The Cambrian-Ordovician boundary in South America: High resolution biostratigraphy, global correlation and paleoenvironments

ALBANESI, G. L.; ORTEGA, G.; ZEBALLO, F. J.; PACHECO, F.

Congreso; International Palaeontological Congress; 2010

The base of the Ordovician System was formally established 120 years after C. Lapworth in 1879proposed this system to be interposed between the Cambrian and the Silurian in Great Britain.According to the GSSP in western Newfoundland, the FAD of the conodont Iapetognathus fluctivagus Nicoll et al. defines the Cambrian-Ordovician boundary. This species is recorded for the first time in South America in the Amarilla section at Cajas range, Cordillera Oriental of Jujuy, northwestern Argentina. High resolution biostratigraphy in other localities of the same basin, such as Alfarcito and Salto Alto, provides information regarding the homotaxial succession of key graptolite and trilobitespecies, in relation with conodont ranges. Rhabdinopora f. cf. canadensis (Lapworth) is recordedbelow the first appearance of Anisograptus matanensis Ruedemann, suggesting the presence of thelowest Ordovician R. f. parabola Zone, as verified worldwide. The FAD of the trilobite Jujuyaspiskeideli Kobayashi has up to now been considered as a proxy for the Cambrian-Ordovician boundary in the absence of key conodonts or graptolites. However, our recent studies demonstrate that J. keideli occurs from the lower Cordylodus intermedius Zone of late Cambrian age, up to the Iapetognathus Zone in the lowermost Ordovician. The new data allow for precise regional correlation with other Argentine basins, such as Famatina and Precordillera. A thorough analysis of the conodont Faunas reveals the presence of different faunal provinces for these basins in relation to their respective paleogeographic positions in the Iapetus Ocean and the Gondwanan margin of South America.