Sediment distribution in the oceans: The argentine basin

Continuous seismic profile measurements made over several thousand kilometers of traverse in the Argentine basin reveal a greater accumulation of sediments than has been found in any other ocean basin. Horizontally layered sediments attain a thickness of more than 2500 meters and overlie a typically rough basement. The basement, which has an average topographic amplitude of 400 m and a wavelength of 15 km, was traced from the base of the continental rise to exposures on the mid-Atlantic ridge. A unique sub-bottom reflector, designated reflector A, was observed to be the most prominent and continuous of the sedimentary reflecting horizons. The coherent bubble pulse pattern of the reflections from reflector A and especially from the ocean floor are in marked contrast to the highly reverberant and noncoherent echoes produced by the basement. Reflector A is generally conformable to the topography of the ocean floor and is unaffected by topographic expression in the basement. One region contains a crater-like sedimentary structure about 350 km in diameter but too shallow to affect the basement relief. It is concluded that most of the basin sediments were derived from the continent and transported to the deep ocean floor by some process which deposited them as smooth, nearly horizontal layers. The structure of the sediments suggests that the basin has been exceptionally free from deformation, excluding broad crustal warping, throughout the period of deposition of the sediments.