Abstract Permian rocks are preserved throughout most of the eastern Cordillera and locally, in the Peace River-Liard River area, on the Interior Platform (Fig. 4F.1, 4F.2, 4F.3). They are absent from the remainder of the Interior Platform and from most of the Mackenzie Mountains through truncation at several disconformities beneath Mesozoic strata. Permian sediments were deposited mainly along the margin of the North American plate in a Permian depositional basin, here named Ishbel Trough, extending from the 49th parallel to the Ancestral Aklavik Arch in northern Yukon Territory. The trough occupies approximately the same position as the Carboniferous Prophet Trough (Richards et al., Subchapter 4E in this volume). In the Peace River-Liard River area, Permian sediments were also deposited on the western cratonic platform. The western margin of Ishbel Trough has not been identified. It (Fig. 4F.2, 4F.3) may have been in the area presently occupied by Cariboo Terrane (Struik and Orchard, 1985; Struik, 1986), which lacks Permian strata and may have been partly subaerially exposed during the Permian Period. A marginal basin to the west of Cariboo Terrane (Barkerville Subterrane of Kootenay Terrane; Monger and Price, 1979) contains a remnant of Permian strata (Sugar Limestone). The eastern margin of Ishbel Trough was a broad hinge-line along the western margin of the cratonic platform. In northeastern British Columbia and southwestern District of Mackenzie the hinge coincided with a zone of normal faulting, but generally the position of the eastern trough margin is unclear, because of eastward truncation of Permian strata (Fig. 4F.2, 4F.3).

Abstract The pre-Late Devonian Cordilleran miogeocline consisted of extensive shallow-water platforms upon which carbonate-clastic deposits accumulated. They were flanked to the west by deep-water environments where shale and carbonate accumulated (Rocky Mountains Assemblage). Clastic sediments were largely craton-derived. During the Late Devonian sedimentation patterns changed dramatically as turbiditic, chert-rich clastics, derived from the west and north, flooded the northern Cordillera (Earn and Imperial assemblages). Shale (Besa River Assemblage) was deposited far out onto the miogeocline and InteriorPlatform; the carbonate front of the Rundle Assemblage retreated far to the east and south of its Middle Devonian position. By mid-Mississippian time the clastic influx waned and normal marine shelf carbonate and clastic sedimentation resumed, once again with clastics derived from the craton. Devono-Mississippian plutonism occurred only in northernmost Yukon Territory, and volcanism was restricted to central Yukon and south-central British Columbia.Pre-Late Mississippian folding occurred in northern Yukon but elsewhere deformation is expressed only by local high-angle faults and disconformities. Devono-Mississippian tectonism in the northern Yukon involved uplift and granitic intrusion in Frasnian to Early Mississippian time, resulting in an upward shoaling and southward-prograding clastic wedge. The sequence consists of shale at the base, flyschoid sediments near the middle, and partly fluvial-deltaic strata at the top. Deformation migrated southward from the area of uplift until the clastics themselves were folded prior to the mid-Carboniferous. The source of Devono-Mississippian sediments in the central Cordillera was uppermost Precambrian quartzose clastics and lower Paleozoic chert from the western miogeocline. Western coarse clastics are typified