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TitleU-Pb detrital zircon dating supports Early Jurassic initiation of the Cordilleran foreland basin in southwestern Canada
AuthorPana, D I; Poulton, T P; DuFrane, S A
SourceGeological Society of America Bulletin 2018 p. 1-17, https://doi.org/10.1130/B31862.1
Year2018
Alt SeriesEarth Sciences Sector, Contribution Series 20160415
PublisherGeological Society of America
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceAlberta; British Columbia
NTS82G; 82J; 82K; 82N; 82O; 83B; 83C; 83D; 83E; 83F; 83G
AreaRocky Mountains
Lat/Long WENS-120.0000 -114.0000 54.0000 49.0000
Subjectsgeochronology; tectonics; stratigraphy; radiometric dating; uranium lead dating; zircon dates; tectonic history; depositional history; magmatism; island arcs; terranes; basin evolution; foredeeps; orogenies; thermal history; bedrock geology; lithology; sedimentary rocks; igneous rocks; volcanic rocks; volcanic ash; clasts; provenance; lead geochemistry; modelling; Canadian Cordillera; Omenica Belt; Cordilleran Foreland Basin; Belt-Purcell Supergroup; Rocky Mountain Fold-and-thrust Belt; Western Canada Sedimentary Basin; Cadomin Formation; Kootenay Formation; Nikanassin Formation; Fernie Formation; epicratonic basins; Phanerozoic; Mesozoic; Cretaceous; Jurassic; Paleozoic; Precambrian; Proterozoic
Illustrationsgeoscientific sketch maps; stratigraphic correlations; tables; graphs; Concordia diagrams; schematic models
ProgramShale Reservoir Characterization, Geoscience for New Energy Supply (GNES)
AbstractU-Pb geochronology of detrital zircon from Lower Jurassic to Lower Cretaceous strata of the southern Canadian Rocky Mountains fold-and-thrust belt documents the presence of zircon ages close to the time of sediment accumulation throughout this succession. The identification of syndepositional zircons in Lower Jurassic strata indicates proximity of Cordilleran island arcs and terranes to the Western Canada epicratonic basin, consistent with the Jurassic sudden appearance of ash layers in the basin stratigraphy. The association of syndepositional zircon grains with Paleozoic arc-related zircons and zircons in the “North American Magmatic Gap”-likely derived from the Mesoproterozoic Belt-Purcell Supergroup-hints at possible geographic connections to the west or southwest since Early Jurassic, long before the inferred Kimmeridgian initiation of the ancestral Rocky Mountain foredeep trough in the region. Paleozoic and older grains in the Jurassic strata reflect the pre-history of the basin distributive province and show an episodic pattern that includes well-defined lower Paleozoic and Grenvillian maxima, and early Neo- to Paleoproterozoic populations, which may reflect recycling of detrital zircons from older clastic formations uplifted in the Cordilleran orogen. The youngest peaks in the probability diagrams provide maximum depositional ages for several imprecisely dated stratigraphic units. Discordant data modeling suggests a Pb-loss event in the Early Cretaceous (ca. 125-115 Ma). Our provenance data and the Fernie stratigraphic record suggest initiation of Jurassic deposition either in the backbulge or the distal foredeep depozones. We propose two alternative Jurassic foreland basin evolutionary models that explain the Fernie stratigraphic record in the examined epicratonic southwestern Canada as the result of vertical stacking of migrating foreland depozones, east of the encroaching Cordilleran orogen. The two possible initial settings, backbulge or distal foredeep, require either normal cratonward migration of a forebulge or cratonward migration interrupted by a Callovian phase of orogenward retreat, respectively. Besides filling a long-standing knowledge gap, our data allow direct comparison between the southern Canada and northern United States segments of the Cordilleran foreland basin.
Summary(Plain Language Summary, not published)
The Canadian Cordillera comprises a complicated amalgam of many different terranes that were previously offshore in the ancient Pacific Ocean. This is the second of two planned reports on the zircon crystals that were transported from volcanic and granitic rocks in the Cordillera and deposited into the Alberta sedimentary basin. The age of their formation is known from the rate of radioactive decay of Uranium to Lead that is trapped within the crystals. The age of these crystals allows them to be connected back to their original source in the Cordillera during the Jurassic. This new knowledge provides a basis for understanding the history of sediment accumulation in the basin and its potential for Jurassic source rocks and reservoirs. This project leverages funding from the Alberta Geological Survey, utilizing the geochronology labs at the University of Alberta.
GEOSCAN ID299847