Gravity and Magnetic Modeling of the Ames Structure, North Central Oklahoma

Judson L. Ahern

The Ames Structure in Oklahoma has been attributed to meteorite impact, volcanic activity, dissolution collapse, etc. Analysis and modelling of the gravity and magnetic field over the Ames Structure places constraints on possible models for its origin.

The residual Bouguer gravity anomaly reveals a highly circular negative anomaly of about 1 mgal that coincides with the central structural depression defined by Sylvan Shale structure contours. This low is surrounded by an annular high with a radius of 6 km and an amplitude of about 0.5 mgal; this positive anomaly ring coincides with the structural high comprising the rim of the Ames Structure.

The gravity signature of impact craters is relatively distinctive and the relationship between impact effects and density is somewhat straightforward. The amplitude, shape and character of gravity over the Ames Structure are consistent with observations of other structures believed to be caused by meteorite impact.

A magnetic low over the Ames structure is also consistent with magnetic field observations over other impact craters, although the magnetic field associated with impact craters is less distinctive than their gravity field.

A 2 1/2-D gravity and magnetic model and a 3-D gravity model have been constructed with the impact model in mind. The density and magnetization structure derived from modelling, like the fields themselves, is similar to that found from geophysical modeling of known meteorite impact craters.

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