A stratigraphic section of the Los Rastos Formation have been recognized at Rio Gualo. A detailed description of the sedimentology of the section was used to interpret the facies assemblage and to reconstruct the depositional environment. Systematic palynological sampling was conducted; and this paper is based on the study of 15 samples. Laboratory procedures followed conventional practices. Carbonates and silicates were removed by treatment with hydrochloric and hydrofluoric (70%) acids. Residues were sieved on a 25 µm mesh and mounted in unstained glycerine jelly as well as in Cellozise on glass slides. Specimens were examined under a Leitz Orthoplan binocular microscope. Photomicrographs were taken with a Leitz Orthomat camera using AGFAPAN APX25 and ILFORDPAN NF50 films. Palynological slides are prefixed BAFC-Pl. The illustrated specimens are identified with a slide number and England Finder coordinates. The slides are deposited at the Geological Sciences Department, Buenos Aires University. E.G. Ottone prepared the palynological section of the paper. A.C. Mancuso collected the samples and provided geological information. M. Resano collaborated in the study of the Chlorococcales.