Patagonia, Argentina, is well-known for fossils of unique and extinct South American mammals. Gran Barranca, the "Great Cliff" has the most complete fossil record of the Cenozoic (Eocene-Miocene, 42-18.5 million years ago) in South America, and it contains abundant faunal remains entombed in datable volcanic rocks. Fossils at Gran Barranca demonstrate faunal evolution, and a record of ancient vegetation in the form of plant-silica is preserved. Regan E. Dunn and colleagues present a new chronology for the Sarmiento Formation based on high-resolution U-Pb isotopic dating techniques. The new dates provide key tie-points for magnetostratigraphy and allow for a new age model to date fossil samples. Because Gran Barranca is the most complete section of its age in South America, it serves as a rosetta stone for estimating ages of similar faunal assemblages found elsewhere. Our data along with other published ages for vertebrate sites in South America provide ages and durations of the so-called South American Land Mammal Ages. The new dates confirm that South America contains the oldest record of "grazer-like" tooth morphologies among Cenozoic plant-eaters globally, and that Gran Barranca preserves the only fossiliferous terrestrial section spanning the Eocene-Oligocene (about 34 million years) in the Southern Hemisphere.
|Contact: Kea Giles|
Geological Society of America