Isothermal remanent magnetization (IRM) analysis of 77 selected samples was done on the ship using an Analysis Services Company impulse magnetizer model IM-10, which is capable of applying magnetic fields from 0.02 to 1.35 T. We used the impulse magnetizer to impart a series of remanent magnetizations on a sample in steps of 25, 50, 75, 100, 200, 300, 400, 500, 750, and 1000 mT (Table T1). For seven samples of Core 191-1179C-25X the impulse series was 25, 50, 100, 150, 200, 300, 400, 500, 750, and 1000 mT (Table T1). At each step, the magnetic intensity of each sample was measured on the 2G Enterprises pass-through cryogenic magnetometer.
We analyzed 28 samples from Lithostratigraphic Unit I in Cores 191-1179C-1H, 2H, 9H, 12H, and 19H, ranging in depth from 1.30 to 219.68 mbsf. The measured magnetic intensities range from a minimum of 0.00658 A/m for Sample 191-1179C-19H-2, 38–40 cm (25-mT impulse field), to a maximum of 13.160 A/m for Sample 9H-4, 38–40 cm (750-mT impulse field) (Table T1). The magnetic intensities reported in Table T1 for samples from Cores 191-1179C-12H and 19H are ~50% of the true values, due to an error in placement of the discrete sample tray; the samples were 10 cm from the center of the 30-cm measuring width of the pass-through cryogenic magnetometer, but 85% of the input comes from within 20 cm of the central measuring point (Shipboard Scientific Party, 2001a).
IRM analyses were run on 23 samples from Lithostratigraphic Unit II in Cores 191-1179C-20H, 21H, and 22H, ranging from 229.44 to 243.68 mbsf. The measured magnetic intensities range from a minimum of 0.7059 A/m for Sample 191-1179C-21H-1, 68–70 cm (25-mT impulse field), to a maximum of 6.2634 A/m for Sample 22H-1, 48–50 cm (750-mT impulse field).
For lithostratigraphic Unit III, 26 samples from Cores 191-1179C-22H, 25X, and 26X were analyzed. The depth range of the samples was from 247.64 to 283.29 mbsf, and the magnetic intensities range from a minimum of 1.9544 A/m for Sample 191-1179C-22H-6, 134–136 cm, to a maximum of 28.645 A/m for Sample 26X-CC, 10–12 cm.
For all 77 of the samples analyzed for IRM, the magnetization carrier was determined to be magnetite.