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.
1200–1000 million years ago
The Byron Formation is a geologic formation in Michigan and Wisconsin. It preserves fossils dating back to the Silurian period.Cambrian Series 2
Cambrian Series 2 is the unnamed 2nd series of the Cambrian. It lies above the Terreneuvian series and below the Miaolingian. Series 2 has not been formally defined by the International Commission on Stratigraphy, lacking a precise lower boundary and subdivision into stages. The proposed lower boundary is the first appearance of trilobites which is estimated to be around 521 million years ago.Cambrian Stage 3
Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approximately to the first appearance of trilobites, about 521 million years ago, though the globally asynchronous appearance of trilobites warrants the use of a separate, globally synchronous marker to define the base. The upper boundary and beginning of Cambrian Stage 4 is informally defined as the first appearance of the trilobite genera Olenellus or Redlichia around 514 million years ago.Cambrian Stage 4
Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission on Stratigraphy. One proposal is the first appearance of two trilobite genera, Olenellus or Redlichia. Another proposal is the first appearance of the trilobite species Arthricocephalus chauveaui. Both proposals will set the lower boundary close to 514 million years ago. The upper boundary corresponds to the beginning of the Wuliuan.Chattian
The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene epoch/series. It spans the time between 28.1 and 23.03 Ma. The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage of the Miocene).Freda Sandstone
The Freda Sandstone is a geologic formation in Michigan. It dates back to the Proterozoic. Lithologically, the Freda Sandstone is a lithic, red-brown, cyclic sequence of sandstones, mudstones and shales (conglomerates are rare).Furongian
The Furongian is the fourth and final series of the Cambrian. It lasted from 497 to 485.4 million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed 10th stage of the Cambrian.Geological period
A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place.
These periods form elements of a hierarchy of divisions into which geologists have split the Earth's history.
Eons and eras are larger subdivisions than periods while periods themselves may be divided into epochs and ages.
The rocks formed during a period belong to a stratigraphic unit called a system.Hendricks Formation
The Hendricks Formation is a geologic formation in Michigan. It preserves fossils dating back to the Silurian period.Katian
The Katian is the second stage of the Upper Ordovician. It is preceded by the Sandbian and succeeded by the Hirnantian stage. The Katian began 453 million years ago and lasted for about 7.8 million years until the beginning of the Hirnantian 445.2 million years ago.List of geological groups of Great Britain
This is a sortable list of the groups into which the rock succession of Great Britain and surrounding seas is formally divided. Rock sequences are described by geologists by dividing them hierarchically thus: individual 'beds' of rock (or in the case of certain volcanic rocks, 'flows') are grouped into 'members', members are grouped into 'formations', formations into 'groups' and groups occasionally into 'supergroups'. Some groups are also subdivided into 'subgroups'. Not all of these hierarchical layers are necessarily present or defined within a particular rock succession. Many of these groups will be encountered as 'series' in older geological literature or indeed simply as the proper name e.g. 'Dalradian' or 'Millstone Grit' though care needs to be exercised as many of the names have or have had other meanings which may not coincide with the assemblage of rocks referred to formally through designation as a 'group'.
Note that with all such stratigraphical terms as 'groups', 'formations' and 'members' it is standard practice to capitalise both the proper name and the 'term-word' as per the recommendation of the International Commission on Stratigraphy e.g. Wentnor Group and not Wentnor group.Notes:
Column 1 indicates the name of the geological group. Those marked with an asterisk are no longer formally recognised but are included as they occur widely in literature.Column 2 indicates during which geological period the rocks of each group were deposited. Note that where more than one period is indicated deposition stretched across the period boundary in at least a part of the group's geographical extent but not necessarily across the whole of its extent.Column 3 permits sorting by period in chronological order ie Quaternary Period is 01; Neogene,03; Palaeogene,05; Cretaceous,07; Jurassic,09 Triassic,11; Permian,13; Carboniferous,15; Devonian,17; Silurian,19; Ordovician,21; Cambrian,23; Ediacaran,25; Cryogenian,27; Tonian,29; Stenian, 31; and Ectasian, 33 - the last five being some of the periods into which the Proterozoic Eon is divided.Column 4 indicates in which of the three nations of Great Britain, the group is known to occur, followed by which of the surrounding sea areas (if any), including specifically: Atlantic Ocean, Celtic Sea, English Channel, Irish Sea, North Sea. (At present, for the purposes of this table 'Celtic Sea' also includes the Bristol Channel whilst 'Atlantic Ocean' includes all sea areas off the west coast of Scotland.) Note that the Isle of Man is not a part of Great Britain but is included here for convenience.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.Misquah Hills
The Misquah Hills are a range of mountains in northeastern Minnesota, in the United States. They are located in or near the Boundary Waters Canoe Area Wilderness within Superior National Forest. Eagle Mountain, the highest point in Minnesota at 2,301 feet (701 meters), is considered to be part of the Misquah Hills.Neda Formation
The Neda Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.Obazoa
Obazoa (Brown et al., 2013) is a proposed sister clade of Amoebozoa (which together form Amorphea). Obazoa is composed of Breviatea, Apusomonadida and Opisthokonta, and specifically excludes the Amoebozoa. Determining the placement of Breviatea and Apusomonadida and their properties is of interest for the development of the opisthokonts in which the main lineages of animals and fungi emerged. The relationships among opisthokonts, breviates and apusomonads are not conclusively resolved (as of 2018), though Breviatea is usually inferred to be the most basal of the three lineages. Ribosomal RNA phylogenies do not usually recover Obazoa as a clade (see for example:), probably reflecting their stemming from a very ancient common ancestor, and little phylogenetic signal remains in datnsisting of one or a few genes.Riphean (stage)
The Riphean is a stage or age of the geologic timescale from 1,600 to 650 million years ago. The name Riphean is used in the Proterozoic stratigraphy of Russia and the Fennoscandian Shield in Finland. It was also used in a number of older international geologic timescales but, in the most recent timescales of the ICS, it is replaced by the Calymmian, Ectasian, Stenian, Tonian and Cryogenian periods of the Neoproterozoic and Mesoproterozoic eras.
The word 'Riphean' comes from the ancient Riphean Mountains, sometimes identified with the Ural Mountains.
The Riphean has been divided by geologists into the Early Riphean (1600–1400 Ma), Middle Riphean (1400–1000 Ma) and Late Riphean (1000–650 Ma) subdivisions.Sandbian
The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species Nemagraptus gracilis around 458.4 million years ago. The Sandbian lasted for about 5.4 million years until the beginning of the Katian around 453 million years ago.Timeline of natural history
This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans. Times are listed in millions of years, or megaanni (Ma).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.