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A new chronology for middle Eocene-early Miocene South American land mammal ages

Regan E. Dunn, Richard H. Madden, Matthew J. Kohn, Mark D. Schmitz, Caroline A. E. Stroemberg, Alfredo A. Carlini, Guillermo H. Re and James Crowley
A new chronology for middle Eocene-early Miocene South American land mammal ages
Geological Society of America Bulletin (December 2012) 125 (3-4): 539-555


Cenozoic South American Land Mammal Ages (SALMAs) have historically been correlated to the geologic time scale using (super 40) Ar/ (super 39) Ar dating and magnetostratigraphy. At Gran Barranca (68.7 degrees degrees W, 45.7 degrees S)-one of South America's key areas for constraining SALMAs-existing radioisotopic ages have uncertainties of up to 4 m.y. To better constrain the ages of mammalian assemblages, we employed high-precision (+ or -<40 k.y.) U-Pb dating using single zircon crystals. We dated nine tuffs from the Sarmiento Formation containing middle Eocene-early Miocene faunas (Barrancan, Mustersan, Tinguirirican, Deseadan, Colhuehuapian, and "Pinturan"). The new dates span from 39.861+ or -0.037 Ma to 19.041+ or -0.027 Ma. The La Cancha Tuff, occurring within the Tinguirirican faunal level yielded an age of 33.581+ or -0.015 Ma, confirming that the Vera Member contains the only fossiliferous geologic section encompassing the Eocene-Oligocene transition in the Southern Hemisphere. The pre-Deseadan fauna, La Cantera, is < or =30.77 Ma, the age of the Colhuehuapian is expanded to 21.1-20.1 Ma, and the Pinturan may be as old as ca. 19 Ma. The new U-Pb dates confirm that atmospheric temperatures and vegetation remained constant across the Eocene-Oligocene transition in Patagonia and that hypsodonty occurred in South American ungulates much earlier than on any other continent. Additionally, refinement of the SALMA boundaries will eventually provide the context necessary to compare faunal transitions across continents, although currently too much data are missing to allow such comparisons. Finally, the new ages provide a high-resolution age model from which hypotheses about rates of environmental and evolutionary change at Gran Barranca can be tested.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 125
Serial Issue: 3-4
Title: A new chronology for middle Eocene-early Miocene South American land mammal ages
Affiliation: University of Washington, Department of Biology, Seattle, WA, United States
Pages: 539-555
Published: 20121210
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 94
Accession Number: 2013-009626
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2013071
Illustration Description: illus. incl. strat. col., 3 tables, sketch map
S45°42'49" - S42°45'49", W68°44'16" - W68°44'16"
Secondary Affiliation: University of Chicago, USA, United StatesBoise State University, USA, United StatesUniversidad Nacional de La Plata y Museo, ARG, ArgentinaUniversidad de Buenos Aires, ARG, Argentina
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201307
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