Surficial lineaments and their structural implications in the Williston Basin

Lineaments of apparent geostructural origin are observable on air photos of the Williston basin. The pattern formed by these lineaments has the appearance of a broad system of interconnecting wrench faults such as occur on the adjacent Canadian shield. On this basis it is hypothesized that a broad system of left-lateral wrench faults may underlie the Williston basin region and possibly the entire continental foreland structural province. Structures in the Williston basin are readily adaptable to this interpretation. The Nessen anticline appears to consist of a north-south realignment of a N. 40° E.- trending Precambrian high which was segmented by left-lateral, en echelon wrench faults and displaced to its present position. The Antelope anticline may be a drag fold associated with a major left-lateral shear zone. The Cedar Creek anticline is apparently the surface reflection of high angle reverse faulting along the southwestern edge of an elongate, N. 30° H. trending, crustal block which has tilted slightly basin ward. Surface and subsurface studies support these interpretations. Oil fields are offset across lineaments indicating that they may be the surface reflection of buried wrench faults. Lineaments also define permeability barriers which divide or terminate oil fields. These fields step down structurally toward the center of the basin indicating segmentation by faulting. Subsurface studies ix indicate that the Paleozoic rocks in the Williston basin are more deformed than the overlying units and that closure on some structures increases with depth. Deformation related to faulting may be far more common than formerly suspected. Surficial lineaments reflecting this buried structure may provide a clue to the location of some pro spective oil traps