The Pleistocene Manych straits: Their structure, evolution and role in the Ponto-Caspian basin development

The paper considers setting and history of the Pleistocene straits in the Manych Trough and estimates their role in the development of the Ponto-Caspian basins. The system of the straits is located in the lowermost part of the Manych Trough. As viewed from above, it presents a broken knee-shaped line, probably due to the tectonic control. A characteristic feature of the strait morphology is that landforms in the younger straits are mostly inherited from older ones. The maximum depths of the straits are confined to the central part of the depression. The very small gradient of the strait bottom, together with fine composition of the marine deposits, suggests the water flow in the straits was slow and quiet. The Manych impact on the evolution of the adjacent sea basins – Pontian and Caspian – differed considerably depending on whether a continuous waterway (a system of straits and lakes) existed within the depression or if it was interrupted by land bridges of a kind. The opening of the straits resulted in the Caspian Sea level drop, while in the Black Sea the input of the Caspian water caused a rise of the regressive basin level. The water entering the Black Sea had the Caspian type of salinity, which accounts for practically one-way migration of the Caspian malacofauna into the Pontian basin where it mixed with the Black Sea and Mediterranean aboriginal species.