Carrot Creek field consists of a series of long, narrow conglomerate bodies oriented roughly parallel to regional strike and encased in marine shales. Here, the Upper Cretaceous Cardium Formation comprises two coarsening-upward sequences. The lower "b" sequence contains offshore bioturbated mudstones and is capped by a gritty siderite interpreted to represent a pause in deposition. The upper "a" sequence begins with bioturbated mudstones, overlain by hummocky cross-stratified sandstones and conglomerates. Sandstone-conglomerate bodies of this type have traditionally been interpreted as offshore ridges or "terrace bars," posing major problems concerning sand and gravel transport from a distant (unidentified) shoreline.

Our cross sections clearly demonstrate a major erosional surface, of about 20 m relief, at the base of the conglomerate. The conglomerate can rest on various facies within the "b" and "a" sequences but is not genetically related to them. A structure map of the erosional surface shows three topographically distinct areas: (1) a rather smooth terrace, (2) a major bevel where the "b" and "a" sequences are truncated, and (3) a basinward erosional topography of remnant bumps and hollows.

The erosion is believed to have taken place during a rapid relative lowering of sea level, and the erosional bevel represents a newly established shoreface. Gravel supplied at lowstand was reworked along this shoreface and into the hollows by waves. The elongate gravel accumulations were buried by marine shales during the ensuing transgression.