A COMPARATIVE-ANALYSIS OF THE ICHNOLOGY OF WAVE-DOMINATED AND RIVER-DOMINATED ALLOMEMBERS OF THE UPPER CRETACEOUS DUNVEGAN FORMATION

The Upper Cretaceous (Cenomanian) Dunvegan Formation is a siliciclasti c unit, which lies in the subsurface of western Alberta and crops out in the west-central portion of the province. The Dunvegan is deltaic i n origin. Previous workers have subdivided the Dunvegan into 7 allocyc lic members (A through G) in the subsurface, based on detailed sedimen tological and stratigraphic analyses. Each allomember corresponds to a deltaic lobe and exhibits varying degrees of wave and river dominance , Allomembers D and E were chosen to test ichnological variations in d eltaic systems because D is strongly wave-dominated and E is strongly river-dominated. Tidally influenced end members were not included in t he scope of this study. The study area comprises Townships 59 to 67, a nd Range 20 W5M to 8 W6M. Fifteen cores, totaling 269 m in length, wer e analysed sedimentologically and ichnologically in order to compare t he ichnological characteristics of river-and wave-dominated deltas. Al lomember E is characterized by an overall lower intensity of bioturbat ion, a lower diversity of ichnogenera within proximal facies, and a ge neral suppression of the Skolithos ichnofacies. In contrast, Allomembe r D shows a greater intensity of burrowing, a generally higher ichnoge neric diversity, and a diverse Skolithos ichnofacies. The contrasting ichnology provides insights into the ethology exhibited by infauna in the different depositional settings. More importantly, the differences observed are independent of bathymetry and emphasize the influences t hat environmental parameters such as variability in salinity, temperat ure, sedimentation rates, water turbidity, and substrate consistency p lay in an organism's selection of an ethological survival strategy. As such, ichnological data can be successfully integrated with physical sedimentological data in order to form predictive models that may be u sed to better comprehend and ultimately differentiate between these tw o depositional systems.