Conodonts and graptolites of the Santa Rosita Formation (Tremadocian) at the Nazareno area, Santa Victoria Range, Cordillera Oriental de Salta, Argentina

Abstract

The Nazareno area is located to the southeast of the Santa Victoria range in the Cordillera Oriental of Salta, Argentina, with extensive exposures of Ordovician rocks (Ortega and Albanesi, 2002; Brussa et al., 2003; Astini, 2003; Albanesi et al., 2008, and references therein). At this area a thick siliciclastic succession of the Santa Rosita Formation from the Lower Ordovician crops out (Turner, 1960) (Fig. 1). Previous works describe a succession that consists of sandstones and shales, and subordinate calcareous rocks with abundant fossils of early Tremadocian age (e.g., trilobites, braquiopods, gastropods, conodonts, acritarchs) (Harrington and Leanza, 1957; Vilela, 1961; Manca et al., 1995). The Paltodus deltifer conodont Zone of the upper middle Tremadocian was first identified in this area by Manca et al. (1995), who reported the presence of Paltodus deltifer Lindström, Drepanodus arcuatus Pander, Acodus deltatus deltatus (Lindström), among other taxa, however, the illustrations of these specimens do not allow a definite determination...