The natural remanent magnetization (NRM) of the archive half of each core section was either initially measured and remeasured after alternating field (AF) demagnetization or, because of time constraints, measured and only after demagnetization. Cores 202-1242A-1H through 12H were measured and then AF demagnetized at 10 and 20 mT. Additionally, Section 202-1242A-11H-2 was demagnetized at 30 and 40 mT. Cores 202-1242A-13H through 28X, 202-1242B-1H through 15H, and 202-1242C-1H through 8H were measured and then demagnetized at 20 mT. Cores 202-1242B-16H through 26H, 202-1242C-9H through 18H, and all cores from Hole 1242D were only measured after demagnetization at 20 mT. Sections obviously affected by drilling disturbance were not measured.
The NRM intensity before demagnetization at the top of Hole 1242A was in the range of ~0.01 A/m (Fig. F23). After 20-mT demagnetization, the NRM intensity is ~1 order of magnitude lower, varying around 10-3 A/m (Fig. F23). The difference between demagnetized and nondemagnetized intensity increases downhole (~1.5 orders of magnitude lower at the base) because of a reduction in magnetic intensity after demagnetization with essentially no change in the intensity before (Fig. F23). This observation is consistent with a slight decrease in the finer-grained magnetic components downhole and could be a reflection of reduction diagenesis at Site 1242. Aside from the slight downhole trend, the intensity variations look promising for geomagnetic paleointensity studies. Because of time constraints, only a quick look at the susceptibility-normalized NRM intensity was possible. Such analysis suggests that through careful postcruise studies a detailed high-resolution paleointensity record may be forthcoming from Site 1242.
Steep positive inclinations observed prior to demagnetization and resulting from the drill string magnetic overprint are at least partially removed after 20-mT AF demagnetization (Fig. F24). The expected inclination at Site 1242 is ~15°, but the observed inclination after demagnetization for the upper 90 mcd, the interval that should correspond to the Brunhes Chron according to the biostratigraphic datums (see "Biostratigraphy"), averages ~35°. The inclinations are more steeply positive in sediment cored with the normal steel core barrel, whereas shallower inclinations closer to the expected values are present in sediment cored with the nonmagnetic core barrel. The overprint still remains after demagnetization but is apparently easier to clean when cored with the nonmagnetic core barrel. No reversed inclinations are observed even in sediments that should be clearly Matuyama in age, and therefore higher levels of demagnetization may be required to remove the overprint from these sediments.
The declinations within individual cores at Site 1242 are generally consistent (show similar directions) in most of the APC-cored part of Holes 1242A and 1242B (Fig. F25). This suggests that the drill string overprint is not pervasive and that geomagnetic information is preserved at Site 1242. Tensor tool measurements will be used to help decipher the polarity stratigraphy. Postcruise studies should allow us to successfully remove the overprint and isolate the geomagnetic record.