GENERAL CHARACTERISTICS AND GEOLOGICAL HISTORY 359 



that the preceding basin had very small quantities of productive deposit and 

 its /waters were almost completely fresh. The Akchagyl basin must have re- 

 ceived, from somewhere, both the main mass of the saline water filling it 

 and the corresponding fauna, which had a clearly expressed Sarmatian 

 aspect* (Andrussov, 1902). Although the existence of a link in the west be- 

 tween the Akchagyl and Kuyalnits basins has lately been established, the 

 former could not have obtained its marine forms from the latter, which was 



Fig. 176. Kuyalnits (/) and Akchagyl (2) basins 

 (Archangelsky). 



at that time a brackish-water basin of the Caspian or Pontic type, and itself 

 could rather have obtained a part of its forms from the east, from the Akchagyl 

 basin. A. Archangelsky (1934) admits only 'one single possible route for the 

 fauna from the southeast, from Persia, perhaps from the region of the Persian 

 Gulf. The originally poor Akchagyl fauna became very rich in species at the 

 middle of the existence of this basin. During its last phase the Akchagyl Sea 

 was connected with the Black Sea region through the discharge of its waters 

 to the west, south of Manych. At that time a certain number of Ackhagyl 

 forms penetrated to the west. Later the Akchagyl Sea began to contract 

 rapidly, its waters lost their salinity, and the rich Akchagyl fauna died out 

 almost completely except for some gastropods — Cardidae. Many of the 

 Dreissensiidae appeared simultaneously. 



The Apsheron and Baku basins 



The size of the Caspian basin became greatly reduced during the Apsheron 

 period (Fig. 177). The Apsheron basin, and the Baku basin which followed it, 



* V. Kolesnikov (1940), however, considers the similarity between the Akchagyl 

 and Sarmatian faunas as purely extraneous. In his opinion this fauna has no connection 

 with the south-Russian Miocene or Pliocene. 



