Oligocene-Miocene freshwater gastropods from the Oltu-Narman Basin in eastern Turkey

摘要

We describe the first record of a late Oligocene or early Miocene freshwater gastropod fauna from the Susuz Formation of the Oltu-Narman Basin in northeastern Anatolia. The assemblage consists of only six species, indicating the presence of a well-oxygenated lake, pond or anabranch rich in vegetation. Only two of the taxa are related to European Oligo-Miocene species. The fauna might be the first indication of a yet undocumented Eastern Anatolian freshwater biogeographic region, characterized by high endemism and minor influence from the coeval Peri-Paratethyan and Aegean-Anatolian regions in the west. The biostratigraphic value of the assemblage is low but might rather point to a Miocene age of the upper part of the Susuz Formation. Theodoxus susuzianus, Bithynia erzurumensis, and Valvata koehleri are described as new species.