A high-resolution marine sedimentary record of geomagnetic intensity during the Brunhes Chron

This investigation of paleointensity employs data from four cores taken from two sites in the Sulu Sea during Leg 124 of the Ocean Drilling Program. These sediments accumulated at a rate of about 10 cm/ky; yet they provide strong, stable magnetizations — a combination rarely found in the deep-sea environment. This study examines the interval of the last glacial cycle (since ∼ 130 Ka) in most detail, using paleomagnetic measurements from discrete samples to explore a variety of normalization parameters. Paleomagnetic remanence and susceptibility measurements taken aboard ship at ODP Site 769 extend the paleointensity record to the Brunhes-Matuyama boundary. After normalization by susceptibility, the shipboard intensity data compare well with the more detailed measurements from discrete samples (in the intervals for which such data are available) and so complete a Brunhes-age (0 – 0.78 Ma) history of paleointensity for the Sulu Sea. That record shows a number of short duration decreases in paleointensity that appear to be useful stratigraphic markers. These results also indicate that the average geomagnetic dipole moment during the Brunhes Chron may have been considerably lower than the present value.