Abstract

Seven reversed seismic refraction profiles were made extending from the Heliport Coast Guard Station, off Long Island, New York, to 45 miles offshore. The profiles show a thin layer of mud above the sedimentary wedge that covers the basement. The mud layer was found to have a compressional velocity of 5030–5260 ft/sec, the unconsolidated sediments, 5700–6040 ft/sec, the semiconsolidated sediments, 6370–6770 ft/sec, and the consolidated sediments, 7470–10,700 ft/sec. Consolidated sediment was found only in the profile farthest offshore. Basement velocities ranged from 16,300 to 18,300 ft/sec. The thickness of the sedimentary column in a section extending 45 miles offshore was found to increase from 1927 feet to 7598 feet, the greatest increase coinciding with the appearance of the consolidated layer. Comparison of the seismic profiles with well logs obtained in the area indicates that the unconsolidated sedimentary layer can be correlated with the Upper Cretaceous Magothy Formation of Long Island and the semiconsolidated sedimentary layer can be correlated with the Upper Cretaceous Raritan Formation which overlies the gneisses and schists that constitute the basement beneath Long Island. Strong evidence for a fault was found 8 miles offshore and again 19 miles offshore.

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