A ROCK-MAGNETIC STUDY OF GIANT PISTON CORE LL44-GPC3 FROM THE CENTRAL NORTH PACIFIC AND ITS PALEOCEANOGRAPHIC IMPLICATIONS

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.