| Popis: |
A re-evaluation of the age of the formations comprising the Eagle Plain Group of northern Yukon was necessitated by widely disparate age determinations in recent years from various authors. Maximum age estimates for the base of the group have varied from middle Albian to Cenomanian, and age estimates for the uppermost strata varied by an even greater range, from Cenomanian to late Maastrichtian. A re-examination of new and archival foraminiferal and palynological data indicates an age range of Cenomanian to late Maastrichtian for the Eagle Plain Group. The late Maastrichtian age is derived from palynology from the northeasternmost area of Eagle Plain. However, the stratigraphic relationship of these youngest beds within Eagle Plain Group remains uncertain. Marine strata of the Eagle Plain Group contain foraminiferal indices that correlate with long-established regional foraminiferal zones from the Mackenzie Delta area. The Cenomanian Zone of Trochammina superstes occurs in the Parkin and Boundary Creek formations of Eagle Plain and Mackenzie Delta, respectively. The Haplophragmoides bilobatus and overlying Glaphyrammina spirocompressa zones occur in the Burnthill Creek and Smoking Hills formations of Eagle Plain and Mackenzie Delta, respectively. Reworked microfossils are a conspicuous feature of strata within the Eagle Plain Group. The basal sandstone of the Parkin Formation, for example, contains an assemblage of foraminifera that is entirely reworked. Palynomorph assemblages through the Eagle Plain Group have been estimated at as much as 99% reworked in some strata. |
