Neoproterozoic

The Neoproterozoic Era is the unit of geologic time from 1,000 to 541 million years ago.[1]

It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran Periods. It is preceded by the Mesoproterozoic era and succeeded by the Paleozoic era.

The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets reached the equator and formed a possible "Snowball Earth".

The earliest fossils of multicellular life are found in the Ediacaran, including the Ediacarans, which were the earliest animals.

According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.[2]

Neoproterozoic Era
1000–541 million years ago
Key events in the Neoproterozoic
-1000 —
-950 —
-900 —
-850 —
-800 —
-750 —
-700 —
-650 —
-600 —
-550 —
Neoproterozoic
An approximate timescale of key Neoproterozoic events.
Axis scale: millions of years ago.

Geology

At the onset of the Neoproterozoic the supercontinent Rodinia, which had assembled during the late Mesoproterozoic, straddled the equator. During the Tonian, rifting commenced which broke Rodinia into a number of individual land masses.

Possibly as a consequence of the low-latitude position of most continents, several large-scale glacial events occurred during the Neoproterozoic Era including the Sturtian and Marinoan glaciations of the Cryogenian Period.

These glaciations are believed to have been so severe that there were ice sheets at the equator—a state known as the "Snowball Earth".

Subdivisions

Neoproterozoic time is subdivided into the Tonian (1000 - 720 Ma), Cryogenian (720 - 635 Ma) and Ediacaran (635 - 541 Ma) periods.[3]

Russian regional timescale

In the regional timescale of Russia, the Tonian and Cryogenian correspond to the Late Riphean; the Ediacaran corresponds to the Early to middle Vendian.[4] Russian geologists divide the Neoproterozoic of Siberia into the Mayanian (from 1000 to 850 Ma) followed by the Baikalian (from 850 to 650 Ma, loosely equivalent to the Cryogenian).[5]

Paleobiology

The idea of the Neoproterozoic Era was introduced in the 1960s. Nineteenth-century paleontologists set the start of multicelled life at the first appearance of hard-shelled animals called trilobites and archeocyathid sponges. This set the beginning of the Cambrian Period. In the early 20th century, paleontologists started finding fossils of multicellular animals that predated the start of the Cambrian. A complex fauna was found in South West Africa in the 1920s but was inaccurately dated. Another fauna was found in South Australia in the 1940s but was not thoroughly examined until the late 1950s. Other possible early fossils were found in Russia, England, Canada, and elsewhere (see Ediacaran biota). Some were determined to be pseudofossils, but others were revealed to be members of rather complex biotas that are still poorly understood. At least 25 regions worldwide yielded metazoan fossils older than the classical Cambrian boundary at 541 million years ago.[6]

A few of the early animals appear possibly to be ancestors of modern animals. Most fall into ambiguous groups of frond-like organisms; discoids that might be holdfasts for stalked organisms ("medusoids"); mattress-like forms; small calcareous tubes; and armored animals of unknown provenance.

These were most commonly known as Vendian biota until the formal naming of the Period, and are currently known as Ediacaran Period biota. Most were soft bodied. The relationships, if any, to modern forms are obscure. Some paleontologists relate many or most of these forms to modern animals. Others acknowledge a few possible or even likely relationships but feel that most of the Ediacaran forms are representatives of unknown animal types.

In addition to Ediacaran biota, two other types of biota were discovered in China (the Doushantuo Formation and Hainan Formation).

Terminal period

The nomenclature for the terminal period of the Neoproterozoic Era has been unstable. Russian and Nordic geologists referred to the last period of the Neoproterozoic as the Vendian, while Chinese geologists referred to it as the Sinian, and most Australians and North Americans used the name Ediacaran.

However, in 2004, the International Union of Geological Sciences ratified the Ediacaran Period to be a geological age of the Neoproterozoic, ranging from 635 to 541 million years ago.[1] The Ediacaran Period boundaries are the only Precambrian boundaries defined by biologic Global Boundary Stratotype Section and Points, rather than the absolute Global Standard Stratigraphic Ages.

