Ediacaran

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Ediacaran
~635 – 538.8 ± 0.2 Ma
Marinoan glaciation
Palaeopascichnids
Stratigraphic scale of the
PeriodStratigraphic unitSystem
Time span formalityFormalLower boundary definition
  • Worldwide distinct cap carbonates.
  • Beginning of a distinctive pattern of secular changes in
    carbon isotopes
    .
Lower boundary GSSPEnorama Creek section,
ppm

(16 times pre-industrial)Mean surface temperaturec. 17 °C
(3 °C above modern)

The Ediacaran period (

eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian period marks the start of the Phanerozoic eon where recognizable fossil evidence of life
becomes common.

The Ediacaran period is named after the

, approximately 55 km (34 mi) southeast of the Ediacara Hills fossil site.

The Ediacaran marks the first widespread appearance of complex

Cambrian Explosion
some 35 million years later.

The supercontinent Pannotia formed and broke apart by the end of the period. The Ediacaran also witnessed several glaciation events, such as the Gaskiers and Baykonurian glaciations. The Shuram excursion also occurred during this period, but its glacial origin is unlikely.

Ediacaran and Vendian

The Ediacaran Period overlaps but is shorter than the Vendian Period (650 to 543 million years ago), a name that was earlier, in 1952, proposed by Russian geologist and

Boris Sokolov. The Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian.[11][12]

Paleontological substantiation of this boundary was worked out separately for the

The lower boundary of the Vendian was suggested to be defined at the base of the

The Vendian in its type area consists of large subdivisions such as Laplandian,

Rovno
regional stages with the globally traceable subdivisions and their boundaries, including its lower one.

The Redkino, Kotlin and Rovno regional stages have been substantiated in the type area of the Vendian on the basis of the abundant organic-walled

The lower boundary of the Vendian could have a

biostratigraphic substantiation as well taking into consideration the worldwide occurrence of the Pertatataka assemblage of giant acanthomorph acritarchs.[15]

Upper and lower boundaries

The 'golden spike' (bronze disk in the lower section of the image) or 'type section' of the Global Boundary Stratotype Section and Point (GSSP) for the base of the Ediacaran System
The 'golden spike' marking the GSSP

The Ediacaran Period (c. 635–538.8 Mya) represents the time from the end of global

Treptichnus pedum (Seilacher, 1955)).[6]

Although the Ediacaran Period does contain soft-bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer that is referred to as a "cap carbonate", because it caps glacial deposits.

This bed is characterized by an unusual depletion of 13

global boundary stratotype section (GSSP) of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina diamictite
in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia.

The

Treptichnus pedum
(Seilacher, 1955). In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition.

Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and

ichnofossils are disputable.[15][17]

Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation)[vague] and usually siliciclastic sediments laterally replace the cap carbonates in a rather short distance but cap carbonates do not occur above every tillite elsewhere[clarification needed] in the world.

The C-isotope chemostratigraphic characteristics obtained for contemporaneous cap carbonates in different parts of the world may be variable in a wide range owing to different degrees of secondary alteration of carbonates, dissimilar criteria used for selection of the least altered samples, and, as far as the C-isotope data are concerned, due to primary lateral variations of δ l3Ccarb in the upper layer of the ocean.[15][18]

Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram[19] Formation that is clearly away from any glacial evidence[20] strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events.[21] Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs.[22]

As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky, because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the level of T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.[15][23]

Subdivisions

The Ediacaran Period is not yet formally subdivided, but a proposed scheme[24] recognises an Upper Ediacaran whose base corresponds with the Gaskiers glaciation, a Terminal Ediacaran Stage starting around 550 million years ago, a preceding stage beginning around 575 Ma with the earliest widespread Ediacaran biota fossils; two proposed schemes differ on whether the lower strata should be divided into an Early and Middle Ediacaran or not, because it is not clear whether the Shuram excursion (which would divide the Early and Middle) is a separate event from the Gaskiers, or whether the two events are correlated.

Absolute dating

The dating of the rock type section of the Ediacaran Period in South Australia has proven uncertain due to lack of overlying igneous material. Therefore, the age range of 635 to 538.8 million years is based on correlations to other countries where dating has been possible. The base age of approximately 635 million years is based on U–Pb (uraniumlead) and Re–Os (rheniumosmium) dating from Africa, China, North America, and Tasmania.[25][26][27][28][29]

Biota

Archaeaspinus, one of the members of the Ediacaran biota which is one of the representatives of the Phylum Proarticulata which also includes Dickinsonia, Karakhtia and numerous other organisms.[30]

The fossil record from the Ediacaran Period is sparse, as more easily fossilized hard-shelled animals had yet to evolve. The Ediacaran biota include the oldest definite

