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

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

Londres

Congreso; 3th Internacional Palaeontological Congreso; 2010

IPA

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 fluctivagusNicoll et al. defines the Cambrian-Ordovician boundary. This species is recorded for the first time inSouth America in the Amarilla section at Cajas range, Cordillera Oriental of Jujuy, northwesternArgentina. High resolution biostratigraphy in other localities of the same basin, such as Alfarcito andSalto 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 boundaryin 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 theIapetognathus Zone in the lowermost Ordovician. The new data allow for precise regional correlationwith other Argentine basins, such as Famatina and Precordillera. A thorough analysis of the conodontfaunas reveals the presence of different faunal provinces for these basins in relation to theirrespective paleogeographic positions in the Iapetus Ocean and the Gondwanan margin of SouthAmerica.