Ichnological signature of a brackish water deposit: an example from the lower Cretaceous Grand Rapids Formation, Cold Lake Oil Sands Area, Alberta

The Lower Cretaceous Grand Rapids Formation within the southern portion of the Cold Lake oil sands deposit is characterized by a well-developed brackish water ichnofossil assemblage. Fifteen ichnogenera have been identified, including: Asterosoma, Bergaueria, Chondrites, Cylindrichnus, Gyrolithes, Helminthopsis, Macaronichnus, Monocraterion, Palaeophycus, Planolites, Rhizocorallium, Rosselia, Skolithos, Teichichnus and Zoophycos. In addition, common non-descript, passively-filled burrows and fugichnia (escape structures) were also observed. The abovemention ichnogenera and their associated non-descript structures can be arranged into eight distinct recurring ichnofossil associations within the Grand Rapids Formation. Each association is comprised of a distinct grouping of ichnofossils which collectively reflect specific environmental conditions which were recurrent in space and time during deposition of the Grand Rapids Formation. The majority of these ichnofossil assemblages reflect deposition in brackish water settings. Ichnologic and sedimentologic criteria which may be utilized to recognize brackish water deposits will be discussed in this paper and illustrated in the accompanying core display.