Fig. 1. An example showing the remanent and induced magnetizations (J_r and J_i) in the formation and the remanent and induced field anomalies they cause in the borehole (B_fr and B_fi). Given a sediment magnetization, J_r, of 0.1 A/m, the observed anomaly in the borehole, B_fr, is 80 nT (see text). The example is from the southern hemisphere, at the latitude of Hole 1096B, where the field inclination is −60.6°. Note that the fields in the borehole do not have the same direction as the sediment magnetizations that produce them.

Fig. 2. Dependence on the field inclination of the remanent anomaly, B_frp, in the borehole due to a 0.1 A/m remanent magnetization. Note that at an inclination of ±35°, no remanent anomaly is observed, because B_fr is perpendicular to the earth's field (see Fig. 1B).

Fig. 3. An example from Hole 1096B showing the derivation of the remanent anomaly from the measured magnetic susceptibility and total field logs. The original measured logs are susceptibility and the total field. The induced anomaly is calculated from the susceptibility, and then the remanent anomaly is calculated by subtraction of the induced anomaly, the pipe effect, and a constant value from the total field. Polarity can be determined from (a) the sign of the remanent anomaly and from (b) the correlation analysis method (positive gradients in black, negative gradients in green). In each case a polarity column is given, with black indicating normal polarity, green reversed polarity, and white undetermined polarity. The depth window employed in the correlation analyses are (from left to right) 1.5, 2.5, 4.5, 8, and 13 m. Paleomagnetic data from Hole 1096B after demagnetization in peak fields of 20 mT and the GPTS of Cande and Kent (1995) are given for comparison.

Fig. 4. Remanent (B_frp) vs. induced (B_fip) anomalies for the interval from 400 to 420 mbsf in Hole 1096C, covering the Gilbert–Gauss polarity reversal, illustrating the principles of the correlation analysis method. Correlation between B_frp and B_fip indicates normal polarity, and anti-correlation indicates reversed polarity.

Fig. 5. A comparison of the in-situ formation NRM with the initial core NRM and the core NRM after AF demagnetization in peak fields of 20 mT. Note that the overprint present in the initial core NRM is not present in the in-situ formation.

Fig. 6. Examples of remanent anomalies (re-calculated for this review) and their magnetostratigraphic interpretation from ODP Holes 884E (Leg 145, North Pacific), 987E (Leg 162, North Atlantic), and 1084A (Leg 175, eastern South Atlantic). C + K 1995: the Cande and Kent (1995) geomagnetic polarity timescale (GPTS).

Fig. 7. Plots of the Koenigsberger ratio, representing relative paleointensity, from two passes of the GHMT in Hole 1095C. The linear best fit to the data in each of the polarity intervals is also plotted—the paleointensity decays with time in the 10 out of 17 polarity intervals, suggesting a preference for the saw-tooth pattern from 5 to 10 Ma.

Fig. 8. Comparison of time-averaged Koenigsberger ratios in different sediment types (see text).

Magnetic field and magnetic susceptibility logs were obtained by the GHMT in the holes listed in this table

The amplitude ranges of the remanent and induced anomalies are approximate values for decameter scale variation. The number of invalid data spikes are classified here as none (if the spikes are absent or negligible), present (if spikes are present in all or part of the log and can be removed to leave good data), or abundant (if the spikes dominate the log and prevent analysis). GHMT-based magnetostratigraphies can generally be produced from holes where the remanent anomaly is equal to or higher than the induced anomaly. The GHMT data is available from http://iodp.ldeo.columbia.edu/DATA/index.html.