Two sites were logged during Leg 199, Sites 1218 and 1219. Bulk density measurements were provided by the Hostile Environment Litho-Density Tool (HLDT), and the Dipole Sonic Imager (DSI) was used to measure velocity. The HLDT measures density by irradiating the borehole wall with gamma rays and measuring the flux between the radiation source and the receivers. The source and receivers are pressed against the borehole by an eccentralizing arm. At both Sites 1218 and 1219, the hole diameter over much of the logged intervals is close to or greater than the maximum extent of the eccentralizing arm. Despite the enlarged holes, however, it was determined that there appears to be little deterioration in the data quality of the density logs (Lyle, Wilson, Janecek, et al., 2002). Because of borehole rugosity and the low velocity of the sediments drilled at Sites 1218 and 1219, the sonic logs generated by the DSI are of low quality and were not used.
The character of the density logs matches that displayed by the discrete sample wet bulk density and the GRA density data (Lyle, Wilson, Janecek, et al., 2002). If it is assumed that the logging density accurately represents the in situ sediment bulk density, the amount of elastic rebound experienced by the sediment when it is extracted from the borehole can be estimated by comparing the core and logging data. As a result of elastic rebound and the process of splicing sections from adjacent holes, the length of the composite sections at Sites 1218 and 1219 is longer than the total penetration at each site. In order to compare the core and logging data, the core depths must be compressed and shifted. Because of the closer spacing of the GRA density data, it was used in the correlation with the logging data. The depth profiles of the HLDT logs at Sites 1218 and 1219 and the composite GRA density records shifted to match the HLDT logs are shown in Figure F9. The overall match of the two different density measures at Sites 1218 and 1219 is good; however, the logging density is not consistently larger than GRA density. This pattern is also evident in the crossplot of GRA density and HLDT density (Fig. F10). In the crossplot, GRA density for clay and radiolarian ooze intervals is consistently less than the HLDT density. The values for the nannofossil ooze and chalk are, however, more or less evenly distributed around the one-to-one line for the two density measures. The patterns shown in Figure F10 are not dependent on the selection of the GRA density for the comparison. The same patterns are present when the discrete sample wet bulk density is chosen for comparison with the HLDT density.