Seismic-reflection profiles and magnetometer measurements were made over approximately 1,250 km of track on cruise E-6B-74 of R/V Eastward. Eight east-west profiles were tied to existing Caldrill and DSDP drill holes on the Delaware continental slope. One of the interesting features found was a domal structure near the shelf edge just north of Wilmington Canyon. Extrapolation of the reflections from the drill holes to the shelf indicates that a Tertiary reflector surface of probable early Miocene age is involved in the doming.

The dome is on the linear East Coast magnetic anomaly trend which has its origins deep in the basement. Coincident with the dome, however, is a circular magnetic anomaly of about +100 gammas superimposed on the linear trend and somewhat obscured by it. This anomaly suggests structural control of the dome from below and rules out a pinnacle-reef origin. Tertiary emplacement of a circular igneous intrusive at depth or renewed uplift of an igneous basement protuberance are possible causes for the doming. Another possibility is that a salt pillow or piercement dome has intruded the sedimentary column to uplift the Tertiary strata, while at the same time uplifting more magnetic Upper Cretaceous greensands.

The position of the dome near Wilmington Canyon suggests that it influenced the late Tertiary drainage in the area, causing the canyon to orient north-south as drainage was deflected around the dome.

Although the closure involved in the mapped seismic reflector is small, about 25 m (75 ft), there could be a more significant structural closure if the dome persists at depth. If the latter is true the structure would be an interesting petroleum prospect.

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