The Tubara Formation in the arroyo Piedras Creek (169 m) is divided in three segments: The lower is interpreted as the result of siliciclastic sedimentation in an alluvial/deltaic plain; the intermediate as the result of sedimentation on a lagoon and/or coastal swamps, and the upper in the foreshore/bay – upper shoreface transition. The succession is dominated by the benthonic foraminifera assemblages Criboelphidium-Hanzawaia (CbHz) and Hanzawaia-Textularia-Criboelphidium (HzTCb) in the lower segment; Ammonia-Hanzawaia (AmHz) in the intermediate segment and Hanzawaia-TextulariaQuinqueloculina-Triloculina (HzQT) in the upper segment. The occurrence of the planktonic foraminifera taxa, Globigerinoides obliquus, Globigerinoides ruber and Truncorotalia aff crassaformis s.l. allows us to precise the age of the Tubara Formation as Early Pliocene.