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Ediacaran period
630 - 542 million years ago
O
S
D
C
P
T
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K
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Mean atmospheric O2 content over period duration ca. 8 Vol %[1]
(40 % of modern level)
Mean atmospheric CO2 content over period duration ca. 4500 ppm[2]
(16 times pre-industrial level)
Events of the Ediacaran period
view • discuss •  edit
-640 —
-630 —
-620 —
-610 —
-600 —
-590 —
-580 —
-570 —
-560 —
-550 —
-540 —
-530 —
-520 —
-510 —
-500 —
 
 
Ediacaran
 
 
 
 
 
 
Last Ediacaran communities
Last putative Ediacaran
First Ediacaran megafossil
Gaskiers
Glaciation
Aspidella
discs
Neoproterozoic
(last era of the Precambrian)
Palæozoic
(first era of the Phanerozoic)
Axis scale: millions of years ago.
References: Waggoner 1998,[3] Hofmann 1990[4]

The Ediacaran Period (pronounced /ˌiːdiˈækərən/; named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon. Its 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] The type section is in the Flinders Ranges in South Australia.

Contents

Ediacaran and Vendian

Ediacaran period overlaps, but is shorter than the Vendian period, a name that was earlier, in 1952, proposed by Russian geologist/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.[8][9] Paleontological substantiation of this boundary was worked out separately for the siliciclastic basin (base of the Baltic Stage of the Eastern-European Platform [10]) and for the carbonate basin (base of the Tommotian Stage of the Siberian Platform [11]). The lower boundary of the Vendian was suggested to be defined at the base of the Varanger (Laplandian) tillites.[9][12]

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.[9][13] 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 acantomorph acritarchs.[12]

Borders of the Ediacaran

The Ediacaran Period (ca. 635-542 Ma) represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Trichophycus pedum).[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 (this bed is characterized by an unusual depletion of 13C), referred to as a "cap carbonate", because it caps glacial deposits and indicates a sudden climatic change at the end of the Marinoan ice age. The lower boundary GSSP of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina diamictite in the Enorama Creek section, 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 ichnofossils Treptichnus pedum. 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.[12][14]

Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation) and usually siliciclastic sediments replace laterally the cap carbonates in a rather short distance and cap carbonates do not occur above every tillite elsewhere 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.[12][15] Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram[16] Formation that is clearly away from any glacial evidence[17] strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events[18]. 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 T. pedum in Namibia, Spain and Newfoundland, and possibly, in the west of USA. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.[12][19]

Dating

No dating has been possible at the type section of the Ediacaran Period in South Australia. Therefore the age range of 635 to 542 million years before the present is based on correlations to other countries where dating has been possible. The base age of approximately 635 million years ago is based on U-Pb (uranium-lead) isochron dating from Namibia[20] and China.[21 ] Applying this age to the base of the Ediacaran assumes that individual cap carbonates are synchronous around the world and that the correct cap carbonate layers have been correlated between Australian and Namibia. This is controversial because an age of about 580 million years has been obtained in association with glacial rocks in Tasmania which some scientists tentatively correlate with those just beneath the Ediacaran rocks of the Flinders Ranges.[22] The age of the top is the same as the widely recognised age for the base of the Cambrian Period[23] 542± 0.3 Ma (million years ago).[24]

Biota

The animal fossil record from this period is sparse, possibly because animals had yet to evolve hard shells, which make for easier fossilization. The Ediacaran biota include the oldest definite multicellular organisms with tissues, and the most common types resemble segmented worms, fronds, disks, or immobile bags. They bear little resemblance to modern lifeforms, and their relationship even with the later lifeforms of the Cambrian explosion is difficult to interpret. More than 100 genera have been described, and well known forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Onega, Pteridinium, and Yorgia.

In addition, there are unverified claims of "footprints" - tracks made by legged organisms thought to resemble arthropods or legged worms. The significance of these finds awaits their publication.[25]

