Collón Curá Formation

The Collón Curá Formation (Spanish: Formación Collón Curá) is a Middle Miocene fossiliferous geological formation of the southern Neuquén Basin in northwestern Patagonia and the western Cañadón Asfalto Basin of central Patagonia, Argentina. The formation crops out from the southern Neuquén Province, the western Río Negro Province to the northern Chubut Province.

Collón Curá Formation
Stratigraphic range: Langhian-earliest Tortonian
(typically Colloncuran)
~16.1–10.7 Ma
TypeGeological formation
Sub-unitsTobaceo Las Bayas & Pilcaniyeú Ignimbrite Members
UnderliesCaleufú Formation & Chenqueniyeu Basalt (Neuquén Basin)
El Mirador, Río Negro Formation & alluvium (Cañadón Asfalto Basin)
OverliesCerro Bandera, Huitrera & Cerro Petiso Formations, crystalline basement (Neuquén Basin)
Ñirihuau, Lefipán & La Pava Formations (Cañadón Asfalto Basin)
ThicknessUp to 300 m (980 ft)
Lithology
PrimaryTuff, sandstone
OtherSiltstone, marl, limestone, calcareous concretions, pumice
Location
Coordinates40.0°S 70.8°W / -40.0; -70.8
Approximate paleocoordinates40.6°N 66.4°W / 40.6; -66.4
RegionNeuquén, Río Negro & Chubut Provinces
Country Argentina
ExtentCañadón Asfalto & Neuquén Basins
Type section
Named forCollón Curá River & Estancia Collón Curá
Named byYrigoyen
LocationLácar Department
Year defined1969
Coordinates40°04′56.6″S 70°51′55.3″W
RegionNeuquén Province
Country Argentina
Thickness at type section50 m (160 ft)

Outcrop locations of the Collón Curá Formation

The formation, with a maximum thickness of 300 metres (980 ft), comprises tuffs and sandstones with minor siltstones, marls and limestones, deposited in a fluvial, deltaic and shallow to deep lacustrine environment in small basins separated by faults. The formation dates from the Langhian to earliest Tortonian epochs of the Middle to Late Miocene, typically Colloncuran.

The Collón Curá Formation is named after Estancia Collón Curá (1 on the map in the infobox) along the Collón Curá River (2), a tributary of the Limay River in the Río Negro watershed, and lends its name to the Colloncuran, one of the South American land mammal ages. The formation has provided many fossils of mammals, reptiles, among others the snake Waincophis australis, and the largest terror bird Kelenken guillermoi. The rodent Galileomys colloncurensis and the typothere Protypotherium colloncurensis were named after the formation.

Description
Geologic map of outcrops of the formation
Middle Miocene (15 Ma)

The strata of the Collón Curá Formation were first recognized by Roth in 1899, based on a 50 metres (160 ft) thick succession of grey tuffs in the valley of the Collón Curá River. In 1929, Groeber named the unit Colloncurense, separating the sediments from the older Santa Cruz Formation, that Roth had grouped in the same unit. Yrigoyen in 1969 formally defined the stratigraphic unit as Collón Curá Formation. The type section of the formation is on both sides on the Collón Curá River. The maximum recorded thickness in the Collón Curá river valley is 130 metres (430 ft).[1]

In the Chapelcó Range of the Neuquén Basin, the formation is unconformably overlain by the Caleufú Formation,[2] while basaltic lava flows[3] of the El Mirador Formation,[4] and Quaternary alluvium overly the Collón Curá Formation in the Cañadón Asfalto Basin.[5][6] In the Collón Curá valley, the formation covers Paleogene sediments of the Huitrera and Cerro Petiso Formations and in places overlying crystalline basement.[1] In other parts of the Neuquén Basin, the formation overlies the Early Miocene Cerro Bandera Formation or the Late Cretaceous Angostura Colorada Formation.[7][8] In the Cañadón Asfalto Basin, the Collón Curá Formation overlies the Ñirihuau Formation,[9] and in the area around the Chico River in the same basin, the formation overlies the La Pava Formation. In this location, the Collón Curá Formation is unconformably overlain by the Río Negro Formation.[10]

