ABSTRACT

The Campanian Chungo Member of the Wapiabi Formation in the Foothills and the equivalent Milk River Formation in the southern Alberta subsurface prograde to the southeast. New correlation of previously described Chungo Member outcrops indicates that it comprises a set of offlapping parasequences terminated by a widespread ravinement surface marked by chert pebbles. The parasequences downlap to the northeast into a widespread log marker coinciding with the top of the First White Specks, which probably represents a condensed section.

The new correlations indicate that the "Chungo shoreface" interfingers southwestward with the Chungo nonmarine and passes southeastward into the mudstone of the Hanson and Thistle members, a relationship also indicated for the Milk River and its equivalents in the subsurface. The member boundaries are interfingering and diachronous, not sheet-like as previously interpreted.

Re-evaluation of the age of the Milk River Formation, based on palynological data, shows that it youngs to the northeast. These data support the new correlations. A widespread unconformity is also documented between the Milk River/Chungo and the overlying transgressive marine shale of the Nomad, which is probably coincident with the ravinement surface.

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