in]). Over one 5-m interval (365-370 mbsf), the hole size was less than 10 cm (4 in). This is thought to be caused by clay swelling because it occurs in one of the most clay-rich units of the borehole (see description, "Log Unit
L5").
Four logging runs were recorded in Hole 1109D: one triple combo run that logged from a total depth of 786 mbsf to above mudline, two FMS-sonic runs that logged the top and bottom parts of the hole, and a VSP run. "Vertical Seismic Profile and Depth Conversion" describes the VSP data and operations, and this section concentrates on the other logging runs.
For the first run, the pipe was raised to 99 mbsf, and the triple combo with dual induction tool (DIT) (see Table T7 and Fig. F15 both in the "Explanatory Notes" chapter) was lowered downhole. HNGS data were monitored during the descent in the pipe to locate the mudline where the string was stopped for 3 min to provide a depth reference for the TLT. Upon reaching open hole, HNGS and DIT data were logged during the descent (Table T19). The tool had difficulty going down between 350 and 375 mbsf but was finally worked down to nearly total depth (786 mbsf; Table T19). An upward log was then recorded at 300 m/hr. A 7.5-kN (1500 lb) overpull was necessary to pass through the 375-350 mbsf interval. The pipe was then raised to 79 mbsf, and the log was recorded up to 68 m above mudline. The tool string was then lowered again to 141 mbsf for a short, second repeat pass up to 24 mbsf. It was then stopped at the mudline for a few minutes both to run calibrations and to give the TLT data a depth reference.
The caliper log from the lithodensity tool (Fig. F88) revealed four intervals between 330 and 375 mbsf where the borehole diameter was smaller than drill-bit size (25.1 cm [9-
in]). Over one 5-m interval (365-370 mbsf), the hole size was less than 10 cm (4 in). This is thought to be caused by clay swelling because it occurs in one of the most clay-rich units of the borehole (see description, "Log Unit
L5").
For the second run, the pipe was lowered again to 99 mbsf, and the FMS-sonic string (see Table T7 and Fig. F1, both in the "Explanatory Notes" chapter) was lowered downhole. The string could not pass the 351-mbsf restriction; therefore, the log was run from 351 mbsf up to the bottom of pipe, which was again raised to 79 mbsf (Table T19). The logging speed was 300 m/hr.
After the tools were out of the hole, the pipe was lowered to 381 mbsf (drill-pipe depth) to allow the tools to pass below the 350-mbsf restriction. A second descent was made with the FMS-sonic string. This time, the tool encountered serious drag just below the pipe but was finally worked through and reached the total depth (786 mbsf; Table T19). The upward log was then recorded at 300 m/hr. When the tool reached 344 mbsf, it encountered serious drag that required 9 kN (2000 lb) overpull. The FMS calipers would not close entirely upon reaching the pipe. After multiple opening and closing sequences and washing with circulating fluid, they closed enough for the tool to be dragged inside the pipe up to the rig floor with a slight overpull.
The mudline wireline depth (Table T19), which defines the depth shift from meters below rig floor to meters below seafloor, was located by its associated natural gamma-ray decay for the triple combo run (Fig. F89). The depth shift for the first and second FMS-sonic runs were derived by correlating the NGR with that of the triple combo run, respectively, within the 140-170 mbsf (Fig. F90) and 570-600 mbsf (Fig. F91) intervals that were chosen for their large, characteristic variations.
Generally, natural gamma-ray magnitude is proportional to clay content, but a surprising aspect of the log response in Hole 1109D is that the formations containing the least clay actually exhibit the highest gamma-ray values. One is left to rely upon the relationship between the neutron and density porosity (APLC and DPHI; see "Lithologic Analysis" in "Downhole Measurements" in the "Explanatory Notes" chapter) to discriminate high-clay and low-clay (clean) lithologies.
Also in Hole 1109D, uranium content varies little, and the total gamma ray appears to be controlled mainly by the thorium and potassium contents, which are often correlated.
The log analysis, combined with the results of core analysis, defines 11 logging units (Fig. F92); shows the recurrence of a carbonate to sand to clay sequence; confirms that sonic velocity increases are correlated mostly with increased carbonate content (a result obtained from physical properties measurements; see "Comparison of Core Data with Results of Downhole Measurements"); and reveals several potential seismic reflectors not recovered in the cores.
