Paleomagnetic measurements were conducted using a 2G Enterprises model 755 rock magnetometer housed in a magnetically shielded room at the Rosenstiel School, University of Miami. All samples were collected on board the JOIDES Resolution in standard plastic cubes, ~6 cm3 in size. After measurement of natural remanent magnetization (NRM), samples were demagnetized at progressively higher alternating fields (AF), usually at 2- to 3-mT steps, depending on the magnitude of intensity reduction. The maximum AF field depended on the intensity of the sample and was concluded either when the sample became magnetically unstable or when it became too weak for consistent, repeatable measurement. Paleomagnetic data were analyzed using a least-squares method (Kirschvink, 1980) to determine sample inclination and declination. Inclination values were used in the unoriented cores to assign a polarity. In some cases where the APC was oriented, both the inclination and the declination values could be used to assess polarity. Twenty-seven of the hydraulic piston cores were oriented during collection using the Tensor orientation tool (see Shipboard Scientific Party, 1997a). A maximum angular deviation (MAD) value was calculated as part of the least-squares technique in order to assess the relative quality of the paleomagnetic orientation data.
Saturation experiments were conducted on discrete samples using an ASC Scientific model IM-10 impulse magnetizer to produce an applied field. Isothermal remanent magnetization (IRM) associated with progressively stronger applied fields (to saturation) was measured at each step with the cryogenic magnetometer. Additional IRM results for carbonate sediments are given in the Leg 166 Initial Reports volume (Shipboard Scientific Party, 1997c).
The discrete samples were classified in three categories (A, B, or C) based on their relative quality. Class A samples usually exhibited a stronger NRM remanence (>1 × 10-7 Am2/kg), near-linear decay during demagnetization, a MAD value <15°, and the absence of very steep (>70°) NRM inclination. Class B samples typically had slightly lower intensities and MAD values between 15° and 20°, reflecting less linear decay and a decay component only partially stable (although all the demagnetization steps maintained the same polarity). Class C samples exhibited complete or almost complete instability during the initial AF demagnetization steps and had measurements that could not be immediately replicated. Principal component analysis that resulted in MAD values >20° were also grouped with the Class C samples. Most of these samples were not even analyzed because of their inherent instability.
Class A samples are likely reliable for magnetostratigraphic purposes, despite the unusually liberal (as much as 15° MAD limit) classification criteria for these samples. Class B samples should be viewed with caution in developing a magnetostratigraphy. These samples may be reliable if they form part of a sequence containing adjacent Class A samples of similar polarity. Class C sample data were discarded and are not suitable for polarity determination.
Low-field magnetic susceptibility was measured for each discrete sample using a Bartington MS2 susceptibility meter with a single-sample sensor. Data are reported in (10-6) cgs units. No volume correction has been applied to convert cgs units to SI units.