Pleistocene Manych straits and their role in the history of Pontian-Caspian basins
Svitoch A.A.
The
occurrence of four straits periodically connecting the Pontian – Caspian basins
has been recorded in the Pleistocene history of the Manych Valley: Bakinian –
Late Chauda, Early Khazarian – Early Euxinian, Late Khazarian- Karangatian, and
Early Khvalynian – New Euxinian.
It is
typical for their morphology the heredity of the basic features of the straits’
relief from the structure of the older strait’s beds. In today’s relief of the
Manych Depression only traces of the Early Khvalynian Strait and preceding
Burtas Lake are displayed. Small gradients of the Strait’s primary bed and
relatively fine grained sediments infilling the Strait testify to a quiet
hydrological regime. The active hydraulics with a deep erosional incision
periodically occurred in the eastern and western mouths of the Strait and is
associated with the existence of a “plug” (high threshold) near Zunda – Tolga
and variability of the water level regime of the Azov – Black Sea basin.
The role of the Manych
in the history of Pontian – Caspian basins was different due to the occurrence
of strait or land neck in its depression. Occurrence of the Manych Straits had
always been connected with the rise of the Caspian Sea level and elevation of
the threshold near Zunda – Tolga. The Caspian waters entered the Pontian basins
consequently caused changes in their level, salt composition and migration of
the fauna. The Caspian Sea level after opening of the Strait was lowering, but
the Black Sea level was rising. The infilling of the Black Sea with the water
of Caspian type salinity and one -way migration of the brackish Caspian fauna
were recorded. There is no proper evidence of the Black Sea water inflow into
the Caspian Sea, and Pontian fauna appeared only in Manych and adjacent areas
of the Northern PreCaspian. The maximal impact of Caspian waters on the Black
Sea was recorded during Bakinian and Early Khazarian transgressions, a small
impact – during Early Khvalynian transgression, and a minimal influence – in
the Late Khazarian time.