362 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



the Mediterranean, on the other by the general climatic conditions of the 

 glacial and post-glacial periods and, in the first place, by the inflow of river- 

 waters, mainly from melting ice. 



At the beginning of the Quaternary Period the Black Sea had a low salinity 

 and was populated by a Pontic fauna differing but little from that of the 

 Pontic basin ; its boundaries, moreover, have hardly changed at all up to the 

 present. Only along the Kumo-Manych depression is the Black Sea fauna 

 found, in deposits lying far outside its present boundaries. However, the 

 Black Sea salinity and its fauna underwent several substantial changes as 

 time went on. 



The so-called Ancient Euxine basin with a Caspian type of fauna was con- 

 nected with the Sea of Marmora ; the latter, however, had no link with the 

 Aegean Sea and the Mediterranean and had the same Caspian fauna. After 

 the formation of the Dardanelles, the Black Sea was filled with Mediterranean 

 water and the Mediterranean fauna, while the Caspian fauna was pushed far 

 into the corners of the sea, which had lost some of their salinity. Later the 

 entry of the Mediterranean waters into the Black Sea was interrupted by new 

 risings of the bottom, and the body of water again lost some of its salinity, its 

 Mediterranean fauna died out, and it was occupied by Caspian fauna. The 

 latest subsidences of the shores again caused an inflow of Mediterranean 

 waters and the arrival of its fauna, while the Caspian autochthonous forms 

 were pushed away into the river mouths and inlets. The salinity of the water 

 column increased from 7 to 22% from the time when a connection between 

 the Black Sea and the Mediterranean was established ; at present, however, 

 the salinity balance of the Black Sea is near the equilibrium point (S. P. 

 Brujevitch, 1952). The alternations of the south- Russian basins during the 

 Quaternary Period, according to A. Archangelsky (1932), are given in Table 

 142. 



A. Archangelsky and N. Strahov (1938) suggest that the glaciation periods 

 correspond to the low-salinity phases, and the interglacial periods to the 

 phases of increasing salinity. 



The Caspian Sea during the Quaternary Period 



The history of the Caspian Sea in the Quaternary Period begins in the Baku 

 basin with a fauna similar in its general features to the present one. This fauna 

 passes over into the subsequent post-Baku basins. Adacna, Monodacna and 

 Dreissensia are the most characteristic among the molluscs. The fluctuations 

 of salinity during the Ice Age and post-glacial period are mainly reflected in 

 a greater or smaller admixture of brackish- and fresh-water forms (Neritina, 

 Corbicula, Clessinia, Micromelania, Paludina, Unio, Valvata, Anodonta and 

 others). In the Caspian Sea, however, salinity did not reach the high level of 

 the Karangat basin during its high-salinity periods, but instead its waters 

 became more fresh than those of the Black Sea basin during the periods of 

 decreasing salinity. As a result the marked changes of fauna characteristic 

 of the Black Sea are absent in the Quaternary history of the Caspian Sea. 

 The main difficulty in the Quaternary history of the Caspian Sea is the 