The APLC is larger than the DPHI, which indicates a significant clay content. However there are many short intervals where the two porosity logs converge, indicating thin, clean beds. Three clean intervals are thicker than 1 m: 156-161 mbsf (Fig. F93), 192-200 mbsf, and 209-211 mbsf (Fig. F94). The two upper intervals exhibit the same lithologic sequence, beginning at the bottom with a layer that is carbonate rich as shown by the high photoelectric effect (PEFL) and confirmed by CaCO3 analysis at 161 mbsf (see "CaCO3, Sulfur, Organic Carbon, and Nitrogen") and that displays low gamma-ray magnitude and a marked sonic velocity increase. Just above the inferred carbonate is a clean interval with high gamma-ray magnitude interpreted to be a radioactive sandy layer. In the case of the 156-161 mbsf interval, the sandy layer has the highest gamma-ray magnitude in Unit L1 and the second highest gamma-ray magnitude encountered in this borehole. It also coincides with the presence of K-feldspars, as reported in the lithostratigraphy section. The lowest interval shows mainly a low (50%) porosity sandy layer and sonic velocity increase. Another thin bed (<1 m) of low clay content is located at 176 mbsf.
This is the third thickest clean unit in the borehole and one of the most prominent seismic reflectors at this site, as described in "Vertical Seismic Profile and Depth Conversion." It follows the pattern seen in clean intervals in log Unit L1: a thin lower carbonate-rich layer grading into a thick radioactive sandy layer (Fig. F94). The sonic velocity increase is associated with a decrease in porosity, although the velocity peak at the bottom is associated with the higher carbonate content. This unit also exhibits the highest Th/U value in the borehole (Fig. F88), which suggests the presence of volcanic minerals (Shipboard Scientific Party, 1997). This interval was poorly recovered in core and corresponds to an observed increase in grain size (see Fig. F94F and "Lithostratigraphy").
This unit is clay dominated, similar to Unit L1, but has a slightly lower gamma radioactivity and a slightly higher porosity, especially if its greater burial is considered. There are no significantly thick, clean beds in the interval.
This unit is more compacted than Unit L3 and displays higher gamma-ray magnitude and a thin, clean bed at 305 mbrf (Fig. F95). Thus, it has more affinity with Unit L1. Two sharp peaks of gamma-ray counts at 307 and 315 mbrf (Fig. F95) arise close to where mixed-layer clays were observed (see "Lithostratigraphy").
This unit, like Unit L3, shows lower gamma-ray magnitude and a near absence of clean beds: the only thin clean interval is located at 365 mbsf. Moreover, the divergence between the two porosity curves is consistently large, indicating a completely clay-dominated unit. It also corresponds to the zone where borehole diameter was under drill-bit size (Fig. F88). A change in clay mineralogy may be partly responsible for the differences between this and other zones. In addition, this unit contains a fault zone (Fig. F92) described in "Structural Domain IV."
This unit has some similarity with the top part of Unit L1: high gamma-ray counts, high clay content as shown by the divergence of the two porosity curves, and numerous thin, clean beds located at 415.5, 442, 455.2, 476, 518, 528, 534, 571, and 593 mbsf. Below 500 mbsf, carbonate content increases smoothly as shown by PEFL.
This unit (Fig. F96) marks a sharp change of trends from Unit L6: gamma-ray counts increase, porosity drops, and the formation is consistently clean. This unit appears to be dominated by radioactive sands as in Unit L2, with some carbonate and clay added to the mixture. In the uppermost part (602 mbsf), a thin layer shows a high carbonate content, as indicated by PEFL and sonic velocity increase.
This is a carbonate-dominated, clean unit with some sand and clay, high PEFL, high sonic velocity, higher resistivity, and very low gamma ray (Fig. F96). Together, Units L8, L7, and the bottom part of L6 seem to repeat the carbonate to sand to clay pattern on a much larger scale than observed above in the hole.
This unit (Fig. F96) is characterized by high gamma ray counts, low PEFL, and higher uranium content than any other unit. It corresponds very closely to lithostratigraphic Unit VIII. It also corresponds to a zone of thin washouts (Fig. F88).
This unit is defined by a very sharp drop in gamma-ray radioactivity. It shows alternations of low-resistivity layers that correlate with large washouts, alternating with high-resistivity layers that have similar log response to dolerite in Unit L11 (Fig. F88). Resistive layers are likely to be dolerite conglomerate recovered in core. Washed-out layers are unconsolidated material of low sonic velocity, probably sand, silt, and clay. The contrast between these layers suggests that the boundaries are excellent seismic reflectors.
This unit is distinguished by a slight increase in gamma ray radioactivity, a hole perfectly in gauge, the highest borehole resistivity, and the lowest porosity, and corresponds to the dolerite of lithostratigraphic Unit XI.
