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Ediacaran

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For other uses, see Ediacara.

Ediacaran
~635 – 538.8 ± 0.2 Ma
A map of the world as it appeared during the mid-Ediacaran. (600 ma)
Chronology
Etymology
Name formalityFormal
Name ratified1990
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitPeriod
Stratigraphic unitSystem
Time span formalityFormal
Lower boundary definition
  • Worldwide distinct cap carbonates.
  • Beginning of a distinctive pattern of secular changes in carbon isotopes.
Lower boundary GSSPEnorama Creek section, Flinders Ranges, South Australia
31°19′53″S 138°38′00″E / 31.3314°S 138.6334°E / -31.3314; 138.6334
Lower GSSP ratifiedMarch 2004[1]
Upper boundary definitionAppearance of the Ichnofossil Treptichnus pedum
Upper boundary GSSPFortune Head section, Newfoundland, Canada
47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W / 47.0762; -55.8310
Upper GSSP ratified1992[2]
Atmospheric and climatic data
Mean atmospheric O2 contentc. 8 vol %
(40 % of modern)
Mean atmospheric CO2 contentc. 4500 ppm
(16 times pre-industrial)
Mean surface temperaturec. 17 °C
(3.5 °C above pre-industrial)

The Ediacaran Period ( /iːdiˈækərən, ɛdi-/ ee-dee-AK-ər-ən, ed-ee-)[3] is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya.[4] It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.

The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years.[5][6][7] Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946,[8] the type section is located in the bed of the Enorama Creek[9] within Brachina Gorge[10] in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E / 31.331611°S 138.633361°E / -31.331611; 138.633361.

The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, which is represented by now-extinct relatively simple animal phyla such as Proarticulata (bilaterians with articulation including Dickinsonia and Spriggina), Petalonamae (sea pen-like animals including Charnia), Medusoids (radial-shaped animals including Cyclomedusa) and Trilobozoa (animals with tri-radial symmetry including Tribrachidium). Most of those organisms appeared during or after the Avalon explosion event 575 million years ago and died out during an End-Ediacaran extinction event 539 million years ago. Some modern groups of animals also appeared during this period, including cnidarians and early bilaterians such as Xenacoelomorpha. Mollusc-like Kimberella also lived during Ediacaran. Fossilized organisms with shells or skeletons were yet to evolve in the Cambrian, the superseding period of the Phanerozoic eon.

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

See also: Riphean (stage) and Jotnian

The Ediacaran Period overlaps, but is shorter than the Vendian Period, a name that was earlier, in 1952, proposed by Russian geologist and paleontologist 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 siliciclastic basin (base of the Baltic Stage of the Eastern European Platform[13]) and for the carbonate basin (base of the Tommotian stage of the Siberian Platform).[14] The lower boundary of the Vendian was suggested to be defined at the base of the Varanger (Laplandian) tillites.[12][15]

The Vendian in its type area consists of large subdivisions such as Laplandian, Redkino, Kotlin and 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 microfossils, megascopic algae, metazoan body fossils and ichnofossils.[12][16]

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 Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Treptichnus pedum (Seilacher, 1955)).[5]

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 13C that indicates a sudden climatic change at the end of the Marinoan ice age. The lower 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 GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossil 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 557 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's 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 (uranium–lead) and Re–Os (rhenium–osmium) dating from Africa, China, North America, and Tasmania.[25][26][27][28][29]

Biota

Main article: Ediacaran 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 multicellular organisms (with specialized tissues), the most common types of which resemble segmented worms, fronds, disks, or immobile bags. Auroralumina was a cnidarian.[31][32]

Some hard-shelled agglutinated foraminifera are known from latest Ediacaran sediments of western Siberia.[33]

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. More than 100 genera have been described, and well known forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Cephalonega, Pteridinium, and Yorgia.

