Regional significance of normal fault systems in the western Canadian Beaufort Sea (Mackenzie delta)

The Beaufort-Mackenzie fold and thrust belt in Arctic Canada corresponds to the offshore part of the Cordilleran orogen in Yukon and Alaska. Previous tectonic studies in this area focussed on contractional structures, and comparatively little attention has been paid to normal faults, even though they are ubiquitous in the shallow Beaufort Sea. Normal faults dip either seaward or landward and most faults are located on the apex of anticlines. Despite the clear spatial relationship with anticlines, normal faults initiated after fold development as the delta front migrated seaward. Accordingly, Oligocene to Pliocene extensional structures are interpreted as recording gravity-driven deformation superimposed on an existing, mainly Eocene, fold and thrust belt. Several normal faults extend downward onto one of the anticline limbs, but the control of the fold geometry on the dip of the faults (seaward or landward) remains poorly understood. Seismic amplitude anomalies suggest that normal faults acted as fluid (most probably thermogenic gas) migration pathways.