Colorado Basin, Argentina

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Colorado Basin
Cuenca del Colorado
Field(s)
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The Colorado Basin (Spanish: Cuenca del Colorado) is a sedimentary basin located in northeastern Patagonia. The basin stretches across an area of approximately 180,000 square kilometres (69,000 sq mi), of which 37,000 square kilometres (14,000 sq mi) onshore in the southern Buenos Aires Province and the easternmost Río Negro Province extending offshore in the South Atlantic Ocean.

The basin comprises a sedimentary succession dating from the

Pangea
and the formation of the South Atlantic. Long hiatuses exist in the succession.

The basin is of paleontological significance for hosting fossiliferous stratigraphic units dating to the Late Miocene. The Arroyo Chasicó Formation defines the Chasicoan South American land mammal age and contains a rich mammal and other vertebrate fauna. The contemporaneous Cerro Azul Formation has provided fossil rodents, armadillos and opossums. The Middle to Late Miocene Gran Bajo del Gualicho Formation contains vertebrate fossils of the cetacean Preaulophyseter gualichensis. The Río Negro Formation has provided fossils of the glyptodont Plohophorus figuratus. The Permian succession in the basin has provided flora microfossils.

Contrasting with the South Atlantic passive margin basins to the north (

Seals are provided by the Early Paleocene Pedro Luro Formation
.

Description

View of Viedma and Carmen de Patagones, separated by the Río Negro

The Colorado Basin stretches across an approximate area of 180,000 square kilometres (69,000 sq mi) with about 37,000 square kilometres (14,000 sq mi) onshore, underlying the southernmost

Viedma in Río Negro Province, the earliest founded city in Patagonia. The onshore part of the basin is crossed by the eponymous Colorado and Río Negro rivers. Surrounding the Río Negro, many salt lakes are present in the basin.[1]

Some authors group the basin together with the Claromecó Basin to the north.[2] The offshore part of the Colorado Basin laterally correlates with and gradually ranges into the sub-parallel Salado Basin and the deeper offshore Argentina Basin.[3][4] The offshore extension of the basin into neighboring basins led to different definitions of its area, some authors use a surface area of 125,000 square kilometres (48,000 sq mi).[5]

The Colorado Basin is bound to the north by the Ventania High,[6] Sierra de la Ventana,[7] or Sierras Australes,[2] separating the basin from the Claromecó Basin, and to the south by the Rawson,[8] or Río Negro High.[9] In the northwest, the basin grades into the Macachín Basin and the western boundary is formed by the San Rafael Block.[9]

Basin evolution

Pangea in the Permian (~250 Ma). The Colorado Basin experiences glaciations and a marine transgressive phase in the south polar region.
Sketch of the paleogeographic situation of South America during the Late Cretaceous and Early Paleogene, roughly 85 to 63 Ma. The Colorado Basin, located north of the North Patagonian Massif in the South Gondwanan Province (grey), is exposed and eroded during the Maastrichtian.

The basin started forming in the

Karoo and Kalahari Basins. The Early Permian sediments are characterized by the presence of diamictites. A transgression in the Permian led to the deposition of the Piedra Azul Formation.[13] The succession contains several hiatuses, dating to the Triassic and Early Jurassic, Albian and Paleogene.[14]

The early

fluvial Río Negro Formation,[21][22] outcropping in a thin band along the eponymous river.[1]

Stratigraphy

Age Group Formation Environment Tectonic regime Maximum thickness Petroleum geology Notes
Quaternary alluvium Passive margin
Early Pliocene
 Río Negro
fluvial
 480 m (1,570 ft) [21][22]
Late Miocene
Chasicoan-Huayquerian Cerro Azul Eolian 180 m (590 ft) [19][23]
Chasicoan Arroyo Chasicó Floodplain [24]
Mayoan Gran Bajo de Gualicho Shallow marine 57 m (187 ft) [17]
Laventan
Colloncuran
Friasian
Santacrucian
Mid Miocene Barranca Final Marine 300 m (980 ft) [16]
Oligocene Hiatus
Late Eocene
Middle Eocene
 Elvira [14]
Early Eocene
 Hiatus
Late Paleocene
Early Paleocene
 Pedro Luro Drift
Seal
 [14]
Maastrichtian Hiatus
Campanian Colorado
fluvial
 Sag Reservoir [14]
Santonian
Coniacian
Turonian
Cenomanian
Albian Hiatus
Aptian Fortín Syn-rift Reservoir
Source		 [15]
Barremian
Middle Jurassic Hiatus
Early Jurassic
Triassic
Late Permian
 Pillahuincó Tunas Pre-rift 1,500 m (4,900 ft) Source [2]
Early Permian
 Bonete Source [2]
Piedra Azul [2]
Sauce Grande [2]
Pennsylvanian Ventana Lolén Basement [11]

