THE MECHANISM OF THE CASPIAN-MEDITERRANEAN CORRIDOR FORMATION. THE PARATETHYS SEA EVOLUTION

The formation of the Caspian-Mediterranean corridor is one of the insufficiently studied global exogenic processes. The degradation of the Paratethys Sea (Par.S) is usually explained in the literature as a result of tectonic processes. But tectonics is not the only factor, and not even the main factor in the significant reduction of basin area. After the closure of the Par.S, the area of the resulting Sarmatian Sea-Lake (S.SL) was determined by climatic factors — the volume of incoming water and the coefficient of evaporation per unit area. The lake area always tends toward a stable state in which the volume of inflowing water equals the volume of evaporating water.

According to the results of geological research, Popov et al. (2009) concluded that the glacioeustatic fluctuations in the World Ocean level (WOL) continued for at least the last 20 million years. The S.SL was formed about 14 million years ago. Consequently, this basin has been affected by global process of formation and melting of continental glaciers throughout its entire existence.

Assessment of the current Black Sea water regime allows us to simulate: How did the level of the Par.S change during the fluctuations in WOL? Calculations have shown that in the case of an overlapping relation between the Black and Marmara seas at the present time the level of the Black Sea would rise about 30 m. There would be runoff into the Caspian Sea and its level would rise about 19 m. The total area of the seas would rise on 308000 km². During the intensive melting of glaciers the total area of the two seas would be approximately 2,850,000 km². With such a configuration, the shape of the consequent basin resembles closely the proposed paleoreconstruction of the S.SL (Nevesskaya, 1986).

Over the course of its evolution, the Par.S was significantly changed in both depth and size of the water area. During the periods of peak freshwater inflow, canyons were formed. Erosion of the canyon bottoms gradually lowered the level of the Par.S. It follows that the Bosphorus and Dardanelles straits have erosional origins like the Gibraltar Strait (Esin et al., 1986). With the deepening of the canyons (under conditions of WOL fluctuations and the Messinian Salt Crisis), the processes affecting changes in Par.S level and average salinity were complicated by periodic penetration of Mediterranean water.