Cañadón Asfalto Basin

The Cañadón Asfalto Basin (Spanish: Cuenca de Cañadón Asfalto) 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.

Cañadón Asfalto Basin
Cuenca de Cañadón Asfalto
Map showing the location of Cañadón Asfalto Basin
Map showing the location of Cañadón Asfalto Basin
Location of the basin in Argentina
Coordinates42°51′S 67°56′W
LocationSouthern South America
RegionPatagonia
Country Argentina
State(s)Chubut & Río Negro Provinces
CitiesGastre, Paso del Sapo
Characteristics
On/OffshoreOnshore
BoundariesNorth Patagonian Massif (N & E), Cotricó High (S), Ñirihuau Basin (W)
Part ofSouthern Atlantic rift basins
Area~80,000 km2 (31,000 sq mi)
Hydrology
River(s)Chico River, Chubut River
Lake(s)Gran Laguna Salada, Laguna del Hunco
Geology
Basin typeRift
PlateSouth American
OrogenyOpening of the South Atlantic (Mesozoic)
Andean (Cenozoic)
AgeEarly Jurassic-Quaternary
StratigraphyStratigraphy

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
View of Gastre, in the center of the basin
Altar Valley in the southern part of the basin, bounding the Chubut River

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.[1]

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.[2]

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
Sketch of the paleogeographic situation of South America during the Late Cretaceous and Early Paleogene, roughly 85 to 63 Ma. The Cañadón Asfalto Basin, located south of the North Patagonian Massif in the South Gondwanan Province (grey), is experiencing a marine transgression.

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.[3] 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.[4]

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.[5]

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.[6]

During the Paleogene, in the Cañadón Asfalto Basin the volcaniclastic Laguna del Hunco Formation,[7] and volcanic Sarmiento Group were deposited.[8] The Neogene succession in the basin comprises the Early Miocene alluvial volcaniclastics of the La Pava Formation,[8][9] 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 flows[10] of the El Mirador Formation,[11] the basalts of the Cráter Formation, and Quaternary alluvium.[12][13] 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.[14][15]

Stratigraphy
Outcrops of the Collón Curá Formation in the basin (9 & 10)
Outcrops of the Las Leoneras and other formations
Outcrop areas of the Cañadón Asfalto and Calcáreo Formations

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

AgeGroupFormationSequenceEnvironmentMaximum
thickness		Notes
Quaternaryalluvium
Mid-Late PleistoceneCráterBasalt3 m (9.8 ft)[16]
Early PlioceneRío NegroEolian, fluvial & marine[14]
Late Miocene
El MiradorVolcanic[11]
ColloncuranCollón CuráFluvial, lacustrine, deltaic300 m (980 ft)[8]
Early MioceneLa PavaAlluvial volcaniclastic15 m (49 ft)[8][9]
SarmientoVolcanic[8]
Late Eocene
Early EoceneLaguna del HuncoVolcaniclastic[7]
Late PaleoceneHiatus
DanianBarda ColoradaVolcaniclastic[17]
LefipánTidal & shallow marine380 m (1,250 ft)[17]
Maastrichtian
La ColoniaTidal & shallow marine240 m (790 ft)[18]
Paso del SapoEstuarine & shallow marine150 m (490 ft)[17]
Campanian
SantonianHiatus
Coniacian
Turonian
Cenomanian
AlbianChubutCerro BarcinoKFluvial, alluvial, lacustrine[19]
Aptian
BarremianLos AdobesAlluvial & fluvial[20]
HauterivianHiatus
Valanginian
Berriasian
TithonianSierra de OlteCañadón CalcáreoJ2Fluvial & lacustrine[21]
Kimmeridgian
Oxfordian
CallovianHiatus
Bathonian
BajocianCañadón AsfaltoJ1Lacustrine carbonate platform600 m (2,000 ft)[22][23]
Aalenian
Toarcian
Lonco TrapialVolcaniclastic800 m (2,600 ft)[24][25]
Pliensbachian
Sinemurian
HettangianLas LeonerasFluvial & lacustrine372 m (1,220 ft)[26][27]
TriassicHiatus
PaleozoicBasementMamil Choique & Cushamen[28][29]

