m).Logging operations in Hole 1195B were shortened as a result of deteriorating hole conditions. Only one run with the triple combo and three check shots with the WST in shallow depths were completed (Table T14). Operations began at 0315 hr on 29 January with the rigging of the triple combo with the LDEO temperature, acceleration, pressure tool at the bottom and the LDEO multisensor gamma ray tool (MGT) at the top. The tools reached total depth (TD) at 517.5 mbsf, which was ~2 m above TD cored. A successful first pass retrieved excellent logging data (Fig. F28). Already recognizing two narrow spots on the caliper in the upper part of the hole, it was decided to abandon the second run with the MGT in favor of running the WST because an accurate time-depth conversion was crucial for achieving the objectives at this site. In a first attempt of deployment, the WST did not pass the bottom of the pipe and the pipe became stuck. Despite a subsequent wiper trip, hole conditions worsened. In a second attempt, the WST could only be lowered to a newly developed tight spot at ~150 mbsf. Three check shots were completed using the 300-in3 air gun above this depth (Table T15). At 1745 hr, it was decided to abort further logging in this hole.
During the first run, the almost smooth borehole yielded high-quality logging data (Fig. F28). The exception is the interval above 185 mbsf, where the caliper shows a maximum aperture of 17 in, causing the tool to loose contact with the borehole wall. In these intervals, the quality of the density and porosity measurements are somewhat degraded, whereas natural gamma ray (HSGR) and deep resistivity are little affected.
The air gun produced a sharp high-amplitude signal that allowed easy picks of the first arrivals captured by the WST. In contrast, shots with the water gun used at the previous site had a precursor signal that severely hindered the picking of the first arrivals on the seismograms, resulting in unreliable data.
Comparison of logs with core data (Fig. F29) shows a good correlation of the data profiles. In the upper 170 m of the logged section (80-250 mbsf), the absolute values of GRA densities are slightly higher than the log values because the density measurements downhole were affected by an enlarged hole. Between 250 and 370 mbsf, the two data sets match well. However, below 370 mbsf, the core values are slightly lower than the downhole log values. The absolute values of natural gamma radiation are not comparable, as they have different units.
The logged interval of Hole 1195B is divided into five logging units (Fig. F28). Logging Unit 1/2 and 4/5 boundaries correspond roughly with lithologic Unit II/III and III/IV boundaries, respectively. In the lower part of the drilled interval, the logs suggest the possibility of additional lithologic subdivisions. In general, log values display little variability down to 240 mbsf, which is in concert with the rather homogeneous lithology of unconsolidated skeletal wackestone to packstone in this interval (see "Lithostratigraphy and Sedimentology"). Below 240 mbsf, the logs have a cyclic appearance, which again correlates well with the alternations of light gray and greenish gray sediments observed in the cores (see "Lithostratigraphy and Sedimentology").
Logging Unit 1 shows relatively low resistivity and HSGR (~20 gAPI) values with generally minor variations in all log values (Fig. F28). A small log change occurs at 134.5 mbsf that is characterized by an excursion to higher HSGR and lower resistivity values. Below 134.5 mbsf, log responses are similar to the interval above. Logging Unit 1 roughly coincides with lithologic Unit II, consisting of unconsolidated skeletal wackestone to packstone (see "Lithostratigraphy and Sedimentology"). Sediments in lithologic Subunit IIC are progressively more consolidated downhole. They are separated from the more unconsolidated sediments above by glauconite-rich beds at the base of lithologic Subunit IIB that might be the cause of the high HSGR values at 134.5 mbsf. These beds also mark the seismic Megasequence C/D boundary (see "Seismic Stratigraphy").
The boundary of logging
Unit 2 (240 mbsf) is marked by an increase in density, resistivity, and HSGR
values (Fig. F28).
In this logging unit, the log curves display more variability. Below 328 mbsf,
the frequency of log peaks is much higher and the amplitude of the HSGR log
increases (20 to 40 gAPI), as does the amplitude in the resistivity log (from 2
to 4 m).
