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Gaiman Formation

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Coordinates: 43°18′S 65°18′W / 43.3°S 65.3°W / -43.3; -65.3
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Gaiman Formation
Stratigraphic range: Burdigalian (Colhuehuapian)
~19.8–17.5 Ma
↓
Gaiman Formation stratigraphy at Cerro Castillo
TypeGeological formation
UnderliesPuerto Madryn Formation
OverliesSarmiento Formation
Thickness70 m (230 ft)
Lithology
PrimaryMudstone, sandstone
OtherTuff, phosphate
Location
Coordinates43°18′S 65°18′W / 43.3°S 65.3°W / -43.3; -65.3
Approximate paleocoordinates44°00′S 59°12′W / 44.0°S 59.2°W / -44.0; -59.2
RegionChubut Province
CountryArgentina
ExtentPeninsula Valdés Basin
Type section
Named forGaiman
Named byMendía & Bayarsky
Year defined1981
Gaiman Formation is located in Argentina
Gaiman Formation
Gaiman Formation (Argentina)

The Gaiman Formation (Spanish: Formación Gaiman), in older literature also referred to as Patagonian Marine Formation (Spanish: Formación Patagonia Marino, Patagoniense), is a fossiliferous geologic formation of the Peninsula Valdés Basin in the eastern Chubut Province of northwestern Patagonia, eastern Argentina.

The 70 metres (230 ft) thick formation overlies the Sarmiento Formation and is overlain by the Puerto Madryn Formation and comprises grey and white tuffaceous mudstones and sandstones, deposited in a shallow marine environment.

The Gaiman Formation has provided fossils of many extinct penguins, among which five species in the genus Palaeospheniscus, as well as whales and dolphins, most notably Aondelphis talen, Prosqualodon australis, Idiorophus patagonicus and Argyrocetus patagonicus, indeterminate seal and turtle fossils, shark and other fossils. The richness of the formation, and the other formations in the area, such as the underlying Sarmiento Formation, led to the establishment of the Bryn Gwyn Paleontological Park [es], with a Welsh name, reflecting the number of Welsh settlers in the region.

Description

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Outcrop map and stratigraphic column of the Gaiman Formation in the Peninsula Valdes Basin

The Gaiman Formation was first defined by Mendía & Bayarsky in 1981,[1] and further described by Mendía in 1983, taking its name from Gaiman in Chubut Province, eastern Patagonia.[2] Gaiman in the local language of the native Tehuelche people means "rocky point".[3] The formation crops out in the lower course of the Chubut River,[4] and overlies the continental Trelew Member of the Sarmiento Formation and is overlain by the Late Miocene Puerto Madryn Formation. The formation is 70 metres (230 ft) thick,[5] and comprises marine tuffs, tuffaceous mudstones, sandstones and coquinas.[1]

The Gaiman Formation is correlated with the Chenque Formation of the Golfo San Jorge Basin and the Monte León Formation of the Austral Basin to the south, the Saladar Member of the lower Gran Bajo del Gualicho Formation of the Colorado Basin to the north and the Vaca Mahuida Formation of the Neuquén Basin to the northwest.[6]

Depositional environment

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The basal stratum of the Gaiman Formation is a thin transgressive lag with some gravels, bones and teeth from marine vertebrates.[5] The unit displays a concentration of phosphatic concretions, ooids, bones and teeth.[7] The marine sediments overlying this basal stratum are composed of white, tuffaceous, thoroughly bioturbated mudstones and fine sandstones with occasional mollusk molds and thin oyster horizons, deposited in a shallow shelf environment.[5]

The marine transgression leading to the deposition of the Gaiman Formation is the first of two major South Atlantic transgressions of the Miocene, the second causing the deposition of the overlying Puerto Madryn Formation.[8]

Facies analysis shows that the formation represents a transgressive-regressive stratigraphic cycle, with palaeoenvironments including coastal, storm-dominated shoreface, inner shelf embayment and open inner shelf.[9]

The age of the Gaiman Formation is established on stratigraphic correlations to other absolutely-dated sections in Patagonia and biostratigraphic data and dates to the Early Miocene (Burdigalian, or Colhuehuapian in the SALMA classification).[5]

Paleontological significance

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Fossils of the Gaiman Formation in the Bryn Gwyn Paleontological Park

The Gaiman Formation has provided several fossil penguins, of which nine are assigned to specific species and include five species of the genus Palaeospheniscus. Also, shark teeth, fossils of indeterminate seals and turtles, and several dolphins, baleen and toothed whales have been found in the formation. Argentine paleontologist Florentino Ameghino described an isolated tooth from the formation first as an ichthyodectiform fish, Portheus patagonicus in 1901, however this fossil was assigned to a delphinoid cetacean of the family Kentriodontidae by Cione and Cozzuol in 1990.[10] Fish recorded from the formation are hexanchiform hexanchids, lamniform isurids, odontaspidids, cetorhinids, carcharhiniform carcharhinids, heterodontiform heterodontids, squatiniform squatinids myliobatiform myliobatids, perciform oplegnathids and labrids, and tetraodontiform molids.[11] Rays are abundant in the formation.[12] The lack of somatic remains of most molluscs, bryozoans, polychaetes and cirripeds in the formation is attributed to the high-energy and corrosive environment at time of deposition, as well as diagenesis after the formation was deposited.[13]

