Beaufort-Mackenzie Basin sediments of Late Jurassic to Tertiary age were shortened in an arcuate trend during Tertiary Brookian orogenesis. A major pulse of Early Eocene folding and thrust faulting affected much of the central and western Beaufort-Mackenzie Basin. Concurrent longitudinal normal faulting occurred on land, in the western Beaufort and near the southeast basin margin (Taglu fault zone). A second major orogenic pulse of Miocene age caused deformation concentrated in the distal part of the deformed belt, in Demarcation subbasin-Herschel high, and between the Taglu and Tarsiut-Amauligak fault zones. A large area of southwestern Beaufort-Mackenzie Basin was largely undeformed by this pulse but was transported basinward on a decollement zone(s). Seismic images of many offshore structures show obvious asymmetry; other structures are clearly detached. Onshore, important decollement horizons occur at several stratigraphic levels. Concurrent extension occurred principally in the Tarsiut-Amauligak fault zone.
In general, the deformation shows a foreland-younging trend, away from the craton. Temporal and spatial variations in tectonic shortening require secondary accommodation by right-lateral transcurrent faulting, concentrated along the southeast basin margin and in a zone trending northeastward from near Kay Point through the Tarsiut area. Although minor at the basin scale, transcurrent faulting may be locally very significant at the scale of individual prospects.
