Facies Architecture of the Doe Creek Member of the Kaskapau Formation, NW Alberta<subtitle>Utilizing Ichnology to Enhance Deltaic Depositional Models</subtitle>

Abstract

The Upper Cretaceous (Cenomanian) Doe Creek Member, encased in the predominantly marine mudstones of the Kaskapau Formation in northwest Alberta, comprises a series of retrogradationally stacked northeast-southwest trending shoreline deposits. An integrated ichnological and sedimentological analysis of these shorelines reveals a complex depositional relationship between deltaic and open-marine shoreface successions. The shoreline trends in the Doe Creek Member display substantial variability in thickness, sedimentology, and ichnological character along depositional strike stemming from proximity to deltaic point sources. The Doe Creek Member exhibits excellent core control in the subsurface, allowing detailed facies analysis of these multifaceted shoreline deposits. The integration of ichnological and sedimentological analysis yields eleven distinct facies in the Doe Creek Member. The facies represent a variety of depositional environments, including fully marine offshore to shoreface deposits and deltaic deposits (e.g., prodelta, delta front, distributary channels and distributary mouth bars). These facies can be divided into two facies associations, based on recurring vertical successions of regressive delta deposits and open-marine shoreface deposits. The deltaic shorelines consistently develop thicker delta front sandstone packages, fed by associated distributary channels. Penecontemporaneous open marine shoreface sandstones, deposited laterally adjacent to the delta fronts, are typically much thinner and display significantly higher bioturbation intensities, resulting in a lower quality reservoir. This dichotomy of reservoir potential and quality has significant implication for hydrocarbon exploration and exploitation. Unfortunately, the deltaic and open-marine shoreface successions appear almost indistinguishable on gamma-ray well log signatures; this renders well-log cross-sections meaningless in terms of understanding the Doe Creek depositional system. In contrast, detailed core-based cross-sections reveal the complex facies architecture of the coeval deltaic and non-deltaic successions. The facies successions and facies architecture of the ancient shorelines of the Doe Creek Member highlight the inherent complexities induced by deltaic influences on a given coastal environment. Deltaic and open-marine shoreface successions are merely the endmembers of a spectrum of coastal regimes in which there exist degrees of deltaic influence. Within each regressive shoreline trend, it can be shown that the degree of deltaic character is determined by the lateral proximity to a riverine point source. Therefore it is possible, based on integrated ichnological and sedimentological facies analysis, to locate riverine point sources on a given shoreline trend in the subsurface, which could provide significant economic returns.