There is evidence for a mass extinction during this period from early animals changing the environment.[34]

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.[35]

Documentaries

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

See also

References

  1. ^ Knoll, Andrew H.; Walter, Malcolm R.; Narbonne, Guy M.; Christie-Black, Nicholas (3 March 2006). "The Ediacaran Period: a new addition to the geologic time scale" (PDF). Lethaia. 39: 13–30. doi:10.1080/00241160500409223. Retrieved 6 December 2020.
  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. ^ 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.
  6. ^ Knoll, A. H.; Walter, MR; Narbonne, G. M; Christie-Blick, N (30 July 2004). "A new period for the geologic time scale" (PDF). Science. 305 (5684): 621–622. doi:10.1126/science.1098803. PMID 15286353. S2CID 32763298.
  7. ^ Knoll, A. H.; Walter, M. R.; Narbonne, G. M. & Christie-Blick, N. (March 2006). "The Ediacaran Period: A new addition to the geologic time scale" (PDF). Lethaia. 39: 13–30. doi:10.1080/00241160500409223. Archived from the original (PDF) on 21 February 2007.
  8. ^ 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.
  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)
  16. ^ Khomentovsky, V. V. (2008). "The Yudomian of Siberia, Vendian and Ediacaran systems of the International stratigraphic scale". Stratigraphy and Geological Correlation. 16 (6): 581–598. Bibcode:2008SGC....16..581K. doi:10.1134/S0869593808060014. S2CID 128966206.
  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. ^ Bristow, T. F.; Kennedy, M. J. (2008). "Carbon isotope excursions and the oxidant budget of the Ediacaran atmosphere and ocean" (PDF). Geology. 36 (11): 863–866. Bibcode:2008Geo....36..863B. doi:10.1130/G24968A.1. Archived from the original (PDF) on 7 May 2020. Retrieved 5 May 2007.
  19. ^ Le Guerroué, E.; Allen, P. A.; Cozzi, A. (2006). "Chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in Earth history: The Neoproterozoic Shuram Formation (Nafun Group, Oman)". Precambrian Research. 146 (1–2): 68–92. Bibcode:2006PreR..146...68L. doi:10.1016/j.precamres.2006.01.007.
  20. ^ Le Guerroué, E.; Allen, P. A.; Cozzi, A.; Etienne, J. L.; Fanning, C. M. (2006). "50 Myr recovery from the largest negative δ13C excursion in the Ediacaran ocean". Terra Nova. 18 (2): 147–153. Bibcode:2006TeNov..18..147L. doi:10.1111/j.1365-3121.2006.00674.x. S2CID 140710102. Archived from the original on 5 January 2013.
  21. ^ Le Guerroué, E.; Allen, P. A.; Cozzi, A. (2006). "Parasequence development in the Ediacaran Shuram Formation (Nafun Group, Oman): primary origin stratigraphic test of negative carbon isotopic ratios". Basin Research. 18 (2): 205–220. Bibcode:2006BasR...18..205L. doi:10.1111/j.1365-2117.2006.00292.x. S2CID 128910191. Archived from the original on 5 January 2013.
  22. ^ Gong, Zheng; Kodama, Kenneth; Li, Yong-Xiang (2017). "Rock magnetic cyclostratigraphy of the Doushantuo Formation, South China and its implications for the duration of the Shuram carbon isotope excursion". Precambrian Research. 289: 62–74. Bibcode:2017PreR..289...62G. doi:10.1016/j.precamres.2016.12.002.
  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.
  24. ^ Xiao, Shuhai; Narbonne, Guy M.; Zhou, Chuanming; Laflamme, Marc; Grazhdankin, Dmitriy V.; Moczydlowska-Vidal, Malgorzata; Cui, Huan (2016). "Towards an Ediacaran Time Scale: Problems, Protocols, and Prospects". Episodes. 39 (4): 540555. doi:10.18814/epiiugs/2016/v39i4/103886.
