A palynological analysis of middle Cretaceous strata in the Hume River section, Northwest Territories, Canada

Abstract

The Hume River section northwest of the town of Norman Wells, Northwest Territories consists of a 2-km-thick succession of Cretaceous strata deposited in a foreland basin ahead of the advancing Mackenzie Mountains thrust-and-fold belt. Rocks in the section have been assigned (from bottom to top) to the Martin House, Arctic Red, Slater River and Trevor formations. The Martin House Formation rest unconformably on Paleozoic strata, and an unconformity separates the Arctic Red and Slater River formations. In terms of paleoenvironments, the section represents fluctuating fully marine to non-marine deposits near the margin of the Western Interior Seaway. Previous age determinations have encompassed an Aptian to Turonian age range for the section as a whole. My analyses indicate an early to middle Albian age for the Martin House Formation, a middle to late Albian age for Arctic Red Formation (which accords with a late Albian U-Pb radiometric date for the unit), a late Albian age for the lowest part of the Slater River Formation (in contrast to Cenomanian age determined by the most recent foraminiferal analyses), and a Cenomanian or younger age for the upper part of the Slater River Formation and for the Trevor Formation. I found no conclusive evidence for an age younger than Cenomanian. The Albian-Cenomanian boundary may be within the basal part of the Slater River Formation rather than at the unconformity between that formation and the underlying Arctic Red Formation. Interesting parallels can be drawn with lithological units and dinocyst assemblages in other parts of the Western Interior Basin, notably in northern Alberta. Perhaps there too, the Albian-Cenomanian boundary is within the basal part of the Fish Scales Marker Bed (equivalent to the Slater River Formation) rather than at its base.