Mesoproterozoic

The Mesoproterozoic Era is a geologic era that occurred from 1,600 to 1,000 million years ago. The Mesoproterozoic was the first period of Earth's history of which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), but little is known about them. The continental masses of the Mesoproterozoic were more or less the same ones that exist today.

Mesoproterozoic Era
1600–1000 million years ago
Key events in the Mesoproterozoic
-1600 —
-1550 —
-1500 —
-1450 —
-1400 —
-1350 —
-1300 —
-1250 —
-1200 —
-1150 —
-1100 —
-1050 —
-1000 —
Mesoproterozoic
An approximate timescale of key Mesoproterozoic events.
Axis scale: millions of years ago.

Major events and characteristics

The major events of this era are the breakup of the Columbia supercontinent, the formation of the Rodinia supercontinent, and the evolution of sexual reproduction.

This era is marked by the further development of continental plates and plate tectonics. The first large-scale mountain building episode, the Grenville Orogeny, for which extensive evidence still survives, happened in this period.

This era was the high point of the Stromatolites before they declined in the Neoproterozoic.

The era saw the development of sexual reproduction, which greatly increased the complexity of life to come. It was the start of development of communal living among organisms, the multicellular organisms.

It was an Era of apparently critical, but still poorly understood, changes in the chemistry of the sea, the sediments of the earth, and the composition of the air. Oxygen levels had risen to perhaps 1% of today's levels at the beginning of the era and continued rising throughout the Era.

Clearly the era did see large quantities of organisms in at least some areas at some periods: The EIA/ARI Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States of June 2013 estimated around 194 trillion cubic feet of gas in place (ca. 44 trillion recoverable) and around 93 billion barrels of oil in place (ca. 4.7 billion recoverable) in the Lower Kyalla and Middle Velkerri formations alone of the Beetaloo Basin in Australia's Northern Territory.[1]

Subdivisions

The subdivisions of the Mesoproterozoic are arbitrary divisions based on time. They are not geostratigraphic or biostratigraphic units. The base of the Mesoproterozoic is defined chronometrically, in terms of years, rather than by the appearance or disappearance of some organism. This gives an illusory sense of certainty. Radiometric dating is a good tool, and gets better each decade. This creates some problems. As a practical matter, radiometric dates have an error margin of 1-2%. That sounds good, but it means that two sites, both measured to be at the exact base of the Ectasian, might differ in age by over 50 My. Since the Ectasian is only 200 My long, these differences dramatically influence its timescale. And this accounts only for random error, ignoring systematic errors. Systematic errors can be caused by extraterrestrial events, by geochemical or biochemical sorting of isotopes, and human error. Thus far, biostratigraphy has usually proved considerably more exact. In addition, a thoughtful choice of biological marker can be used as a signal to expect a whole host of ecological changes. The difference between a Changhsingian and an Induan deposit isn't just a matter of a few years. The world changed significantly at the end of the Permian.

By contrast, the transition from Calymmian to Ectasian has no meaning beyond calendar time. The usual reason given for the use of a chronometric system is that there is insufficient biological activity or geochemical change to find useful markers. That is a position which is now a little uncertain and is going to become increasingly tenuous over the next few years. For example, there are a number of good potential markers in the rise and decline of "Christmas tree" stromatolites, in the ebb and flow of banded iron formations, the appearance of stable carbon-13 isotope (13C) excursions, and so on. These have real meaning for the geologist and paleontologist.

For that matter, they are not completely without biological markers. There has been considerable progress in studying and identifying fossil bacteria and Eukarya. The cyanobacterium Archaeoellipsoides is one relatively common form, apparently known from several species. It is probably related to the extant Anabaena and indicates the presence of significant free oxygen. Oxygen levels also had significant effects on ocean chemistry; continental weathering rates increased and provided sulfates and nitrates as nutrients. It would be remarkable if this didn't result in new populations of both bacterial and eukaryotic organisms. Since the presence of these cells would be tied directly to important geochemical events, they would make ideal organisms for biostratigraphy.

For the time period from 1780 Ma to 850 Ma, an unofficial period based on stratigraphy rather than chronometry, named the Rodinian, is described in the geological timescale review 2012 edited by Gradstein et al.,[2] but as of February 2017, this has not yet been officially adopted by the IUGS.

See also

References

  1. ^ U. S. Energy Information Administration/Advanced Resources International, Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside of the United States, June 2013, p. III-46. The Lower Kyalla and Middle Velkerri formations are identified as Mesoproterozoic in references, p. III-49.
  2. ^ Gradstein, F.M. et al. (editors) (2012). The Geologic Time Scale 2012. 1. Elsevier. p. 361. ISBN 978-0-44-459390-0.CS1 maint: Extra text: authors list (link)

External links

Calymmian

The Calymmian Period (from Greek κάλυμμα (kálymma), meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.

