All cores from Holes 1132B and 1132C with sufficient recovery to make long-core measurements feasible were measured as half cores using the 2-G 760-R magnetometer. Measurements were made of natural remanent magnetization (NRM) and after 20-mT demagnetization. Four sections of whole cores were measured to compare with the standard archive half-core measurement. The experimental nonmagnetic shoe was used for odd-numbered cores from Hole 1132B from Cores 182-1132B-3H to 13H. The nonmagnetic shoe again had a significant effect on the coring contamination (see "Appendix: Magnetics Experiment"). Discrete samples were taken from both soft sediments cored using APC and from biscuits in the XCB and RCB cores for NRM and rock magnetic analysis. However, the magnetization of these samples was so weak that their NRM could not be measured; thus, their analysis must await shore-based studies.
Long-core measurements revealed an extensive section of normally magnetized sediments, continuing through all of the APC cores and most of the XCB cores. In the XCB cores, the signal was weak, and measurement was confounded by the presence of mud, which had become remobilized and remagnetized in the coring process. We therefore measured large discrete biscuits from cores to improve the signal-to-noise ratio. The first indication of reversed rocks came in Core 182-1132B-21X. Subsequent analysis of large biscuits in Core 182-1132B-22X confirmed that there was indeed a change of polarity between Cores 182-1132B-20X and 22X. However, Core 182-1132B-21X was badly disturbed by coring, and only small biscuits remained. It is possible that the few reversed readings at the bottom of Core 182-1132B-21X mark the end of the normal sequence at 190 mbsf. Certainly in Section 182-1132B-22X-2 at 194 mbsf, the results are reversed (Fig. F11). A substantial sequence of predominantly reversed rocks occurred below the reversal, until a return to normal polarity at 230 mbsf. This polarity was maintained for the remainder of the available record from Hole 1132B.
After removal of readings from the beginning and end of cores and sections, the intensity of magnetization showed some fluctuations with a wavelength of ~15 m (Fig. F11). These are comparable with those seen in the cores from other sites with high sedimentation rates (e.g., at Site 1127). The intensity fluctuations at Site 1132 were obscured by noise, although there is a possibility of high-resolution correlation between sites with high sedimentation rates.
In Hole 1132C, poor recovery precluded long-core measurements, with the exception of Cores 182-1132C-31R to 35R. These cores included a hardground with a mineralized crust. The intensity of magnetization was anomalously high in the region of strong mineralization and remained high in red skeletal limestones below. A polarity change, associated with the hardground, extended to a depth of ~10 cm below the mineralized crust.
The comparison between whole core and archive core was performed in conjunction with the coring tests using the nonmagnetic cutting shoe and APC assembly and will be discussed in more detail in the "Appendix: Magnetics Experiment." However, it is noteworthy that the comparison between archive-half and whole-core measurements showed no significant difference in the core taken using the nonmagnetic shoe, whereas significant differences were observed in the core taken using the standard core-barrel assembly.
Magnetic susceptibility measured using the multisensor track (MST) yielded negative diamagnetic values near the noise level of the instrument. From ~159 to 250 mbsf, the magnetic susceptibility (MS) approaches zero, suggesting an increase in ferrimagnetic susceptibility (Fig. F12). At the mineralized hardground, the susceptibility is strongly positive and continues at high levels in the underlying red skeletal limestone below.
The Brunhes/Matuyama boundary is placed in Core 182-1132B-21X because of individual XCB biscuits, which recorded normal polarity in Core 182-1132B-20X and reversed polarity in Core 182-1132B-22X (Fig. F13). The occurrence of the Brunhes/Matuyama boundary at ~180 m gives a sedimentation rate of ~230 m/m.y. for the Brunhes. The return to normal polarity at 230 mbsf is possibly the Jaramillo termination. If the sedimentation rate calculated from the Brunhes/Matuyama boundary extends below the boundary, the 200,000 yr of the Matuyama above the Jaramillo should be represented by between 40 and 50 m of section. The observed section depth is ~40 m; thus, we interpret the polarity change as the top of the Jaramillo and suggest that the sedimentation rate of ~230 m/m.y. does indeed continue to the Jaramillo (Fig. F13). A second possibility, which is more consistent with biostratigraphic data (see "Biostratigraphy"), places the Jaramillo between 186 and 193 mbsf and the termination of the Olduvai between 222 and 229 mbsf.