Cañadón Asfalto Basin

The Cañadón Asfalto Basin () is an irregularly shaped sedimentary basin located in north-central Patagonia, Argentina. The basin stretches from and partly covers the North Patagonian Massif in the north, a high forming the boundary of the basin with the Neuquén Basin in the northwest, to the Cotricó High in the south, separating the basin from the Golfo San Jorge Basin. It is located in the southern part of Río Negro Province and northern part of Chubut Province. The eastern boundary of the basin is the North Patagonian Massif separating it from the offshore Valdés Basin and it is bound in the west by the Patagonian Andes, separating it from the small Ñirihuau Basin.

The basin started forming in the Early Jurassic, with the break-up of Pangea and the creation of the South Atlantic, when extensional tectonics, including rifting, formed several basins in eastern South America and southwestern Africa. The accommodation space in the Cañadón Asfalto Basin was filled by volcanic, fluvial and lacustrine deposits in various geologic formations, separated by unconformities related to transtensional and transpressional tectonic forces. The Cenozoic evolution of the basin is mainly influenced by the Andean orogeny, producing folding and faulting in the basin.

The basin is of paleontological significance as it hosts several fossiliferous stratigraphic units providing many fossils of dinosaurs, turtles, mammals, plesiosaurs, pterosaurs, crocodylomorphs, fish, amphibians and flora in the Mesozoic and mammals, amphibians, fish and flora in the Cenozoic. The Collón Curá Formation, that is also present in the southern Neuquén Basin, is the defining formation for the Colloncuran, used within the SALMA classification, the geochronology for the Cenozoic used in South America.

Description

The Cañadón Asfalto Basin was not defined as a separate sedimentary basin until the 1990s. Until then, the sediments deposited in the basin were considered part of the North Patagonian Massif. Homovc et al. (1991) and Figari & Courtade (1993) started defining the stratigraphic units in megasequences indicative of the evolution of a rift basin, resulting from the break-up of Pangea and Gondwana in particular.Figari et al., 2015, p.137

The basin has an irregular shape, comprising several depocenters defining sub-basins. The basin stretches from and partly covers the North Patagonian Massif in the north and east towards the Cotricó High to the south of the Paso del Sapo Sub-basin, separating the Cañadón Asfalto Basin from the Golfo San Jorge Basin in the south. In the west, the basin is bound by uplifted areas with the small Ñirihuau Basin.Figari et al., 2015, p.138

The area of the basin is sparsely populated, with Gastre and Paso del Sapo representing some of the few villages in the basin. The Chubut River crosses the basin in the south in the Altar Valley.

Basin evolution

The Cañadón Asfalto Basin started forming in the earliest Jurassic on top of Permian basement constituted by the igneous-metamorphic Mamil Choique and Cushamen Formations.Di Pietro, 2016, p.28 Two main phases of basin evolution are recognized; the Jurassic and Cretaceous megasequences. Figari et al. in 2015 describe two Jurassic megasequences, J1 in the Early Jurassic and J2 in the Late Jurassic. During these phases, the basin went through an extensional tectonic regime, with transtensional movements. Several distinct tectonic reactivation cycles occurred, with block rotation due to transpressional forces. The geodynamic movements are noted in the stratigraphy by regional unconformities. The predominantly extensional movement was overprinted by a compressional setting, active since the early Cenozoic. This compressional phase is noted in folds and compressional faults present in the basin.Di Pietro, 2016, p.23

The sedimentary infill of the Early and Middle Jurassic in the basin is characterized by fluvial and lacustrine sediments of the Las Leoneras, Cañadón Asfalto and Cañadón Calcáreo Formations covering the volcanic Lonco Trapial Formation, which comprises intermediate volcanic rocks sourced by magmas coming from the mantle. This succession is unconformably covered by lacustrine, fluvial and volcaniclastic rocks of the approximately 10 to 15 million year ranging Chubut Group comprising the older Los Adobes Formation and the younger Cerro Barcino Formation. The western side of the basin during the Late Cretaceous experienced a marine transgression of the Atlantic Ocean, depositing the fluvial and estuarine Paso del Sapo and Lefipán Formations.Echaurren, 2017, p.94

The marine sediments of the Lefipán Formations have been correlated to the Salamanca Formation of the Golfo San Jorge Basin to the south and the Lefipán sediments were sourced from the North Patagonian Massif. To the west of the Cañadón Asfalto Basin, another basin started forming in these times, the Ñirihuau Basin, characterized by the deposition of the felsic to intermediate volcanic Don Juan Formation, the basaltic Tres Picos Prieto Formation and the Huitrera Formation. In the Ñirihuau Basin, this sequence is covered by the Oligocene to Miocene Ventana Formation.Echaurren, 2017, p.95

During the Paleogene, in the Cañadón Asfalto Basin the volcaniclastic Laguna del Hunco Formation,Figari et al., 2015, p.154 and volcanic Sarmiento Group were deposited.Figari et al., 2015, p.155 The Neogene succession in the basin comprises the Early Miocene alluvial volcaniclastics of the La Pava Formation,Di Pietro, 2016, p.46 and the Middle to Late Miocene volcaniclastic, fluvial, lacustrine and deltaic tuffs, sandstones and carbonates of the Collón Curá Formation.

