"most likely only consisted of plants similar to non-vascular bryophytes. The Ordovician came to a close in a series of extinction events that, taken together, comprise the second largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. The only larger one was the Permian–Triassic extinction event. The extinctions occurred approximately 447–444 million years ago and mark the boundary between the Ordovician and the following Silurian Period. At that time all complex multicellular organisms lived in the sea, and about 49% of genera of fauna disappeared forever; brachiopods and bryozoans were"
"form the Variscan orogeny in the succeeding Devonian and Carboniferous Periods. Both orogenies resulted in the assembly of a super-continent, Pangaea, which was essentially complete by the end of the Carboniferous. In the Ordovician Period, a land mass, which has been named Gondwana (present day South America, Africa, Antarctica and Australia), straddled the space between the South Pole and the Equator on one side of the globe. Off to the west were three other masses: Laurentia, Siberia and Baltica, located as if on the vertices of a triangle. To the south of them was a large archipelago, the terrane Avalonia,"
"Ordovician during a marine transgression. The Misty Creek embayment in the south Ogilvie Mountains and the edge of the basin in Faro have alkali basalts erupted during the period. Into the Devonian, the Road River Group chert, siltstone and mudstone built up in the basin, supplied with high temperature brines from seafloor vents which created zinc-lead deposits in Howards Pass and Anvil Ridge. Similar sediments are exposed in the Richardson Mountains in the north. In the Middle Devonian, 390 million years ago, eastern Yukon was blanketed in sandstone, black shale and siltstone during a major marine advance. However, the Selwyn"
"including Siberia, Australia, North America, and China, but Africa and South America had a warm temperate climate. In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common. The Devonian Period is formally broken into Early, Middle and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. The Early Devonian lasted from and began with the Lochkovian stage, which lasted until the Pragian. It spanned from , and was followed by the Emsian, which lasted until"
"Early Ordovician The Tremadoc corresponds to the (modern) Tremadocian. The Floian corresponds to the lower Arenig; the Arenig continues until the early Darriwilian, subsuming the Dapingian. The Llanvirn occupies the rest of the Darriwilian, and terminates with it at the base of the Late Ordovician. The Sandbian represents the first half of the Caradoc; the Caradoc ends in the mid-Katian, and the Ashgill represents the last half of the Katian, plus the Hirnantian. During the Ordovician, the southern continents were collected into Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole."
"diversification of two new orders, the Endocerida and Tarphycerida, evolution of new families within the Ellerocerida (e.g. Baltoceratidae and Bathmoceratidae), and near the end the first of the Orthocerida, Actinocerida, and Discosorida. The limited suprageneric cephalopod diversity of the Gasconadian compared to the ordinal diversity that followed also suggests a relatively short duration for the stage. Gasconadian Stage The Gasconadian Stage is the first stage of the Ordovician geologic period in North America and of the Lower Ordovician Canadian Epoch, coming immediately after the Late Cambrian Trempealeauan and preceding the middle Canadian Demingian Stage. The Gasconadian is equivalent to the"
"during the Caledonian orogeny of the Silurian period, about 420 million years ago. In the Gedinnian/Lochkovian (Early Devonian) the southern part of the Caledonian mountain belt became a region of north-south extension. An elongated basin was formed parallel to the continental margin. It separated the London-Brabant Massif to the north from the Normannian and Mid-German Highs to the south. In the Middle Devonian (from 390 million years ago) a subduction zone existed south of Laurussia, where oceanic lithosphere of the Rheic Ocean subducted beneath the Mid-German/Normannian highs. Volcanism above the subduction zone created a cordillera-type mountain chain, the Ligerian cordillera."
