Reconnaissance survey of the abyssal plain south of Newfoundland

Abstract

This paper presents a new chart of the abyssal plain south of Newfoundland, contoured in 5-fathom intervals, based on a survey with a newly developed precision depth recorder. The area is of interest in connection with the 1929 Grand Banks earthquake. The abyssal plains are flat, nearly level areas which occupy the deepest portions of many of the ocean basins. The development of a precision depth recorder with an accuracy better than ± 1 fathom was required before an effective study of the abyssal plains could be made. In 1953 a reconaissance survey was run with such a recorder on the abyssal plain south of Newfoundland. The gradient of the plain decreases from 1:1,000 at its northern margin near 41°N to 1:5,000 near latitude 32°N. South of 32°N the gradient probably flattens still more before the southern margin of the plain is reached. The plains have been interpreted by various writers as: (1) atectonic areas; (2) subaerial erosion surfaces; (3) lava plains; (4) areas of long continued sedimentation; (5) surfaces produced by the spreading of extremely fine sediments by bottom currents; (6) areas in which the original relief has been buried by the deposit of turbidity currents. Every core obtained from the abyssal plains to date contains evidence of turbidity currents either in the form of graded bedding, shallow water foraminifera or excessively high calcium carbonate content. The plains slope away from areas adjacent to sediment sources. The present writers consider it likely that all abyssal plains represent areas in which most of the original relief is buried beneath the deposits of turbidity currents. Only the partly buried isolated hills and seamounts which rise from the abyssal plain remain of the original topography. Continued turbidity current transport of material into the basins continually extends the abyssal plains.