Abrupt changes in structural style across cross-strike valleys have been mapped in the Foothills of northeastern British Columbia. These changes, which can be characterized as differing degrees of structural disharmony, appear to correspond with changes in thickness of the mechanically weak Triassic Toad-Grayling Formation. The pattern of inferred thickness changes is interpreted to reflect a pre-contractional configuration of small-offset normal faults, linked by minor, cross-strike, oblique-slip faults. Subsequent Laramide contractional deformation resulted in a combination of “thin-skinned” detachment folding and relatively “thick-skinned” reactivation of the pre-existing normal faults (perhaps involving thick Proterozoic units). The cross-strike fault zones, caught up within the contractional structures, are interpreted to have localized prominent, linear drainage patterns that are seen throughout the general area. The inferred pre-existing normal faults and associated cross-strike transfer faults may have influenced thickness and/or facies distributions of Carboniferous through Triassic rocks, many of which are targets of active hydrocarbon exploration.

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