OLIGOCENE MOLLUSKAN FAUNA OF THE UKRAINIAN CARPATHIANS

Abstract

The marine Oligocene molluskan fauna has been studied from two levels of the Outer Carpathians in Ukraine. The mollusks have been collected from Subchert Member of the Boryslav-Pokut Unit, immediately below the Lower Chert Level: the Pistynka river section at Kosmach and the Rybnica river at Kosov, as well as from two localities of the Skibas Unit: the Chechva river section at Spas and the Luzhanka river section at Stankivci from the basal part of the Middle Menilite (Lopianca) Subformation. The richest molluskan fauna at the Kosmach locality includes 38 bivalve species representing 14 families and 10 gastropod species belonging to 10 families. Kosov assemblage is similar to the preceding and contains 15 bivalve and 5 gastropod species. From the presence of large specimens of Glycymeris sp., Nemocardium (Habecardium) sp., venerids, caliptreas - typical dwellers of shallow-water environments, as well as lithological indicators, it can be concluded that molluskan fauna occurs in the Subchert Member as an allochthonous assemblage. The main difference between the molluskan assemblages from these localities and those from the northern seaside of the Eastern Paratethys Oligocene lies in the occurrence of Barbatia, diverse lucinids, representatives of gastropod families Turritellidae, Volutidae, Conidae in the Carpathians, all being warm-water taxa. Any species which are characteristic of the Early Oligocene assemblages of the Eastern Paratethys are missing from the Carpathian associations. The fauna of the Lopianca Subformation at the Spas locality includes 29 bivalve species belonging to 12 families and the representatives of 4 gastropod families. This molluskan fauna indicates shallow-water environment and presence of Cardita s.s., Lucina s.s., diverse venerids, lucinids, turritellids distinguishes it from impoverished assemblages of the northern margins of the Eastern Paratethys. No Paratethyan endemics known from the Eastern Paratethys occur here.