Abstract

At one horizon in the Cardium Formation (Burnstick Member) there are four sand bodies, each 80 to 100 km long, and 2 to 7 km wide, which were previously interpreted as “offshore bars”. These sand bodies, along with smaller Burnstick Member “pods”, line up to form three parallel and continuous belts up to 350 km long. The sand bodies average about 3 m in thickness, contain internal sequences that become cleaner upward, and have sharp bases with a pebble lag. Each sand body rests “within” an asymmetrical, one-sided, erosional surface, which is labelled the E4 surface. The erosional surface drops systematically across each field with a relief of 3 to 7 m.

All four sand bodies have been reinterpreted as incised shoreface deposits that were localized on the Cretaceous shelf as a result of relative sea-level changes. Before the deposition of the four sand bodies the shoreface was located west of the study area in a position parallel to the north-northwest trending Cordillera. A large drop in relative sea level (? tectonically influenced) moved the shoreface toward the east, producing the easternmost erosional surface and sand body (Garrington). A subsequent transgression with superimposed stillstands resulted in the incision of the erosional surfaces along the Caroline/Crossfield, and Lochend trends, and the deposition of these three sand bodies.