After completion of drilling operations at Hole 1134A, the hole was prepared for logging (see "Operations"). The end of the bottom-hole assembly was placed at 105 mbsf. The wireline heave compensator (WHC) was used during all logging runs and performed moderately well in the medium-to-high heave conditions, except on the first pass with the FMS/sonic tool string. Three different logging strings were deployed in the following order: (1) triple combo, (2) FMS/sonic tool, and (3) WST (Table T17; see "Logging Tools and Tool Strings" in "Downhole Measurements" in the "Explanatory Notes" chapter). Approximately 10 m of fill caused by loose sands was recorded at the base of the hole during the first logging run.
Before the main run with the triple combo, a short quality control run was made from 386 mbsf (11 m short of drilled depth) to 296 mbsf. The main run was logged from 386 mbsf to mudline. Two passes were made with the FMS/sonic. During the first pass from 386 to 118 mbsf, the WHC reached the maximum limit of heave correction at 158 mbsf and the FMS calipers were closed immediately to protect them from downheave. During the second pass from 386 to 129 mbsf, the WHC operated normally. Seven check-shot stations were recorded between 381 and 138 mbsf. Seven shots were stacked per station, with individual stations located near log breaks and at estimated depths of significant seismic reflectors (see "Seismic Stratigraphy").
The general data quality from the triple combo and FMS/sonic tool strings was good, although borehole rugosity may have affected porosity measurements in some intervals (Fig. F19). Negative potassium concentrations between 230 and 250 mbsf are probably an artifact of the tool's inability to measure low potassium concentrations. Formation MicroScanner images were affected by moderate to rough heave conditions, and further shorebased processing will be necessary to fully compensate for heave effects. Although the sonic digital tool (DTCO output) performed well, the analog modes provided poor-quality data with only 50%-60% coverage of the logged interval. The signal recorded by the WST was clipped, as gun pressure was increased to 1500 psi to obtain consistent first-break arrival times. A comparison between downhole logging and sediment physical properties measurements is difficult because of poor core recovery below 145 mbsf (see "Physical Properties").
The overall log pattern at Hole 1134A is similar to Hole 1126D, which is situated in a similar setting further to the east, although gamma radiation is higher in Hole 1134A than in Hole 1126D. The succession has been divided into six logging units on the basis of variations in measured parameters. The logging unit boundaries correlate closely with most lithostratigraphic boundaries (see "Lithostratigraphy").
Logging Unit 1 was logged through pipe to 105 mbsf and is divided into three subunits on the basis of the spectral gamma-ray log (Fig. F20). Subunit 1A (0-31 mbsf) is characterized by relatively high gamma-ray values (8-10 American Petroleum Institute [API] units), with three distinct gamma-ray lows. Subunit 1A can be correlated with logging Unit 1 in Hole 1126D, where a similar gamma-ray pattern is observed (Fig. F26, in the "Site 1126" chapter). This elevated gamma radiation is likely to be diagenetic in origin. The lower boundary of Subunit 1A is defined by a decrease in gamma radiation, which correlates with the base of lithostratigraphic Unit I (see "Lithostratigraphy"). Logging Subunit 1B (31-57 mbsf) is characterized by variable NGR, with a marked decrease at the base of the unit (Fig. F20). Subunit 1C (57-152 mbsf) is characterized by low gamma-ray values in the pipe and in the open-hole logged interval (Figs. F20, F21). The origin of the positive separation of density and porosity logs for most of this unit is unclear. The base of Unit 1 is marked by an increase in NGR values (Fig. F21).
Logging Unit 2 is characterized by an increase in gamma radiation compared to Unit 1 (~12-14 API units), caused mainly by increased thorium concentrations (Fig. F21). Separation of the density and porosity logs is less than in Unit 1, and photoelectric effect (PEF) values are relatively constant near 3.6 barn/e-, with low variability in resistivity, density, and sonic logs (Fig. F19). This unit correlates to lithostratigraphic Unit IV, which is composed of an alternation of wackestones, grainstones, and chalk with variable lithification (see "Lithostratigraphy"). Except for the basal 15 m of this unit, where there is some evidence for fluid invasion, resistivity values remain nearly constant (Fig. F19). In the basal 15 m, thin chert beds occur, which appear as low-porosity peaks and coincide with decreased PEF and peaks in shallow resistivity. This is confirmed by FMS images, which show several thin (< 10 cm), resistive layers, alternating with thicker (1-3 m), more conductive layers. The base of Unit 2 is defined by a marked change in the character of all logs toward more variable values (Fig. F19), and by increasing frequency and thickness of the chert layers as indicated by the FMS images. Despite the fact that the gamma radiation values are higher in Unit 2, this unit may be correlated with logging Unit 3 in Hole 1126D, mainly on the basis of porosity-density, PEF, and sonic logs.