The oldest age for the formation has been given as 16.1 Ma,[11] and the top of the formation has been dated to 11 ± 1, and more precisely to 10.7 Ma.[1] 40Ar/39Ar analysis on amphibole crystals, collected from fresh pumice clasts, revealed an age of 14.86 ± 0.13 Ma for the middle section of the Collón Curá Formation in the Gastre Sub-basin of the Cañadón Asfalto Basin.[12] Earlier estimates based on K/Ar dating on biotite minerals of the Pilcaniyeú Ignimbrite Member were given as 15 Ma (1980) and 14.1 Ma (1990). Overall, the age of the formation ranges from Langhian to earliest Tortonian.[13]

Lithologies

In its type locality, the Collón Curá Formation is characterized by homogeneous greyish-yellow well-consolidated massive vitrocrystalline tuffs without visible sedimentary structures, but with calcareous concretions. The tuffaceous sediments contain pieces of white pumice with a vesicular character up to 2 millimetres (0.079 in) in size. The volcanic crystals in the tuff comprise andesine, hornblende and hypersthene in an argillaceous matrix. The concretions in the formation can reach up to 10 centimetres (3.9 in) in size and result from secondary diagenesis replacing the primary porosity of the sediments.[1]

Around the Río Chico in the Cañadón Asfalto Basin, the formation is about 300 metres (980 ft) thick and comprises siltstones, sandstones, marls and limestones.[10]

Depositional environment
Significant drop in both temperatures after the Middle Miocene Climatic Optimum

The formation was deposited in a fluvial and lacustrine environment dominated by pyroclastic flows in small basins, separated by faults.[14] The sub-Andean region of Argentina went through a phase of marine transgression during the Middle Miocene, approximately 15 to 13 Ma.[15] The Collón Curá Formation shows growth strata in the Cañadón Asfalto Basin, indicating syn-tectonic deposition.[3] In this basin, the formation ranges from a shallow lacustrine setting in the basal section, a deep lacustrine system with deltaic facies in the middle and upper parts.[10] The Collón Curá Formation is correlated with the contemporaneous fluvial and lacustrine tuffaceous Chichinales Formation of the central Neuquén Basin.[16]

The Collón Curá Formation, together with the underlying Ñirihuau Formation in the Cañadón Asfalto Basin, was deposited in a fragmented, possibly by pull-apart tectonic activity,[17] foreland basin setting.[18]

The climate in the early middle Miocene was hot, a period known as the Middle Miocene Climatic Optimum. This thermal maximum was followed by a period of cooling, the Middle Miocene disruption, probably related to glacial growth and the reestablishment of the ice of the East Antarctic Ice Sheet. Atmospheric concentrations of CO2 are estimated to have dropped from about 300 to 140 ppm.[19]

Paleontological significance
See also: Colloncuran
Lower dentition of Protypotherium endiadys
Skull and upper dentition of P. endiadys
Post-cranial bones of P. endiadys

The mammal fauna of the Collón Curá Formation led researchers to establish the Colloncuran age in the SALMA classification, ranging from 15.5 to 13.8 Ma. This age, used in South America as subdivision for the Cenozoic, follows on the Friasian age, defined from the Chilean Río Frías Formation of the Aysén Basin and precedes the Laventan age, named after the Konzentrat-Lagerstätte La Venta pertaining to the Honda Group of the Upper Magdalena Valley of central Colombia.

