Abstract. The Late Cretaceous Atlantic transgression in southern South America is recorded in western Argentina in the upper part of the Malargüe Group. The Cerro Butaló section outcrops in the south of Mendoza Province and comprises sediments attributable to the Jagüel and Roca formations. Well-preserved palynological associations were recovered from this section. Only the marine associations – dinoflagellate cysts, acritarchs and green algae – are considered in this article. A Late Maastrichtian age is suggested for the Roca and Jagüel formations based on the presence of Deflandrea galeata and Disphaerogena carposphaeropsis in the lower part of the section and Glaphyrocysta perforata in the upper part of the section and the absence of any Danian cosmopolitan markers. Variations in dinoflagellate cyst species diversity throughout the section permit recognition of two intervals that are probably related to different palaeoenvironmental conditions connected with episodes of sea-level fluctuation.