Ichnology and Facies Analysis of Enigmatic Reservoir Intervals in the Triassic Doig Formation, West-Central Alberta

Kerrie L. Bann¹ and Peter Proverbs^2
1Ichnology, Ichnofacies Analysis Inc., Calgary, AB, Canada
²Geology, Huron Energy Corp., Calgary, AB, Canada

This study integrates detailed sedimentology and ichnology to refine the paleoenvironmental interpretations and depositional history of the Triassic Doig Formation, in the Wembley-Valhalla region, west-central Alberta. A comprehensive facies scheme is established and utilized to ascertain the origin of Anomalously Thick Sandstone Bodies (ATSB), which comprise prolific hydrocarbon reservoirs in the region.

Bioturbation is sporadically distributed throughout the succession and although on a local scale it ranges from absent to intense, overall levels are low. Trace fossil assemblages commonly display reduced diversity, reductions in the relative size of ichnogenera as compared to fully-marine counterparts and a dominance of forms that represent opportunistic feeding strategies. These features reflect persistent physico-chemical environmental stresses.

The succession contains a number of recurring facies associations that display complex and variable stacking patterns. The ATSB have been interpreted previously, by various authors, to reflect estuarine deposits in incised valleys, deltaic deposits, lowstand shorefaces, growth-fault grabens filled with shoreface deposits and shelf- or slope-slumps filled with turbidites or shoreface deposits. The basal contacts of the ATSB are generally sharp and erosional and the overlying facies contain sedimentological and ichnological signatures that reflect a range of physico-chemical conditions and paleoenvironmental stresses, such as variations in substrate consistencies, sedimentation rates, salinities, oxygenation, energy conditions, increased turbidity levels and episodic deposition associated with river floods. There is compelling ichnological and sedimentological evidence to suggest that the facies were actually deposited in a variety of sub-environments, most of which were affected by marine to marginal-marine influence.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas