Major Glacial period
- Worldwide distinct cap carbonates.
- Beginning of a distinctive pattern of secular changes in carbon isotopes.
(16 times pre-industrial)
(3 °C above modern)
The Ediacaran Period (
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. Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E / 31.331611°S 138.633361°E.
The Ediacaran marks the first appearance of widespread
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, a name that was earlier, in 1952, proposed by Russian geologist and
Paleontological substantiation of this boundary was worked out separately for the
The Vendian in its type area consists of large subdivisions such as Laplandian,
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
Upper and lower boundaries
The Ediacaran Period (c. 635–538.8 Mya) represents the time from the end of global
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
Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and
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.
Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram Formation that is clearly away from any glacial evidence strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events. Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs.
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.
The Ediacaran Period is not yet formally subdivided, but a proposed scheme 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.
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.
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
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. 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.
There is evidence for a mass extinction during this period from early animals changing the environment, dating to the same time as the transition between the White Sea and the Nama-type biotas. Alternatively, this mass extinction has also been theorised to have been the result of an anoxic event.
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.
A few English language documentaries have featured the Ediacaran Period and biota:
- ABC Science; Part 1 of 4).
- The Geological History of Canada, as part of The Nature of Things series, CBC-SRC; 2011; Eastern Canada.
- The first episode of a BBC documentary titled Life on Earth, with David Attenborough as narrator.
- Another documentary narrated by David Attenborough titled First Life featuring Charnia, Dickinsonia, Spriggina, Funisia, and Kimberella animated in CGI.
- In our time - Ediacara Biota, BBC, 9 July 2009
- List of fossil sites (with link directory)
- Avalon explosion
- End-Ediacaran extinction
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- Introduction to the Vendian Period
- Introduction to the Ediacaran Fauna
- transcript – Catalyst (Australian Broadcasting Corporation)
- Mistaken Point Fauna: The Discovery
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