NORTH AMERICA/Northern Cordillera 41 Figure Features accompanying Cordilleran orogenesis: magmatic arcs and associated accretionary complexes; basins resulting from contraction, crustal thickening, uplift, and erosion; and syn and post accretionary structures Terrane names, abbreviated herein as AX, WR etc; are in Appendix B Younger glaciogenic sediments (Varanger equivalent?) occur locally in the upper Windermere A second major rifting episode at the top of the succession is recorded by an angular unconformity beneath Cambrian rocks and by coarse siliciclastic deposits and associated magmatic rocks dated at 550–600 Ma Rifting culminated in complete supercontinental separation by about 540 Ma at latitudes 48–55 N, but took place earlier further north Early Cambrian to Late Jurassic (540–150 Ma) miogeoclinal strata were deposited along the newly formed continental margin of Laurentia In the south, the continental shelf appears to have been relatively narrow and contains abundant shallowwater carbonates, but in the north it is broader and deeper water sediments are more abundant, characteristics that have been ascribed to asymmetric rifting Cambrian to Late Devonian carbonates with locally interbedded shales exhibit lateral facies changes from incomplete platform successions about km thick below the plains and in the eastern mountains, to shallow-water accumulations up to 10 km thick that were deposited on the former continental shelf Beyond the shelf, the strata are replaced by calcareous shale and shale, and further west by deep-water carbonaceous shale with local intercalated mafic volcanic rocks and coarse-grained siliciclastic deposits Devonian– Mississippian and Permian–Triassic siliciclastic rocks, widespread along the Laurentian continental margin from northern Alaska to north-eastern Washington, have distinctive detrital zircon and geochemical signatures indicating their derivation from northern source areas The predominance of latest Palaeozoic and Early Mesozoic siltstone and shale over carbonate may reflect relocation of this margin to higher latitudes as a result of the northward drift and rotation of Laurentia Latest Jurassic to Palaeogene (150–40 Ma) clastic deposits were eroded from older rocks that