The Orosirian Period ( /ˌɒroʊˈsɪəriən/; Greek: ὀροσειρά, romanized: oroseirá, meaning "mountain range") is the third geologic period in the Paleoproterozoic Era and lasted from 2050 Mya to 1800 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
Two of the largest known impact events on Earth occurred during the Orosirian. At the very beginning of the period, 2023 Mya, a large asteroid collision created the Vredefort impact structure. The event that created the Sudbury Basin structure occurred near the end of the period, 1850 Mya.
For the time period from about 2060 to 1780 Mya, an alternative period based on stratigraphy rather than chronometry, named the Columbian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of February 2017, this has not yet been officially adopted by the IUGS.
2050–1800 million years ago
Vredefort crater is believed to have formed in this period
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).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.Geology of Guyana
Guyana occurs within the northern part of the Guiana Shield.The Guiana Shield forms the northern part of the Amazonian Craton, the core of the South American continent.
Most of the geology of northern Guyana consists of Palaeoproterozoic Orosirian greenstone belts (Barama and Mazaruni Supergroups) intruded by granites. These are overlain unconformably by the Statherian Burro-Burro Group, which consist of the Muruwa Formation sandstones and Iwokrama Formation felsic volcanics. Both are intruded by granites associated with the Iwokrama Formation. Some folding occurred before these were overlain by the locally unconformable almost flat lying Roraima Group.
Major mafic sills and dykes of the Avanavero Suite intrude all of the older rocks, and are part of a Large Igneous Province (LIP). Numerous mafic dykes intruded the basement in the late Permian and Early Jurassic, associated with the start of the separation of Africa from South America. These are part of the Central Atlantic Magmatic Province (CAMP).
The northern Guiana Shield, including Guyana is separated from Southern Guiana Shield by ENE to NE trending Tumbes /Guayaquil - Tacutu Tectonic Lineament. This is a major regional pre-Cambrian shear zone / mega-shear which is believed to have been re-activated several times. At the beginning of the Mesozoic when Africa and South America started to separate this re-activated again and was involved in formation of the Takutu Graben in the lower Rupununi area and the Guyana-Suriname basin near the coast and offshore. Both these sedimentary basins have oil potential, and in 2015 significant oil was found in a deep water area off Guyana. During the Mesozoic the headwaters of the Upper Orinoco and Rio Branco flowed through the Takutu Graben via the Essequibo either to the current river mouth, to the Corentyne, the Berbice or the Canje Rivers. Tilting associated with rifting of the Atlantic Ocean resulted in complex patterns of river capture, so now the headwaters of the Rio Branco flow to the south via the Amazon, and the headwaters of the Upper Orinoco flow to the west and north. Water and sediment volumes directly flowing east are now much reduced.Historical geology
Historical geology or paleogeology is a discipline that uses the principles and techniques of geology to reconstruct and understand the geological history of Earth. It focuses on geologic processes that change the Earth's surface and subsurface; and the use of stratigraphy, structural geology and paleontology to tell the sequence of these events. It also focuses on the evolution of plants and animals during different time periods in the geological timescale. The discovery of radioactivity and the development of several radiometric dating techniques in the first half of the 20th century provided a means of deriving absolute versus relative ages of geologic history.
Economic geology, the search for and extraction of fuel and raw materials, is heavily dependent on an understanding of the geological history of an area. Environmental geology, including most importantly the geologic hazards of earthquakes and volcanism, must also include a detailed knowledge of geologic history.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.Miaolingian
The Miaolingian is the third Series of the Cambrian period, and was formally named in 2018. It lasted from about 509 to 497 million years ago and is divided into 3 stages: the Wuliuan, the Drumian, and the Guzhangian. The Miaolingian is preceded by the unnamed Cambrian Series 2 and succeeded by the Furongian series.Paleoproterozoic
Paleoproterozoic Era ( ;), spanning the time period from 2,500 to 1,600 million years ago (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's geological history. It was during this era that the continents first stabilized.
Paleontological evidence suggests that the Earth's rotational rate during this era resulted in 20-hour days ~1.8 billion years ago, implying a total of ~450 days per year.Rupununi
The Rupununi is a region in the south-west of Guyana, bordering the Brazilian Amazon. The Rupununi river, also known by the local indigenous peoples as Raponani, flows through the Rupununi region. The name Rupununi originates from the word rapon in the Makushi language, in which it means the black-bellied whistling duck found along the river.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.Supercontinent
In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, many earth scientists use a different definition: "a clustering of nearly all continents", which leaves room for interpretation and is easier to apply to Precambrian times.Supercontinents have assembled and dispersed multiple times in the geologic past (see table). According to the modern definitions, a supercontinent does not exist today. The supercontinent Pangaea is the collective name describing all of the continental landmasses when they were most recently near to one another. The positions of continents have been accurately determined back to the early Jurassic, shortly before the breakup of Pangaea (see animated image). The earlier continent Gondwana is not considered a supercontinent under the first definition, since the landmasses of Baltica, Laurentia and Siberia were separate at the time.System (stratigraphy)
A system in stratigraphy is a unit of rock layers that were laid down together within the same corresponding geological period. The associated period is a chronological time unit, a part of the geological time scale, while the system is a unit of chronostratigraphy. Systems are unrelated to lithostratigraphy, which subdivides rock layers on their lithology. Systems are subdivisions of erathems and are themselves divided into series and stages.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).Tournaisian
The Tournaisian is in the ICS geologic timescale the lowest stage or oldest age of the Mississippian, the oldest subsystem of the Carboniferous. The Tournaisian age lasted from 358.9 Ma to 346.7 Ma. It is preceded by the Famennian (the uppermost stage of the Devonian) and is followed by the Viséan.Tremadocian
The Tremadocian is the lowest stage of Ordovician. Together with the later Floian stage it forms the Lower Ordovician epoch. The Tremadocian lasted from 485.4 to 477.7 million years ago. The base of the Tremadocian is defined as the first appearance of the conodont species Iapetognathus fluctivagus at the Global Boundary Stratotype Section and Point (GSSP) section on Newfoundland.Viséan
The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from 346.7 to 330.9 Ma. It follows the Tournaisian age/stage and is followed by the Serpukhovian age/stage.