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TitleCause and effect: Late Cretaceous tectonic inversion and basin history in the southern Canadian Cordillera
AuthorMahoney, J B; Haggart, J W; Kimbrough, D L; Grove, M
SourceGeological Society of America, Abstracts With Programs vol. 45, no. 7, 2013 p. 517
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130172
PublisherGeological Society of America
MeetingGeological Society of America, Annual Meeting; Denver; US; November 4-7, 2013
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia
Subjectspaleontology; tectonics; basins; basin evolution; basin analyses; tectonic interpretations; tectonic setting; sedimentation; sedimentary facies; Nanaimo Group; Nanaimo Basin; Mesozoic; Cretaceous
ProgramFrontier basin analysis, Geoscience for New Energy Supply (GNES)
AbstractRapid orogenic exhumation in the southern Canadian Cordillera is recorded by the tectonic inversion of the Cretaceous Methow basin, coupled with rapid basinal subsidence and initiation of the peripheral foreland Nanaimo basin.
The composite Methow/Methow-Tyaughton basin records a complex basin evolution that initiated with Neocomian to Albian sedimentation in a forearc basin receiving easterly-derived volcanoplutonic detritus. Facies variations, subsidence rates, and the association between sedimentation and contractional deformation all suggest that the forearc basin was superseded in middle Albian time by structurally controlled subsidence in a complex hybrid foreland basin setting. Sedimentation in the Methow/Methow-Tyaughton basin ended by at least Coniacian time, coincident with the culmination of deformation in the Coast Belt thrust system along the western margin of the basin.

The Nanaimo basin is a peripheral foreland basin formed along the western edge of the Insular Superterrane in southwestern British Columbia. Subsidence initiated in Turonian time in response to contractional crustal thickening in the southern Coast Belt and Cascade Range to the east and southeast. Subsidence increased dramatically during the late Santonian to Maastrichtian, and episodic sedimentation produced a thick succession (>4 km) of complexly intertonguing shelf and submarine fan deposits. The basin contains a distinctly bimodal detrital zircon signature, with a major population of Cretaceous (68 to 100 Ma) zircon representing first cycle plutonic detritus eroded during active contractional tectonism within the Coast Plutonic Complex. A smaller population of Jurassic and Cretaceous zircon was derived from uplifted plutons and Methow basin strata to the east. A small yet distinct population of Meso- and Paleoproterozoic (1300-1800 Ma) zircon is consistently present, and is strikingly similar to that of the Mesoproterozoic Belt Supergroup from the western edge of Laurentia. These zircon data suggest that the arc system was locally breached by one or more large rivers by early Campanian time, allowing extraregional sediment from the distal back arc region to prograded northwestward into the basin.
Summary(Plain Language Summary, not published)
This is an abstract of a talk to be presented at a scientific meeting. During the Cretaceous period, from 85-65 million years ago, sediments accumulated in marine oceans that covered parts of ancient British Columbia. These deposits were eventually transformed into the sedimentary rocks found today along the coast of Vancouver Island and the adjacent Gulf Islands, and are associated with possible oil and natural gas deposits. Some of the rocks contain microscopic grains of natural zircon, which form deep within the Earth¿s crust but are sometimes ejected into the atmosphere during volcanic eruptions. The authors have precisely dated the zircon grains by analyzing very small amounts of radioactive isotopes preserved within them. The authors have also identified the precise areas of North America that the zircon grains came from, allowing them to produce a model of the geography of western Canada during Cretaceous time. Such information is important for petroleum exploration in assessing how hydrocarbon deposits may have accumulated and formed in the western Canada region.