Chapter 5 The Paleozoic Western Craton Margin

Abstract

Abstract The western margin of the Paleozoic Laurentian continental margin is now largely buried beneath the accreted terranes and fold-thrust belt of the Cordilleran Orogen. An extensional continental margin developed from Mexico to Yukon during the breakup of Rodinia about 900–800 Ma, commencing with a series of Precambrian rift basins, followed by the development of a wedge of Paleozoic continental margin (“miogeoclinal”) sediments up to 6 km thick. Shallow-water carbonate and clastic sediments characterize most of the preserved sediment pile. Slope and deep-basin sedimentary rocks are rarely preserved. An arc collided with this continental margin from southeastern California to central Idaho between the latest Devonian or Early Mississippian generating the Antler Orogeny and the emplacement of the Roberts Mountains Allochthon on the continental margin, above a thrust belt. Most of the Canadian portion of the margin remained an extensional margin until the Nicola Arc was thrust eastward over the margin during the Jurassic. The Canadian Margin may have developed by simple-shear extension during the Paleozoic, that portion lying south of the 60th parallel forming the upper-plate margin and the margin north of the 60th parallel constituting the lower-plate margin, with the Liard Line functioning as a transfer fault across which the shear polarity reversed direction.