The upper boundary of logging Unit 2 is ~15 m above that of the lithologic Unit III boundary (Fig. F28). This boundary also coincides with the seismic Megasequence B/C boundary (see "Seismic Stratigraphy" and "Lithostratigraphy and Sedimentology"). The transition from lithologic Unit II to Unit III is one of the major changes in sedimentation; Unit III is characterized by alternations of light gray and darker greenish gray layers that also have textural variations. The dark layers are related to increased terrigenous input, as shown by the increased quartz and clay content of the sediment (see "Lithostratigraphy and Sedimentology"). The HSGR variations between 240 and 328 mbsf are predominantly related to variations in uranium content, whereas those between 328 and 418 mbsf are mainly caused by changes in thorium and potassium concentration (Fig. F30). Glauconite-rich layers occur in the upper portion of lithologic Unit III and appear to be correlated with increased uranium concentrations. Light layers, which are enriched in neritic material and show lower HSGR, also have lower porosity and higher resistivity values, indicating increased cementation. The thorium and potassium enrichment, however, correlates with an increased terrigenous input (see "Lithostratigraphy and Sedimentology").
The boundary between
logging Units 2 and 3 is marked by an increase in density and resistivity
values, which are generally above 2.2 g/cm3 and 3.4 m,
respectively, and a decrease in variability in all neutron porosity and HSGR
values to ~35 pu and 25 gAPI, respectively (Fig. F28).
Toward the bottom of logging Unit 3, HSGR and resistivity amplitudes increase.
This pattern of high variation in the lower part of the interval and less
variation in the upper part is similar to logging Unit 2, suggesting a
repetition of the sedimentation pattern, although with reduced thickness.
No lithologic boundary is recognized at the upper boundary of logging Unit 3 (418 mbsf), but the boundary correlates well with seismic Megasequence Boundary A/B at ~408 mbsf (Fig. F28) (see "Seismic Stratigraphy"). Logging Unit 3 occurs within the lower part of lithologic Subunit IIIB, which is composed of fining-upward sequences of skeletal packstone with well-preserved burrows (see "Lithostratigraphy and Sedimentology").
Logging Unit 4 shows
generally lower variability in all measured physical properties with overall
slightly lower density (2.05 g/cm3), resistivity (3 m)
and HSGR values (22 gAPI) (Fig. F28).
The lower boundary of this logging unit is placed at 468.5 mbsf, where
resistivity sharply decreases. A HSGR peak at the bottom of this unit, with the
highest uranium values (~10 ppm) measured in Hole 1195B (Fig. F29),
correlates to a glauconite-rich layer observed in the sediments (see "Lithostratigraphy
and Sedimentology").
Logging Unit 4 corresponds to the lowermost 15 m of lithologic Subunit IIIB, which consists mainly of grainstone with rare quartz grains and a glauconite-rich layer at the base (see "Lithostratigraphy and Sedimentology").
At 468.5 mbsf, the
resistivity drops to 1 m,
marking the boundary to logging Unit 5 (Fig. F28).
Within the unit, the logs are characterized by high HSGR values up to 78 gAPI;
uranium values peak at 3-6 ppm, and potassium is generally high with maximum
values of 1.5 wt% (Fig. F30).
The upper boundary of logging Unit 5 coincides with the lithologic boundary from
Unit III to Unit IV. Lithologic Unit IV consists of greenish gray, well-sorted
fine- to medium-grained packstone, grainstone, and quartz sandstone with
abundant rounded glauconite (see "Lithostratigraphy
and Sedimentology").
Temperature data were recorded from the seafloor to 517.5 mbsf (Fig. F31). The temperature curve shows an unusual shape. The downgoing temperature gradient is rather steep, as the tool was lowered rapidly (>4000 ft/hr) and the sensor did not have time to stabilize. At the bottom of the hole, the tool had several minutes to get into equilibrium with the surrounding water and to measure the borehole temperature of 26°C at that time. After beginning to log uphole, the temperature increased slightly. When the tools were lowered a second time because of software problems, the temperature at the bottom of the hole reached 29°C (Fig. F31). The increase of 3.0°C occurred within 12 min and 43 s, indicating that high formation temperatures cause the heating of the borehole water at the bottom of the hole.