The supercontinent Columbia broke up during the Calymmian some 1500 Mya.

Coppermine River Group

The Coppermine River Group is a sequence of Mesoproterozoic continental flood basalts forming part of the Mackenzie Large Igneous Province in the Northwest Territories and Nunavut, Canada. It is among the largest flood basalt province on Earth, covering the area with a volume of approximately 650,000 km3 (155,943 cu mi).

Ectasian

The Ectasian Period (from Greek ἔκτασις (éktasis), meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from 1400 Mya ago to 1200 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

Geologically the name refers to the continued expansion of platform covers during this period.

This period is interesting for the first evidence of sexual reproduction. The 1.2 billion years old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire organism from just the germ cells.

Sexual reproduction and the ability of gametes to develop into an organism are the necessary antecedents to true multicellularity. In fact, we tend to think of sexual reproduction and true multicellularity as occurring at the same time, and true multicellularity is often taken as a marker for sexual reproduction.

Gothian orogeny

The Gothian orogeny (Swedish: Gotiska orogenesen) or Kongsberg orogeny was an orogeny in western Fennoscandia that occurred between 1750 and 1500 millions years ago. It precedes the younger Sveconorwegian orogeny that has overprinted much of it. The Gothian orogeny formed along a subduction zone and resulted in the formation of calc-alkaline igneous rocks 1700 to 1550 million years ago, including some of the younger members of the Transscandinavian Igneous Belt.The deformation associated with the orogeny can be seen in metatonalite, paragneiss and biotite orthogneisses in southeast Norway. These rocks were all subject to amphibolite facies metamorphism.

Grenville orogeny

The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, from Labrador to Mexico, as well as to Scotland.

Grenville orogenic crust of mid-late Mesoproterozoic age (c. 1250–980 Ma) is found worldwide, but generally only events which occurred on the southern and eastern margins of Laurentia are recognized under the "Grenville" name.These orogenic events are also known as the Kibaran orogeny in Africa and the Dalslandian orogeny in Western Europe.

Gulf of Bothnia

The Gulf of Bothnia (Finnish: Pohjanlahti; Swedish: Bottniska viken, i.e. Bottenviken + Bottenhavet) is the northernmost arm of the Baltic Sea. It is situated between Finland's west coast and Sweden's east coast. In the south of the gulf lie the Åland Islands, between the Sea of Åland and the Archipelago Sea.

Hallandian-Danopolonian event

The Hallandian-Danopolonian event was an orogeny and thermal event that affected Baltica in the Mesoproterozoic. The event metamorphosed pre-existing rocks and generated magmas that crystallized into granite. The Hallandian-Danopolonian event has been suggested to be responsible for forming an east-west alignment of sedimentary basins hosting Jotnian sediments spanning from eastern Norway, to Lake Ladoga in Russia. The alignment of subsidence is thought to correspond to an ancient back-arc basin parallel to a subduction zone further south.

Kibaran orogeny

The Kibaran orogeny is a term that has been used for a series of orogenic events in what is now Africa that began in the Mesoproterozoic around 1400 Ma and continued until around 1000 Ma when the supercontinent Rodinia was assembled.

The term "Kibaran" has often been used for any orogenic rocks formed during this very extended period.

Recently it has been proposed that the term should be used in a much narrower sense for an event around 1375 Ma and a region in the southeast of the Democratic Republic of the Congo (DRC).

Mackenzie dike swarm

The Mackenzie dike swarm, also called the Mackenzie dikes, form a large igneous province in the western Canadian Shield of Canada. It is part of the larger Mackenzie Large Igneous Province and is one of more than three dozen dike swarms in various parts of the Canadian Shield.

The Mackenzie dike swarm is the largest dike swarm known on Earth, more than 500 km (310 mi) wide and 3,000 km (1,900 mi) long, extending in a northwesterly direction across the whole of Canada from the Arctic to the Great Lakes. The mafic dikes cut Archean and Proterozoic rocks, including those in the Athabasca Basin in Saskatchewan, Thelon Basin in Nunavut and the Baker Lake Basin in the Northwest Territories.

The source for the Mackenzie dike swarm is considered to have been a mantle plume center called the Mackenzie hotspot. About 1,268 million years ago, the Slave craton was partly uplifted and intruded by the giant Mackenzie dike swarm. This was the last major event to affect the core of the Slave craton, although later on some younger mafic magmatism registered along its edges.

Mackenzie hotspot

The Mackenzie hotspot was a volcanic hotspot that existed about 1.3 billion years ago across Canada from the Northwest Territories and Nunavut.

