Abstract

Magnetic studies of five North Pacific piston cores taken from around a giant piston core at 30°20'N, 157°49'W show three major intervals with distinctly different remanent magnetizations. The sediments deposited during the last 2.43 m.y. have a stable remanence and reversal pattern that corresponds to the standard geomagnetic reversal sequence. Core to core variations in sedimentation rates reach as much as a factor of two, but the variations are very consistent for each of the magnetic units of the dated interval. From 2.43 to about 55 m.y. ago, the sediments were deposited an order of magnitude more slowly than the younger deposits, and are magnetically unstable. The transition from unstable to stable magnetic properties is attributed to the dilution of a magnetically unstable authigenic sediment component by a massive influx of eolian debris carrying magnetically stable minerals. The oldest sediments in the giant piston core (55 to about 65 m.y. old) are more like the surface deposits, and carry a stable remanent magnetization that indicates deposition at a paleolatitude of about 11°N. This is consistent with van Andel and others' (1975) model of rotation of the Pacific plate but not with Dalrymple and others' (1977) model.

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