GENERAL CHARACTERISTICS AND GEOLOGICAL HISTORY 



357 



Caspian Sea) had a fauna characterized by a marked predominance of 

 Dreissensiidae and Cardidae which retained a certain successive link with 

 the Maeotic basin fauna. 



'Any geosyncline,' writes A. Archangelsky (1927), 'situated between 

 two platforms, at certain stages of its development is bound to undergo a 

 stage of dismemberment into a system of basins similar to that of the Caspian- 

 Mediterranean Sea. . . . The rise of some parts of the geosyncline and the 

 lowering of others can break up the geosyncline basin into a complex system 

 of deep bodies of water, some connected with the open sea, some entirely cut 

 off from it.' 



'The development of the Pontic basin', write M. Gerasimov and K. 

 Markov (1939), 'is closely connected with the considerable loss of salinity of 



Fig. 174. Pontic Lake-Sea (Andrussov). 



the Maeotic basin with the replacement of the "semi-marine" "Euxine" 

 conditions by those of a greatly diluted inland lake-sea of the "Caspian" 

 type. Only the Cardidae, some Gastropoda and Dreissensiidae of the Maeotic 

 fauna passed over into the Pontic basin ; the numerous forms of the Melanop- 

 sidae, Paludinidae and Limnaeidae families were added to it in great numbers 

 from the rivers and lakes. The true Cardium are no longer there, only the 

 Limnocardium ; but Didacna, Monodacna and Prosodacna are numerous.' 

 N. Andrussov (1918) assumes that this Pontic community was formed in the 

 west in the Middle-Danube lake-sea and was then propagated to the east. 



According to A. Archangelsky (1934) the basin of the Caspian Sea was 

 separated, either at the end of the Pontic Period or after it, by the rise of its 

 floor from the Black Sea part of the Pontic Lake-Sea, and since then the 

 development of the fauna of both parts proceeded independently (Fig. 1 75). 



The Black Sea basin during the Middle and Upper Pliocene 



In the western half, in the Cimmerian basin, the Pontic type of the fauna was 

 further developed. The Pontic fauna became considerably impoverished in 

 the subsequently somewhat less saline and warm Kuyalnits basin. 



The fauna of the last of the Pliocene basins, in the area of the present Black 

 Sea — the Chaudinsk Lake-Sea — differs greatly from that of the Kuyalnits one ; 

 according to Andrussov it is a derivative of the Pontic fauna, although it has 

 a great similarity with that of the present Caspian Sea. 



The history of the fauna of the Caspian part of the Pontic basin is different. 



