Producción CyT
Congreso
Autoría
Clyde, W. C.
;
Barnum, T.
;
KRAUSE, JAVIER MARCELO
;
Ibañez-Mejía, M.
Fecha
2013
Editorial y Lugar de Edición
Society of Vetebrate Paleontology
ISSN
1937-2809
Resumen
Información suministrada por el agente en
SIGEVA
The Río Chico Group in the San Jorge Basin of Patagonia (Argentina) preserves some of the most important records of Paleogene biotas in South America. The Itaboraian and Riochican South American Land Mammal Ages (SALMAs), and the less well defined "Carodnia Zone", are based, at least in part, on fossil assemblages collected from the Río Chico Group. The precise age of the Río Chico formations, and thus their faunas,is poorly resolved making it difficult to know ho...
The Río Chico Group in the San Jorge Basin of Patagonia (Argentina) preserves some of the most important records of Paleogene biotas in South America. The Itaboraian and Riochican South American Land Mammal Ages (SALMAs), and the less well defined "Carodnia Zone", are based, at least in part, on fossil assemblages collected from the Río Chico Group. The precise age of the Río Chico formations, and thus their faunas,is poorly resolved making it difficult to know how Paleogene SALMAs correlate to the geological timescale and to land mammal age frameworks on other continents. For instance, it is not known whether Paleogene mammalian turnovers in the southern hemisphere coincided with those in the holarctic. Precisely dating these units is hindered by the fact that the mammal faunas themselves are highly endemic and the deposits are exposed across ~300 km distance, creating the possibility for significant diachroneity from one part of the basin to the other. Here we report new paleomagnetic and geochronological results from the Río Chico Group in the Las Flores area of the western San Jorge Basin. We collected 171 paleomagnetic samples from 40 sites within a 115 meter stratigraphic section spanning the upper Peñas Coloradas, Las Flores and Koluel Kaike formations of the Río Chico Group. Measurements of dual frequency magnetic susceptibility, three-axis isothermal remanent magnetization, and characteristic remanent magnetization via step-wise demagnetization were used to develop a reliable magnetostratigraphy for this section. Four apparent volcanic ashes were also sampled from the section (in addition to one more from a nearby section) for U/Pb dating using laser ablation HR-MC-ICP-MS. Magnetostratigraphic results show that the upper Peñas Coloradas Fm. is characterized by reversed polarity with a change to normal polarity within the base of the Las Flores Fm. The Las Flores Fm. is characterized by normalpolarity, however many of the samples in this part of the section exhibited superparamagnetic behavior and thus did not provide a reliable polarity determination. Samples from the Koluel Kaike Fm. exhibited very stable paleomagnetic behavior and clearly record three polarity reversals in that unit. These magnetostratigraphic results will be combined with the new U/Pb ages and recent chronostratigraphic results from the underlying Salamanca Formation to correlate the Río Chico units to the Geomagnetic Polarity Timescale and better constrain the correlation of the associated SALMAs to land mammal age frameworks on other continents.
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Palabras Clave
Río Chico GroupPaleogene SALMAGeochronologyMagnetostratigraphy