Logging Unit 3 is characterized by decreasing trends in gamma radiation, increasing bulk density, and increased variability in all other measured parameters (Figs. F19, F21). Within logging Unit 3, there are numerous low-porosity excursions that cross over the bulk density curve and correlate with peaks in shallow resistivity and sonic velocity (Fig. F19). These variations reflect thin chert layers observed in recovered sediments (see "Lithostratigraphy") and appear as thin (10-50 cm) resistive layers alternating with thicker (1-2 m), more conductive layers in the FMS images. Values of PEF increase slightly within logging Unit 3 (~3.4-4.1 barn/e-). Excursions in shallow resistivity within Unit 3 indicate that fluid invasion is occurring within this sedimentary sequence (Fig. F19). The high variability in the sonic logs is easily correlatable to the upper part of logging Unit 4 at Site 1126. The base of Unit 3 occurs at a marked increase in gamma-ray values (28-22 API units), dominantly caused by increased thorium and potassium (Fig. F21). Logging Unit 3 corresponds to the upper part of lithostratigraphic Unit V (see "Lithostratigraphy").
Logging Unit 4 is characterized by relatively high gamma-ray values (~20-28 API units), with variability controlled by the uranium content of the formation (Fig. F21). As with the above units, porosity-density crossovers correlated to sonic velocity and shallow resistivity peaks indicate chert horizons (Fig. F19). Formation MicroScanner images clearly show that chert layers are thinner (5-20 cm) and less frequent (~2-4 m separation) than in logging Unit 3. Photoelectric effect values show a slight increasing trend with increasing depth in the unit. Resistivity values are generally constant within logging Unit 4, and there are fewer excursions of shallow resistivity compared to the unit above. Sonic velocity increases slightly within Unit 4 and has reduced variability relative to logging Unit 3. Logging Unit 4 corresponds to the middle part of lithostratigraphic Unit V, which contains mudstone to packstones, although recovery was poor for this interval (see "Lithostratigraphy"). The base of Unit 4 is marked by a peak in uranium gamma radiation, followed by an abrupt decrease, defining the boundary between Units 4 and 5 (Fig. F21).
Total gamma-ray values display low variability and nearly constant values within logging Unit 5. However, individual radioactive elements display marked variations, defining two subunits within Unit 5 (Fig. F21). Subunit 5A is defined by a downhole increase in uranium and a decrease in thorium concentrations. The base of Subunit 5A is marked by an abrupt decrease in uranium and slight increases in thorium and potassium (Fig. F21). Within logging Unit 5, PEF values remain constant (~4.6 barn/e-), whereas porosity decreases, and density, resistivity, and velocity increase, characteristic of a normal compaction trend (Fig. F19). As with the units above, porosity-density crossovers, corresponding to resistivity and sonic peaks, are interpreted as thin chert beds and/or partly silicified layers. This is confirmed by FMS images, which show a succession of thin (5-10 cm) resistive beds alternating with thicker (1-3 m) more conductive layers. Near the base of physical properties Unit 5, there are excursions of shallow resistivity indicating minor fluid invasion. Logging Unit 5 corresponds to the basal part of lithostratigraphic Unit V (see "Lithostratigraphy"), and is correlated with logging Units 6 and 7 in Hole 1126D.
Density, PEF, caliper, and resistivity are the only logs available for logging Unit 6, as the length of the tool strings and sediment fill in the hole prevented acquisition of a full logging suite. This unit is characterized by two PEF peaks (~5.8 barn/e-) associated with high density values (~2.1 g/cm3), and highly variable resistivity with major excursions of shallow resistivity (Fig. F19). This unit corresponds to the poorly recovered lithostratigraphic Unit VI, consisting of limonitic sandstones (see "Lithostratigraphy"). Logging Unit 6 correlates with logging Unit 8 of Hole 1126D.