TheRheic Ocean (/ˈreɪɪk/;RAY-ik) was anocean which separated two majorpaleocontinents,Gondwana andLaurussia (Laurentia-Baltica-Avalonia). One of the principal oceans of thePaleozoic, itssutures today stretch 10,000 km (6,200 mi) fromMexico toTurkey and its closure resulted in the assembly of the supercontinentPangaea and the formation of theVariscan–Alleghenian–Ouachitaorogenies.[1]
The ocean located between Gondwana and Laurentia in the EarlyCambrian was named forIapetus, inGreek mythology the father ofAtlas (from which source the Atlantic Ocean ultimately gets its name),[2] just as theIapetus Ocean was the predecessor of theAtlantic Ocean. The ocean between Gondwana and Laurussia (Laurentia–Baltica–Avalonia) that existed from the EarlyOrdovician to the EarlyCarboniferous was named the Rheic Ocean afterRhea, sister of Iapetus.[1][3]
At the beginning of the Paleozoic Era, about 540 million years ago, most of the continental mass on Earth was clustered around the south pole as the paleocontinent Gondwana. The exception was formed by a number of smaller continents, such asLaurentia andBaltica. The Paleozoic ocean between Gondwana, Laurentia and Baltica is called theIapetus Ocean. The northern edge of Gondwana had been dominated by theCadomian orogeny during theEdiacaran period. This orogeny formed acordillera-typevolcanic arc whereoceanic crust subducted below Gondwana. When amid-oceanic ridgesubducted at an oblique angle,extensional basins developed along the northern margin of Gondwana.[4] During the lateCambrian toEarly Ordovician these extensional basins had evolved arift running along the northern edge of Gondwana.[5] The rift in its turn evolved into a mid-oceanic ridge that separated small continental fragments such as Avalonia andCarolina from the main Gondwanan land mass, leading to the formation of the Rheic Ocean in the Early Ordovician.[6]
As Avalonia-Carolina drifted north from Gondwana, the Rheic Ocean grew and reached its maximum width (4,000 km (2,500 mi)) in the Silurian. In this process, the Iapetus Ocean closed as Avalonia-Carolina collided with Laurentia and theAppalachian orogeny formed.[7]
The closure of the Rheic began in the Early Devonian and was completed in theMississippian when Gondwana and Laurentia collided to form Pangaea. This closure resulted in the largest collisional orogen of the Palaeozoic: theVariscan andAlleghanian orogens between Gondwana's West African margin and southern Baltica and eastern Laurentia and theOuachita orogeny between the Amazonian margin of Gondwana and southern Laurentia.[7]
The Prague Basin, which was anarchipelago of humidvolcanic islands in the Rheic Ocean on the outer edges of what was then the Gondwanan shelf during the Silurian, was a major hotspot ofplantbiodiversity during the early stages of theSilurian-Devonian Terrestrial Revolution. The geologically rapid environmental changes associated with the formation and erosion of volcanic islands and high rates ofendemism associated withisland ecosystems likely played an important role in driving the rapid early diversification ofvascular plants.[8]
It is believed that the closure of the Rheic, alongside the simultaneous onset of theLate Palaeozoic Ice Age, may have sparked theCarboniferous-Earliest Permian Biodiversification Event, an evolutionary radiation of marine life dominated by increase in species richness offusulinids andbrachiopods.[9][10]
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