Application of the Glossifungites Ichnofacies to the Recognition of Sequence Stratigraphic Boundaries: Examples from the Cretaceous of the Western Canada Sedimentary Basin, Alberta, Canada
MACEACHERN, J. A., S. G. PEMBERTON, I. RAYCHAUDHURI, and S. VOSSLER, University of Alberta, Edmonton, Alberta, Canada
The Glossifungites ichnofacies is a substrate-controlled assemblage of trace fossils, characterized by sharp-walled, unlined, passively filled, vertical to subvertical domichnia, excavated into semiconsolidated (firmground) substrates. In Cretaceous siliciclastic rocks of the Western Canada sedimentary basin, the assemblage is dominated by the ichnogenera Diplocraterion, Skolithos, Arenicolites, Thalassinoides, and Rhizocorallium.
The Glossifungites assemblage demarcates discontinuity surfaces that reflect pauses in sedimentation accompanied by erosion. Colonization of erosionally exhumed substrates and excavation of domiciles occur predominantly within marine to marginal marine settings. In the subsurface of Alberta, several of these discontinuity surfaces correspond to important sequence stratigraphic boundaries.
Sequence boundaries marked by Glossifungites assemblages reflect settings lying in marine to marginal marine positions immediately succeeding sea level lowstand erosion. These settings are largely limited to incised valley fills and incised shorefaces. More favorable to firmground development and colonization are marine flooding surfaces (parasequence boundaries) with accompanying transgressive ravinement. Under such conditions, generation of the discontinuity surface occurs within a marine setting, permitting immediate colonization by opportunistic organisms. Examples of amalgamated lowstand erosion and transgressive ravinement surfaces have also been recognized. These are produced where lowstand conditions exhume the substrate but marine conditions allowing colonization do not occur until the following transgressive phase.
Caution must be employed when applying these discontinuity surfaces to regional stratigraphic problems. These surfaces can also develop in response to autocyclic processes including tidal channel migration and episodic storm erosion. Consequently, the sequence stratigraphic significance of Glossifungites-demarcated discontinuity surfaces can only be resolved through detailed regional mapping.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)