"the allochthon. They relate to the further widening of Iapetus during the Cambrian, the start of closure during the Early Ordovician with the accretion of terranes and ophiolite obduction during the Late Ordovician and continent-continent collision at the end of the Silurian. Within the entire exposed 1800 kilometre length of this orogenic belt the following sequence is recognised from the base upwards: This vertically stacked sequence thus represents the passive margins of Baltica and Laurentia and intervening island arcs and back-arc basins telescoped together and emplaced on top of the Baltic Shield, involving hundreds of kilometres of shortening. Devonian age"
"Ordovician Period (about 440–480 million years ago), a change in plate motions set the stage for the first Paleozoic mountain building event (Taconic orogeny) in North America. The once quiet, Appalachian passive margin changed to a very active plate boundary when a neighboring oceanic plate, the Iapetus, collided with and began sinking beneath the North American craton. With the birth of this new subduction zone, the early Appalachians were born. Along the continental margin, volcanoes grew, coincident with the initiation of subduction. Thrust faulting uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion"
"Rhuddanian In the geologic timescale, the Rhuddanian is the first age of the Silurian period and of the Llandovery epoch. The Silurian is in the Paleozoic era of the Phanerozoic eon. The Rhuddanian age began 443.7 ± 1.5 Ma and ended 440.8 ± 1.2 Ma (million years ago). It succeeds the Himantian Age (the last age of the Ordovician Period) and precedes the Aeronian age. The GSSP for the Silurian is located in a section at Dob's Linn in an artificial excavation created just north of the Linn Branch Stream.Two lithological units (formations) occur near the boundary. The lower is"
"strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies between 1820 and 1850 of the strata and fossils of Europe produced the sequence of geologic periods still used today. Early work on developing the geologic time scale was dominated by British geologists, and the names of the geologic periods reflect that dominance. The ""Cambrian"", (the classical name for Wales) and the ""Ordovician"", and ""Silurian"", named after ancient Welsh tribes, were periods defined using stratigraphic sequences from Wales. The ""Devonian"" was named"
"of the Central Sudetic ophiolite in the Devonian period. In the Early Caboniferous the joint Góry Sowie-Kłodzko-Orlica-Śnieżnik terrane collided with the Brunovistulian terrane. This last terrane was part of the Old Red Continent and could correspond either to Baltica or the eastern tip of the narrow Avalonia terrane. Also by the Early Carboniferous the Saxothuringian terrane collided with the Góry Sowie-Kłodzko-Orlica-Śnieżnik terrane closing the Rheic Ocean. Once the main phase of deformation of the orogeny was over basins that had formed in-between metamorphic rock massifs were filled by sedimentary rock in the Devonian and Carboniferous periods. During and after sedimentation"
"Early in the Ordovician, the continents of Laurentia (in present-day North America), Siberia, and Baltica (present-day northern Europe) were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move towards Laurentia later in the period, causing the Iapetus Ocean between them to shrink. The small continent Avalonia separated from Gondwana and began to move north towards Baltica and Laurentia, opening the Rheic Ocean between Gondwana and Avalonia. The Taconic orogeny, a major mountain-building episode, was well under way in Cambrian times. In the early and middle Ordovician, temperatures were mild, but at the beginning"
"complete sedimentary succession from the Cambrian right up to the Mississippian. The Cambrian starts with basal rhyolites, followed by the Grès de Marcory, a sandstone formation, by archaeocyathid-bearing limestones, shales and more sandstones. The Ordovician and the Silurian consist mainly of shales, whereas the Devonian is made up exclusively of carbonates in Mediterranean facies. Along the northern side of the Montagne Noire the series is more incomplete, the entire Upper Ordovician is missing. As a recompense one can study here the gradual changeover of the nonmetamorphic Cambro-Silurian system into the metamorphic equivalents of the Albigeois. In the Morvan Devonian sediments"
"Caledonian orogeny The Caledonian orogeny was a mountain-building era recorded in the northern parts of Ireland and Britain, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly 490–390 million years ago (Ma). It was caused by the closure of the Iapetus Ocean when the continents and terranes of Laurentia, Baltica and Avalonia collided. The Caledonian orogeny is named for Caledonia, the Latin name for Scotland. The name was first used in 1885 by Austrian geologist Eduard Suess for an episode of mountain building in"
"as the period progressed, drifted toward the South Pole. Early in the Ordovician the continents Laurentia, Siberia and Baltica were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move toward Laurentia later in the period, causing the Iapetus Ocean to shrink between them. Also, Avalonia broke free from Gondwana and began to head north toward Laurentia. The Rheic Ocean was formed as a result of this. By the end of the period, Gondwana had neared or approached the pole and was largely glaciated. The Ordovician came to a close in a series of"
