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