Ichnology and Sedimentology of Transgressive Deposits, Transgressively-Related Deposits and Transgressive Systems Tracts in the Viking Formation of Alberta.

Abstract Within transgressive systems tracts, sedimentary facies can be subdivided into 1) transgressive deposits, comprising those generated by the process of transgressive erosion as well as those produced while sea level is rising but not linked to progradational cycles, and 2) transgressively-related deposits, made up of progradational facies associated with periods of stillstand. Locally, transgressively-filled incised valleys may be important, but are excluded from this discussion. In the Viking Formation of the Western Canada Sedimentary Basin of Alberta, transgressive deposits can be differentiated into six distinct facies. Facies A and B are assigned an origin associated with transgressive erosion. The Glossifungitesichnofacies, consisting of Diplocraterion habichi, Skolithos, Arenicolitesand Thalassinoides,are commonly developed on the transgressive surfaces of erosion, cross-cutting the original softground trace fossil suite. Facies C and D reflect distal stillstand progradational cycles within the overall transgression, possibly traceable landward into more substantial stillstand shoreface successions. Facies E and F correspond to deposition under conditions of rapidly(?) rising sea level, and are unrelated to progradational cycles. The high degree of vertical and lateral variability in the observed facies associations point to a complex history of transgression in the upper part Viking Formation. This variability is not deemed peculiar to the Viking Formation; transgressive systems tracts appear to be more complex than hitherto suspected.