See also

References

  1. ^ Image:Sauerstoffgehalt-1000mj.svg
  2. ^ Image:Phanerozoic Carbon Dioxide.png
  3. ^ Waggoner, Ben (1998). "Interpreting the Earliest Metazoan Fossils: What Can We Learn?". Integrative and Comparative Biology 38 (6): 975—982. doi:10.1093/icb/38.6.975. ISSN 1540-7063. http://intl-icb.oxfordjournals.org/cgi/content/abstract/38/6/975. Retrieved 2007-03-08.  
  4. ^ Hofmann, H.J.; Narbonne, G.M., Aitken, J.D. (1990). "Ediacaran remains from intertillite beds in northwestern Canada". Geology 18 (12): 1199-1202. http://geology.geoscienceworld.org/cgi/content/abstract/18/12/1199.  
  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, GM; Christie-Blick, N (2004). "A new period for the geologic time scale". Science 305 (5684): 621–622. doi:10.1126/science.1098803. PMID 15286353. http://www.stratigraphy.org/bak/ediacaran/Knoll_et_al_2004b.pdf.  
  7. ^ Knoll, A.H., Walter, M.R., Narbonne, G.M., and Christie-Blick, N. (2006). "The Ediacaran Period: A new addition to the geologic time scale". Lethaia 39: 13–30. doi:10.1080/00241160500409223. http://geol.queensu.ca/people/narbonne/KnollWalterNarbonneChristieBlick_Lethaia_2006.pdf.  
  8. ^ 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.  
  9. ^ a b c Sokolov, B.S. (1997). "Essays on the Advent of the Vendian System." 153 pp. KMK Scientific Press, Moscow. (in Russian)
  10. ^ Sokolov B. S. (1965) "Abstracts of All-Union Symposium on Paleontology of the Precambrian and Early Cambrian." Nauka, Novosibirsk.
  11. ^ 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., and 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.  
  12. ^ a b c d e M.A. Fedonkin, B.S. Sokolov, M.A. Semikhatov, N.M.Chumakov (2007). "Vendian versus Ediacaran: priorities, contents, prospectives." In: "The Rise and Fall of the Vendian (Ediacaran) Biota. Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493, August 20-31, 2007, Moscow." Moscow: GEOS.
  13. ^ Khomentovsky, V. V. (2008). "The Yudomian of Siberia, Vendian and Ediacaran systems of the International stratigraphic scale". Stratigraphy and Geological Correlation 16: 581–598. doi:10.1134/S0869593808060014.   edit
  14. ^ 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
  15. ^ Bristow, T.F. and Kennedy, M.J. (2008). "Carbon isotope excursions and the oxidant budget of the Ediacaran atmosphere and ocean". Geology 36 (11): 863–866. doi:10.1130/G24968A.1. http://taylorandfrancis.metapress.com/index/PUNM6BQLNW1BJMFN.pdf. Retrieved 2007-05-05.  
  16. ^ 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. doi:10.1016/j.precamres.2006.01.007.. http://www.sciencedirect.com/science/article/B6VBP-4JCBPH6-1/2/ef9fad10f3c37b22afaad23a936d5e13.  
  17. ^ Le Guerroué, E.; Allen, P.A., Cozzi, A., Etienne, J.L. and Fanning, C.M. (2006). "50 Myr recovery from the largest negative δ13C excursion in the Ediacaran ocean.". Terra Nova 18 (2): 147–153. doi:10.1111/j.1365-3121.2006.00674.x. http://www3.interscience.wiley.com/journal/118624047/abstract.  
  18. ^ 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: 205-220. doi:10.1111/j.1365-2117.2006.00292.x. http://www3.interscience.wiley.com/journal/118629748/abstract.  
  19. ^ A. Ragozina, D. Dorjnamjaa, A. Krayushkin, E. Serezhnikova (2008). "Treptichnus pedum and the Vendian-Cambrian boundary". 33 Intern. Geol. Congr. August 6- 14, 2008, Oslo, Norway. Abstracts. Section HPF 07 Rise and fall of the Ediacaran (Vendian) biota. P. 183.
  20. ^ Hoffmann, K.H.; Condon, D.J.; Bowring, S.A.; Crowley, J.L. (2004-09-01). "U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation". Geology 32 (9): 817–820. doi:10.1130/G20519.1. http://geology.geoscienceworld.org/cgi/content/abstract/32/9/817.  
  21. ^ Condon, D., Zhu, M., Bowring, S., Wang, W., Yang, A., and Jin, Y. (1 April 2005). "U-Pb Ages from the Neoproterozoic Doushantuo Formation, China" (abstract). Science 308 (5718): 95–98. doi:10.1126/science.1107765. PMID 15731406. http://www.sciencemag.org/cgi/content/abstract/308/5718/95.  
  22. ^ Calver, C.R.; Black, Lance P.; Everard, John L.; Seymour, David B. (2004-10-01). "U-Pb zircon age constraints on late Neoproterozoic glaciation in Tasmania". Geology 32 (10): 893–896. doi:10.1130/G20713.1. http://geology.geoscienceworld.org/cgi/content/abstract/32/10/893.  
  23. ^ Ogg, J.G. (2004). "Status of Divisions of the International Geologic Time Scale". Lethaia 37 (2): 183–199. doi:10.1080/00241160410006492. http://taylorandfrancis.metapress.com/index/PUNM6BQLNW1BJMFN.pdf. Retrieved 2007-05-05.  
  24. ^ Amthor, J. E.; Grotzinger, John P.; Schröder, Stefan; Bowring, Samuel A.; Ramezani, Jahandar; Martin, Mark W.; Matter, Albert (2003). "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman". Geology 31: pp 431–434. doi:10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2. doi:10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2 .  
  25. ^ Earliest Animal Footprints Ever Found -- Discovered in Nevada Newswise, Retrieved on October 5, 2008. Reporting on a poster session at the Geological Society of America

