Three logging runs including the triple combo tool string configuration, FMS-sonic tool string configuration, and vertical seismic profiling using the three-component Well Seismic Tool (WST-3) (see Fig. F6 in the "Explanatory Notes" chapter) were planned for Hole 1263A. After completion of the APC and XCB drilling operation (bit size = 97/8 in) at 345.6 mbsf, the hole was displaced with 120 bbl of 8.9-lb/gal sepiolite mud and the bit was withdrawn to 85 mbsf in preparation for logging. A summary of the logging operation is provided in Figure F30, and a breakdown of the chronology is provided in Table T14, including some details of the tools used. The tool rig-up began at 0230 hr on 1 April and was completed by 0030 hr on 2 April after a blockage at 174 mbsf during the first FMS-sonic run and the identification of a progressive hole collapse prevented further tool penetration. The WST-3 run was canceled.
The triple combo tool string configuration with the Lamont-Doherty Earth Observatory high-resolution Multi-Sensor Gamma Ray Tool (MGT) on top and the Temperature/Acceleration/Pressure (TAP) tool on bottom was run to the bottom of the hole (3075 mbrf; 345 mbsf), and logging began at 0700 hr on April 1. The lockable flapper valve was not latched open, and the tool string reentered the pipe only after pumping water through the pipe for some time. Because of this problem, the tool string was run out of the hole to the rig floor at 1000 hr and the MGT run was cancelled. The caliper readings from the triple combo tool string suggested that the upper section of the hole was enlarged to 18 in (i.e., wider than the maximal caliper extension). Inspection of the tool at the end of the run revealed that the caliper was broken and that the hole condition might have been better than it appeared. The tool sustained no serious damage.
The FMS-sonic tool string was rigged up, and the first run was blocked just outside the pipe. A wiper trip was run and the tool string was run into the hole again, reaching a new blockage at 174 mbsf. Logs were taken from that point. The caliper readings from the FMS-sonic tool string suggested that the hole (at least the upper section) was slowly collapsing (some intervals <8.5 in). The FMS-sonic tool string was retrieved from the rig floor, and logging operations were completed by 0030 hr on 2 April. The heave conditions were excellent, typically <1 m throughout the logging operation. Consequently, the wireline heave compensator experienced no problems during this operation.
The triple combo caliper indicated that the hole conditions were very good in the lower 60 m of the borehole (XCB drilling). Above this interval, the hole shape is characterized by washouts that increase uphole (Fig. F31A). Apparently, the worst section of the hole logged with the caliper is between 118 (caliper closed) and 127 mbsf, where the hole diameter is >18 in (and the caliper was probably broken). A hole diameter of this magnitude normally would degrade the quality of the data acquired with tools that require contact with the borehole wall (e.g., the density or porosity tools). However, little evidence of deterioration of data quality exists uphole in these logs (Fig. F32).
Tool string accelerometer data from the TAP tool, which integrates the effects of heave, sidewall contact, and wireline stretch on the tool string, indicate that hole conditions and stick-slip of the tool remained at low levels until the cable head entered the BHA (Fig. F31B). As a further check, a wavelet analysis of these accelerometer data was undertaken. The wavelet transform (WT) analysis of the acceleration data allows the multiscale components of the tool acceleration to be deciphered (Fig. F31C). The analyzed record (133–277 mbsf) is characterized by acceleration/deceleration, mainly over a range <1 m. Major washouts are characterized by localized stick-slip displacement over intervals of intermediate scale (~4–7 m). The high-frequency component could be explained by incomplete heave compensation; the other components are related to hole condition (size of the washout). The comparison of the wavelet representation and hole shape shows that the intervals where tool acceleration changes correspond to changes in hole diameter (Fig. F31A, F31C).
The FMS-sonic caliper readings clearly show a much smaller hole than the triple combo caliper readings showed 12 hr earlier. These observations suggest that damage sustained by the triple combo caliper arm in the open hole may have caused an overestimation of the recorded hole size or, alternatively, showed the progressive collapse of the hole, resulting in the blockage of the tool string at 174 mbsf (Fig. F31D). As for the triple combo tool string, acceleration of the FMS-sonic tool string remained at low levels (Fig. F31E).
The original logs were depth-shifted to the seafloor (–2727 m). The seafloor depth was based on the step in the Hostile Environment Natural Gamma Ray Sonde (HNGS) gamma radiation logs (triple combo tool string). The seafloor depth determined in this manner differs by 1.2 m from the seafloor depth determined from the mudline. Because of the lack of clear correlatable features between the computed gamma radiation logs of the triple combo HNGS tool and the FMS-sonic Scintillation Gamma Ray (SGT) tool, particularly given the short section where FMS-sonic calipers were open (Fig. F31F), no unambiguous depth match between the runs with the two tool strings could be established (Fig. F31G). Therefore, the same depth shift to the seafloor (–2727 m) was applied to the FMS-sonic logs.
The logged section is characterized by very subtle variations around very low mean values. For example, total gamma radiation does not exceed 33 API and is mostly below 10 API. As total radioactivity is low, the absolute abundance of each contributing element (uranium, thorium, and potassium) is also low (Fig. F32A, F32B, F32C). The resistivities (spherically focused resistivity [SFLU], medium-induction phasor-processed resistivity [IMPH], and deep-induction phasor-processed resistivity [IDPH]) are commonly plotted on a logarithmic scale because of the typically wide range of these values over several orders of magnitude. Here, resistivities are between 0.3 and 2.2 
m and are plotted on a linear scale (Fig. F32D). Highest variabilities are recorded in porosity (APLC) and density (RHOM) logs (Fig. F32E, F32F) and their associated parameters, namely the formation capture cross section (
f) and the photoelectric factor (PEF). In the upper part of the logged section (base of pipe to 170 mbsf), the porosity is >57% and the density <1.9 g/cm3. Below 170 mbsf, the porosity decreases to ~50% with a concomitant increase in density to ~2.0 g/cm3.