  25. ^ Rooney, Alan D.; Strauss, Justin V.; Brandon, Alan D.; Macdonald, Francis A. (2015). "A Cryogenian chronology: Two long-lasting synchronous Neoproterozoic glaciations". Geology. 43 (5): 459–462. Bibcode:2015Geo....43..459R. doi:10.1130/G36511.1. ISSN 1943-2682.
  26. ^ Rooney, Alan D.; Yang, Chuan; Condon, Daniel J.; Zhu, Maoyan; Macdonald, Francis A. (1 June 2020). "U-Pb and Re-Os geochronology tracks stratigraphic condensation in the Sturtian snowball Earth aftermath". Geology. 48 (6): 625–629. Bibcode:2020Geo....48..625R. doi:10.1130/G47246.1. ISSN 0091-7613. S2CID 218815302.
  27. ^ Zhang, Shihong; Jiang, Ganqing; Zhang, Junming; Song, Biao; Kennedy, Martin J.; Christie-Blick, Nicholas (2005). "U-Pb sensitive high-resolution ion microprobe ages from the Doushantuo Formation in south China: Constraints on late Neoproterozoic glaciations". Geology. 33 (6): 473. Bibcode:2005Geo....33..473Z. doi:10.1130/G21418.1. ISSN 0091-7613.
  28. ^ Schmitz, M.D. (2012), "Radiometric ages used in GTS2012", The Geologic Time Scale, Elsevier, pp. 1045–1082, doi:10.1016/b978-0-444-59425-9.15002-4, ISBN 978-0-444-59425-9, retrieved 2 April 2022
  29. ^ Calver, C.R.; Crowley, J.L.; Wingate, M.T.D.; Evans, D.A.D.; Raub, T.D.; Schmitz, M.D. (2013). "Globally synchronous Marinoan deglaciation indicated by U-Pb geochronology of the Cottons Breccia, Tasmania, Australia". Geology. 41 (10): 1127–1130. Bibcode:2013Geo....41.1127C. doi:10.1130/G34568.1. ISSN 1943-2682.
  30. ^ Fedonkin, Mikhail A.; Sciences), Mikhail A. (Head Fedonkin, Laboratory of Precambrian Organisms Russian Academy of; Gehling, James G.; Museum), James G. (Senior Curator Gehling, retired 6 27 2019 South Australian; Grey, Kathleen; Narbonne, Guy M.; Vickers-Rich, Patricia; University), Patricia (Director Vickers-Rich, Monash (16 March 2007). The Rise of Animals: Evolution and Diversification of the Kingdom Animalia. JHU Press. ISBN 9780801886799. Retrieved 7 August 2022 – via Google Books.{{cite book}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  31. ^ Dunn, F. S.; Kenchington, C. G.; Parry, L. A.; Clark, J. W.; Kendall, R. S.; Wilby, P. R. (25 July 2022). "A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK". Nature Ecology & Evolution. 6 (8): 1095–1104. doi:10.1038/s41559-022-01807-x. PMC 9349040. PMID 35879540.
  32. ^ Amos, Jonathan (25 July 2022). "Ancient fossil is earliest known animal predator". bbc.co.uk. BBC News. Retrieved 7 August 2022.
  33. ^ Kontorovich, A. E.; Varlamov, A. I.; Grazhdankin, D. V.; Karlova, G. A.; Klets, A. G.; Kontorovich, V. A.; Saraev, S. V.; Terleev, A. A.; Belyaev, S. Yu.; Varaksina, I. V.; Efimov, A. S. (1 December 2008). "A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)". Russian Geology and Geophysics. 49 (12): 932–939. Bibcode:2008RuGG...49..932K. doi:10.1016/j.rgg.2008.06.012. ISSN 1068-7971.
  34. ^ Evidence that Earth's first mass extinction was caused by critters not catastrophe, ScienceDaily
  35. ^ Williams, George E. (2000). "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics. 38 (1): 37–60. Bibcode:2000RvGeo..38...37W. CiteSeerX 10.1.1.597.6421. doi:10.1029/1999RG900016. S2CID 51948507.
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