Carnian

Source: Wikipedia, the free encyclopedia.
For the Carnian Alps, see Carnic Alps.
Carnian
~237 – ~227 Ma
Ammonite Daxatina canadensis
Lower boundary GSSPPrati di Stuores, Dolomites, Italy
46°31′37″N 11°55′49″E / 46.5269°N 11.9303°E / 46.5269; 11.9303
Lower GSSP ratified2008[6]
Upper boundary definitionNot formally defined[7]
Upper boundary definition candidatesBase of Stikinoceras kerri ammonoid zone and near FAD of Metapolygnathus echinatus within the M. communisti conodont zones[7]
Upper boundary GSSP candidate section(s)

The Carnian (less commonly, Karnian) is the lowermost

million years ago (Ma).[8] The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event (known as the Carnian pluvial episode characterized by substantial rainfall) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations.[9] Another extinction occurred at the Carnian-Norian boundary, ending the Carnian age.[10]

Stratigraphic definitions

index fossil
for the lower Carnian

The Carnian was named in 1869 by

Carinthia (Kärnten in German)[11] or after the Carnia historical region in northeastern Italy.[citation needed] The name, however, was first used referring to a part of the Hallstatt Limestone cropping out in Austria.[11]

The base of the Carnian Stage is defined as the place in the stratigraphic record where the

ammonite species Daxatina canadensis first appears. The global reference profile for the base is located at the Stuores-Wiesen near Badia in the Val Badia in the region of South Tyrol, Italy.[12]

The top of the Carnian (the base of the Norian) is at the bases of the ammonite biozones of Klamathites macrolobatus or Stikinoceras kerri and the conodont biozones of Metapolygnathus communisti or Metapolygnathus primitius.

Subdivisions

There is no established, standard usage for the Carnian subdivisions, thus, while in some regional stratigraphies a two-substage subdivision is common:

  • Julian
  • Tuvalian

others prefer a three-substage organization of the stage as follows:

  • Cordevolian
  • Julian
  • Tuvalian

Biostratigraphy

In the Tethys domain, the Carnian Stage contains six ammonite biozones:

The Otischalkian land vertebrate

faunachron corresponds to the latest Carnian.[13]

Paleogeography and climate

Carnian Earth

The paleogeography of the Carnian was basically the same as for the rest of the Triassic. Most continents were merged into the supercontinent Pangaea, and there was a single global ocean, Panthalassa. The global ocean had a western branch at tropical latitudes called Paleo-Tethys. The sediments of Paleo-Tethys now crop out in southeastern Europe, in the Middle East, in the Himalayas, and up to the island of Timor. The extreme land-sea distribution led to "mega-monsoons", i.e., an atmospheric monsoon regime more intense than the present one.

As for most of the Mesozoic, there were no ice caps. Climate was mostly arid in the tropics, but an episode of wet tropical climate is documented at least in the Paleo-Tethys. This putative climatic event is called the "

Carnian Pluvial Event
", its age being between latest early Carnian (Julian) and the beginning of late Carnian (Tuvalian).

Carnian life

Main page: Category:Carnian life

In the marine realm, the Carnian saw the first abundant occurrences of calcareous nanoplankton, a morphological group including the coccolithophores.

Invertebrates

There are a few invertebrates which are typical and characteristic of the Carnian. Among molluscs, the

ammonoid genus Trachyceras is exclusive to the lower Carnian (i.e., Julian of the two-substages subdivision, see above). The family Tropitidae and the genus Tropites appear at the base of the upper Carnian (Tuvalian). The bivalve genus Halobia, a bottom-dweller of deep sea environments, differentiated from Daonella at the beginning of this age. Scleractinian
coral reefs, i.e., reefs with corals of the modern type, became relatively common for the first time in the Carnian.

Vertebrates

The earliest unequivocal

Ma
.

In this stage the

therapsids, which included the ancestors of mammals
, decreased in both size and diversity, and would remain relatively small until the extinction of the dinosaurs.

