The natural remanent magnetization (NRM) of archive half sections was initially measured and then remeasured after alternating-field (AF) demagnetization at selected levels. Sections obviously affected by drilling disturbance were not measured. Cores 202-1238A-1H through 8H were demagnetized at peak fields of 20 and 25 mT. Cores 202-1238A-9H through 46X and Holes 1238B and 1238C were demagnetized at peak fields of 25 mT.
Initial NRM intensities ranged from 10-2 to 10-4 A/m (Fig. F26). Below 200 mcd in Hole 1238A, the XCB cores have a low average but highly variable intensities possibly as a result of coring disturbance (Fig. F26). Cyclic variability in NRM intensity within the uppermost 100 mcd (Fig. F26) may at least be partially related to the alternating use of the nonmagnetic and normal steel (magnetic) core barrels (Fig. F27) (see Lund et al., this volume). After AF demagnetization at peak fields of 25 mT (Fig. F26), a one order of magnitude decrease in intensity was observed for the upper 50 mcd that increases to ~1.5 orders of magnitude below. Additionally, both the initial and demagnetized NRM lose ~95% of their initial intensity within the first meter of sediment (Fig. F28). The downcore changes in NRM intensity reflect the creation and/or destruction of magnetic phases as a response to biogenic, depositional, or diagenetic causes.
As observed at the previous sites, inclinations prior to AF demagnetization are steeply positive, reflecting the effect of the drill string magnetic field. Within the upper 40 mcd, AF demagnetization at 25 mT removes much of the drill string overprint and inclinations are close to the expected axial dipole inclination for this site (-3.7°) (Fig. F29). Below 40 mcd, steep positive inclination are observed even after 25 mT AF demagnetization, suggesting that much of the overprint remains (Fig. F29). The paleomagnetic data do not clearly record any polarity reversals, and therefore, no shipboard magnetic stratigraphy is available for this site.