Browsing by Autor "Bruce J. MacFadden"

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Magnetic polarity stratigraphy of Inchasi: a Pliocene mammal-bearing locality from the Bolivian Andes deposited just before the Great American Interchange
(Elsevier BV, 1993) Bruce J. MacFadden; Federico Anaya; Jaime Argollo
Middle Pleistocene age of the fossiliferous sedimentary sequence from Tarija, Bolivia
(Cambridge University Press, 2013) Bruce J. MacFadden; Peter K. Zeitler; Federico Anaya; John M. Cottle
Abstract The highly fossiliferous sediments of the Tolomosa Formation from Tarija, southern Bolivia, represent one of the most important localities in South America that documents the Great American Biotic Interchange. Over the past several decades, chronostratigraphic studies have indicated a middle Pleistocene age for the Tolomosa Formation from ~ 1.1 to 0.7 Ma. This interval correlates to the Ensenadan South American Land Mammal Age as it is characterized from classic localities in Argentina. Recently, however, a new interpretation based on AMS 14 C ages indicates that the fossiliferous sediments from Tarija are latest Pleistocene, i.e., < 44 ka, and thus of Lujanian age. Here we report a new age of 0.76 ± 0.03 Ma (2σ) based on 11 U–Th/Pb and U–Th/He individual determinations from the Tolomosa Formation. This is indistinguishable from the age published from the same ash in 1983, and was originally used to calibrate the magnetostratigraphic section at Tarija. The new age confirms that the age of the Tolomosa Formation is middle Pleistocene, and not latest Pleistocene. The age of the Tarija Fauna has significant implications with regard to the stage of evolution biochronology for Pleistocene fossil mammals in South America, and in particular, the classic and important reference sections in Argentina.
New Data on Miocene Neotropical Provinciality from Cerdas, Bolivia
(Springer Science+Business Media, 2009) Darin A. Croft; Federico Anaya; David Auerbach; Carmala N. Garzione; Bruce J. MacFadden
Revised age of the Salla beds, Bolivia, and its bearing on the age of the Deseadan South American Land Mammal “Age”
(Taylor & Francis, 1998) Richard F. Kay; Bruce J. MacFadden; Richard H. Madden; H A Sandeman; Federico Anaya
ABSTRACT The Salla beds of Bolivia contain a mammalian faunal assemblage assigned to the Deseadan South American Land Mammal “Age” (SALMA), known elsewhere principally in Patagonia. The earliest platyrrhine monkey Branisella comes from a single stratigraphie level in these beds. The age of the Salla beds is debated; new radiometrie dates constrain the age of the Deseadan SALMA in Bolivia and clarify the timing of the first record of platyrrhines in South America. The oldest vertebrate fossils from the Salla beds are contained within the magnetic polarity interval ClOr, between 28.8 and 29.4 Ma. The youngest fossils occur above the 275 m ash in Chron C7Ar, between 25.65 to 25.82 Ma. The best known faunas, including those of the Branisella level, come from several localities within Chron C8 (25.82 to 27.02 Ma). If the recent suggestion by Flynn and S wisher (1995) that redating indicates that the Deseadan in Patagonia spans only about 27 to 29 Ma, then the bulk of the Salla fauna is younger than that of Patagonia.
South American fossil mammals and carbon isotopes: a 25 million-year sequence from the Bolivian Andes
(Elsevier BV, 1994) Bruce J. MacFadden; Yang Wang; Thure E. Cerling; Federico Anaya
Spatial–temporal changes in Andean plateau climate and elevation from stable isotopes of mammal teeth
(Elsevier BV, 2009) John Bershaw; Carmala N. Garzione; Pennilyn Higgins; Bruce J. MacFadden; Frederico Anaya; Herculano Alvarenga