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The Palaeozoic geography of Laurentia and western Laurussia: A stable craton withmobile margins

L. Robin M. Cocks a, Trond H. Torsvik b,c,d,⁎a Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UKb PGP and Geosciences, University of Oslo, PO Box 1048, N-0316 Oslo, Norwayc Geodynamics Centre, Geological Survey of Norway, Leif Eirikssons vei 39, N-7491 Trondheim, Norwayd School of Geosciences, University of Witwatersrand, WITS 2050, South Africa

a b s t r a c ta r t i c l e i n f o

Article history:Received 9 November 2009Accepted 24 January 2011Available online 3 February 2011

Keywords:PalaeozoicpalaeogeographyLaurentia

The large Palaeozoic continent of Laurentiawas largely inNorth America, but included parts ofmodern Europe. Itwas independent from late Neoproterozoic times at about 570 Ma until it merged with Avalonia–Baltica in the430–420 Ma Silurian Caledonide Orogeny, after which it formed the major western sector of the combinedLaurussia Supercontinent. Laurussia in turn became part of the even larger Pangea Supercontinent in the LateCarboniferous, as documented by the oblique Laurussia–Gondwana collision seen in the Laurentian sector in theOuachita Orogeny. Laurentia's margins and the many peri-Laurentian terranes are reviewed. Those parts ofnortheast Siberiawhich today formparts of theNorthAmerica Plate, butwere not part of Laurentia or Laurussia inthe Palaeozoic, are also reviewed. A revised Apparent Polar Wander Path (APW) for the Laurentian Craton ispresented for all of the Palaeozoic. Laurentiawas at equatorial palaeolatitudes throughout and rotated little, apartfrom shortly after its collisionwith Avalonia–Baltica in the Silurian Caledonide Orogeny; however, in contrast, itsposition and orientation were much less affected in the Ouachita Orogeny at the time of Pangean assembly. TheLaurentian Craton was variably flooded at many times with epeiric seas, which formed optimal numbers ofecological niches which in turn encouraged animal speciation and evolution. A summary is presented of thePalaeozoic geological history of Laurentia and its surrounding areas, and the Laurentian sector of Laurussia duringand after its integration within Pangea, together with new palaeogeographical maps from the Cambrian to theend of the Permian. On thosemaps there are plotted areas of land, shallow shelf, deeper shelf and oceans derivedfrom much pre-existing data, as well as reefs, volcanic and plutonic rocks and some selected faunas and floras.The substantial number of terranes at the margins of the continent through time are briefly reviewed, notablythose in Mexico, the Appalachians, and northwestern parts of Europe which were once parts of Laurentia. Themany terranes containing Palaeozoic rocks in the northwestern part of the North American Plate, and formingmuchof theCordillera innorthwest Canada andAlaska aswell as northeast Siberia, are itemised: somewereperi-Laurentian, some peri-Siberian, and others originally oceanic in the Palaeozoic. The concept of an ArctidaMicrocontinent is discussed. That microcontinent had originally been postulated as existing from theNeoproterozoic to the Devonian, and to have consisted of the composite Arctic Alaska and the Seward, Yorkand Farewell terranes in Alaska, and the Pearya Terrane of Ellesmere Island, as well as the Chukotka Peninsula,New Siberian Islands, Severnaya Zemlya, northern Taimyr and adjacent areas now in the northeast of modernSiberia. Many parts of that area contain faunas of both Siberian and Laurentian aspect, which are reviewed andanalysed. It is concluded that there was a smaller independent continent in the Lower Palaeozoic, which wasoriginally somewherebetweenSiberia andLaurentia in theCambrian, butwhichdidnot include theNewSiberianIslands, Kolyma and Omolon (which were parts of Siberia), Severnaya Zemlya and northern Taimyr (theindependent KaraMicrocontinent), or the Farewell Terrane (independent until theMesozoic). The eastern end ofthat Arctic Alaska–Chukotka Microcontinent docked with northwestern Laurussia (Ellesmerian margin) in theDevonian, but it did not reach its present positionwithin North America until after rotation in the Cretaceous. TheCordilleran terranes ofWrangellia, Alexander and some smaller units are confirmed as having existed as anothermicrocontinent independent from North America until the Mesozoic. However, there appear to be no terranesnow in western North America which originated from Baltica. The Pearya Terrane, now forming northernEllesmere Island, was probably involved in the most northerly sector of the Silurian Caledonide Orogeny.

© 2011 Elsevier B.V. All rights reserved.

Earth-Science Reviews 106 (2011) 1–51

⁎ Corresponding author at: PGP and Geosciences, University of Oslo, PO Box 1048, N-0316 Oslo, Norway.E-mail addresses: [email protected] (L.R.M. Cocks), [email protected] (T.H. Torsvik).

0012-8252/$ – see front matter © 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.earscirev.2011.01.007

Contents lists available at ScienceDirect

Earth-Science Reviews

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Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. The North American Plate today . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33. Laurentian Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54. Palaeomagnetic review of the Laurentian Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55. The margins of Palaeozoic Laurentia and western Laurussia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66. Mexico and Central America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6.1. Caborca Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96.2. Sierra Madre and Cortez terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96.3. Mixteca and Oaxaquia terrranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96.4. Yucatan Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96.5. Chortis and Tarahumara terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

7. Cordilleran and northeastern Siberian units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97.1. Terranes original to Laurentia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

7.1.1. Porcupine and Livengood areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.1.2. Yukon-Tanana Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.1.3. Slide Mountain and Kootenay terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.1.4. Cassiar Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

7.2. Peri-Laurentian terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.2.1. Roberts Mountain and Golconda allochthons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.2.2. Eastern Klamath, Yreka, Trinity and adjacent terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.2.3. North Sierra and Black Rock terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.2.4. Quesnel Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.2.5. Stikinia Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.2.6. Ruby and Innoko terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7.3. Terranes originally exotic to Laurentia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.3.1. Farewell Terrane (including the Mystic, Dillinger and Nixon Fork subterranes) . . . . . . . . . . . . . . . . . . . . . . . . 127.3.2. Arctic Alaska Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.3.3. Seward and York terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.3.4. Chukotka Terrane (including Wrangel Island) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137.3.5. New Siberian Islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137.3.6. Kolyma and Omolon terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7.4. Terranes of mid-oceanic origin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137.4.1. Alexander Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137.4.2. Wrangellia, Peninsular and Chilliwack terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147.4.3. Angayucham and Goodnews terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147.4.4. Cache Creek and Bridge River terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147.4.5. Chulitna Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

8. Summary of Cordilleran and northeastern Siberian units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149. Northern Canada, eastern U.S.A. and European units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9.1. Northern units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159.1.1. Arctic Ocean fragments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159.1.2. Pearya Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9.2. European units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159.2.1. Svalbard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159.2.2. Bjørnøya (Bear Island) and Jan Mayen Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159.2.3. Highlands of Northern Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169.2.4. Midland Valley of Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169.2.5. Southern Uplands of Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169.2.6. Northwestern Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169.2.7. Grangegeeth Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169.2.8. Norwegian nappes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

9.3. Appalachian units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.3.1. Humber Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.3.2. Dunnage Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.3.3. Gander Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.3.4. Avalon Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179.3.5. Meguma Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189.3.6. Carolina and associated terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189.3.7. Alabama terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

9.4. Florida (Suwanee) Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189.5. Precordillera (Cuyania) Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

10. Geological history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1811. Precambrian prelude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1912. Cambrian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

12.1. Tectonics and igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2012.2. Facies and faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

13. Ordovician . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2113.1. Tectonics and igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2113.2. Facies and faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2 L.R.M. Cocks, T.H. Torsvik / Earth-Science Reviews 106 (2011) 1–51


14. Silurian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2514.1. Tectonics and igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2514.2. Facies and faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

15. Devonian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2815.1. Tectonics and igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2815.2. Facies and faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

16. Carboniferous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3116.1. Tectonics and igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3216.2. Facies and faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

17. Permian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3617.1. Tectonics and igneous activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3617.2. Facies and faunas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

18. Mesozoic to Recent postscript . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3919. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

19.1. The reality and extent of an Arctida Continent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4119.1.1. Previous work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4219.1.2. Faunal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4419.1.3. Conclusions on Arctida and Arctic Alaska–Chukotka . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

19.2. The Farewell Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4519.2.1. Previous work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4519.2.2. Faunas and floras . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4519.2.3. Conclusions on the Farewell Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

19.3. Wrangellia, Alexander and associated terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4519.4. The Pearya Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

20. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Appendix 1. Orogenies in the Palaeozoic of North America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

1. Introduction

A glance at any geological map of North Americamade over the pasttwohundred years, from the times of thegreat early nineteenth-centurytraverses of Charles Lyell andWesley Powell, gives the initial impressionof a vast and stable Precambrian craton uponwhich lies a palimpsest oflayer-cake Palaeozoic and later rocks. That impression still holds goodfor much of the centre of the continent, but is very far from the truthwhen its margins, both ancient and modern, are considered. It is thepurpose of this review to tease out and map a Palaeozoic history for theregion (Fig. 1) and to consider its changing palaeogeography throughtime. One practical problem is the deluge of data that has accumulatedfrom North America and its marginal areas over the past two centuries,principally from the U.S.A. and Canada, but also from northeast Siberia,Greenland, Spitsbergen, the northern British Isles, Mexico and otherintegral or adjacent parts of old Laurentia, and we apologise to theauthors of the thousands of publications not quoted here. This paperdoes not attempt a detailed synthesis of themany varied components ofthe geology and palaeontology of North America and adjacent regions,but presents new terrane and palaeogeographical maps for theCambrian to Permian. The story of Laurussia in the Upper Palaeozoicwas the subject of a landmark book by Ziegler (1989), but thesubstantial amount of new data published in the twenty-two yearssince then makes the present review seem timely.

The Neoproterozoic and Palaeozoic continent of Laurentia is namedafter the Laurentian Shield which occupies so much of Canada today, butthe terranewasmuch larger than that shield area in the Palaeozoic. It wasonly a separate terrane from the late Precambrian at about 570 Ma untilthe time of its collision with the combined Avalonia–Baltica continent inthe middle of the Silurian (430–420Ma) at the peak of the CaledonideOrogeny, and thereafter it formed the western sector of Laurussia. Thispaper continues to chart the history of the region until the end of thePalaeozoic at 250 Ma, by which time the Laurussian area had become asubsidiary, but still very substantial, part of the enormous supercontinentof Pangea. As can be shown from palaeomagnetic data (Figs. 2 and 3), theLaurentianCraton straddled theEquator for the entire Palaeozoic, and alsodid not rotate very much. It only changed orientation and palaeolatituderelatively quickly during the Silurian Caledonide Orogeny, but during the

Carboniferous Ouachitan Orogeny collision with Gondwana to formPangea therewas less displacement or rotation, probably becausemost ofthe stresses of that amalgamation were largely taken up by east–westtrending strike slip fault movements not mirrored by changingpalaeomagnetism. Since then, despite the substantial post-Pangeainteractions with the Pacific Plate and the accretion of many terranesonto itsWmargin,NorthAmerica and itsprecursorpalaeocontinentshaveremained in a comparable orientation up to the present day, although ithas gradually moved to more northerly latitudes.

A generally good understanding of the Palaeozoic geology overlyingthe Precambrian craton was achieved more than a century ago.However, in contrast, the documentation and elucidation of the manysmaller and mostly complex marginal terranes, termed peri-Laurentia,is in many cases much weaker in basic data, and there are also variableopinions on their evolving Palaeozoic tectonic history. In our review ofPalaeozoic Siberia (Cocks and Torsvik, 2007) we largely ignored thesubstantial parts of modern northeast Siberia which lie today on theNorth American Plate. It transpires that we were wrong to do so, sincethat area and also much of Alaska and NW Canada consist ofindependent terranes, some of which were not far from Siberia aswell as Laurentia, as described and discussed below.

Like our treatments of other major Palaeozoic continents, namelyBaltica and Siberia (Cocks and Torsvik, 2005, 2007) and sectors ofGondwana (Torsvik and Cocks, 2009, in press),wewillfirstly review thecomponents of Laurentia and its successor continents as parts ofLaurussia, Pangea and North America as well as the relevantneighbouring terranes, including the palaeomagnetic data available(Sections 2–9). That is followed by a geological history, particularlyfocussed on the successive systems of Palaeozoic time, accompanied bynew palaeogeographical reconstructions (Sections 10–17), and a verybrief Mesozoic to Recent postscript (Section 18). There are somediscussion and conclusions in Sections 19 and 20.

2. The North American Plate today

Fig. 1 shows the margins of the North American Plate in NorthAmerica and northern Eurasia. Its eastern margin lies underneatheastern Siberia, and is there bordered in its west by the Verkhoyansk

3L.R.M. Cocks, T.H. Torsvik / Earth-Science Reviews 106 (2011) 1–51


Fig. 1.Modernmap of North America and part of Eurasia, showing the North American Plate margin (thick black line) and adjacent areas. AR, Alpha Ridge; BI, Bjørnøya (Bear Island);FJL, Franz Josef Land; K–O, Kolyma and Omolon; KP. Kara Plate; NSI, New Siberian Islands; NZ, Novaya Zemlya. Thin black lines, old terrane boundaries; white star, North Pole. The redline is the Iapetus Suture of the Caledonide Orogeny. The smaller map is an enlargement of some of Arctic Canada and Greenland, and also shows the rocks affected by the TertiaryEurehan Orogeny there.



Mountain range. The northern boundary lies under the Arctic Ocean(Eldholm et al., in Grantz et al., 1990) to the east of theNorth Pole and tothe N of Svalbard, Franz Josef Land and the shelf of the Kara Sea. Theeastern boundary continues in a largely southerly direction along theline of the Mid-Atlantic Ridge and through Iceland. The Mid-AtlanticRidge today continues southwards beyond the Equator, but eastof theCaribbean there is a triple junction between the Eurasian, NorthAmerican and South American plates. The North American–SouthAmerican plate boundary runs approximately east–west under theAtlantic to reach another triple junction with the Caribbean Plate. TheCaribbean–North American plate boundary then curves to the south ofthe Puerto Rico Trench and Cuba, and south of the Yucatan Peninsulabefore reaching another triple junctionwith theCocos Plate, fromwhichthewesternboundary of NorthAmerica runs subparallel to theWcoastsofMexico, the United States and Canada up to the south of Alaska. NorthAmerica is bordered to its west chiefly by the vast Pacific Plate, but alsothe much smaller Gorda and Juan de Fuca plates until reaching thesouthern margin of the Aleutian Trench. That trench merges with theKuril Trench to its west, and south of Kamchatka, and the plate margincontinues along it until reaching another triple junction (between theNorth American, Pacific and Eurasian plates) to the S of Sakhalin Island,from where the Eurasian–North American plate boundary runsnorthwards under the shelf of the Sea of Okhotsk and up to thesouthern margin of the Verkhoyansk Mountains of Siberia.

Thus it can be seen that the old Proterozoic and Lower PalaeozoicLaurentian continent and its successors, the Laurentian sector ofLaurussia, Pangea and Laurasia in turn, are chiefly situated on themodern North American Plate, but do not occupy all of it. Comparably,it has also been known since the time of the classic paper of Wilson(1966), that Palaeozoic Laurentia included sectors which now formparts of the Eurasian Plate in Europe (Fig. 1).

3. Laurentian Craton

There is an enormous amount of literature on the geology of theLaurentian craton, particularly the United States and Canadian parts of

it. However, relatively little of it will be cited here, particularly sincethis paper concentrates chiefly on the Palaeozoic and not thePrecambrian or the Mesozoic to Recent. The many volumes publishedwithin the Decade of North American Geology (DNAG) series by theGeological Society of America and the Geological Survey of Canadabetween 1988 and 1998 (e.g. Hatcher et al., 1989; Plafker and Berg,1994) are invaluable sources for the geology of the continent, as is thebook on the evolution of Laurussia from the latest Silurian to the endof the Permian by Ziegler (1989). Rather than being emergent lands,much of the craton was covered by shallow seas for substantial partsof the Palaeozoic, some shallow enough to harbour hypersalineevaporitic deposits, which can be very large; for example, in theMichigan Basin of the Great Lakes region of the U.S.A. Some referencesto the abundant work on the craton are included in the geologicalhistory presented below (Sections 12–17), and the cratonmargins arereviewed in Section 5.

4. Palaeomagnetic review of the Laurentian Craton

Few new Palaeozoic palaeomagnetic poles from the ‘stable’ cratonof North America have been reported during the last decade, andinput poles and derived apparent polar wander (APW) paths (Table 1)shown in Fig. 2 are chiefly based on compilations by Van der Voo(1989, 1993) and Torsvik et al. (1996, 2001, 2008). However, twonewer Lower Palaeozoic poles, the 532±2 Ma Mont Rigaud andChatham–Grenville pole (McCausland et al., 2007; Q-factor 5 of Vander Voo, 1993) and the 550±3 Ma Skinner Cove Volcanic (McCaus-land and Hodych, 1998; Q-factor 4) have been included in ouranalysis. We have generated two different APW paths for NorthAmerica, one using a spherical spline with low smoothing (Fig. 2a),and one using a standard running mean path (Fig. 2b). Both paths arecomparable, and the great circle distances (GCD) between poles of thesame age averages 4.0±2.7°. With respect to North America, theSouth Pole path starts in the South Atlantic and shows a tight loop orcusp during Cambrian and Ordovician times. By the Silurian (430–420 Ma), the pole was located in Brazil, followed by yet another cusp

Fig. 2. Revised Apparent Polar Wander Path (APW) for the Laurentian Craton in the Palaeozoic. (a) Palaeomagnetic input poles drawn with dp/dm 95% ovals and a smoothedspherical spline path weighted by quality factor Q (Van der Voo, 1993); no errors along spline path generated with this method (see Torsvik et al., 1996). (b) Running mean pathbased on input poles in (a) shown with A95 confidence circles. We also show a composite Laurussia–Pangea path from 430 Ma. Numbers denote ages in million years. Orthographicprojection.



during the Devonian. By the end of the Palaeozoic, the South Pole waslocated at Patagonia in South America.

In the Silurian (c. 430 Ma), Laurentia (including most of NorthAmerica, Greenland and Scotland) collided with Baltica (includingScandinavia) and Avalonia (including England), and thus we are ableto produce a joint APW path for the whole of Laurussia from 430 Ma.In addition, many continents merged to form Pangea at around320 Ma, and so we can construct a nearly global APW path from thenon. This is illustrated in Fig. 2b (black 430–250 Ma line with a fewannotated ages in bold italics) and the path is grossly similar (withinerrors) to that calculated from North American data alone; and theGCD between the two runningmean paths averages 4.7° or ca. 522 km(based on Table 1, but not counting purely interpolated mean poles).In our reconstructions we use the pure North America APW path fromCambrian to Silurian times (Figs. 5–15) and then the compositeLaurussia (430–330 Ma) and Pangea (320–250 Ma) path for theMiddle and Upper Palaeozoic (Figs. 16–27). Relative fits are mostlythose of Torsvik et al. (2008) and between 430 and 330 Mawe use theBullard et al. (1965) fit for North America to Europe. The compositepath has been listed in Torsvik and Cocks (2005), but in European co-ordinates, and the APW path calculated from Table 1 has simply beenrecalculated to North American co-ordinates using a rotation pole of88°N and 27°E (rotation angle of −38°).

Based on North American data alone, we have calculated the driftand rotation history for core North America (Fig. 3). The continentwas mostly located in tropical latitudes during the entire Palaeozoicbut a pronounced southerly drift (as much as 16 cm/year) isrecognized from Late Silurian to Early Devonian times (420 to400 Ma), shortly after its collision with Baltica/Avalonia. This strikingchange (that before the collision Laurentia was quite stationary andstraddling the Equator, whilst in contrast Baltica/Avalonia wasmoving towards Laurentia from the south) has been known forsome time, and can be explained by True Polar Wander (e.g. Van derVoo, 1994; Torsvik et al., 1996) caused by a major change in thesubduction pattern. North America gradually rotated counter-clock-wise during most of the Lower and Middle Palaeozoic, except duringthe Early Cambrian, which was characterized by rather fast clockwiserotation (more than 1.5°/Ma). That rotation (between 550 and530 Ma) is based on the Skinner Cove Volcanic pole of McCauslandand Hodych (1998), which has changed the conclusions published byTorsvik et al. (1996).

5. The margins of Palaeozoic Laurentia and western Laurussia

The margins of the core of the old Laurentian continent will now bebriefly reviewed, starting in northern Canada and proceeding clockwise

Fig. 3. (a) Revised orientations for the Laurentian Craton through the Palaeozoic (numbers denote ages in Ma). The arrow in the centre of each diagram points to today's North Pole.(b) Latitudinal drift rates for North America, separated into north and southward motion. (c) Angular rotation rates for the craton through time. All calculations based on the NorthAmerica running mean path in Fig. 2b (Table 1).



round the craton and beyond it round to Alaska and Siberia.Understanding of the multiplicity of stratigraphical and tectonic termsis sometimes difficult for workers outside North America, not leastbecause many terms which were coined before plate tectonics wereunderstood continue to be used without precise redefinition; forexample, the ‘Franklinian’ of Schuchert (1923), which has been usedmore recently in various different ways.

The Arctic Ocean and its surrounding areas were reviewed in themany papers in Grantz et al. (1990) and Trettin (1991), but withinnorthern Canada, Alaska and the adjacent Arctic Ocean much of thegeology is obscured by the substantial ice cover; and sincemuch of theLaurentian Plate margin lies beneath the ocean there, it is oftendifficult to be precise about the location of the craton margin inPalaeozoic times. The numerous Lower Palaeozoic rocks to be seen innorthern Canada were chiefly deposited in shallow-water basins onthe craton, but there are some deeper-water marginal basinspreserved. Dixon and Dietrick (in Grantz et al., 1990) have describedthe strata underlying the Beaufort Sea, Banks Island, and theAmundsen Gulf, all north of Yukon Territory. There are substantialCambrian to Early Devonian platformal successions, although thereare also some Cambrian volcanics in the Romanzof Uplift. The LateDevonian is represented by clastics deposited during the EllesmerianOrogeny, and above those rocks is an unconformity below the Triassic,apart from on the mainland of northwest Yukon, where there areCarboniferous and Permian conglomerates and shales with coals, inturn overlain by shales with some thin limestones.

Further to the east, there was a passive margin during the LateProterozoic and Cambrian (Dewing et al., 2004) on which wasdeposited largely shallow-water facies. Lateral to these typicallycratonic facies and characterised in later rocks, the Sverdrup Basin,which has been developing continuously from the Early Carboniferous

until today, is at the craton margin and was reviewed by Davies andNassichuk (in Trettin, 1991). That basin is about 1300 km innortheast–southwest length, stretching from Albert Island to Elles-mere Island, and up to 400 km wide, and covers an area of more than300,000 sq. km, about half of which is onshore and half under theArctic Ocean. Its inception followed the relaxation of Late DevonianEllesmerian orogenic compression (Embry, 1991, 2000), and isassociated with uplift in other Arctic Islands in the Visean. The basinappears to have been formed within a failed rift system. There areassociated alkaline volcanics in northwestern Ellesmere Island andAxel Heiberg Island, and the Carboniferous and Permian sedimentsare 1300 m thick. Evaporites of the Middle Carboniferous Otto FjordFormation represent the first marine incursions into that area, andmany of the other Upper Palaeozoic sediments are also relativelyshallow-water in origin: they include clastic sandstones and somePermian reefs. Some Carboniferous and Permian bituminous shalesare important hydrocarbon source rocks. Shallow-water and carbon-ate sedimentation gave way to deeper-water sedimentation in theLate Permian.

Further east, to the north of Ellesmere Island, the Lincoln Sea Basinconsists of isoclinally folded Lower Palaeozoic flysch, presumablyoriginally deposited at the Laurentian margin, which was metamor-phosed prior to the deposition of overlying unmetamorphosedCarboniferous strata (Haimila et al., in Grantz et al., 1990). Thoserocks are juxtaposed against the Pearya Terrane, reviewed by Trettin(e.g., 1998) and considered below in Sections 9.1.2 and 19.4. Betweenthe Canadian Shield and Pearya lies the Emma Fjord Fault Zone, whichcontains the accreted remains of an Ordovician island arc (Klaper,1992). On the North American mainland, shallow-water rocks (oftentermed ‘miogeoclinal’), mainly carbonates, were deposited near themargin of the craton. In the Late Silurian to Early Devonian of northern

Table 1Revised apparent polar wander (APW) paths for the North American craton. The running mean path was generated with a 20 Ma window. N=number of input poles; A95=95%confidence circle. The spherical spline path (smoothing parameter=300) was weighted by the Q-factor (Torsvik et al., 1996) in order to anchor the path to the most reliable data.Numbers in brackets (420–330 Ma) refer to a mean path for Laurussia (North America, Scotland/England and Baltica) and a global APW path (320–250 Ma), all listed in NorthAmerican co-ordinates (see text). GCD is great circle distance (shortest distance on a sphere) between a purely North American and Laurussia/Global APW paths.

Age(Ma)

N Running mean path Spherical spline path

A95 Pole latitude Pole longitude GCD Pole latitude Pole longitude

250 16(35) 3.5(4.2) −51.3(−56.2) 294.1(298.7) 5.7 −51.4 296.8260 6(26) 4.5(4.9) −50.3(−54.5) 301.7(300.2) 4.4 −47.8 304.8270 3(28) 8.4(4.1) −48.3(−48.7) 305.4(304.8) 0.5 −44.2 306.0280 15(57) 2.7(2.4) −43.6(−44.0) 305.7(308.9) 2.4 −43.1 305.6290 21(67) 2.0(1.7) −42.4(−41.9) 305.7(308.1) 1.9 −42.4 306.8300 9(36) 3.0(2.1) −40.8(−40.6) 305.8(310.6) 3.7 −41.8 305.8310 4(20) 10.5(4.7) −37.8(−38.9) 308.2(313.8) 4.5 −38.9 306.2320 5(10) 9.3(8.6) −32.3(−33.1) 306.3(310.4) 3.6 −34.2 307.5330 5(8) 9.2(10.1) −30.5(−27.0) 308.1(304.1) 4.9 −25.7 305.6340 2(5) 21.1(11.4) −24.6(−17.9) 306.4(297.1) 10.9 −19.5 302.9350 ***(1) ***(0) −21.4(−12.7) 300.3(293.9) 10.7 −14.2 297.1360 ***(1) ***(0) −18.0(−12.7) 294.4(293.9) 5.3 −9.6 289.2370 ***(*) ***(***) −14.5(−9.4) 288.7(290.3) 5.9 −6.6 282.4380 ***(*) ***(***) −10.8(−6.0) 283.3(286.8) 6.6 −4.8 277.1390 2(5) 41.1(9.9) −7.1(−2.5) 277.9(283.3) 7.0 −5.2 275.7400 2(7) 41.1(6.7) −7.1(−1.9) 277.9(282.6) 7.0 −7.8 280.1410 3(11) 29.2(8.1) −10.7(−5.9) 286.7(288.2) 5.0 −12.6 291.2420 2(16) 9.6(7.0) −18.0(−12.9) 307.0(299.8) 8.7 −17.0 303.8430 2(11) 9.6(5.1) −18.0(−17.6) 307.0(307.5) 0.6 −19.2 313.1440 *** −16.7 314.6 −19.5 319.3450 *** −15.2 322.0 −18.6 323.3460 1 0.0 −13.4 329.3 −17.2 326.4470 2 11.1 −15.4 330.8 −15.9 330.2480 3 14.7 −13.8 336.1 −14.3 336.3490 7 7.9 −7.5 342.7 −9.3 342.2500 8 6.2 −3.8 344.5 −2.7 344.9510 4 12.9 −1.1 345.6 4.9 349.3520 *** 5.5 355.0 10.1 356.3530 1 0.0 11.9 4.6 10.0 0.2540 2 96.7 −1.6 350.9 1.6 354.1550 1 0.0 −15.0 337.0 −12.5 340.5

*** Interpolated (no data).



Canada, tectonic flexuring caused the Boothia Uplift seen in theBoothia Peninsula and adjacent Devon Island, as well as the InglefieldUplift on southeastern Ellesmere Island (Okulitch et al., in Trettin,1991).

