Graptolites are the most important biostratigraphic tool in the study of the Silurian of the Argentine Precordillera. Since, however, the graptolites are concentrated primarily in the Lower Llandovery and Ludlow of the region, the ages of parts of some stratigraphic units are poorly known. The recovery of a small Upper Llandovery graptolite assemblage in the lower one-third of the La Chilca Formation of the Talacasto area helps in resolving this problem, and that assemblage is the focus of this study. Brachiopods, trilobites, bivalves, and ostracodes are present in the same stratigraphic intervals, but are less common and less studied and,...

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