Ediacarium

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Aeonothem Arathem system Age
( mya )
later later later
P
r
o
t
e
r
o
z
o
i
k
u
m

Duration:

1959
Ma 		Neoproterozoic
Jungproterozoikum
Duration: 459 Ma 		Ediacarium 541
⬍
635
Cryogenium 635
⬍
720
Tonium 720
⬍
1000
Mesoproterozoic
Mittelproterozoikum
Duration: 600 Ma 		Stenium 1000
⬍
1200
Ectasium 1200
⬍
1400
Calymmium 1400
⬍
1600
Paleoproterozoic
Altproterozoikum
Duration: 900 Ma 		Statherium 1600
⬍
1800
Orosirium 1800
⬍
2050
Rhyacium 2050
⬍
2300
Siderium 2300
⬍
2500
earlier earlier earlier

The Ediacarium is a period in the earth's history about 600 million years ago. The oldest fossil finds of multicellular animal life are dated to this period.

The Ediacarium is the most recent chronostratigraphic system and the most recent geochronological period of the Proterozoic . It started around 635 million years ago and ended around 541 million years ago. It follows the Cryogenium and is replaced by the Cambrian .

History and naming

The term was officially adopted by the International Commission on Stratigraphy (ICS) in May 2004 and confirmed by the International Union of Geological Sciences . The Ediacarium is named after the famous fossils of the Ediacara fauna from the Ediacara Hills , an area in the Flinders range in the Australian state of South Australia . There the geologist Reginald Claude Sprigg found imprints of apparently soft organisms in 1946, which had been preserved mainly on the underside of quartzite and sandstone slabs. Older names such as the term Vendium become invalid with this official name confirmation.

Ediacarium
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Cryogenium
Ediacarium
Cambrian
 
 
 
 
 
 
 
←
Last Ediacaran
communities
←
Last
presumed Ediacaran forms
←
←
←
First Ediacaran
megafossils
Aspidella
slices
Charnia
Scale axis: millions of years ago.

Definition and GSSP

The beginning of the Ediacariums is the basis of late marinoischen Deckkarbonate (engl. Cap carbonates ) of Nuccaleena formation that the Elatina- diamictite superimpose immediately. The upper limit is the base of the Cambrian , which is defined with the first appearance of the trace fossil Treptichnus (formerly Phycodes ) pedum . The reference profile ( GSSP ) for the Ediacarium is the Enorama Creek profile at 31 ° 19 ′ 53 ″  S , 138 ° 38 ′ 0 ″  E in the Flinders Range in the Australian state of South Australia. However, the absolute dating of the lower limit is still controversial. The maximum age is to be set at 635 million years, the minimum age at approx. 621 million years. Even more precise dates can be expected here in the future.

Subdivision of the Ediacarium

Despite its long duration of probably over 90 million years, the Ediacarium is not (yet?) Divided into stages like the systems or periods of the Phanerozoic . This is mainly due to the rarity of fossils, which in the Phanerozoic were primarily used for further subdivision. Organisms were certainly not uncommon in the Ediacarium, but with a few exceptions these had no hard parts and thus an extremely small fossilization potential. Furthermore, the rate of evolution of the organisms in the Ediacarium seems to have been considerably lower, so that practically no biostratigraphically usable key fossils are known .

Some prominent events can still be used to subdivide the system to a certain extent. The appearance of the first animal fossils, microscopic eggs, embryos and segmented tubes has been geochronologically dated to 599 ± 4 mya. After the Gaskiers Ice Age , which was widespread in the region, the first macroscopic fossils appear in the sediments immediately above in Newfoundland ( Canada ). These are attributed to the Ediacara fauna; they are thus interpreted as the first appearance of this fauna. These layers are dated 579 million years ago. The first traces of bilateral animals or bilateria appear around 555 mya . Around 550 mya, i.e. shortly before the beginning of the Cambrian, the first organisms with mineralized hard parts have already been identified. Most of the Ediacaran fauna became extinct at the beginning of the Cambrian.

Paleogeography

One of the several possible continent arrangements before 550 ma - Rodinia has already disintegrated

The disintegration of Rodinia had formed three major continents ( Laurentia , Baltica and Sibiria ) and the major continent Gondwana . Gondwana extends from the South Pole to well over the equator and into the northern hemisphere. Laurentia and Baltica were in high southern latitudes, Siberia a little closer to the equator (around 30 degrees of latitude), but also in the southern hemisphere. Northern South America was then near the South Pole, and the Panthalassa also covered the North Pole. Between Laurentia and Gondwana, the Iapetus Ocean had opened up before the beginning of the Ediacarium, and it steadily expanded in the course of the Ediacarium. Between Baltica and Sibiria on the one hand, which were separated by the Aegir Ocean, and Gondwana on the other, a subduction zone had formed in front of Gondwana, through which this part of Gondwana was tectonically deformed and thermally changed ( cadomic orogeny ). Parts of this part of Gondwana broke off several times in the Paleozoic and were later welded to Laurentia and Baltica and today form the subsurface of parts of Central Europe and the east coast of North America ( Avalonia and Hun-Superterran ).

climate

The beginning of the Ediacarium is marked by the end of the great Ice Ages of the Cryogenium . Accordingly, the climate at the beginning of the Ediacarium is characterized by a very marked rise in temperatures. Only around 580 Ma is there a regional glaciation with the Gaskiers glaciation and thus a decrease in temperatures.

