Upper Devonian to Middle Jurassic Assemblages
Published:January 01, 1991
S.P. Gordey, H.H.J. Geldsetzer, D.W. Morrow, E.W. Bamber, C.M. Henderson, B.C. Richards, A. McGugan, D.W. Gibson, T.P. Poulton, J.W.H. Monger, J.O. Wheeler, H.W. Tipper, H. Gabrielse, T. Harms, L.C. Struik, R.B. Campbell, C.J. Dodds, G.E. Gehrels, J. O’Brien, 1991. "Upper Devonian to Middle Jurassic Assemblages", Geology of the Cordilleran Orogen in Canada, H. Gabrielse, C.J. Yorath
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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
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Geology of the Cordilleran Orogen in Canada
Seven stratigraphic chapters cover time slices from Precambrian to Neogene; also included are chapters covering tectonic framework, paleomagnetism, physiographic evolution, Quaternary glaciation, volcanic and plutonic regimes, metamorphism, structural styles, metallogeny, energy and ground resources, and natural hazards. A tectonic synthesis chapter and a summary of outstanding problems round out the volume. Accompanying plates include physiographic, tectonic assemblage, terrane and metamorphic maps, correlation charts, structural cross sections, and special maps showing distribution of Proterozoic and Miocene plutonic suites and the metallogeny of terranes.