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U-Pb detrital zircon dating supports Early Jurassic initiation of the Cordilleran foreland basin in southwestern Canada

D. I. Pana, T. P. Poulton and S. A. DuFrane
U-Pb detrital zircon dating supports Early Jurassic initiation of the Cordilleran foreland basin in southwestern Canada
Geological Society of America Bulletin (February 2019) 131 (1-2): 318-334


U-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.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 131
Serial Issue: 1-2
Title: U-Pb detrital zircon dating supports Early Jurassic initiation of the Cordilleran foreland basin in southwestern Canada
Affiliation: Alberta Geological Survey, Alberta Energy Regulator, Edmonton, AB, Canada
Pages: 318-334
Published: 201902
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 135
Accession Number: 2019-009249
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2018184
Illustration Description: illus. incl. 1 table, geol. sketch map
N49°00'00" - N54°00'00", W120°00'00" - W114°00'00"
Secondary Affiliation: Geological Survey of Canada, CAN, CanadaUniversity of Alberta, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 2019
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