Abstract

I postulate that a major dextral transcurrent fault truncated the pre-Tertiary continental framework of western Washington and southern Vancouver Island during the Late Cretaceous and early Tertiary. The fault trace trends north and is covered in the Puget Lowland; it corresponds to the west-trending San Juan and northwest-trending Survey Mountain faults on southern Vancouver Island. The geometry of the structure has probably been greatly modified by subsequent deformation. Sedimentary basins that formed marginal to the fault are characterized by rapid fades changes and sediment accumulation rates, abrupt stratigraphic thinning and thickening, irregular basin margins, petrographic mismatches, and other features consistent with origin in a zone of strike-slip faulting. The structure was probably part of a network of intracontinental Late Cretaceous-early Tertiary strike-slip faults in the northern North American Cordillera. As an outboard member of this fault network, it likely served as a major avenue of northward translation along the northeast margin of the Pacific basin.

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