See also

References

  1. ^ a b Ogg, James G.; Ogg, Gabi; Gradstein, Felix M. (2008). The Concise Geologic Time Scale. Cambridge University Press. p. 184. ISBN 978-0-521-89849-2.
  2. ^ Rino, S.; Kon, Y.; Sato, W.; Maruyama, S.; Santosh, M.; Zhao, D. (2008). "The Grenvillian and Pan-African orogens: World's largest orogenies through geologic time, and their implications on the origin of superplume". Gondwana Research. 14 (1–2): 51–72. Bibcode:2008GondR..14...51R. doi:10.1016/j.gr.2008.01.001.
  3. ^ Walker, J.D., Geissman, J.W., Bowring, S.A., and Babcock, L.E (2018). "GSA Geologic Time Scale v.5.0" (PDF). doi:10.1130/2018.CTS005R3C. Retrieved 29 May 2019.CS1 maint: Uses authors parameter (link)
  4. ^ Craig, J. (26 November 2015). "Global Climate, the Dawn of Life and the Earth's Oldest Petroleum Systems". Retrieved 15 March 2019.
  5. ^ Khomentovsky, V; Nagovitsin, K; Postnikov, A (2008). "Mayanian (1100–850 Ma) – Prebaikalian Upper Riphean of Siberia". Russian Geology and Geophysics. 49 (1): 1. Bibcode:2008RuGG...49....1K. doi:10.1016/j.rgg.2007.12.001.
  6. ^ Knoll, A. H.; Walter, M.; Narbonne, G.; Christie-Blick, N. (2006). "The Ediacaran Period: a new addition to the geologic time scale". Lethaia. 39 (1): 13–30. doi:10.1080/00241160500409223.

External links

Beaverhead crater

The Beaverhead crater is an impact structure spanning the U.S. states of Idaho and Montana. Estimated at 60 kilometers (37 mi) in diameter, it is one of the largest impact craters on Earth.

With an estimated age of 600 million years (Neoproterozoic), the impact's original shatter cones along the crater's perimeter provide some of the structure's only remaining visible evidence.

It is named for the Beaverhead region of southwestern Montana in which it was first discovered.

Brasiliano orogeny

Brasiliano orogeny or Brasiliano cycle (Portuguese: Orogênese Brasiliana and Ciclo Brasiliano) refers to a series of orogenies of Neoproterozoic age exposed chiefly in Brazil but also in other parts of South America. The Brasiliano orogeny is a regional name for the larger Pan-African/Brasiliano orogeny that extended not only in South America but across most of Gondwana. In a wide sense the Brasiliano orogeny includes also the Pampean orogeny. Almeida et al. coined the term Brasiliano Orogenic Cycle in 1973. The orogeny led to the closure of several oceans and aulacogens including the Adamastor Ocean, the Goianides Ocean, the Puncoviscana Ocean and the Peri-Franciscano Ocean.Attempts to correlate the South American Brasiliano belts with the African Pan-African belts on the other side of the Atlantic has in many cases been problematic.

Cariri Velhos belt

The Cariri Velhos belt is a belt of rocks in Brazil that were deformed and metamorphosed in the Early Neoproterozoic. The belt runs from the Atlantic more than 700 kilometres (430 mi) inland in a SWW direction. The width of the belt varies from 100 to 50 kilometres (62 to 31 mi).The Cariri Velhos belt lies intercalated in a mosaic with various Brasiliano cycle belts in the Borborema Province, a geologic province in Northeastern Brazil. The belt includes a series of orthogneisses, metavolcanic and metasedimentary rocks. It is not known if the plate tectonic events that led to the formation of the belts are related to the assembly of the supercontinent Rodinia.

Colonsay Group

The Colonsay Group is an estimated 5,000 m thick sequence of mildly metamorphosed Neoproterozoic sedimentary rocks that outcrop on the islands of Colonsay, Islay and Oronsay and the surrounding seabed. They have been correlated with the Grampian Group, the oldest part of the Dalradian Supergroup.

Cryogenian

The Cryogenian ( , from Greek κρύος (krýos), meaning "cold" and γένεσις (génesis), meaning "birth") is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.

The Sturtian and Marinoan glaciations occurred during the Cryogenian period, which are the greatest ice ages known to have occurred on Earth. These events are the subject of much scientific controversy. The main debate contests whether these glaciations covered the entire planet (the so-called "Snowball Earth") or a band of open sea survived near the equator (termed "slushball Earth").

