Olenekian

Coordinates: 31°57′55″N 78°01′29″E / 31.9653°N 78.0247°E / 31.9653; 78.0247
Source: Wikipedia, the free encyclopedia.
Olenekian
251.2 – 247.2 Ma
Spiti valley, India[6]
Upper boundary definitionNot formally defined
Upper boundary definition candidates
Upper boundary GSSP candidate section(s)

In the

Ma and 247.2 Ma (million years ago).[7] The Olenekian is sometimes divided into the Smithian and the Spathian subages or substages.[8] The Olenekian follows the Induan and is followed by the Anisian (Middle Triassic).[9]

The Olenekian saw the deposition of a large part of the Buntsandstein in Europe. The Olenekian is roughly coeval with the regional Yongningzhenian Stage used in China.

Stratigraphic definitions

The Olenekian Stage was introduced into scientific literature by Russian stratigraphers in 1956.

Olenëk in Siberia
. Before the subdivision in Olenekian and Induan became established, both stages formed the Scythian Stage, which has since disappeared from the official timescale.

The base of the Olenekian is at the lowest occurrence of the

GSSP
(global reference profile for the base) has not been established as of December 2020.

In the 1960s, English paleontologist Edward T. Tozer (sometimes collaborating with American geologist Norman J. Silberling) crafted Triassic timescales based on North American ammonoid zones, further refining it in the following decades. Tozer's nomenclature was largely derived from Mojsisovics's work, who coined most of the Triassic stages and substages, but he redefined them using North American sites. He recommended the Lower Triassic series be divided into the Griesbachian, Dienerian, Smithian, and Spathian. The latter two roughly correspond with the Olenekian. Tozer's timescale became popular in the Americas.[11] He named the Smithian after Smith Creek on Ellesmere Island, Canada (the creek itself is named after geologist J. P. Smith). The Smithian is defined by the Arctoceras bloomstrandi ammonoid zone (contains Euflemingites romunderi and Juvenites crassus) and the overlying Meekoceras gracilitatis and Wasatchites tardus subzones. He named the Spathian after Spath Creek on Ellesmere Island (this creek is named after geologist L. F. Spath), and defined it by the Procolumbites subrobustus ammonoid zone.[8]

Olenekian life

Life was still recovering from the severe

birds - first evolved from archosauriform ancestors during the Olenekian. This group includes ferocious predators like Erythrosuchus
.

In the oceans,

conodonts diversified, but both suffered losses during the Smithian-Spathian boundary extinction[16]
at the end of the Smithian subage.

Ray-finned fishes largely remained unaffected by the Permian-Triassic extinction event. Coelacanths show their highest post-Devonian diversity during the Early Triassic.[17][18] Many fish genera show a cosmopolitan distribution during the Induan and Olenekian, such as Australosomus, Birgeria, Parasemionotidae, Pteronisculus, Ptycholepidae, Saurichthys and Whiteia. This is well exemplified in the Griesbachian (early Induan) aged fish assemblages of the Wordie Creek Formation (East Greenland),[19][20] the Dienerian (late Induan) aged assemblages of the Middle Sakamena Formation (Madagascar),[21] Candelaria Formation (Nevada, United States),[22] and Mikin Formation (Himachal Pradesh, India),[23] and Daye Formation (Guizhou, China),[24] and the Smithian aged assemblages of the Vikinghøgda Formation (Spitsbergen, Norway),[25][26][27] and Thaynes Group (western United States),[28][29] and Helongshan Formation (Anhui, China),[30] and several Early Triassic layers of the Sulphur Mountain Formation (western Canada).[31] Ray-finned fishes diversified after the mass extinction and reached peak diversity during the Middle Triassic. This diversification is, however, obscured by a taphonomic megabias (Smithian-Bithynian Gap, SBG)[32] during the late Olenekian and early middle Anisian. The earliest large durophagous neopterygian is known from the SBG, suggesting an early onset of the Triassic actinopterygian revolution.[33]

Olenekian

extinct
during the Early Triassic.

Marine

amphibians, such as the superficially crocodile-shaped trematosaurids Aphaneramma and Wantzosaurus, show wide geographic ranges during the Induan and Olenekian ages. Their fossils are found in Greenland, Spitsbergen, Pakistan and Madagascar.[37] Others, such as Trematosaurus
, inhabited freshwater environments and were less widespread.

The first marine reptiles appeared during the Olenekian.

Era
.

An example of an exceptionally diverse Early Triassic assemblage is the

Such diverse assemblages show that organisms diversified wherever and whenever climatic an environmental conditions ameliorated.

