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Book Chapter

Provenance of the Upper Cretaceous Nanaimo Group, British Columbia: Evidence from U-Pb Analyses of Detrital Zircons

By
Peter S. Mustard
Peter S. Mustard
Geological Survey of Canada, 100 West Pender Street, Vancouver, British Columbia, V6B 1R8, Canada
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Randall R. Parrish
Randall R. Parrish
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, KIA 0E8, Canada
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Vicki McNicoll
Vicki McNicoll
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, KIA 0E8, Canada
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Published:
January 01, 1995

Abstract:

The Nanaimo Group of southwest British Columbia overlies the Wrangellia terrain and the western Coast Belt and is in fault contact with the northwestern margin of the Cascades to the southeast. Generally interpreted as deposits of a Late Cretaceous forearc basin, a foreland basin model is preferred for the Nanaimo Group, in large part due to the recent recognition of major, westerly-directed thrust systems in the Coast Belt to the east and northwestern Cascades, coupled with new age constraints which indicate that thrusting in part overlaps with Nanaimo Group sedimentation. As a test of the foreland basin model, U-Pb ages of twenty-two detrital zircons from three formations of the Nanaimo Group provide new evidence about changing source areas with time for Nanaimo Group deposition. Zircons from the lower Campanian Extension and Protection Formations indicate that Coast Belt and San Juan thrust systems were the dominant source areas, and Wrangellia was not a major source of detritus. Submarine fan sandstone of the uppermost Gabriola Formation (Maastrichtian age) contains abundant detrital titanite, epidote, and zircon with ages as follows: Precambrian zircons, zircons of late Mesozoic age with Precambrian inheritance, concordant 87 Ma zircons, and a predominant 72–73 Ma population of zircons. These results indicate derivation from varied sources which may include the eastern Coast Belt (87 Ma), Paleozoic or late Precambrian sedimentary rocks (recycled Precambrian zircons), and a combination of the Idaho Batholith and Omineca Belt plutons (72–73 Ma grains and grains with inheritance). The Idaho Batholith as a possible source is consistent with the position of the basin prior to latest Cretaceous-(?)-Eocene transcurrent dextral faulting. Thus, the source areas for upper Nanaimo Group sediments were considerably more widespread than previously believed, suggesting that major fluvial drainage systems were active in the western Cordillera during the late Maastrichtian.

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Contents

SEPM Special Publication

Stratigraphic Evolution of Foreland Basins

Steven L. Dorobek
Steven L. Dorobek
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Gerald M. Ross
Gerald M. Ross
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SEPM Society for Sedimentary Geology
Volume
52
ISBN electronic:
9781565761766
Publication date:
January 01, 1995

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