The concept of an Extreme Inundation Epoch (EIE) in NW Eurasia is presented. A massive flood during the Late Valdai deglaciation (17–11 ky BP) appears to have resulted from marine and lacustrine flooding. These transgressions are here considered as having all occurred in a “Cascade of Eurasian Basins (CEB)” that included the Aral, Caspian (Khvalynian) Black Sea (Neoeuxinian), Sea of Marmara, and the connecting straits (spillways), including the Manych-Kerch, Bosphorus, and Dardanelles. The Khvalynian basin was the epicenter of this flood, revealing catastrophic inundations during the maximum stage at 17–15 ky BP. Sea-level rose to 200 m and spread over 1 million km2 (including an inundated extension of 850,000 km2); water volume was 130,000 km3. The total CEB was over 3500 km long, with an area of 1.5 million km2 water volume of 700,000 km3.

River inundations (superfloods) left great macromeanders. Water discharge was several times more than today's and appears to have been the main source for the Khvalynian and Neoeuxinian marine transgressions. Slope inundation and sand accumulation were caused by solifluction processes. Interfluvial inundation was related to thermokarst processes and permanent lake formation. All these inundation processes covered a total area of more than 10 million km2 in NW Eurasia from the Atlantic to Eastern Siberia.

In the Black Sea, extreme inundations began with the Khvalynian influx via the Manych-Kerch strait, causing a sea-level rise of 35–40 m from –90 to –50 m asl. This first rise of the Neoeuxinian basin water level flooded 30–40,000 km2 of the outer shelf. The Neoeuxinian sea-level rise is reflected in deep water sediments by a clay layer 0.5–2 m thick with an unusual reddish-brown color. These clays are similar in appearance and age (17–14 ky BP) to the “chocolate clays” of the Khvalynian basin. The main source of this clay was permafrost melting and slope solifluction. Mollusks include the Caspian Dreissena rostriformis, Monodacna, Adacna, etc., the same forms found in the Sea of Marmara. These data show the strong influence of the Khvalynian sea water spill into the Black Sea and Sea of Marmara. Yet, to the west of the Manych valley, the most significant Caspian mollusc, Didacna, is absent. This can be explained by the Black Sea water being refreshed by fluvial superfloods of the Danube, Dnieper, and Don Rivers during the EIE.