Cretaceous (Albian to Cenomanian) Strata of Eagle Plain, Yukon: Subsurface Foraminiferal Biostratigraphy, Regional Correlations and Paleoenvironments

Abstract

The Eagle Plain, located in the northeastern Yukon Territory, Canada, forms a northern segment of the Cretaceous Western Interior Sea. Its preserved mid-Cretaceous strata document an active structural regime with sea-level fluctuations and changing sediment supply areas. The mid-Cretaceous rocks are unconformably underlain by either Paleozoic or younger Mesozoic formations. Recent paleontological evidence, including pollen, foraminifera and macrofossils from outcrop sections in the Eagle Plain, suggested that Albian to Cenomanian aged strata are preserved. This package includes the Whitestone River, Parkin, Fishing Branch, Burnthill Creek and Cody Creek formations. This project tests new subsurface stratigraphy hypotheses by examining two continuous cores (Molar P-34 and Ellen C-24) and their benthic foraminiferal assemblages. It compares subsurface faunal changes with those obtained from outcrop samples by Haggart et al (2013) and integrates those to well log signatures that are used to establish the subsurface architecture. Three new biostratigraphic zones are recognized; the Early Albian Gaudryina tailleuri Zone in the lower Whitestone River Formation, the Middle to early Late Albian Gaudryina canadensis Zone in the Upper Whitestone River and sandstone member of the Parkin Formation, and the latest Albian Miliammina manitobensis Zone in the shale member of the Parkin Formation and lowermost Fishing Branch Formation. The biostratigraphic framework established in the subsurface correlates well with the fauna observed in outcrops. Foraminiferal assemblages are almost entirely dominated in both cores by agglutinated specimens that document a response to regionally recognized fluctuating sea-level changes during the Albian. Observations of foraminiferal morphogroups and their relative proportions allow for iii paleoenvironmental reconstruction, including oxygen and nutrient conditions. The Ellen C-24 well represents a fully marine, well oxygenated proximal shelf deposited during the lower to early Late Albian Whitestone River Formation. The Molar P-34 well represents a deep water, offshore setting with increased accommodation space marked by sediment slumping, demonstrating a northwestward deepening of the basin. This interpretation is supported by the presence of abundant tubular suspension feeders which are less common in the Ellen C-24 well. In both settings a marked lithological change from mudstone to sandstone occurs between the Whitestone River and Parkin formations, corresponding to a distinct faunal changeover from rich to impoverished fauna. The Whitestone River Formation documents Albian sea-level fluctuations of the Moosebar, Hulcross, Joli Fou and Mowry seas. These are distinguished from each other by faunal reductions that mark regressive phases and shifts in log signatures, and can be correlated to the northern Polar Sea and southern Western Interior Sea basins, as well as globally. The latest Albian disconformity is believed to occur in the terrestrial sandstones of the Fishing Branch Formation. Whi...