The bird species Eretiscus tonnii solely occurs in the Gaiman Formation.[14] Bite marks on several of the penguin bones are attributed to terrestrial mammals such as didelphid or hathliacyniid sparassodont marsupials, common in Patagonia during the Miocene.[15] Other ichnofossils found on the bones are presumably caused by dental erosion by regular echinoids,[16] and bite marks by sharks, as Galeocerdo aduncus.[17]

The paleontological richness of the formation, as well as the more fossiliferous underlying Sarmiento Formation, led to the establishment of the Bryn Gwyn Paleontological Park [es].[18]

Fossil content

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The formation has provided the following fossils:[19][20][21][22][23]

Class Group Fossils Image Notes
Mammals Dolphins Aondelphis talen [24]
Dolgopolis kinchikafiforo [25]
Kentriodon sp.
[12]
Eurhinodelphinidae indet. [20]
Toothed whales Argyrocetus patagonicus [12]
Crisocetus lydekkeri [26]
Idiorophus patagonicus [27]
Phoberodon arctirostris [12]
Prosqualodon australis [12][28]
Squalodontidae indet. [20]
Baleen whales Aglaocetus moreni
[27]
Morenocetus parvus [27]
Plesiocetus dyticus [27]
Seals Phocidae indet. [22]
Birds Penguins Apterodytes ictus [21]
Eretiscus tonnii [29]
Palaeospheniscus bergi
syn Palaeospheniscus planus, P. rothi		 [29][19]
Palaeospheniscus bilocular [29]
Palaeospheniscus gracilis [20]
Palaeospheniscus patagonicus
syn Palaeospheniscus affinis, P. intermedius, P. interruptus		 [19][30]
Palaeospheniscus wimani [22]
Paraptenodytes antarcticus
[29]
Paraptenodytes robustus
syn. Treleudytes crassa		 [19][30]
Arthrodytes sp. [20]
Sphenisciformes indet. [20]
Anseriformes Cayaoa bruneti [4][31]
Anseriformes indet. [20]
Reptiles Turtles Dermochelyidae indet. [20]
Fish Sharks Carcharoides totuserratus [17]
Echinorhinus pozzii [12]
Galeocerdo aduncus [17]
Megascyliorhinus trelewensis [12]
Heterodontus sp. [12]
Odontaspis sp. [12]
Pristiophorus sp. [12]
Squalus sp. [12]
Oplegnathidae Oplegnathus sp. [12]
Tetraodontiformes cf. Ranzania sp. [32]
Mollusks Bivalves Crassostrea ?hatcheri [23]
Balanus sp. [33]
Gastropods Turritella sp. [33]
Ichnofossils Bioturbation Chondrites, Ophiomorpha, Planolites, Skolithos [11]
Bite marks Gnathichnus pentax [16]
Entobia [16]

See also

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References

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  1. ^ a b Cione et al., 2010, p.434
  2. ^ Rodríguez, 2015, p.198
  3. ^ (in Spanish) Significado de los nombres de los Municipios de Chubut
  4. ^ a b Noriega & Tambussi, 2008, p.272
  5. ^ a b c d Viglino et al., 2018, p.263
  6. ^ Reichler, 2018, p.185
  7. ^ Cione et al., 2011, p.424
  8. ^ Cuitiño, 2017, p.47
  9. ^ Cuitiño et al., 2019
  10. ^ Cione & Cozzuol, 1990, p.451
  11. ^ a b Cione et al., 2010, p.443
  12. ^ a b c d e f g h i j k l Cione et al., 2010, p.429
  13. ^ Cione et al., 2010, p.450
  14. ^ Chávez Hoffmeister, 2008, p.82
  15. ^ Cione et al., 2010, p.437
  16. ^ a b c Cione et al., 2010, p.439
  17. ^ a b c Cione et al., 2010, p.441
  18. ^ (in Spanish) Parque paleontológico Bryn Gwyn
  19. ^ a b c d Cerro del Castillo, Trelew at Fossilworks.org
  20. ^ a b c d e f g h Bryn Gwyn at Fossilworks.org
  21. ^ a b Patagonian at Fossilworks.org
  22. ^ a b c Gaiman (marine vertebrates) at Fossilworks.org
  23. ^ a b Playa Santa Isabel, south at Fossilworks.org
  24. ^ Viglino et al., 2018, p.264
  25. ^ Viglino et al., 2020
  26. ^ Gaetán, C. Maximiliano; Paolucci, Florencia; Buono, Mónica R. (2023-08-15). "A new squaloziphiid-like odontocete from the Early Miocene of Patagonia expands the cetacean diversity in the southwestern Atlantic Ocean". Journal of Vertebrate Paleontology. 42 (6). doi:10.1080/02724634.2023.2232425. ISSN 0272-4634. S2CID 260947656.
  27. ^ a b c d Cione et al., 2011, p.428
  28. ^ Gaetán, 2019
  29. ^ a b c d Cione et al., 2010, p.433
  30. ^ a b Acosta et al., 2008, p.568
  31. ^ Tonni, 1979, p.12
  32. ^ "Tetraodontiformes (Osteichthyes, Actinopterygii) from the Miocene of Argentina: with the southernmost record of fossil Tetraodontidae". Comptes Rendus Palevol. 20 (27): 585–596. 2021.
  33. ^ a b Acosta et al., 2008, p.566

Bibliography

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Geology
Paleontology

Further reading

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