East African Orogeny

The East African Orogeny (EAO) is the main stage in the Neoproterozoic assembly of East and West Gondwana (Australia–India–Antarctica and Africa–South America) along the Mozambique Belt.

Ediacaran

The Ediacaran Period ( ), spans 94 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 541 Mya. 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.

Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacara 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.

Iapetus Ocean

The Iapetus Ocean was an ocean that existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia. The ocean disappeared with the Acadian, Caledonian and Taconic orogenies, when these three continents joined to form one big landmass called Euramerica. The "southern" Iapetus Ocean has been proposed to have closed with the Famatinian and Taconic orogenies, meaning a collision between Western Gondwana and Laurentia.

Because the Iapetus Ocean was positioned between continental masses that would at a much later time roughly form the opposite shores of the Atlantic Ocean, it can be seen as a sort of precursor of the Atlantic. The Iapetus Ocean was therefore named for the titan Iapetus, who in Greek mythology was the father of Atlas, after whom the Atlantic Ocean was named.

Moine Supergroup

The Moine Supergroup is a sequence of Neoproterozoic metamorphic rocks that form the dominant outcrop of the Scottish Highlands between the Moine Thrust Belt to the northwest and the Great Glen Fault to the southeast. The sequence is metasedimentary in nature and was metamorphosed and deformed in a series of tectonic events during the Late Proterozoic and Early Paleozoic. It takes its name from A' Mhòine, a peat bog in northern Sutherland.

Pan-African orogeny

The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.

Pannotia

Pannotia (from Greek: pan-, "all", -nótos, "south"; meaning "all southern land"), also known as Vendian supercontinent, Greater Gondwana, and the Pan-African supercontinent, was a relatively short-lived Neoproterozoic supercontinent that formed at the end of the Precambrian during the Pan-African orogeny (650–500 Ma) and broke apart 560 Ma with the opening of the Iapetus Ocean.

Pannotia formed when Laurentia was located adjacent to the two major South American cratons, Amazonia and Río de la Plata. The opening of the Iapetus Ocean separated Laurentia from Baltica, Amazonia, and Río de la Plata.

Proterozoic

The Proterozoic ( ) is a geological eon spanning the time from the appearance of oxygen in Earth's atmosphere to just before the proliferation of complex life (such as trilobites or corals) on the Earth. The name Proterozoic combines the two forms of ultimately Greek origin: protero- meaning "former, earlier", and -zoic, a suffix related to zoe "life". The Proterozoic Eon extended from 2500 mya to 541 mya (million years ago), and is the most recent part of the Precambrian "supereon." The Proterozoic is the longest eon of the Earth's geologic time scale and it is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic.The well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic; several glaciations, which produced the hypothesized Snowball Earth during the Cryogenian Period in the late Neoproterozoic Era; and the Ediacaran Period (635 to 541 Ma) which is characterized by the evolution of abundant soft-bodied multicellular organisms and provides us with the first obvious fossil evidence of life on earth.

Rhizaria

The Rhizaria are a species-rich supergroup of mostly unicellular eukaryotes. Except from the Chlorarachniophyte and three species in the genus Paulinella, they are all non-photosyntethic. A multicellular form, Guttulinopsis vulgaris, a cellular slime mold, has also been described.

This supergroup was proposed by Cavalier-Smith in 2002. Being described mainly from rDNA sequences, they vary considerably in form, having no clear morphological distinctive characters (synapomorphies), but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all have mitochondria with tubular cristae.

Rodinia

Rodinia (from the Russian родить, rodít, meaning "to beget, to give birth", or родина, ródina, meaning "motherland, birthplace") is a Neoproterozoic supercontinent that was assembled 1.1–0.9 billion years ago and broken up 750–633 million years ago.Valentine & Moores 1970 were probably the first to recognise a Precambrian supercontinent, which they named 'Pangaea I'. It was renamed 'Rodinia' by McMenamin & McMenamin 1990 who also were the first to produce a reconstruction and propose a temporal framework for the supercontinent.Rodinia formed at c. 1.23 Ga by accretion and collision of fragments produced by breakup of an older supercontinent, Columbia, assembled by global-scale 2.0–1.8 Ga collisional events.Rodinia broke up in the Neoproterozoic with its continental fragments reassembled to form Pannotia 633–573 million years ago. In contrast with Pannotia, little is known yet about the exact configuration and geodynamic history of Rodinia. Paleomagnetic evidence provides some clues to the paleolatitude of individual pieces of the Earth's crust, but not to their longitude, which geologists have pieced together by comparing similar geologic features, often now widely dispersed.

