Abstract

Siliciclastic strata of Triassic age that are exposed in the Rocky Mountains have been sampled for isotopic studies in order to determine their provenance. Sm-Nd analyses of whole rock shale and sandstone samples from northeast British Columbia and the Bow Corridor of western Alberta are isotopically homogeneous with epsilon Nd values of -6.7 to -10.5 at the time of deposition. These values are part of a distinct isotopic provenance signature that characterizes the Devonian through Jurassic of the miogeocline of western Canada and thus the sources of Triassic sediments are part of a larger provenance signature within the miogeocline. These isotopic data do not support sediment derivation from the exposed Canadian Shield and our present working model is that most of the sediment is detrital material reworked from the Innuitian (Ellesmerian) clastic wedge. No evidence has been found in the Nd data to suggest that magmatic arc rocks of Triassic age to the west of the miogeocline (e.g., Quesnellia) made any contribution to the sediment record. U-Pb geochronology of detrital zircons from Triassic sandstones in the Pine Pass and Kananaskis areas are dominated by Precambrian grains with only a few Silurian grains. Comparison with detrital zircons dated from the Devonian Ellesmerian clastic wedge of Arctic Canada show a similar pattern and strengthen the contention that sedimentary strata of the western miogeocline were derived from reworking of Innuitian clastic strata which must have been formerly more widespread and covered the Canadian Shield.

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