Abstract: Basement Control of Oil and Gas Traps: More Common Than We Thought

S. Parker Gay

Mapping of the basement fault block pattern in 18 petroleum basins throughout the U.S. since 1982 has revealed literally hundreds of correlations of areomagnetically defined basement faults, or shear zones, and oil and gas traps and structures. These range from simple fault traps, to horst blocks, to dolomitized fracture systems, to asymmetrical folds over reverse faults, Additionally, many types of stratigraphic traps correlate with basement shear zones. Some examples are Pennsylvanian algal mounds in the Paradox Basin that evidently formed on fault scraps on the sea floor, oolite shoals in Kansas also on subsea fault scarps, and offshore bars in the Powder River Basin that formed over fault-caused sea floor highs. A separate category of basement related oil and gas trap are gravitionally induced compaction structures, or graviclines. In the Basin and Range we cannot document basement faults, but it is probable that most structures in the area are rooted in such faults.

A wall chart by N.J. Hyne published in 1984 lists 29 basic types of oil and gas traps. Of these 29, our studies demonstrate that 20 of them (69%) result from basement control. I will show field examples of most of these categories.

Basement control is pervasive in structural and stratigraphic geology. It is an important factor in the formation of a high percentage of oil and gas traps and reservoirs although it is not always taught in college or even in professional short courses. Basement structures can often be delineated in the field with areomagnetics.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada