New high precision U-Pb ages for the Vinchina Formation: Implications for the stratigraphy of the Bermejo Andean foreland basin (La Rioja province,western Argentina) |
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| Institution: | 1. Departamento de Ciencias Geológicas- IGeBA, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires – CONICET. Ciudad Universitaria, Pabellón 2, 1° piso, C1428EHA Buenos Aires, Argentina;2. UBC-EOS PCIGR, 6339 Stores Road, Vancouver, BC V67 1Z4, Canada;1. Instituto Superior de Correlación Geológica (INSUGEO-CONICET), Universidad Nacional de Tucumán, Miguel Lillo 205, T4000JFE, San Miguel de Tucumán, Argentina;2. Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de Tucumán, Miguel Lillo 205, T4000JFE, San Miguel de Tucumán, Argentina;3. Paleontología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Centro Científico Tecnológico CONICET Mendoza, Avda. Ruiz Leal s/n, 5500, Mendoza, Argentina;1. INGEOSUR-CONICET, Departamento de Geología Universidad Nacional del Sur, San Juan 670, 8000, Bahía Blanca, Buenos Aires, Argentina;2. Departamento de Geología Universidad Nacional del Sur, San Juan 670, 8000, Bahía Blanca, Buenos Aires, Argentina;3. Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Avenida Uruguay 151, 6300, Santa Rosa, La Pampa, Argentina;1. Universidade do Vale do Rio dos Sinos – UNISINOS, Av. Unisinos, 950, CEP 93022-000 São Leopoldo-RS, Brazil;2. Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, CEP 91509-900 Porto Alegre-RS, Brazil;3. Instituto de Geociências, Universidade de São Paulo, Rua do Lago, 562, Cidade Universitária, São Paulo 05508-080, SP, Brazil;1. Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Uruguay 151, 6300, Santa Rosa, La Pampa, Argentina;2. Instituto de Geología y Recursos Minerales, Servicio Geológico Minero Argentino, 1650, San Martín, Buenos Aires, Argentina;3. Paleobiología y Paleoecología, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET-Mendoza, Avda. Ruiz Leal s/n. M5500, Mendoza, Argentina;4. Sección Mastozoología, División Zoología Vertebrados, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s/n, 1900, La Plata, Buenos Aires, CONICET, Argentina;5. Museo Paleontológico Egidio Feruglio, Av. Fontana 140, Trelew, U9100GYO, Chubut, Argentina;6. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina;7. Instituto Geológico del Sur, Departamento de Geología, Universidad Nacional del Sur- CONICET, Avenida Alem 1253, 8000, Bahía Blanca, Buenos Aires, Argentina;1. Centro de Investigaciones Geológicas (CONICET–UNLP), Diag. 113 # 275, La Plata, 1900, Argentina;2. División Paleontología Vertebrados, Unidades de Investigación Anexo Museo de La Plata, Facultad de Ciencias Naturales y Museo, UNLP. CONICET. 122 y 60, La Plata, 1900, Argentina;3. INGEOSUR-CONICET, Departamento de Geología, Universidad Nacional del Sur. San Juan 670, Bahía Blanca, 8000, Argentina;4. INCITAP (CONICET-UNLPam), Universidad Nacional de La Pampa, Mendoza 109, Santa Rosa, 6300, Argentina;5. División Paleontología Vertebrados, Museo de La Plata, CIC. Paseo Del Bosque s/n, La Plata, 1900, Argentina;6. University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, T1K 3M4, Canada;7. CADIC-CONICET, Laboratorio de Geomorfología y Cuaternario, Universidad Nacional de Tierra del Fuego, Bernardo Houssay 200, Ushuaia, 9410, Argentina |
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| Abstract: | The Vinchina Formation is one of the thickest Cenozoic units related to the Andean orogeny in Argentina totaling more than 5100 m in thickness. Different ages, from Eocene to latest Miocene, have been postulated for this red-bed succession based on fission track, magnetostratigraphy and whole rock isotopic analyses. Two new high precision U-Pb zircon ages are reported herein for this unit. A maximum U-Pb age of 15.6 ± 0.4 Ma was obtained from detritic zircons collected from a thick tuffaceous interval of the Lower Member of the Vinchina Formation at La Cueva (Precordillera), while a depositional U-Pb age of 9.24 ± 0.034 Ma was derived from volcanic zircons collected from a thin tuff bed in the Upper Member at Quebrada de Los Pozuelos (Northwestern Sierras Pampeanas).At La Cueva, the Vinchina Formation unconformably overlies eolian sandstones of the Vallecito Formation and was divided into four units representing 1) deposits of high-sinuosity ephemeral rivers associated with 2) a playa-lake passing upwards to 3) low-sinuosity sandy ephemeral rivers and finally, 4) a gravelly-sandy braided plain. The tuffaceous level corresponding to unit 1 is located 280 m above the base of the formation.At Quebrada de Los Pozuelos, the Vinchina Formation unconformably overlies the Vallecito Formation and is covered by a deeply incised surface at the base of the Toro Negro Formation. We divided the Vinchina Formation into four units. Unit 1 represents sedimentation in shallow fluvial channels with sandy to muddy floodplains. Units 2 and 3 record sedimentation in braided, meandering and anastomosing rivers. Finally unit 4 represents deposition in braided and wandering fluvial systems. The sampled tuff is located within unit 4 at ～3470 m above the base of the formation.The new ages indicate that the bulk of the Vinchina Formation is Miocene in age but they do not preclude a longer time span for the sedimentation of the whole unit. Ages of the sampled volcanic zircons match an important episode of volcanism recorded in the Cerro Las Tórtolas Formation, located ～90 km to the west in the Andean Cordillera, but also the upper tuff could be related to the late Miocene Puna volcanism. Comparison of the new ages with previous chronological data suggests coetaneous sedimentation along different depocenters of the Bermejo basin (e.g., Vinchina and Talampaya depocenters in Western Sierras Pampeanas and La Troya depocenter and Huaco-Mogna sections in Precordillera) and strenghten the need for correlation among them. In addition the age of 15.6 ± 0.4 Ma constrains the end of the severe arid conditions recorded in the Sierras Pampeanas and Precordillera region. |
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| Keywords: | Vinchina formation U-Pb ages Miocene Andean foreland basin |
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