Geomagnetic Polarity Transition Records from Five Hydraulic Piston Core Sites in the North Atlantic
Eleven geomagnetic polarity transition records from five hydraulic piston core sites in the North Atlantic are presented. The Matuyama-Brunhes reversal was sampled at five sites and the upper and lower Jaramillo and upper Olduvai transitions were each sampled at two sites. The wet sediment was sampled by taking U-channel samples across the reversals, as defined by conventional shipboard magnetostratigraphic studies. The U-channel samples were subsampled on shore by taking successive 0.5-cm-thick slices of the sediment. The amount of detail contained in the records of these transitions is not always directly related to sedimentation rate. In seven out of eleven transitions, detailed sampling of cores deposited at moderate to high sedimentation rates (30-50 m/m.y.) failed to produce detailed transition records. The lack of intermediate directions demonstrated to be carried by single-component magnetizations indicates that these sections do not contain accurate records of transitional field behavior. The four transitions sampled from Hole 609B (82.5 m/m.y.), however, exhibit intermediate directions that are carried by univectorial magnetizations. A progression of directions through these reversals is also observed. These records therefore satisfy the basic criteria required to allow this interpretation in terms of geomagnetic field behavior. Data from these mid-northern latitude transitions place additional constraints on existing transitional field models of the Matuyama-Brunhes reversal. The lower Jaramillo and upper Olduvai transitions obtained in this study are compared with records of these same reversals at a midsouthern latitude site. Comparison of these transitions reveals symmetries that are dependent upon the sense of the reversal with respect to the hemisphere on which the site is located. These symmetries are predicted by two different transitional field models in which an axisymmetric quadrupole term is dominant.
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- Initial Reports of the Deep Sea Drilling Project