Between Ellesmere Island (Canada) and Greenland lies the NaresStrait, where many authors have thought there to be a substantialstrike–slip fault within the Laurentian Craton, thus displacing itsmargin. However, the Nares Strait area has been thoroughlyremapped and the geology is seen to be similar on both sides.Dawes (reviewed in 2009) has proved the lack of any appreciablestrike–slip movement along that strait, which largely represents arelatively recent erosional feature.

The Greenland sector of Laurentia also mainly consists of aPrecambrian craton, but that is bordered to the north by the east–west trending North Greenland Foldbelt, which developed on the siteof the Lower Palaeozoic Franklinian Basin during the end-DevonianEllesmerian Orogeny, all reviewed by Higgins et al. (in Trettin, 1991)and Henriksen (2008). Further round the margin, in the east ofGreenland, there are the 1300 km East Greenland Caledonides, whichform the northern sector of the Caledonian–Scandian–Appalachianorogenic belt stitching Laurentia to Avalonia–Baltica and whichdeveloped in the mid-Silurian Caledonide Orogeny, reviewed byHiggins et al. (2008). However, there were some earlier LateOrdovician granites in the E of Greenland (Kalsbeck et al., 2008) aswell as those of Silurian age which probably represent a northwardextension of the contemporary granite belt in Scotland. The easternpart of Greenland formed the Franz Joseph Allochthon which, prior tothe Caledonide Orogeny, originally lay 200–400 km to the east of itspresent position (Smith and Rasmussen, 2008), and whose marginsare shown on Figs. 12–15.

On today's eastern margin of North America and southwest ofGreenland, in Newfoundland and adjacent areas within the MaritimeProvinces of Canada, the westernmost of the tectonic zones defined byWilliams (summarised in 1995) is the Humber Zone (Section 9.3.1),which, although now allochthonous, originally formed part of coreLaurentia, and, through the deeper-water shelf-edge rocks of the CowHead Group, defines the craton margin there. However, the zones tothe east of the Humber Zone, commencing with the Dunnage Zone(also reviewed in Section 9.3 below), were not originally Laurentian,and represent terranes accreted in the Taconic, Caledonide and laterorogenies (van Staal et al., 2009). On the eastern North Americanmainland to the south of Newfoundland, the Appalachians stretchalong most of the border of the Laurentian Craton. Their westernmargins are largely made up of tectonised fragments of coreLaurentia, as are many parts of the Appalachians themselves, as alsoreviewed below in Section 9. However, Ganis et al. (2001) havecharacterised the Hamburg Klippe of Pennsylvania as Lower toMiddleOrdovician trench-fill deposits allochthonously displaced onto thecraton at the end of the Ordovician or perhaps a little later.

To the south of the Appalachians, the southeastern U.S.A. isdominated by Mesozoic to Recent rocks, but in Georgia and Alabamathose rocks conceal an east–west trending Palaeozoic suture zone (theSuwannee–Higgins Suture) dividing core Laurentia from the peri-Gondwanan Florida Terrane (see Section 9.4). Westward from Florida,the Ouachita orogenic belt stretches from Alabama to western Texasand divides the Laurentian Craton to its north from the Mexican andother terranes to its south, which were largely of Gondwanan origin(Section 6). The DNAG volume edited by Hatcher et al. (1989)contains a wealth of detail on the region, which has also beenreviewed more recently by Nielsen (2005). There a passive margincontinued until early Carboniferous time, when the Ouachita Basinbegan subsiding rapidly prior to the amalgamation of Laurussia withGondwana to form Pangea, and the basin became quickly filled by asubstantial turbidite sequence. The rocks continue upwards into asynorogenic sequence of Late Carboniferous age, which was laterdeformed inMesozoic times. In the northwest of Mexico, the so-called

Caborca Terrane area (Section 6.1) is now known to be more simply apart of the Laurentian craton offset during the accretion of Gondwana(Dickinson and Lawton, 2001).

Further on north-westwards round the modern continent thereare successively the Southern and the Northern Cordillera, whosewestern margins are delimited by the active margin of today's NorthAmerican Plate. However, many of the individual Cordilleran terranes,which are reviewed below in Sections 7 and 8, and discussed inSection 19, did not form parts of the Laurentia Craton in thePalaeozoic. As in the Arctic area mentioned above, the definition ofthe true Laurentian Craton margin is somewhat arbitrary in manyplaces in the Cordilleran areas from Alaska to Mexico because oftectonic events. In particular, the Late Devonian Antler Orogeny thrustmuch of the erstwhile miogeocline and shelf deposits eastwards on tothe present craton, which is why we show the craton as apparentlyextending into the ocean in our Cambrian to Silurian maps. Inaddition, Early Tertiary strike–slip faulting which runs from the SevierThrust belt of California northwards through the Tintina Fault rightup to the Arctic Ocean margin near the boundary between Alaskaand Yukon, has displaced a sizeable sector of the craton, termedthe Parautochthon, and the gap between that and the cratonis represented by the yellow shading on our terrane maps, forexample Fig. 5. However, there is a distinction between basin andplatform facies through much of the Cordilleran region; for example,Pyle and Barnes (2003) documented an Early Ordovician to EarlySilurian platform-to-basin sequence and their included conodontsin NE British Columbia, which defines the craton margin there, asdid Cook and Taylor (1977) in the Late Cambrian to Early Ordovicianmargin in Nevada. Most of today's Cordilleran margin was largelypassive during the Palaeozoic, but not without tension, and thereare several basins and platforms on the so-called ‘miogeocline’.For example, the Selwyn Basin, largely in Yukon, represents acontinental rift that was episodically reactivated from the Cambrianto the Devonian, with associated largely alkaline volcanics. There area variety of igneous rocks preserved within the craton nearits Cordilleran margin, and the Okanagan High between themiogeocline and the continental slope was probably a ribbon ofhighlands for much of the late Neoproterozoic to the end of theLower Palaeozoic (Thompson et al., in Colpron and Nelson, 2006). TheNeoproterozoic to Devonian potassic alkali volcanics of Canadawere reviewed by Goodfellow et al. (1995), and their records areplotted on our Cambrian to Devonian palaeogeographical maps: theywere extruded, mostly as diatremes, in shallow-marine extensionalbasins.

Throughout the Palaeozoic, the cratonic core of Laurentia consistedof the same amalgamation of Precambrian terranes that had built up instages during the Proterozoic and before, but surrounding that corethere are numerous and mostly smaller terranes and other structurallydistinct units, and these are now reviewed in turn (Sections 6 to 9).

6. Mexico and Central America

In today's south of Laurentia, adjacent to the Ouachita Suture,there are a variety of terranes making up the southernmost UnitedStates, Mexico and Central America. Their definitions and Palaeozoichistory are very complex and somewhat controversial. Keppie (e.g.,2004) has, in substantial reviews, redefined the many terranes in theregion, and we largely follow Keppie's groupings in the brief summaryhere. Most of Mexico and adjacent parts of Central America consists ofa large number of tectonised fragments representing many disparateterranes all of which formed parts of peri-Gondwana in the LowerPalaeozoic until after the Laurussian–Gondwanan amalgamation inthe Carboniferous, apart from the Caborca Block, which originallyformed part of the Laurentian Craton. Keppie et al. (2008) and Nanceet al. (2009) reviewed the accretionary history of the various terranesto Laurussia in the Late Palaeozoic. Most of the area was later covered



byMesozoic to Recent rocks and thus the Palaeozoic record is laterallydiscontinuous and the palaeogeography shown on our maps isextremely tentative.

Ortega-Gutiérrez et al. (1999) concluded that the AcatecanOrogeny of Late Ordovician and Silurian age seen within the AcatlánComplex of south Mexico formed part of the accretion of that terraneto Laurentia as part of the closure of the Iapetus Ocean. However, sincethat area lies to the south of the indisputably peri-Gondwananterranes of the bulk of Mexico, this appears unlikely, and we followKeppie's (2004) conclusion that that area was also originally part ofperi-Gondwana, as well as Nance et al. (2009) in their history of therocks within the Acatlán Complex.

6.1. Caborca Block

This area, in Sonora Province in the northwest of Mexico, becamedetached and distorted during the Middle Carboniferous to EarlyPermian Ouachita Orogeny. Once thought to have formed anindependent Caborca Terrane, it is now seen to have been anautochthonous part of Laurentia which was separated from it duringCarboniferous times and then thrust back on to the craton in the LatePermian or Triassic, probably in the same Sonoma Orogeny whichaffected Nevada and California (Dickinson and Lawton, 2001). Thatwas confirmed by the varied Precambrian zircons recovered from theLate Devonian of the laterally attached Mina México foredeep, whichare all of Laurentian origin, as described by Poole et al. (2008), whosework redefined the Early Palaeozoic craton margin of Laurentia there.The Early Devonian brachiopods described by Boucot et al. (2008) arealso typically western Laurussian. Thus we have included the area aspart of the main Laurentian Craton in our reconstructions.

6.2. Sierra Madre and Cortez terranes

The Cortez (or Cortes) Terrane lies at the west end of the OuachitaFront. There Late Ordovician quartzites, carbonates and cherts areoverlain byDevonian, Carboniferous and Permian psammitic and peliticrocks, all of which are overstepped by Late Jurassic to Cretaceousmagmatic arc rockswhich becamepart of western North America in theTertiary Laramide Orogeny (Sánchez-Zavala et al., 1999). To the E of theCortez Terrane, the SierraMadre Terrane (including the TampicoBlock),reviewed by Keppie (2004), consists of a metamorphosed basement ofuncertain age overlain by Silurian (Wenlock) sediments themselvesunconformably overlain by Triassic and later rocks. The two terranes aretogether marked SM on our maps, and their Palaeozoic positions arepoorly constrained.

6.3. Mixteca and Oaxaquia terrranes

These terranes have together been termed parts of the MiddleAmerican Continent by Keppie (2004). They both have Proterozoicbasements overlainbyPalaeozoic rocks and fringed theAmazonia sectorofGondwana fromthe lateNeoproterozoic until theCarboniferous: bothareas show great similarities in their Precambrian zircon signatures(Nance et al., 2009). Faunal interchange between Laurentia and theOaxaquia Terrane started in the Early Carboniferous, and deformationassociated with Laurentian–Gondwanan collision took place in the LateCarboniferous (Keppie et al., 2008). Possibly associated with theOaxaquia Terrane in the Lower Palaeozoic and certainly by theCarboniferous is the adjacentMixteca Terrane, also reviewed by Keppie(2004), which has Ordovician granites and associated rifted tholeiites.The two terranes are together marked MO on our maps.

6.4. Yucatan Terrane

The Yucatan (or Maya) Terrane is a fragmented area, probablycomposite and much masked by Mesozoic to Recent rocks, on the

southeast coast of the Gulf of Mexico and the Yucatan Peninsula(including the Chiapas Block). It is adjacent to the Chortis terrane toits north, and the geology was reviewed by Dickinson and Lawton(2001), who concluded that it was displaced southwards during theJurassic in the formation of the Gulf of Mexico. There are Neoproter-ozoic metamorphic rocks and Late Carboniferous to Middle Permianshelf clastics, carbonates and metavolcanics which were probablydeposited on an earlier island arc fringing Gondwana (Keppie, 2004).

6.5. Chortis and Tarahumara terranes

In southern Mexico, Belize, Honduras and Guatemala, Palaeozoicoutcrops are very sporadic, and may represent several terranes;nevertheless they are grouped together here as the Chortis Terrane.There are Proterozoic basement fragments, a Late Silurian (418 Ma)granite in Belize, and Late Carboniferous and Permian clastics andcarbonates unconformably overlain by Jurassic rocks. Dickinson andLawton (2001) concluded that it was ‘nuclear South America’.However, since it was severely displaced in the assembly of Pangea,it is omitted from our pre-Carboniferous maps. The TarahumaraTerrane in northernMexico lies just to the south of the Ouachita Front.It was also reviewed by Keppie (2004), and consists of poorly datedbasinal facies which were deformed and metamorphosed in thePermian before being unconformably overlain by Late Jurassic rocks. Itis uncertain whether those earlier rocks were adjacent to Laurentia orMiddle America in the Palaeozoic (Sedlock et al., 1993). It is omittedfrom our reconstructions.

7. Cordilleran and northeastern Siberian units

Between today's west of the Laurentian craton and the continent–ocean boundary with the Pacific, a large area was accreted to NorthAmerica in the Mesozoic and afterwards, but many of the Palaeozoicrocks were originally exotic to Laurentia. Over fifty separate terraneshave been identified within the Cordillera (Fig. 1), of which more thantwenty contain Palaeozoic rocks; however, some terranes which areseparate todaymayhave been originally united. The Cordillera reflects amixture of largely extensional tectonics in the Palaeozoic, followed byincreasingly compressional subduction-related tectonics during theLate Permian, Mesozoic and Early Tertiary. Because of the intensetectonic activity in Mesozoic and later times, many of the terranes aremade up of disconnected slivers, some of which may have originallyrepresented separate terranes; and thus the true identities of Palaeozoicterranes and their boundaries are often hard to decipher, making theterrane definitions and our reconstructions somewhat artificial.

The area was described in the DNAG volumes edited by Grantz et al.(1990), Gabrielse and Yorath (1992), and Plafker and Berg (1994), butthere has been substantial subsequent research, much of it publishedwithin the volumes edited by Haggart et al. (2006), Colpron and Nelson(2006) and Blodgett and Stanley (2008). A listing of the terranes in thewhole northern Pacific margin and their Phanerozoic history andevolution was given by Nokleberg et al. (2000), and the area was alsosummarised by Dickinson (2009) and its Palaeozoic history by Colpronand Nelson (2009). The Cordilleran terranes which include Palaeozoicrocks are divided here into, firstly, terranes originally associated withLaurentia (with a subdivision between parautochthonous and peri-Laurentianunits); secondly, terranes of continental origin, but originallyexotic to Laurentia; and, thirdly, terraneswhichoriginated inoceans andwhich were also originally exotic to Laurentia.

7.1. Terranes original to Laurentia

These are terranes that had their originswithin or at themargins ofthe old Laurentian Continent, as determined both by their containedfaunas and also by the Precambrian detrital zircons present inmany ofthem, which correlate best with those also to be found within the



Laurentian Craton. However, we do not think that the correlation ofsediments and facies between terranes, as undertaken by someauthors, is usually viable, since similar facies were often originallydeposited in quite separate times and places.

7.1.1. Porcupine and Livengood areasAs well as the specific terranes listed below, there are several

tectonically-affected areas which were also originally part of thecraton and are now adjacent to it, such as the so-called PorcupineTerrane of east-central Alaska, which includes the very distinctive andlarge Early Ordovician gastropod Palliseria amongst other typicallyLaurentian Province fossils; and we have simply incorporated thoseareas within the Laurentian Craton and its Parautochthon in ourmaps.The Livengood–Selwyn Basin area, lying within the White Mountainsarea of the Yukon-Tanana Upland, is highly complex, consisting ofeleven structurally separated belts, reviewed by Dover (in Plafker andBerg, 1994). Cambrian, Ordovician, Silurian, Devonian and Permianrocks have all been identified, both shallower and deeper-water inorigin, as well as Ordovician volcanics. Some contain typicallyLaurentian Province Ordovician brachiopods.

7.1.2. Yukon-Tanana TerraneThis composite terrane in east-central Alaska and southern Yukon

includes largely metamorphosed Palaeozoic continental and islandarc rocks including some Devonian fossils from carbonates. Thegeology was reviewed by Dusel-Bacon et al. (in Colpron and Nelson,2006). Arc magmatism was strong in Late Devonian to EarlyCarboniferous times (365–345 Ma), together with the intrusion oflarge calc-alkaline plutons; and Devonian metavolcanics have beendated from 387 to 370 Ma. There was Early Carboniferous metamor-phism (Devine et al., in Colpron and Nelson, 2006) and also Middle toLate Permian (260 Ma) felsic magmatism and plutons. Most authorsconsider that this terrane was linked to the Kootenay Terrane,although Foster et al. (in Plafker and Berg, 1994) considered that thearea may have been linked to peri-Siberia rather than Laurentia in thePalaeozoic. However, we prefer the analysis summarised by Colpronand Nelson (2009), which placed the terrane near the westernLaurentian margin (Figs. 18 and 20) in the Palaeozoic (apart frombetween latest Devonian to mid-Permian times, when it lay to thewest of the Slide Mountain Ocean); not least because some of thecontained Proterozoic zircons match well with those from Laurentia.The terrane arrived near its present position during the Triassic,although there was a 450 km displacement along the Tintina Fault toits east during the Eocene (Murphy et al., in Colpron and Nelson,2006).

7.1.3. Slide Mountain and Kootenay terranesThe Kootenay Terrane of southern British Columbia and Washing-

ton State includes Lower Cambrian carbonates with archaeocyathids,and clastics all overlying Neoproterozoic rocks which are similar tothose in the nearby Laurentian Craton, and probably represents thecraton margin. The Lower Palaeozoic rocks host massive sulphidebodies which probably arose through fluids venting along seafloorgrowth faults (Nelson and Colpron, 2007). Isaacson (in Blodgett andStanley, 2008) has identified and illustrated Late Devonian (Frasnian)brachiopods fromWashington State which indicate that the KootenayTerrane was then undoubtedly peri-Laurussian. There are alsoCarboniferous limestones and clastics in the Milford Group, whichpasses westward laterally into a more clastic sequence which includesminor tholeiitic lavas (Gordey et al., in Gabrielse and Yorath, 1992).There are substantial Late Devonian and Visean arc volcanics andcoeval calc-alkaline granites, and Gabrielse and Yorath (1992)concluded that by the Carboniferous the terrane was linked to theLaurussian Craton. The nearby SlideMountain Terrane, whose geologywas summarised by Dusel-Bacon et al. (in Colpron and Nelson, 2006),consists of at least three separate allochthons (not all of which were

necessarily originally parts of the same terrane); and contains amixture of ocean-floor volcanics and sediments which are mostlydeepwater cherts, shales and turbidites of Early Carboniferous toMiddle Permian in age, some including Permian foraminifera. Theterrane probably represents the remains of a marginal rift basin thatonce lay beside Laurentia, together with a belt of rifted peri-cratonicfragments which formed the cores of various Devonian and later arcs.There is a Permian (288 Ma) tonalite intrusion. Some fault-boundedslices (the Sylvester Allochthon) of the Slide Mountain Terrane are inthe Cassiar Mountains (although not in the Cassiar Terrane). The SlideMountain and Kootenay terranes have closely comparable EarlyCarboniferous sequences which mark the boundary of the SlideMountain Ocean, that began to open in the latest Devonian andreached its maximum breadth in the Early Permian (Nokleberg et al.,2000; Colpron and Nelson, 2006).

7.1.4. Cassiar TerraneFritz et al. (in Gabrielse and Yorath, 1992), have reviewed this

terrane in British Columbia, which consists of an area with LateCambrian and Early Ordovician island arc volcanics and clastics andthin carbonates. Orchard (in Gabrielse and Yorath, 1992) summarisedthe Ordovician conodonts found there, which are of Laurentianaffinity. These are overlain by more extensive Late Ordovician andLower Silurian carbonates (the Sandpile Group), and there are alsobasin deposits with Ordovician shales overlain by Llandovery andWenlock siltstones and shales, all disconformably overlain bydolostones and shales of probable Early Devonian age. These arethemselves overlain by Middle Devonian arc volcanics and carbonateswhich have yielded the brachiopod Stringocephalus, and are followedby more massive Frasnian limestones. Above them is a sequenceranging from Late Devonian to Triassic in age, and the whole terrane,although displaced some 450 km northwards along the Tintina Fault(Gabrielse et al., in Gabrielse and Yorath, 1992), appears to have beenpart of the Laurentian Craton during the Palaeozoic.

7.2. Peri-Laurentian terranes

Although the rocks of the Eastern Klamath and associated terraneshave Lower Palaeozoic faunas of Laurentian affinity, the opening ofthe Slide Mountain Ocean in the latest Devonian or earliestCarboniferous divided Stikinia, Quesnellia, Eastern Klamath, NorthSierra and other terranes from the main Laurussian Craton, and thatocean did not close until about the very end of the Palaeozoic(Nokleberg et al., 2000; Colpron et al., 2007).

7.2.1. Roberts Mountain and Golconda allochthonsDickinson (2000) has summarised the units seen in Nevada and

adjacent California in which rocks are oriented northeast–southwestat high angles with respect to the Mesozoic and later Cordilleranmargin. These are termed the Roberts Mountains Allochthon, whichconsist of fault-bounded packets of largely oceanic and island arcrocks imbricated into a tectonic wedge which was thrust on to theLaurentian Craton in the Late Devonian to Early Carboniferous AntlerOrogeny, and whose stratigraphy was reviewed by Wright and Wyld(2006). It contains largely deeper-water deposits from MiddleCambrian to Earliest Carboniferous in age, with a variety of clasticand volcanic rocks which were probably deposited near the cratonmargin. The contained zircons are of Laurentian affinity (Gehrels et al.,in Soreghan and Gehrels, 2000). The shallower-water Silurian andDevonian faunas of the Roberts Mountains are well known (e.g.Johnson and Prendergast, 1981). Widespread and thin-bedded largelyOrdovician rocks, termed the Vinini Formation in the east and theValmy and Parmett Formations in the west of the area, are apparentlydeep-water in origin, but appear to have been cryptically imbricatedduring later orogenensis. The Vinini includes Ordovician limestoneclasts with typically Laurentian fossils presumably derived from the



craton. The Roberts Mountain Allochthon is unconformably overlainby Late Carboniferous to Permian shelf deposits.

The Golconda Allochthon lies adjacent to the western edge of theRobertsMountainsAllochthon, and consists of highly-imbricated clastic,carbonate and volcanic rocks of the Late Devonian (Famennian) andCarboniferous Havallah sequence, some of which overlies parts of theRoberts Mountain Allochthon. The zircons are also of Laurentianderivation (Riley et al., in Soreghan and Gehrels, 2000). Associatedturbidites were deposited until the end of the Carboniferous. TheGolconda Allochthon was emplaced onto the Roberts Mountains sectorof the Pangea Craton during the Permian to Triassic Sonoma Orogeny.

7.2.2. Eastern Klamath, Yreka, Trinity and adjacent terranesWithin these largely Californian units is the composite Eastern

Klamath Terrane, inwhich the Yreka, Trinity, Fort Jones, North Fork, andForest Mountain units have also been recognised, and each of which aresometimes termed terranes. Deformed Cambrian to Devonian rocks inthe Klamath and northern Sierra Nevada ranges, including island arcassemblages and ophiolites, indicate southeastern vergence within anaccretionary prism. Fossil assemblages, particularly brachiopods, havebeen extensively described from the Ordovician of the Klamath area, forexample by Potter et al. (1990a); and also from the Middle Devonian(e.g. Savage and Boucot, 1978), all indicating that they were peri-Laurentian in those times.However, theywere separated fromLaurussiain the Late Palaeozoic by the SlideMountainOcean (Colpron andNelson,2009). Watkins (1999), whilst describing Visean, Bashkirian andWolfcampian biostromes in the Eastern Klamath Terrane, was able todocument that there were island arcs still active in that area duringCarboniferous and Permian times, and those were also reviewed byDickinson (2000).

Pre-Devonian tectonised basement rocks in the eastern KlamathMountains of California and Nevada, and adjacent to the Eastern KlamathTerrane, form the Ediacaran and probably Cambro-Ordovician ophiolitecomplex of the Trinity Terrane, which is cut by post-tectonic Ordovician,Silurian, and Devonian plutons as summarised by Dickinson (2000). Themuch-tectonised slivers of the Yreka Terrane, which includes rocks as oldas Neoproterozoic andwhich is thrust over the Trinity Terrane, have beeninterpreted as a forearc/trench complex related to mid-Palaeozoicsubduction (Lindsley-Griffin et al., in Blodgett and Stanley, 2008). Mostauthors have concluded that the Yreka and Trinity terranes wereamalgamated to each other in the latest Silurian or earliest Devonian.Although Wright and Wyld (2006) considered that the relationships ofthese terranes with the Eastern Klamath Terrane remain uncertain, wefollow Potter et al. (1990a), who considered them all to be closely relatedbecause of their similar and distinctive essentially Laurentian Ordovicianfaunas. In addition, the Devonian brachiopods in the Gregg RangeComplex are similar to those in Nevada, i.e. peri-Laurentian. Lindsley-Griffin et al. (in Blodgett and Stanley, 2008) concluded that what theytermed the Eastern Klamath Superterrane (in which they included theYreka and Trinity Subterranes) was well away from Laurentia/Laurussiauntil its merger with it (by then North America) during the Cretaceous;but we endorse the earlier interpretation of the faunas (Potter et al.,1990a,b) as clearly indicating that Eastern Klamath was peri-Laurentianfrom at least Early Ordovician times onwards, and that conclusion issupported by analysis of the contained zircons (Gehrels and Miller, inSoreghan and Gehrels, 2000).

7.2.3. North Sierra and Black Rock terranesThe geology of this area in Nevada and California, reviewed byWright

and Wyld (2006) and Colpron and Nelson (2009), includes themetamorphosed Lower Palaeozoic Shoo Fly Complex, which consistsof at least four separate allochthons including some clastic rocks,calcalkaline basalts and ophiolites, and which were probably developedin an accretionary wedge associated with an easterly-dipping subductionzone. They wedge contains fragments varying from Neoproterozoic toLate Ordovician in age, and their included zircons were derived from

Laurentia (Harding et al., in Soreghan and Gehrels, 2000). All thoserocks are unconformably overlain by unmetamorphosed LateDevonian toPermianarc-relatedrocksand intrudedby378–364MaDevonianplutons.The terrane had arrived near its present position at the Laurentianmarginby Early Carboniferous times, although it was subsequently separatedfrom the craton by the SlideMountainOcean (Colpron andNelson, 2009).Potter et al. (1990b) listed the varied late Ordovician faunas from theSierra City Mélange within the Shoo Fly, whose key components arebrachiopods and sponges. They are essentially peri-Laurentian, but alsoinclude some endemic species occurring only in the Shoo Fly and theYreka Terrane, which is why we consider the whole North Sierra Terraneas a single unit here, in contrast to the palaeogeographical conclusions ofWright andWyld (2006). The adjacent Black Rock Terrane of Nevada (notindicated separately on ourmaps) includes Late Devonian to Permian andlater rocks, whose base is an amphibolitewhich is followed by limestonesandclastics including theMid-CarboniferousBuckarooTuff. Thecontainedzircons again indicate Laurentian derivation (Darby et al., in Soreghan andGehrels, 2000).

