Geology and Petroleum Potential of Upper Cretaceous and Tertiary Strata, Beaufort-Mackenzie Area, Northwest Canada (1)

Abstract

Upper Cretaceous to Holocene strata on the Beaufort Sea continental margin were deposited as a series of northward-prograding delta complexes totaling 12-16 km thick. The succession contains eleven regionally extensive transgressive-regressive sequences that were deposited during four large-scale tectonostratigraphic phases, each phase terminated by a major tectonic event. During the Cenomanian to middle Maastrichtian, sedimentation was limited to relatively thin, organic-rich muds on an outer shelf to basinal environment. From the late Maastrichtian to middle Eocene, deltaic depocenters were located along the southwestern margin of the Canadian Beaufort Sea. During the third depositional phase (middle Eocene to late Miocene), sedimentation was concentrated in the central Canadian Beaufort Sea. Depocenters shifted to the eastern Beaufort Sea during the fourth depositional phase (Pliocene to ?early Pleistocene). The modern Mackenzie delta may represent a new phase of deposition. Considerable volumes of oil and gas have been discovered in Tertiary rocks, principally in Eocene and Oligocene delta-front strata, with lesser volumes in Paleocene and Miocene strata. Three families of oils have been recognized in Tertiary reservoirs, the most important of which appears to have been derived from the Eocene Richards sequence. In general, Tertiary strata have modest TOC (total organic carbon) values (1-2%) and low thermal maturity to drilled depths (4000-4500 m) in the more extensively explored central Beaufort-Mackenzie area. However, thermal and subsidence modeling of Tertiary strata suggest that maturity rapidly increases between 5000 and 6000 m.