Since 1972, the U. S. Geological Survey has been carrying on an extensive program of geophysical and geological investigations of the structure of the Atlantic continental margin of the United States. Results of the work in the Baltimore Canyon Trough area are based on profiles covering a distance of about 5,000 km of 24-and 48-channel CDP reflection seismic data, a high-sensitivity aeromagnetic survey, and gravity, and seismic refraction data integrated with subsurface geologic information from the approximately 5-km deep COST hole B-2, several 300-m cores from the USGS Atlantic margin drilling program (1976) and other core information.

Sedimentary rock thicknesses as much as 15 km underlie the continental shelf east of New Jersey. Relatively high seismic velocities (3 1/2 to 5 km/sec) increase with depth from 2 1/2 to 15 km. These velocities are associated with rocks marked by moderately low amplitude (~-20 mgal) gravity anomalies and indicate the presence of higher density older rocks underlying the continental margin in the area compared with the Gulf of Mexico. Acoustic and magnetic basements appear to be coincident near the coast at a depth of 1 km. They deepen seaward to 10 km about 50 km offshore, further seaward they diverge. In the area of the upper slope, the deepest magnetic horizons (about 6 to 9 km) are shallower than the deepest seismic reflectors, suggesting magnetic contrasts within the sedimentary ro k section. There is no evidence in the CDP seismic data for the previously postulated "basement ridge" beneath the outer shelf. The best available recent data suggests the possibility of a reef (?) buried about 5 km beneath the upper slope. The East Coast magnetic anomaly is interpreted as the boundary between oceanic

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and continental crust. A domal structure (~39°23^primeN, 73°5^primeW) 20 to 30 km in diameter is marked by magnetic and gravity anomalies and prominent seismic reflectors. An intrusive body of probable Cretaceous age which has its top at a depth of about 3 1/2 km is the inferred source or these geophysical anomalies.

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