Paleontological significance

Neocavia pampeana of the Cerro Azul Formation

The Miocene formations cropping out onshore have provided a rich mammal fauna. The Arroyo Chasicó Formation is the defining formation for the Late Miocene Chasicoan South American land mammal age, ranging from 10 to 9 million years ago.[25] The formation contains many mammal species, birds and reptiles.[26] The Cerro Azul Formation contains fossils of the rodents Chasichimys bonaerense,[27] Neocavia pampeana,[28] Reigechimys plesiodon and R. simplex,[29] the armadillos Chasicotatus ameghinoi,[23] and Macrochorobates scalabrinii,[27] and the opossum Zygolestes tatei,[30] among other mammals. The Río Negro Formation has provided fossils of the glyptodont Plohophorus figuratus.[31]

The marine Gran Bajo de Gualicho Formation contains many

echinoid fossils,[32] and the cetacean Preaulophyseter gualichensis.[33] The Eocene succession in boreholes of the basin has provided many species of dinoflagellates,[34] and in the Permian sequence 131 species of spores, algae, funghi and pollen were registered.[35]

Petroleum exploration

Contrary to other Southern Atlantic marginal basins, as the

Hunt Oil and after seismic acquisition in the 1970s by YPF,[37] some wells were drilled in 1977 by the same company. Renewed exploration started in the mid-1990s with several wells drilled by Union Texas and Shell.[38] The offshore Cruz del Sur x-1 well provided oil shows of 39° API.[39]

See also

References

  1. ^ a b Geologic Map Hojas 4163-II/IV & I/III, 2006
  2. ^ a b c d e f g Balarino, 2012, p.344
  3. ^ Pucci, 2006, p.17
  4. ^ ENARSA, s.a., p.3
  5. ^ a b ENARSA, s.a., p.2
  6. ^ Daners et al., 2016, p.285
  7. ^ Balarino, 2009, p.20
  8. ^ ENARSA, s.a., p.1
  9. ^ a b Barredo & Stinco, 2010, p.60
  10. ^ Geologic Map Hojas 3963-III & IV, 2009, p.42
  11. ^ a b Balarino, 2009, p.24
  12. ^ Balarino, 2009, p.22
  13. ^ Balarino, 2009, p.23
  14. ^ a b c d e f g ENARSA, s.a., p.4
  15. ^ a b Barredo & Stinco, 2010, p.52
  16. ^ a b Geologic Map Hojas 3963-III & IV, 2009, p.39
  17. ^ a b Reichler, 2010, p.192
  18. ^ Reichler, 2010, p.183
  19. ^ a b Visconti et al., 2010, p.259
  20. ^ Geologic Map Hojas 3963-III & IV, 2009, p.5
  21. ^ a b Pérez, 2010, p.7
  22. ^ a b Geologic Map Hojas 3963-III & IV, 2009, p.8
  23. ^ a b Scillato Yané et al., 2010, p.51
  24. ^ Zárate et al., 2007
  25. ^ Chasicoan at Fossilworks.org
  26. ^ Arroyo Chasicó at Fossilworks.org
  27. ^ a b Verzi et al., 2008
  28. ^ Madozzo Jaén et al., 2018, p.250
  29. ^ Sostillo et al., 2014
  30. ^ Goin et al., 2000, p.108
  31. ^ Punta Bermeja at Fossilworks.org
  32. ^ Reichler, 2010, pp.191-192
  33. ^ Buono, 2013, p.36
  34. ^ Daners et al., 2016, p.293
  35. ^ Balarino, 2012, p.343
  36. ^ Rossello, 2016, p.175
  37. ^ ENARSA, s.a., p.8
  38. ^ ENARSA, s.a., p.5
  39. ^ Pucci, 2006, p.18

Bibliography

General
Geologic maps
Arroyo Chasicó Formation
Cerro Azul Formation
Gran Bajo del Gualicho Formation
Río Negro Formation
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