Abstract

Several apparent sediment drifts of Tertiary age occur in the central northwest Pacific, and some form east-trending bands of thick sediment north and south of the axis of a major near-surface current, the Kuroshio Extension. The intervening area of thin sediment is located directly below the present axis of the Kuroshio Extension. These spatial relationships suggest that the zone of condensed sediment section and the adjacent sediment drifts are causally related to the Kuroshio Extension. The condensed section probably results from the partial insulation of the sea floor from the normal "pelagicrain" due to the high-energy portion of the Kuroshio and from the erosion of the sea floor by benthic storms associated with the Kuroshio. The bordering sediment drifts may represent the preferential deposition of fine sediments transferred from the high-energy to the low-energy portion of the water column.

The interplay between the Kuroshio Extension and the northwestward drift of the Pacific plate should result in predictable variations in the timing and locations of pronounced sedimentation-rate changes. Such variations will depend both on the intensity and spatial stability of the Kuroshio, as well as direction and rate of Pacific plate motion. If the Kuroshio has remained spatially stable and active for at least several million years, then sites presently north of the Kuroshio should exhibit two periods of increased sedimentation. These periods represent the times when the site came into the influence of the high-sedimentation zones, first south and later north, of the Kuroshio. There should also be a diachronous unconformity in areas north of the Kuroshio that separates the two periods of increased sedimentation and represents the effect of passage of the plate directly beneath the Kuroshio. We conclude that some regional unconformities and zones of anomalously high sediment accumulation both in the northwest Pacific and elsewhere may arise largely independent of regional variations in bottom-water flow induced by climate change.

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