ABSTRACT: Application of Seismic Techniques to Mapping Devonian Salt Dissolution Tectonics in the Williston Basin and the Implications for Oil Exploration

Arnold H. Jennings

Devonian salt dissolution tectonics in the Williston basin generally occur between the original salt depositional zero edge and the present dissolution zero edge. Regional mapping shows salt dissolution has occurred on the western flank of the basin in northeastern Montana and on the eastern flank in Bottineau, Renville, Ward, and McHenry Counties, North Dakota. Between these two areas there is little, if any, salt dissolution.

Structures resulting from salt dissolution are: (1) "structural drape" of overlying sections over the crest of a retreating salt "scarp," (2) "potholes" that become structural highs as a result of later salt dissolution, (3) "re-entrants" from salt dissolution that can create local reversals, (4) "outliers" of salt remnants left behind the retreating salt that form local structural highs, and (5) "outlier dissolution" resulting in later structural reversal with thinning or missing sections.

Where the magnitude of the salt dissolution is great enough the structures formed can be seismically mapped. The conversion of seismic isotime to isopach feet can predict the former salt thickness and the present possible size of salt tectonic features. Where salt still occurs it commonly is an excellent seismic marker.

Devonian salt dissolution has occurred through all major formation times above the time of salt deposition. It is still going on today.

The economic importance of salt dissolution tectonics is the creation of significant structures in otherwise structurally featureless areas. A number of these are oil productive today.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990