Midcontinent Rift System

The Midcontinent Rift System (MRS) or Keweenawan Rift is a 2,000 km (1,200 mi) long geological rift in the center of the North American continent and south-central part of the North American plate. It formed when the continent's core, the North American craton, began to split apart during the Mesoproterozoic era of the Precambrian, about 1.1 billion years ago. The rift failed, leaving behind thick layers of igneous rock that are exposed in its northern reaches, but buried beneath later sedimentary formations along most of its western and eastern arms. Those arms meet at Lake Superior, which is contained within the rift valley. The lake's north shore in Ontario and Minnesota defines the northern arc of the rift. From the lake, the rift's eastern arm trends south to central lower Michigan, and possibly into Indiana, Ohio, Kentucky, Tennessee, and Alabama. The western arm runs from Lake Superior southwest through portions of Wisconsin, Minnesota, Iowa, and Nebraska to northeastern Kansas, and possibly into Oklahoma.

Neoproterozoic

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

Ourasphaira giraldae

Ourasphaira giraldae is an extinct process-bearing multicellular eukaryotic microorganism. Loron et al. (2019) argues that it was an early fungus. It existed approximately a billion years ago during the time of the transition from the Mesoproterozoic to Neoproterozoi periods, and was unearthed in the Amundsen Basin in the Canadian Arctic.

Protogine Zone

The Protogine Zone is a geological boundary zone in western Sweden. There are two slightly different definitions of the Protogine Zone. In the lithological definition it forms the limit between the gneisses of western Sweden and the relatively underformed eastern granites. As such it makes up the limit of deformation and metamorphism attributed to the Sveconorwegian orogeny. In the tectonic definition it is a zone of strong deformation that follows roughly the same course as the lithological Protogine Zone. In the two definitions of the Protogine Zone it runs from Scania across Lake Vättern into the upper course of Klarälven and then into Norway. The tectonic Protogine Zone has anastomosing branches and splits south of Lake Vättern into various diverging arms. The two westernmost of these arms follow the valleys of the Nissan and Lagan rivers. A more eastern branch is reflected in the alignment of the lakes Rusken, Rymmen and Möckeln.The origin of the Protogine Zone has been traced to the Mesoproterozoic when it was a zone of weakness in the crust. About 1575–1562 Ma ago the Progine Zone was intruded by mafic magma during the same time spans as Rapakivi granites intruded more easterly domains in Fennoscandia. Later 1224–1215 and ca. 1204 Ma ago the progine zone was subject to extensional tectonics perhaps being a back-arc basin. The Protogine Zone obtained its final configuration during the Sveconorwegian orogeny 1130–950 Ma ago.

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.

Sunsás orogeny

The Sunsás orogeny was an ancient orogeny active during the Late Paleoproterozoic and Mesoproterozoic and currently preserved as the Sunsás orogen in the Amazonian Craton in South America. About 85% of the belt is covered by Phanerozoic sediments. Among the remaining 15% of the orogen exposed at surface the best outcrops lies around the Bolivia-Brazil border. It is thought that the original orogen once spanned an area from Venezuela to Argentina and Paraguay. The western and southeastern fringes of the Sunsás orogen have been incorporated into the Andean orogeny and the Brasiliano orogeny respectively. The Sunsás orogeny was active during four separate phases:

Santa Helena orogeny 1465–1427 Ma

Candeias orogeny 1371–1319 Ma

San Andrés orogeny ca. 1275 Ma

Nova Brasilândia orogeny 1180–1110 Ma

Sveconorwegian orogeny

The Sveconorwegian orogeny was an orogenic system active 1140 to 960 million years ago and currently exposed as the Sveconorwegian orogenic belt in southwestern Sweden and southern Norway. In Norway the orogenic belt is exposed southeast of the front of the Caledonian nappe system and in nappe windows. The Sveconorwegian orogen is commonly grouped within the Grenvillian Mesoproterozoic orogens. Contrary to many other known orogenic belts the Sveconorwegian orogens eastern border does not have any known suture zone with ophiolites.

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.

White Sea Rift System

The White Sea Rift System is a complex of rifts manifested as numerous individual grabens located chiefly in the White Sea but including onshore areas and a strip of the Barents Sea. The rifts run in a subparallel manner from northwest to southeast where the rift system continues under the East European Platform. The system or complex originated due to extensional tectonics acting during the Middle to Late Riphean in the Proterozoic. This tectonic environment is believed to have been related to the break-up of the ancient supercontinent Palaeopangea. During the Riphean the graben structures were filled by Jotnian sediments. During the Middle Paleozoic the rift system was reactivated resulting in intrusion of alkaline magmas. In the Late Cenozoic the rift system was reactivated again resulting in the formation of the modern White Sea.The White Sea Rift System includes the following rifts:

the Onega–Kandalaksha Rift (its northwestern graben is known as the Kandalaksha Trough or Kandalaksha Graben). The Kandalksha graben is about 220 km long and 60 km broad. Its southwestern slopes are steeper than its northwestern slopes.

the Kerets–Leshukonsky Rift (including the Kerets Graben).

the Barents Rift.Many of the grabens are filled with Jotnian sediments.

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)

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