Gaiman Formation Explained

Gaiman Formation
Type:Geological formation
Period:Burdigalian
Age:Burdigalian (Colhuehuapian)
~
Prilithology:Mudstone, sandstone
Otherlithology:Tuff, phosphate
Namedfor:Gaiman
Namedby:Mendía & Bayarsky
Year Ts:1981
Region:Chubut Province
Country:Argentina
Coordinates:-43.3°N -65.3°W
Paleocoordinates:-44°N -59.2°W
Underlies:Puerto Madryn Formation
Overlies:Sarmiento Formation
Thickness:70m (230feet)
Extent:Peninsula Valdés Basin

The Gaiman Formation (Spanish; Castilian: Formación Gaiman), in older literature also referred to as Patagonian Marine Formation (Spanish; Castilian: 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 70m (230feet) 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, with a Welsh name, reflecting the number of Welsh settlers in the region.

Description

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 70m (230feet) thick, 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.[5]

Depositional environment

The basal stratum of the Gaiman Formation is a thin transgressive lag with some gravels, bones and teeth from marine vertebrates. The unit displays a concentration of phosphatic concretions, ooids, bones and teeth.[6] 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.[7]

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).[7]

Paleontological significance

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 .[18]

Fossil content

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

Class Group Fossils Image class=unsortable Notes
Mammals Dolphins Aondelphis talen align=center [24]
Dolgopolis kinchikafiforo align=center [25]
Kentriodon sp. align=center
align=center
Toothed whales Argyrocetus patagonicus align=center
Crisocetus lydekkeri[26]
Idiorophus patagonicus align=center
Phoberodon arctirostris align=center
Prosqualodon australis align=center [27]
align=center
Baleen whales Aglaocetus moreni align=center [28]
Morenocetus parvus align=center
Plesiocetus dyticus align=center
Seals align=center
Birds Penguins Apterodytes ictus align=center
Eretiscus tonnii align=center [29]
Palaeospheniscus bergi
syn Palaeospheniscus planus, P. rothi
align=center
Palaeospheniscus bilocular align=center
Palaeospheniscus gracilis align=center
Palaeospheniscus patagonicus
syn Palaeospheniscus affinis, P. intermedius, P. interruptus
align=center [30]
Palaeospheniscus wimani align=center
Paraptenodytes antarcticus align=center
Paraptenodytes robustus
syn. Treleudytes crassa
align=center
Arthrodytes sp. align=center
align=center
Cayaoa bruneti align=center [31]
align=center
Reptiles Turtles align=center
Sharks Carcharoides totuserratus align=center
Echinorhinus pozzii align=center
Galeocerdo aduncus align=center
Megascyliorhinus trelewensis align=center
Heterodontus sp. align=center
Odontaspis sp. align=center
Pristiophorus sp. align=center
Squalus sp. align=center
Oplegnathus sp. align=center
Tetraodontiformescf. Ranzania sp.[32]
Mollusks Bivalves Crassostrea ?hatcheri align=center
Balanus sp. align=center [33]
Gastropods Turritella sp. align=center
Ichnofossils Chondrites, Ophiomorpha, Planolites, Skolithos align=center
Bite marks Gnathichnus pentax align=center
Entobia align=center

See also

References

Bibliography

Geology
Paleontology

Notes and References

  1. Cione et al., 2010, p.434
  2. Rodríguez, 2015, p.198
  3. Significado de los nombres de los Municipios de Chubut
  4. Noriega & Tambussi, 2008, p.272
  5. Reichler, 2018, p.185
  6. Cione et al., 2011, p.424
  7. Viglino et al., 2018, p.263
  8. Cuitiño, 2017, p.47
  9. Cuitiño et al., 2019
  10. Cione & Cozzuol, 1990, p.451
  11. Cione et al., 2010, p.443
  12. 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. Cione et al., 2010, p.439
  17. Cione et al., 2010, p.441
  18. Parque paleontológico Bryn Gwyn
  19. http://www.fossilworks.org/cgi-bin/bridge.pl?a=collectionSearch&collection_no=47303 Cerro del Castillo, Trelew
  20. http://www.fossilworks.org/cgi-bin/bridge.pl?a=collectionSearch&collection_no=45886 Bryn Gwyn
  21. http://www.fossilworks.org/cgi-bin/bridge.pl?a=collectionSearch&collection_no=74645 Patagonian
  22. http://www.fossilworks.org/cgi-bin/bridge.pl?a=collectionSearch&collection_no=142513 Gaiman (marine vertebrates)
  23. http://www.fossilworks.org/cgi-bin/bridge.pl?a=collectionSearch&collection_no=80914 Playa Santa Isabel, south
  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 . en . 10.1080/02724634.2023.2232425 . 260947656 . 0272-4634.
  27. Gaetán, 2019
  28. Cione et al., 2011, p.428
  29. Cione et al., 2010, p.433
  30. Acosta et al., 2008, p.568
  31. Tonni, 1979, p.12
  32. 2021 . Tetraodontiformes (Osteichthyes, Actinopterygii) from the Miocene of Argentina: with the southernmost record of fossil Tetraodontidae . Comptes Rendus Palevol . en . 20 . 27 . 585–596.
  33. Acosta et al., 2008, p.566