Measurements with the MST have been obtained at 2-cm intervals for GRA bulk densiometer measurements and P-wave velocity, at 4-cm intervals for magnetic susceptibility, and at 12-cm intervals for NGR. Below 290 mbsf, the sampling interval for GRA bulk density and P-wave velocity has been changed to 4 cm. P-wave velocity was not measured on RCB cores. MST results in XCB and RCB cores were degraded in quality because of drilling disturbance associated with coring and the smaller diameter of the core relative to that of the core liner. This disturbance is illustrated by a comparison of GRA bulk densities with discrete density determinations (see "Moisture and Density Measurements"). In Figure F59, we present edited MST data from Hole 1165B measured on APC cores (0-150 mbsf). Measurements from deeper intervals may be also useful to identify lithologic changes but need more extensive postcruise editing. All MST measurements (raw data) are available and can be downloaded from the ODP Janus database (see the "Related Leg Data" contents list).
The general trend in magnetic susceptibility shows a decrease from average values of 80 × 10-5 SI at 0.3 mbsf to 10 × 10-5 SI at 145 mbsf. Superimposed on this trend, the smoothed susceptibility record displays meter-scale variability, which is most likely related to variations in the relative amount of biogenous and terrigenous sediment components. Susceptibility (maxima) of >200 × 10-5 SI can be correlated with the presence of lonestones.
GRA bulk densities show no significant trend in the upper 150 mbsf and display meter-scale variability around an average value of 1.56 g/cm3. A covariation of GRA bulk density and magnetic susceptibility is observed throughout the upper 150 mbsf. An interval of lower density (~1.50 g/cm3) possibly stretches from 35 to 85 mbsf (gap from 53 to 63 mbsf), most likely indicating a zone of higher biosiliceous content. IRD (lonestones) can be identified by high-density spikes.
P-wave velocities measured with the P-wave logger (PWL) in soft sediments from directly below the seafloor (i.e., 0-5 mbsf) appear to be too high by ~5% when compared to data from other areas (e.g., Barker, Camerlenghi, Acton, et al., 1999). This might be caused by an incorrect calibration of the distance transducers. A comparison of the PWL measurements with discrete velocity data obtained from split cores (P-wave sensor [PWS]) shows a consistent offset of 70 m/s throughout the upper 150 mbsf (Fig. F60). This offset has been subtracted from the raw velocity data obtained with the PWL. In general, P-wave velocity increases from 1510 m/s close to the seafloor to 1580 m/s at 130 mbsf. Meter-scale variability is also seen in the velocity data but shows no consistent correlation with GRA bulk density and magnetic susceptibility. Although some intervals show a positive correlation between density and velocity (e.g., 105-120 mbsf), others are characterized by an inverse relationship (e.g., 20-40 mbsf), which indicates a complex sedimentological control mechanism on velocity changes. Lonestones appear as high-velocity spikes in the record.
In Figure F61, NGR data from Holes 1165B and 1165C are combined and compared to the bulk mineralogy derived from XRD measurements. For Hole 1165B, whole-core NGR emissions were counted for 10 s with a constant background correction of 10.36 counts per second (cps) being subtracted automatically from the values measured by the MST. For Hole 1165C, a constant background correction of 6.28 cps was used. This induces an apparent mismatch between the corrected, but not the measured, values between Holes 1165B and 1165C (see the "Related Leg Data" contents list). In Figure F61, the different backgrounds were taken into account by adding 4.08 cps to the values for Hole 1165B before plotting. Variations in NGR emissions are caused by changes in the composition of the sediment, usually the content of clays and K-feldspars. Similar trends are observed in both the total clay mineral content of the bulk mineralogy ("Lithostratigraphy") and the NGR data.
Energy spectra from the radioactive elements potassium (40K), uranium (238U series, mainly 214Bi), and thorium (232Th series, mainly 228Ac) have characteristic energies. Spectra of detector channels 100 to 248 (1.16 to 2.99 MeV) of the NGR system were binned for different depth intervals. These intervals were chosen to improve counting statistics because they had differing NGR intensities (Fig. F61) and to trace the shifts in the peak intensities of the potassium, uranium, and thorium series. Such shifts would indicate mineralogical changes. The spectral results indicate that the 238U and 232Th peaks are not present or are poorly defined throughout the hole. The absence of the 238U and 232Th peaks may either result from insufficient total measuring time for the individual bins or indicate a mineralogy with an abundance of potassium-rich minerals such as illite and K-feldspars. The presence of these potassium-rich minerals is supported by clay and bulk mineralogical analyses (see "Lithostratigraphy"). Kaolinite, which is also a major component of the clay-sized fraction (see "Lithostratigraphy"), has a relatively greater content of Th than illite. The relatively low total clay content may result in the small magnitude of the Th peak.
