Oligocene magnetostratigraphy for equatorial Pacific ODP Sites

U-channel samples were measured at 1 cm intervals and were stepwise demagnetized in alternating fields (AF) up to a maximum peak field of 80 mT. The magnetization directions were determined at 1 cm intervals by principal component analysis of demagnetization steps in the 20 to 60 mT peak field range.

A similar treatment was carried out on the discrete samples, which confirmed the results obtained with u-channel measurements. Sites 1218 and 1219 were precisely correlated based on multisensor track, paleontological and shipboard magnetostratigraphic data; this correlation is substantiated by u-channel measurements. Although the magnetostratigraphy obtained from the u-channels is similar to the interpretation deduced from shipboard measurements based on blanket demagnetization at peak AF of 20 mT, the u-channel results are substantially more robust since many interpretative uncertainties are resolved by the stepwise demagnetization and higher stratigraphic resolution.