The corrected and calibrated MGT and HNGS logs from 160 to 230 mbsf in Hole 1179D are shown in Figure F3. In general, the comparison of the total gamma ray values from both tools is excellent, whereas substantially greater vertical resolution is observed in the MGT log. Peaks in gamma ray intensity can be largely attributed to ash-bearing and clay-rich layers in marine ooze. A number of ash layers were observed in the recovered core over the interval from 180 to 230 mbsf (Kanazawa, Sager, Escutia, et al., 2001). These correlate to sharp, well-defined peaks in the MGT log and broader peaks in the HNGS log. Double peaks at 187–188 mbsf in the MGT log, for example, form a single broad peak in the HNGS log. Overall, the MGT resolves layers several times thinner than the HNGS. The slight offset in gamma ray values between the logs may be attributed to difference in the borehole size between the two passes.
In Figure F4, the main and repeat HNGS passes are shown in comparison with the MGT over an expanded depth scale from 220 to 225 mbsf. The peak-to-peak correlation among these logs is very good. The offset in gamma ray values between the main and repeat HNGS logs is attributed to the difference in the borehole size between the two passes above 256 mbsf. This difference far exceeds the offset in gamma ray values between the MGT and HNGS. The MGT nevertheless correlates peak to peak with both the main and repeat HNGS logs.