Lithostratigraphic Unit I (0-63.8 mbsf) is characterized in its upper part (0-40 mbsf) by an increasing NGR intensity (~5-6 cps) above an interval of decreasing intensities. The Unit I/Unit II boundary is at the minimum in the NGR curve. Only two XRD samples were analyzed from the upper 40 m of Unit I, one of which was from a layer of foraminifer-rich clay. The NGR increases in Subunit IIA (63.8-160.1 mbsf) to a maximum at ~100 mbsf with an underlying decline to a constant value of ~6 cps, with a similar trend in the total clay mineral plus K-feldspar content. The uniform NGR values between 160.1 and 254.4 mbsf characterize Subunit IIB, whereas the drop to ~5 cps with the associated decrease in total clay mineral content and K-feldspars marks Subunit IIC (254.4-307 mbsf).
Unit III constitutes the remainder of the hole. There is a general slow decrease in the NGR values downcore, interrupted by higher levels at ~700 m. These higher NGR values may be attributed to an increase in the K-feldspar content, but this relationship is not clear. The NGR data combined with the bulk mineralogy, therefore, indicate that the most prominent compositional change—possibly the most prominent change in depositional environment—occurred during the transition from Unit III to Unit II at 307 mbsf.
Decimeter- to meter-scale changes in sediment color from greenish gray to dark gray intervals in lithostratigraphic Unit II are characterized by L* variations (see "Lithostratigraphy"). Plotting L* vs. magnetic susceptibility and bulk density for Cores 188-1165B-14H and 15H (Fig. F62) demonstrates that these lightness variations closely covary with changes in GRA bulk density and magnetic susceptibility. Darker intervals have higher densities and susceptibilities. This suggests that the color changes are at least partly caused by changes in the sediment composition.
Gravimetric and volumetric determinations of moisture and density (MAD) were made for 353 samples from Hole 1165B (Cores 188-1165B-1H through 74X) and 187 samples from Hole 1165C (Cores 188-1165C-1R through 35R). Two samples were taken, where possible, from each section of Cores 188-1165B-1H through 21X and from Core 188-1165C-1R. For the remaining cores, one sample was taken per section where possible. Samples were not taken from the disturbed sediment surrounding the "biscuits" in the XCB cores or in flow-in regions of APC cores. No moisture and density samples were taken from Hole 1165A. Wet mass, dry mass, and dry volume were measured, and from these measurements, percentage water weight, porosity, dry density, bulk density, and grain density were calculated (see "Physical Properties" in the "Explanatory Notes" chapter; also see the "Related Leg Data" contents list).
The grain densities measured at Site 1165 are shown in Figure F63A. Eighty determinations of grain density were made in lithostratigraphic Unit I (0-63.8 mbsf), giving an average value of 2.61 g/cm3, with a range of 2.37-2.74 g/cm3. The measured values show a decrease from top to bottom of the unit, with values on the order of 2.7 g/cm3 near the seafloor and decreasing to 2.5 g/cm3 and lower near the base of the unit.
A total of 163 determinations of grain density were made in lithostratigraphic Unit II (~63.8 to ~305 mbsf). In Subunit IIA, the mean value is 2.54 g/cm3, with a range of 2.37-2.70 g/cm3. Similar to Unit I, the measured values show a decrease from top to bottom of Subunit IIA, with values on the order of 2.65 g/cm3 near the top of the subunit and decreasing to 2.5 g/cm3 or lower near the base of the subunit at 160.1 mbsf. In Subunit IIB, the mean value is 2.56 g/cm3, with a range of 2.39-2.71 g/cm3. In Subunit IIC, the mean value is 2.62 g/cm3, with a range of 2.55-2.67 g/cm3. Subunits IIB and IIC show an increase in grain density from top to bottom.
Within lithostratigraphic Unit III (305-998.27 mbsf), 292 determinations of grain density were made, giving an average value of 2.66 g/cm3, with a range of 2.49-3.14 g/cm3. The measured values show an increase from top to bottom of the unit, with values around 2.62 g/cm3 near the top of the unit and increasing to 2.72 g/cm3 near the bottom of the hole.
The two zones of low grain density, one in lithostratigraphic Unit I (36-50 mbsf) and one in Unit II (120-160 mbsf), appear to be associated with diatomaceous material in those units (see "Lithostratigraphy"). Siliceous tests of diatoms have a density of 2.0-2.25 g/cm3 (Klein and Hurlbut, 1977). If the lower grain density measured in these zones is due solely to such diatom tests and the remaining material within these zones has a grain density of ~2.65 g/cm3, then diatom tests would make up 40%-50% of the mass of the sediment. The zone of low grain density at 140 mbsf occurs at the same depth where a loss of the magnetic signal is observed (see "Paleomagnetism").