The accelerometer data of the FMS-sonic run show that the hole deviation remains below a half degree (Fig. F97). They also show a more dispersed acceleration magnitude for the upper run than for the lower one (Fig. F98), which indicates a more irregular tool movement and lower quality raw images, as was observed during logging.
The FMS caliper data reveal periodic enlargement in the 240-330 mbsf and 440-600 mbsf intervals (Fig. F99). The spacing between these washouts corresponds to the core length of ~9.5 m. They are probably caused by the circulation that is maintained when the drill bit progression halts during core retrieval.
During the lower FMS run, the tool string rotated as expected (Fig. F100). However, during the upper run the tool orientation remains remarkably constant: Pad 1 is oriented north and west in the 110-275 mbsf and 280-360 mbsf intervals, respectively. It is particularly interesting to note that despite the 90° rotation of the tool at ~280 mbsf, the orientation of the largest borehole diameter remains north-south, even in the washout intervals. Thus, the borehole is consistently enlarged in the north-south direction. This preferential direction of enlargement, if stress related, would indicate a north-south minimum principal stress direction (i.e., a north-south relative extension).
The magnetometer measurements yield both inclination and magnitude of the total field. These measurements are strongly influenced by the pipe when approaching it. The inclination decreases from -29.9° at the top of the logged section to -30.8° at the bottom (Fig. F101). Both inclination and intensity (Fig. F102) are anomalous in Unit L2 (219-234 mbsf) and in the bottom part of Unit L6 (520-580 mbsf), suggesting the presence of magnetic minerals.
The FMS image interpretation is organized according to log units defined in this chapter from the triple-combo and sonic logs. The FMS image quality is best between ~115 and 350 mbsf in the upper section and between 390 and 778 mbsf in the lower section, with the exception of large, periodic washouts below 680 mbsf. Log Unit L5 was not recorded by the FMS and, thus, is not discussed. Processing steps applied to the images discussed in this section included speed correction, depth shifting (Table T19), and static and dynamic normalization using a 1-m moving window. Statically normalized images were used for recognizing large-scale features and correlating FMS images with the triple combo and sonic logs. Dynamically normalized images were used for interpreting the small-scale structures and textures of individual stratigraphic units. Boundaries between the lithologic units were recognized in the FMS images in several instances, according to changes in either large-scale resistivity and/or small-scale bedding patterns and deformation structures. A preliminary examination of bedding dips revealed shallow 5°-10° dips that range from southeast to southwest throughout most of Hole 1109D (Fig. F103).
The shallowest interpretable section of FMS data from Hole 1109D begins at 115 mbsf within lithostratigraphic Unit II, which is largely composed of greenish gray clays with abundant volcaniclastic sand interbeds (see "Lithostratigraphic Unit II"). Large-scale resistivity is relatively uniform as shown in the statically normalized FMS images, as well as in the dual induction resistivity logs. Normally graded, 1-m-thick turbidite units are recognized by resistive, sandy bases that grade upward into more conductive, clayey tops. Carbonate grains or cementation are also occasionally observed to produce a high-resistivity signature at the base of some turbidites. Thin, 10-cm layers of distinctive, highly resistive sands commonly occur in couplets at the base of these units. Bed boundaries are generally diffuse, which is inferred to be caused by bioturbation, as recognized in the core sections (see "Lithostratigraphic Unit II"). Bed boundaries dip from 5° to 8° to the south-southeast. South-southwest dips of 5°-8° also are present intermittently in this unit and increase in frequency with depth, suggesting a gradual change in source direction or structure. The base of lithostratigraphic Unit II shows up clearly in the FMS images at 161.5 mbsf as the base of a 4.5-m-thick turbidite unit that is composed of a 1-m-thick basal carbonate sand that fines upward to 157 mbsf (Fig. F104). This unit correlates well with the conventional logs, which display large gamma-ray values over this interval, as well as a sharp spike in the triple combo resistivity curves at 161.5 mbsf. Below this turbidite unit, bed boundaries are more clearly defined, suggesting decreased bioturbation.
A 15-m-thick highly resistive (possibly carbonate rich) sand is clearly indicated in both the conventional logs and FMS images between 219 and 234 mbsf (Fig. F105). Synthetic seismograms computed from both logs and physical properties measurements show that this layer correlates with a pronounced positive-polarity reflection in the seismic reflection data (see "Vertical Seismic Profile and Depth Conversion"). The unit is bounded at the top by a thinner, 30-cm highly resistive sandy layer at 219 mbsf and at the bottom by a sandy, carbonate layer at 234 mbsf. The structure and lithologic composition of this unit is relatively homogeneous and contains only minor thin, conductive, clayey layers.
