During Ocean Drilling Program (ODP) Leg 172, ~6 km of Pliocene/Pleistocene deep-sea sediments was recovered from three sediment drifts (Keigwin and Jones, 1989) of the western North Atlantic Ocean: the Blake Outer Ridge (Sites 1054-1061), the Bahama Outer Ridge (Site 1062), and the Bermuda Rise (Site 1063) (Keigwin, Rio, Acton, et al., 1998). These sediment drifts are regions of anomalously high sediment accumulation rates (typically 10-40 cm/k.y.), and they contain perhaps the highest resolution record of geomagnetic field variability ever recovered from deep-sea sediments. Sediments in the uppermost 150-220 m of each site were collected using the advanced piston corer (APC), which is capable of recovering mechanically undisturbed cores of soft sediment. During ODP Leg 172, we measured the archive halves of all sediment cores using a new long-core cryogenic magnetometer (Model 760 from 2G Enterprises) with an in-line alternating-field (AF) demagnetizer, which was installed after ODP Leg 169. From the long-core measurements, we were able to estimate the pattern of geomagnetic field secular variation (both directions and intensities) for the Brunhes Chron and identify 14 "plausible" Brunhes-aged magnetic field excursions (Fig. F1; Table T1) (Lund et al., 1998; Keigwin, Rio, Acton, et al., 1998). This number of excursions is larger than all previous good-quality Brunhes excursions noted worldwide.
This paper summarizes new paleomagnetic and rock magnetic results derived from U-channel measurements of more than 150 m of Brunhes-aged sediment collected from Sites 1060-1063. These results confirm the existence of 12 of the 14 originally defined excursions. They also identify one new excursion not previously noted in the long-core measurements. Comparison of the U-channel and long-core measurements indicates that long-core measurements, on the whole, can almost always identify paleomagnetic secular variation (PSV) and excursions, but biases in the measurements are present that slightly alter the true paleomagnetic record (as defined by U-channel and selected discrete sample measurements). In a few unusual cases associated with low intensity natural remanent magnetization (NRM) or fast directional changes, the long-core results are significantly different from U-channel or discrete sample measurements.