Abstract

A survey of 300 piston cores from the North Pacific has defined the distribution of volcanic ash and turbidites in this region. Ash occurs within a broad zone 600 to 800 miles wide seaward of the island arcs and continental land areas that constitute the margins of the North Pacific Basin. Active volcanoes at the periphery of the basin provide an adequate source. Layers of ash were not encountered in cores taken north of the volcanic Hawaiian Ridge.

Turbidite deposition is restricted to the sea floor off the western coast of North America, axial portions of the circum-Pacific trench system, and around the Hawaiian Ridge. The greatest seaward extension of Pleistocene turbidites occurs due west of Oregon on the southern end of the Tufts Abyssal Plain. Here sediment dispersal is directly related to the availability of large amounts of terrigenous material and the absence of regional traps and barriers to basinward movement of coarse sediment.

No turbidites occur in cores from the Aleutian Abyssal Plain. The cores contain pelagic deposits and support the view that this plain is a relict feature. Similarly, turbidites are lacking in cores taken from much of the Alaskan Abyssal Plain and the western and northern parts of the Tufts Abyssal Plain. It is suggested that these features are also products of earlier sedimentary regimes.

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