Biostratigraphic implications of Kallidontus nodosus Pyle and Barnes in the Ordovician of the Eastern Cordillera, Argentina

A biostratigraphic reevaluation of the conodont faunas of the Acoite Formation at the La Ciénaga de Purmamarca, northwestern Argentina, is presented here to constrain its depositional age and improve its regional correlation. The new conodont assemblage, consisting of 636 elements, includes Balognathidae indet., Drepanodus arcuatus, Drepanoistodus pitjanti, D. cf. andinus, D. sp. A, Gothodus andinus, Kallidontus nodosus, Paroistodus sp., and Zentagnathus argentinensis. These species were obtained from the same beds sampled by previous authors, who attributed varying ages to the conodont assemblage. Of special importance is the record of K. nodosus, which allows for precise correlation of the lower levels of the Gothodus andinus Zone with the early Floian Prioniodus elegans Zone (Fl 1). This finding is consistent with the graptolite and trilobite data available at the La Ciénaga de Purmamarca, and it raises caution regarding the taxonomic determination of Baltoniodus triangularis, the index fossil for the Lower-Middle Ordovician Series boundary in other stratigraphic sections of the Acoite Formation along the Eastern Cordillera.