Georgia Basin sedimentary assemblage 

(Late Cretaceous (Turonian) to Tertiary (Miocene)) 

(Southern part of Canadian Cordillera, unit TKs)

Older part (Nanaimo Group) consists chiefly of marine to nonmarine deep-water, deltaic, and fluvial 
sandstone, shale, and conglomerate, derived locally from the Wrangellia superterrane, but mainly from 
eastern Coast and Cascade belts to the east and southeast. Younger part (mainly Chuckanut Group) entirely 
nonmarine sedimentary rocks that were derived mainly from Coast Belt and North Cascades (Johnson, 
1984; England and Calon, 1991; Mustard, 1991). Although a forearc setting is postulated for the 
Cretaceous strata (England and Calon, 1991), deposition of the strata of the Georgia Basin in a foreland 
basin underlain by the Wrangellia superterrane and the overlying Gravina-Nutzotin-Gambier belt is 
favored. Deposition is interpreted as occurring in response to Late Cretaceous to Paleogene 
contraction/transpression, rapid uplift, and erosion of the eastern Coast Belt and North Cascade orogen 
(Brandon and others, 1988; Monger, 1991c; Monger and Journeay, 1992). Early Tertiary deposition was 
probably in a transtensional setting (Johnson, 1984). REFERENCES: Johnson, 1984; Brandon and others, 
1988; Monger, 1991c; Monger and Journeay, 1992.