The investigation of magnetic properties at Site 1086 included the measurement of magnetic susceptibility of whole-core sections and the natural remanent magnetization (NRM) of archive-half sections. The Tensor tool was used to orient Cores 175-1086A-3H, 4H, 5H, 21H, and 22H, 175-1086B-4H through 23H, except for 12H (Table 5). Cores 175-1086A-6H through 20H were not oriented because of technical problems with the Tensor tool.
Measurements of NRM were made on all archive-half core sections from Holes 1086A and 1086B. All sections were demagnetized by AF at 20 mT. Magnetic susceptibility measurements were made on whole cores from all holes as part of the MST analysis (see "Physical Properties" section, this chapter).
The intensity of NRM after 20-mT demagnetization is between ~10–3 and 10–5 A/m, and magnetic susceptibility ranges between 0 and 3 × 10–5 (SI volume units). In general, these two properties show parallel variations.
Except for the uppermost ~30 mbsf, the cores show significant coring-induced magnetization (CIM) with a radial-inward direction (see "Paleomagnetism" section, "Site 1077" and "Site 1081" chapters, this volume). The CIM is evident from the clustering of declinations around 0° before orientation. In contrast, inclinations showed distinct polarity biases after 20-mT demagnetization, from which an interpretation of the magnetic polarity was possible.
We identified the polarity of the NRM mainly from the inclinations (Fig. 11). Considering constraints from the biostratigraphy (see "Biostratigraphy and Sedimentation Rates" section, this chapter), we interpreted the observed polarity reversal sequence from Chrons C2n (Olduvai Subchron) to C4n (~7.5 Ma; Berggren et al., 1995). Magnetostratigraphic interpretation is summarized in Table 6. Figure 12 displays the relation between depth below seafloor and age. The sedimentation rate dropped from ~40 to 25 m/m.y. at ~4 Ma. Sediments of Pleistocene age are very thin, 15 m or less, within which we could not obtain a good magnetostratigraphy, partly because of physical disturbance of the surface sediments.