One logging run was made in Hole 1229A with the triple combo tool string (see "Downhole Logging" in the "Explanatory Notes" chapter). After recovery of Core 201-1229A-22H at 0500 hr on 8 March, the hole was conditioned for logging. The wiper trip only reached 187 mbsf, indicating that there was ~7 m of fill at the bottom. The hole was then displaced with 100 bbl of sepiolite, and the bottom of the drill string was positioned at 80 mbsf. Logging rig-up started at 0830 hr. Despite a limited velocity of only 1.2 kt, the current generated strong vibrations in the short drill string and particular care was taken in tightening the connections while assembling the logging string. The 35-m-long tool string started downhole at 1030 hr, and two passes were made without difficulty. Both passes reached the bottom of the hole at the wireline depth 187 mbsf (351 meters below rig floor), and the bottom of the drill string was raised by 10 m during logging, allowing data recording in the open hole to 70 mbsf. Logging operations and rig-down were completed by 1430 hr (see Table T10 for a detailed summary of the operations).
The caliper log (Fig. F25A) shows that the borehole wall was generally smooth and that the caliper arm maintained good contact with the formation over the entire logged interval, a requirement for high-quality data recording measurements made on core samples. Logging data are also consistent with physical property measurements from discrete samples. Except for a 30-m interval (between 125 and 155 mbsf) where core measurements were not made because of poor recovery, the MAD density and porosity data available generally agree well with the logs.
Because of the short length of the open hole interval (~117 m), a second pass was made over its entire length to control the quality of the data. Figure F26 compares some of the logs of the two passes (pass 1 = dashed green line and pass 2 = solid red line). The gamma ray values from the second pass are slightly higher than those for the first pass, indicating that the formation was still activated because of the minitron source of the Accelerator Porosity Sonde used during the first pass (see "Downhole Logging" in the "Explanatory Notes" chapter). Despite this generally uniform offset, both gamma ray logs agree very well. The density and resistivity curves also display a good repeatability over most of the interval, except between 136 and 150 mbsf, where there is a depth offset of almost a meter in some places between the two passes. All identifiable features are apparent and similar in both passes, but the depth offset indicates that the tool was sticking more strongly to the formation during pass 1 over this interval, generating higher depth values.
The general trend of the logs is characterized by a succession of deposition phases of various nature, in particular fining-upward sequences and intervals with a strong biogenic component. The fining-upward sequences indicate changing terrigenous sedimentation controlled by sea level rise or sinking of the basin. Whereas overall the sediments recovered are mostly terrigenous, the relative importance of the types of sedimentation can be seen in the ratio of thorium to uranium concentration (Fig. F25D), which can be used as an indicator of the relative strength of marine and terrestrial deposition (Rider, 1996). High values of this ratio indicate a greater relative input of terrestrial material. Low values indicate sediments of marine origin. Based on variations of this indicator and on individual deposition cycles, we have identified three logging units. We divided these units into logging subunits that correspond to distinct sedimentation phases.
Logging Unit 1 (70-87 mbsf) is characterized by high porosity (~65%) and relatively low resistivity and density. The thorium/urianium ratio increases steadily upward, indicating an increase in terrigenous sediments. The two logging Subunits 1A (70-76 mbsf) and 1B (76-87 mbsf) correspond to two distinct sequences. These sequences are separated by peaks in gamma ray, density, and resistivity that could indicate phosphorite layers generated by reworking of phosphate nodules between sedimentation phases. Logging Subunit 1B is a well-defined fining-upward sequence indicating a sea level rise or subsidence of the basin.
The top of logging Unit 2 (87-137 mbsf) is defined by a sharp increase in density and resistivity, which appears to be the top of a very distinct fining-upward sequence corresponding to logging Subunit 2A (87-97 mbsf). This interval is also characterized by high values of thorium and of the thorium/uranium ratio, indicating the almost exclusively terrigenous nature of the sediments. This subunit corresponds to the lower part of lithostratigraphic Subunit IB (see "Description of Lithostratigraphic Units" in "Lithostratigraphy"), and its base is defined by a sharp drop in resistivity and density. The base of this subunit corresponds to an erosional surface overlain by shell debris (see "Lithostratigraphy"). This erosional surface was also recovered at Site 681 during Leg 112 (Shipboard Scientific Party, 1988). Logging Subunit 2B (97-128 mbsf) corresponds to the two upper intervals of lithostratigraphic Subunit IC (see "Description of Lithostratigraphic Units" in "Lithostratigraphy"), which display a downhole increase of biogenic sediments, mostly diatom ooze. This downhole increase in biogenic material in the cores corresponds to a steady downhole decrease of the thorium and of the thorium/uranium ratio in this logging subunit. The uphole increase in these properties indicates the progressive shift in time from marine sedimentation in the lower half of logging Subunit 2B to a mostly terrigenous, fining-upward sedimentation. At the base of logging Subunit 2B, peaks in gamma ray, uranium, density, and resistivity and the presence of phosphate nodules in the core (see "Lithostratigraphy") indicate reworked phosphorite layers. Logging Subunit 2C (128-137 mbsf) is a fining-upward sequence similar in character to logging Subunit 2A, with high thorium/uranium values and slight upcore increase in density and resistivity. It corresponds to the lower portion of lithostratigraphic Subunit IC (see "Description of Lithostratigraphic Units" in "Lithostratigraphy").
Logging Unit 3 (137-185 mbsf) corresponds to lithologic Unit II (see "Description of Lithostratigraphic Units" in "Lithostratigraphy"). This lithologic unit is characterized by well-sorted and rounded sand and silt with variable clay content. The top of the logging unit is defined by an increase in density and resistivity and by a drop in porosity. This logging unit is characterized by significant fluctuations in most logs, corresponding to the alternation of sand and silt as noted in the "Site 1229 Core Descriptions." Logging Subunit 3B (155-185 mbsf) was logged fully only by the resistivity sonde, but it is marked by a slight decrease in resistivity, an apparent increase in porosity, and two distinct 2-m-thick intervals with lower density (at 156 and 165 mbsf, respectively).
Temperatures were recorded with the Lamont-Doherty Earth Observatory (LDEO) Temperature/Acceleration/Pressure (TAP) memory tool attached at the bottom of the triple combo tool string. Because only a few hours had passed since the end of drilling operations and hole conditioning, the borehole temperature is not representative of the actual equilibrium temperature distribution of the formation. In the case of Hole 1229A, the surface seawater and the sepiolite mud pumped during and after drilling generated borehole fluid temperatures higher than the formation temperatures. Discrete measurements made with the DVTP indicate a maximum formation temperature of 19.2°C at 164.8 mbsf (see "In Situ Temperature Measurements" in "Downhole Tools") and a temperature of 19.9°C was recorded at 187 mbsf at Site 681 (Shipboard Scientific Party, 1988), whereas the maximum temperature recorded by the TAP tool at 186 mbsf is 25.6°C (see Fig. F27). The generally lower temperatures during the second pass indicate a progressive return to equilibrium. The variations measured at 70 and 80 mbsf while logging downhole correspond to the tool exiting the drill string. The drops in temperature on the uphole run at 100 and 150 mbsf are likely related to operations, and the smoother second pass indicates some recovery between the two passes. Surprisingly, these features were not recorded on the downhole run and are difficult to explain because the logging speed was uniform during the two passes and no stop was made. The consistently small difference between the two passes in the two directions between 80 and 100 mbsf is also unexpected and will need further explanation.