The porosities measured at Site 1165 are shown in Figure F63B. A total of 243 determinations of porosity were calculated in lithostratigraphic Units I and II (0 to ~305 mbsf). Within Unit I, the average value of porosity is 70%, with a range of 64%-77%. Within Unit II, the average value of porosity is 67%, with a range of 57%-72%. Both Units I and II show a gradual decrease in porosity with increasing depth and overburden pressure.
Within lithostratigraphic Unit III, 292 determinations of porosity were made. The porosity generally decreases with depth and increasing overburden pressure (Fig. F63B). There are two significant features in the porosity plot of Unit III, the first at ~620 mbsf and the second at ~800 mbsf. An abrupt decrease in porosity from 54% to 44% occurs at 620 mbsf. This decrease correlates with an increase in velocity and density (see below) but does not coincide with an identified lithostratigraphic boundary. Below 620 mbsf, the porosity remains essentially constant until the second feature, a change of the slope of the plot, is reached. Within the uppermost portion of Unit III (305-620 mbsf), the mean value is 57%, with a range of 31%-64%. From 620 to 800 mbsf, the mean porosity is 43%, with a range of 35%-52%. From 800 mbsf to the bottom of Hole 1165C, the mean value of porosity is 37%, with a range of 28%-54%.
Other parameters that are derived from the measured data include bulk density, dry density, water content, and void ratio. Bulk density and dry density values are presented in Figure F64. A total of 535 determinations of bulk and dry density were made on samples from Holes 1165B and 1165C. Bulk density shows only a slight increase with depth from the surface to ~200 mbsf (0.000117 g/cm3/m), and then a more rapid increase below that depth to the termination of Hole 1165C at 998.27 mbsf (0.000811 g/cm3/m). Dry density reveals a similar trend, with an increase of 0.000371 g/cm3/m from the surface to 200 mbsf and an increase of 0.001271 g/cm3/m from 200 mbsf to the termination of the hole.
Water content (as a percentage of dry mass corrected for salt content) and void ratio are presented in Figure F65. These plots show trends similar to those observed in the porosity data.
A common feature of density, porosity, and water content records of Site 1165 is the change to higher gradients below 200 mbsf that occurs within lithostratigraphic Unit II. Whereas the gradient observed below 200 mbsf is expected for a normal compaction of clay-rich sediments, the almost constant porosity in the upper part is uncommon. A possible explanation is the higher biogenic silica content in the upper 200 mbsf, which could inhibit compaction as described by Bryant and Rack (1990).
As described previously in this section, bulk-density data were also obtained from the GRA bulk densiometer in addition to the discrete MAD measurements. To compare the GRA bulk-density data to the discrete MAD measurements, the GRA data set was cleaned by first removing the data points at the top and bottom of each core section. Examination of the remaining data set showed that ~25% of data points lay outside the modal trend. The points outside the modal trend were biased to low bulk-density values, caused by voids in the core and gaps between the core and the core liner. This was especially apparent in the RCB cores. The outlier points were removed from the data set if they exceeded a critical range. The critical range was determined at each depth interval by computing the average and standard deviation for 50 data points on either side of the depth interval. The critical range for the depth interval was then taken as the average value ±0.75 of the standard deviation. The cleaning procedure removed 5962 data points from the data set, or 27% of the raw data. The trend line through the resulting cleaned data set was calculated using an exponential smoothing routine.
Figure F66A presents the GRA bulk-density trend line described above, superimposed on the bulk densities computed from the discrete MAD measurements. The plot demonstrates that there is good agreement between the two measurement methods to ~500 mbsf; below this depth, the discrete measurements are consistently higher than the GRA bulk-density measurements. The ratio of the discrete bulk-density measurements to the GRA bulk-density measurements for corresponding depths (Fig. F66B) is relatively constant and equal to 0.97 for APC cores (0-147 mbsf), 1.04 for XCB cores (147-673 mbsf), and 1.16 for RCB cores (673 mbsf to the termination of the hole at 998.27 mbsf). This indicates that different calibration constants should be used for the GRA depending on the coring method being employed or that GRA measurements on different core types using the same GRA calibration should be scaled to correct the measurements.
Figure F67 illustrates the calculated effective overburden pressure (total overburden pressure minus hydrostatic pressure) using the two data sets. The two curves are in good agreement to 500 mbsf, but by the bottom of the hole, the cumulative error in the GRA-based curve is on the order of 1440 kPa. This error results from the systematic error in the GRA measurements described above.
At Site 1165, P-wave velocities on split cores were measured at a frequency of one measurement per section. In soft sediments, the velocity probes PWS1 and PWS2 were inserted into sediments allowing measurements in z- and y-directions. Below 114 mbsf, the sediments became too stiff to insert the probes, and P-wave velocities were only measured in the x-direction (through the core liner) by using probe PWS3. Below 607 mbsf, the sediments became lithified enough to cut out blocks and measure the P-wave velocity in x-, y-, and z-directions by using PWS3. The laboratory velocity measurements presented here were not corrected to in situ temperature and pressure conditions. Velocity data are compiled in Table T12 (also see the "Related Leg Data" contents list).
