Graptolite-trilobite biostratigraphy in the Santa Victoria area, northwestern Argentina. A key for regional and worldwide correlation of the Lower Ordovician (Tremadocian-Floian)

TORO, B.A; MEROI, F.; MUNOZ, D.; WAISFELD, B.G.; DE LA PUENTE G.S.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

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

0002-7014

Abstract. New graptolite-trilobite records provide relevant information for the biostratigraphic framework of the Lower Paleozoic in western Gondwana. Aorograptus victoriae (T. S. Hall), together with Adelogratus cf. A. altus Williams and Stevens and Ancoragraptus bulmani (Spjeldnaes) are described for the first time in the Santa Victoria area. These species come from the upper beds of the Santa Rosita Formation, expanding 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 at a single locality in the Cordillera Oriental, indicating a late Tremadocian?late Floian age for the upper deposits of the Santa Rosita Formation and the Acoite Formation in the studied area. The co-occurrence of trilobites with the records of these graptolite biozones enable a better resolution of the upper boundary of the Notopeltis orthometopa Biozone and the definition of associations partially filling gaps in the succession of traditional trilobite biozones [Asaphellus cf. A. stenorhachis / Leptoplastides and M. (Ekeraspis) associations]. It also contributes towards clarifying the distribution of some members of the well-known Thysanopyge Fauna (T. taurinus, T. victoriensis and T. clavijoi). Together with the proposed framework, we also discuss previous records of conodonts and key palynomorphs (particularly chitinozoans) related to graptolite occurrences. Additionally, we provide new insights on regional and intercontinental correlation with classic Early Ordovician sections in northwestern Argentina (e.g., Pascha?Incamayo, Los Colorados, Mojotoro range and Humahuaca  area), southern Bolivia and Balto-Scandinavia.