Abstract

A study of bathymetric and seismic-reflection profiles across the apron of sediments which surrounds the Samoan Islands (southwest Pacific) was supplemented by acoustic and photographic observations from a deeply towed instrument package, by bottom current measurements, and by examination of five short cores. The apron is composed of two parts: a distal turbidite plain (average thickness 150 m) and a proximal wedge of acoustically transparent sediments up to 1 km thick, which is covered with hummocks that probably were formed by progressive slumping. Sediment is brought to the apron by ash falls, settling of planktonic debris from the overlying water, and sliding of terrigenous and pelagic sediment off steep insular slopes. It is moved across the apron by progressive slumping, turbidity currents, and a western boundary current. Tectonic deformation has affected part of the apron, particularly the distal plain south of the Islands, which is adjacent to a major plate boundary. There is also a circumferential arch resulting from isostatic compensation of the lithosphere beneath the weight of the islands. Undeformed parts of the apron ore morphologically and structurally similar to the continental-rise and abyssal-plain systems of many continental margins, and there may be similarities in origin and economic potential.

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