Most members of the Ediacaran biota bear little resemblance to modern lifeforms, and their

relationship even with the immediately following lifeforms of the Cambrian explosion is rather difficult to interpret.[33][34] More than 100 genera have been described, and well known forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Cephalonega, Pteridinium, and Yorgia. However, despite the overall enigmaticness of most Ediacaran organisms, some fossils identifiable as hard-shelled agglutinated foraminifera (which are not classified as animals) are known from latest Ediacaran sediments of western Siberia.[35] Sponges recognisable as such also lived during the Ediacaran.[36]

Four different biotic intervals are known in the Ediacaran, each being characterised by the prominence of a unique ecology and faunal assemblage. The first spanned from 635 to around 575 Ma and was dominated by acritarchs known as large ornamented Ediacaran microfossils.[37] The second spanned from around 575 to 560 Ma and was characterised by the Avalon biota. The third spanned from 560 to 550 Ma; its biota has been dubbed the White Sea biota due to many fossils from this time being found along the coasts of the White Sea. The fourth lasted from 550 to 539 Ma and is known as the interval of the Nama biotic assemblage.[38]

There is evidence for a mass extinction during this period from early animals changing the environment,[39] dating to the same time as the transition between the White Sea and the Nama-type biotas.[40][41] Alternatively, this mass extinction has also been theorised to have been the result of an anoxic event.[38]

Astronomical factors

The relative proximity of the Moon at this time meant that tides were stronger and more rapid than they are now. The day was 21.9 ± 0.4 hours, and there were 13.1 ± 0.1 synodic months/year and 400 ± 7 solar days/year.[42]

Documentaries

A few English language documentaries have featured the Ediacaran Period and biota:

See also

References

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  2. ^ Brasier, Martin; Cowie, John; Taylor, Michael. "Decision on the Precambrian-Cambrian boundary stratotype" (PDF). Episodes. 17. Retrieved 6 December 2020.
  3. ^ "Ediacaran". Dictionary.com Unabridged (Online). n.d.
  4. ^ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Retrieved 20 April 2022.
  5. ^ Sprigg, Reg. C. (1947). "Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia". Transactions of the Royal Society of South Australia. 71 (2): 212–224.
  6. ^ a b A. Knoll, M. Walter, G. Narbonne, and N. Christie-Blick (2004) "The Ediacaran Period: A New Addition to the Geologic Time Scale." Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy.
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  9. ^ "Geological time gets a new period: Geologists have added a new period to their official calendar of Earth's history—the first in 120 years". London: BBC. 17 May 2004. Accessed 27 December 2010.
  10. ^ South Australian Museum Newsletter April 2005 Archived 17 February 2011 at the Wayback Machine Accessed 9 August 2010.
  11. ^ B. M. Sokolov (1952). "On the age of the old sedimentary cover of the Russian Platform". Izvestiya Akademii Nauk SSSR, Seriya Eologicheskaya. 5: 21–31.
  12. ^ a b c Sokolov, B.S. (1997). "Essays on the Advent of the Vendian System." 153 pp. KMK Scientific Press, Moscow. (in Russian)
  13. ^ Sokolov B. S. (1965) "Abstracts of All-Union Symposium on Paleontology of the Precambrian and Early Cambrian." Nauka, Novosibirsk.
  14. ^ Rozanov, A.Y.; Missarzhevskij, V.V.; Volkova, N.A.; Voronova, L.G.; Krylov, I.N.; Keller, B.M.; Korolyuk, I.K.; Lendzion, K.; Michniak, R.; Pykhova, N.G. & Sidorov, A.D. (1969). "The Tommotian Stage and the problem of the lower boundary of the Cambrian". Trudy Geologičeskogo Instituta AN SSSR. 206: 1–380.
  15. ^ a b c d e M. A. Fedonkin; B. S. Sokolov; M. A. Semikhatov; N. M. Chumakov (2007). "Vendian versus Ediacaran: priorities, contents, prospectives". Archived from the original on 4 October 2011. In: "The Rise and Fall of the Vendian (Ediacaran) Biota" (PDF). Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493n Moscow: GEOS. 20–31 August 2007. Archived from the original (PDF) on 22 November 2012. (82mb)
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  17. ^ Comments By B. S. Sokolov, M. A. Semikhatov, And M. A. Fedonkin. (2004) Appendix 2 in: "The Ediacaran Period: A New Addition to the Geologic Time Scale." Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy. pp. 32–34
  18. doi:10.1130/G24968A.1. Archived from the original
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  19. .
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  21. S2CID 128910191. Archived from the original
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  22. .
  23. ^ A. Ragozina, D. Dorjnamjaa, A. Krayushkin, E. Serezhnikova (2008). "Treptichnus pedum and the Vendian-Cambrian boundary Archived 4 October 2011 at the Wayback Machine". 33 Intern. Geol. Congr. August 6–14, 2008, Oslo, Norway. Abstracts. Section HPF 07 Rise and fall of the Ediacaran (Vendian) biota. P. 183.
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  32. ^ Amos, Jonathan (25 July 2022). "Ancient fossil is earliest known animal predator". BBC News. Retrieved 7 August 2022.
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External links