level with various fluctuations at the initial sub-stage of the Black Sea transgression. The New Black Sea sub-stage with a sea level 2 m above the present-day one, increased salinity and rich biodiversity of Mediterranean species is dated between 6020±140 and 5530±120 years ago; 5 – the Phanagorian regression with insignificant desalination of the Kerch Strait due to increased influence of the Don River water. The age of the event is 2570±140 years; 6 – the modern stage characterized by the dispersal of Mediterranean euryhaline and moderately stenohaline species.

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