Abstract

Georgia Basin is a Cretaceous to Cenozoic forearc basin that overlaps the Wrangellian part of Vancouver Island and the Coast Belt at the leading edge of the North American Plate. The basin overlies the presently subducting oceanic Juan de Fuca Plate. The basin postdates the mid- to Late Cretaceous amalgamation of the Wrangellia Terrane into the North American Cordillera at the latitude of Vancouver Island. Major episodes of sedimentation in Georgia Basin, based on the remnant sedimentary record, are linked to periods of rapid convergence between the Farallon/Kula and North American plates; reduced rates of plate convergence resulted in uplift and erosion in the basin. The primary phase of basin subsidence in the Late Cretaceous accommodated 3 to 5 km of dominantly marine siliciclastic sediments of the Nanaimo Group. In late Maastrichtian to early Paleocene time, diminished rates of plate convergence resulted in local uplift, erosion, and recession of marine waters from the basin. Plate convergence increased greatly in the Late Paleocene to Late Eocene, resulting in a second phase of rapid subsidence and the accumulation of 3 to 6 km of siliciclastic, mainly nonmarine sediment of the Huntingdon and Chuckanut formations. Basin depocentres migrated to southeastern Georgia Basin. The contemporaneous acme of magmatic activity in the Coast Belt and in Georgia Basin during the Eocene reflects rapid subduction of hot, juvenile oceanic crust beneath the North American Plate at this time. In the mid-Eocene, Georgia Basin was contracted on a series of basement-involved thrusts coincident with outboard accretion of the Pacific Rim and Crescent terranes. Since Eocene time, increasingly oblique and diminished rates of plate convergence has resulted in widespread basin uplift and erosion of western Georgia Basin. Only a small depocentre in southeastern Georgia Basin is being maintained by pull-apart along a Neogene strike-slip fault. Georgia Basin remains in the arc-trench gap at present and part of it remains topographically low, but subsidence of the central part of basin (if any) under the Strait of Georgia may be more related to downwarping caused by uplift of western Vancouver Island above the outboard Late Cenozoic accretionary wedge.

You do not currently have access to this article.