ABSTRACT: Late Quaternary ostracod and foraminifera assemblages from five piston cores in Pelotas Basin, southern Brazilian margin, were analyzed in this paper. The study revealed a diverse bathyal fauna of ostracods, with abundance of the genera Apatihowella, Cytheropteron and Cytherella, interspersed with peaks of allochthonous neritic faunas. Benthic foraminifera are represented mainly by the genera Bolivina, Bulimina, Cassidulina, Epistominella, Globobulimina, Globocassidulina, Nonion, Oridorsalis and Uvigerina. Biostratigraphic analysis of planktic foraminifera positioned the samples in Pleistocene-Holocene interval. The ostracod genera Paracytherois, Cytheropteron, Cytherella, Macropyxis and the species Krithe hunti, Krithe reversa, Henryhowella asperrima, Eucytherura fossapunctata, Rimacytheropteron longipunctatum, Apatihowella besnardi and Apatihowella convexa, and also the benthic foraminifera Bolivina, Bulimina, Nonion, Nonionellina, Oridorsalis, Uvigerina, Epistominella and Cassidulina are related to environments of gas hydrates and associated with a chemosynthetic community in eutrophic-mesotrophic environments.