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15-630: Predominantly, during Miocene and Pliocene times, a medium-sized volcanic field of overlapping vents occurred in British Columbia's Interior Plateau . The distribution is assumed to engulf up to 50,000 km of the Pacific Northwest , forming a medium-sized large igneous province , of volume 3300 km. Volcanism occurred as late as Oligocene time, but continues sporadically up to present. Eruptions were most vigorous 6-10 million years ago and 2-3 million years ago, when most of

30-659: Is at the extinction of the foram genus Chiloguembelina (which is also the base of foram biozone P21b). An official GSSP for the Chattian Stage was ratified in October of 2016. The top of the Chattian Stage (which is the base of the Aquitanian Stage, Miocene Series and Neogene System ) is at the first appearance of foram species Paragloborotalia kugleri , the extinction of calcareous nanoplankton species Reticulofenestra bisecta (which forms

45-598: Is followed by the Chattian Stage. The stage is named after the small river Rupel in Belgium, a tributary to the Scheldt . The Belgian Rupel Group derives its name from the same source. The name Rupelian was introduced in scientific literature by Belgian geologist André Hubert Dumont in 1850. The separation between the group and the stage was made in the second half of the 20th century, when stratigraphers saw

60-570: Is still up for debate, however, the most widely accepted idea is that a back-arc basin behind the Cascadia subduction zone initiated the widespread and voluminous basaltic volcanism. Some centers erupted along pre-existing brittle fault systems while volcanism along its northern portion is most widely believed to have been related to a centre of upwelling magma called the Anahim hotspot (similar to that associated with present-day Hawaii), creating

75-647: The Fish Canyon eruption of La Garita with a magnitude of 9.2 and VEI of 8. It has been dated to 27.51 Ma ago. Rupelian The Rupelian is, in the geologic timescale , the older of two ages or the lower of two stages of the Oligocene Epoch / Series . It spans the time between 33.9 and 27.82 Ma . It is preceded by the Priabonian Stage (part of the Eocene) and

90-684: The Rainbow , Ilgachuz and Itcha Range shield volcanoes which also in turn form part of the Anahim Volcanic Belt . The exact nature of the relationship between the Anahim hotspot and the Chilcotin Group is unknown, however. Volcanoes of the Chilcotin Group include: 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

105-576: The Snake River Plain in Idaho and parts of Iceland (Bevier, 1983). The distribution and volume of the Chilcotin Group is unknown due to extensive Pleistocene glacial cover. This presumably glacial "drift" is very thick, and in most regions completely obscures the volcanism. Individual vents for basalt volcanism include small cinder cones , volcanic plugs , and gabbroic feeders, which locally crosscut lava flows. Recent studies indicate that

120-680: The Rupelian Stage (the base of the Chattian) is at the extinction of the foram genus Chiloguembelina (which is also the base of foram biozone P21b). The Rupelian overlaps the Orellan , Whitneyan and lower Arikareean North American Land Mammal Ages , the upper Mustersan and Tinguirirican South American Land Mammal Ages , the uppermost Headonian , Suevian and lower Arvernian European Land Mammal Mega Zones (the Rupelian spans

135-558: The basalt was released. Less extensive eruptions continued 0.01 to 1.6 million years ago. These lava flows have been dominantly exposed by erosion resulting from the great floods that flowed in this region throughout the past ice ages, which laid bare many layers of the basalt flows along the Fraser Canyon from Soda Creek south to Canoe Creek elsewhere along the Chilcotin , Chilko , Chilanko and Taseko Rivers , and also to

150-584: The base of nanoplankton biozone NN1), and the base of magnetic C6Cn.2n. The Chattian is coeval with regionally used stages or zones such as the upper Avernian European mammal zone (it spans the Mammal Paleogene zones 30 through 26 and part of 25 ); the upper Geringian and lower Arikareean mammal zones of North America; most of the Deseadan mammal zone of South America; the upper Hsandgolian and whole Tabenbulakian mammal zone of Asia;

165-646: The east of the Fraser River at Chasm Provincial Park and along the Upper Deadman River . Prior to Late Pleistocene glacial erosion these centers formed a series of coalesced, low-profile shield volcanoes of unknown volume and distribution. The Chilcotin Group were thought to potentially be linked to the partly coeval Columbia River Basalt Group . However, its morphology and geochemistry have been proven much similar to other volcanic plateaus such as

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180-630: The need to distinguish between lithostratigraphic and chronostratigraphic names. The base of the Rupelian Stage (which is also the base of the Oligocene Series) is at the extinction of the foraminiferan genus Hantkenina . An official GSSP for the base of the Rupelian has been assigned in 1992 ( Massignano , Italy). The transition with the Chattian has also been marked with a GSSP in August 2017 ( Monte Conero , Italy). The top of

195-677: The time between 27.82 and 23.03 Ma . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage of the Miocene ). The Chattian was introduced by Austrian palaeontologist Theodor Fuchs in 1894. Fuchs named the stage after the Chatti , a Germanic tribe. The original type locality was near the German city of Kassel . The base of the Chattian

210-612: The upper Kiscellian and lower Egerian Paratethys stages of Central and eastern Europe; the upper Janjukian and lower Longfordian Australian regional stages; the Otaian, Waitakian, and Duntroonian stages of the New Zealand geologic time scale ; and part of the Zemorrian Californian stage and Chickasawhayan regional stage of the eastern US. During the Chattian the largest known single-event volcanic eruption occurred:

225-601: The volume of the Chilcotin Group is much less than previously thought, and that the "Plateau" is likely Eocene in age. This means that the Chilcotin is likely composed of many local volcanic vents, that were of small volumes that fed into the paleo-landscape, and subsequently are found in the major river systems that we see at present. Prior to 16 million years ago, the western Cascade Volcanic Arc stratovolcanoes erupted with periodic regularity for over 27 million years, even as they do today. The ultimate cause of this volcanism

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