The rodent Galileomys colloncurensis, and the typothere Protypotherium colloncurensis were named after the formation.[20]

The fossil mammal assemblage of the Collón Curá Formation represents a fauna preceding the evolution of the Caviidae. The oldest true caviid, Prodolichotis pridiana is known from the Villavieja and La Victoria Formations of La Venta, Colombia. Sister taxa of these caviids first appeared in the Colloncuran; Guiomys unica and Microcardiodon williensis, found in the Collón Curá Formation.[21] In alternative classification proposed in 2012 by Pérez and Pol, Guiomys is considered an optional early caviid, pushing back the lineage to the Colloncuran.[22]

Fossil content
GroupFossilsImagesNotes
TypotheriaProtypotherium colloncurensis
[20][23]
Protypotherium endiadys
[12][24][23]
[25][26][27]
Epipatriarchus sp., Interatherium sp.
[23][28]
PrimatesProteropithecia neuquenensis, Cebidae indet.
[26][29][30]
[31][32]
RodentsGalileomys colloncurensis, Guiomys unica, Maruchito trilofodonte, cf. Microcardiodon williensis, Neosteiromys tordillense, Protacaremys denisae, Acarechimys sp., Alloiomys sp., Megastus sp., Neoreomys sp., Prolagostomus sp., Stichomys sp., Dasyproctidae indet., Echimyidae indet., Eocardiidae indet., Erethizontidae indet.
[21][23][26]
[29][32][33]
[34][35][36]
HegetotheriaHegetotherium sp., Pachyrukhos sp.
[23][28]
SparassodontaPatagosmilus goini, cf. Arctodictis sp.
[33][37]
LitopternaTheosodon sp.
[23][28]
CingulataProeutatus sp.
[23][28][29]
[32][38][39]
Paraeucinepeltus raposeirasi, Peltephilus pumilus, Prozaedyus sp., Stenotatus sp., Stegotheriini indet.
Pilosa?Neotamandua australis
[40]
PaucituberculataAbderites aisenense
[41]
BirdsKelenken guillermoi
[40][42]
ReptilesChelonoidis gringorum, Waincophis australis, Boinae indet., Lacertilia indet.
[10][29][32]
[40][43]
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See also

References
  1. Escosteguy & Franchi, 2010, p.422
  2. Escosteguy & Franchi, 2010, p.418
  3. Echaurren et al., 2016, p.103
  4. Echaurren et al., 2016, p.102
  5. Echaurren et al., 2016, p.105
  6. Echaurren, 2017, p.102
  7. Geologic Map, 2007, p.112
  8. Prez & Massaferro, 2013, p.223
  9. Echaurren, 2017, p.96
  10. Río Chico Colloncuran at Fossilworks.org
  11. Di Pietro, 2016, p.47
  12. Estancia Collón Cura at Fossilworks.org
  13. Escosteguy & Franchi, 2010, p.423
  14. Figari et al., 2015, p.154
  15. Náñez & Malumián, 2019, p.193
  16. Geologic Map, 2007, p.49
  17. Dalla Salda & Franzese, 1987, p.11
  18. Echaurren, 2017, p.97
  19. Pearson & Palmer, 2000, p.699
  20. Vera et al., 2017, p.855
  21. Pérez & Pol, 2012, p.6
  22. Pérez & Pol, 2012, p.12
  23. Pilcaniyeu Viejo at Fossilworks.org
  24. Vera et al., 2017, p.848
  25. Chico River at Fossilworks.org
  26. Cañadon del Tordillo at Fossilworks.org
  27. Collón Cura River at Fossilworks.org
  28. Bondesio et al., 1980
  29. Estancia Campionario at Fossilworks.org
  30. Kay et al., 1998
  31. Silvestro et al., 2017, p.14
  32. Pardiñas, 1991
  33. RCH 018S at Fossilworks.org
  34. Vucetich & Kramarz, 2003
  35. Pérez, 2010
  36. Pérez & Vucetich, 2011
  37. Forasiepi & Carlini, 2010
  38. González Ruiz et al., 2011, p.569
  39. González Ruiz et al., 2013, p.323
  40. Comallo at Fossilworks.org
  41. Abello & Rubilar, 2012, p.180
  42. Bertelli et al., 2007
  43. Albino, 1996

Bibliography
Geologic map
Geology
Paleontology
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