Stratigraphy of the Danek Bonebed (Upper Cretaceous Horseshoe Canyon Formation, central Alberta) and correlations with strata in the Drumheller and Grande Prairie regions

Abstract

Although considerable work has been conducted on the stratigraphy and dinosaur assemblages of the Horseshoe Canyon Formation of southern Alberta, equivalent strata and assemblages in central Alberta remain poorly understood. Data from the Danek Bonebed (Edmonton, Alberta) are beginning to fill this gap. The bonebed occurs 4mabove the #9 Big Island Coal Seam. This stratigraphic position lies just below the middle of the Horseshoe Canyon Formation in the Edmonton region, and also lies below a thick, stratigraphically significant non-coaly interval that is expressed throughout central and southern Alberta. The stratigraphic position of the Danek Bonebed equates best with the uppermost Horsethief Member of the Horseshoe Canyon Formation in the Drumheller region and the upper part of Unit 4 of the Wapiti Formation in the Grande Prairie region. In both Drumheller and Grande Prairie, the correlated position of the bonebed underlies a zone of marine transgression (Drumheller Marine Tongue), which, in turn, includes the Campanian-Maastrichtian boundary. In the context of Geologic Time Scale 2004, we infer a late Campanian age of 71.0-71.3 Ma for the bonebed. The Danek's dinosaurian assemblage is limited taxonomically, but compares well with the 'Edmontosaurus regalis - Pachyrhinosaurus canadensis' fossil assemblage zone in the Drumheller region. We propose that a mega-herbivore faunal assemblage, characterized by 'Edmontosaurus' and 'Pachyrhinosaurus', extended continuously across the climatically wet coastal plain of latest Campanian southern and central Alberta, and likely extended northwest into the North Slope of Alaska, where it persisted into the early Maastrichtian.