7.2.4. Quesnel TerraneThe Quesnel Terrane, sometimes termed Quesnellia, extends from

the north of Washington State into the south of British Columbia, andinto the Yukon. It separates the Cache Creek and Slide Mountainterranes, and its geology was reviewed by Beatty et al. (in Colpron andNelson, 2006). Within it there are the essentially island arc HarperRanch Subterrane and the largely ocean-floor Okanagan Subterrane.There are Latest Devonian to Permian rocks, largely clastics but withcarbonate interbeds in which faunas occur, including brachiopods,corals, trilobites, foraminifera and ammonoids, which are best knownfrom the Permian strata. Chert breccias include Ordovician microfossilswith few palaeogeographical signals. Volcaniclastic rocks and basaltsalso occur, including Latest Devonian and Carboniferous pillow basaltsand orthogneisses, all rocks representing an island arc. It was linked tothe Yukon-Tanana Terrane from Carboniferous times onwards, andwaswith it at the western margin of the Permo-Carboniferous SlideMountain Ocean. However, although Thompson et al. (2006) debatedwhether some or all of the terrane was truly separate from Laurentia inthePalaeozoic, Colpron andNelson (2009) concluded that, becauseof itsprimitive geochemical and isotopic characters, at least the oceanicOkanaganSubterranewasnot linked to any continent inDevonian times(at around 370 Ma), and was thus then distinct from Laurentia, eventhough the northerly Harper Ranch Subterrane had more advancedgeochemical characters and may therefore have been more closelyrelated to thewestern sector of Laurussia. The Quesnel Terrane accretedto North America during the Late Triassic or Jurassic.

7.2.5. Stikinia TerraneThe Stikine or Stikinia Terrane of central British Columbia includes

Devonian carbonate rocks, Carboniferous arc-type volcanics andassociated sedimentary rocks including carbonates with foraminiferaand macroinvertebrates reviewed by Monger et al. (in Gabrielse andYorath, 1992). Orchard (in Gabrielse and Yorath, 1992) summarised theDevonian conodonts found. There are also Lower Permiandeeper-waterclastics, and Lower and Upper Permian platform limestones (Gehrelsand Berg, in Plafker and Berg, 1994), including a thick Permianlimestone deposited upon tholeiitic metabasalts. Like the QuesnelTerrane, it was not accreted to North America until the Jurassic, but wasprobably not far from it in the Palaeozoic, apart from its Late Palaeozoicpositioning on the west side of the opening and closing Slide MountainOcean (Nelson and Colpron, 2007), a conclusion supported by theanalysis of the diverse mid-Carboniferous shelly faunas, particularlycorals, undertaken by Gunning et al. (2006).

7.2.6. Ruby and Innoko terranesThe Ruby Terrane in central Alaska (Fig. 1) consists entirely of

possibly Precambrian and certainly Palaeozoic metamorphic



sedimentary and volcanic rocks, reviewedbyPatton et al. (in Plafker andBerg, 1994),whoalso linked itwith the adjacentDevonian toCretaceousInnokoTerrane,whichhasmany tectonised rocks of similar ages.MiddleOrdovicianandMiddleDevonian conodonts are known fromthe area, aswell as Devonian volcanic arc rocks and granite gneiss. The Palaeozoicfaunal affinities and geographical positions are uncertain and thereforethese two relatively small areas are neither mentioned further in thisreview nor shown on our palaeogeographical maps. Although Nokle-berg et al. (2000) considered the Ruby and Innoko units to have formedpart of the Laurentian Craton during the Palaeozoic; most authors,reviewed by Sunderlin (in Blodgett and Stanley, 2008), consider therocksmore likely to have been laid down in ocean basins and island arcsoff the margin of Laurentia.

7.3. Terranes originally exotic to Laurentia

Although the great majority of today's modern Siberia formedparts of the Siberian (including peri-Siberian) continent during thePalaeozoic (as reviewed by Cocks and Torsvik, 2007), a substantialportion of northeast Siberia today forms part of the North AmericanPlate (Fig. 1). The tectonic units there and also in the Cordillera weredocumented by Nokleberg et al. (2000) within a wider survey of thewhole North Pacific rim. It has become clear that many of theseterranes originated elsewhere than in Laurentia/Laurussia at varioustimes in the Palaeozoic, and they are discussed further in Section 19.

7.3.1. Farewell Terrane (including the Mystic, Dillinger and Nixon Forksubterranes)

The Farewell Terrane in south-central Alaska (Fig. 1) is composite,and parts are variously termed the Nixon Fork, Dillinger and Mysticterranes or subterranes. Some authors, for example Patton et al. (inPlafker and Berg, 1994), thought theNixon Fork to be a separate terrane;however, most have concluded that the Nixon Fork Subterranerepresents a predominantly shallow-water carbonate platform whichis probably the lateral equivalent of the deeper-water rocks of theDillinger Subterrane, together with the adjacent Minchumina Terrane.The Farewell Terrane has a Neoproterozoic basement above which arePalaeozoic fragments representing a continental platform, reviewed byBradley et al. (2003). Palmer et al. (1985) recorded Middle Cambriantrilobites from the Taylor Mountains of the Nixon Fork area, and St Johnand Babcock (1997) described and analysed another Middle Cambriantrilobite fauna from the White Mountain area. Blodgett (1998) andBlodgett et al. (2002) documented and reviewed Late Ordovicianbrachiopods including Tcherskidium; Rigby et al. (1994) distinctiveLate Silurian aphrosalpingid sphinctozoan sponges in stromatoliticlimestones; Frýda and Blodgett (in Blodgett and Stanley, 2008) EarlyDevonian (Emsian) gastropods; Blodgett and Boucot (1999) Devonian(Emsian) brachiopods; and Johnson and Blodgett (1993) corals andEifelian brachiopods. The Dillinger Subterrane includes Neoproterozoicpericratonic rockswith ophiolites, Ordovician calcareous turbidites withincluded graptolitic shales, Early Silurian laminated limestones withgraptolite shales, and Late Silurian sandstone turbidites and shales, aswell as Late Silurian andEarlyDevonian clastic and carbonate sediments,all of which are much tectonised. The Mystic Subterrane, overlies boththe Dillinger and Nixon Fork subterranes, and has also yielded Emsianbrachiopods (Blodgett, 1998; Blodgett and Boucot, 1999). There areextensiveUppermost Devonian to Early Carboniferous radiolarian chertsand Early Permian greywackes, The Early Permian (about 285 Ma)Browns Fork Orogeny deformed and metamorphosed much of theterrane and led to the deposition of a clastic wedge including rocks ofterrigenous origin (Bradley et al., 2003), and Mamay and Reed (1984)identified Lower Permian plants from the Mount Dall Conglomeratewithin that wedge. The Farewell Terrane is shown on ourmaps from theEarly Silurian (Fig. 12) onwards. It accreted to North America at the endof the Jurassic, and is discussed further in Section 19.2.

7.3.2. Arctic Alaska TerraneThis is a large composite terranewhichmakes up the northern part

of Alaska and adjacent northwest Canada (Fig. 1), and consists ofNeoproterozoic to Jurassic strata, reviewed by Moore et al. (in Plafkerand Berg, 1994), Dumoulin et al. (2002), and Nelson and Colpron(2007). It is made up of the Coldfoot, De Long Mountains, EndicottMountains, Hammond, North Slope, and Slate Creek subterranes.

The Coldfoot Subterrane includes the Ambler sequence, whichrepresents an Upper Devonian (386–378 Ma) island arc intruded by co-magmatic plutons. The De Long Mountains Subterrane has poorly-preserved Devonian (Eifelian and Givetian) brachiopods and better-preserved Early Carboniferous plants, all reviewed in Blodgett et al.(2002). The EndicottMountains Subterrane comprises a large (900 km)allochthon starting with a regressive Upper Devonian sequence ofmetamorphosed sedimentary rocks including Frasnian megafossils.These are followedby the thickEndicott and LisburneGroups, consistingof a Late Devonian (Frasnian) to Early Carboniferous (Late EarlyMississippian)marine sequence overlain by a fluvial-dominated deltaicclastic wedge, including redbeds, and a Middle to Late Carboniferouscarbonate platform representing a passive margin, to the southwest ofwhich lay a starved basin. From the fluvial deposits Early Carboniferouslepidodendrid plants are known (Spicer and Thomas, 1987). Substantialgranites are probably of Late Devonian age. The Hammond Subterranelies in the western and central parts of the Brooks Range and includes abasement with Neoproterozoic and possibly Earliest Cambrian (970–540 Ma)metamorphosed rocks. Dumoulin and Harris (1994) describedthe Cambrian to Devonian sequences and the Cambrian and Ordovicianconodont faunas. There are Middle Cambrian phyllites with trilobites(Palmer et al., 1984), and Early Ordovician (Arenig) to Lower Silurianclastics and carbonates with conodonts. Blodgett et al. (2002) reviewedLate Ordovician brachiopods, including the type species of the largepentamerid Tcherskidium, T. unicum. There are also Middle to UpperDevonian rockswith brachiopods and Lower Carboniferousmetaclasticsand carbonates with plants. The terrane is intruded by several granitesvarying from Middle Devonian (402Ma: Emsian) to Late Devonian(366Ma: Famennian) in age (Moore et al., in Plafker and Berg, 1994).

The North Slope Subterrane outcrops in the northeastern BrooksRange and extends westwards in the subsurface (Dumoulin et al.,2002, Fig. 2). It has a Precambrian and Lower Palaeozoic basementoverlain by Early Carboniferous conglomerates and later carbonates.There are Early and Late Cambrian trilobites (A.R. Palmer, in Dutro etal., 1972), and Late Ordovician brachiopods include Tcherskidium(Blodgett et al., 2002). The area was affected by the RomanzofOrogeny in the Devonian, and the emplacement of some post-orogenic granite plutons has been dated at from 375 to 362 Ma, whichis Late Devonian (Famennian). The Arctic Alaska Terrane is boundedto its south by the Cretaceous Kobuk Suture (Miller et al., 2006), butopinions on its Palaeozoic history and position differ, and arediscussed further in Section 19.

7.3.3. Seward and York terranesThese terranes are situated on both sides of the Bering Straits in the

Chukotka Peninsula of Siberia and the Seward Peninsula of Alaska, asdescribed by Churkin (1972), and we also include here St. LawrenceIsland, all reviewed by Till andDumoulin (in Plafker andBerg, 1994). TheSeward Terrane consists largely of deformed fragments of continentalorigin, some as old as Neoproterozoic, but including Ordovicianconodonts as well as Middle Devonian and Early Carboniferous arcrocks which were all metamorphosed in end Permian times. St.Lawrence Island has thick Devonian and Lower Carboniferous shallow-water carbonates unconformably overlain by a condensed Triassicsequence, faulted against adjacent Permian and later deformed deeper-water rocks. The Seward Terrane can be groupedwith the adjacent YorkTerrane, which has an Early Cambrian (539 Ma) gabbro (Amato et al.,2009) and largely shallow-water Palaeozoic rocks, from which Blodgettet al. (2002) have reviewed Early Ordovician trilobites, Late Ordovician



brachiopods, corals and gastropods, and Early Devonian (Emsian)brachiopods and corals. Of particular note is the Early Ordoviciantrilobite Monorakos, recorded by Ormiston and Ross (1976). Theseterranes are also discussed in Section 19.

7.3.4. Chukotka Terrane (including Wrangel Island)Forming the northeasternmost part of Siberia (Fig. 1) and the

western margin of the Bering Straits, the Chukotka Peninsularcontains the important Chegitun River area described by Natalin etal. (1999) and reviewed by Dumoulin et al. (2002). AMesoproterozoic(1.9 to 1.6 Ga) and Neoproterozoic (650–550 Ma) basement isoverlain by Ordovician to Lower Carboniferous rocks, which haveyielded the Early Ordovician trilobite Monorakos (Ormiston and Ross,1976), Middle to Late Ordovician brachiopods, Middle Siluriangraptolites and Late Silurian to Early Devonian metacarbonates.Some of the faunas were reviewed by Oradovskaya and Obut(1977). Wrangel Island lies in the Arctic Ocean to the north of theChukotka Peninsula, and Late Silurian (Ludlow) and Upper Palaeozoicshallow-water marine rocks unconformably overlie the Late Protero-zoic Wrangel Complex (Kosko et al., 1990, 1993). These arecomparable to strata in the Chukotka Peninsula, and we link thetwo areas in our reconstructions. There are also Late Devonian andEarly Carboniferous volcanics. During the Permian the sedimentationchanged from shallow-water to basinal. The Palaeozoic positions ofChukotka and Wrangel Island are discussed in Section 19. Chukotkahad arrived in its current position by the Cretaceous, which is whenthe South Anyui Suture Zone stitched it to the Omolon and other peri-Siberian terranes to its south (Miller et al., 2006).

7.3.5. New Siberian IslandsTo the east of the Laptev Sea, the New Siberian Islands (NSI on Fig. 1)

is an archipelago whose geology was reviewed by Kosko et al. (1990)and Kuzmichev and Pease (2007). Many contain only Mesozoic toRecent rocks, but some have Palaeozoic outcrops. The biggest is KotelnyIsland, which has a largely complete Cambrian to Devonian succession,including a substantial EarlyOrdovician toDevonian carbonateplatformwith shallow-water faunas which include the Early Ordovician trilobiteMonorakos (Ormiston and Ross, 1976), brachiopods and conodonts (asreviewed by Dumoulin et al., 2002); as well as Early Silurianbrachiopods and deeper-water deposits with graptolites. These areoverlain by Carboniferous and Permian clastics and carbonates, somewith shelly fauna. The adjacent Belkov Island has a Devonian (Frasnian)to Carboniferous (Serpukhovian) succession yielding ammonoids andother fauna (Nikolaeva et al., 2009), as well as the latest Permianvolcanics of the Siberian Traps analysed by Kuzmichev and Pease(2007). Bolshoi Lyakhov Island has Neoproterozoic (Rhiphean) meta-volcanic rocks as inlierswithin PermianandMesozoic fold belts. BennettIsland has fragmented Cambrian clastics, which have yielded theimportant Middle Cambrian trilobite fauna monographed by Holmand Westergaard (1930), overlain by a 1200 m thick Ordoviciansuccession consisting mainly of turbidites, interbedded with Tremado-cian to Darriwilian graptolitic shales. Henrietta Island has tectonisedclastics and volcanics of probable Carboniferous age. The affinities ofthese faunas and the Palaeozoic palaeogeography of the New SiberianIslands are discussed in Section 19.

7.3.6. Kolyma and Omolon terranesTo the east of the Verkhoyansk Mountains, which overlie the

western boundary of the North American Plate today, and to the southof the Chukotka Terrane, lie the Kolyma and Omolon areas (K–O inFig. 1), which include the Okhotsk and Omolon Massifs within whichseveral terranes have been identified. Only the westernmost Omu-levka Terrane contains a continuous Lower Ordovician to MiddleDevonian (Givetian) sequence overlying a Late Proterozoic to MiddleCambrian basement, reviewed in Dumoulin et al. (2002). Someauthors, including Sengor and Natalin (1996, Fig. 21.40) have plotted

the area within what we term the peri-Siberian Terrane Assemblage(Cocks and Torsvik, 2007, p. 48). However, an Omolon Terraneseparate from Siberia is shown on the Permian reconstructions ofZiegler et al. (e.g. 1997), following Zonenshain et al. (1990, p. 127).Parfenov and Kuzmin (2001) suggested that Kolyma and Omolonwere two separate terranes until they amalgamated in the LateJurassic, and which were in turn welded to the Siberian sector ofLaurasia during the Cretaceous. Ganelin and Biakov (2006) stated thatthe Kolyma Terrane was itself made up of several different units;however, the substantial Permian biostratigraphy they describedindicates that the Kolyma, Omolon and Verkhoyansk areas were allclose enough to each other to be parts of the same well-defined andrelatively small faunal province in the Permian. There are shallow-water marine carbonates on the Omolon Massif itself, offshore towhich were deeper-water clastics, including turbidites, and latePermian volcanics in parts of Omolon and much of Kolyma. Ganelinand Biakov (2006) divided the Permian succession into 18 zoneslargely characterised by brachiopods and bivalves. Thus the Kolymaand Omolon areas did not form parts of peri-Laurentia/Laurussia inthe Palaeozoic, and neither did they then have close ties with theChukotka and Alaskan Cordillera terranes, although they adjoin themtoday. They probably formed a high-latitude independent micro-continent near Siberia, as deduced by Shi (2006) from the Permianbrachiopod zoogeography.

7.4. Terranes of mid-oceanic origin

A few Cordilleran terranes have Palaeozoic faunas of neitherexplicitly Laurentian/Laurussian nor Siberian affinity as well as moresoutherly palaeomagnetically-derived palaeolatitudes. We discussAlexander and Wrangellia in Section 19. The Palaeozoic positions ofthe Angayucham, Goodnews, Cache Creek, Bridge River and Chulitnaterranes are all poorly constrained, and thus we do not show themseparately in our maps.

7.4.1. Alexander TerraneThe composite Alexander Terrane in northwestern British Columbia,

southeast Alaska and southwest Yukon includes the Admiralty(Ordovician to Permian), and Craig (Ordovician to Triassic) subterranes.Nearby is the Wrangellia Terrane of southeast Alaska (see below), andAlexander and Wrangellia are together sometimes termed the InsularSuperterrane. As well asmetamorphic rocks, the Alexander Terrane hasmany relatively unmetamorphosed Palaeozoic rocks up to 10 km thick,which were reviewed by Gehrels and Saleeby (1987), Gehrels and Berg(in Plafker and Berg, 1994) and Wright and Wyld (2006). Above someNeoproterozoic rocks, the terrane includes Middle to Late Cambrian(including carbonates with the brachiopods Billingsella and Ocner-orthis?) to EarlyOrdovicianvolcanic arc rocks, includingvery substantialbasalts, particularly in the Cambrian. Some have oxidised tops,suggesting a subaerial environment (Souther, in Gabrielse and Yorath,1992). There was a pre-Ordovician, probably Cambrian, Wales Orogenyof uncertain cause. Orchard (inGabrielse andYorath, 1992) summarisedthe Ordovician and Devonian conodonts found. Orchard interpreted theOrdovician chert and argillites on Admiralty Island and elsewhere, ashaving formed in a marine basin behind the arc system. There are alsoEarly Silurian island arc volcanics and cogenetic calc-alkaline plutons, aswell asMiddle Silurian to Early Devonianplutons. The arc activity endedin the Middle Silurian to Earliest Devonian Klakas Orogeny, mostprevalent in the southern parts of the terrane, during which there wasmuchmetamorphism. There are Middle Ordovician and Early Devoniangraptolites from deep-water shales (Norford and Mihalynuk, 1994).Blodgett et al. (2010) reviewed the Silurian brachiopods, which includethe pentamerides Brooksina, Kirkidium andHarpidium. In addition, thereare Late Silurian algal build-ups and stromatolitic reefs includingdistinctive aphrosalpingid sphinctozoan sponges brachiopods andgastropods (Soja and Krutikov; Rohr and Blodgett: both in Blodgett



and Stanley, 2008); latest Silurian to Early Devonian terrigenous andshallow-water marine deposits; Early Devonian (Emsian) brachiopodsin shallow-water carbonates (Soja, 1988); Middle Devonian (Eifelian)molluscs, including ammonoids; and Middle to Late Devonian brachio-pods (Savage et al., 1978). There are also Late Carboniferous (309Ma)and Early Permian (290–270 Ma) alkaline to calc-alkaline granitoids.

7.4.2. Wrangellia, Peninsular and Chilliwack terranesWrangellia (not to be confused with Wrangel Island off north-

eastern Siberia) is a complex and composite terrane which stretchesover 2500 km from the Wrangell Mountains of Alaska, down toVancouver Island and beyond in British Columbia. The geology wasreviewed by Gordey et al. (in Gabrielse and Yorath, 1992) and Colpronand Nelson (2009). In Alaska and Yukon the oldest rocks are LateCarboniferous and Permian island arcs, but further south, in BritishColumbia, there are extensive volcanic rocks, including tuffs, pillowlavas, and rhyolites dated at about 370 Ma (Famennian), andsynvolcanic quartz-porphyry and gabbro plutons as old as LateDevonian (Souther, in Gabrielse and Yorath, 1992), all representingisland arcs built on oceanic crust. Nokleberg et al. (2000) recognisedfour separate arcs in Wrangellia. Those Devonian and Carboniferousvolcanic rocks are overlain by Permian carbonates, from which faunasare known, all reviewed by Nokleberg et al. (in Plafker and Berg,1994), including brachiopods, bryozoa and conodonts of EarlyPermian age, some of which are interbedded with the volcanics(Richter, 1976). The Alexander Terrane and Wrangellia were stitchedtogether by a Late Carboniferous pluton (Gardner et al., 1988), andthere are voluminous Late Triassic plume-related ocean plateauterrane basalts analogous to those known from Ontong Java. Togetherwith the Alexander Terrane, it was not accreted to North America untilthe Jurassic or Cretaceous. Colpron and Nelson (2009) place the twoterranes at the westernmost edge of the Slide Mountain Ocean duringthe Late Palaeozoic.

The Peninsular Terrane of southern Alaska consists of possibleCambrian and certain Ordovician to Devonian shales and carbonateswhich unconformably overlie a probably Precambrian metamorphicbasement, and there are Middle Permian limestones. The Palaeozoicparts of the terrane may represent slivers of Wrangellia. Anothersmaller terrane, the Chilliwack River Terrane, which straddles theboundary between British Columbia and Washington State, includesrocks of Late Cambrian to Middle Permian age. Although adjacent tothe peri-Laurentian Quesnel Terrane; after analysis, Monger andStruik (2006) concluded that Chilliwack may have originally formedpart of the Wrangellia Terrane in the Palaeozoic.

7.4.3. Angayucham and Goodnews terranesBoth these terranes in central northwestern Alaska are much

tectonised remnants of oceanic and marginal basins ranging in agefrom the Devonian to the Late Jurassic, and are now integrated withthe Koyukuk, Nyac and Togiak island arcs of Late Jurassic andCretaceous age which accreted to the western Alaskan area in theCretaceous. The Goodnews area includes blocks from Ordovician toPermian in age in a Mesozoic mélange thrust against the DillingerTerrane, reviewed by Decker et al. (in Plafker and Berg, 1994): some ofthe Devonian blocks contain parts of algal mounds which were clearlyof shallow-water marine origin. The Angayucham Terrane, sum-marised by Moore et al. (in Plafker and Berg, 1994), includes faultslivers with sedimentary rocks containing Devonian to Permianfossils, as well as volcanics which have been interpreted as havingbeen exuded on either sea mounts or oceanic island arcs. The TozitnaTerrane is usually included within the Angayucham Terrane. Patton etal. (in Plafker and Berg, 1994) also included the Coldfoot Terrane andSlate Creek units (listed in Section 7.3.2. above as subterranes of theArctic Alaska Terrane) within the same terrane, but they seem morelikely to have been separate from Angayucham in the Palaeozoic. Boththe Angayucham and Goodnews terranes are highly tectonically

disrupted, and their original Palaeozoic positions in relation to eachother are unknown, but there is no clear indication that they wereclose to Laurentia or any other continent in the Lower Palaeozoic, andthey are not shown in our maps.

7.4.4. Cache Creek and Bridge River terranesThe Cache Creek Terrane of southern British Columbia and

southernmost Yukon consists of Early Carboniferous (Latest Visean)to Early Jurassic rocks whose fragments may have subsequentlybecome parts of an accretionary prism outboard of the Slide MountainTerrane. There are small lenses of pillowed volcanic rocks and moresubstantial basalts interbedded with massive Permian limestones, allof oceanic origin and summarised by Monger et al. (in Gabrielse andYorath, 1992). The Cache Creek includes the French Range, Nakina andSentinel Subterranes. An area comparable in age is the neighbouringBridge River Terrane, but that lacks substantial carbonates, and it isuncertain whether or not the two were a single united terrane in theUpper Palaeozoic. There are altered diorites and granites of Permianage. Permian foraminiferans of the family Verbeekinidae found in theCache Creek and adjacent terranes are characteristic of the so-calledTethyan Province, and are virtually unknown from elsewhere in NorthAmerica, but similar to those in eastern Asia (Ross and Ross, 1983).However, since the Palaeozoic positions of both terranes are unknownand might have been far away from Pangea, neither are shown in ourreconstructions.

7.4.5. Chulitna TerraneNokleberg et al. (in Plafker and Berg, 1994) reviewed this terrane,

which consists of a number of thrust slivers which include asubstantial ophiolite of Devonian age, Upper Carboniferous cherts,and Permian limestones, argillite and volcaniclastic rocks, all of whichare different from rocks found elsewhere in Alaska. The area isthought to have originated as a Devonian oceanic island, and becauseof strong similarities between the overlying Early Triassic ammonoidswith those found in California, Nevada and Idaho, it may have lainsomewhere off southwestern Laurussia in the Late Palaeozoic;however, it is not shown in our maps.

8. Summary of Cordilleran and northeastern Siberian units

The Cordilleran terrane areas considered abovewhichwe think areautochthonous or parautochthonous to Laurentia are Porcupine,Livengood, Yukon-Tanana, Slide Mountain, Kootenay and Cassiar. Inaddition, the RobertsMountain and Golconda allochthons, the EasternKlamath Terrane Group (including Yreka and Trinity), North Sierra,Quesnel, Stikinia, Ruby and Innoko Terranes, whilst mostly originatingas island arcs or microcontinents apart from Laurentia, neverthelessremained close enough to the continent to be regarded as peri-Laurentian. However, many of themwere separated from Laurussia inthe Carboniferous by the opening of the Slide Mountain Ocean,although that ocean had closed by the end of the Permian.

In contrast, in the discussion in Section 19 belowwe reviewwhywethink that various terranes combined to form the separate ArcticAlaska–ChukotkaMicrocontinent: thesewere the Arctic Alaska Terrane,the Seward Terrane, the York Terrane, and the Chukotka Terrane(including Wrangel Island), as well as the Arctic Ocean areas ofNorthwind and perhaps Chukchi and Mendeleev. That microcontinent,which had a Proterozoic core, lay somewhere within the substantialocean between Laurentia, Siberia and Baltica at the start of thePalaeozoic, but its (today's) eastern end accreted to northwesternLaurussia in the LateDevonian.However, itwas not until theCretaceous,the age of the Kobuk Suture at the southern margin of the Arctic AlaskaTerrane, that the Arctic Alaska–Chukotka Microcontinent reached itspresent orientation with respect to the North American Craton. TheWrangellia, Alexander, and associated terranes formedanother separatemicrocontinentwhichdidnot amalgamatewithNorthAmerica until the



Jurassic, as did the Farewell Terrane. We also conclude that the NewSiberian Islands formed part of Siberia itself during the Palaeozoic andthat the Kolyma and Omolon Terranes were peri-Siberian.

