Chronostratigraphy of the mammal-bearing Paleocene of South America

Land mammal faunas of Paleocene age in the southern Andean basin of Bolivia and NW Argentina are calibrated by regional sequence stratigraphy and magnetostratigraphy. The local fauna from Tiupampa in Bolivia is similar to 59.0 Ma, and is thus early Late Paleocene in age. Taxa from the lower part of the Lumbrera Formation in NW Argentina (long regarded as Early Eocene) are between similar to 58.0-55.5 Ma, and thus Late Paleocene in age. A reassessment of the ages of local faunas from the Rio Chico Formation in the San Jorge basin, Patagonia, southern Argentina, shows that the local fauna from the Banco Negro Inferior is similar to 60.0 Ma, making this the most ancient Cenozoic mammal fauna in South America. Critical reevaluation of the Itaborai fauna and associated geology in SE Brazil favors the interpretation that it accumulated during a sea-level lowstand between similar to 58.2-56.5 Ma. All known South American Paleocene land mammal faunas are thus between 60.0 and 55.5 Ma (i.e. Late Paleocene) and are here assigned to the Riochican Land Mammal Age, with four subages (from oldest to youngest: Peligrian, Tiupampian, Itaboraian, Riochican s.s.). Based on the fact that notable taxonomic reorganization of Riochican faunas begins similar to 58.2 Ma, an Early (Peligrian, Tiupampian; 60.0-similar to 58.2 Ma) and Late (Itaboraian, Riochican s.s.; similar to 58.2-55.5 Ma) subdivision for this land mammal age is formally recognized. An interchange event for continental taxa between North and South America is identified between 58.2 and 56.5 Ma, which correlates with a sea-level lowstand and was probably enhanced by a major tectonic event beginning similar to 59.5 Ma that uplifted the Andean margin. (C) 1997 Published by Elsevier Science Ltd.