Smithian–Spathian boundary event

Neoselachii, 17. Omphalosaurus skeleton, 18. Placodus

An important extinction event occurred during the Olenekian age of the Early Triassic, near the Smithian and Spathian subage boundary. The main victims of this Smithian–Spathian boundary event, often called the Smithian–Spathian extinction,

Palaeozoic species that survived the Permian–Triassic extinction event and flourished in the immediate aftermath of the extinction;[42] ammonoids, conodonts, and radiolarians in particular suffered drastic biodiversity losses,[43][42] which is accentuated, among others, by the cosmopolitan distribution of the ammonoid Anasibirites.[44][45] Marine reptiles, such as ichthyopterygians and sauropterygians, diversified after the extinction.[37]

The

gymnosperms) were the dominant plants during most of the Mesozoic. Until recently[when?] the existence of this extinction event about 249.4 Ma ago[47] was not recognised.[48]

The Smithian–Spathian boundary extinction was linked to late eruptions of the

Oxygen isotope studies on conodonts have revealed that temperatures rose in the first 2 million years of the Triassic, ultimately reaching sea surface temperatures of up to 40 °C (104 °F) in the tropics during the Smithian.[56] The extinction itself occurred during a subsequent drop in global temperatures (ca. 8°C over a geologically short period) in the latest Smithian; however, temperature alone cannot account for the Smithian-Spathian boundary extinction, because several factors were at play.[13][47] An alternative explanation for the extinction event hypothesises the biotic crisis took place not at the Smithian-Spathian boundary but shortly before, during the Late Smithian Thermal Maximum (LSTM), with the Smithian-Spathian boundary itself being associated with cessation of intrusive magmatic activity of the Siberian Traps,[57] along with significant global cooling,[58][59] after which a gradual biotic recovery took place over the early and middle Spathian,[57] along with a decline in continental weathering[60] and a rejuvenation of ocean circulation.[61]

In the ocean, many large and mobile species moved away from the

bivalves disappeared.[62] Conodonts decreased in average size as a result of the extinction.[63] On land, the tropics were nearly devoid of life,[64] with exceptionally arid conditions recorded in Iberia and other parts of Europe then at low latitude.[65] Many big, active animals
returned to the tropics, and plants recolonised on land, only when temperatures returned to normal.

There is evidence that life had recovered rapidly, at least locally. This is indicated by sites that show exceptionally high biodiversity (e.g. the earliest Spathian

food webs were complex and comprised several trophic levels
.

Notable formations

* Tentatively assigned to the Olenekian; age estimated primarily via terrestrial tetrapod biostratigraphy (see Triassic land vertebrate faunachrons)

References

  1. .
  2. .
  3. ^ Retallack, G. J.; . Retrieved 2007-09-29.
  4. .
  5. .
  6. ^ "Global Boundary Stratotype Section and Point". International Commission of Stratigraphy. Retrieved 23 December 2020.
  7. ^ According to Gradstein (2004). Brack et al. (2005) give 251 to 248 Ma
  8. ^ .
  9. ^ See for a detailed geologic timescale Gradstein et al. (2004)
  10. ^ Kiparisova & Popov (1956)
  11. S2CID 129648527
    .
  12. .
  13. ^ .
  14. .
  15. .
  16. .
  17. .
  18. .
  19. .
  20. ^ Nielsen, Eigil (1936). "Some few preliminary remarks on Triassic fishes from East Greenland". Meddelelser om Grønland. 112 (3): 1–55.
  21. ^ Beltan, Laurence (1996). "Overview of systematics, paleobiology, and paleoecology of Triassic fishes of northwestern Madagascar". In G. Arratia; G. Viohl (eds.). Mesozoic Fishes—Systematics and Paleoecology. München: Dr. Friedrich Pfeil. pp. 479–500.
  22. S2CID 155564297
    .
  23. .
  24. .
  25. ^ a b Stensiö, E. (1921). Triassic fishes from Spitzbergen 1. Wien: Adolf Holzhausen. pp. xxviii+307.
  26. ^ Stensiö, E. (1925). "Triassic fishes from Spitzbergen 2". Kungliga Svenska Vetenskapsakademiens Handlingar. 3: 1–261.
  27. .
  28. doi:10.3140/bull.geosci.1337.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  29. ^ .
  30. .
  31. .
  32. .
  33. .
  34. .
  35. .
  36. .
  37. ^ .
  38. ^ .
  39. ^ .
  40. ^ Special issue on Paris Biota: https://www.sciencedirect.com/journal/geobios/vol/54
  41. .
  42. ^ . Retrieved 12 December 2022.
  43. . Retrieved 12 December 2022.
  44. ^ .
  45. .
  46. .
  47. ^ .
  48. . Extinctions with and at the close of the Triassic
  49. . Retrieved 3 January 2024 – via Elsevier Science Direct.
  50. . Retrieved 12 January 2023.
  51. .
  52. . Retrieved 18 December 2022.
  53. . Retrieved 18 December 2022.
  54. . Retrieved 16 September 2022.
  55. . Retrieved 28 October 2022.
  56. ^ Marshall, Michael (18 October 2012). "Roasting Triassic heat exterminated tropical life". New Scientist.
  57. ^ . Retrieved 11 January 2023.
  58. .
  59. . Retrieved 12 January 2023.
  60. . Retrieved 16 January 2023.
  61. . Retrieved 16 January 2023.
  62. .
  63. . Retrieved 28 October 2022.
  64. .
  65. . Retrieved 11 December 2022.

Further reading

External links

31°57′55″N 78°01′29″E / 31.9653°N 78.0247°E / 31.9653; 78.0247