The development over the past few years of a high-resolution biostratigraphic scheme based on joint occurrences of Radiolaria, nannofossils, and planktonic Foraminifera enables us to make new progress on problems of paleogeography, paleoceanography, sedimentation, and tectonics in the Pacific. Results from the Deep Sea Drilling Project, combined with other geologic and geophysical data, suggest the following post-Jurassic history for the Pacific plate.

Sedimentary facies patterns reflect a northward motion of the plate relative to the equatorial zone of high biologic fertility, as well as progressively increasing sea-floor depths as newly formed crust moves away from the East Pacific Rise. Superimposed on these gross patterns are evidences of fluctuations in the width of the zone of high productivity, changes in the calcium carbonate compensation depth, and variations in the intensity of bottom-water circulation.

Extensive Early Cretaceous volcanism inundated much of the older western part of the plate and was succeeded by the building and subsidence of long chains of seamounts as the plate moved northwestward, possibly over hot spots beneath the lithosphere. Comparison of plate motion, as indicated by equatorial-zone sediments, with motion indicated by trends and age progressions in seamount chains leads to the hypothesis of a south-moving counter flow in the asthenosphere.

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