Correlation of paleointensity variation records in the Brunhes/Matuyama polarity transition interval
Paleomagnetic records of the 0.78 Ma Brunhes/Matuyama (B/M) polarity reversal interval described from high resolution (8–11 cm/kyr) deep-sea sediments from western equatorial Pacific ODP Sites 767B and 769A show two successive and marked decreases in paleointensity, of about 15 kyr wavelength each, and a shift from full reversed to fuli normal polarity directions in only ∼ 2 kyr, associated with the uppermost paleointensity decrease. In contrast, transition records from deep-sea sediments with lower sedimentation rates tend to show simpler paleointensity variation with more complex patterns of directional change; for example, the B/M transition record described from deep-sea sediment core V16–58 from the southern Indian Ocean. We suggest that the twin 10Be peaks reported in V16–58 correspond to increased production of this cosmogenic isotope, associated with the double paleointensity dips recorded in ODP 767B/769A,. The low-resolution V16–58 paleomagnetic record can be accounted for by modeling of the geomagnetic field history in ODP 767B at a nominal recording rate of 1 cm/kyr and using an exponential lock-in process filter with a half fixing depth of 16 cm. The double paleointensity dips become a single, broad magnetization low and the change in paleomagnetic directions is offset by about 16 cm below the actual level of the polarity transition, similar to what we infer for V16–58. The low resultant magnetizations will be especially prone to overprinting, which, if in the present field, will tend to give an Americas VGP path. The main features of the 10Be profile will be unaffected by the remanence lock-in process and, consequently, retain their usefulness for correlation as a proxy of geomagnetic dipole intensity variation.
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Also Published In
- Earth and Planetary Science Letters