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doi:10.2204/iodp.proc.340.111.2013

Paleomagnetism

Cores 340-U1401A-1H through 4H were recovered with the APC using nonmagnetic core barrels; all other APC cores were recovered using standard steel core barrels. The FlexIt core orientation tool was not used to orient declination at this site; thus, declination remains uncorrected. Expected inclination for the site is 27.6° during normal polarity and –27.6° during reversed polarity, assuming a geocentric axial dipole (GAD) model. Archive halves of cores from Holes U1401A–U1401D were measured on the three-axis superconducting rock magnetometer (SRM) at 2.5 cm intervals. NRM was measured before (NRM₀) and after stepwise alternating field demagnetization at 20 mT (NRM₂₀).

Results

Sediments recovered from Site U1401 were heterogeneous in composition. Generally hemipelagic sediment is discontinuous and restricted to the zone above 10 mbsf in all cores, below ~5–10 mbsf sediment is dominated by coarse volcaniclastic sand and gravel (see “Lithostratigraphy”).

Intensity at NRM₀ and NRM₂₀, inclination at NRM₂₀, and arbitrarily corrected declination at NRM₂₀ for Holes U1401A–U1401D are shown in Figure F7. As at other sites, NRM₀ intensity shows a similar signature to magnetic susceptibility (see “Physical properties”). These parameters, particularly magnetic susceptibility, are strongly related to the concentration of ferrimagnetic minerals (e.g., magnetite) and correlate well with depositional units of volcanic origin (see “Lithostratigraphy”).

Where available, SRM inclination data show positive values and a normal GAD-like inclination. Declination shows some scatter, but coupled with the positive inclination data, suggests all sediment was deposited under normal polarity conditions. If this was during the Brunhes Chron, it agrees with biostratigraphic ages, which give a late Pleistocene age for the site.

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