Resumen
Middle Darriwilian to lower Sandbian conodonts were recorded from the Las Aguaditas Formation at
its type section in the Argentine Precordillera. A total of 9,974 conodont specimens were recovered from 46 carbonate
samples, which represent 68 species of 38 genera. A biostratigraphic study verified a middle Darriwilian age for the interval
spanning the contact between the San Juan and the Las Aguaditas formations. The following zones are determined in the
study section: the Lenodus variabilis Zone, with the Periodon gladysae and Paroistodus horridus subzones following
the Precordilleran scheme; the L. variabilis, Yangtzeplacognathus crassus, and the Eoplacognathus pseudoplanus
zones with the Microzarkodina hagetiana and M. ozarkodella subzones, and the Pygodus anserinus Zone, according
to the Scandinavian scheme; the Periodon macrodentatus Zone, with the Histiodella sinuosa, H. holodentata and H.
cf. holodentata subzones, and the P. zgierzensis Zone with the H. kristinae Subzone that correlates the North American
scheme. A stratigraphic gap was recognized between the lower and middle members of the Las Aguaditas Formation.
It comprises the Eoplacognathus suecicus and Pygodus serra zones, and the lower subzone of the Pygodus anserinus
Zone. The variation of conodont diversity through the study section conforms to shallowing and deepening patterns,
which accompanies the changes of the provenance lithology. Three conodont assemblages were quantitatively recognized:
a) Diverse conodont association, b) Low diversity conodont association and c) Recovery phase association. We propose to
use the North American biozonal scheme of conodonts for the Central Precordillera because of the affinity of documented
index taxa, which provides a more accurate intercontinental correlation for the global Middle Ordovician Series.