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The Upper Cretaceous paralic to nonmarine Horseshoe Canyon Formation (HCFm) of southern Alberta is divided into seven mappable members: Strathmore, Drumheller, Horsethief, Morrin, Tolman, Carbon, and Whitemud (bottom to top). This subdivision, based on combined outcrop and subsurface analyses, reflects lithostratigraphic variations related to changes in sea level (previously recognized) and newly documented changes in climate, volcanism, and orogenesis in an evolving foreland basin. Million-year-scale cycles of orogenesis resulted in changes in sediment supply and rates of subsidence in the basin and are interpreted in the context of a simple, two-phase foreland-basin sequence stratigraphic model: ( i) overthrust loading resulting in reduced rates of sediment supply and subsidence in the most distal portions of the Alberta foredeep (our field area); ( ii) tectonic quiescence leading to increased rates of sediment supply and subsidence during proximal-foredeep rebound. During the first ∼2.5 Ma of its history (Strathmore and Drumheller members), the HCFm was tectonically and climatically 'stable', and depositional style and stratigraphic architecture were influenced by vertical aggradation and modest progradation of shorelines. During the remaining ∼4.5 Ma (Horsethief, Morrin, Tolman, Carbon, and Whitemud members), there were more complex and frequent changes in climate, volcanism, orogenesis, landscape weathering, and soil formation. Understanding this previously unrecognized complexity is critical for correctly assessing hydrocarbon resource distributions and biostratigraphic and taphonomic patterns. [ABSTRACT FROM AUTHOR]

The overall palynology of the upper Horseshoe Canyon Formation to lower Scollard Formation within the Edmonton Group is reviewed providing new insights into biostratigraphic relationships for the interval, including the recognition of unconformities in the stratigraphic package. The palynomorph recovery from the Horseshoe Canyon Formation and overlying units documents a number of significant events that allow the subdivision of the section. The Albertosaurus bonebed occurs within the lower Maastrichtian portion of the Edmonton Group. The bonebed is situated just below the base of the Scollardia trapaformis Palynomorph Zone, an important marker assemblage that has been documented from areas of the Yukon, Northwest Territories, Alberta, and Saskatchewan. This indicates that the bonebed lies at the top of the Mancicorpus vancampoi Zone. The transition between the zones is marked by a colour change in the sediments, the appearance of coals and organic-rich sediments above the transition, a decrease in numbers of vertebrate fossils, and the appearance of new pollen species. It is inferred that the observed changes reflect a climatic switch from dry to wetter conditions. At a large scale, palynomorph assemblages across this transition do not clearly indicate marked differences that can be attributed to the climatic change, with the exception of the appearance of Scollardia trapaformis and Mancicorpus gibbus in the assemblages. On a microscale of a few metres, there are changes in relative abundance of plant groups. Un examen de la palynologie globale de la partie supérieure de la Formation de Horseshoe Canyon à la partie inférieure de la Formation de Scollard, du Groupe d'Edmonton, jette un nouvel éclairage sur les relations biostratigraphiques dans cet intervalle, dont la reconnaissance de discordances stratigraphiques. Les palynomorphes trouvés dans la Formation de Horseshoe Canyon et les unités sus-jacentes documentent un certain nombre d'évènements importants qui permettent de subdiviser cet intervalle. Le lit à ossements d'Albertosaurus se trouve dans la partie maastrichtienne inférieure du Groupe d'Edmonton, juste en dessous de la zone de palynomorphe à Scollardia trapaformis, un important assemblage repère qui a été documenté dans diverses régions du Yukon, des Territoires du Nord-ouest, de l'Alberta et de la Saskatchewan. Cela indique que le lit à ossements se situe au sommet de la zone à Mancicorpus vancampoi. La transition d'une zone à l'autre est marquée par un changement de couleur des sédiments, l'apparition de charbons et de sédiments riches en matière organique au-dessus de la transition, la diminution du nombre de fossiles de vertébrés et l'apparition de nouvelles espèces de pollen. Les changements observés refléteraient le passage d'un climat sec à un climat plus humide. À grande échelle, les assemblages de palynomorphes qui caractérisent cette transition ne révèlent clairement aucune différence marquée pouvant être attribuée à des changements climatiques, à l'exception de l'apparition de Scollardia trapaformis et Mancicorpus gibbus au sein de l'assemblage. À l'échelle de quelques mètres, l'abondance relative de certains groupes de plantes varie. [ABSTRACT FROM AUTHOR]