LAUSR

Abstract The Eagle Plain region, located in the northeastern Yukon Territory, Canada, forms a northern segment of the Cretaceous Western Interior Sea. Its preserved mid-Cretaceous strata (Whitestone River Formation and Eagle Plain Group) document an active structural regime, sea-level fluctuations, paleoecosystem changes and the paleogeographic evolution south of the gateway to the Polar Sea. This study integrates foraminiferal assemblages recovered from two wells (Molar P-34 and Ellen C-24) and one Late Albian bentonite age with well log signatures and previously established outcrop data. The proposed biostratigraphic framework correlates well between both wells and with the fauna observed in outcrops. Three biostratigraphic zones are recognized allowing for regional correlations; the Early Albian Gaudryina tailleuri Zone, the Middle to early Late Albian Gaudryina canadensis Zone, and the latest Albian Miliammina manitobensis Zone. A new 206Pb/238U age of 105.56 ± 0.25 Ma places the upper Whitestone River Formation into the Late Albian. Foraminiferal morphogroups and their relative proportions allow for paleoenvironmental reconstruction, including oxygen and nutrient conditions. The Ellen well represents deposition in a fully marine, well oxygenated proximal shelf setting during the Early to early Late Albian, resulting in the Whitestone River Formation. The Molar well represents a deep water, offshore setting with increased accommodation space marked by an increase in tubular suspension feeders, demonstrating a northwestward deepening of the basin. Foraminiferal assemblages of the Albian Whitestone River Formation reflect the widely recognized depositional cycles of the Western Interior Sea (Moosebar, Hulcross, Joli Fou and Mowry seas). During Albian time the northern gateway between the Polar and Western Interior seas was widely inundated, contrasting with an either short lived closure or severely restricted phase during the Albian/Cenomanian boundary interval.