Despite the assertions of some authors, we do not think that any ofthe Cordilleran terranes originated from (or were close to) Baltica,since the bulk of Laurentia lay between the Cordilleran terranes andBaltica in the Lower Palaeozoic, and the mechanism for tectonictransfer is hard to imagine. In addition, there are no faunas ofdominantly Baltic Lower Palaeozoic affinity in any of them. Further-more, none of the many suspect terranes in North America further tothe west than Pearya in northern Ellesmere Island appear to havebeen directly affected by the major Caledonide Orogeny.

In the Southern Cordillera, including California and Nevada, theLaurentian/Laurussian Craton margin was passive from the LateProterozoic until the Late Devonian Antler Orogeny, inwhich the EasternKlamath and associated terranes were thrust eastwards over the craton.

9. Northern Canada, eastern U.S.A. and European units

9.1. Northern units

There is a large part of the modern North American Plate whichunderlies and adjoins the Arctic Ocean and within which there isvariable evidence of Palaeozoic rocks, but their details and marginsare poorly constrained.

9.1.1. Arctic Ocean fragmentsThe continental shelf north of southeastern Siberia and Alaska is

wide today, and it is probable that Palaeozoic rocks underlie much ofit. Grantz et al. (1998) have recorded Palaeozoic fossils from shallow-water marine carbonates in a core at Northwind Ridge, which lies inthe Amerasia Basin (Fig. 1) north of Alaska at 76° N and 155° W,whose origins they link to the nearby ‘Franklinian’ margin on themainland. Only conodonts have been identified from the LateCambrian and Ordovician parts of the core, and are cosmopolitantaxa. However, from the core Stevens and Ross (1997) described LateCarboniferous foraminifera, which are endemic to Northwind Ridgeand other nearby Arctic rocks. Early Permian bryozoa and brachiopodsare also recorded from higher shallow-water marine carbonates, aswell as more fusulinid foraminifera, and there are Mid-Permianrhyodacite ash falls. On our maps we plot several distinct units: theNorthwind Ridge area, the Chukchi Platform, the Mendeleev Ridge,and the Lomonosov Ridge. However, there are no Palaeozoic data forthe Chukchi Plateau (apart from the interpretive seismic stratigraphyshown by Haimila et al. in Grantz et al., 1990), the Mendeleev Ridge,and the Lomonosov Ridge. Thus the Palaeozoic palaeogeographyshown on our maps for those areas is largely speculative, althoughthere is not much space for manoeuvre in today's Arctic area, as can beseen from our end Palaeozoic map (Fig. 26).

9.1.2. Pearya TerraneAlthough ‘Pearya’ was coined by Schuchert (1923) for a shadowy

Precambrian continent lying under the Arctic Ocean to the north ofthe ‘Franklinian Geosyncline’, the concept was completely redefinedby Trettin (1987), who we follow. Pearya comprises the northernsides of Ellesmere and Axel Heiberg Islands and the adjacent shelf, andis a composite terrane juxtaposed against the Laurentian craton: itsgeology was described by Trettin (1987, 1991, 1998) and reviewed inwider contexts by Gee and Trebenkov (2005) and Colpron and Nelson(2009). Middle Proterozoic metamorphosed rocks are unconformablyoverlain by Late Proterozoic to Middle Ordovician metasediments andarc volcanics, together with Ordovician (approximately 480 to460 Ma) granite plutons. Some of the latter are unmetamorphosedand were therefore intruded after the local Mid-Ordovician M'Clin-tock Orogeny. There are also unconformably overlying and unmeta-morphosed Late Ordovician and Silurian sediments and volcanics

representing both deep- and shallow-water regimes. Although theLate Ordovician (Late Katian) rocks include the coral Sibiriolites,elsewhere known only from Siberia; more importantly, SiberianProvince conodonts, such as those known from the Arctic–AlaskaTerrane, have not been found in Pearya (Trettin, 1998). The publisheddates of docking of this terrane with Laurentia vary: Klaper (1992)supposed it to be Late Ordovician to pre-Ludlow, Lane (2007) EarlySilurian, and Colpron and Nelson (2009) late Early Devonian;however, we see no reason to disagree with Trettin's original(1987) date of Late Silurian. The Pearya Terrane is discussed furtherin Section 19.3.

9.2. European units

As initially recognised in the classic paper by Wilson (1966),today's Atlantic Ocean did not open along the same suture lines as thatformed by the closure of the Lower Palaeozoic Iapetus Ocean in theOrdovician and Silurian, and thus some parts of the British Isles andelsewhere in Europe contain segments of the old Laurentia. Some ofthese units, such as most of northern Scotland, had been integral partsof the Laurentian Craton during the Palaeozoic, whilst most of theothers represent some of the many islands within Iapetus, someoriginally peri-Laurentian, peri-Avalonian, or peri-Baltican island arcs,and some having originally formed onmid-ocean ridges. All were firstamalgamated with either Laurentia or to Baltica–Avalonia andsubsequently either subducted to oblivion or remain represented astectonised slivers within the extensive Iapetus Suture Zone formed inthe Caledonide Orogeny (Fig. 14).

9.2.1. SvalbardSeveral terranes make up the pre-Devonian Svalbard Archipelago,

whose largest island is Spitsbergen, and they were reviewed by Geeand Trebenkov (2005), Smith and Rasmussen (2008), andMazur et al.(2009). Western Svalbard consists of the metamorphosed Neoproter-ozoic and Lower Palaeozoic rocks formerly known as the Hecla Hoek‘Formation’, which is now divided into the Northwestern TerraneGroup and the Southwestern Terrane Group. We have grouped the‘Western’ and ‘Central’ terrane areas of some authors together as‘West Svalbard’. In contrast to West Svalbard, the Nordaustlandet andNy Friesland areas in the northeast of Svalbard are much lessmetamorphosed and carry rich Cambrian and Ordovician faunas,such as the Early Ordovician trilobites documented by Fortey (e.g.,1975). Those fossils are typically Laurentian Province, and theyinclude a succession of shallower- to deeper-water communitieswhose faunal components, particularly the trilobites, undoubtedlyindicate that the area then formed a marginal sector of the LaurentianCraton. Spitsbergen became united during the Caledonide Orogenyand subsequently formed part of the Old Red Sandstone Continent inthe Devonian. The Carboniferous and Permian rocks are a mixture offluvial deposits and shallow-water carbonates, the latter with richmegafossils of typically Laurussian aspect. Worsley (2008) andSmelror et al. (2009) published palaeogeographical maps of theBarents Sea, including Svalbard and Bjørnøya, from Devonian timesonwards.

9.2.2. Bjørnøya (Bear Island) and Jan Mayen TerraneBjørnøya, or Bear Island, forms part of the western margin of the

Barents Sea, and its geology was reviewed by Worsley et al. (2001). Itconsists of a Neoproterozoic basement unconformably overlain byOrdovician carbonate and clastic rocks, themselves unconformablyoverlain by Latest Devonian (Famennian) basin sediments and by aMiddle Carboniferous to Triassic carbonate platform, the lattercomparable to rocks of the same age in Spitsbergen. The LowerPalaeozoic rocks were also reviewed by Smith and Rasmussen (2008),who concluded that Bjørnøya was attached to eastern NorthGreenland from Proterozoic to Cretaceous time, thus forming an



extension and integral part of the north Canadian Franklinian Basinduring the Lower Palaeozoic. Situated to the east of Greenland, JanMayen Island, which consists of Oligocene and later volcanic rocks, isthe only part above sea level of a microcontinent which today makesupmuch of the shelf under the Greenland Sea. Although no Palaeozoicrocks are known from Jan Mayen, geophysical data suggest that afragment of the Laurentian Craton may form its basement.

9.2.3. Highlands of Northern ScotlandThe substantial area north of the Highland Boundary Fault in

Scotland was originally part of the core Laurentian Craton, andcontains many rocks of Archaean and later Precambrian ages. It alsocontains a typically Laurentian Province Early to Middle Ordovicianbathyurid trilobite fauna in the Durness Limestone of the Highlandsand the Isle of Skye. To its south there is the Highland Border Complex,which represents an old island arc preserved only as slivers within theHighland Boundary Fault Zone, and from which Ingham et al. (1985)described an Early Ordovician (Whiterockian: Dapingian) trilobiteand brachiopod fauna, including bathyurids and other trilobites whichare related even at the species level to those known from Utah andNevada. Thus that island arc, although tectonically divorced, cannotoriginally have been far from the Laurentian Craton margin. TheScottish Highlands were spectacularly affected by the Middle to LateOrdovician (470 to 455 Ma) Grampian Orogeny, reviewed by Strachan(in Woodcock and Strachan, 2000), in which much metamorphismand nappe thrusting were caused by the collision of another intra-Iapetus island arc with the Laurentian Craton. Late Ordovician granitesand gabbros were also intruded, as were very substantial Silurian andEarly Devonian granites (430 to 410 Ma) following the CaledonideOrogeny. Thick non-marine clastics of Devonian age were laid down,particularly in the Orcadian Basin, when the area was part of the OldRed Sandstone Continent. It is possible that the islands of Rockall(Fig. 1) and the Shetlands (off northeast Scotland) represent otherLaurentian or peri-Laurentian terranes, as depicted by Smith andRasmussen (2008), but no definite Lower Palaeozoic rocks or faunasare known from either of them, and we do not show them separatelyon our maps.

9.2.4. Midland Valley of ScotlandThe Girvan area adjacent to the west Scottish coast, has yielded

prolific Lower Palaeozoic faunas whose Lower and Middle Ordoviciancomponents, exemplified by the brachiopods monumentally mono-graphed byWilliams (1962), are of Laurentian aspect. There are theremany genera and even some species which are the same as those fromVirginia and adjacent areas of the U.S.A. described by Cooper (1956).Most of the surrounding Ordovician and Silurian rocks in Girvan, apartfrom the Lower Ordovician Ballantrae Ophiolite, are substantialturbidite sequences which were deposited in basins marginal to theLaurentian Craton. However, some units, particularly the Ordovician(Earliest Katian: Late Burrellian) Craighead Limestone, representshallower-marine deposits with pisolitic oolites, and the LateOrdovician and Llandovery rocks contain rich shelly faunas depositedon the shelf. The Girvan succession terminates upwards in the thin,shallow-water Knockgardner Formation, which carries a LowestWenlock shelly fauna with brachiopods, which is succeeded by ‘OldRed Sandstone’ rocks of deltaic and terrestrial facies which are of LateSilurian age, as the area changed from sea to land as a result of theCaledonide Orogeny (Cocks and Toghill, 1973). There are alsosubstantial Upper Palaeozoic rocks, including true Old Red SandstoneContinent Devonian clastics and extensive Early Carboniferouscarbonates and Late Carboniferous marginal sediments of shallow-water clastics and deltaic deposits with coals, including rocksrepresenting minor marine incursions. In addition, tholeiitic dykesand other igneous rocks, many substantial, were intruded during theLate Carboniferous, all reviewed by Guion et al. (in Woodcock andStrachan, 2000).

9.2.5. Southern Uplands of ScotlandAlthough the Southern Uplands lie to the north of the main suture

where the Iapetus Ocean closed inMid-Silurian times, and would thusnaturally be considered as peri-Laurentian; neverthess detrital zirconsof apparently Avalonian origin were found within a Late Ordovician(Katian: Caradoc) pyroxene-bearing sandstone (Phillips et al., 2003).This led to support for the supposition (e.g., by Leggett et al., 1979),that the Southern Uplandswere deposited in amid-ocean basinwhichwas subsequently preserved as part of an accretionary wedge duringthe Caledonide Orogeny. However, the Southern Uplands also containrare but biogeographically important fossils which are of Laurentianaffinity, such as the Late Ordovician (Katian) brachiopods at Kilbucho(Candela and Harper, 2010). Thus it is unsurprising that, followingmore substantial work on the Late Ordovician detrital zircons,Waldron et al. (2008) concluded that they were of Laurentian, notAvalonian, provenance, and supported a more active subduction–accretion model for the Southern Uplands. There are also manysubstantial post-Caledonide Devonian granites there.

9.2.6. Northwestern IrelandNorthwestern Ireland is essentially a southwestern extension of

the tripartite divisions seen in Scotland (the Highlands, MidlandValley and Southern Uplands). The Ordovician faunas preserved todayin the South Mayo Trough are unambiguously peri-Laurentian. Forexample, the brachiopods of Dapingian age described from theTourmakeady Limestone by Williams and Curry (1985) are ofdominantly Laurentian affinity, although, interestingly, 8 out of the41 genera there are endemic. They and the surrounding TourmakeadyVolcanics all indicate that the area formed part of a peri-Laurentianisland arc. The 464 Ma (Late Darriwilian) zircons found in the nearbyMweelrea Formation ignimbrites are also of Laurentian derivation(McConnell et al., 2009). The later (Sandbian: Early Caradoc)essentially Laurentian Province brachiopods along strike, in theBardahessiagh Formation at Pomeroy, monographed by Mitchell(1977), are very similar to those of the same age from Girvan in theMidland Valley of Scotland. The two halves of Ireland were unitedduring the Caledonide Orogeny, and then, firstly, Old Red Sandstonenon-marine clastic rocks of Devonian age were deposited inintermontane basins, followed by extensive Lower Carboniferouscarbonates and Upper Carboniferous clastic rocks. These were in turnoverlain by some Permian rocks, whose outcrops are confined to thenortheast of the island. The latter were largely of terrestrial origin,although there was a shallow-marine incursion in which theMagnesian Limestone (also seen in northern England) was deposited.

9.2.7. Grangegeeth TerraneWithin the Iapetus Suture zone in central Ireland there lies the

relatively small Grangegeeth Terrane, whose Middle Ordovician(Sandbian: Caradoc) brachiopods and trilobites were described byOwen et al. (1992), who concluded that the fauna was ‘Scoto-Appalachian’ (i.e. Laurentian). However, upon reanalysis, Fortey andCocks (2003) perceived that they were not entirely Laurentian, but infact demonstrated an intriguing mix of genera which had variablyoriginated in both Laurentia and Avalonia–Baltica. Thus Grangegeethapparently formed part of a mid-Iapetus island arc in the Ordovician,part of which was fortuitously preserved within the Iapetus SutureZone resulting from theMid-Silurian Caledonide Orogeny, and islandsin that arc served as important stepping-stones for Ordovician inter-continental faunal migration.

9.2.8. Norwegian nappesAs has been known since the classic paper of Reed (1932), the Upper

Allochthon of the Scandinavian Caledonides in the Trondheim area ofwest-central Norway (SHT on our reconstructions, e.g. Fig. 7), partic-ularly the Hølanda and Smøla areas, contains Lower and MiddleOrdovician shallow-marine brachiopods, trilobites and other fossils,



many of Laurentian affinities. Those faunas were reviewed by, forexample, Harper et al. (1996), who concluded that the animals probablylived on island arcs within the Iapetus Ocean close to Laurentia in theOrdovician. It is probable that the adjacent Uppermost Allochthon øfcentral Norway was also originally Laurentian or peri-Laurentian,although no diagnostic Lower Palaeozoic faunas are known from it(Smith and Rasmussen, 2008). The nappes were thrust over Balticaduring the Silurian Caledonide Orogeny, which is often termed theScandian Orogeny in that area.

9.3. Appalachian units

A great deal has been published on the geology of the Appalachiansof eastern North America and their tectonic history, which has beensummarised by Hatcher et al. (1989), Williams (1995), van Staal(2005) and van Staal et al. (2009), and many other authors. They aredominated by the effects of several orogenies, particularly theCaledonide Orogeny. In a comparable way to the Scottish and Irishterranes outlined above, the many units in today's eastern NorthAmerica were either originally parts of Laurentia to the west of theIapetus Ocean, or of Baltica or Avalonia to the east of Iapetus, orrepresented island arcs within the Iapetus before it closed. Those arcswere initially mid-oceanic or near either Laurentia or Avalonia/Baltica. The most substantial suspect terranes there, includingCarolina, Avalonia andMeguma (see below), were originally marginalsectors of Gondwana before leaving that superterrane at various timesin the Ordovician. As the Atlantic Ocean opened in the Mesozoic, theold Avalonian Terrane area became divided and parts were left onboth sides of the Atlantic; nevertheless, Avalonia was a single unitduring the Palaeozoic, as reviewed by Cocks and Fortey (2009), andnot the two separate ‘East’ and ‘West’ Avalonian terranes of someauthors. Originally defined in Newfoundland and adjacent areas ofCanada, Williams (summarised in 1995) identified several ‘zones’ inthe area, which are reviewed briefly progressing outwards from theLaurentian Craton in turn below. Those reviews are followed bysummaries of the geologically discrete areas further to the south,down today's Atlantic seaboard.

The Appalachian area was substantially affected by at least fiveseparate Palaeozoic orogenic events (Hatcher et al., 1989; van Staalet al., 2009): the Ordovician Taconic Orogeny (460–430 Ma), theSilurian Caledonide Orogeny, locally termed the Salinic Orogeny(430–423 Ma), the Latest Silurian to Early Devonian Acadian Orogeny(421–400 Ma), the Early to Late Devonian (400–360 Ma) NeoacadianOrogeny (380–345 Ma), and the Late Carboniferous to PermianAlleghanian Orogeny (335–260 Ma), and the rocks are thus extremelycomplex. In thewest of the area there aremany tectonic units, some ofwhich represent discrete terranes, such as the Tugaloo, Chopawamsic,Potomac and Baltimore terranes, which were originally peri-Laur-entian. Further eastwards the Mid-Palaeozoic Cat Square Terraneconsists of metasedimentary rocks with no preserved fossils whichhas been interpreted as either peri-Laurentian or as having beendeposited in an Iapetus ocean basin, but is not shown separately onour maps.

9.3.1. Humber ZoneWilliams (e.g. 1995) divided the northern Appalachians of E Canada,

including Newfoundland, and northeastern U.S.A. as far south as NewYork State, into several tectonic ‘zones’, themost westerly of which, theHumber Zone, was part of core Laurentia (Fig. 5). Late Proterozoic(Grenvillian) to Ordovician rocks were deposited on a passive margin,although rift-drift basin sediments reflect the initial riftingof the IapetusOcean at about 570 Ma. In western Newfoundland the Humber ArmAllochthon consists largely of deeper-water sediments deposited in adebris apron at the foot of the continental margin, but their containedlimestone boulders characterise an important Cambrian and EarlyOrdovician shelf to basin sequence of trilobite communities (Kindle and

Whittington, 1958). The international ‘golden spike’ of the base of theOrdovician lies within that section. The Dashwoods Microcontinent,independent only between Late Neoproterozoic and Early Cambriantimes (and thus too early to be shown separately on ourmaps), forms asector within the Humber Zone (Waldron and van Staal, 2001).

9.3.2. Dunnage ZoneThe two zones adjacent to the eastern margin of the Humber Zone,

the Dunnage Zone and the Gander Zone, are a structurally andsedimentologically complex series of rocks, many of them olistos-tromes of Cambrian and Ordovician ages. Both zones containremnants of island arcs which were accreted to Laurentia andAvalonia at various times in the Late Cambrian and Ordovician andthere are also some intra-Iapetus ocean basin rocks, mostly fortu-itously preserved in the Caledonide Orogeny. The Dunnage Zone isdivided into a western Notre Dame Subzone and an eastern ExploitsSubzone, and the main Iapetus Ocean suture is taken to be at thejunction between them, locally termed the Red Indian Line. The NotreDame Subzone includes the Middle Cambrian to Early Ordovician(Tremadocian) Baie Verte oceanic tract in Newfoundland, and also thenotable Notre Dame Island Arc (whose lateral extension is known inNew England as the Shelburne Falls Arc), which was intermittentlyactive from Late Cambrian to Early Silurian times. Van Staal et al.(2007) realised that the Notre Dame Arc was composite, andrepresenting three phases of the Taconic Orogeny, each recordingthe accretion of different island arcs to Laurentia: Taconic 1 at 495 Ma(Late Cambrian: Furongian), Taconic 2 from 470 to 460 Ma (MiddleOrdovician: Dapingian–Darriwilian) and Taconic 3 from 454 to443 Ma (Late Ordovician: Katian and Hirnantian). It was duringTaconic 3 that the Baie Verte oceanic tract was thrust on to theHumber Margin (van Staal et al., 2009).

9.3.3. Gander ZoneThe Gander Zone, reviewed byWilliams (1995) and van Staal et al.

(1996), was originally defined in the central Newfoundland area andextends southwest into New Brunswick. Much of it consists of arelatively monotonous and lightly metamorphosed sequence ofmostly Cambrian rocks extending upwards into the Lower Ordovician(Tremadocian), but there are also basement rocks of Archaean,Mesoproterozoic, Neoproterozoic and earliest Cambrian ages insporadic outcrops. There is a 543 Ma gabbro intrusion. Since thetectonic history is different from both the Laurentian Craton andAvalonia, particularly in the Ordovician and Silurian, some authors,e.g., van Staal (e.g. 2005), have defined a separate Ganderia Terraneoutboard from Avalonia in the Lower Palaeozoic, with a fringingPenobscot island arc to its N. That microcontinent was, like Avalonia,peri-Gondwanan rather than peri-Laurentian in origin, as can bededuced from the early Ordovician Mediterranean Province brachio-pods (characteristic of Northern Gondwana) from Gander Lakediscussed and figured by McKerrow and Cocks (1977), but it waspositioned outboard from Avalonia in the Lower Palaeozoic IapetusOcean.

9.3.4. Avalon ZoneThe Avalon Zone adjoins the Gander Zone, and makes up most of

the Avalon Peninsula of Newfoundland. The latter gave its name to thesubstantial Avalonia Terrane, of which it formed part in the LowerPalaeozoic. Avalonia originated in Gondwana, as reviewed by Cocksand Fortey (2009), and it had no connection with Laurentia until thetwo amalgamated in the Silurian Caledonide Orogeny. It was thesimilarity of Cambrian trilobites from the Avalon Peninsula to thosefromWales, and the difference between them and coeval faunas fromthe Laurentian Craton, which formed one of the chief originalarguments by Wilson (1966) for the very existence of an IapetusOcean.



9.3.5. Meguma TerraneThe Meguma Terrane is exposed inland only in Nova Scotia,

Canada, but, as reviewed by Schenk (1997), van Staal (2005), and vanStaal et al. (2009), it extends for a far more substantial area undertoday's North American shelf from the Grand Banks of Newfoundlandto east of Cape Cod, Massachusetts. Meguma consists of latestNeoproterozoic to Early Ordovician (Arenig) rocks, mainly turbiditesover 10 km thick and black shales perceived to have been deposited ina continental-rise prism, probably on the West African margin ofGondwana. Those are overlain unconformably by Late Ordovician toEarly Devonian shallow-marine clastics within which are EarlySilurian (442–438 Ma) drift-related bimodal volcanic rocks andEarly Devonian (380–370 Ma) granite plutons. Although Megumawas later substantially affected by the Early to Middle Devonian(Emsian–Eifelian, 395–388 Ma) Acadian and Carboniferous Neoaca-dian orogenies, we accept the analysis of Murphy (2007) that itprobably formed the southernmost part of the Avalonian TerraneAssemblage, and its accretion to Laurentia formed part of theCaledonide Orogeny.

9.3.6. Carolina and associated terranesMost authors consider that the largely metamorphosed Carolina

Slate Belt, and adjacent areas in the very east of the Appalachians,stretching from Virginia to Alabama, formed an independent CarolinaTerrane in the Lower Palaeozoic, and it is sometimes termed asuperterrane since it consists of various tectonic fragments. Itsgeology was described by Hibbard et al. (2005). Like Avalonia, itwas originally part of the margin of Gondwana rather than Laurentia,and consists of Neoproterozoic to Lower Palaeozoic island arcassemblages, together with 600–550 Ma plutons. Plutonism contin-ued into the Early Cambrian (530 Ma) and there are also MiddleOrdovician andesites and dacites. Middle Cambrian trilobites weredescribed by Samson et al. (1990), which, although they are notstrongly terrane-diagnostic, bear little resemblance to contemporaryLaurentian Province faunas, and are most similar to faunas fromPerunica (Bohemia), then part of Gondwana. No terrane-diagnosticEarly Ordovician fossils have yet been found in the Carolina Terrane,although graptolites are abundant in places. Adjacent to the CarolinaTerrane to its west is the Smith River Allochthon, another probableperi-Gondwanan terrane which is thought to have accreted toLaurentia in the Early Ordovician, and which is intruded by an EarlySilurian gabbro. The docking time of the Carolina Terrane withLaurentia is poorly constrained: it may have been during the EarlySilurian Caledonide Orogeny or in the Neoacadian Orogeny in the lateDevonian.

9.3.7. Alabama terranesMuch of the Palaeozoic of Alabama is hidden under later cover, but

at the southernmost end of the Appalachians the Talladega Belt hasbeen described by Tull et al. (e.g. 2007). There are there UpperOrdovician (468 Ma) island arc rocks, many of which are termed theHillabee Greenstone, which were thrust over the now-metamor-phosed Lower Cambrian to uppermost Ordovician Laurentian marginduring the Devonian. The Hillabee probably originally coveredhundreds of square km and includes ignimbrites, tholeiitic basaltsand calcalkaline rhyolite/dacite suites, all of which probably originat-ed in the early stages of back-arc opening in an extensionalenvironment. There are also plutons of slightly later (460 Ma)Ordovician age, as well as a suite of substantial post-accretionaryLate Devonian granites, dated at 369 Ma (Famennian).

9.4. Florida (Suwanee) Terrane

To the east of the Mexican terranes, the surface outcrops of thearea lying in the southeast of the U.S.A., and which includes most ofFlorida, consist of Mesozoic and later rocks. However, it is known from

borehole data, that those rocks unconformably overlie LowerPalaeozoic rocks. The latter form what has been termed the SuwaneeTerrane, which is bounded to the north by an east–west trendingsuture zone in southern Georgia and Alabama. The Upper Proterozoicand Lower Palaeozoic include volcanic arc rocks, some dated to about550 Ma. Other rocks have yielded Ordovician trilobites, such asPlaesiocomia, of undoubted Gondwanan affinity (Whittington, 1953),indicating that Florida did not then form part of Laurentia, andpresumably did not approach it until the formation of Pangea in theCarboniferous.

9.5. Precordillera (Cuyania) Terrane

An area today in northwestern Argentina is termed the Precordil-lera (or Cuyania) Terrane, whose history has been hotly debated bymany authors. Its Cambrian and earliest Ordovician trilobite andbrachiopod faunas are of undoubted Laurentian affinity; however, bythe Late Silurian it was certainly either an integral part of westernGondwana or very close to it, as may be deduced by the high-latitudeMalvinokaffric Clarkeia shelly faunas present there. Most authors (e.g.Benedetto et al., 1999) believe that it was a Laurentian or peri-Laurentian terrane in the Cambrianwhichmigrated across the IapetusOcean to dockwith Gondwana by around the end of the Ordovician. Incontrast, some other workers (e.g. Finney, 2007) believe that,although the Early Cambrian olenellid trilobites and other faunasfound in the Precordillera are of undisputed Laurentian affinity, theterrane was peri-Gondwanan throughout the Lower Palaeozoic asdemonstrated by its contained zircons, and that the Laurentian faunashad reached it by travelling across a narrow Iapetus at the samepalaeolatitude. However, we favour the former scenario, since themodern Precordillera area of Argentina is the only part of theGondwanan supercontinent to carry Laurentian faunas, and also sincethe palaeomagnetic data indicates that that part of Gondwanawas notclose to Laurentia during the Cambrian.

