Palynology of Eocene strata in the Sagavanirktok and Canning Formations on the North Slope of Alaska

Abstract

This paper describes, illustrates, and interprets Eocene palynomorph assemblages from the North Slope of Alaska, mainly from 31 outcrop samples from seven stratigraphic sections at Franklin Bluffs on the Sagavanirktok River. The top of the Sagwon Member of the Sagavanirktok Formation is shown to be a thin, coaly, apparently nonmarine sequence almost certainly of early Eocene age; the remainder of the member has long been known to be Paleocene in age. The remaining six sections at Franklin Bluffs contain silty, sandy, and clayey strata and are in the Franklin Bluffs Member of the Sagavanirktok Formation in the type area of this member. Dinocyst and pollen data from the Franklin Bluffs Member suggest mainly an early Eocene age, but some strata might be middle Eocene. In all samples from the type Franklin Bluffs Member that contained reasonably well preserved dinocyst assemblages, the environment of deposition was nearshore marine or estuarine. The Franklin Bluffs Member is the temporal equivalent of the marine Mikkelsen Tongue of the Canning Formation, whose type locality is approximately 90 km to the east–northeast. Previous pollen and plant megafossil data from the Arctic showed that the early to middle Eocene climate of the North Slope of Alaska was warm temperate, perhaps nearly subtropical. At least 20 pollen taxa present in the Eocene of the North Slope also occurred as far south in North America as the Gulf Coast and therefore had enormous latitudinal ranges. Several of these taxa appear to have migrated north to the Arctic Coast, probably mainly in the latest Paleocene, at the beginning of the climatic thermal maximum for the Tertiary. However, there is also evidence that plants producing modern-looking grains of Carya, Juglans, and Liquidambar migrated southward from the Arctic to the Gulf Coast after the early Eocene.