ABSTRACT

A total of 40 formations were picked from approximately 2200 oil well wireline logs. Isopach maps and structure contour maps were constructed from these data for each of the formations. Individual structural features were delineated through a combination of trend surface and residual analysis. Analysis of the isopach maps and of structural relief permitted the determination of the timing of tectonic events for the individual structures and the area as a whole.

In addition to the major structures, several less prominent structures, both positive and negative, have been identified. Although the subsidence of the basin was the principal regional tectonic activity, the structural features in southwestern North Dakota were intermittently decoupled from the larger-scale basin movement, producing local highs and lows. All of these structural features appear to have behaved independently of each other through time. Basin initiation and subsequent subsidence are the only recognizable pre-Devonian activity in the area. Most of the development of the individual structures took place during the Devonian and Mississippian, although the relief on some structures was enhanced by Laramide activity at the end of the Cretaceous.