10. Geological history

There now follows a sequential history for Laurentia and peri-Laurentia for the Lower Palaeozoic and for the Laurentian parts of,successively, Laurussia and Pangea for the Upper Palaeozoic. From theCambrian to the Permian we have divided the brief reviews for eachsystem between tectonic and igneous activity and facies and faunas.We have constructed new palaeogeographical maps for the area andits immediate surroundings at intervals, showing the land, deep andshallow shelves and the oceans, using the fresh APW path (Fig. 2) forthe Laurentian Craton, as well as a wealth of varied faunal andsedimentological data, and have been careful to maintain kinematiccontinuity between the successive maps. For the lithologies, whichunderpin the palaeogeography of the cratonic area, we have drawn onthe many Phanerozoic maps previously published for North America,such as those in the DNAG volumes (e.g. Bally and Palmer, 1989), aswell as Ziegler (1989) and Golonka (2007), and also Nalivkin andPosner (1969) for Siberia, and Smelror et al. (2009) for the BarentsSea, in addition to many smaller papers on specific areas. Many reefshave been inserted from Geldsetzer et al. (1988) and Kiessling et al.(2002), although often we have found space for only one or two reefsymbols, whereas many more individual reefs have been recordedfrom those areas in many cases. The distribution of lands and seas atthe continental margins is often very speculative, due both tosubstantial later tectonics and also to the lack of rocks of the specificages of each map there.

Global stratigraphy has long been bedevilled by poor correlationand a multiplicity of local series and stage names, but the correlationof North American units with the international standards are nowmuch improved, as reviewed for the Lower Palaeozoic by Cocks et al.(2010).



Themapswere all constructed using the SPlates system, developedfor Statoil, in which the modern world is divided into ancient platepolygons (Labails et al., 2009). Thus, the outlines of the units shownon our maps are those represented at the present day. However, thismakes for very artificial boundary shapes: for example, the NorthSierra and the adjacent Roberts Mountains area of the western U.S.A.are shown as occupyingmuch larger areas than they would have donein the Palaeozoic, when their underlying island arc volcanics andother rocks were first laid down.

11. Precambrian prelude

The craton of Laurentia was the product of the union of severaldiscrete older terrane units, and its Precambrian history can be brieflysummarised as follows. Over a timespan of some 200 my, from about2.0 to 1.8 Ga, the core of ‘Laurentia’ was formed by the progressiveamalgamation of 6 or 7 large fragments of Archaean crust (reviewedin Bleeker, 2002), the most impressive of which are today exposed inthe Canadian Shield, and the largest of which is the Superior Craton. Inaddition, there is the Nain or North Atlantic Craton underlyingGreenland (Henriksen, 2008). At around 1 Ga, these united fragmentsformed part of the Rodinia Supercontinent. Published reconstructions,some reviewed by Dickinson (2009), differ on exactly where the‘Laurentian’ sector was within Rodinia, but today's western margin ofNorth America appears to have formed part of the margin of thereduced supercontinent after its separation from West Australia andEast Antarctica (Fig. 4), and the east and north margins were probablyattached to one or more of the other major terranes: whether or notthe latter included some or all of Gondwana, Baltica and Siberia isuncertain.

Rodinia broke up progressively (Torsvik, 2003) and Laurentiabecame an independent continent at some time in the Neoproter-ozoic. Exactly when that was is contentious due to enigmatic age datesand palaeomagnetic data, and detailed discussion of the problem isoutside the scope of this paper, but we estimate that Laurentia did notleave the area now to its east (Gondwana, Baltica and adjacent areas)until probably fairly late in the Neoproterozoic and perhaps at about570 Ma. That rifting along the Appalachian margin of the cratoncaused basins to develop in which were deposited the lower rocks ofthe Ocoee Supergroup from Georgia to Virginia, which locally exceed15 km in thickness andwhich unconformably overlie the billion-year-

old Grenvillian basement, as reviewed by Hatcher et al. (1989). AsLaurentia left Rodinia, probably at a fairly high southerly palaeolati-tude, the expanding Iapetus Oceanwas progressively formed betweentoday's eastern and southern margins of Laurentia, on the one hand,and Gondwana and Baltica on the other hand. Today's northern andwestern margins of Laurentia faced the vast Panthalassic Ocean,which was of comparable size to the Pacific Ocean today and whichapparently persisted for the whole of the Palaeozoic. Although severalauthors have proposed that Laurentia was united with Siberia duringthe late Precambrian, there appears to be no substantial evidence forthat, even though the two were at comparable equatorial palaeola-titudes by the beginning of the Palaeozoic: the Early Cambrian faunaldifferences were certainly substantial. The global distributions of theprimitive Late Neoproterozoic (Ediacaran) invertebrate faunas havebeen considered significant by some authors, but we can see noreliable patterns of provinciality within them, and thus they are notconsidered further here.

Much of the Laurentian Craton was little affected by activetectonism in the late Neoproterozoic. For example, the 950 to450 Ma successive Eleonore Bay Supergroup, Tillite Group and KongOscar Fjord Group, all in Greenland, are relatively flat-lying andunmetamorphosed overmuch of their extensive outcrops (Henriksen,2008). However, analysis of the Dashwoods Block within theLaurentian Humber Zone in Newfoundland by Waldron and vanStaal (2001) concluded that the rift-drift transition at the start ofocean spreading occurred at about 560 Ma in that area and that a so-called Humber Seaway opened between the Dashwoods Microconti-nent and the Laurentian Craton. In contrast, today's westernmargin ofLaurentia remained a passive margin throughout most of the lateProterozoic and the Palaeozoic up to the late Devonian Antler Orogenyin California, Nevada, and adjacent areas.

12. Cambrian

Although the base of the Cambrian is dated at 543 Ma, our firstnew reconstruction shows the crustal units (Fig. 5) and thepalaeogeography (Fig. 6) in the Middle Cambrian at 510 Ma. Thecorrelation of the traditional North American series with the recently-developed international system of series and stages is shown in Cockset al. (2010).

Fig. 4. Possible continental distributions at 750 Ma, when the Rodinia Supercontinent was breaking up (modified from Torsvik, 2003).



12.1. Tectonics and igneous activity

The Early Cambrian was not marked by any very substantialtectonic events in Laurentia, which at that time straddled the Equator(Fig. 3a). A passive Laurentian margin existed in today's northernCanada continuously from the Late Neoproterozoic to the Silurian(Dewing et al., 2004), and that extended eastwards to include NorthGreenland, as reviewed by Bradley (2008). Today's western marginwas also passive from Mexico to eastern Alaska, although much of itwas separated as a large parautochthon, shown on Fig. 5, until itsTertiary reunification with the main Laurentian Craton. At least in thesouthern Cordillera there was the Okanagan High, which bordered thewestern margin of the craton, and divided the relatively flatmiogeocline from the shelf edge of the Panthalassic Ocean (Thompsonet al., in Colpron and Nelson, 2006); however, we are not certain thatit was above sea level and therefore do not show it on Fig. 6. There wasalso some calcalkaline igneous activity in both the southern andnorthern areas of the Cordillera, reflecting extension in basins there,as plotted on our maps. Those eruptions were submarine and oftenviolent, locally with associated diatreme breccias with clasts cemen-ted by ferroan carbonates (Goodfellow et al., 1995). However, wehave not found enough good data from the margins of Laurentia toconstruct an Early Cambrian palaeogeographic map which would nothave been extremely speculative, and thus begin our series ofreconstructions with a map for 510 Ma, at about halfway throughCambrian time.

The Precordillera Terrane of Argentina (Section 9.5) undoubtedlyformed some part of Laurentia or peri-Laurentia in the Cambrian andEarly Ordovician, but its detailedwhereabouts is unconstrained beforeits Silurian docking with Gondwana, and thus the Precordillera is not

shown on the maps presented here; although the southwesternmargin of Laurentia was that nearest to Gondwana,

In the Newfoundland area, the Humber Seaway between Laurentiaand the Dashwoods Terrane had continued its steady opening until, atnear the end of Cambrian time at 495 Ma (Furongian), subductionstarted at the western margin of the Dashwoods Terrane, and theseaway started to close (Waldron and van Staal, 2001). Thisculminated in the Latest Cambrian (Furongian) Taconic 1 event,which van Staal et al. (2009) dated at about 495 Ma. At about the sametime, the first of several island arcs in the Notre Dame Arc within theDunnage Zone of westernNewfoundland became accreted to Laur-entia in the first phase of the Taconic Orogeny (van Staal et al., 2007).

12.2. Facies and faunas

The massive Early Cambrian faunal radiations caused a funda-mental change in the prevalent carbonate-dominated sediments onthe various cratons, with the characteristic late Proterozoic andearliest Cambrian soft substrates sealed by microbial mats graduallygiving way to more ‘modern’ sediments which were much reworkedby bioturbation (Dornbos and Bottjer, 2000). Proof of those globalradiations is best known from Laurentia, partly because of theequatorial position which naturally maximised the biodiveristy, andpartly because of the large numbers of extensive monographspublished on the fossil faunas over the past 200 years. The shelfmargin of the Laurentian Craton has preserved within it one of themost famous lägerstatten deposits anywhere, the Burgess Shale ofBritish Columbia, which has yielded a large variety of MiddleCambrian animals which are not often found as fossils.

Fig. 5. Terrane map of Laurentia for the Middle Cambrian at 510 Ma.Yellow shading represents probable continental areas and terrane extensions.



Much of the Laurentian Craton was flooded at different timeswithin the Cambrian, and relatively small sea level changes causednumerous transgressions and regressions. Many of the transgressionsbrought newly evolved trilobite species inshore, and those speciesgroups have been termed ‘biomeres’. The biomeres have often beenused as correlation tools; although, since the transgressions were notnecessarily instantaneous, some of the ‘correlations’ have subsequent-ly proved to have been diachronous. The early Cambrian OlenellusFaunawaswell established overmuch of the craton; for example, nearthe Laurentian passive margin in Ellesmere Island (Dewing et al.,2004), but, since the characteristic genus also occurs in the ArcticAlaska–Chukhotka Terrane reviewed below in Section 19, that fauna isnot so unequivocally Laurentian as is sometimes stated. A shallow- todeep-water sequence of Late Cambrian trilobite communities at thecraton margin is preserved in limestone boulders within the off-shelfsediments of the Cow Head Group in western Newfoundland (Kindleand Whittington, 1958). Cook and Taylor (1977) also documented ashallow to deep-water sequence at thewesternmargin of the craton inNevada, and noted that the basinal trilobites there had previously beenthought of as having ‘Asian’ affinities: those forms have subsequentlytherefore been considered as cosmopolitan.

Lefebvre and Fatka (2003) reviewed the echinoderm faunasglobally and noted how distinct and varied the low-latitudeLaurentian faunas were by comparison with those from Gondwana,Baltica and other areas at higher palaeolatitudes. That endorses theconclusion that the width of the Iapetus Ocean was alreadysubstantial by the beginning of the Cambrian, perhaps as much as5000 km.

The Late Middle Cambrian trilobite fauna from the FarewellTerrane of Alaska described by St. John and Babcock (1997) originated

in a cool-water outer shelf setting, and that fauna has strongresemblance to Siberian faunas of the same age (and some similarityto faunas in Baltica) but has nothing in common with those inLaurentia, That reinforces the suggestion that the Farewell Terranewas at some distance from Laurentia at the time, as discussed furtherin Section 19.

13. Ordovician

The Ordovician lasted from 490 Ma to 443 Ma, and our reconstruc-tions show the terranes and palaeogeography in the Early Ordovician(Late Tremadocian) at 480 Ma (Figs. 7 and 8) and the Late Ordovician(Sandbian: Early Caradoc) at 460 Ma (Figs. 10 and 11).


The Iapetus Ocean was at its widest in the Early Ordovician, but, tojudge from faunal diversity, it started to close at about Floian time.From then on, although the central part of the Laurentian Cratonremained stable for most of the Ordovician period, there wassubstantial tectonic activity on many of its margins. On today'seastern seaboard of North America and also in its Palaeozoic extensioninto Scotland and Ireland, several island arcs were progressivelyaccreted, reviewed by Mac Niocaill et al. (1997). Prior to thoseaccretions, some of the island arcs had been near the Laurentiancontinental margin, some on the Gondwanan or Baltica continentalmargins, and somewere developed onmid-ocean sites within Iapetus.Also at the eastern Laurentian margin, the closure of the HumberSeaway in the Newfoundland area, which had started in the LateCambrian, progressed steadily through subduction beneath the

Fig. 6. Palaeogeographical map of Laurentia for the Middle Cambrian at 510 Ma.



Dashwoods Terrane, and that narrow ocean finally closed in Floiantimes at about 470 Ma (Waldron and van Staal, 2001).

The Taconic Orogeny has been defined in various ways as affectingthe Appalachian area during the Middle to Late Ordovician, but vanStaal (reviewed in 2005) concluded that it started by the final closureof the Humber Arm Seaway between the Dashwoods Terrane and themain Laurentian Craton, which triggered a second phase of NotreDame Arcmagmatism andmetamorphism in the later Ordovician. vanStaal et al. (2007, 2009) described two Ordovician phases of theTaconic Orogeny in the Notre Dame Arc of Newfoundland, Taconic 2,from 470 to 460 Ma (Dapingian and Darriwilian), and Taconic 3, from454 to 442 Ma (Katian and Hirnantian), both phases reflecting theaccretion of separate island arcs to Laurentia. At the same time asTaconic 2 (470–460 Ma), the tholeiitic island arc preserved within theHillabee Greenstone of Alabama was active. That arc originated at468 Ma in the extensional environment of a back-arc basin, to befollowed at 460 Ma by the intrusion of plutons (Tull et al., 2007).Ganis et al. (2001) interpreted the Hamburg Klippe of Pennsylvania asLower to Middle Ordovician trench-fill deposits allochthonouslyemplaced onto the craton at the end of the Ordovician or perhaps alittle later. Bradley (e.g. 1989) documented the effect of the TaconicOrogeny on the turbidite deposition at different times, whichcommenced in the Early Ordovician Isograptus victoriae Zone inNewfoundland, and migrated southwestwards until the Mid-Ordovi-cian pygmaeus Zone of southern Quebec. That process resulted incrustal shortening, which is estimated to have been up to 270 km. TheLate Ordovician saw the beginning of the crustal shortening inGreenland, with some granites in southeastern Greenland dated at466 Ma (Kalsbeck et al., 2008).

Today's northernmargin of Laurentia hadbeenpassive since the LateNeoproterozoic, but at about Ordovician–Silurian boundary time

(443Ma), Surlyk and Hurst (1984) documented the creation and theinitial filling of a turbidite basin in northernmost Greenland andEllesmere Islandwhich heralded the arrival and subsequent accretion ofthe Pearya Terrane in the Silurian. However, also within northernEllesmere Island and to the south of the Pearya Terrane, within theEmma Fjord Fault Zone, Klaper (1992) has described the remnants of anOrdovician island arc, which must have been previously situated at anactive subduction zone south of Pearya, rather than at the passivemargin of Laurentia. The Arctic Alaska–Chukotka Microcontinent wasstill some away from the Laurentian margin, but the distance betweenthem was closing, with a substantial strike–slip element. The westernCordilleran margin of Laurentia remained passive, but there wassubmarine alkaline igneous activity in the extensional basins borderingthe Okanagan High near the edge of the craton in the United States,particularly in the Early to Middle Ordovician (Goodfellow et al., 1995).


Laurentia remained stretched across the Equator for the whole ofthe period, and the craton was repeatedly flooded by epeiric seas.Useful summary correlations for Canada were published by Barnes etal. (1981), and it is at the shelf edge of the craton in the Cow HeadPeninsula of western Newfoundland that the global stratotype of theCambrian–Ordovician boundary and the concomitant base of thelowest stage of the Ordovician, the Tremadocian, is defined. The upperhalf of the Ordovician saw the maximummarine transgressions, withconsequent large sediment thicknesses building up in the marginalbasins; for example, the 9 km thick pile on today's Arctic margin(Trettin, 1991). Global temperatures were relatively high. Althoughvarious oxygen and carbon isotope excursions are known (e.g.Bergström et al., 2010), there were no glacial intervals until the

Fig. 7. Terrane map for the Early Ordovician of Laurentia at about Tremadocian–Floian boundary time at 480 Ma. SHT, Smøla–Hølanda Terrane. Yellow shading represents probablecontinental areas and terrane extensions.



end-Ordovician Hirnantian glaciation (the mid-Ordovician eventreported from North Africa can be discounted: for review see Torsvikand Cocks, in press). However, in the Late Ordovician (Early Katian:mid-Mohawkian) there is a marked change in the sedimentsoverlying a substantial part of the southeastern Laurentian Cratonfrom underlying warm-water limestones to overlying limestones ofmuch more temperate origin; a change which had been ascribed bysome authors to the advent of ice caps near the poles. That change hasbeen explained by Ettensohn (2010), who, after reviewing both therocks and the literature, concluded that the more temperate stratawere deposited after tectonism to the southeast in the TaconicOrogeny forced deep cool oceanic waters into the Sebree Trough andon to the adjacent Lexington Platformwhere the carbonates were laiddown, in contrast to the earlier and warmer-water carbonates on thecraton, which had been deposited without influence of the coolerinflux.

Laurentia has been well-documented since the early nineteenthcentury as home to someof themost diverseOrdovicianmarine faunasknown from anywhere. Some of the faunas on the craton werereviewed by Fortey and Cocks (2003) who endorsed earlier usage ofthe term Bathyurid Province for the endemic trilobite-dominatedfaunas which were chiefly situated in Laurentia during Early MiddleOrdovican times. However, bathyurids had not yet diversified in theearliest part of the Ordovician (Tremadocian, locally termed Ibexian orEarly Whiterock), and endemic hystricurid trilobites took the bath-yurids' place as terrane-diagnostic taxa. There are some differencesbetween thewestern and eastern Laurentian Craton trilobite faunas asdiscussed at some length by Fortey and Cocks (2003, Fig. 7), with thewestern faunas including endemic asaphids such as Aulacoparia and

Lachnostoma not found further east, where there are comparablyendemic genera such as Bathyurellus. However, the reason for thiseast–west faunal differentiation is unknown: for example, there is noobvious land barrier between them. The distribution of those trilobitesis shown in Fig. 8 here. There was a decrease in the proportion ofendemics within the trilobite faunas towards the end of theOrdovician, quantified by Lees et al. (2002), when the Baltic andAvalonian faunas were gradually combined with those from Laurentiaas the Iapetus Ocean closed.

Early Ordovician articulated brachiopods were less diversified andmany, such as the abundant Syntrophina and Nanorthis, appear to havebeen pan-tropical. However, in contrast, there was much more genericendemism in the Middle Ordovician (Dapingian–Darriwilian: White-rockian) brachiopods, reflecting the substantial global brachiopodprovinciality at that time, with the faunas of Laurentia, includingOrthidiella longwelli and Ingria cloudi (Fig. 9), well documented fromNorth America by Cooper (1956) and from Scotland byWilliams (1962).Potter and Boucot (1992) showed that the east and west margins of theLaurentian Craton carried the same communities in the Middle and LateOrdovician, although only the shallower-water benthic assemblages (BA)2 to3wereusually present on thecraton, in contrast to thewiderBA2 to5range developed on the margins. By the Late Ordovician (Sandbian andKatian: locally termed Mohawkian and Cincinnatian) the distinctive andlargely endemic Richmondian brachiopod faunas, notably Megamyonia,Hypsiptycha, Hiscobeccus and Lepidocyclus, had become establisheduniquely in Laurentia. Those faunas are best known from the easternparts of the craton, such as the Cincinnati area of Ohio and also New YorkState. However, their sites extend northwards; for example, in theHudson Bay and Manitoba areas extensive faunas have been described

Fig. 8. Palaeogeographical map for the Early Ordovician of Laurentia at about Tremadocian–Floian boundary time at 480 Ma. Shading as in Fig. 6. The Eastern andWestern Laurentiantrilobite sites are also shown (data from Fortey and Cocks, 2003).



from the Red River and Stony Mountain Formations by Jin and Zhan(2001). Many of these Laurentian brachiopods are large, abundant andwell-preserved, such asHebertella, Strophomena and Rafinesquina (Fig. 9),and many of them have been well known since the classic earlymonographs of Hall (e.g. 1847).

Within the bryozoa, four global provinces have been defined inthe Ordovician, as reviewed by Taylor (in Webby et al., 2004), one ofwhich is termed North American, and their distribution is very similarto the brachiopods. Bryozoa were also analysed by Anstey et al. (2003),who characterised five associations (which they termed biochores)within awiderNorthAmerican–SiberianProvince in the LateOrdovician(Katian), including the Cincinnati–Maquoketa Biochore, whichinhabited the same area as the Richmondian brachiopod fauna. Bivalvesdid not reach Laurentia from Gondwana before the Late Ordovician(Cope, in Webby et al., 2004), and their subsequent appearancesare sporadic, but they are occasionally abundant. The distribution ofcorals is complex, and, although some genera were cosmopolitan,many forms were very local; for exampleWebby et al. (inWebby et al.,

2004) distinguished four biogeographically significant coral divisionswithin the Late Ordovician (Katian) of the eastern Laurentian cratonicseas alone. Turner et al. (in Webby et al., 2004) list endemic Laurentianfish genera which radiated during the Late Ordovician. Ostracodsare benthic arthropods which are abundant at various sites, some ofwhich are plotted on Fig. 11. Some previous workers (e.g. Cocksand Fortey, 1982), had considered them as more provinciallyrestricted between Laurentia, Avalonia and Baltica than they haveproved to be. For example, Schallreuter and Siveter (1985), afterrevising the faunas on both sides of the present Atlantic, concludedthat, although there were almost no Early Ordovician genera incommon between the three continents, in the later rocks (fromSandbian (Caradoc) times onwards) significant elements of theostracodfaunas were similar on both sides of the Iapetus Ocean. Thus,surprisingly, the ostracods appear to have been less endemic than thebrachiopods.

The marginal faunas around Laurentia are not so well known asthose from the craton, partly because they are obscured or deleted by

Fig. 9. Endemic Laurentian terrane-diagnostic brachiopods from the Ordovician. a, b, d, e, Pogonip Formation (Floian), Frenchman's Flat, Nevada; a, b, Orthidiella longwelli (Ulrich andCooper), ventral and brachial interiors, BC 58868–69; d, e, Ingria cloudi (Ulrich and Cooper), ventral and brachial interiors, BC 58870–71, X 3. c, f, Apatomorpha pulchella (Raymond),Athens Formation (Sandbian), Riceville, Tennessee, moulds of ventral and brachial interiors, BC 12849–50, X 2. g–n, Trenton Group (Katian), Cincinnati, Ohio, X 1.5; g–j, Strophomenaplanumbona (Hall), ventral and brachial interiors and dorsal and posterior exteriors, AMNH 918/5, 30247–8; k, Hebertella occidentalis (Hall), ventral interior, BB 16022; l–n,Rafinesquina alternata (Conrad), ventral and lateral views of exterior, BB 53894, and dorsal interior; BB 13088. BB, BC, Natural HistoryMuseum, London; AMNH, AmericanMuseum ofNatural History, New York.



subsequent Caledonian and other orogenic activities. However, afauna collected from the Early Ordovician (Floian) of the White InyoMountains of California (Fortey and Cocks, 2003) is characteristic ofthe deeper-water Nileid trilobite biofacies, which was originallydescribed by Fortey (1975) from the marginal peri-Laurentiandeposits at the other end of the continent in the ValhallfonnaFormation of Spitsbergen. A shelf to deeper-water sequence of EarlyOrdovician trilobite communities is preserved in the redepositedlimestone boulders within the Cow Head Group of western New-foundland (Kindle and Whittington, 1958). Near the southern marginof the craton, deeper-water basin sequences are preserved, particu-larly in the Marathon Mountains of Texas, from where a virtuallycomplete succession of Ordovician graptolite zones is known,although the rocks there were deformed in the Late CarboniferousOuachita Orogeny.

Originally living offshore of the eastern Laurentian area,distinctive and often endemic shallow-water marine faunas,particularly the well-documented trilobites and brachiopods, arepreserved in rocks from many of the Iapetus Ocean island arcsequences. Many of those faunas include Laurentian genera alsowell known from the craton itself. However, others, such as thosein the Grangegeeth Terrane of Ireland, display a mixture ofLaurentian and Baltic–Avalonian affinities (Owen et al., 1992).Other distinctive and often endemic genera are also found only atsingle sites. Those Ordovician mid-Iapetus faunas, sometimestermed the Celtic Province, have been described in a series ofpapers reviewed by Harper et al. (1996).

The Arctic Alaska–Chukotka Microcontinent was situated betweenSiberia and Laurentia, at a distance close enough to both continents toallow some faunal mixing, as shown by the brachiopods and othermegafossils reviewed by Blodgett et al. (2002) and the conodontsdescribed by Dumoulin and Harris (1994), all considered further inSection 19. Among other faunas, the Chukotka and Seward terraneswithin that microcontinent have yielded Monorakos (Ormiston andRoss, 1976), a trilobite whose whole family is normally considered asendemic to Siberia.

At the end of the Ordovician there occurred the relatively shortHirnantian glacial interval. Although no Hirnantian glaciogenic rockshave been found in Laurentia, since it was at low palaeolatitudes, thatglaciation affected the area in two ways; firstly in the eustaticlowering of sea level which led to widespread unconformities,particularly on the craton, between rocks of Ordovician and Silurianages; and, secondly, in the breakdown of many of the relatively fragilemarine ecosystems. The latter led to widespread extinctions, such asthat of the previously characteristic eastern Laurentian Richmondianbrachiopod fauna. In the latest Ordovician (Hirnantian), the Edge-wood assemblage (based on the faunas described by Amsden (1974)from Oklahoma) of Laurentia is somewhat different from the morecosmopolitan Kosov assemblage; but both are subsets of the cooler-water and glacially related Hirnantia Fauna, as reviewed by Rong et al.(2002), which was very widespread.

Themost complete latestOrdovician sequences in Laurentia are tobefound at the margins of the terrane; the best example of which is atAnticosti Island, in the St Lawrence estuary of eastern Canada, reviewedby Copper (2001). However, there is even there aminor paraconformityat the Ordovician–Silurian boundary, and it is noticeable that the basalSilurian (Early Llandovery: Rhuddanian) Becscie Formation rockscontain almost no warmer-water limestones and no bioherms, incontrast to the carbonates dominating the highest Ordovician (Hirnan-tian) Ellis Bay Formation beneath the paraconformity.

14. Silurian

Our reconstructions show the terranes and palaeogeography in theEarly Llandovery (Rhuddanian) at 440 Ma (Figs. 12 and 13), whenLaurentia was still an independent continent; and the Late Ludlow

(Ludfordian) at 420 Ma (Figs. 14 and 15), soon after Laurentia hadmerged with Avalonia–Baltica.


