Shipboard paleomagnetic measurements for Holes 1147A, 1147B, and 1147C consisted of long-core measurements of the natural remanent magnetization (NRM) at 8-cm intervals before and after alternating field demagnetization up to 20 mT, which was carried out on the archive halves of all APC cores. In addition, 41 discrete samples were collected from the working halves of Hole 1147A at an average spacing of one sample per section (1.5 m). Cores 184-1147A-3H through 9H, 184-1147B-3H through 9H, and 184-1147C-3H through 9H were oriented using the Tensor tool.
Long-core measurements of NRM and subsequent demagnetization steps were carried out at 8-cm intervals with two demagnetization steps at 10 and 20 mT.
The direction of the NRM (after demagnetization at 20 mT and correction using the Tensor tool data where available) is shown in Figure F8. Above 59 mcd, declination and inclination generally oscillate around values expected for a geocentered dipole field at this latitude (0° and 38°, respectively), with an amplitude consistent with the secular variation of the geomagnetic field. At 59.3 mcd, the Brunhes/Matuyama boundary is identified by a sudden swing of the declination to 180° and a change in inclination to negative values. The upper Jaramillo transition occurs at 72 mcd; the lower, at 76.1 mcd. A short period of reverse declinations and inclinations follows the lower Jaramillo between 76.1 and 80.7 mcd. Below 79.5 mcd to the bottom of Hole 1147A (88.5 mcd), the data are highly scattered, and no further magnetostratigraphic information could be obtained. Table T10 shows a summary of the magnetostratigraphic information for this site as well as sedimentation rates based on polarity transitions.
Long-core measurements were made at Hole 1147B at 8-cm intervals, with one demagnetization step of 10 mT for Cores 184-1147B-1H through 4H and two demagnetization steps of 10 and 20 mT for Cores 184-1147B-5H through 9H (Fig. F9). The Brunhes/Matuyama boundary was encountered at a depth of 57.4 mcd. Farther downcore, the upper Jaramillo transition occurred at 70.8 mcd; the lower Jaramillo, at 76.1 mcd. Besides these transitions, a declination change of 90° was noted between 63.4 and 64.9 mcd. This 90° change occurs only in Section 184-1147B-7H-2. The section was inspected, and no evidence was found that it was split 90° off normal.
Long-core measurements were made at Hole 1147C at 8-cm intervals, with one demagnetization step of 10 mT for Cores 184-1147C-1H through 5H and two demagnetization steps of 10 and 20 mT for Cores 184-1147C-6H through 9H. The Brunhes/Matuyama boundary was found at a depth of 57 mcd. Farther downcore, the upper Jaramillo transition occurred at 72.3 mcd; the lower, at 76.1 mcd (Fig. F10).
The results from all three holes correlate very well, with the exception of the 90° declination shift that occurs only in Hole 1147B. Because it is found in only one of these holes and is contained in one complete section, we believe this shift is an artifact and should be disregarded.