GRAPTOLITE-TRILOBITE BIOSTRATIGRAPHY IN THE SANTA VICTORIA AREA, NORTHWESTERN ARGENTINA. A KEY FOR REGIONAL AND WORLDWIDE CORRELATION OF THE LOWER ORDOVICIAN (TREMADOCIAN/FLOIAN)

TORO BLANCA; MEROI ARCERITO F.R.; D.F. MUÑOZ; B.G. WAISFELD; DE LA PUENTE SUSANA

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2015 vol. 52 p. 535 - 557

0002-7014

New graptolite-trilobite records provide relevant information for the biostratigraphic scheme of the Lower Paleozoic from western Gondwana. Aorograptus victoriae (T. S. Hall) with Adelogratus cf. A. altus Williams and Stevens and Ancoragraptus bulmani (Spjeldnaes) are described for the first time in the area, from the upper levels of the Santa Rosita Formation, allowing to spread out the distribution of the A. victoriae Biozone. The complete succession of the Aorograptus victoriae, Araneograptus murrayi, Hunnegraptus copiosus, Tetragraptus phyllograptoides, T. akzharensis, Baltograptus cf. B. deflexus and Didymograptellus bifidus biozones is confirmed for the first time in a single locality of the Cordillera Oriental. This graptolite biozonation indicates a late Tremadocian/late Floian age for the upper deposits of the Santa Rosita Formation and the Acoite Formation in the studied area. Co-occurrence of trilobites with the records of these graptolite biozones allows the refinement of the upper boundary of the Notopeltis orthometopa Biozone, the definition of associations that partially fill gaps in the succession of traditional trilobite biozones (Asaphellus cf. A. stenorhachis / Leptoplastides and M. (Ekeraspis) associations), and the refinement of the distribution of some members of the well-known Thysanopyge Fauna (T. taurinus, T. victoriensis and T. clavijoi). According to the proposed scheme, previous records of conodonts and key palynomorphs (particularly chitinozoans) related to graptolite occurrences are also discussed. New insights for regional and intercontinental correlation with classic Early Ordovician successions from north-western Argentina (e.g. Pascha?Incamayo, Los Colorados, Mojotoro range and Humahuaca creek area), southern Bolivia and Balto-Scandinavia are additionally provided.