SEDIMENTOLOGIC-ICHNOLOGIC APPROACH TO RECONSTRUCT PALEOENVIRONMENTS: AN EXAMPLE FROM THE LOWER CRETACEOUS WABISKAW MEMBER OF CLEARWATER FORMATION, ALBERTA, CANADA

The Lower Cretaceous Wabiskaw Member of Clearwater Formation is a significant producer of bitumen in northeast Alberta, Canada. Previous studies addressing the depositional environment of the Wabiskaw Member are scarce, and a comprehensive geological model has yet to be put forward. This study integrates sedimentology and ichnology to characterize the depositional environments of the Wabiskaw Member strata in the study area. The strata have been characterized using nine sedimentary facies grouped into four facies association.

Facies association 1 (FA1) is comprised of dark grey to blue grey mudstone with distinctly lenticular appearance. FA1 were formed in prodelta environments, comprising distal and proximal prodelta, and are ichnologically represented by stressed archetypal Cruziana ichnofacies.

Facies association 2 (FA2) consists of fine to lower medium grained sandstone interbedded with thin mudstone (1-15%). Soft sediment deformation structures are common. The sandstone appears to be massive, wavy parallel, planar parallel to low angle cross stratified. Stressed ichnological suite of mixed Skolithos-Cruziana ichnofacies is present. This facies association is interpreted to be deposited in delta front setting.

Facies association 3 (FA3) is dark grey to bluish grey mudstone with minor siltstone interbeds. The mudstone is planar parallel, massive to lenticular bedded. Sideritized zones up to 15 cm thick commonly occur near the basal contact of FA3. FA3 is moderately bioturbated. The ichnological suite represents an archetypal Cruziana Ichnofacies. FA3 is interpreted as being deposited in the offshore environment.

Facies association 4 (FA4) comprises fine to very fine glauconitic sandstone. Light steel grey to blue mudstone interbeds may occur. The sandstone and mudstone beds are homogenized by bioturbation. FA4 is characterized by high diversity, high-density trace assemblage. This trace fossil suite represents a proximal expression of Cruziana ichnofacies. FA4 is interpreted to represent deposition in distal lower to middle Shoreface environment.

By constructing depositional environment and stratigraphic framework based upon detail facies and wireline analyses, reservoir distribution, shape and thickness are correlated and predicted with greater confidence.