The natural remanent magnetization (NRM) of archive-half sections from Holes 1239A, 1239B, and 1239C were initially measured then remeasured after alternating-field (AF) demagnetization at selected levels. XCB cores from Hole 1239B were stored as whole rounds without paleomagnetic measurements. Sections within Cores 202-1239A-1H through 6H and 202-1239B-1H through 5H were then AF demagnetized at peak alternating fields of 20 and 25 mT and measured. A few sections from Cores 202-1239A-6H and 7H were demagnetized at a peak AF of 60 mT to further evaluate the strength of the drilling overprint. Archive-half sections from Cores 202-1239A-7H through 55X, 202-1239B-6H through 18H, and all core sections from Hole 1239C were measured after demagnetization at 25 mT only.
NRM intensities prior to demagnetization averaged ~10-2 A/m at the top and decreased to ~10-3 A/m by ~100 mcd. After AF demagnetization at 25 mT, NRM intensities are generally one order of magnitude lower (Fig. F22). The XCB cores from Hole 1239A displayed a significantly wider range of intensities (Fig. F22), probably due to biscuiting and core deformation. Within the first meter (composite depth) the NRM intensity before and after demagnetization displays a large (95%) decrease (Fig. F23) that may reflect a redox boundary. The same pattern was noted at Site 1238 and may reflect the reducing conditions of these sediments (see "Geochemistry"). Alternation of the nonmagnetic core barrel with a normal steel (magnetic) core barrel resulted in a cyclicity at the NRM intensity that reflects core-length variations resulting from the varying intensity of the magnetic overprint (Fig. F24) (see Lund et al., this volume).
As observed at the previous sites, inclinations prior to AF demagnetization are steeply positive, characteristic of a drill string-induced magnetic overprint. For the uppermost 40 mcd, inclination values after 25-mT AF demagnetization are closer to the expected value for Site 1239 (-3.7°) (Fig. F25). Below 40 mcd, the sediments are strongly overprinted with steep positive inclinations even after AF demagnetization. Inclinations and declinations within the XCB-cored interval are essentially random and uninterpretable.
Declinations within individual cores of the upper 80 mcd show consistent directions, suggesting that at least some geomagnetic information is retained (Fig. F25). Declinations shifts of ~180° are observed within a few cores, which may represent polarity reversals. These declination shifts occur at ~46 ± 2 mcd in Hole 1239A, ~47 ± 2 mcd in Hole 1239C, ~55 ± 2 mcd in Hole 1239A, and ~54 ± 2 mcd in Hole 1239C, and at ~59 ± 2 mcd in Hole 1239B and 58 ± 2 mcd in Hole 1239C. However, the interpretation of these is not straightforward, as the uppermost declination shift is clearly older than the Brunhes/Matuyama boundary (0.78 Ma) (see "Biostratigraphy"). These may, therefore, represent polarity transition within the Matuyama. Additional shore-based work will be needed to take the magnetostratigraphic interpretation at Site 1239 any further.