The bivalve faunas as a basis for reconstruction of the Middle Miocene history of the Paratethys

Abstract

The paper deals with the Paratethyan bivalve fauna recorded in Middle Miocene marine shallow-water sandy facies. Of the 429 recognized species, 343 occur in the Lower Badenian, 71 in the Chokrakian, 316 in the Upper Badenian, and 97 in the Konkian. Bivalve faunas are analyzed in order to determine the degree of similarity of contemporaneous assemblages from the Central and Eastern Paratethys, as well from Mediterranean and Atlantic bioprovinces.

The study of Lower Badenian and Chokrakian bivalve faunas (isochronous with the Langhian fauna of the Mediterranean) reveals that the Eastern Paratethys was cut off intermittently from communication with the Central Paratethys. Biogeographic affinities and the geographic pattern of Chokrakian bivalve assemblages indicates that the south-eastern part of the Eastern Paratethys was connected with the world ocean by a passage towards the East Mediterranean named the Middle Araks Straight. The species composition of Lower Badenian bivalve assemblages indicates a wide connection between the Central Paratethys and the Mediterranean. Apart from the western passage named the Transtethyan Trench Corridor, The East Mediterranean connection is postulated.

Comparision of the species composition of Konkian and Upper Badenian bivalve assemblages (isochronous with the lower Serravallian assemblages of the Mediterranean) suggests active faunal interchange between the Eastern and Central Paratethys. The distributional pattern of the Konkian bivalve fauna also indicates a seawy connection towards the East Mediterranean throught the re-opened Middle Araks Straight. The strong similarity between the Upper Badenian fauna from the Central Paratethys and the Middle Miocene fauna of the Mediterranean and Atlantic bioprovinces shows the existence of open marine connection and faunal interchange despite the closure of the Transtethyan Trench Corridor.