Abstract: Paleogeomorphology of Fred and George Creek Area, Toole County, Montana

Jerry L. Branch

The Fred and George Creek oil field, in the Sweet-grass Hills near the Canadian border, produces oil and gas from the basal Cretaceous sandstones of the Kootenai Formation. These Sunburst sandstones lie directly on the pre-Cretaceous unconformity, and their depositional distribution is related directly to the paleogeomorphology of this past erosional surface.

It is possible, by mathematical flattening of post-Jurassic structure, to reconstruct the pre-Cretaceous land surface. This is accomplished by flattening time-parallel thin bentonite beds that directly overlie the unconformity and thus restoring relative elevations on the old erosional surface. The resulting contoured drainage pattern aids field extension and exploration efforts by allowing application of modern principles of sand distribution on a premapped erosional surface.

This paper considers only a stream-drainage paleogeomorphic surface; however, the method should work equally well while following old shorelines along paleoelevations.

AAPG Search and Discovery Article #90971©1976 AAPG-SEPM Rocky Mountain Sections 25th Annual Meeting, Billings, Montana