Geological Society of America bulletin, 2017-03-16, Vol.129 (7-8), p.886-903
The Rio Chico Group in the San Jorge Basin of central Patagonia (Argentina) preserves some of South America's most significant Paleogene records of biotic and climatic change. Three of its constituent formations, the Penas Coloradas, Las Flores, and Koluel-Kaike, host vertebrate faunas referred to the "Carodnia faunal zone," the Itaboraian South American Land Mammal Age (SALMA), and the Riochican SALMA. However, the precise absolute ages of these units, and thus their associated faunas and paleoclimate records, are poorly resolved. Herein, we report new paleomagnetic and geochronologic results from these formations in south-central Chubut Province, Argentina. U-Pb dating of four volcanic ashes, using both laser ablation-multicollector-inductively coupled plasma-mass spectrometry and high-resolution chemical abrasion-isotope dilution-thermal ionization mass spectrometry, indicates ages of igneous crystallization of 51.403 ± 0.037 (0.045) [0.071] Ma for a level within the middle Las Flores Formation and 46.714 ± 0.012 (0.026) [0.057] Ma, 44.579 ± 0.013 (0.026) [0.054] Ma, and 42.856 ± 0.017 (0.027) [0.054] Ma for levels in the lower, middle, and upper Koluel-Kaike Formation, respectively. Combining these with previous isotopic ages in our new magnetostratigraphic framework, we correlate the Penas Coloradas Formation to chrons C27n-26r (ca. 62.5 to ca. 61.6 Ma; late Danian) and the section from the middle Las Flores to the uppermost Koluel-Kaike to chrons C23n to C19r (ca. 51.4-42.2 Ma; mid Ypresian-late Lutetian). We combine these data with other recently published chronostratigraphic results from Paleogene units in Patagonia to better constrain the ages of noteworthy Paleogene plant and mammal fossil sites in Patagonia and to develop a revised temporal calibration of the Las Flores, Vacan, and "Sapoan" faunas.
absolute age ; Argentina ; biozones ; Cenozoic ; Chordata ; chronostratigraphy ; Chubut Argentina ; Eocene ; Geochronology ; Geomorphology ; Koluel-Kaike Formation ; Las Flores Formation ; lithostratigraphy ; lower Paleogene ; magnetostratigraphy ; Mammalia ; nesosilicates ; Observations ; orthosilicates ; Paleocene ; paleoclimatology ; Paleogene ; paleomagnetism ; Patagonia ; Penas Coloradas Formation ; Rio Chico Group ; San Jorge Basin ; Sarmiento Formation ; sedimentary rocks ; silicates ; South America ; Stratigraphy ; terrestrial environment ; Tertiary ; Tetrapoda ; U/Pb ; Vertebrata ; zircon ; zircon group
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