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Cuneo R.,Museo Paleontologico Egidio Feruglio | Cuneo R.,CONICET | Ramezani J.,Massachusetts Institute of Technology | Scasso R.,University of Buenos Aires | And 8 more authors.
Gondwana Research | Year: 2013

The fluvial, lacustrine and tuffaceous sedimentary succession of the Cañadón Asfalto continental basin exposed in the Argentinean Chubut Province of central Patagonia preserves an extraordinary record of Jurassic fauna and flora that marks key events in the evolution of Dinosauria, early mammals and major South American plant groups. However, basin-wide correlation of the fossiliferous units is complicated by fault displacements, unconformities and repetitive lithofacies. New U-Pb analyses of zircon (CA-TIMS method) from five primary tuff beds interstratified with the lacustrine strata establish a new chronostratigraphic framework for the sedimentary and volcanic units of Cañadón Asfalto Basin, constraining ca. 33. m.y. of depositional history and biotic evolution that spans nearly all three epochs of the Jurassic. Five major vertebrate- and plant-rich stratigraphic intervals have been identified, and are being actively investigated, that range in age from Pliensbachian to Kimmeridgian (or younger). Our combined biostratigraphic and high-precision geochronologic results indicate that the major faunal turnover of the sauropodomorph dinosaurs which led to the rise of the eusauropods took place in the Early Jurassic, earlier than previously recognized. Similarly, the first successful radiation of the ornithischian dinosaurs (heterodontosaurids), as well as the evolutionary diversifications of the araucarian conifers and the osmundaceous ferns, all occurred before the end of the Early Jurassic. The diverse palynofloral assemblage of the Cañadón Calcáreo Formation that was once considered to be early Cretaceous in age, is now entirely constrained to the Late Jurassic. © 2012 International Association for Gondwana Research. Source

Gonzalez Riga B.J.,National University of Cuyo | Gonzalez Riga B.J.,Instituto Argentino Of Nivologia | David L.O.,National University of Cuyo
Ameghiniana | Year: 2014

Quetecsaurus rusconii gen. et sp. nov. is a new titanosaur (Dinosauria, Sauropoda) from the Neuquén Basin of Mendoza Province, Argentina. The specimen comes from red mudstones of the Cerro Lisandro Formation (middle-late Turonian, Upper Cretaceous), and is the first sauropod with well-preserved remains to be discovered in this formation. The holotype includes a postorbital, teeth, the atlas, a posterior cervical vertebra, an incomplete dorsal vertebra, a posterior caudal centrum, dorsal ribs, a coracoid, fragments of a humerus, radius and ulna, and five metacarpals. It is characterized by the following combination of autapomorphies: (1) intercentrum of atlas with a prominent anteroventral border and expanded posteroventral processes; (2) posterior cervical neural spines with incipient lateral expansions; and (3) humerus with strongly sigmoid proximal border, rounded proximomedial border, and angular proximolateral corner. A preliminary dadistic analysis placed Quetecsaurus as a sister taxon of Lognkosauria (Mendozasaurus + Futalognkosaurus). Quetecsaurus shares with the lognkosaurs the presence of cervical neural spines with 'lateral laminae', but relatively reduced in comparison with those taxa. This discovery provides new information on the diagnosis of Lognkosauria within South American titanosaurs. Source

Pepin E.,French National Center for Scientific Research | Carretier S.,French National Center for Scientific Research | Herail G.,French National Center for Scientific Research | Farias M.,U. de Chile | And 2 more authors.
Basin Research | Year: 2013

The study of the Las Tunas River incisions, located in the eastern Andean foreland front (33{ring operator}20' S in Argentina), provides new clues for the interpretation of deep piedmont entrenchments. Both the Las Tunas mountain catchment and its piedmont are strongly entrenched with maximal incision of over 100 m at the mountain front. Three main terrace levels are well exposed and are labelled T1, T2 and T3 from the youngest to the oldest. We combined geological and geomorphological field observations, kinematic GPS data, satellite data and aerial photos with geochronological 40Ar/39Ar and 10Be analysis to provide a detailed description of terrace organization and a discussion of the evolution of the Las Tunas landscape. The surprisingly constant 10Be concentrations in surface layers as deep as 1.5 m show that gently dipping alluvial surfaces can be continuously and deeply mixed. Our data show a first period of deposition (Mesones Fm) before 0.85 Myr (minimum T3 age), followed by deep erosion and a second sedimentation period (Las Tunas Fm) that includes a ca. 0.6 Myr ash deposit. T2 and T1 are inset in the Las Tunas Fm and were abandoned ca. 15-20 kyr ago. The similar ages for T2 and T1 show that post-20 kyr entrenchment occurred very rapidly. Despite Quaternary deformation in the Las Tunas piedmont, terrace entrenchment is best explained by paleo-climatic changes. The terrace organization reveals that the erosion-sedimentation phases affected the entire system from the piedmont toe to 10 km upstream of the mountain front. Finally, contrary to the neighbouring more deeply incised Diamante River system, where late Quaternary piedmont uplift is more likely to have been a factor causing incision, the more stable Las Tunas system provides an incomplete geomorphological record of Pleistocene and Holocene climate variations. We suggest that climate variations are better recorded in uplifting piedmonts than in stable ones, where the magnitude of incision and sedimentation and the fact that they occur repeatedly at the same elevation can erase a large part of the record. © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists. Source

Mergili M.,University of Vienna | Fellin W.,University of Innsbruck | Moreiras S.M.,Instituto Argentino Of Nivologia | Stotter J.,University of Innsbruck
Natural Hazards | Year: 2012

A GIS-based model framework, designed as a raster module for the Open Source software GRASS, was developed for simulating the mobilization and motion of debris flows triggered by rainfall. Designed for study areas up to few square kilometres, the tool combines deterministic and empirical model components for infiltration and surface runoff, detachment and sediment transport, slope stability, debris flow mobilization, and travel distance and deposition. The model framework was applied to selected study areas along the international road from Mendoza (Argentina) to Central Chile. The input parameters were investigated at the local scale. The model was run for a number of rainfall scenarios and evaluated using field observations and historical archives in combination with meteorological data. The sensitivity of the model to a set of key parameters was tested. The major scope of the paper is to highlight the capabilities of the model-and of this type of models in general-as well as its limitations and possible solutions. © 2011 The Author(s). Source

Branham Jr. R.L.,Instituto Argentino Of Nivologia
Revista Mexicana de Astronomia y Astrofisica | Year: 2013

New orbits are calculated for Comets Humason (C/1960 M1) and Bowell (C/1980 E1). Humason's orbit is based on 34 observation made over 348 days and Bowell's on 203 observations made over nearly eight years. Both comets have hyperbolic orbits. Backwards integrations indicate that both comets had originally highly elliptical orbits which changed to hyperbolas by the injection of energy from the Solar System. Given that both of their perihelions are more than 3 AU from the Sun, the possibility of nongravitational forces is remote. For Comet Secchi (C/1853 E1), however, the orbit is hyperbolic at more than 100000 AU from the Sun and with no indication of nongravitational forces. If the orbit is a hyperbola at that distance, could the comet's origin not be from beyond the Oort cloud?. © Copyright 2013: Instituto de Astronomía, Universidad Nacional Autónoma de México. Source

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