North Pacific sediment layers measured by seismic profiling

A reconnaissance survey of the sediment thickness in the North Pacific Ocean has been accomplished through the use of the continuous seismic profiler. A major division in the sediment cover, based on acoustic properties, is recognized and, according to the evidence from sediment cores, corresponds approximately to the Mesozoic-Cenozoic boundary. It thus appears that most, if not all, pre-Cenozoic sediments are in the western part of the basin, generally west of Hawaii. The pattern of accumulation of the Cenozoic sediments closely resembles the present pattern of biological productivity. The major accumulations, aside from turbidites, are found in a belt approximately following the equator and in a belt along the western and northwestern margin of the basin. Deposition in the central part of the basin appears to have been extremely slow throughout the Cenozoic. There is a marked decrease in the thickness of the equatorial sediment belt over the crest of the East Pacific rise, apparently supporting the concept of a spreading sea floor. However, the over-all agreement between the patterns of sediment accumulation and productivity indicates that deposition during much of the Cenozoic occurred under conditions closely resembling those now obtaining. It is concluded that episodic spreading of the sea floor best accounts for the sediment distribution and that the present cycle of spreading commenced approximately 10 to 12 million years ago, having been preceded by a quiescent period of at least 15 million years' duration.