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Stratigraphic and paleogeographic significance of lacustrine molluscs from the Pliocene Viviparus deposits of NW Croatia

Coincidence of climate and geodynamic settings during the Pliocene provided conditions facilitating settlement of extended lacustrine environments in southeastern Europe. Conspicuously, the resulting long-lived paleolakes such as Lake Slavonia, Lake Kosovo, Lake Transylvania and Lake Dacia, were all characterized by explosive adaptive radiations of viviparid snails (HARZHAUSER & MANDIC, 2008). This phenomenon allowed NEUMAYR & PAUL (1875) in their famous, pioneering study on Lake Slavonia mollusks the establishment of regional phylostratigraphy, enabling up to recent an excellent stratigraphic control of that deposits stretching over more than 500 km along the southern margin of the Pannonian Basin. The present samples originate from the region of Kravarsko in Vukomeričke gorice, a low hillrange north of the Kupa River in the area between the towns of Zagreb, Sisak and Karlovac in NW Croatia. Representing the SW margin of the Lake Slavonia the freshwater deposits alternate there with alluvial series, providing altogether about 400-m-thick, Pliocene continental succession, known in literature by the informal name "Paludina beds" (acc. to a junior synonym of Viviparus). The samples comprise 2 bivalve and 11 gastropod species. Expectedly, the most species-rich are viviparids (4 taxa), followed by melanopsids and hydrobiids (each 2 taxa). Further families (valvatids, neritids, bithyniids, unionids, and sphaeriids) are represented by only one species each. The distribution pattern in the revealed mollusk assemblages proved up to three flooding events of Lake Slavonia into the investigated area, correlating with the Viviparus fuchsi Zone, the Viviparus dezmanianus Zone, and the Viviparus hoernesi Zone. This study is a partial contribution to the project "Freshwater systems in the Neogene and Quaternary of Europe: Gastropod biodiversity, provinciality, and faunal gradients" financed by the Austrian Science Fund (FWF project no. P25365- B25) and to the project “Basic Geological map of Republic of Croatia 1:50 000” financed by the Ministry of Science, Education and Sports of the Republic of Croatia (project no. 181- 1811096- 1093).

Lake Slavonia; Pliocene; Paludina beds; mollusc taxonomy; stratugraphy

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