A rock‐magnetic study of giant piston core LL44‐GPC3 from the central North Pacific and its paleoceanographic implications

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Previous magnetostratigraphic studies of nonfossiliferous pre‐Pliocene age pelagic clay cores from the central north Pacific have proven unsuccessful because of the unstable behavior of the natural remanent magnetization. The inability to obtain a reliable magnetostratigraphy has severely limited the temporal resolution that can be achieved in paleoceanographic studies of these nonfossiliferous pelagic clays. We carried out a rock‐magnetic study of core LL44‐GPC3, which spans the interval 0‐70 m.y. ago, to determine whether rock‐magnetic parameters can be used to construct a high‐resolution stratigraphic framework for paleoceanographic studies of central north Pacific pelagic clays despite the instability of the natural remanence. In addition, we tested the ability of rock‐magnetic methods to detect and characterize the paleoceanographic changes that are recorded in the sediments of LL44‐GPC3. Stratigraphic variations in rapid and nondestructive rock‐magnetic parameters and related ratios reflect changes in the concentration, mineralogy, and grain size of the magnetic minerals within the sediments. Rock‐magnetic parameters exhibit coherent fluctuations within both the stable and unstable sections of LL44‐GPC3. This result suggests the potential use of these parameters for regional correlation and relative dating of the nonfossil‐bearing pelagic clays of the central north Pacific gyre. Major fluctuations in rock‐magnetic parameters plotted as accumulation rates correspond to intervals of paleoenvironmental change that have been previously detected by other paleoceanographic methods. In addition, variations in a parameter proportional to the concentration of goethite/hematite correlate remarkably well with the mass accumulation rate of the total eolian component, suggesting that in some situations it can be used as a proxy indicator for eolian activity. Copyright 1988 by the American Geophysical Union.

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