ABSTRACT

The Cardium Formation comprises a terrigenous, muddy, sandy and conglomeratic clastic wedge that penetrated the Alberta Foreland Basin margin during the Turonian and Coniacian stages of the Upper Cretaceous. The formation is a lithostratigraphic unit sandwiched within a thick succession of black mudstones; a sedimentary assemblage ascribed throughout the Provinces of Alberta and British Columbia to the Colorado and Alberta groups. The Cardium Formation clastic wedge in plan view has a fan-like outline and projects into the basin from the British Columbia-Alberta border in an arcuate band approximately 200 km wide. The formation is 100 m thick along exposures in the Foothills and thins in subcrop to a zero edge by pinchout and progressive lithofacies change. Within this interval, typical lithotypes, in order of decreasing relative abundance, are mudstone, sandstone and conglomerate.

The Cardium Formation is of significant geological interest for two principal reasons: 1) it represents a complex tectono-sedimentary pulse during the period of maximum inundation of the Mesozoic foreland basin, and 2) it possesses a colossal hydrocarbon storage capacity that is expressed in a series of stratigraphic traps, of which the Pembina Field is its most notable example. Sedimentological responses identified within the formation indicate that accumulation took place in inner shelf, shoreface, lagoonal and coastal plain settings. The deposits cycled through coarse- and fine-grained stages that were controlled by both autocyclic and allocyclic processes. Combined responses to these processes resulted in a complex sedimentary mosaic in which different architectural elements provide a framework for varied and abundant stratigraphic traps and reservoirs. Oils stored in these reservoirs appear to have been sourced from neighboring rocks, and are typically light and sweet. Reservoirs occur at shallow depths between 1200 and 2700 m.

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