After reaching the maximum coring depth of 452.6 mbsf, Hole 1144A was filled with viscous mud, reamed, and flushed of debris. We first ran one full pass and a shorter repeat pass with the triple combo tool string, including the hostile environment natural gamma-ray sonde (HNGS), accelerator porosity sonde, hostile environment lithodensity sonde (HLDS), and dual-induction tool (DIT; resistivity). The Lamont-Doherty Earth Observatory temperature/acceleration/pressure tool was not run because it failed during Hole 1143A operation, and attempts to fix it were unsuccessful. Next, we ran two full passes with the FMS, long-spaced sonic (LSS), and natural gamma-ray tool (NGT) string. Finally, we ran two full passes with the GHMT tool string, including the nuclear magnetic remanence sonde, susceptibility measurement sonde, and NGT (Fig. F33; see "Wireline Logging" in the "Explanatory Notes" chapter). (The raw data are given on the "Related Leg Data" contents list.) The wireline heave compensator (WHC), which was fixed by Sedco mechanics after Hole 1143A logging, did a fine job. Sea heave was generally <1 m for the duration of the logging. All of the tool strings went to the bottom of the hole without any trouble, and a pipe trip was not required. Logging operations started at 1145 hr on 15 March and finished at 0530 hr on 16 March (Table T16).
All three tool strings reached within several meters of the bottom, indicating that little debris fell from the borehole wall. The two passes for the three tool-string runs showed generally excellent repeatability for all the log parameters.
The hole was mostly in good shape. Borehole caliper measurements revealed that the lower part of the hole typically had a 10-in diameter, yielding good data. However, the area between 320 and 380 mbsf showed zones of washout reaching an 18.1-in diameter (Fig. F34). The washed-out zones resulted in poor contact with the borehole wall and, hence, bogus spikes on both the density and porosity logs. The shallow resistivity values from the spherically focused log (SFL) yielded a constant offset of ~30 ppmv less than the medium and deep resistivity (medium induction phasor-processed resistivity [IMPH] and deep induction phasor-processed resistivity [IDPH]) values from the DIT (Fig. F34). The offset is greatest in some of the rugose areas. Despite this, the three resistivity curves show excellent agreement in their variations with depth throughout the entire log interval.
The FMS results once again demonstrated that even when the WHC is working perfectly, it does not provide perfect compensation. The observed stick-slip of the tool string was on the order of 0.25 m. This effect on the data was corrected during the processing of the FMS images with the Geoframe software. Despite an aspect ratio close to unity in the lower part of the hole, the FMS pads in the second pass perfectly tracked the first pass.
The magnetic intensity data recorded during the GHMT runs displayed the typical random spikes that were expected from this tool. Most of these spikes were on the order of 20 nT, but a few were hundreds of nT. In general, the spikes do not repeat between the two passes, so a good splice should be possible. These spikes were edited out in the data presented in Figure F35. Disregarding the spikes, the intensity does not vary by more than 50 nT from top to bottom.
The LSS log is of good quality for the entire hole; the two P-wave velocity measurements are almost completely superimposed (Fig. F34). In general, standard gamma ray (HSGR) and computed gamma ray (HCGR) from the HNGS tool in the triple combo run read 10% to 25% higher than spectroscopy gamma ray or computed gamma ray from the NGT tool in the FMS-LSS run, a difference easily accounted for by eccentricity and hole-size correction. Contrary to the NGT, the HNGS corrects for borehole diameter and potassium in the borehole fluid. The HNGS is more sensitive than the NGT; hence, its results are presented in Fig. F34 (column 1).
P-wave velocities from the split-core samples were limited to the top 35 m of the core (see "Physical Properties," Fig. F34) On the other hand, logging P-wave velocities are available below 86 mbsf, precluding comparison between them. Unfortunately, the MST core-logging measurements of the core P-wave velocities were also of poor quality because of gas expansion. The most striking features in the logging P-wave velocity curve are the major changes in velocity gradient at depths of 230, 290, and 375 mbsf. Above 230 mbsf, the velocity increases slightly with depth; between 230 and 290 mbsf, it decreases with depth. After an sudden increase of 0.06 km/s at 290 mbsf, the velocity again decreases slightly with depth between 290 and 375 mbsf. Another jump of 0.08 km/s occurs at a depth of 375 mbsf. Below this, the velocity increases with depth, showing the common compaction trend also seen in the porosity records. Because no obvious differences in lithology were found between the sediment units defined by these depth intervals (see "Lithostratigraphy"), we suggest that the discontinuities in the velocity profile may reflect differences in the style of compaction within various sediment units.
Other logging parameters, including bulk density and resistivity as well as magnetic susceptibility, also show significant increases at 375 mbsf (Fig. F34). Magnetic susceptibility shows a jump of ~30%-40% with much higher amplitude variations at 370 mbsf and an increasing trend down to the bottom of the hole. Lithologic description reveals that the amount of pyrite in the sediments increases below 350 mbsf (see "Lithostratigraphy").
The potassium measurements from the NGT of the FMS-LSS run agree reasonably well with those from the HNGS of the triple combo run (Fig. F36). Above 160 mbsf, the values from the NGT are consistently lower than those from the HNGS tool by ~0.5%. The thorium values from the NGT, on the other hand, are consistently higher than those from the HNGS tool. The uranium measurements between the NGT and HNGS tools do not agree well; the NGT yields larger amplitude variations (Fig. F36).
The absolute values of gamma-ray attenuation bulk density data from cores and downhole logs generally agree (Fig. F35). Above 250 mbsf, however, the MST measurements are systematically less than the logging densities by 0.1 g/cm3. We noted that this depth corresponds to where coring changed from APC to XCB. Severe gas expansion in the recovered cores, particularly the APC cores, may be responsible for lower average values from the core-logging data. The trends of the CaCO3 measurements of core samples (see "Organic Geochemistry") and photoelectric effect (PEF) from downhole logging are constant from 220 to 330 mbsf (Fig. F37). Lithostratigraphic observation reveals that pyrite in the sediments increases at the bottom of the hole (Fig. F34; see "Lithostratigraphy"). Magnetic susceptibility from downhole logging is in excellent agreement with that from the MST whole-core measurements (Fig. F37).
The total magnetic field recorded by the GHMT reaches a minimum value at 210 mbsf. Above this depth, the total magnetic field may be influenced by the proximity to the bottom of the drill pipe (Fig. F35). Further analysis and interpretation of the total magnetic field awaits shore-based investigation. Natural gamma-ray data from core and downhole logging agree well in their pattern in the entire section (Fig. F35) but are offset in value. Above 230 mbsf, where coring changed from APC to XCB, the MST measurements are systematically lower than the logging values. This again may be explained by the gas expansion in the cores. Porosity calculated from downhole bulk density and that calculated from the moisture content of core samples agree well between 100 and 240 mbsf (Fig. F35). Between 240 and 380 mbsf, the log density porosity shows much greater amplitude in its variability. We noted that this depth interval corresponds to a rugose section of the hole as shown by the caliper on the triple combo tool string (Fig. F34). The FMS records reveal frequent alternation of relatively conductive (dark) and resistive (light) sediment layers in the entire log (Fig. F38). The implications of these fine-scale variations are yet to be explored.