Basinwide Fold Evolution and Geometric Development of Cratonic - Foreland Basin Interaction

Pal Redly and Zoltan Hajnal

Latest results of the Williston Basin Project incorporate a north-south regional seismic line, which is crossing the deepest part of the Williston Basin from Saskatchewan to South Dakota. The integration of this new profile to the two, existing east-west regional seismic sections, gives a quasi-3D image of the basin. The combined seismic data illustrate alternating extensive and compressive phases during basin development, marked by basinwide circular and radial folds. This alternating pattern of basin subsidence is the very nature of cratonic basin evolution. The structural necessity for compressive phases during cratonic basin subsidence, is shown in a regional scale interpretation that has undergone an Earth-curvature correction.

The geometrical evolution of the neighboring foreland basin is also interpreted from data that has been corrected with the Earth-curvature function. It shows that basinwide folds sub-parallel and perpendicular to the longitudinal axis of the basin are analogous to the circular and radial folds of the cratonic basins. These folds, in the foreland belt, are less pronounced because larger scale structural elements can overprint them.

Where the cratonic and foreland basins overlap, a complex, deformed zone is present, and contains late stage volcanism, in this area.

The geometry of the Williston Basin can be modeled by the Sloss-type 'inverted Gaussian function' that is modified by the periodic westward tilting of the basin and the Earth-curvature function.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California