The Lower Kaskapau Formation (Cenomanian): A Multiple-Frequency, Retrogradational Shelf System, Alberta, Canada

Abstract

The Cenomanian to earliest Turonian (Cretaceous) Kaskapau Formation in northwestern Alberta and adjacent British Columbia contains three shallow-marine shelf sandstone bodies encased in shale: the Doe Creek, Pouce Coupe, and Howard Creek members. These sandstone bodies were deposited in a retrogradational pattern, subparallel to the paleoshoreline of the underlying Dunvegan Formation. They represent distal-deltaic sedimentation during sea level lowstands or stillstands that punctuated the overall transgression represented by the shale of the Kaskapau Formation. A thin, slightly to nonbioturbated finely interbedded sandstone, siltstone, and shale facies containing syneresis cracks and no benthic foraminifera (facies 4) may be important paleoenvironmentally, representing th leading edge of a progradational wedge. The sandstone bodies are bounded by disconformities. The lower disconformity is erosive, perhaps the result of wave scour associated with a minor fall in relative sea level. The upper disconformity is a flooding surface formed as relative sea level subsequently rose. Within the Doe Creek Member, the overlapping I, N, and A reservoir sandstone bodies suggest an oscillatory shoreline caused by high-frequency, relative sea level fluctuations during the overall transgression. As such, the succession represents a transgressive, high-frequency sequence set. The Howard Creek Member is directly overlain by the Second White Speckled Shale (Turonian), which represents a condensed section having good source rock potential. The latter unit was deposited durin the peak of the marine transgression corresponding to an eustatic highstand.