"have occurred somewhat earlier than in the autochthon at about 420 Ma ago. Following the subduction of the Baltican continental margin and thrusting of the nappes over the Baltican basement, the orogen began to collapse in the Early Devonian, which was associated with extensional tectonics and sinistral motion between the Laurentian and Baltican tectonic plates. The Caledonian orogeny put in place most of the bedrock now seen in the Scandinavian Mountains. Caledonian rocks overlie rocks of the much older Svecokarelian and Sveconorwegian provinces. The Caledonian rocks form large nappes () that have been thrust over the older rocks. Much of"
"from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, and the Ludfordian stage. The Early Devonian lasts from 419.2 ± 2.8 to 393.3 ± 2.5 and begins with the Lochkovian stage, which lasts until the Pragian. This spans from 410.8 ± 2.8 to 407.6 ± 2.5, and is followed by the Emsian, which lasts until the Middle Devonian begins, 393.3± 2.7 million years ago. The Middle Devonian comprises two subdivisions, the Eifelian giving way to the Givetian 387.7± 2.7 million years ago. Finally, the Late Devonian starts with the Frasnian,"
"middle Ordovician with closure of the Terksey Basin and then underwent deformation. Coarse molasse sediments lie unconformably on top of subduction-related granite intrusions and volcanic rocks. North and south of the Terksey Suture, formed during the event, late Ordovician collision-related granites. Into the Silurian, the Sandalash magmatic arc remained along the southern margin of the Kyrgyz Block. Turkestan oceanic crust was subducated beneath the Sandalash magmatic arc. By the early Devonian, magmatic activity was taking place in the northern Tien Shan mountains, likely as a result of the subducting Turkestan crust. Sedimentation occurred in shallow seas and on the passive"
"resolved by the definition of the Devonian period in the geological timescale. The Great Devonian Controversy was a long period of vigorous argument and counter-argument between the main protagonists of Roderick Murchison with Adam Sedgwick against Henry De la Beche supported by George Bellas Greenough. Murchison and Sedgwick won the debate and named the period they proposed as the Devonian System. While the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy (Ogg, 2004), the Devonian extends from the end of the"
"Cambrian The Cambrian Period ( or ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago (mya) to the beginning of the Ordovician Period mya. Its subdivisions, and its base, are somewhat in flux. The period was established (as “Cambrian series”) by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of sedimentary deposits, sites of exceptional preservation"
"Caledonian orogeny. The Lvov-Volyn Depression developed in the Volyn-Podolia Platform during the Devonian and Carboniferous. Further tectonic changes came about with the Hercynian orogeny, beginning the formation of the Prichernomorian Depression. Basalt and alkaline volcanic rocks intruded the Dnieper-Donets rift zone during this time and the Dnieper-Donets Depression and Donets Basin formed. These syncline structures were flooded by the sea in the Middle Devonian. In the late Paleozoic, from the Permian into the Triassic, dry land continental conditions returned. Much of the Ukrainian Shield was flooded during the Cimmerian orogeny as a large anticline formed. The crust downwarped in the"
"these Caledonian deformed terranes were accreted again to Laurussia during the Hercynian orogeny. Caledonian orogeny The Caledonian orogeny was a mountain-building era recorded in the northern parts of Ireland and Britain, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly 490–390 million years ago (Ma). It was caused by the closure of the Iapetus Ocean when the continents and terranes of Laurentia, Baltica and Avalonia collided. The Caledonian orogeny is named for Caledonia, the Latin name for Scotland. The name was first used in"
"to the bifidus shale and the Lower Llandeilo Series. In the geologic timescale, the ""Arenig"" or Arenigian refers to an age of the Lower Ordovician epoch, between 478.6 ± 1.7 and 471.8 ± 1.6 million years ago, contemporary with the more recently proposed Floian by the ICS, based on a section in Sweden (Diabasbrottet quarry) and with the same boundaries. The Arenigian and Floian are the upper part of the Lower Ordovician and follow the Tremadocian (Gasconadian in North America) which is the lower part. Either is followed by the Middle Ordovician ICS Dapingian or by the Llanvirnian of older"
"in south Wales and are well displayed on the Cardiganshire coast. The Silurian and earlier rocks were folded, faulted, and distorted several times, notably during the late Ordovician, and late Silurian, by which time the area had begun to rise above sea level as mountain ranges were uplifted to the north-west. This was caused by the collision of a proto-North America (""Laurentia"") and the present southern Britain (""Eastern Avalonia""). The intervening sea, the Iapetus Ocean, closed as a result of plate tectonic movements, similar to those that now close the Mediterranean Sea between Europe and Africa. The succeeding Devonian period"
"the buildup of an oxygen-rich atmosphere. This second, follow-on event is known as the oxygen catastrophe, which, some geologists believe triggered the Huronian glaciation. Since the time period from 2420 Ma to 2250 Ma is well-defined by the lower edge of iron-deposition layers, an alternative period named the Oxygenian, based on stratigraphy instead of chronometry, was suggested in 2012 by Gradstein ""et al."" in a geological timescale review but, , this has not yet been officially adopted by the IUGS. Siderian The Siderian Period (; , meaning ""iron"") is the first geologic period in the Paleoproterozoic Era and lasted from"
"million years ago. The few indications of the Silurian/Devonian hiatus in N Lugicum are not of retional significance. Higher ages of the amphibolites (ophiolite) complex of the Marinaska Lazne (486 Ma) point to an early Ordovician extension (Bowes and Aftalion, 1991, Medaris, Jelinek and Misaf 1994) and c. 500 Ma granite gneisses of the Lugicum (Kroner, Hegner and Jaeckel, 1994) early Ordovician magmatic activity, However, these ages have to be considered as minimum ones. In the Brunovistulicum the transgression of early Devonian conglomerates on the pre-Devonian of rome precisely the Pan-Afican basement seaks favorably of its geotectonic independence on W"
"fossils in the northeast belong to the Early Ordovician. Marines sedimentation took place during the Ordovician, Silurian and Devonian. Continuous sedimentation went on in the east into the Carboniferous, but elsewhere a marine regression brought erosion. The Permian and Carboniferous brought renewed marine deposition of sandstone, shale and limestone as well as some terrestrial deposits like coal found near Vietiane and Saravane. The limestone forms a prominent karst topography in the north and east. Marine sedimentation only continued in a few sedimentary basins during the Triassic at the start of the Mesozoic, such as the Sam Neua area. Volcanic rocks"
"which, from an economic point of view, would be the Cambrian and Ordovician slates of North Wales. The northeast to southwest 'grain' of much of the country was imparted at this time with a series of major fault zones persisting from that time to the present, some of which, particularly in the northwest, are believed to represent terrane boundaries. The siliciclastic deposits of the succeeding Devonian period represent in large part the rapid attrition of the extensive Caledonian Mountain belt created by the Caledonian collision. Devonian age rocks are broadly synonymous with the Old Red Sandstone (commonly referred to as"
"Llandovery epoch In the geological timescale, the Llandovery epoch (from 443.7 ± 1.5 million years ago to 428.2 ± 2.3 million years ago) occurred during the Silurian period. The epoch follows the massive Ordovician-Silurian extinction events; the second largest extinction event after the Permian-Triassic extinction event million of years later. The epoch was named after Llandovery in Wales. The Llandovery epoch is subdivided into three stages: Rhuddanian, Aeronian and Telychian. The Lower Llandovery rocks consist of conglomerates, sandstones and slaty beds. At Llandovery they rest upon Ordovician rocks. These rocks occur with a narrow crop in Pembrokeshire, which curves round"
"Dapingian The Dapingian is the third stage of the Ordovician and the first stage of the Middle Ordovician. It is preceded by the Floian and succeeded by the Darriwilian. The top of the Floian is defined as the first appearance of the conodont species ""Baltoniodus triangularis"" which happened about million years ago. The Dapingian lasted for about 2.7 million years until about million years ago. The Dapingian is named after a village that lies nearby the Dapingian GSSP (Huanghuachang section, in Huanghuachang) where there is also an outcrop of similar rocks, the ""Chenjiahe section"" (formerly ""Daping section"") in Chenjiahe. The"
"closure of Iapetus occurred during the Devonian Acadian orogeny, with the resulting continental collision causing deformation of the Ordovician rocks, including folding, thrusting and cleavage development. The Dent Group was deposited in a shallow water environment. Dent Group The Dent Group is a group of Upper Ordovician sedimentary and volcanic rocks in north-west England. It is the lowermost part of the Windermere Supergroup, which was deposited in the foreland basin formed during the collision between Laurentia and Avalonia. It lies unconformably on the Borrowdale Volcanic Group. This unit was previously known as the Coniston Limestone Group or Coniston Limestone Formation"
"Silurian Mya, to the beginning of the Carboniferous Mya (in North America, the beginning of the Mississippian subperiod of the Carboniferous). In nineteenth-century texts the Devonian has been called the ""Old Red Age"", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is ""Age of the Fishes"", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian and Farlovian stages, the latter three"