The Late Miocene to Quaternary succession comprises mostly the basaltic lava flowsEchaurren et al., 2016, p.103 of the El Mirador Formation,Echaurren et al., 2016, p.102 the basalts of the Cráter Formation, and Quaternary alluvium.Echaurren et al., 2016, p.105Echaurren, 2017, p.102 In the northern part of the basin, the Late Miocene and Early Pliocene is represented by the fluvial, marine and eolian Río Negro Formation, a formation extending into the Colorado Basin.Pérez, 2012, p.7Pérez, 2012, p.10

Stratigraphy

The stratigraphy of the Cañadón Asfalto Basin covers the following units:

Age Group Formation Sequence Environment Maximumthickness Notes Quaternary alluvium Mid-Late Pleistocene Cráter Basalt Di Pietro, 2016, p.49 Early Pliocene Río Negro Eolian, fluvial & marine Late Miocene El Mirador Volcanic Colloncuran Collón Curá Fluvial, lacustrine, deltaic Early Miocene La Pava Alluvial volcaniclastic Sarmiento Volcanic Late Eocene Early Eocene Laguna del Hunco Volcaniclastic Late Paleocene Hiatus Danian Barda Colorada Volcaniclastic Lefipán Tidal & shallow marine Maastrichtian La Colonia Tidal & shallow marine Gasparini et al., 2015 Paso del Sapo Estuarine & shallow marine Figari et al., 2015, p.153 Campanian Santonian Hiatus Coniacian Turonian Cenomanian Albian Chubut Cerro Barcino K Fluvial, alluvial, lacustrine Figari et al., 2015, p.152 Aptian Barremian Los Adobes Alluvial & fluvial Figari et al., 2015, p.151 Hauterivian Hiatus Valanginian Berriasian Tithonian Sierra de Olte Cañadón Calcáreo J2 Fluvial & lacustrine Figari et al., 2015, p.147 Kimmeridgian Oxfordian Callovian Hiatus Bathonian Bajocian Cañadón Asfalto J1 Lacustrine carbonate platform Figari et al., 2015, p.146Di Pietro, 2016, p.42 Aalenian Toarcian Lonco Trapial Volcaniclastic Figari et al., 2015, p.144Di Pietro, 2016, p.39 Pliensbachian Sinemurian Hettangian Las Leoneras Fluvial & lacustrine Figari et al., 2015, p.142Di Pietro, 2016, p.31 Triassic Hiatus Paleozoic Basement Mamil Choique & Cushamen Figari et al., 2015, p.143Olivera et al., 2015, p.3

Paleontological significance The Cañadón Asfalto Basin has provided several fossils of various groups of flora and fauna. One of the largest dinosaurs known, the titanosaur Patagotitan mayorum, and one of the largest theropods, Tyrannotitan chubutensis, were found in the Cerro Barcino Formation.Carballido et al., 2017Novas et al., 2005 Fossils of Leonerasaurus taquetrensis, an early Sauropodomorph, were found in and named after the Las Leoneras Formation.Pol et al., 2011 The La Colonia Formation has provided fossils of a mammal; Argentodites coloniensis,Kielan-Jaworowska et al., 2007, p.257 and a nearly complete skeleton of the theropod Carnotaurus sastrei. Remains of the plesiosaur Aristonectes parvidens were found in the Maastrichtian section of the Lefipán Formation.Gasparini et al., 2003

Fossil flora (pollen, spores, algae and macroflora) have been recovered from the Lonco Trapial Formation (Cupressaceae),Escapa et al., 2008a and the Cañadón Asfalto Formation and comprise several families of plants, indicative of climatic conditions in the Late Jurassic; Osmundaceae, Caytoniaceae, Araucariaceae, Cheirolepidiaceae, Podocarpaceae, Botryococcaceae, Zygnemataceae, Prasinophyceae, Filicales and Taxodiaceae.Olivera et al., 2015, p.6 The same formation also provided fossils of two species of the frog Notobatrachus,Escapa et al., 2008b the turtle Condorchelys antiqua,Sterli, 2008 the pterosaur Allkaruen koi,Codorniú et al., 2016 and several mammals.Gaetano & Rougier, 2011

Fossil fish of Condorlepis groeberi were retrieved from the Cañadón Calcáreo Formation,López Arbarello et al., 2013 and the crocodylomorphs Almadasuchus figarii (Cañadón Calcáreo Formation),Pol et al., 2013 and Barcinosuchus gradilis (Cerro Barcino Formation),Leardi & Pol, 2009 come from the Mesozoic strata in the basin.

Fossil leaves of Lefipania padillae and Araucaria lefipanensis come from and were named after the latest Maastrichtian within the Lefipán Formation.Martínez et al., 2018Andruchow-Colombo et al., 2018 The Paleocene (Tiupampan) strata of the Lefipán Formation have provided fossils of the mammal Cocatherium lefipanum and fish Hypolophodon patagoniensis.Cione et al., 2013Goin et al., 2006

The Early Eocene (Casamayoran to Mustersan) Laguna del Hunco Formation has provided fossils of the fish Bachmannia chubutensis,Azpelicueta & Cino, 2011 the frog Shelania pascuali,Báez & Trueb, 1997 and fossil flora.Wilf et al., 2005

The Collón Curá Formation, that defines the Colloncuran South American land mammal age, stretches across the Neuquén Basin to the northwest of the North Patagonian Massif and the western part of the Cañadón Asfalto Basin. The formation has provided many mammal, reptile and bird fossils, among which the largest terror bird Kelenken.Bertelli et al., 2007 Along the Chico River in the basin (localities 9 and 10 on the map), fossils of the sparassodont Patagosmilus goini, two new species of Protypotherium,Vera et al., 2017, p.855 and the rodents Guiomys unica and Microcardiodon williensis were found.Forasiepi & Carlini, 2010Pérez, 2010Pérez & Vucetich, 2011

See also

Austral Basin Cuyo Basin Paraná Basin Salta Basin Santos Basin

References

Bibliography General

Paleontology

Further reading