Although the Silurian was the shortest Palaeozoic system, lastingfor only 28 million years from 443 Ma to 416 Ma, it is notable forincluding the final closure of the Iapetus Ocean during the climax ofthe Caledonide Orogeny, again the subject of countless papers notcited or reviewed in detail here, in which Laurentia became unitedwith Avalonia–Baltica to become Laurussia after the two lattercontinents had amalgamated with each other at the very end of theOrdovician. However, the whole Orogeny was prolonged andcomplex; for example, Van Wagoner et al. (2002) reviewed thebimodal volcanism seen in New Brunswick and concluded that theMid-Silurian basalts and rhyolites present were erupted in anextensional rather than a compressional environment. In the northernAppalachians, the Ganderia Terrane collided obliquely with Avaloniain a phase of the Caledonides locally termed the Salinic Orogenybetween 430 and 422 Ma (van Staal, 2005; van Staal et al., 2009).

Within and around the complex suture zone representing the closureof the Iapetus Ocean a large number of relatively small terrane unitswerefinally accreted to the newly enlarged continent.We support the analysisof Murphy (2007), who concluded that the Meguma Terrane probablyjoined the southern margin of Avalonia during the Caledonide Orogeny,although the timing is not well constrained. A further result of theCaledonide Orogeny was the compression by 200–400 km in the easternpart of Greenland, and the welding of the Franz Joseph Parautochthon tothe Greenland part of the craton (Smith and Rasmussen, 2008), andgranites there have been dated as Early Silurian (Kalsbeck et al., 2008).

In the Canadian Arctic islands the cratonwas deformed in the latestSilurian to form the north–south trending Boothia Uplift, whose firstphases may have caused local unconformities as early as Cambrian inage. The cause of the uplift is uncertain: it reached its maximum ataround Siluro-Devonian boundary time, and may have been due topost-Caledonide pressure causing readjustment of the Precambrianbasement there (Okulitch et al., in Trettin, 1991). The Pearya Terraneand associated rocks in North Greenland were probably accreted toLaurussia in the Late Silurian, as originally suggested by Trettin (1987),and are also reviewed in Section 19. Colpron andNelson (2009, Fig. 11)postulated a different mid-Silurian palaeogeography, in which theYreka and Alexander terranes were welded to the Uralian margin ofBaltica, and Farewell to the northwest of Siberia, but we do not followthem, as also discussed in Section 19.

At today's western margin of the craton in the Cordilleran region,submarine alkaline igneous activity wasmuch less evident in the Silurianthan in the Ordovician or Devonian (Goodfellow et al., 1995), but thereare some diatremes near the cratonmargin in the Selwyn Basin of Yukon.Offshore of the craton in the Californian region, a series of rocks preservedtoday in the peri-Laurentian terranes in the Klamath Mountains and theShooFlyComplexof the SierraNevada represent remnants of oneormoreOrdovician and Silurian accretionary prisms which underlie the sub-Devonian unconformity there (Dickinson, 2000).

At the very end of the Silurian the northern Alaska area was affectedby the Romanzof Orogeny, which was probably a preliminary phase ofthe Ellesmerian Orogeny, which peaked in the Devonian, and whichmost affected the Arctic Alaska sector of the Arctic Alaska–ChukotkaMicrocontinent, as well as the Laurentian Craton margin further to theeast in Arctic Canada, as discussed below in Section 19. In the AlexanderTerrane of the Cordillera, the Klakas Orogeny of Late Silurian to EarlyDevonian age represents a collision between two entities, but whetherthey were both island arcs or whether one was a palaeocontinent isuncertain; if the latter it remains poorly defined. However, Alexander,Wrangellia and their associated Cordilleran terranes were situated inthe Panthalassic Ocean at somedistance beyond thewesternmargins ofour reconstructions, as discussed in Section 19.2.




In contrast to the palaeoequatorial position of Laurentia, Siberiawas a large palaeocontinent quite separate from all others (apart fromthe adjacent Mongolian Terrane Assemblage) in the Lower Palaeozoic.Siberia's palaeomagnetic history shows that it was also geographicallyinverted by comparison with today (Cocks and Torsvik, 2007) andmost of it lay to the north of the Equator in the Silurian. Thetemperate-latitude Silurian faunas (now to be found in Altai-Sayan,Mongolia and NW China as well as in political Siberia, all in the thennorthern but today southern parts of the Siberian Continent),particularly the Tuvaella brachiopod fauna, were substantiallydifferent from those elsewhere in the world, and contrastedparticularly with the benthic faunas in Laurentia, which thenstraddled the palaeoequator. Those palaeomagnetically anchoredpositions negate the maps published by some authors, e.g. Golonkaet al. (2003, Fig. 7), which show Siberia as joined to both the ChukotkaPeninsula and also Laurentia during much of Lower Palaeozoic time.Berry and Boucot (1970) provided outcrop maps and correlationcharts for the whole North America and Greenland Silurian, althoughthey now need revision.

We have already published a palaeogeographical reconstructionwith land, and shallow and deeper-water shelves for the easternsector of Laurussia just after its accretion to Avalonia–Baltica in themid-Silurian (Wenlock) at 425 Ma (Cocks and Torsvik, 2005, Fig. 9),and that map also includes some of the western (Laurentian) sector.Laurentia/Laurussia remained at low latitudes, with the equatorpassing through northern Greenland and northern Canada, but,because most of the other major terranes were at least partly atcomparable palaeolatitudes, many of the faunas were similar over

much of the world (reviewed in Fortey and Cocks, 2003). Due to thepreceding Hirnantian glaciation, sea-level stands were low at the startof the Silurian (Earliest Llandovery: Rhuddanian). This resulted in theextensive Ordovician–Silurian boundary unconformities prevalentover most of the Laurentian Craton, apart from in Oklahoma andadjacent areas (Amsden, 1974), but those unconformities seem asmuch due to the sediments never being laid down or perhaps erodedsoon after deposition, since there is little evidence for substantialemergent land areas over much of the Laurentian Craton, as can beseen from the Silurian map of Canada published by Norford (1997).

However, in some marginal parts of Laurentia, most notablyAnticosti Island, Quebec, the richly fossiliferous sequence of largelycarbonate sediments extended from the Late Ordovician to near the endof Llandovery time with only minor paraconformities (Barnes, 1989).Themajority of the brachiopod stocks, both in Laurentia and elsewhere,appear to have recovered well from the extinction phases associatedwith the Hirnantian glacial episode, even though abundances were lessthan average at virtually all localities (Cocks andRong, 2008).Hurst et al.(1985) documented the evolution of the craton margin and adjacentshelf during the Silurian inNevada,where anEarliest Silurian subtidal toperitidal carbonate ramp was drowned during the second half of theLlandovery. That drowned ramp evolved into a rimmed shelf during theLatest Llandovery and Wenlock.

By the Late Llandovery, the faunas had become exceptionallycosmopolitan, with the Pentamerus and Pentameroides Communitiesand their contemporary deeper-shelf Stricklandia and ClorindaCommunities, which are found in Iowa, Anticosti Island, andelsewhere in Laurentia. That community sequence was originallydescribed from theWelsh Borderland sector of Avalonia (Ziegler et al.,1968), but, in addition to Laurentia, it has been recognised from

Fig. 10. Terrane map of Laurentia, the Pearya Terrane and part of the Arctic Alaska–Chukotka Microcontinent in the Late Ordovician (Sandbian; Early Caradoc) at 460 Ma. SHT,Smøla–Hølanda Terrane. Yellow shading represents probable continental areas and terrane extensions.



Baltica, Siberia, and some of the Kazakh terranes, and there are alsoclosely comparable assemblages known from South China.

Upon the craton there were numerous basins and highs, which havebeen identified for over 150 years.However, it is difficult to be surewhichof the highs were above sea level and forming land; for example, most ofWyoming lacks preserved Silurian rocks. However, since some of therocks on the craton are of tidal or peri-tidal origin, theyprobably borderedlow-lying landmasses.Watkins andKuglitsch (1997) documented faunalassemblages representing steady water-deepening in the mid-Llandov-ery (Aeronian) of the substantial Michigan Basin. From there theydescribed a depth-related range from tidal flat deposits of BA (BenthicAssemblage) 1, dominated by ostracods and with just two brachiopods,Hercotrema and Alispira; a much more diverse and just subtidal BA 2assemblage dominated by corals and stromatoporoids and with 12different brachiopod genera; three different BA 3 mid-shelf assemblagesdominated by stromatoporoids, corals and the brachiopod Pentamerus,and a BA 4–5 deeper-shelf assemblage dominated by crinoids andsponges. Exceptionally substantial microbial reefs, as much as 1.3 kmthick, occurred in the Canadian Arctic (de Freitas and Dixon, 1995).

After the latest Ordovician (Hirnantian) glacial event, the globalpalaeotemperature increased steadily (Cocks, 2007), particularly duringthe Llandovery (which lasted for more than half of Silurian time). By theWenlock, widespread bioherms had formed, particular those well-known from Kentucky, Oklahoma, and in the Niagara area of New YorkState and Ontario. This reef belt extended eastwards into the Avalonia–Baltica sector of Laurussia, most famously in Sweden (Gotland), Estonia,and theWenlock Limestone of England (reviewed in Cocks and Torsvik,2005). As well as corals, the reefs had frameworks of various differentorganisms, such as sromatoporoids, algae and bryozoa, and theirdistributions during the Silurian and Devonian were plotted by Copper(2002). In the succeeding Ludlow period there was extensive evaporitic

deposition, including the notable Lockport and Salina dolomites of theMichigan Basin and New York State. Eurypterid and phyllocaridarthropods had been rare in the Ordovician, but they subsequentlydiversified, and there aremanyendemic Laurentian eurypterids, someofgiant size, particularly in the waters of lower salinity. However, Siluriantrilobites were far less diverse than their ancestors in the Ordovician.

As Silurian time progressed, many of the shallow-water marinefaunas, such as the brachiopods, became increasingly provincial(Boucot and Blodgett, 2001). With the increasing ambient tempera-tures, large endemic pentameride brachiopods, forming densely-packed beds on the sea floor comparable to oyster beds today, becameabundant and widespread over the whole terrane: these have beensubstantiallymonographedbymany authors from theU.S.A., includingAlaska, as well as northern and central Canada and Greenland. Forexample, Johnson (1975) documented beds of the PentamerusCommunity extending over much of Iowa. Watkins (1994) describeda time-related sequence of communities of large brachiopods fromWisconsin and surrounding areas, commencing with the MiddleLlandoveryVirgianaCommunity, the Late Llandovery to EarlyWenlockPentamerus and Pentameroides Communities, and theMiddleWenlockand Ludlow Kirkidium and Apopentamerus Communities. Only the firstand last (Virgiana and Apopentamerus) were largely endemic toLaurentia. On Fig. 13 some of the records of Virgiana are plotted,with data from Berry and Boucot (1970), Watkins (1994) and others,together with contemporary Late Rhuddanian and Aeronian faunas ofapparently the same environment (BA 3) in Avalonia–Baltica andScotland (Girvan) from which Virgiana is notably absent. Jin et al.(1999) described comparable communities in the Williston Basin ofSaskatchewan and Manitoba, and the Virgiana Beds are used locally tocharacterise the base of the Silurian in the many hydrocarbonexploration wells drilled there.

Fig. 11. Palaeogeographical map of Laurentia, Pearya and part of Arctic Alaska–Chukotka in the Late Ordovician (Sandbian; Early Caradoc) at 460 Ma. Shading as in Fig. 6.Monographed ostracod localities are plotted, partly from Schallreuter and Siveter (1985).



15. Devonian

Our reconstructions show the terranes and palaeogeography of theLaurentian sector of Laurussia in the Early Devonian (Emsian) at about400 Ma (Figs. 16 and 17), and the Late Devonian (Famennian) at370 Ma (Figs. 18 and 19).


During the Devonian the Rheic Ocean between Laurentia andGondwana, which had been at its widest inMid-Silurian time, steadilyclosed (Torsvik and Cocks, 2004). Near the beginning of the Devonian,the Acadian Orogeny of the Appalachians, including the MegumaTerrane, was characterised by polyphase deformation and regional

metamorphism. That was accompanied by voluminous magmatism,which ceased between 395 Ma and 380 Ma and was followed by aperiod of quiescence according to Murphy et al. (1999). The sameauthors reviewed the diachronous migration of Acadian deformationfrom about 415 Ma in the southeast to about 370 Ma in the northwest,over the whole Appalachian area, and which extended for more than600 km into the continental interior, and concluded that it may havebeen caused by the migration of Laurussia over a mantle plume.However, van Staal et al. (2009) divided tectonic activity in theNorthern Appalachians between an Acadian Orogeny, which hadbegun in the Latest Silurian at 421 Ma and continued until Emsiantimes at about 400 Ma, and a Neoacadian Orogeny, which lasted fromthe Emsian to about 360 Ma, near the end of the Devonian. There wasalso substantial activity further south in the Appalachians; for

Fig. 12. Terranemap of Laurentia, Arctic Alaska–Chukotka and adjacent areas in the Early Silurian (Early Llandovery: Rhuddanian) at 440 Ma. The white lines from eastern Greenlandto Scotland and in Norway denote Caledonide compression (Smith and Rasmussen, 2008). CH, Chukchi; ML, Mendeleev; NW, Northwind; SVB, Svalbard; SHT, Smøla–HølandaTerrane; TS, Thor Suture; WI, Wrangel Island. Yellow shading represents probable continental areas and terrane extensions.



example, Tull et al. (2007) documented the Devonian metamorphismof the Ordovician Hillabee Greenstone island arc of Alabama as it wasthrust westwards onto the Laurentian margin, and that was closelyfollowed by the intrusion of 369 Ma (Famennian) granite plutons.

The western margin of Laurussia had been passive since thebreakup of Rodinia in the Neoproterozoic at about 750 Ma, but thatceased in Early Devonian (Pragian to Early Eifelian) times. At least onenew island arc formed in the Yreka Terrane, today preserved in theeastern Klamath Mountains of California (Dickinson, 2000). LateDevonian (Frasnian–Famennian) to Earliest Carboniferous arcs alsoformed in the northern Sierra Nevada Mountains of California andeastern Nevada, including the extrusion of volcanic lavas over 5 kmthick. That extensional tectonism was subsequently reversed, whichresulted in the Late Devonian Antler Orogeny, in which the Roberts

Mountains Allochthon was thrust on to the Laurentian Craton, asreviewed by Dickinson (2000, 2009). A great clastic wedge, the AntlerFlysch, was shed eastwards from the resulting highlands into a broadforedeep that included much of eastern Nevada and extended intoUtah. Comparable relationships are seen in the Pioneer Mountains ofcentral Idaho and to the southwest in roof pendants in the SierraNevada Batholith. Opinions have differed on the cause of the AntlerOrogeny, but it seemsmost likely to have been due to the collapse of aback-arc basin following the change from a passive to an activecontinental margin, and the subsequent accretion of the arc toLaurussia, as originally postulated by Johnson and Prendergast(1981).

Further north in the Cordillera there was a further pulse of alkalinemagmatism in the Early Devonian due to extension in the craton

Fig. 13. Palaeogeographical map of Laurentia, Arctic Alaska–Chukotka and adjacent areas in the Early Silurian (Early Llandovery: Rhuddanian) at 440 Ma. Shading as in Fig. 6. Somelocalities of the abundant pentameride brachiopod Virgiana are plotted, as well as comparable Benthic Assemblage 3 localities in Avalonia–Baltica and Scotland where Virgiana isabsent.



(Goodfellow et al., 1995). In addition, ophiolites were intruded alongmuch of the Cordillera during the Middle and Late Devonian,reviewed by Nelson and Colpron (2007). Arc magmatism began inthe Kootenay terrane in the Late Devonian and the magmatismextended onto the neighbouring Laurussian craton margin in theEarliest Carboniferous. A spreading centre developed in the LateDevonian between the craton and the Kootenay and associatedterranes which developed with time into the substantial SlideMountain Ocean (Nokleberg et al., 2000; Colpron and Nelson, 2009).

In the northern end of the Cordillera, at the north-western Arcticmargin of Laurussia, a substantial area was affected by the EllesmerianOrogeny,whichwas causedby the oblique collision of the eastern end ofthe Arctic Alaska–ChukotkaMicrocontinentwith the Laurussian Craton,and the deformation there continued on past the end of the Devonian.The relationship between the Romanzof Orogeny, which was largelyEarly toMiddleDevonian, andmostly consistedof shorteningwithin theArctic Alaska–Chukotka Microcontinent, and the generally later Elles-merian Orogeny is not entirely clear: we provisionally conclude thatthey were essentially the same series of events, but more work on thattopic seems desirable. Since the microcontinent was positioned at rightangles from its orientation today, from theMiddle to theLateDevonianathick clastic wedge filled the resultant foreland basin which developedin the present-day Arctic islands of Canada between themicrocontinentand the craton (Embry, 1991). There was also deformation in the ArcticislandsaroundEllesmere,where theEllesmerianOrogenywasoriginallydefined for Late Devonian (Famennian) to Early Carboniferousdisturbances there (Harrison et al., in Trettin, 1991).


The continuing equatorial position of the Laurentian part ofLaurussia during this period, which lasted from 416 to 359 Ma,ensured that the shallow seas were warm enough to support a veryvaried shelf benthos, including the largest trilobites known, whichwere over 1 m in length. To judge by the distribution of reefs throughthe period (Geldsetzer et al., 1988), themaximumwarmthwas duringthe Frasnian; and that was confirmed by the oxygen isotope studies ofJoachimski et al. (2009).

Johnson (1974) produced facies maps for the Middle and LateDevonian covering the western half of the U.S.A., and showed that theshelf-basin boundary at the craton margin remained remarkablystable from the Ordovician to the Early Devonian. Most of thenorthern part of the craton was occupied by the Old Red SandstoneContinent land area, which extended eastwards to cover much of theformer Avalonian sector and other parts of northern Europe (Ziegler,1989). Friend et al. (2000) ably summarised that Old Red SandstoneContinent, particularly in the central Laurussian sector in the BritishIsles. Similar red sandstone facies are also developed in the Balticasector of Laurussia, but for most of the Devonian there appears to havebeen an intervening seaway running approximately north–south andseparating the two large land areas along the approximate sites of theNorth Sea and Barents Sea today.

The Earliest Devonian was a time of relatively low sea-level stands,which caused much emergence and a significant number of landbarriers within the craton areas of Laurussia. This resulted in niche

Fig. 14. Terrane map of western and central Laurussia and adjacent areas in the Late Silurian (Late Ludlow and Pridoli) at 420 Ma, with the area of Caledonide orogenic deformationtinted light brown. The white lines from east Greenland to Scotland and in Norway denote Caledonide compression (Smith and Rasmussen, 2008). CH, Chukchi; FJL, Franz Josef Land;IS, Iapetus Suture; ML, Mendeleev; NSI, New Siberian Islands; NW, Northwind; NZ, Novaya Zemlya; SVB, Svalbard; WI, Wrangel Island. Yellow shading represents probablecontinental areas and terrane extensions.



partitioning which ensured that there was considerable provincialismwithin the shallow-marine benthic faunas, both globally and insideLaurentia, as documented for the brachiopods in a classic paper byBoucot et al. (1969). A palaeogeographical map for the Pragian at410 Ma was published by Boucot et al. (2008), which showed that themacrofauna of Laurentia, particularly the brachiopods, were dividedbetween a Nevada Subprovince in the western of the craton, and anAppohimchi Subprovince in the east, stretching as far round to thesouth of the continent as Sonora in Mexico. These subprovinces wereseparated by a substantial landmass termed the TranscontinentalArch, and their subsequent Emsian distribution is shown in Fig. 17,where it can be seen that the Appohimchi Province is apparentlyconfined to the large embayment west of the Appalachians. However,those subprovinces broke down and were united into a singlebiogeographic unit by the transgression termed the Taghanic Onlapnear the end of the Middle Devonian (Givetian), as originallydocumented by Johnson (1970). Stigall Rode and Lieberman (2005)analysed Middle and Late Devonian brachiopod, bivalve and phyllo-carid faunas, and also showed how the lands on the craton (oftentermed ‘rises’ in the literature) much affected the distribution of thosebiota. Blieck and Cloutier (2000) reviewed fish from around the OldRed Sandstone continent. Tetrapods evolved from fish in the LateDevonian, and the oldest known are from Greenland, but their knowndistributions are too patchy to be palaeogeographically significant.

Among Upper Devonian (Frasnian and Famennian) and LowerCarboniferous strata there are substantial black shales reflectingdeepwater anoxia present in many of the cratonic basins, particularlyin Illinois and the Appalachians, but some extending as far north as

Alberta. Algeo et al. (2007), following analyses of molybdenum andother trace elements, have concluded that the black shales werecaused by high plankton productivity. That occurred at the same timeas organic buildups which in some places were extensive. Retallack etal. (2009) described the palaeosols present in the Famennian ofPennsylvania and concluded that they were alternately semihumidand subarid: only the former climatic conditions could support thetetrapodsHynerpeton and Densignathus, whose remains are entombedthere.

The closure of the Rheic Ocean to the southeast of Laurussia wasreflected in the progressive similarities between the terrane-diag-nostic faunas, reviewed by McKerrow et al. (2000). For example, theRhenish Province of Europe and North Africa originally defined byBoucot et al. (1969) on brachiopods and which had not hitherto beenplotted on a plate-tectonically basedmap, was shown byMcKerrow etal. to have resulted from differing palaeolatitudes, rather than beingterrane-controlled.

16. Carboniferous

The system, whilst internationally considered as a unity, has longbeen divided by North American geologists into an earlier Mississip-pian, which lasted from 359 Ma to 318 Ma, and a later Pennsylvanian,from 318 to 299 Ma, and those two names are now officially classifiedas subsystems. Our new reconstructions show the palaeogeography ofthe Laurentian sector of firstly Laurussia in the Early Carboniferous(Visean) at 340 Ma (Figs. 20 and 21), and subsequently Pangea in theLate Carboniferous (Moscovian) at 310 Ma (Figs. 22 and 23).

Fig. 15. Palaeogeography of western and central Laurussia and adjacent areas in the Late Silurian (Late Ludlow and Pridoli) at 420 Ma, soon after the amalgamation of the Laurentianand the Baltica–Avalonia Terranes in the Caledonide Orogeny. Shading as in Fig. 6. The white lines in eastern Greenland to Scotland and in Norway denote Caledonide compression.




The most dramatic event in the period was the amalgamation ofLaurussia with Gondwana to form Pangea, but their initial collisionconsisted of an oblique and relatively soft docking. Thus theorientation of the Laurentian sector appears to have been littleaffected, as can be seen from Fig. 3, even though the primeLaurussian–Gondwanan collision zone is located in southern U.S.A.and adjacent Central America. The southern margin of Laurentia hadpreviously remained passive since the late Neoproterozoic (Bradley,2008). The Gondwanan collision was heralded by the Early Carbon-iferous downwarping of the Ouachita Basin, and is reflected directly inthe compressional deformations first recorded in the MiddleCarboniferous of Oklahoma; and orogenesis peaked in the LateCarboniferous. The final phase was complete by the earliest Permian,as recorded in the rocks of Texas, where 12–14 km thickness ofCarboniferous sediments were deposited in the Ouachita Mountains,including olistostromes and several thin volcaniclastic units. Thoserocks are succeeded upwards by deltaic deposits of Latest Carbonif-

erous age. The whole episode is termed the Ouachita Orogeny. On theGondwanan side of the suture, in Mexico, Nance et al. (2009) showedthe Acatlán and Granjeno continental rises to the north of the Chortisand Oaxaquia terranes being tectonised by much strike–slip move-ment just before the collision of the twomain continents. The amountof lateral translation involved in the Ouachitas was minimallyestimated as between 50 and 100 km by Nielsen (2005), but weassess it as much greater than that over the whole suture zone(compare Fig. 20 with Fig. 22). The southwestern margin of Laurussia,including California, was also much affected, with substantial sinistralfault movements there, as reviewed by Stevens and Stone (2007). The‘Pangea A’ fit, which we use in preference to other published modelsfor the relationship between Gondwana and Laurussia, was discussedby Torsvik and Cocks (2004).

In the Canadian Arctic islands, the Sverdrup Basin continued itsdevelopment, with the Ellesmerian Orogeny continuing on into theTournaisian, but ceasing before the Visean, although subsequentdeepening of the basinwas caused by rifting (Davies and Nassichuk, inTrettin, 1991), with associated volcanics of Namurian age. In the

Fig. 16. Terrane map of Laurussia (including the Laurentian sector) and adjacent areas in the Early Devonian (Emsian) at 400 Ma. Gondwana (South America, Africa, Florida and theMexican terranes) is seen approaching. CH, Chukchi; FJL, Franz Josef Land; ML, Mendeleev; MO, Mixteca–Oaxaquia; NSI, New Siberian Islands; NW, Northwind; NZ, Novaya Zemlya;SA, Sardinia; SI, Siberia; SM, Sierra Madre; SVB, Svalbard; WI, Wrangel Island. Yellow shading represents probable continental areas and terrane extensions.



Cordilleran area to the west of the craton, the sea-floor spreading,which had started in the Late Devonian, continued. A variety of islandarcs, some preservedwithin the North Sierra, Klamath, Quesnellia andStikinia terranes, were positioned on the western margin of thewidening Slide Mountain–Golconda Ocean (Nokleberg et al., 2000;Colpron and Nelson, 2009), an ocean which reached its maximumextent in the Early Permian. In particular, Late Carboniferous and EarlyPermian voluminous basalts indicative of sea floor spreading arepreserved in the Slide Mountain Terrane of Yukon and BritishColumbia, and there was metamorphism as high as eclogite grade inthe Cordilleran Yukon-Tanana Terrane (Devine et al., in Colpron andNelson, 2006).

In today's Atlantic margins, and extending eastwards as far asEgypt, the Variscan Orogeny was at its maximum (compare our Earlyand Late Carboniferous maps), including the closure of the RheicOcean and turbulent events in Europe reviewed by many authors (e.g.Franke, 2006; McCann, 2008). In Britain, Early Carboniferousextensional tectonics caused grabens such as the Midland Valley ofScotland. The Variscan is represented in eastern North America in theAppalachian Orogen, locally termed the Alleghanian Orogeny, which

involved much crustal shortening and other complex tectonic activity(Hatcher, 2002), and which extended northwards into New England.


As the intervening seaway between Laurussia and Gondwanaclosed, the benthic invertebrate faunas changed from being overallcosmopolitan to becoming largely provincial in nature at the specieslevel. However, the overall faunal control was not only due tophysical separation but also to latitudinal differences, which were inturn linked to local temperatures. Thus the western Pangean marginhad the Midcontinent–Andean Province and the eastern margin theTethyan–Uralian–Franklinian Province, largely defined by fusulineforaminifera. From Early Permian times onwards the furtherevolutionary separation of those faunas caused Ross and Ross(1983) to upgrade the classification in the two sectors fromprovinces to realms.