Development of the fauna

Marine life in the Ediacarium

In the Ediacarium, the first tissue animals (Eumetazoa) probably arose in the sea. Initially, however, they did not have any internal or external mineralized skeletal parts that could be easily preserved as fossils . Accordingly, their fossils are very rare and have only been found in a few areas of the world. They are the first fossils visible to the naked eye. With the discovery of the first Ediacara fossils ( Vendobionts ) from around 575 mya, the term “ Cambrian explosion ” of life is also relativized . Therefore one speaks today of the Cambrian radiation .

This development to the tissue animals took place after several presumably global ice ages had previously dominated the climate on earth ( snowball earth ). The Marino Ice Age was the last of these great ice ages and the basis of the post- Ice Age "Cap Carbonate" also defines the beginning of the Ediacarium. The “Cap Carbonates” are currently seen as an indication of the strong warming after the end of the Ice Age or the very rapid melting of the ice and the rise in sea level. Immediately above the last tillites , the first animal fossils appear in the phosphorites of the Doushantuo Formation ( Guizhou Province , South China): microscopic eggs, embryos and segmented tubes and the first representatives of the bilaterals such as Vernanimalcula . They have been geochronologically dated to 599 ± 4 mya. The oldest macroscopically visible fossils were discovered in 2003 in the Drook Formation of Newfoundland, with Trepassia wardae as the oldest fossil in the Ediacaran fauna . These layers are dated 579 million years ago. Kimberella , one of the oldest Bilateria fossils, was found on the Russian White Sea coast in sediments of the Ust Pinega Formation, which have been dated to around 555 Ma. The first traces and structures were found in the same sediments. Around 550 Ma, i.e. shortly before the beginning of the Cambrian, the first organisms with calcified hard parts have already been identified ( Cloudina , Namacalathus ), through which Cloudina was also able to form reefs. The oldest spicules of sponges have also been described from these layers . At the end of the Ediacarium, most Ediacarium forms disappeared, only about a handful crossed the Ediacarium-Cambrian border. The last Ediacara forms are proven from the Upper Cambrian.

Development of flora

Almost nothing is known about the flora of the Ediacarium. The development to higher plants did not take place until the Paleozoic . Hence only microscopic vegetable life can be assumed in the Ediacarium. Red algae, yellow-brown algae and green algae were certainly already present.

Geological tradition

In Europe

Ediacaric rocks are mostly open on a small scale in some German low mountain ranges ( Thuringian Slate Mountains , Ore Mountains ) as well as in Great Britain , Scandinavia and Eastern Europe . However, the typical Ediacara fossils were only found in a few localities (e.g. in Russia, Sweden and England).

The following lithostratigraphic units in Europe fall into the Ediacarium:

Outside of Europe

The "Golden Spike" of the Ediacarium at the base of the Nuccaleena Formation in the GSSP outcrop at Enorama Creek, Flinders Range, South Australia

The following lithostratigraphic units outside Europe fall (partially) into the Ediacarium:

literature

  • Jim G. Ogg: Status of Divisions of the International Geologic Time Scale . In: Lethaia 37, 2004, ISSN  0024-1164 , pp. 183-199
  • Andrew H. Knoll, Malcolm R. Walter, Guy M. Narbonne, Nicholas Christie-Blick: A New Period for the Geologic Time Scale. In: Science 305, 2004, ISSN  0036-8075 , pp. 621-622. doi: 10.1126 / science.1098803
  • Guy M. Narbonne, James G. Gehling: Life after snowball: The oldest complex Ediacaran fossils. In: Geology 31, 2003, ISSN  0091-7613 , pp. 27-30
  • MW Martin, DV Grazhdankin, SA Bowring, DAD Evans, MA Fedonkin, JL Kirschvink: Age of Neoproterozoic Bilatarian Body and Trace Fossils, White Sea, Russia. Implications for Metazoan Evolution. In: Science 288, 2000, ISSN  0036-8075 , pp. 841-845, ( PDF , 526 kB)
  • Guy M. Narbonne: The Ediacara Biota: Neoproterozoic Origin of Animals and Their Ecosystems. In: Annual Revue of Earth and Planetary Sciences 33, 2005, ZDB -ID 124813-3 , pp. 421-442, doi : 10.1146 / annurev.earth.33.092203.122519

Web links

Commons : Ediacarium  - collection of images, videos and audio files

A series of articles in FAZ.NET with pictures of the Ediacaran fauna:

Individual evidence

  1. ↑ Paul Selden , John Nudds: Window on Evolution - Famous Fossil Findings of the World (translated by Jens Seeling), Elsevier Spektrum Akademischer Verlag, Munich 2007, ISBN 978-3-8274-1771-8 , p. 10 and p. 11
  2. ^ GA Shields-Zhou, AC Hill; BA Macgabhann: The Cryogenian Period . Chapter 17 in Felix M. Gradstein, James G. Ogg, Mark Schmitz, Gabi Ogg (editors): The Geological Time Scale . Elsevier, 2012. doi : 10.1016 / B978-0-444-59425-9.00017-2
  3. ↑ Daniel Condon, Maoyan Zhu, Samuel Bowring, Wei Wang, Aihua Yang, Yugan Jin (2005): U-Pb Ages from the Neoproterozoic Doushantuo Formation, China . Science 308 (5718): 95-98. doi : 10.1126 / science.1107765
  4. ↑ AM Penny, R. Wood, A. Curtis, F. Bowyer, R. Tostevin, K.-H. Hoffman: Ediacaran metazoan reefs from the Nama Group, Namibia. Science June 27, 2014: Volume 344, No. 6191, pp. 1504–1506, DOI: 10.1126 / science.1253393
  5. ↑ Narbonne, p. 422