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.[30][31] Fossils of Leonerasaurus taquetrensis, an early Sauropodomorph, were found in and named after the Las Leoneras Formation.[32] The La Colonia Formation has provided fossils of a mammal; Argentodites coloniensis,[33] 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.[34]

Fossil flora (pollen, spores, algae and macroflora) have been recovered from the Lonco Trapial Formation (Cupressaceae),[35] 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.[36] The same formation also provided fossils of two species of the frog Notobatrachus,[37] the turtle Condorchelys antiqua,[38] the pterosaur Allkaruen koi,[39] and several mammals.[40]

Fossil fish of Condorlepis groeberi were retrieved from the Cañadón Calcáreo Formation,[41] and the crocodylomorphs Almadasuchus figarii (Cañadón Calcáreo Formation),[42] and Barcinosuchus gradilis (Cerro Barcino Formation),[43] 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.[44][45] The Paleocene (Tiupampan) strata of the Lefipán Formation have provided fossils of the mammal Cocatherium lefipanum and fish Hypolophodon patagoniensis.[46][47]

The Early Eocene (Casamayoran to Mustersan) Laguna del Hunco Formation has provided fossils of the fish Bachmannia chubutensis,[48] the frog Shelania pascuali,[49] and fossil flora.[50]

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.[51] 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,[52] and the rodents Guiomys unica and Microcardiodon williensis were found.[53][54][55]

See also
Wikimedia Commons has media related to Cañadón Asfalto Basin.

References
  1. Figari et al., 2015, p.137
  2. Figari et al., 2015, p.138
  3. Di Pietro, 2016, p.28
  4. Di Pietro, 2016, p.23
  5. Echaurren, 2017, p.94
  6. Echaurren, 2017, p.95
  7. Figari et al., 2015, p.154
  8. Figari et al., 2015, p.155
  9. Di Pietro, 2016, p.46
  10. Echaurren et al., 2016, p.103
  11. Echaurren et al., 2016, p.102
  12. Echaurren et al., 2016, p.105
  13. Echaurren, 2017, p.102
  14. Pérez, 2012, p.7
  15. Pérez, 2012, p.10
  16. Di Pietro, 2016, p.49
  17. Figari et al., 2015, p.153
  18. Gasparini et al., 2015
  19. Figari et al., 2015, p.152
  20. Figari et al., 2015, p.151
  21. Figari et al., 2015, p.147
  22. Figari et al., 2015, p.146
  23. Di Pietro, 2016, p.42
  24. Figari et al., 2015, p.144
  25. Di Pietro, 2016, p.39
  26. Figari et al., 2015, p.142
  27. Di Pietro, 2016, p.31
  28. Figari et al., 2015, p.143
  29. Olivera et al., 2015, p.3
  30. Carballido et al., 2017
  31. Novas et al., 2005
  32. Pol et al., 2011
  33. Kielan-Jaworowska et al., 2007, p.257
  34. Gasparini et al., 2003
  35. Escapa et al., 2008a
  36. Olivera et al., 2015, p.6
  37. Escapa et al., 2008b
  38. Sterli, 2008
  39. Codorniú et al., 2016
  40. Gaetano & Rougier, 2011
  41. López Arbarello et al., 2013
  42. Pol et al., 2013
  43. Leardi & Pol, 2009
  44. Martínez et al., 2018
  45. Andruchow‐Colombo et al., 2018
  46. Cione et al., 2013
  47. Goin et al., 2006
  48. Azpelicueta & Cino, 2011
  49. Báez & Trueb, 1997
  50. Wilf et al., 2005
  51. Bertelli et al., 2007
  52. Vera et al., 2017, p.855
  53. Forasiepi & Carlini, 2010
  54. Pérez, 2010
  55. Pérez & Vucetich, 2011

Bibliography
General
Paleontology

Further reading
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