ABSTRACT
The eastern occurrence zone of the Villa Soriano Fm (=Vizcaino Fm) has been scarcely studied in relation to its fossiliferous content. In this work, a total of eleven species of bivalves and sixteen gastropods have been recorded from three outcrops located in the surroundings of the Merin Lagoon. The detailed evaluation of its taphonomic characteristics shows that they are parautochthonous accumulations. The associations indicate a littoral, mesohaline (fluvio-marine) environment, with warmer waters than in the present Uruguayan coasts. There are also species whose distribution boundary can be found nowadays displaced to the north. The diversity is variable, but the equitability is low, as there is a strong dominance by three species (Heleobia australis, H. charruana and Erodona mactroides). This feature is specially stressed in one of the localities, where the mentioned species are almost the only ones present showing a stronger fluvial influence.