External links

Preceded by Archean eon 2.5 Ga - Proterozoic eon - 542 Ma Followed by Phanerozoic eon
2.6 Ga - Paleoproterozoic era - 1.6 Ga 1.6 Ga - Mesoproterozoic era - 1.0 Ga 1.0 Ga - Neoproterozoic era - 542 Ma
Siderian Rhyacian Orosirian Statherian Calymmian Ectasian Stenian Tonian Cryogenian Ediacaran
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Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

Contents

English

Adjective

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Wikipedia has an article on:

Wikipedia Ediacaran (comparative more Ediacaran, superlative most Ediacaran)

Positive
Ediacaran

Comparative
more Ediacaran

Superlative
most Ediacaran

  1. (geology) of a geologic period within the Neoproterozoic era from about 620 to 542 million years ago

Noun

Ediacaran

  1. (geology) the ediacaran period

See also


Simple English

The Ediacaran period (about 635–542 million years ago), was named after the Ediacara Hills of South Australia. It is the last geological period of the Proterozoic Eon. The Edicaran is followed by the Cambrian, the first period of the Paleozoic Era and the Phanerozoic Eon.

The period is famous for the first larger-bodied fossils, which are probably the first recorded metazoans. These were trace fossils, first found in England's Charnwood Forest, Leicestershire.[1][2] They did not know what it was that they had found, and it was over 60 years later before fossils from the same period were found in South Australia.[3][4]

The status of the Ediacaran as an official geological period was confirmed in 2004 by the International Union of Geological Sciences (IUGS). This made it the first new geological period declared in 120 years.[5]

The Vendian

The Ediacaran period was previously called the Vendian period. The Vendian period was proposed in 1952 by Russian geologist/paleontologist Boris Sokolov.[6][7] The term Vendian is still widely used.

Borders of the Ediacaran

The Ediacaran Period represents the time from the end of global Marinoan glaciation to the first appearance worldwide of certain trace fossils (Trichophycus pedum) at the base of the Cambrian.[8] Although the Ediacaran Period does contain soft-bodied fossils (the Ediacaran biota), its start is defined at the base of a carbonate layer, referred to as a "cap carbonate". It caps glacial deposits and indicates a sudden climatic change at the end of the Marinoan ice age.

The Ediacaran lasts for about 90 million years, of which only the last 50 million years show the soft-bodied fossils. The period starts with the end of the 200-million year long Cryogenian (Snowball Earth) period. Between that and the fossils comes another severe but short glacial period known as the Gaskiers glaciation.

The period ends with the mass extinction of virtually all the Ediacaran fauna: Cambrian fauna are quite different. The causes of this extinction are poorly understood.

References

  1. Hill E & Bonner T.G. 1877. The PreCarboniferous rocks of Charnwood Forest. Q.J. Geol Soc. 33, 754-789.
  2. Bottjer, David J. 2002. Enigmatic Ediacara fossils: ancestors or aliens? In Bottjer et al (eds) Exceptional fossil preservation: a unique view on the evolution of marine life. Columbia, N.Y.
  3. Sprigg R.C. 1947. Early Cambrian (?) jellyfish from the Flinders Ranges, South Australia. Trans Roy Soc South Australia 71, 212-224.
  4. Glaessner M.F. 1984. The dawn of animal life: a biohistorical study. Cambridge.
  5. Knoll A.H. 2002. A new period for the geologic time scale. Science 305, 621.
  6. Sokolov B. (1952). [Expression error: Unexpected < operator "On the age of the old sedimentary cover of the Russian Platform"]. Izvestiya Akademii Nauk SSSR, Seriya eologicheskaya 5: 21–31. 
  7. Sokolov B. 1997. Essays on the advent of the Vendian System. KMK Scientific Press, Moscow. (in Russian)
  8. 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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