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1 October 2015 Graptolite-Trilobite Biostratigraphy in the Santa Victoria Area, Northwestern Argentina. A Key for Regional and Worldwide Correlation of the Lower Ordovician (Tremadocian—Floian)
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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 enables 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 Megistaspis (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.

Blanca A. Toro, Facundo R. Meroi Arcerito, Diego F. Muñoz, Beatriz G. Waisfeld, and G. Susana De La Puente "Graptolite-Trilobite Biostratigraphy in the Santa Victoria Area, Northwestern Argentina. A Key for Regional and Worldwide Correlation of the Lower Ordovician (Tremadocian—Floian)," Ameghiniana 52(5), 535-557, (1 October 2015). https://doi.org/10.5710/AMGH.16.06.2015.2905
Received: 16 March 2015; Accepted: 1 June 2015; Published: 1 October 2015
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