Resumen
The presence of stromatolites from Cretaceous outcrops at the headwaters of the río Chico locality in the Golfo San Jorge Basin is reported for the first time. They are present in the uppermost part of the Lago Colhué Huapi Formation (Coniacian-Maastrichtian) of the Chubut Group. The presence of, up to now, four structures interpreted as stromatolites in this locality are not only important because it is the first record in the basin, but because it contributes to the knowledge of these bioconstructions in continental environments. The stromatolite called E1, which is characterized and discussed in detail, is associated with an abundant and diverse fossil record represented by palynomorphs, fragments of silicified trunks, dinosaur remains and eggshells. The study, integrated mainly with the recorded pollen and spores, is important for paleoenvironmental interpretations of the site and contributes to the paleoecological and paleoclimatic understanding of the most modern stratigraphic interval of the Chubut Group.