Allostratigraphic subdivision of the Upper Cretaceous Dunvegan, Shaftesbury, and Kaskapau formations in the northwestern Alberta subsurface

The mid-Cenomanian Dunvegan Formation is a lithostratigraphically defined clastic wedge comprising sandstones, siltstones, and mudstones. Over the 30 000 km² study area, the Dunvegan Formation has been subdivided into seven allomembers (from youngest to oldest, A to G). A radioactive shale horizon (FSU marker) occurs throughout the study area. It lies between 10 and 40 m above the Fish Scale Marker Horizon within the underlying upper Shaftesbury. The allostratigraphic relationships show that the lower allomembers pass into the upper Shaftesbury Formation and downlap onto this marker, which is interpreted as a major condensed section. The Shaftesbury shales above the FSU marker are interpreted as being genetically related to the progradational phase of the Dunvegan Formation. The overlying allomembers B and A pass laterally into shales of the Kaskapau Formation and are interpreted as being genetically related to the ensuing Kaskapau transgression. -from Authors