Neotectonics and Sedimentation on the Central Continental Shelf of Western Canada

MOSLOW, THOMAS F., University of Alberta, Edmonton, Alberta, Canada, J. L. LUTERNAUER, Geological Survey of Canada, Vancouver, British Columbia, Canada, and K. ROHR, Geological Survey of Canada, Sidney, British Columbia, Canada

Analysis of high resolution seismic profiles from the central Canadian continental shelf provides substantial evidence for Quaternary faulting. Along the northwestern margin of Moresby Trough, one of three large-scale Quaternary canyons cutting across the shelf, a divergence of reflectors, thickening of seismic units, and concavity of reflectors suggestive of drag are seen along the downthrown side of listric normal faults. Faulting appears to be syndepositional. Some of the faults are interpreted as growth or compaction faults. Fault traces commonly terminate below the seabed. Deformation of Quaternary sediments due to faulting is non-brittle in nature, and maximum offset of the reflectors thus far seen is 2.5 m. It is suggested that the Quaternary faulting observed is a product of r pid deposition and loading of late Quaternary sediment rather than being related to seismicity. Listric normal faults may have been activated by glacial loading and isostatic rebound.

A multichannel survey in the Queen Charlotte basin gives an excellent image of structure of the sediment-basement interface and Tertiary sedimentary fill. In the Queen Charlotte Sound the basin is divided into several subbasins that are bounded by normal faults. Three crossings of Quaternary canyons show that they cut into sedimentary fill in the subbasins as well as basement highs; from this observation it is inferred that there is little control on their location from Tertiary structure.

Several features in the data indicate that Tertiary structures are not being reactivated. Basement has less than 0.2 s relief under Moresby trough and steep gradients in the seafloor cannot be correlated with basement topography. Canyon erosion and subsequent fill (up to 175

m thick) are probably of Quaternary age and seem to act independently of Tertiary structure.

Investigations of neotectonism on the continental shelf of western Canada are being performed to determine the effect of tectonic patterns on morphology and sedimentation, to extend earthquake history, and possibly to determine the periodicity or cyclicity of major seismic events. An additional concern includes the potential hazards of hydrocarbon exploration and development on the shelf that is posed by Quaternary faulting.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)