Based on (1) the homogeneity of the formation and (2) the previous general description of the formation, one logging unit containing two subunits has been defined. These subunits are differentiated by the density, porosity, and resistivity logs (Fig. F32).
Logging Subunit 1a is characterized by low density (<1.9 g/cm2), high porosity (>55%), and low shallow resistivity (SFLU) values (~0.8 m) (Figs. F32, F33). Logging Subunit 1a partly correlates with lithostratigraphic Subunit IB, containing nannofossil ooze, clay-bearing nannofossil ooze, and chalky nannofossil ooze (see "Subunit
IB" in "Unit I" in "Description of Lithostratigraphic Units" in
"Lithostratigraphy"). The noticeable drop in the gamma counts and density/porosity values and their associated parameters, as well as in the resistivity values at ~106 mbsf, may not correspond to a lithologic change but instead reflects the lack of environmental correction of these logs, as the caliper was closed at this depth.
The upper boundary of logging Subunit 1b is defined by a rapid change in the density and porosity logs (Figs. F32, F33), corresponding to similar changes in logging bulk density and density data from the cores (see "Physical Properties," in the "Explanatory Notes" chapter and "Lithostratigraphy"). The gamma ray counts for this subunit show a major peak at 286 mbsf and a minor one at 273 mbsf. Intermediate (IMPH) and deep (IDPH) resistivities fluctuate little through this subunit but show a very subtle increase downhole. The PEF of logging Subunit 1b is slightly higher than that for logging Subunit 1a above (Fig. F32F), suggesting a change in mineralogy in this interval. This logging subunit correlates with the bottom part of lithostratigraphic Subunit IB, containing nannofossil ooze, clay-bearing nannofossil ooze, and chalky nannofossil ooze, and lithostratigraphic Subunit IC, containing nannofossil ooze and chalky nannofossil ooze (see "Subunit IB" and "Subunit IC" both in "Unit I" in "Description of Lithostratigraphic Units" in "Lithostratigraphy").
Over the logged portion of the hole, all logs display pervasive cyclicity at a number of depth scales (Fig. F33). The density (RHOM) shows stronger variations at longer wavelengths (cycles are ~30, 15, and 10 m) than porosity (APLC), with which it is anticorrelated (Fig. F33). Porosity (APLC) and total gamma radiation (HSGR) logs both show cyclicity down to the submeter scale (Fig. F33). Intermediate (IMPH) and shallow (SFLU) resistivity cycles are similar to density cycles but with greater detail. The changes in the spatial distribution of these localized cycles conform with and thus reinforce the previously defined unit subdivision (note the change in the pattern of the WT representation, particularly density [RHOM] at ~170 mbsf).
Comparison between continuous and in situ logs with the whole-core MST records (gamma radiation, density, and velocity) and discrete sample moisture (porosity) and density (MAD) data provides the basis for depth matching the core-derived composite depth (mcd) scale to the logging depth and thus creating a logging equivalent depth—a necessary step to correct for the expansion of the cores and obtain correct sedimentation and mass accumulation rates (see "Age Model and Mass Accumulation Rates" in the "Explanatory Notes" chapter). The total gamma counts, porosity, density, and velocity, as well as the core recovery, lithostratigraphy, lithologic subunit division, MS, and color reflectance data, have been linearly compressed on the depth axis by 18%, the core-derived composite depth growth rate (see "Composite Depth"). These data are presented at this compressed equivalent logging depth scale in Figure F34. On this scale, core and logging data are in relatively good agreement with regard to depth: within 1 m at 288 mbsf and a few meters below (e.g., compare the gamma ray data in Fig. F34A). However, the match between gamma radiation, porosity, and density is better in logging Subunit 1b than in logging Subunit 1a (especially porosity), indicating the need for a slightly different compression ratio for the cores in these subunits.
Given the data, only the microresistivity (FMS-sonic) images with a vertical resolution of ~5 cm can theoretically resolve higher-frequency cycles seen, for example, in color reflectance data. In the section logged with the FMS-sonic tool string (110–173 mbsf) (Fig. F35A), the static normalized microresistivity image shows an increase in resistivity downhole (Fig. F35B) and the dynamically normalized image (window height = 0.5 m) does not display a clear pattern of lithification (Fig. F35C). Combined factors such as (1) the homogeneity of the formation, (2) its low resistivity values, and (3) the weak coverage of the borehole wall by the FMS-sonic tool string limit the use of the FMS images for further cyclostratigraphic studies.
As a preliminary step in the comparison between logging and core properties, Figure F36 shows the relationship between density vs. sonic velocity measured on the cores (Fig. F36A), downhole density vs. core density (Fig. F36B), and downhole density vs. sonic velocity in cores (Fig. F36C), with all data relative to the equivalent logging depth. Except for the lower part of the hole (equivalent logging depth > 320 mbsf), the core velocity increases as core density increases with depth. Below 320 mbsf, the linear coefficient between the two parameters increases. Where logging data are corrected for environmental effects (caliper is open; below 115 mbsf; blue to red dots), a linear relationship between core and logging densities exists.
