42 NORTH AMERICA/Northern Cordillera were uplifted and exposed above sea-level during folding and thrusting towards, and over, the edge of the continental platform, and accumulated in foreland basins along the margins of the advancing fold and thrust belt The sediments, up to km thick, consist of deltaic and alluvial sandstone, shale, conglomerate, and coal, as well as intertonguing marine sediments deposited during three transgressive–regressive cycles of latest Jurassic and Early Cretaceous, mid-Cretaceous, and Late Cretaceous and Palaeogene ages Rocks of the Orogenic Collage Major components of the orogenic collage have been called terranes These are fault-bounded regions of upper crustal rocks, detached from their lower crust and mantle lithospheres, and with different geological histories from one another Many terranes contain palaeomagnetic, palaeobiogeographical, and/or detrital zircon signatures very different from those of neighbouring terranes and from the north-western (in present co-ordinates) Laurentian margin Most terranes in the Pacific Mountains and Intermontane Plateau Systems south of latitude 60 N are remnants of arcs and accretionary complexes whose generally low Sri and positive eNd values indicate the mantle origins of the magmatic rocks within them Others, mainly in the western Rocky Mountains System and Intermontane Plateau System north of latitude 60 N, are displaced former continental margin deposits (Figure 3; Appendix B) Evidence of terrane provenance and amounts of displacement can be gathered by comparing these signatures with those in coeval rocks of the ancient continental margin, which has been oriented approximately longitudinally since the Late Palaeozoic, and thereby provides latitudinal control Continental margin terranes mostly formed along the Laurentian margin The Arctic Alaska Terrane in the northernmost Cordillera consists of Neoproterozoic to Jurassic continental margin strata The terrane has affinities with parts of the Innuitian Orogen of Arctic Canada in that it contains rocks deformed, metamorphosed, and intruded during the Devonian Ellesmerian Orogeny However, there is disagreement about whether or not it underwent large amounts of counterclockwise rotation or translation relative to the rest of North America during the Early Cretaceous rifting and seafloor spreading that created adjacent parts of the Arctic Ocean basin The Coldfoot, Kootenay, Seward, and Yukon–Tanana terranes contain metamorphosed Neoproterozoic and Palaeozoic strata formed in distal continental margin settings, and some contain Middle Devonian to Early Carboniferous arc magmatic rocks and underwent latest Palaeozoic metamorphism Possible exceptions to a Laurentian provenance are the Dillinger, Mystic, and Nixon Fork terranes in Intermontane Alaska, whose Early and Middle Palaeozoic stratigraphy and faunas are similar to those of the Siberian Craton, and possibly parts of the Kootenay Terrane, for which a peri-Gondwanan provenance has been suggested A key question, whose answer constrains the potential amount of displacement of magmatic arc terranes relative to the former continental margin, is whether subduction was beneath the continent or away from it Mid-Mesozoic and younger magmatic arcs evidently faced away from the continent, because contemporary accretionary complexes are located oceanward of them, with the exception of the Koyukuk–Nyak–Togiak Arc terranes in western Alaska, which are outboard of the oceanic Angayucham terrane The facing directions of Early Mesozoic arc rocks in the Quesnel Terrane and of the Middle Jurassic arc in the Stikine Terrane were also away from the continent, but those of Early Mesozoic and older arcs of the Stikine, Alexander, and Wrangellia terranes are unknown It has been suggested that the facing direction of the Late Palaeozoic arc in the Quesnel Terrane in southern British Columbia was away from the continent, but, conversely, that of a Late Palaeozoic arc in the Yukon–Tanana Terrane, where Carboniferous and Permian subduction evidently involved the Slide Mountain Terrane, is thought to have been towards it Middle and Late Devonian arc rocks extend into continental margin deposits in the southeastern Canadian Cordillera, suggesting that at that time subduction was beneath the continent Terranes mainly in the Intermontane Plateau System south of latitude 60 N have counterparts as far south as central California and north-western Nevada Permian to earliest Jurassic faunas in the Quesnel, Slide Mountain, and Stikine terranes differ from those in rocks deposited on the ancient continental margin in Canada, but are comparable to coeval faunas in the western conterminous USA and Mexico Middle Permian to Middle Triassic faunas in the accretionary complex called the Cache Creek Terrane, located between the Stikine and Quesnel terranes, are similar to faunas found in eastern Asia and in rocks of Permian Tethys The Wrangellia and Alexander terranes in the Pacific Mountains System of Canada and Alaska contain Palaeozoic faunas most similar to those in the Canadian Arctic and Siberia Their Early Mesozoic faunas are more comparable to those further south in the western Cordillera, although Wrangellia also contains an Early Jurassic ammonite of a characteristic Russian species unknown elsewhere from North America The Alexander Terrane features a