CONICET | Buscador de Institutos y Recursos Humanos

In the La Trampa Range crops out in the northern section of the La Trampa Range, southwest of Jáchal in the Central Precordillera of the San Juan Province. There are outcrops of upper Lower to lower Middle Ordovician rocks of the San Juan Formation, which is conformably overlain by the Las Chacritas Formation of early Darriwilian age. This unit is in turn unconformably overlain by the La Chilca Formation, a latest Ordovician ? Silurian fine-grained siliciclastic unit, in the Las Chacritas River section, or at other localities it is paraconformably overlain by the early Sandbian Las Aguaditas Formation. The objective of the present contribution is to review the conodont biostratigraphy of the Las Chacritas Formation based on an integration of previous published information with our new data. This report documents the vertical distribution of the conodont taxa as well as provides precise identification and illustrations of the zone index species in the Middle Ordovician Series of Central Precordillera. The present study has resulted in the establishment of a refined conodont biostratigraphic zone scheme for the Darriwilian Stage of the Central Precordillera. Based on the level of appearance of index species, three conodont zones are recognized in the interval from the top part of the San Juan Formation and through the Las Chacritas Formation, namely the Yangtzeplacognathus crassus, Eoplacognathus pseudoplanus and Eoplacognathus suecicus zones. The presence of the zone index species and the associated conodont faunas permit precise global correlations. Conodont zone schemes from other regions, such as South China, Baltoscandia, and Newfoundland, can be correlated, which enables us to propose a high resolution regional biostratigraphic chart for this interval.