The major axis of the Eastern Officer Basin Bouguer gravity anomaly is displaced about 25 to 50 km north of the major axis of the magnetic basement trough associated with this basin (Fig. 1). During the Department of Mines seismic field season in 1972, some weeks were spent carrying out refraction and reflection profiling along the northern margin of the basin and although reflection results are somewhat indeterminate due to poor velocity information, a re-interpretation of the location of the northern margin of the basin appears necessary as a result of the seismic work. Although overthrusting of 'crystalline basement' along the northern boundary of the basin has been tentatively suggested as the reason for the displacement of the gravity and magnetic effects, the M.S.L. contour of the interpreted depth to magnetic basement has been arbitrarily chosen to represent the northern limit of the basin (Krieg, 1972).