Away from the equatorial areas (which included westernLaurussia) there was extensive and prolonged glaciation, particularlyin the Late Carboniferous, but there seems little evidence that most of

Fig. 17. Palaeogeography of Laurussia (including the Laurentian sector) and adjacent areas in the Early Devonian (Emsian) at 400 Ma. Shading as in Fig. 6. Some sites of theCordilleran, Rhenish and Appohimchi brachiopod provinces are also shown (data updated from Boucot et al., 1969).



western Laurussia wasmuch affected by the coldest climates at higherlatitudes, even though the global temperature gradients must havemuch more diverse than in the preceding periods. Although our map(Fig. 23) showsmuch of the craton as emergent land, sporadicmeltingof high-latitude ice caused much sea level change (Heckel, 1986),with the result that parts of the Laurentian Craton becamesporadically flooded in a comparable way to the northern Englandsector of Laurussia (Stephenson et al., 2010). Greb et al. (2008)documented the sedimentary cycles present in the Late Carboniferousof the Appalachians, where improved U–Pb dating has demonstratedthat the average maximum duration of each cycle was 0.1 my, whichsupports the possibility of short eccentricity-driven influences onsedimentation there. However, the chief variations in sedimentation

seem to have been caused more by tectonic activity in the commence-ment of the Alleghanian Orogoney there, with the glacioeustaticchanges having a less dominant role.

Land plants had become widespread and diverse during Devoniantime, and by the Early Carboniferous they had become segregated intofloral provinces, of which the North American, Euramerian andAngaran are known from our area. The distribution of thosepreviously-defined floral provinces was shown for the first time ontectonic maps by Chaloner and Lacey (1973), and their data pointswith more recent additions are plotted here in Fig. 23. However, thosefloral provinces were apparently more climate-controlled rather thanterrane-specific. This may be seen from the distributions shown byCleal (in McKerrow et al., 2000, Fig. 4), in which the Monilospora

Fig. 18. Terrane map of western and central Laurussia (including the Laurentian sector) and adjacent areas in the Late Devonian (Famennian) at 370 Ma. CA, Calabria; CH, Chukchi;FJL, Franz Josef Land; ML, Mendeleev; MO, Mixteca–Oaxaquia; NW, Northwind; NZ, Novaya Zemlya; SA, Sardinia; SM, Sierra Madre; SVB, Svalbard; WI, Wrangel Island; YT, Yukon-Tanana. Yellow shading represents probable continental areas and terrane extensions.



miospore flora was widespread in the more equatorial parts ofLaurussia and stretching from NW Canada to Scandinavia, in contrastto the more southerly temperate Grandispora flora, which wasprevalent in eastern U.S.A. and southern Europe. There is anexceptionally preserved lagerstatten deposit, with numerous plantsand arthropods among other faunas and floras, and known for manyyears, at Mazon Creek, Illinois.

During the Late Carboniferous, parallic coals were formedabundantly in a wide belt reflecting climate and palaeolatitude acrossLaurussia, particularly in eastern North America, Britain and centralEurope. The coals reached their maximum in the Moscovian and,although present in the succeeding Kazimovian and Gzhelian stages,were less substantial then. That dwindling was probably due to anincrease in aridity caused by global warming, as reviewed by Hiltonand Cleal (2007). The same non-marine bivalves are present in the

Late Carboniferous of both North America and Europe (Eager, inMcKerrow et al., 2000).

Stemmerik (2000) has produced progressive palaeogeographicalmaps of the northeastern area of Laurussia, including easternGreenland, Spitsbergen and Norway, during Carboniferous andPermian times. His analysis of the facies over that substantial areademonstrated a progression there from huge humid flood plains inthe Early Carboniferous through shallow warm seas in the MiddleCarboniferous to Middle Permian to cooler environments in the LatePermian. That progression collectively reflected substantial shifts inpalaeoclimatic and subsidence patterns, which were related to thenorthward drift of the area as well as to ongoing rifting. Further to thenorthwest, in today's Arctic area, substantial sedimentation occurredin the rapidly-deepening Sverdrup Basin, and there are thereextensive Late Carboniferous (Moscovian) bryozoan reefs (which

Fig. 19. Palaeogeography of western and central Laurussia (including the Laurentian sector) and adjacent areas in the Late Devonian (Famennian) at 370 Ma. Shading as in Fig. 6.



always tend to develop most substantially in temperate latitudes) onthe basin margin (Davies and Nassichuk, in Trettin, 1991).

Vai (2003) presented a series of Late Carboniferous to EarlyPermian maps showing the palaeogeography for the whole of Pangea.He also showed some biotic distributions for plants and reptiles, bothof which chiefly reflect the latitudinal belts which crossed the wholesuperterrane. Lethiers and Crasquin-Soleau (1995) used the distribu-tion of successive Carboniferous ostracod faunas to show that someoriginally North American forms had spread eastwards as far asHungary, Egypt and Oman.

17. Permian

Our reconstructions show the terranes and palaeogeography of theLaurentian sector of Pangea in the Early Permian (Artinskian) at

280 Ma (Figs. 24 and 25) and at the end of the Permian at 250 Ma(Figs. 26 and 27).


The Permian, which lasted for a substantial 51 my (from 299 to250 Ma), is most notable for being the time when the supercontinentof Pangea was at its maximum extent. The fusion of Gondwana withLaurussiawas essentially complete by the start of the period. However,in the southeast of our sector there was further consolidation of theMarathon–Ouachita–Appalachian fold belt in the Early Permian. In thesouthwest, the sinistral movement continued on from the Carbonif-erous, accompanied by thrusting of Carboniferous rocks (the LastChance Allochthon) over the western margin of the craton (the BirdSpring Shelf), as reviewed by Stevens and Stone (2007). The region

Fig. 20. Terrane map of western and central Laurussia (including the Laurentian sector) and adjacent areas in the Early Carboniferous (Early Visean) at 340 Ma. FJL, Franz Josef Land;MD, Moldanubia; MO, Mixteca–Oaxaquia; NSI, New Siberian Islands; NZ, Novaya Zemlya; QN, Quesnellia; SM, Sierra Madre; SVB, Svalbard; YR, Yreka; YT, Yukon-Tanana. Yellowshading represents probable continental areas and terrane extensions.



between Greenland and Norway underwent active rifting. The end ofthe Permian is remarkable for the immense Large Igneous Provinceoutpourings of the Siberian Traps in northeastern Pangea (Fig. 27),which extended northwards as far as the New Siberian Islands.

On the western margin of the Laurentian sector, in the southernparts of the Cordillera, early to late Permian island arcs withdiachronous calc-alkaline volcanism developed, such as those pre-served in the Klamath Mountains and Sierra Nevada of California,which had developed offshore during a period of extensionaltectonism in the region which had started in the Carboniferous(Dickinson, 2000). The arcs reached their maximum distance from theLaurussian Craton before the intervening Slide Mountain Oceanstarted to close again, and the terranes on either side were ream-algamated with the craton by Early Triassic times (Nokleberg et al.,2000; Colpron and Nelson, 2009). Early Permian metamorphismoccurred in the Central Metamorphic Belt at thewesternmargin of the

Eastern Klamath Terrane (Barrow and Metcalf, 2006). Belasky et al.(2002) concluded from the faunas that the Eastern Klamath, Stikiniaand Quesnellia Cordilleran terrane group lay 2000–3000 km awayfrom the Laurussian craton at the time, which gives a possibleapproximation for thewidth of the SlideMountainOcean. Belasky et al.(2002) also included the previously combined Wrangellia–AlexanderTerranes within the same group, but the latter had less diverse faunas,andwould seemmore probably to have been separate from the others.

Wrangellia, Alexander and some smaller adjacent terranes wereconsidered by Nokleberg et al. (2000), who determined from palaeo-magnetic data that their palaeolatitude was at about 15° N in Permiantime. However, since the combined terrane, big enough to be termed amicrocontinent, did not dock with North America until the Cretaceous,we are not sure where it was in relation to Laurussia even by thePermian, let alone at older times in the Palaeozoic, when many of theAlexander and Wrangellia faunas were distinctive, as further reviewed

Fig. 21. Palaeogeography of western and central Laurussia (including the Laurentian sector) and adjacent areas in the Early Carboniferous (Early Visean) at 340 Ma. Shading as inFig. 6.



in Section 19. Thus themicrocontinent is not shownon ourmaps since itprobably layoutside theirmargins. The Farewell Terranewasaffectedbythe Browns Fork Orogeny, of uncertain cause, at 285 Ma (Bradley et al.,2003), but, although Farewell is shown on our maps, its position withinthe Panthalassic Ocean is very poorly constrained.

As a consequence of the same subduction zone which closed theSlide Mountain Ocean by the end of the Permian, in Nevada theHavallah sequence was thrust eastwards on to authochthonousshallow-water Upper Palaeozoic strata along the Golconda Thrust inthe Late Permian to Earliest Triassic Sonoma Orogeny, as reviewed byDickinson (2000) and Stevens and Stone (2007).

In the Appalachian area in the east of the U.S.A., deformationoccurred in theAlleghanianOrogeny. Becker et al. (2006)describedhowchanges in thedetrital-zircon-agepopulation there correlatewith a shiftfrom transpressionally-inspired oblique deformation during the LateCarboniferous to foreland-vergent contraction in the Early Permian.


Global Permian terrane distribution and distinctive faunas andfloras were reviewed in a series of papers by Alfred Ziegler and hiscolleagues, e.g. Ziegler et al. (1997) and Rees et al. (2002). Ourdepiction of the land, shallow and deeper-water shelves and oceans inFigs. 25 and 27 have drawn heavily on those for the westernLaurussian area, as well as those in the book by Peter Ziegler (1989).

The major global Permo-Carboniferous glaciation ended at about280 Ma (Sakmarian). In Laurussia, the New Red Sandstone Continenthad originally formed in the Devonian and its successor continued as asubstantial landmass beyond the end of the Palaeozoic. That continentwas already large in the Late Carboniferous, stretching from the ArcticIslands of Canada south into South America and Africa, and itexpanded even further during the Permian, mirrored by a decreasein the size of the epeiric seas which had hitherto covered so much ofthe western Laurussian Craton. Nevertheless, the shallow-watermarine seas on the southern part of the craton have yielded anenormous number of well-preserved fossils, particularly the manyand diverse silicified brachiopods described by Cooper and Grant (e.g.1976) from the Glass Mountains of Texas. During the Early to MiddlePermian there were also many substantial reefs, such as the famous ElCapitan reef of Texas. However, although some global brachiopodprovinciality existed in the Carboniferous and Permian, most ofLaurussia then formed part of the extensive Tethyan Province, asreviewed by Shi (2006). There were extensive Early Permian(Artinskian) bryozoan mounds in the more temperate CanadianArctic islands. A coral belt, typified by Thysanophyllum, stretched allthe way from northern Greenland, through the Canadian ArcticIslands, and down the western edge of the craton into South America,as reviewed by Stevens and Stone (2007).

Early Permian benthic foraminifera, originally identified as asignificant assemblage from the McCloud Formation of California in

Fig. 22. Terrane map of the Laurentian sector of Pangea and adjacent areas in the Late Carboniferous (Moscovian) at 310 Ma. The light brown shading denotes the areas of theAlleghanian and Variscan orogenies. FJL, Franz Josef Land; MO, Mixteca–Oaxaquia; NSI, New Siberian Islands; NZ, Novaya Zemlya; QN, Quesnellia; SM, Sierra Madre; SVB, Svalbard;YR, Yreka; YT, Yukon-Tanana. Yellow shading represents probable continental areas and terrane extensions.



the Eastern Klamath Terrane (Stevens et al., 1990), and thus termed theMcCloud Belt, have been useful in identifying the integrity of theterranes in that area (Nokleberg et al., 2000; Colpron andNelson, 2009).Belasky et al. (2002) analysed brachiopods, fusulinids and corals in theEarly Permianofwestern Laurussia, and concluded that the faunas of theEastern Klamath, Stikinia and Quesnellia Cordilleran terranes were bythen similar to eachother. The conodontswere alsowidespread, andweshow thedistribution of Sweetognathus in theArtinskian,with data fromMei and Henderson (2001), indicating that, despite the contemporaryglaciation, the climate across the Laurentian sector of Pangea wasprobably not sharply differentiated enough to have formed narrowlatitudinally distinctive belts in the ocean.

In the Permian, the well-defined floral provinces continued onfrom the Carboniferous, and, as shown in Torsvik and Cocks (2004,Fig. 10) for the Early Permian, the Laurussian floras were distinct fromthose in Gondwana, China (Cathaysia Province), and Siberia (AngaraProvince). However, some Angaran elements are present in thePermian of the Cordillera. For example, although Mamay and Reed(1984) described an Early Permian flora from theMystic Subterrane ofthe Farewell Terrane which they termed Angaran; further materialfrom the same Mount Dall Formation shows the flora to be a mixtureof Angaran and Euramerican genera (Sunderlin, in Blodgett andStanley, 2008). However, as originally noted by Mamay and Reed(1984), there are no Permian floras known from western Laurussiabetween the Farewell Terrane and the U.S.A. at 40° N today, and thusthe boundary between the Southwestern American and Angaran

floras probably reflected, like the Carboniferous floras, a palaeotem-perature-controlled cline, accompanied perhaps by fluctuations inaridity, rather than abrupt separation.

At the close of the Permian, and essentially defining the Permo-Triassic boundary, there occurred the largest biotic extinction event inthe whole geological record, and the Laurentian sector of Pangea wasas badly affected by it as elsewhere. Those extinctions have beenexhaustively reviewed in many papers, but in the shallow-watermarine realm, the larger foraminifera, larger corals, trilobites andmost of the brachiopods all disappeared, many of which had hithertobeen so significant as palaeogeographical indicators. The prime causesof the extinctions were the colossal eruptions of the Large IgneousProvince (LIP) Siberian Traps, combined with the smaller-than-average lengths of coastlines available to house any great diversityof faunal niches (Wignall, 2007). However, the hitherto varied andabundant fusuline benthic foraminiferans became extinct in NorthAmerica after the Capitanian transgression in the Permian; earlierthan elsewhere in the world. Bond et al. (2010) linked those mid-Capitanian extinctions to the eruptions of the Emeishan LIP floodbasalts in China (Torsvik and Cocks, 2004, Fig. 11).

18. Mesozoic to Recent postscript

Pangea broke up slowly during the Mesozoic and early Tertiary,with initial stretching in the southeast of the Laurentian sectorstarting as early as the Late Permian and the Central Atlantic Ocean

Fig. 23. Palaeogeography of the Laurentian sector of Pangea and adjacent areas in the Late Carboniferous (Moscovian) at 310 Ma, shortly after Laurussia had amalgamated withGondwana. Provincial floral localities are shown, updated from Chaloner and Lacey (1973). Shading as in Fig. 6.



opening during the Early Jurassic. However, the northern part of theAtlantic, between northern Greenland and Norway, did not finallyopen until the Early Eocene at about 55 Ma (Mosar et al., 2002),leaving the eastern part of North America as a part of a passive marginresting on the ocean floor of the North American Plate, whichterminates eastwards at the spreading centre of the Mid-AtlanticRidge. In contrast, along its western leading edge, the North AmericanPlate has been and is overriding subducting oceanic plates at themargin of the Pacific Ocean, which is fuelling arc volcanism along theCascades and Central American margins.

Thus the area has seen the progressive development of accretion-ary complexes, magmatic belts, a mobile igneous and metamorphiccore zone, and a foreland belt of thin- and thick-skinned contractionaldeformation (Nokleberg et al., 2000). This includes the LateCretaceous and Paleogene uplifts of the Rocky Mountain forelandtermed the Laramide Orogeny. It also includes the final accretion tonorthern North America of today's eastern parts of Siberia, includingthe Omolon and Kolyma terranes, which had hitherto formed parts ofperi-Siberia. The last-named terranes are linked to the Cordilleranregion, which remains constantly dynamic, with most of the terranesthere accreting to the North American craton progressively fromTriassic to Palaeogene times, particularly in the Late Jurassic and

Cretaceous; and all accompanied by a substantial amount of strike–slip faulting and other tectonics. The North American Plate motionrelative to the main Pacific Plate remains oblique, resulting in the SanAndreas and other transform fault systems. The plate tectonicevolution of most of the Arctic Ocean area is poorly known but mostmodels include counterclockwise rotation of the Arctic Alaska Platewhich opened the Amerasia Basin (Fig. 1) during Late Jurassic andEarly Cretaceous times (e.g. Embry, 2000; Alvey et al., 2008;Dickinson, 2009). Subsequently the Lomonosov Ridge rifted offEurasia in the Early Tertiary (c. 55 Ma) and opened the EurasianBasin (Fig. 1) in the process.

19. Discussion

Many papers have linked Laurentia (and its successor continents)with Siberia in various ways and at various times during theProterozoic and Palaeozoic. Both continents probably formed partsof Rodinia until its breakup at about 800 Ma, but where they were inrelation to each other within that supercontinent is poorly con-strained. However, we consider that Laurentia probably remainedclose to Baltica and the South American (Amazonia) sectors of thefuture Gondwana in the late Precambrian, as shown in Fig. 4, rather

Fig. 24. Terrane map of the Laurentian sector of Pangea and adjacent areas in the Early Permian (Artinskian) at 280 Ma. FJL, Franz Josef Land; MO, Mixteca–Oaxaquia; NSI, NewSiberian Islands; NZ, Novaya Zemlya; QN, Quesnellia; SM, Sierra Madre; SVB, Svalbard. Yellow shading represents probable continental areas and terrane extensions.



than to the Siberian sector of Rodinia. By the Early Cambrian, bothSiberia and Laurentia were at the palaeoequator, but we estimate thatthere was something like 4000 km between them, although someauthors have regarded them asmuch closer. By the end of the Silurian,Siberia had moved into the northern hemisphere, but was not so farfrom the Baltica sector of Laurussia (Fig. 14).

But where were each of the numerous terranes now within theNorth American Plate and in the Cordillera of Alaska, NW Canada,western U.S.A. and northeastern Siberia situated in the Palaeozoic?Were they originally near or part of Laurentia, or somewhere at adistance from it, perhaps near Siberia or Baltica? The analysis of thediffering Precambrian ages and ratios of the reworked detrital zirconswithin the various terranes can be important clues, as reviewed byNelson and Colpron (2007). Nokleberg et al. (2000) listed and gradedall the palaeomagnetic data then available from the Cordilleraterranes. Some faunal elements, particularly in the benthos, are alsosignificant in deducing terrane positioning. However, true apprecia-tion of the significance of differences between the Earlier Palaeozoicfaunas is made more difficult because both Laurentia and Siberiaoccupied similar palaeolatitudes during the Cambrian and EarlyOrdovician, and most biota are linked to palaeotemperatures, whichin turn roughly reflect the palaeolatitudes. It was not until Silurian

times that Siberia was at a significant distance to the north of theEquator (Cocks and Torsvik, 2007, Fig. 6), in contrast to Laurentia/Laurussia, which remained on the Equator (Fig. 3).

Discussion now follows on some ‘exotic’ microcontinents—ArcticAlaska–Chukotka (parts of the larger Arctida Terrane concept of someauthors), Farewell, Wrangellia-Alexander, and Pearya.

19.1. The reality and extent of an Arctida Continent

There are many different published opinions as to whether or notsome of the terranes now in Alaska and northeastern Siberia weretogether united in a single substantial continent or a smallermicrocontinent in Palaeozoic times, and, if so, which terranes, atwhat times, and where were they in the past? For many years, since,for example, the work of Churkin (1972), it has been realised, that thegeology and faunas of parts of northeastern Siberia, such as theChukotka Peninsula, were not the same as themain Siberian Craton. Inaddition, parts of the Cordillera of Alaska and northwestern Canadawere not prime components of Laurentia/Laurussia in the Early toMiddle Palaeozoic, and the Bering Straits did not form amajor divisionbetween continents during the Palaeozoic.

Fig. 25. Palaeogeography of the Laurentian sector of Pangea and adjacent areas in the Early Permian (Artinskian) at 280 Ma. Shading as in Fig. 6. Localities of the conodontSweetognathus are shown (data from Mei and Henderson, 2001).



19.1.1. Previous workZonenshain and Natapov (1989), building on their earlier

publications, defined an Arctida continent which included the TaimyrPeninsula, Severnaya Zemlya, the New Siberian Islands, WrangelIsland, the northern Chukotka Peninsula, and parts of Alaska and theCanadian Arctic Islands (including Pearya). Its Palaeozoic history wasdescribed in Zonenshain et al. (1990). The site for a suture to the southof such a terranewas seen as the South Anyui Suture Zone, which runsapproximately east–west between the southern margin of thenorthern part of the Chukotka Peninsula and the rest of Siberia, andwhich is of Cretaceous (Neocomian) age (Natalin et al., 1999).

Ziegler (1989, pls 3 to 6) showed a composite terrane from the LatestSilurian to the Late Devonian (Famennian), which had two parts—whathe termed Chukotka (the northeastern Chukotka Peninsula) andArctica(largely the New Siberian Islands) and which were adjacent to eachother and not far from Laurussia, but separated from it by the activeInuitian Fold Belt. In contrast, he considered that the North Slope andadjacent areas of Alaska formed integral parts of Laurussia, as shown inhis Early Carboniferous to Late Permian maps (1989, pls. 7 to 13).

Grantz et al. (in Grantz et al., 1990, p. 396) grouped Chukotka andWrangel Island together with the Arctic Alaska Terrane as an Arctic–Alaska Plate. Sengor and Natalin (1996) recognised what they termedthe Chukotalaskides Orogenic System for the area. That concept wasdeveloped further by Natalin et al. (1999), who proposed the termBennett–Barrovia for a Late Precambrian block and adjacent Palaeozoicterranewhich stretched from the New Siberian Islands eastwards alongthe shelf of the East Siberian Sea, and through Chukotka and WrangelIsland to include much of the Seward, York, and Arctic Alaska terranes.Their LateOrdovician reconstruction (Natalin et al., 1999, Fig. 10) showsthe Bennett–Barrovia block as stretching diagonally across the oceanbetween Siberia and Laurentia, with the New Siberian Islands at itssoutheastern end and very close to the Omolon Terrane, itself portrayedas an extension of the old Siberian continent. Although that combinedBennett–Barrovia Terrane is shown in their diagrams as having aconsiderable area of Late Neoproterozoic (650–550 Ma) basement, thatbasement is only actually exposed west of the Bering Straits in tworather limitedplaces: theChegitunRiver areaof theChukotka Peninsula,and also on Wrangel Island.

Fig. 26. Terrane map of the Laurentian sector of Pangea and adjacent areas at about Permian–Triassic boundary time at 250 Ma. CH, Chukchi; CT, Chortis; EK, Eastern Klamath; FJL,Franz Josef Land; FW, Farewell; K–O, Kolyma–Omolon; LS, Lomonosov Rise; ML, Mendeleev Ridge; MO, Mixteca–Oaxaquia; NS, North Sierra; NSI, New Siberian Islands; NW,Northwind; NZ, Novaya Zemlya; QN, Quesnellia; RM, Roberts Mountains; SM, Sierra Madre; ST, Stikinia; SVB,Wrangel Island; YT, Yukon-Tanana. Yellow shading represents probablecontinental areas and terrane extensions.



Dumoulin and Harris (1994) and Dumoulin et al. (2002) identifieda single large carbonate platform (with conodont faunas discussedbelow) in the Cambrian to Middle Ordovician which included theChukotka, York, Seward, Farewell, and Arctic Alaska terranes, andpossibly also the New Siberian Islands, although they recognised somedeeper-water basins within that platform. Dumoulin et al. (2000)published a schematic Middle Ordovician reconstruction showing a‘Northern Alaska’ Terrane (which presumably included Chukotka)relatively close to Siberia and separated from Laurentia by the PearyaTerrane. However, Nokleberg et al. (2000) showed the Arctic AlaskaTerrane as embedded within the Laurussian Craton in its modernposition before the Devonian.

Lane (in several papers reviewed by him in 2007) concluded,amongst other things, that the Laurussian–Arctic Alaskan amalgam-ation was represented by the Early Devonian (400 Ma) RomanzofOrogeny in the eastern part of the Arctic Alaska Terrane. Embry(2000) disputed some of Lane's conclusions, particularly since theywould mean the rejection of the counterclockwise rotation modelsupported by many authors, which convincingly demonstrates howthe modern Arctic Ocean area evolved during the Mesozoic to Recent.Embry (2000, Fig. 3) illustrated the Arctic Alaska Terrane as close tothe Laurussian Craton in the Devonian, but orientated at right angles

to it, with only today's eastern end adjacent to the craton. Embry didnot ignore the differing Lower Palaeozoic faunas of Dumoulin andHarris (1994), but he suggested that they could have reflected asituation in which Arctic Alaska was in the order of 2000 km awayfrom Laurentia in the Ordovician.

Colpron and Nelson (e.g., 2009, Fig. 11) depicted the Arctic AlaskaTerrane as a separate entity stretching between Siberia andnortheastern Laurentia (north of Pearya) and as a northern extensionof the Caledonide Orogeny in the Late Silurian (425 Ma). Based partlyon Precambrian zircons and partly on the distribution of thedistinctive Silurian aphrosalpingid–stromatolite faunas, they placedthe Yreka and Alexander terranes as welded to the Uralian margin ofBaltica, and the Farewell Terrane as welded to the northwest ofSiberia. By the Early Devonian (395 Ma) they show Arctic Alaska ashaving moved westwards to northwestern Laurentia, where itstayed for the rest of the Palaeozoic. Amato et al. (2009) presenteddetails of the zircons which have been found in the Arctic AlaskaTerrane and emphasised its different Precambrian origins fromLaurentia.

Unfortunately, Palaeozoic palaeomagnetic data from the ‘Arctida’elements (e.g. Farewell, Arctic Alaska, Chukotka, Pearya, WrangelIsland and the New Siberian Islands) are non-existent.

Fig. 27. Palaeogeography of the Laurentian sector of Pangea and adjacent areas at about Permian–Triassic boundary time at 250 Ma. Shading as in Fig. 6. The Siberian Traps LargeIgneous Province is shown in dark red.



19.1.2. Faunal analysisCambrian and Ordovician trilobite faunas have long been known to

have been globally provincial. A.R. Palmer (in Dutro et al., 1972)recorded both Lower Cambrian (Olenellus) and Upper Cambrian(Geragnostus, Saratogia and an unidentified ptychopariid) faunas fromthe Brooks Range in the Arctic Alaska Terrane. In the HammondSubterrane of the Arctic Alaska Terrane, the trilobites Kounamkites,Kootenia andothers came fromMiddle Cambrianphyllites (Palmer et al.,1984). These faunas are mostly of mixed Laurentian–Siberian aspect,although the important and normally typically Laurentian ProvinceOlenellus is not known from Siberia. The records of the Late Ordovician(probably Early Katian) trilobiteMonorakos from the Seward Terrane ofAlaska as well as from the Chukotka Peninsula (Ormiston and Ross,1976) seem very significant, not least because the whole familyMonorakidae is otherwise endemic to Siberia, as reviewed by Forteyand Cocks (2003). Unfortunately, although other aspects of theOrdovician and Silurian palaeontology of the Chukotka Peninsula wereprovisionally described by Oradovskaya and Obut (1977), the limitedfaunas they identified give no clear palaeogeographical signals.

Dumoulin and Harris (1994) and Dumoulin et al. (2002) identifiednumerous Cambrian and Ordovician conodonts from both Alaska andnortheastern Siberia, including many species which are foundelsewhere only in either the North American Province or the SiberianProvince, although both those provinces were subdivisions ofBergström's (1990) Cosmopolitan Realm in the Ordovician. Inaddition to the endemic species, an overwhelming proportion oftaxa are common to both provinces, and Arctic Alaska–Chukotka wasseen to contain a mixture of Siberian and Laurentian faunas. Thus theauthors concluded that the three continents were probably not veryfar apart from each other.

Much emphasis has been placed on the distribution of the LateOrdovician (Katian and Early Hirnantian) pentamerid brachiopodTscherskidium in some analyses, and indeed that unmistakable genusis at its most abundant at many Siberian localities. Nevertheless, it hasalso been recorded sporadically from the Laurentian Craton inGreenland and also occurs in South China, Kara, and elsewhere, aswell as in the Seward, Arctic Alaska and Chukotka terranes, and thusthe genus is best thought of as cosmopolitan. Its absence frommost ofthe Laurentian Craton may have been artificially enhanced by therelative lack of Late Katian and Hirnantian rocks there due to thewidespread and substantial Ordovician–Silurian unconformities.

The faunal signals from the Upper Palaeozoic are more mixed. Themany Devonian macrofossil faunas, particularly brachiopods andgastropods, in the Arctic Alaska, Seward and York terranes (referencesabove in Section 6.3) containmany otherwise characteristically Siberianfossils, but there are also some with more Laurentian affinities. Forexample, the Seward Terrane has Early Devonian (Emsian) brachiopodsand corals (reviewed by Blodgett et al., 2002), many with Siberianaffinities. The De Long Mountains Subterrane of Arctic Alaska hasDevonian (Eifelian and Givetian) brachiopods of general Old World(including Siberian) aspect, also reviewed in Blodgett et al. (2002). Theflora present in the Early Carboniferous of the Arctic Alaska Terraneconsists chiefly of genera best known from the Angara Flora of Siberia(Spicer and Thomas, 1987).

19.1.3. Conclusions on Arctida and Arctic Alaska–ChukotkaThe separate elements of the Arctida Terrane as defined by

Zonenshain and Natapov (1989) are considered in turn. More workhas been done on the Taimyr Peninsula, reviewed by Cocks and Torsvik(2005), and the northern parts of that peninsula, as well as the variousislands of Severnaya Zemlya, are now considered to form the separateKara Terrane, rather than having direct Palaeozoic links with any of theareas further along the current Siberian margin to the east. The KaraCambrian and Ordovician faunas show a mixture of Siberian and Balticaffinities (Rushton et al., 2002), and do not bear a strong resemblance tothose in the more eastern parts of Siberia (including the Chukotka

Peninsula), and none to those in Laurentia. The Palaeozoic positions ofthe Kara Terraneweremapped by Cocks and Torsvik (2005, 2007), whoconcluded that Karawas an independent terrane, and separate from theArctic Alaska–Chukotka Microcontinent.

Whether or not the New Siberian Islands were truly linked to theChukotka Peninsula as a part of the Arctic Alaska–Chukotka Micro-continent is more controversial. Various authors, for example Natalin etal. (1999) and Kuzmichev and Pease (2007), show the South AnyuiSuture Zone (exposed in the Chukotka Peninsula) as extendingwestwards beneath the sea to the south of the New Siberian Islandsand thus separating the latter from the Siberian continent, as do Frankeet al. (2009) and Miller et al. (2009). However, we conclude that thisinterpretation is unlikely, since we believe that those islands formedpart of Siberia itself during the Palaeozoic. Facts supporting thatconclusion are, firstly, Kuzmichev and Pease (2007) published chemicalanalyses of the Permo-Triassic basalts present there on Bel'kov Island,and concluded that they had the characteristic signature of the majorend-Palaeozoic plume-related outpourings of the Siberian Traps LargeIgneous Province, reviewed by Cocks and Torsvik (2007), which couldonly be so if those islands formed part of, or were very close to, theSiberian continent at the end of the Permian. Secondly, the well-monographed (but seldom referenced) Middle Cambrian trilobites ofBennett Island (Holm andWestergaard, 1930), one of the New SiberianIslands, are primarily of Siberian provinciality (with some Balticaffinities), and do not mirror the mix of Laurentian and Siberian faunasfound in the Lower Palaeozoic of the Arctic Alaska–Chukotka Micro-continent as reviewed here. Unfortunately most of the other Palaeozoicfaunas recorded from the New Siberian Islands are either poorly-monographed, consisted of relatively cosmopolitan taxa, or swam (forexample, the cephalopods of Nikolaeva et al., 2009), and are thus nothelpful in being terrane-diagnostic.Wedonot question the reality of thestructures documented through offshore seismic data to the south of theNew Siberian Islands by Franke et al. (2009), but they need notnecessarily represent a westward extension of the South Anyui Suture.

The overall conclusions to be drawn from the faunas are in supportof an independent Arctic Alaska–Chukotka Microcontinent during theLower Palaeozoic and Early Devonian. During the rest of thePalaeozoic, even though today's eastern end of that microcontinenthad become accreted to Laurussia, the fauna included many taxa withSiberian affinities simply because it spanned palaeolatitudes furthernorth than elsewhere in Laurussia, similar to the latitudes of Siberia.

Thus the independent Palaeozoic microcontinent which werecognise consists of the Chukotka, Wrangel Island, Seward, York,and Arctic Alaska terranes on land today, but not Farewell (discussedbelow), Kara or the New Siberian Islands. That is similar to the smallerof the two Arctic Alaska–Chukotka Terrane options of Miller et al.(2009, Fig. 1B). In addition, although today under the Arctic Ocean, wehave also grouped the Northwind Ridge, the Chukchi Platform, andthe Mendeleev Ridge areas within the same microcontinent, eventhough no Palaeozoic rocks are known from the last two and theOrdovician conodonts from Northwind Ridge are not terrane-diagnostic. This is because that solution seems themost parsimonious,since it avoids postulating additional subduction zones. The micro-continent, with its Proterozoic core, was situated somewhere withinthe substantial oceanwhich lay between Laurentia, Siberia and Balticaat the start of the Palaeozoic. It subsequently drifted southwardstowards Laurentia, so that today's eastern end of the Arctic Alaska–Chukotka Microcontinent accreted to Laurentia near the end ofthe Devonian, but at right angles to its current orientation. Themicrocontinent only finally reached its present position within NorthAmerica after the Mesozoic counterclockwise rotation which openedthe Amerasia Basin within the Arctic Ocean, as reviewed by Embry(2000).

A vexed question is what to call the microcontinent. Since it doesnot include the New Siberian Islands, it is inappropriate to followNatalin et al. (1999) in terming it Bennett–Barrovia. Nokleberg et al.



(2000) do not recognise the combined unit. Dumoulin et al. (2002),whilst coming to similar conclusions as ourselves, do not specificallyname the microcontinent. The name Arctic–Alaska would beappropriate except that it is already used for the terrane confinedsolely to northern Alaska and northwestern Yukon, and does notinclude the other elements of the unit. Beringia would be even moreappropriate, but it is used for the variable Tertiary to Recent landbridge across the Bering Straits. Thus, rather than launch yet anothername, we (reluctantly) retain the term Arctic Alaska–Chukotka.

As well as many of the Devonian to Permian marine faunas, ourplacing of the Arctic Alaska–Chukotka Microcontinent (Fig. 23) alsoexplains the otherwise anomalous occurrence of the CarboniferousAngara Province flora within it. We consider that those floras werecontrolled more by temperature than by continental separation, andthat therewas no abrupt border between the Angara and Euramericanprovinces, but simply a biological cline. Thus the transition betweenthose provinces must have been near the junction between ArcticAlaska–Chukotka and themain Laurussian Craton. Both Arctic Alaska–Chukotka and Siberia were then at higher palaeolatitudes than therest of Laurussia.

19.2. The Farewell Terrane

The Farewell Terrane, which includes the Mystic, Dillinger andNixon Fork terranes or subterranes in central Alaska, also requiresevaluation.

19.2.1. Previous workNokleberg et al. (in Plafker andBerg, 1994) andNokleberget al. (2000,

Figs. 8–14) show the Mystic, Nixon Fork, and Dillinger terranes astogether forming a relatively small independent microcontinent fromCarboniferous to Cretaceous times in what they term the GoodnewsOceanoffshore of, but relatively close to, Laurussia until its amalgamationwith North America at the end of the Jurassic. However, they interpretedthat unit as having been derived from Palaeozoic Laurentia, whichwe donot follow here because of the many non-Laurentian aspects of theirfaunas, reviewed below. Dumoulin et al. (2002) identified a single largecarbonate platform in the Early toMiddle Ordovicianwhich included theFarewell in with the Arctic Alaska–Chukotka terranes. Bradley et al.(2003) described the geology and identified the Browns Fork Orogenythere. Colpron and Nelson (2009) showed the Farewell Terrane asforming part of the margin of Siberia in their Silurian to EarlyCarboniferous reconstructions and as subsequently migrating quicklywestwards to an independent position well outboard of Pangea andwithin the Panthalassic Ocean by the end of the Permian.

19.2.2. Faunas and florasSt. John and Babcock (1997) described and figured a Late Middle

Cambrian trilobite fauna from the Farewell Terrane, which, as well asvarious agnostids (which swam and were thus seldom trulyprovincial), contained Proampyx, Juraspis, Bailiaspis, Dasometopus,Hartshillia, Tchaiaspis, Corynexochus, Kootenia, Anopolenus, Paradox-ides, Solenopleura and Parasolenopleura. A.W.A. Rushton kindlyinforms us that that fauna suggests a cool-water, outer shelf setting,and that there is a strong provincial resemblance to Siberia, althoughsome, such as the species of Paradoxides, also occur in Baltica.However, the fauna shows no links with Laurentia.

The distinctive Late Silurian aphrosalpingid sphinctozoan sponges,originally described by Rigby et al. (1994) and reviewed by AntoshkinaandSoja (2006) andSoja andKrutikov (inBlodgett andStanley, 2008), areonly known in the Cordillera from the Alexander and Farewell terranes,but they also occur in Salair (Siberia) and at several localities in thenorthern Urals (Baltica). They have been interpreted by some authors(e.g., Colpron and Nelson, 2009, Fig. 11), as being significant in terranepalaeogeographical reconstructions. However, particularly since they areassociatedwith stromatolites, which are uncommon in the Silurian, these

associations probably lived in a specialised marginal environment, ratherthan their distribution being controlled through being at any particularterrane margin. As can be seen from our previous maps (Cocks andTorsvik, 2002, 2007), the areas fromwhich those sponges are knownwereat substantial distances from each other in the Late Silurian, and thus wedo not consider the sponges useful for indicating terrane positions. Forexample, it is difficult to envisage how the Urals and Salair could havebeen adjacent to each other, let alone to Farewell andAlexander; and thuswe do not follow the Colpron and Nelson (2009) “Northwest Passage”model, which would also involve very substantial post-Silurian move-ments of the Yreka, Alexander and Farewell Terranes.

The Mystic Subterrane has yielded Emsian brachiopods (Blodgett,1998; Blodgett and Boucot, 1999), including the distinctive Ivdeliniaand Sibirirhynchia, which are Rhenish–Bohemian and Siberian generanot otherwise known from the W sector of Laurussia, apart from inother Cordilleran suspect terranes. Blodgett and Boucot (1999)described Devonian (Emsian) brachiopods (including Plicogypa andTaimyrrhynx); and Johnson and Blodgett (1993) corals and Eifelianbrachiopods from the Nixon Fork Subterrane, many of which are nottypically Laurentian. The flora from the Early Permian Mount DallConglomerate of the Farewell Terrane represents taxa of mixedAngaran and Euramerican phytogeographic affinity (Mamay andReed, 1984; Sunderlin, in Blodgett and Stanley, 2008).

19.2.3. Conclusions on the Farewell TerraneThe Farewell is very structurally fragmented, and thus its outline and

positions are arbitrary on our reconstructions. On faunal grounds,particularly the largely Siberian (but not Laurentian) Cambriantrilobites, we conclude that it was microcontinent separate fromLaurentia in the Early Palaeozoic and comparable to, but differentfrom, the Arctic Alaska–Chukotka Microcontinent reviewed above.Schuchert (1923, Fig. 3) perceptively identified a ‘Yukonia’ for much ofthe same ground. However, there are no exclusively Baltica faunalsignals in the Farewell Terranewhichwould justify the placing of it nearBaltica as shown by Colpron and Nelson (2009), and it seems mostsimpleon the availabledata toplace it nearArctic Alaska–Chukotka. Thisis especially since some of its Early Neoproterozoic zircons are similarbetween Farewell and Arctic Alaska (Bradley et al., 2003); otherwiseadditional subduction zones and other fundamental tectonic featureswould need to be invoked for Farewell alone. Its detailed Palaeozoicpositions are poorly constrained, but we show it on our reconstructionsfrom the Early Silurian (Fig. 12) onwards. However, in contrast to ArcticAlaska–Chukotka, there is noevidence that Farewell becamean intrinsicpart of North America until the Jurassic. The significance of the EarlyPermianBrownsForkOrogenyof Bradley et al. (2003) is uncertain, but itmay simply represent the accretion of hitherto separate elementswithin the Farewell to each other.

19.3. Wrangellia, Alexander and associated terranes

In addition to Arctic Alaska–Chukotka and Farewell consideredabove, other Cordilleran terranes contain faunas with substantialproportions of Palaeozoic fossils which originated from elsewherethan Laurentia, most notably Alexander and Wrangellia (includingChilliwack).

The faunas and floras of the Alexander Terrane were reviewed byBlodgett (1998) and Blodgett et al. (2002, 2010), who concluded thatthe whole sequence is better attributed to the Old World Province(including Siberia), rather than to the North American Province.Blodgett et al. (2010) concluded that the Silurian and Lower Devoniansequences and brachiopods are most similar to those in the Omolon(or Ormulev) Terrane of peri-Siberia. However, the brachiopods fromwhich those conclusions were reached, which include Brooksina,Kirkidium, Harpidium, Atrypoidea and Gracianella, are also found in theUrals, so we do not agree a precise link between the Alexander andOmolon terranes. From analysis of the Devonian rugose corals, Pedder



(2006) also concluded that the dominant faunas were not typicallyLaurasian, and that the Alexander Terrane was at about 20° N duringthe Early Devonian (Pragian). In addition, the rich Early Devonian(Emsian) brachiopod fauna from the Alexander Terrane described bySoja (1988) consists of a roughly equal mix of cosmopolitan andendemic species, which led to her conclusion that no close relation-ships with the Uralian or Siberian faunas were to be seen. Some otherbrachiopods have patchy distributions; for example, the rarepentameride Nanukidium is known only from the Late Silurian ofSomerset Island on the Laurentian Craton and from rocks of the sameage in the Alexander Terrane (Savage, 1989), but we do not concludethat those sites were adjacent to each other at the time. The LateDevonian (Frasnian) brachiopods from the Alexander Terrane(Suemez Island) described by Savage et al. (1978) were consideredas ‘unusually provincial at a time when brachiopods were generallycosmopolitan’. The Early Permian corals, brachiopods and fusulinesanalysed by Belasky et al. (2002) showed that those of Wrangellia–Alexander (which had been earlier stitched together by a LateCarboniferous granite) were significantly similar (95% confidencelevel) to Stikinia, and contrasted with those of the Eastern KlamathTerrane.

Nokleberg et al. (2000, Figs. 7–14) show an independent terranecomprising the united Wrangellia and Alexander terranes as quiteseparate from Laurussia, and, through palaeomagnetic data, to haveformed amicrocontinent situated at 8–14° N in the Late Devonian andCarboniferous, 15° N in the Triassic, 25° N in the Lower and MiddleJurassic, 35° N in the Late Jurassic and moving to 60° at the time of itsCretaceous accretion to North America.

Having reviewed all the faunal and palaeomagnetic data, some ofwhich is itemised above and also in Section 7.4, we agree withNokleberg et al.'s (2000) analysis that the Wrangellia, Alexander andassociated terranes made up a microcontinent originating in a mid-oceanic position. However, during the Palaeozoic that microcontinentmust have lain outside the area of the maps presented here andprobably nearer Siberia than Laurentia. Although Blodgett et al.(2002) considered that the closest faunal similarities are with theFarewell Terrane, we do not think that those links are strong enoughto prove that Wrangellia–Alexander microcontinent was necessarilyvery close to the Farewell Terrane during the Devonian.

19.4. The Pearya Terrane

The northernmost part of Ellesmere Island, Arctic Canada, consistsof the Pearya Terrane (Section 9.1.2), whose geology was summarisedby Trettin (1987, 1991, 1998). Precambrian to Middle Ordovicianmetamorphic rocks are deformed by the Middle Ordovician M'Clin-tock Orogeny together with the intrusion of 480–460 Ma graniteplutons. That orogeny appears to have been caused by Pearya'samalgamation with an Ordovician island arc whose remains are onlypreserved within the Emma Fjord Fault Zone, which abuts Pearya toits south (Klaper, 1992) and which we depict on our Ordovician andEarly Silurian maps. The amalgamated terrane later docked with theLaurentian Craton at a date which is poorly constrained, but whichwas plausibly estimated as Late Silurian by Trettin (1987). Dumoulinet al. (2000) published a Middle Ordovician reconstruction showingthe Pearya Terrane as an island arc relatively close to its presentposition north of the Canadian Arctic Islands.

There have been suggestions, reviewed by Gee and Trebenkov(2005) andMazur et al. (2009), that the Southwestern Terrane group ofSpitsbergen may have originally been connected to Pearya in theNeoproterozoic and early Palaeozoic; a conclusion supported byMiddleOrdovician tectonism in Southwestern Svalbard of the same age as theM'Clintock Orogeny in Pearya. Unfortunately there are no EarlyPalaeozoic faunas preserved in Southwestern Svalbard because of themetamorphism there. In our 440 and 420 Mamaps, we have shown the

accretion of Pearya to Laurentia as the northernmost sector of theCaledonide Orogeny, as suggested by Trettin (1991).

20. Conclusions

Laurentia, the second-largest continent after Gondwana in the LowerPalaeozoic,was independent for about 150 my, from the Late Proterozoicat about 570 Ma (when it left other continents with the opening of theIapetus Ocean) until its Silurian collision with Avalonia–Baltica to formLaurussia in the Caledonide Orogeny at around 425Ma. Because itretained its essentially trans-equatorial position throughout that time,and because shallow seas repeatedly flooded the craton (Haq andSchutter, 2008), the diversity of Laurentian shallow-marine faunas, suchas trilobites and brachiopods, remained high during most of the LowerPalaeozoic. The faunal endemism varied, being strong during theCambrian and Early Ordovician, when the Iapetus Ocean was at itswidest, but decreased during the Ordovician as Iapetus narrowed, and,after the end-Ordovician glaciation and during the Silurian, Laurentianfaunas formedpart of amuchmorewidely-distributed cosmopolitan andlessdiverse series of animal communities. ThePearyaTerraneofnorthernEllesmere Island, which docked with Laurentia in the Silurian, probablyrepresents the most northerly sector of the Caledonide Orogeny.

In contrast to most of the Silurian, in the Early Devonian the NorthAmerican brachiopod province and subprovinces were again distinctfrom their European (Rhenish–Bohemian) counterparts, but thatprobably reflects the more varied climatic belts and land divisionswithin Laurussia, rather than terrane separation across the RheicOcean. The continent was dominated by the Old Red Sandstonelandmass, around which the southern and western margins of thecraton were flooded with shallow-water sediments, mainly carbo-nates. Many of those land areas in western Laurussia and subse-quently Pangea persisted until later than the end of the Palaeozoic.Extensional tectonism to the southwest of the Laurentian sector ofLaurussia, in the area in and around California, resulted in theformation of Devonian island arcs, but that trend was eventuallyreversed to lead to the Late Devonian Antler Orogeny and consequenteastward nappe thrusting over the craton there.

Much of the northernmargin of Laurentia and Laurussiawas passiveduring the Lower Palaeozoic, as was the southern margin of thecontinent until the amalgamation of Pangea during the Carboniferousand Permian Ouachita Orogeny. In contrast, the eastern margin wasmuch more active during most of the Palaeozoic, where progressiveisland arc accretion and eventually the CaledonideOrogenyoccurred, allresulting from substantial subduction beneath the Iapetus Ocean. Thewestern margin of the craton was largely passive, although there werecertainly island arcs fringing the continent in the Lower Palaeozoic, ascan be seen from their Laurentian faunas. Some of these were thrusteastwards on to the craton at the time of the Late Devonian AntlerOrogeny, presumably resulting from active subduction under what isnow the Pacific Ocean area.

The Carboniferous was marked by the approach of the supercon-tinent of Gondwana, with which Laurussia eventually collided in theLate Carboniferous, causing the Ouachita Orogeny. Since that collisionwas oblique, much of the collisional stress was taken up throughactive strike–slip faulting. The leading edge of Gondwana wasrepresented not by its main craton, but by the hitherto peri-Gondwanan Mexican terranes and the Florida (Suwanee) Terrane.The Ouachita Orogeny was probably linked to the AlleghanianOrogeny of the Appalachians and the Variscan Orogeny of Europe.

During the Permian, Pangeawas enlarged to the east by the accretionof Siberia, but the Laurentian sector was relatively quiescent until theLate Permian,when further crustal extension producedmore island arcsin the Californian area, and that tectonic activity culminated in the LatePermian to Earliest Triassic Sonoma Orogeny there.

In the Cordillera, some terranes, including Yukon-Tanana, SlideMountain, Kootenay, Cassiar, Eastern Klamath, North Sierra, Quesnel



and Stikinia, as well as the Roberts Mountains and Golcondaallochthons, have faunal and structural components which linkthem to Laurentia in the Palaeozoic, and many were probably formedas offshore island arcs. However, the substantial Arctic Alaska Terrane,and the Seward and York terranes of the Northern Cordillera have adifferent origin, as can be seen by their contained Palaeozoic faunasand Precambrian zircons, and, together with the Chukhotka andWrangel Island terranes of Siberia (and probably the Northwind,Chukchi and Mendeleev terranes of the Arctic Ocean), had anindependent Early Palaeozoic history as a microcontinent betweenSiberia and Laurentia. From the mixed Laurentian and Siberian faunaspresent, we conclude that the Arctic Alaska–ChukotkaMicrocontinentwas probably not more than 2000 km from Laurentia at the start ofthe Palaeozoic, and accreted to it in the Late Devonian. Even thoughmany of the subsequent faunas there also had close links with those ofSiberia, we conclude that this was as much due to their morenortherly latitudinal position rather than to Siberia and the ArcticAlaska–Chukotka Microcontinent being very close to each other. TheAlexander and Wrangellia terranes (which united in the Carbonifer-ous) and the Farewell Terrane, were also apparently independent butdifferent microcontinents within the Panthalassic Ocean, but did notjoin North America until Late Jurassic or Cretaceous time.

Acknowledgements

We are extremely grateful to many geologists for discussion,information and literature, particularly Robert Blodgett, Art Boucot,Dwight Bradley, Julie Dumoulin, Ashton Embry, Richard Fortey, RichardHerrington, Duncan Keppie, Bruce Lieberman, JoAnne Nelson, AdrianRushton, Cees vanStaal, LiadanStevens, PaulWignall, StephanieWernerand David Worsley. Statoil are thanked for funding and The NaturalHistory Museum, London, for the provision of facilities, which includethe photography of brachiopods by Phil Crabb.

Appendix 1. Orogenies in the Palaeozoic of North America

In contrast to most of the rest of the world, where importantorogenies are often extended to inappropriate locations (such as theso-called ‘Caledonian’ Orogeny of China), there are many orogenicnames used in North America, not all of which are universally familiar.Thus we present a short aide memoire here, but it omits the manymore orogenies named in the area in the Precambrian andMesozoic toRecent.

Acadian Orogeny

Middle to Late Devonian (385–370 Ma, Givetian to Frasnian)orogeny in the Appalachians, but the term is sometimes also used forLatest Silurian (415 Ma) events better termed the Salinian Orogeny.

Alleghanian Orogeny

Middle Carboniferous to Middle Permian orogenesis in the Appa-lachians, probably reflecting a variety of separate events, but at leastpartly a western extension of the Variscan Orogeny in Europe (Fig. 22).

Antler Orogeny

Late Devonian to Early Carboniferous tectonism affecting theEastern Klamath Terrane and overthrusting the Roberts MountainAllochthon on to the Laurentian Craton.

Browns Fork Orogeny

Early Permian tectonism in the Farewell Terrane of Alaska (Bradleyet al., 2003).

Caledonian (or Caledonide) Orogeny

The major event peaking in the mid-Silurian caused by thecollision of Laurentia and Avalonia–Baltica.

Ellesmerian Orogeny

Late Devonian to Early Carboniferous orogeny in the Canadian ArcticIslands and parts of Greenland and Svalbard. Also sometimes used forDevonian andCarboniferous orogenesis in theArctic–Alaska Terrane area.

Franklinian

Term usually used for the cratonmargin sediments andmobile beltnear the Arctic margin of northwestern Canada (e.g., Trettin, 1991),rather than for an orogeny. However, Franklinian Orogeny has beenused by various authors (e.g. Golonka et al., 2003) for the Palaeozoicorogenesis in the same area and extending eastwards to NWGreenland; but Moore et al. (in Plafker and Berg, 1994, p. 56)considered the term obsolete, since several orogenic events have beenconflated, and we follow them.

Innuitian Orogen

General term for the orogenically disturbed Arctic margin ofnortheastern Canada and Greenland from the Precambrian to the LatePalaeozoic, including the docking of the Pearya Terrane and theformation of the Sverdrup Basin. Not used in this paper.

Klakas Orogeny

Late Silurian to Early Devonian collision of the Alexander Terraneof Alaska with unspecified neighbouring terrane(s).

M'Clintock Orogeny

Mid-Ordovician deformation within the Pearya Terrane of north-ern Ellesmere Island (Trettin, 1991).

Neoacadian Orogeny

Devonian to Carboniferous orogeny in the Appalachians, some-times termed ‘Late Acadian’ and used variably by different authors.

Ouachita Orogeny

MiddleCarboniferous toEarly PermianOrogeny in the southernU.S.A.reflecting the accretion of Laurussia to Gondwana to form Pangea.

Penobscottian Orogeny

Lower Ordovician orogeny in the Appalachians (van Staal, 2005).

Romanzof Orogeny

Early to Middle Devonian orogenesis (at about 400 Ma) affectingthe Arctic–Alaska Terrane in NW Yukon, including the North Slope ofAlaska, possibly caused by the interaction of that terrane with theLaurussian Craton.

Salinian Orogeny

Latest Silurian to Earliest Devonian orogeny in the northernAppalachians; although van Staal et al. (2009) used ‘Salinic’ Orogenyfor Early to Late Silurian (440–423 Ma) phases of the CaledonideOrogeny there.



Sonoma Orogeny

Permian to Early Trias orogeny in the Cordillera region of Californiaand adjacent areas.

Taconic (or Taconian) Orogeny

Variably used term for events in the western Appalachians rangingfrom Latest Cambrian to Earliest Silurian in age, but chiefly Middle toLate Ordovician. van Staal et al. (2007) defined three separate phases:Taconic 1 (c. 495 Ma—Furongian), Taconic 2 (470–460 Ma—Dapingianand Darriwilian), and Taconic 3 (454–442 Ma—Katian and Hirnantian).

Wales Orogeny

A pre-Ordovician (probably Cambrian) event of uncertain dateaffecting the southern part of the Alexander Terrane.

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