U. S. Geological survey pamphlet introduction, tectonic definitions, acknowledgments


CRATON MARGIN AND OCEANIC ROCK UNITS



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CRATON MARGIN AND OCEANIC ROCK UNITS
NAM North AmericaÑUndisplaced stable craton margin. Late Proterozoic shelfal sedimentary and volcanic strata, chiefly sandstone, shale, argillite, limestone, dolomite (Tindir Group) deposited under paralic to glacial margin conditions. Grades upward into lower and middle Paleozoic carbonate rocks, shale, and chert (Funnel Creek Limestone, Adams Argillite, Hillard Limestone, Road River Formation, McCann Hill Chert, Nation River Formation, and Ford Lake Shale) deposited during a major marine transgression and foundering of continental margin after rifting at about 570 Ma. Younger, upper Paleozoic through mid-Cretaceous shallow-marine to shelfal deposits (Calico Bluff Formation, Tahkandit Limestone, and Glenn Shale). Structurally underlies Kandik River assemblage along northwest-dipping thrusts. Includes the shallow-marine platform deposits of Yukon Territory and Mackenzie District that depositionally onlap the crystalline rocks of the Canadian Shield. Northwest extension of nuclear North America craton margin. REFERENCES: Jones and others, 1981; Howell and Wiley, 1987; Dover, 1990; Howell and others, 1992
PAC Pacific plateÑLate Eocene to late Miocene oceanic crust 7 to 10 km thick overlain by as much as 2.5 km of Eocene to Holocene pelagic, hemipelagic, continental-rise, and glacio-marine deposits. Seismic refraction data indicate that oceanic mantle is overlain layer 3 about 5 km thick, layer 2 about 1 to 1.5 km thick, and layer 1, from less 200 m thick in areas distant from the continent, to more than 2 km thick near the continental margin. Outside of map area, contains chains of sea mounts (Gilbert, Kodiak, and Patton), fracture zones (Aia, Blanco, Sila, Sedna, Surveyor, Sovano), and oceanic spreading ridge (Juan de Fuca) south of southeastern Alaska. REFERENCES: Atwater, and Severinghaus, 1991; Grantz and others, 1991; Kirschner, 1988



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