Upper Paleozoic rocks of the western Canadian Cordillera and their bearing on Cordilleran evolution

Abstract

Volcanic and sedimentary successions of late Paleozoic and locally Mesozoic age in the Canadian Cordillera form six assemblages, based mainly on lithological association and similar stratigraphy. From east to west these assemblages are: (1) Eastern assemblage, located along the Omineca Crystalline Belt and consisting of Mississippian to Permian largely sedimentary rocks overlain by mainly Permian basic volcanics and ultramafics; (2) poorly known rocks in south-central British Columbia characterized by abundant volcaniclastics of Pennsylvanian and Permian ages; (3) Cache Creek – Bridge River assemblage of the Intermontane Bell, ranging from Lower Mississippian to Middle Jurassic and composed of chert, argillite, carbonate, basic volcanics, and ultramafics: (4) Stikine assemblage of northwestern and north-central British Columbia of Mississippian and Permian age, with basic to acidic volcanics, argillite, and carbonate; (5) Chilliwack Group on the west side of the Cascade Mountains, of Pennsylvanian and Permian age, with basic to acidic volcanics overlying a carbonate and clastic succession: and (6) Sicker–Skolai assemblage of Vancouver Island and the Saint Elias Mountains with basic to acidic volcanics overlain by sedimentary rocks. Coeval faunas in several of these assemblages differ. The assemblages may be largely unrelated to one another and came together in the Mesozoic, Their present distribution, with rocks typical of ocean basins (assemblages 1, 3) east of rocks that probably represent island arcs (assemblages, 2, 4, 5, 6) presents major problems. Two hypotheses attempt to explain this distribution. (1) The oceanic assemblages represent Paleozoic and early Mesozoic Pacific Ocean floor obducted over a broad arc terrane in the Jurassic, or (2) they are Paleozoic and early Mesozoic Pacific Ocean floor, trapped east of allochthonous arc terranes (assemblages 4, 5, 6) emplaced in the Mesozoic.

Early Triassic peritidal carbonate sedimentation on a Panthalassan seamount: the Jesmond succession, Cache Creek Terrane, British Columbia, Canada

“…Location of main panel is shown in inset map at the upper right. Abbreviations: CC eastern limit of deformation in the Canadian Cordillera, BC British Columbia, AB Alberta, YT Yukon Territory, and V Vancouver accumulated on the tops of isolated mid-oceanic seamounts (Monger 1977;Tardy et al 2001;Sano and Rui 2001). Fusulinids, conodonts, radiolarians, and corals show that the Cache Creek oceanic rocks remained located within the Panthalassa Ocean far from the North American Craton during Mississippian to Triassic time .…”

“…With an emphasis upon these sedimentological and stratigraphic features, following the estimated paleogeographic setting of the Mississippian to Triassic carbonate rocks of the Cache Creek Terrane (Monger 1977;Struik et al 2001;Tardy et al 2001;Sano and Rui 2001), we consider the Lower Triassic carbonate rocks of the Jesmond succession as a carbonate buildup at the top of an isolated mid-oceanic seamount or oceanic plateau (Jesmond buildup). On the basis of the paleobiogeographic reconstruction , the Jesmond buildup was located in the Panthalassa Ocean, far removed from the cratonic margin of North America.…”

Provenance of the Pythian Cave conglomerate, northern California: implications for mid-Cretaceous paleogeography of the U.S. Cordillera

“…Despite a vast amount of study, the Cretaceous paleogeography of the North American Cordillera remains uncertain (e.g., Monger, 1977;Miller, 1987;Cowan et al, 1997;Ward et al, 1997;DeGraaffSurpless et al, 2003;Dickinson, 2004;Housen and Dorsey, 2005;Haggart et al, 2006;Wyld et al, 2006). Disruption and reorganization of the North American continental margin, extensive Tertiary volcanic cover, and significant erosion since Cretaceous time complicate interpretations of Cretaceous paleogeography.…”

Mississippian Ocean Island Basalts from the Western Palaeo-Pacific Ocean in the Cache Creek Terrane of British Columbia

“…The Cache Creek terrane of the North American Cordillera comprises a subduction melange of limestone and basalt (Monger 1977). Separating accreted terranes which originated marginal to the continent (Eastern Assemblage and Greater Stikinia from fragments of Gondwana in the Greater Wrangellia composite terrane (Fig.…”

“…1), it is the only Cordilleran remnant of a basin the entire width of the Paleo-Pacific Ocean. The strata represent a series of ocean islands and fringing reefs which collided with North America in the Late Triassic (Monger 1977). Tethyan faunas indicate an equatorial western Pacific position from the Mississippian to Permian, with the implication that the origin of the islands is related to events along the eastern margin of Gondwana.…”