Deltaic Deposition in the Upper Cretaceous and Tertiary Beaufort-Mackenzie Basin, Northern Mainland Canada

J. Dixon, J. R. Dietrich, and D. H. McNeil
Geological Survey of Canada, Calgary, AB

A major shift in the tectono-stratigraphic setting and depositional style in northern mainland Canada occurred in the Albian to early Cenomanian, as a result of opening of the oceanic Canada Basin and northward migration of the Cordilleran Foldbelt. Prior to this, deposition during the Jurassic and Early Cretaceous was characterized by thin to moderately thick epicontinental deposits dominated by shoreline quartz arenites grading into shelf shales with source areas from the stable platform and the Precambrian shield to the southeast and east. During the Albian the influence of Cordilleran tectonics began to impinge on the northern mainland with sediment sources shifting to the southwest in advance of the rising foldbelt. From the Cenomanian to the Pliocene the dominant source areas were from the Cordillera, with the sandstones becoming more lithic in character.

A series of large deltaic complexes formed during the Cenomanian to Pliocence, migrating progressively northward. During the Cenomanian to middle Maastrichtian the deltas formed on the craton and are broadly distributed and moderately thick. However, by the late Maastrichtian the locus of sedimentation shifted to the continental margin, with deltaic deposits focused in smaller areas and considerably thicker than the older craton deltaic deposits. From the late Maastrichtian to early Eocene deltaic depocentres were located in the west Beaufort, off the Yukon coast. In the middle to late Eocene depocentres shifted eastward to northeastward, under the modern Mackenzie Delta. During the Oligocence there was a significant shift to the north, such that the deltaic depocentre is located under the modern-day shelf. The Miocene was a period of reduced sedimentation and no significant deltaic depocentres have been identified. A major culmination in tectonic activity and sea-level change in the late Miocene resulted in a large, basin-scale unconformity and subsequent deposition of a thick Pliocene succession.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005