Beyond the Shoreface: Recognizing the Unique Ichnological Character of Subaqueous Delta Deposits in the Doe Creek Member, Northwest Alberta

Scott A. Reid and S. George Pemberton
University of Alberta, Edmonton, AB

The Cenomanian Doe Creek Member of the Kaskapau Formation is host to prolific sandstone reservoirs in northwest Alberta (87 million barrels initial established reserves). The reservoirs found in and around Valhalla Field include deltaic facies such as delta front and channel sandstones as well as interdeltaic shoreface sandstones, each with distinct exploration and exploitation strategies. Understanding this dichotomy of reservoir origin and the inherent sedimentary complexity requires detailed and accurate facies analysis.

Deltas comprise various sub-environments with excellent reservoir potential and therefore are significant targets for petroleum exploration. Locating the deltaic source on a given shoreline trend can yield considerable economic returns. While the stratigraphy, sedimentology, and facies architecture of both modern and well-known ancient deltas have been widely documented, the keys to their recognition are still poorly understood.

Ichnology provides the most reliable indicator of deltaic influence on a shoreline. Physio-chemical parameters associated with deltaic sedimentation (such as increased sedimentation rate, salinity variation, high turbidity, hyperpycnal gravity flows, and deposition of fluid mud) serve to restrict faunal activity. Fully marine traces such as Zoophycos and Rhizocorallium are rare and usually occur as diminutive solitary forms. Elements of the Skolithos ichnofacies are restricted by high turbidity which hampers effective suspension-feeding. The resultant ichnological signature of deltaic deposits consists of a stressed Cruziana assemblage characterized by a reduction in abundance and diversity of ichnogenera and a sporadic distribution of bioturbation. Detailed ichnological analysis in conjunction with physical sedimentology and stratigraphy will generate more accurate facies architectural, paleogeographic, depositional, and reservoir modeling.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005