The extreme cooling of the global climate around 717–635 million years ago (the so-called Snowball Earth of the Cryogenian Period) and the rapid evolution of primitive life during the subsequent Ediacaran and Cambrian periods are thought to have been triggered by the breaking up of Rodinia or to a slowing down of tectonic processes.

Snowball Earth

The Snowball Earth hypothesis proposes that during one or more of Earth's icehouse climates, Earth's surface became entirely or nearly entirely frozen at least once, sometime earlier than 650 Mya (million years ago). Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the implications of the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean and emphasize the difficulty of escaping an all-frozen condition. A number of unanswered questions remain, including whether the Earth was a full snowball, or a "slushball" with a thin equatorial band of open (or seasonally open) water.

The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms, known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity. Another, much earlier and longer snowball episode, the Huronian glaciation, which would have occurred 2400 to 2100 Mya, may have been triggered by the first appearance of oxygen in the atmosphere, the "Great Oxygenation Event".

Stenian

The Stenian Period (from Greek στενός (stenós), meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from 1200 Mya to 1000 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. The name derives from narrow polymetamorphic belts formed over this period.

Preceded by the Ectasian period and followed by the Neoproterozoic Era.

The supercontinent Rodinia assembled during the Stenian. It would last into the Tonian period.

This period includes the formation of the Keweenawan Rift at about 1100 Mya.

Terra Australis Orogen

The Terra Australis Orogen (TAO) was the oceanic southern margin of Gondwana which stretched from South America to Eastern Australia and encompassed South Africa, West Antarctica, New Zealand and Victoria Land in East Antarctica.

Timanide Orogen

The Timanide Orogen (Russian: Ороген Протоуралид-Тиманид, literally: "Protouralian–Timanide Orogen") is a pre-Uralian orogen that formed in northeastern Baltica during the Neoproterozoic in the Timanide orogeny. The orogen is about 3000 km long. Its extreme points include the southern Urals in the south and the Polar Urals, the Kanin and Varanger peninsulas in the north. The Timan Ridge is the type area of the orogen. To the west, at the Varanger Peninsula, the north-west oriented Timanide Orogen is truncated by the younger Scandinavian Caledonide Orogen that has an oblique disposition. The northeastern parts of the orogen are made up of volcanic and sedimentary rocks, granitoids and few ophiolites. In contrast the southwestern part of the orogen is made up mostly of sedimentary rocks. I and A type granitoids and volcanic rocks are common in the orogen.From the Late Neoproterozoic o the Middle Cambrian the Timanide Orogen was associated to a subduction zone that existed to the northeast of it. Most studies interpret subduction as going inward (subducted plate moving southwest) albeit one suggest the opposite (subducted plate moving to the northeast).

In the Cambrian the Timanide Orogen is believed to have developed in a continental collision context as Baltica and Arctida collided between 528 and 510 million years ago. Some researchers do however dissent from this view suggesting there was never such a collision.Erosion of the Timanide Orogen have produced sediments that are now found in the East European Platform, including the Cambrian Sablino Formation near Lake Ladoga. Studies of sediments points that its likely that the erosion of the orogen was beginning in the Cambrian and then became stronger in Ordovician.The first geologists to study the orogen where Wilhelm Ramsay and Feodosy Tschernyschev who published works in 1899 and 1901 respectively. Hans Reusch compiled the existing knowledge on the orogen in 1900.

Tonian

The Tonian (from Greek τόνος (tónos), meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 Mya to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic era and followed by the Cryogenian.

Rifting leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya.

Cenozoic era
(present–66.0 Mya)
Mesozoic era
(66.0–251.902 Mya)
Paleozoic era
(251.902–541.0 Mya)
Proterozoic eon
(541.0 Mya–2.5 Gya)
Archean eon (2.5–4 Gya)
Hadean eon (4–4.6 Gya)

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.