Conodonts were present in Triassic marine sediments. Paragondolella polygnathiformis appeared at the base of the Carnian Stage, and is considered a characteristic species. A partial list of Carnian vertebrates is given below. Many Carnian vertebrates are found in Santa Maria Formation rocks of the Paleorrota geopark.

Classic localities and Lagerstätten

The lower Carnian fauna of the San Cassiano Formation (Dolomites, northern Italy) has been studied since the 19th century. Fossiliferous localities are many, and are distributed mostly in the surroundings of Cortina d'Ampezzo and in the high Badia Valley, near the village of San Cassiano, after which the formation was named. This fauna is extremely diverse, including ammonoids, gastropods, bivalves, echinoderms, calcareous sponge, corals, brachiopods, and a variety of less common fossils. A collection of this fauna is exposed in the "Museo delle Regole", a museum in Cortina d'Ampezzo.

The Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina yielded a very important vertebrate association, including the oldest dinosaurian assemblage.

The Lagerstätte of the Madygen Formation in Kyrgyzstan has provided over 20,000 fossil insects, vertebrates and flora.

Notable Formations

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

References

  1. doi:10.3389/feart.2020.00196
    .
  2. PMID 17919771
    .
  3. ^ Retallack, G. J.;
    doi:10.1130/0016-7606(1996)108<0195:GCGBPT>2.3.CO;2
    . Retrieved 2007-09-29.
  4. S2CID 35498132
    .
  5. ISBN 978-0-444-63771-0
    .
  6. doi:10.18814/epiiugs/2012/v35i3/003
    . Retrieved 13 December 2020.
  7. ^ a b c d "Global Boundary Stratotype Section and Point". International Commission of Stratigraphy. Retrieved 23 December 2020.
  8. ^ "Ics-chart".
  9. PMID 32938682
    .
  10. doi:10.1016/j.palaeo.2015.10.008
    . Retrieved 24 January 2023.
  11. ^
    ISBN 978-0-44-459390-0
    .
  12. ^ The GSSP was firstly proposed by Broglio Loriga et al. (1999) and established by Mietto et al. (2012)
  13. ^ Heckert, A.B. (2004). "Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern USA". New Mexico Museum of Natural History and Science Bulletin. 27: 1. Retrieved 17 November 2021.

Bibliography

  • Brack, P.; Rieber, H.; Nicora, A. & Mundil, R.; 2005: The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale, Episodes 28(4), pp. 233–244.
  • Broglio Loriga, C.; Cirilli, S.; De Zanche, V.; Di Bari, D.; Gianolla, P.; Laghi, G.; Manfrin, S.; Mastandrea, A.; Mietto, P.; Muttoni, G.; Neri, C.; Posenato, R.; Rechichi, M.C.; Rettori R. & Roghi, G.; 1999: The Prati di Stuores/Stuores Wiesen section (Dolomites, Italy): a candidate Global Stratotype section and Point for the base of the Carnian stage, Rivista Italiana di Paleontologia e Stratigrafia 105, pp. 37–78.
  • Furin, S.; Preto, N.; Rigo, M.; Roghi, G.; Gianolla, P.; Crowley, J.L. & Bowring, S.A.; 2006: High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs, Geology 34, p. 1009–1012.
  • Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
  • Gradstein, F.M.; Ogg, J.G., Schmitz, M.D. & Ogg, G.M.; 2012: The Geologic Time Scale 2012, Elsevier.
  • Lucas, S.G.; Luo, Zhe-Xi; 1993: Adelobasileus from the upper Triassic of west Texas: the oldest mammal, J. Vert. Paleont. 13, pp. 309–334.
  • Mietto, P.; Manfrin, S.; Preto, N.; Rigo, M.; Roghi, G.; Furin, S.; Gianolla, P.; Posenato, R.; Muttoni, G.; Nicora, A.; Buratti, N.; Cirilli, S.; Spoetl, C.; Ramezani, J. & Bowring, S.A.; 2012: The Global Boundary Stratotype Section and Point (GSSP) of the Carnian stage (Late Triassic) at Prati di Stuores/Stuores Wiesen section (Southern Alps, NE Italy), Episodes 35, pp. 414–430.

External links

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