Malacofauna of the Holocene tufa in the valley of the Ociemny Stream (Pieniny Mts., southern Poland)

Abstract

A rich molluscan fauna was found in the outcrop of slope sediments and calcareous tufas in the valley of the Ociemny Stream in the Pieniny Mts. The malacological sequence identified there represents the entire Holocene, but it contains several stratigraphical gaps. From this viewpoint, it is a unique finding within the area studied. In nine samples, 11,000 specimens of 71 species of molluscs were identified. The ecological and zoogeographical diversity of the composition and structure enabled the separation of three faunistic assemblages. The oldest assemblage (with <i>Discus ruderatus</i>) corresponds with the cold period of the Early Holocene and represents shadowed habitats overgrown with the coniferous forests of the taiga type. Its characteristic feature is the presence of glacial relics (e.g. <i>Vertigo genesii</i> and <i>Vertigo geyeri</i>). The other younger fauna (with <i>Discus perspectivus</i>) is typical of the humid and warm climate of the Atlantic Phase. It is characteristic of the habitats of mixed and deciduous forests. Numerous Balkan and Mediterranean thermophilous forms appear in this assemblage. The youngest malacoenosis (with <i>Bithynella austriaca</i>) is typical for the historical times. The particular intervals containing molluscan fauna are separated by gaps corresponding to the erosion phases. Because of the land relief in the valley of the Ociemny Stream, which is not conducive to the development of human economy, no marked anthropogenic deforestation occurs.