ASSESSING EVENT SEDIMENTATION IN THE CRETACEOUS BLUESKY FORMATION OF THE PEACE RIVER OIL SANDS (ALBERTA, CANADA) USING THE ICHNOGENUS ROSSELIA

Spectacular examples of well-preserved, stacked Rosselia specimens have been observed in Cretaceous Bluesky Formation core from Alberta’s Peace River oil sands deposit. Stacked Rosselia segments reflect burrow re-adjustments of a single tracemaker following sedimentation. These traces can be used as a ‘measuring stick’ or proxy for determining the magnitude and frequency of sedimentation events. In this study, core with Rosselia was logged, sedimentological and ichnological characteristics were scrutinized and the length and number of stacked segments were measured. Studied sections of the core are interpreted to represent storm-influenced, lower-middle shoreface deposits. Rosselia burrows record one to two post-depositional re-establishments per tracemaker, where each re-adjustment represents an average 3.6 cm of sediment deposition. In extreme cases, up to four re-adjustments totaling nearly 30 cm were observed, reflecting multiple depositional events in a relatively short time frame—months to perhaps two years depending on the lifespan/growth rate of the organism. The use of Rosselia in this study provides high-resolution analysis of modal sedimentation in the Bluesky Formation, a depositional parameter rarely measurable in the rock record but fundamental to understanding sedimentary processes.