The Villafranchian molluscan fauna from the Steggio basin (Treviso, Northeast Italy): Paleoecology and biochronology

Abstract

A rich non-marine molluscan fauna has been recorded from Plio-Pleistocene fluvio-lacustrine deposits of the Steggio basin (Treviso, Northeast Italy) together with Villafranchian vertebrate and macroflora remains. The molluscan assemblages are composed of numerous land gastropods and little freshwater bivalves. The qualitative and quantitative analysis of the molluscs has permitted us to obtain a paleoecological reconstruction of the deposition environment of the Steggio clay unit. The environment seems to be affected by an increase in humidity up to the settlement of a palustrine biotope, characterised by a water saturated ground and testified by the dominance of strongly hygrophilous taxa in the upper part of the succession. A progressive decrease in the arboreal cover and a warm-temperate climate have been detected. The rather modem character of the molluscan assemblages and the presence of two extinct species characterising the Central-Western European and Italian Villafranchian faunas, Carychium (Saraphia) pseudotetrodon Strauch and Gastrocopta (Vertigopsis) dehmi Schlickum & Strauch, makes it possible to attribute the studied molluscan assemblages to the latest Pliocene or to the lowermost Pleistocene.