After completion of drilling operations at Hole 1129D, the hole was prepared for logging (see "Operations"). As a precaution against H2S damage to the wireline cable and logging tools, and also to prevent caving, the hole was loaded with a mixture of sepiolite mud and seawater. The lower end of the BHA was placed at 100 mbsf. The wireline heave compensator (WHC) was used during all logging runs and coped well with the moderate heave conditions. Three different logging strings were deployed in the following order: (1) triple combo, (2) FMS/sonic, and (3) WST (Table T18; see "Downhole Measurements" in the "Explanatory Notes" chapter). All logging runs reached total drilled depth (604 mbsf).
Before the main run with the triple combo, a short quality-control run was made from the base of the hole at 604 mbsf to 550 mbsf. The main run was logged from 604 mbsf to the mudline. A single pass was made with the FMS/sonic from 604 mbsf to the pipe. The FMS calipers were closed at 140 mbsf, when the WHC was closed down. The WST recorded 10 stations, with individual stations located near changes in log character and at estimated depths of significant seismic reflectors (see "Seismic Stratigraphy" in the "Site 1127" chapter).
The overall quality of the data from the triple combo and the FMS/sonic was good, although washouts between 360 and 460 mbsf may have degraded the quality of the porosity log and the FMS images from this interval.
Measurements of NGR from downhole logging and sediment physical properties show good agreement, although there are slight depth discrepancies caused by incomplete recovery and heave effects. Between 100 and 402 mbsf, downhole porosity and density measurements show poor agreement with discrete measurements of density and porosity of the core (MAD), whereas there is good agreement between GRA density and log density. Below 402 mbsf, correlation of the density log to GRA data becomes poor, possibly as a result of biscuiting of the recovered core. Moisture and density data show decreased correlation to log density in this interval, which coincides with a change in the calibration of the pycnometer used in determining MAD parameters between Holes 1129C and 1129D.
The logs acquired in Hole 1129D are remarkably similar to those acquired in Hole 1131A (located immediately seaward of Hole 1129D), although the level of gamma radiation is higher in the upper 267 mbsf of Hole 1129D, possibly reflecting greater sedimentary organic carbon content. The gamma-ray signal is dominated by uranium, which is often associated with organic matter in carbonate successions, although uranium occurring within grain coatings observed in the recovered core may be another potential source. The importance of diagenesis at Site 1129 is clearly seen by the number of gamma-ray peaks associated with lithified intervals (Fig. F28). Three major logging units have been defined at Site 1129, mainly on the basis of variations in gamma-ray and sonic logs.
Logging Unit 1 was measured through pipe to 100 mbsf, and in open hole for the remainder of the interval. Other than a small peak in thorium, the gamma-ray log measured through pipe is generally featureless (Fig. F29). The open-hole portion of Unit 1 is characterized by elevated levels of gamma radiation resulting from high uranium concentrations. These data exhibit high-magnitude, high-frequency excursions throughout Unit 1 (~2-9 ppm) (Fig. F30). Once cleared of pipe effects, photoelectric effect (PEF) values are more or less constant throughout Unit 1 at values of ~4.5 barn/e-, indicating an almost clean carbonate. Within this unit, density and velocity gradually increase, whereas porosity decreases downhole (Fig. F29). There is a slight separation of shallow, medium, and deep resistivity between 150 and 267 mbsf, indicating some fluid invasion into the formation. Within logging Unit 1, peaks in shallow resistivity (205, 235, and 256 mbsf) generally coincide with low porosity and high density, sonic velocity, and gamma-ray values. These intervals are interpreted as lithified horizons or firmgrounds (Fig. F29). On FMS images, these horizons are seen as thin (25-125 cm), highly resistive intervals. The firmground at 235 mbsf corresponds to an overall change from unlithified to partially lithified sediments within lithostratigraphic Unit II (see "Lithostratigraphy"). The base of Unit 1 is marked by a shift to lower and less variable levels of gamma radiation (20-50 American Petroleum Institute [API] units), resulting from decreased uranium content (Fig. F30).
Logging Unit 2 (267-559 mbsf) exhibits cyclic variations in gamma-ray values that are dominated by changes in uranium concentration. The frequency of these cyclic variations decreases toward the base of the unit (Fig. F30). The NGR cyclicity within Unit 2 is similar to the cyclicity seen in logging Unit 2 in Hole 1131A, and patterns can be correlated between the two sites. The correlation with Hole 1127B, further seaward, is not as clear, but seismic reflectors can be used as guidelines for cycle to cycle correlation. Within Unit 2, bulk density and sonic velocity generally increase, whereas porosity decreases, typical of a compaction profile (Fig. F29).
Unit 2 is divided into two subunits at a significant shift (433 mbsf) to higher P-wave velocity, bulk density, resistivity, and NGR (Fig. F29). This shift is interpreted to be a firmground within the sedimentary section within lithostratigraphic Unit II (see "Lithostratigraphy"). Similar, but smaller excursions are seen throughout Unit 2. One of these intervals was recovered in the core (414 mbsf) and contains pyrite, thus explaining the increase in PEF values (Fig. F29). Many of the lithified layers seen in the logs were not recovered during coring. Within Subunit 2A, high-porosity excursions between 370 and 433 mbsf are likely to represent washouts of the borehole wall exhibited by increases in caliper values. As at Hole 1131A, the base of logging Unit 2 is defined by a marked decrease in gamma-ray values. The base of Unit 2 is also clearly seen in the FMS images as a distinct change in the nature of the sediment (Fig. F31).
Logging Unit 3 is characterized by uniformly low gamma-ray values (~10 API units) and variable PEF, indicating an alternation of silica-rich beds with intervals rich in calcium carbonate (Fig. F29). Resistivity logs show a typical fluid-invasion profile (Fig. F29), with the separation of the shallow and deep resistivity curves indicating a permeable formation. The upper boundary of logging Unit 3 corresponds to the top of lithostratigraphic Unit III, which consists mainly of chert and lithified packstone and grainstone (see "Lithostratigraphy"). The alternation between chert horizons and carbonates is clearly seen on FMS images as a succession of thin (~20 cm), resistive chert layers alternating with thicker (~2 m), more conductive carbonate layers (Fig. F31).