Absolute and relative ages of fossil localities in the Santa Cruz and Pinturas Formations

Abstract

Santa Cruz Province, Argentina, has some of the richestfossil mammal localities in the world. However, the absoluteand relative ages of its fossil localities have long beena source of confusion and debate. In particular, there hasbeen longstanding disagreement about the relative ages ofthe fossils from the western part of the province indeposits of the Pinturas Formation compared with thosefrom the numerous localities of the Santa Cruz Formationalong the Atlantic coast. Drawing on recent studies of thetuffaceous sediments in many classic fossil localities, andstudies of fossil representatives of marsupials, rodents,and primates, we provide a synthesis of the temporalrelationship among fossil localities throughout the province.There is broad agreement between the results ofthe tephrochronology and mammalian paleontology. Bothtephra correlations and paleontological comparisons indicatethat the lower units of the Pinturas Formation areolder than the sections of the Santa Cruz Formation preservedat Monte Leon and Cerro Observatorio, supportingAmeghino suggestion that part of the Pinturas Formationrepresents a distinct faunal zone. However, the upperunit of the Pinturas Formation seems to correspond in agewith the lower part of the sections at Monte Leon andCerro Observatorio.