Hole 1132C was prepared for logging after drilling was halted as a result of deteriorating hole conditions (see "Operations"). The lower limit of the BHA was placed at 105 mbsf for both logging runs (Fig. F24). Two logging tool strings were run in the following order: (1) triple combo and (2) FMS/sonic (see "Downhole Measurements" in the "Explanatory Notes" chapter). The triple combo run touched bottom at 561 mbsf. Extensive hole deterioration between triple combo and FMS/sonic runs resulted in only 70 m (140-176 mbsf) of the FMS/sonic tool string being logged after three attempts (Fig. F24). The well seismic tool (WST) and the geologic high-resolution magnetic tool were not run.
While we pulled pipe in preparation for logging, weighted mud was added to the borehole to reduce backflow of fluids out of the hole. Barite contained in this mud adversely affected the photoelectric effect values and, as a result, they were unusable. The borehole diameter was generally smooth during the triple combo run except for enlargements (as much as 38 cm) between 145 and 240 mbsf and between 440 and 510 mbsf (Figs. F25, F26). Despite the larger borehole, the diameter is below the saturation limits of the caliper (42 cm) for the entire interval logged. Of the 36 m of FMS collected, the lower 16 m (160-176 mbsf) was of little use because of the severely rugose and sometimes undergauge hole. The remainder of the record was of good quality.
Downhole logs at Site 1132 were well correlated to lithologic variations observed in the upper 245 mbsf of the section. Below this depth, where recovery was low (~6%), logs will enable the characterization of sedimentary sequences and assist in intersite correlation to provide a detailed record of Eocene to Holocene shelf edge temperate-water carbonate deposition.
The compatibility of wireline log data with physical properties measurements from both whole-core and discrete samples attests to the integrity of the logging data sets (see "Physical Properties"). Overall, downhole measurement trends show the effects of compaction overprinted by the influence of diagenesis and changes in sediment composition. Compaction causes a gradual increase in sonic velocity and bulk density, and a decrease in porosity with depth (Figs. F25, F26). Downhole variations, resulting from changes in lithology and diagenetic alteration, enable logging data from Site 1132 to be divided into four units (Figs. F25, F26, F27).
Logging Unit 1 (0-242 mbsf) is characterized by high and variable gamma-ray values, mainly resulting from increased uranium concentrations (Fig. F26). Within the interval logged in pipe (0-104 mbsf; Fig. F27), gamma-ray values show distinct variability and are moderately correlated to NGR values from the MST (see "Physical Properties"). A prominent gamma-ray peak in the downhole logs is seen between 88 and 92 mbsf (Fig. F27). This peak is likely to be spurious, as the gamma-ray values are greater than expected for these high-carbonate sediments when logged through pipe. In addition, no equivalent peak is seen in the NGR data. High and variable uranium values continue for the remainder of the unit, until an abrupt decrease at the boundary with logging Unit 2 (242 mbsf). This decrease in gamma ray may result from diagenesis, as it corresponds to the depth at which HMC becomes a minor component of the sediments (see "Inorganic Geochemistry"). In the open-hole logged interval of Unit 1, separation of the porosity and density curves indicate a slightly greater density than expected for a clean limestone.
This is likely to result from higher magnesium concentrations occurring within the carbonates of this unit. Downhole resistivity within Unit 1 is nearly constant with a slight separation of shallow and deep values indicating some fluid invasion in the unit (Fig. F25). The base of logging Unit 1 correlates well to the base of the upper Miocene (see "Biostratigraphy") and the base of lithostratigraphic Subunit III (see "Lithostratigraphy"), which marks the lower limit of a lithologically variable sediment sequence.
Logging Unit 2 (242-437 mbsf) is characterized by low gamma-ray values (Fig. F26). Both density and porosity exhibit greater variability than in Unit 1 and an overall downhole increasing trend that steepens near 402 mbsf to a maximum at 432 mbsf, after which values decrease to the base of the unit (Fig. F25). The increased variability in porosity and density correlates well to a sedimentary interval characterized by alternations of chert and bioclastic grainstone (see "Lithostratigraphy"). Resistivity logs from Unit 2 indicate that significant borehole fluid invasion is occurring within this interval, as shown by the separation of shallow- and deep-resistivity traces (Fig. F25). This invasion is likely to be occurring along discrete, relatively thin beds, giving rise to the short wavelength (<1 m) fluctuations in the shallow-resistivity data (Fig. F25). The base of logging Unit 2 correlates well to the base of lithostratigraphic Unit IV, which marks the downhole disappearance of chert in the sedimentary section (see "Lithostratigraphy"). This boundary is characterized by increases in resistivity and decreases in gamma radiation, porosity, and density (Figs. F25, F26).
Logging Unit 3 (437-524 mbsf) is characterized by nearly constant values in all data sets except porosity. The sediments within logging Unit 3 correspond to lithostratigraphic Unit V, which is dominated by apparently homogeneous bioclastic grainstones (on the basis of limited recovery; see "Lithostratigraphy"). The separation of deep- and shallow-resistivity curves indicate that fluid invasion is occurring within Unit 3, although this invasion is more uniform than in the units above and below as expected from the more porous and homogeneous sediments occurring within this unit (Fig. F25). The base of logging Unit 3 is marked by an increase in gamma-ray values, density, and resistivity, and a decrease in porosity (Figs. F25, F26). This boundary is well correlated to the Oligocene/Eocene boundary (see "Biostratigraphy").
Logging Unit 4 (524-537 mbsf) is characterized by increased variability in both gamma-ray and resistivity within the limited section logged (Figs. F25, F26). Resistivity measurements indicate deep invasion of borehole fluids along discrete intervals (Fig. F25). Increased gamma-ray values in Unit 4 largely result from greater Th and K (Fig. F27), indicating the presence of terrigenous minerals within the dominantly carbonate sediments in this unit (~85% CaCO3; see "Organic Geochemistry"). Density values are high and porosity values are low throughout this unit (Fig. F25). Logging Unit 4 correlates well to an interval of Eocene sediments within lithostratigraphic Unit VI (see "Lithostratigraphy").