Sedimentology, Ichnology, and Palaeodepositional Affinity of the Cretaceous Bluesky Formation, Alberta

Abstract

The lower Cretaceous Bluesky Formation of Alberta comprises marginal marine to marine siliciclastic sediments deposited during transgression of the Boreal Sea. The preserved record of sedimentation represents a complex lateral and vertical architecture, making sub-surface correlation challenging. As the Bluesky Formation is the primary host to substantial bitumen deposits of the Peace River heavy oil sands, a refined interpretation of palaeodeposition is crucial to exploration activities. To achieve this objective, high-resolution sedimentological and ichnological data was recorded from a 40 core dataset within an area of approximately 215 km2. Additionally, the process ichnology methodology was utilized to enhance the identification of physical and chemical stresses not revealed through sedimentary analysis. Eleven distinct facies are recognized within the dataset (F1-F11). These facies are the building blocks of four Facies Association (FA1-FA4), which consist of: FA1-wave-dominated, fluvially-influenced delta; FA2-bay-margin shoreface to offshore bay-margin; FA3-wave-dominated marine delta; and, FA4-wave-influenced brackish sedimentation. FA1-FA3 are considered to be coeval, and represent periodic progradation within an overall transgressive marine embayment. FA4 is considered to represent a late-stage change in relative sea-level, juxtaposing brackish-water sediments onto offshore bay-margin, and wave-dominated deltaic facies. By focusing on a relatively understudied area, this work has contributed to the broad-scale understanding of Bluesky Formation architecture. Additionally, it has helped establish the utility of applying the process ichnological methodology to core datasets. Ideally, the combined sedimentological and ichnological characteristics identified within this work will aid in recognition of similar depositional systems in the rock record.