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 full normal polarity directions in only similar to 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; far example, the B/M transition record described from deep-sea sediment core V16-58 from the southern Indian Ocean. We suggest that the twin Be-10 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 Be-10 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.