The top of this unit grades from highly resistive carbonate-rich sands of Unit L2 into clays over an 11-m interval between 234 and 245 mbsf. The base of this interval at 245 mbsf marks the top of litho-stratigraphic Unit IV, which is described as a clayey siltstone and silty claystone (see "Lithostratigraphic Unit IV"). Below this gradational interval, Unit L3 is characterized by uniformly low resistivity suggested to be caused by increased clay content. The FMS images for this unit display an overall grainy appearance and poorly defined bed boundaries, which correlate with sand and carbonate grains and intense bioturbation observed in the cores (see "Lithostratigraphic Unit IV"). Between ~255 and 265 mbsf, normally graded beds with diffuse boundaries ranging in thickness from 1 to 1.5 m display a dramatic increase in dip of ~50°-65° to the southwest (Fig. F106). Thin, 10-cm conductive layers at 255 and 265 mbsf are the only distinctive features that bound this interval from the 5°-10° dipping layers that characterize most of Hole 1109D. Relatively steeply dipping (32°) layers also occur between 272 and 273 mbsf to the southeast. Preliminary studies of core samples suggest that the steeply dipping units are the products of normal faulting; however, fractures were not identified in the FMS images (see "Structural Geology"). Below 282 mbsf, bed boundaries become more distinctive and display a bimodal distribution of southeast and southwest dips of ~5°. A change in bed-form character at 282 mbsf correlates closely with the middle bathyal/upper bathyal paleodepth boundary (see "Biostratigraphy").
The upper 10 m of Unit L4 is characterized by overall high resistivity interpreted to indicate increased sand and carbonate content. Bed boundaries are poorly defined throughout most of Unit L4; however, well-defined bed boundaries are present between 305 and 320 mbsf, with dips of 5°-12° that vary from south-southeast to south-southwest.
Unit L5 is located between the bottom of the upper logged interval and the top of the lower logged interval and was therefore not recorded by the FMS (see "Operations").
Fining-upward turbidite sequences ~1 m in thickness dominate Unit L6 between 390 and 553 mbsf. These turbidite sequences are contained within lithostratigraphic Unit VI, which is a clayey siltstone and silty claystone interbedded with clayey siltstone to coarse sandstone (see "Lithostratigraphic Unit VI"). Thin, 10-cm, highly resistive layers define the bases of the turbidite units and commonly display wavy bases. Highly resistive basal layers are less common below 510 mbsf, where turbidite boundaries are more poorly defined. The unit possesses an overall mottled texture that increases with depth. Between 553 and 587 mbsf, layering is virtually nonexistent, with the exception of rare 10-20 cm resistive layers.
The interval between 592 and 621.5 mbsf contains highly disturbed turbidite sequences with resistive bases. A dramatic change in structure occurs between 621.5 and 625 mbsf, where the formation appears to be composed of large (<0.5 m), irregular resistive nodules; whether this is an artifact of poor FMS pad contact with the borehole wall could not be confirmed from the caliper data at this small scale. Between 625 and 647 mbsf, the unit displays a similar, but more homogeneous texture with occasional resistive layers and nodules that appear to be disturbed resistive beds and clasts.
A massive carbonate-rich unit between 647 and 674.5 mbsf is characterized by high resistivity and a homogeneous distribution of small (<2 cm), angular, randomly oriented resistive fragments that appear to be carbonate clasts, commonly recognized in the cores (see "Interpretation" in "Lithostratigraphic Unit VII").
A single massive turbidite sequence between 674.5 and 681 mbsf is composed of a 15-cm resistive layer and grades upward into clays with a thick, 2-m interval of lenticular, 10-cm-thick clay and silt laminations (Fig. F107). Irregular borehole geometry below ~681 mbsf degraded the FMS images, making interpretation difficult except for a few intervals. A highly resistive interval between 715 and 776 mbsf displays a mottled texture with scattered resistive nodules interpreted to be conglomeratic igneous clasts as recognized in the cores (see "Igneous Clasts (Inferred Conglomerate)"). Massive dolerite underlies the conglomerate at 776.5 mbsf and is characterized by uniformly high resistivity and numerous irregular conductive layers that may indicate flow banding and fractures (Fig. F108). Thin, millimeter-scale conductive features interpreted to be fractures are ubiquitous within the dolerite; however, few of the fractures can be traced confidently from pad to pad.
The temperature profiles within the pipe and in open hole are shown in Figures F109 and F110. The maximum borehole temperature of 12.5°C is reached at 787 mbsf and is consistent with the near-linear thermal gradient inferred above 170 mbsf (see "Temperature Measurements").
