Magnetostratigraphy and relative palaeointensity of late Neogene sedimentsat ODP Leg 167 site 1010 off Baja California

Sediments recovered from the most seaward site of the Baja Transect of the California Margin (ODP Leg 167) yielded a high-fidelity magnetostratigraphi c record spanning the last 6 Myr. Using a long-core cryogenic magnetometer, we made NRM measurements of 59 u-channel samples, which cover the interval from 0 to 78.5 mcd (metres composite depth) of the spliced section of Hole s 1010C and 1010E. Stepwise AF demagnetization between 20 and 60 mT showed that the remanence is essentially composed of a single stable component, wh ich was not affected by a coring-induced magnetization. The investigated se ction can be divided into at least 25 polarity intervals, which are assigne d to the chrons from C3A.n2 to the Brunhes (C1n). The sedimentation rate wa s nearly constant at about 13 m Myr(-1), except for a reduction to 9 m Myr( -1) between 4 and 5 Ma. ARM and IRM measurements of the u-channels revealed that the sediments below 23 mcd exhibit sharp drops in magnetic concentrat ion at several horizons, but that the upper part has a relatively uniform m agnetic concentration, containing magnetite of pseudo-single-domain size. T he upper interval yielded consistent relative intensity records when normal ized with ARM, IRM and shipboard susceptibility data. Several peaks in the relative intensity variations correspond to drops in the S ratio, in partic ular at 0.1 T, or to anomalous peaks in the IRM and magnetic susceptibility profiles, suggesting that the normalized intensity record is partly influe nced by episodic changes in the flux of magnetic grains. The normalized int ensity for the intervals younger than 1.2 Ma shows similarities with publis hed palaeointensity records from the equatorial Pacific, including results from ODP Leg 138. In particular, the intensity minima at 0.05, 0.11, 0.18 a nd 0.29 Ma and those associated with the onset and termination of the Jaram illo subchron are well correlated.