ИСТИНА

The remnants of the ancient rivers much large than the modern ones are widespread in the floodplains of lowland rivers in Black Sea basin on the East European and Pannonian plains. The annual water yield from this territory reached 1000 km3 in millennia and up to 3000 km3 in decennial scale during the period 16-19 ka BP. This huge river runoff was the main factor of the Black sea level for that period. The flow velocity calculations, morphology and lithological composition of deposits of the Bosporus and Dardanelles straits shows that these canals were cleaned of loose sediments by this powerful flow and the basement rocks were exposed. There is an uncertainty with the position of the highest rock sill as the maximum rock altitude was similar in the Dardanelles and in the Bosporus (about -70/-80 m). In this study the sill in the Dardanelles was used with the altitude -70 m, as it is quite probable that the former altitudes of this sill were lowered by the powerful flow to the modern position. When the ocean level was lower than the sill in Dardanelles, the level of the Black Sea was controlled by flow hydraulics on this sill. The spillway flow theory was used to calculate the water level on the sill using discharge, critical velocity of rock erosion initiation and cross section geometry. At the stage of maximum discharge (the “hydrocratic” transgression of the Black Sea) sea level was about -62…-64 m. Later, with diminishing discharge it decreased to -66…67 m. Since c.14 ka BP, when the ocean level exceeded the altitude of the Dardanelles sill, the new stage of “eustatic” transgression had started. The level of the Black Sea was controlled by the ocean level and was close to it.