Acoustic velocities generally increase with depth below seafloor as consolidation increases (Fig. F68). In lithostratigraphic Unit I, P-wave velocities range between 1500 and 1545 m/s and are superimposed on a trend of increasing velocities from ~1500 m/s at the seafloor to ~1535 m/s at 64 mbsf. The top of lithostratigraphic Unit II (64-114 mbsf) has more uniform velocities, around 1535 m/s, compared to Unit I. In the uppermost 114 mbsf, horizontal (y-direction) and vertical (z-direction) velocity values have nearly the same magnitudes, indicating that the sediments are acoustically isotropic. An abrupt change in P-wave velocities is observed at 114 mbsf (within lithostratigraphic Subunit IIA), where horizontal velocities (x-direction) increase from ~1535 to ~1575 m/s. From 114 to 603 mbsf, horizontal P-wave velocities show an increase from 1575 to 1820 m/s, resulting in a depth gradient of 0.5/s. In this interval, no significant velocity changes are observed at the lithostratigraphic boundaries.
From 492 down to 800 mbsf (within lithostratigraphic Unit III), abundant high-velocity spikes (up to 5098 m/s) characterize local lithified calcareous and siliceous (chert nodule) beds. An abrupt increase from 1820 to 2120 m/s in the general velocity trend (x-direction) occurs at 620 mbsf and correlates with changes in density and porosity. There is no obvious lithologic change described for this interval. A possible (at this stage, speculative) explanation for the velocity increase could be an enhanced silica diagenesis below this depth (see "Inorganic Geochemistry") or an increase in the amount of chert. Close to the base of Site 1165, high-velocity zones of ~2660 m/s and ~2840 m/s occur at 880 mbsf and 960 mbsf, respectively, which may explain strong seismic reflectors observed at this depth. Velocities measured in the x- and y- (horizontal) directions in claystones of lithostratigraphic Unit III are 100 to 300 m/s higher than the corresponding velocities in the z-direction. Below 620 mbsf, the acoustic anisotropy increases with depth and is most likely caused by the alignment of clay minerals parallel to the bedding plane.
A total of 237 shear strength measurements were taken using three different instruments (automated vane shear [AVS], fall cone [FC], and pocket penetrometer [PP]). The strength of the sediment determined which instruments could be used. The ranges used were 0-165 kPa, 0-370 kPa, and 66-800 kPa for the AVS, FC, and PP, respectively. The measured undrained shear strengths are tabulated in Table T13 and plotted in Figure F69. The strength of clays normally increases as a function of depth (Brooker and Ireland, 1965; Andresen et al., 1979) because of consolidation caused by the increase of the effective overburden stress (p´o). Figure F70 shows the ratio of undrained shear strength values and the calculated effective overburden stress values derived from the discrete bulk-density data (Fig. F64A). These data were used for the calculation because they are not affected by voids between the core liner and sample, as are the density measurements from the MST. It is usually expected that the ratio of undrained shear strength to effective overburden stress (Cu/p´o) will be between 0.25 and 0.35 for normally consolidated clays of medium plasticity (Brooker and Ireland, 1965; Andresen et al., 1979). Ratios below this range indicate that the clays may have been remolded during the drilling and sampling process. An alternative explanation is that the clay content and plasticity of these sediments are too low for shear strength measurements to be meaningful. The FC values are roughly 50% higher than the AVS results. Cracks that formed in the sediments during AVS measurements are the most likely explanation for the lower values. The FC and PP values are similar in the 130-190 mbsf interval where both methods were used.
Lithostratigraphic Unit I (0-63.8 mbsf) appears to be normally consolidated with undrained shear strengths increasing from close to 0 near the seafloor to ~50 kPa at the base of the unit. Low Cu/p´o ratios between 40 and 60 mbsf indicate that Core 188-1165B-6H may have been remolded during the drilling and sampling process.
The interval between ~125 and ~180 mbsf, spanning the bottom part of lithostratigraphic Subunit IIA and the top of Subunit IIB, may also be disturbed and corresponds to the last cores taken with the APC and the first cores taken with the XCB. The lithologic change from Subunit IIA to Subunit IIB is gradational (see "Lithostratigraphy") with a downward decrease in biosiliceous components. Because small deformation or disturbance of the core can decrease the undrained shear strength of the sediment, alterations in the measured shear strengths may represent a change from a sediment from which it is difficult to retrieve geotechnically undisturbed samples to one in which this is easier. In other words, the change may be an artifact of the sampling process. Alternatively, the change of strength may be a direct function of the change of the lithology. Care was taken to measure within biscuits and not to sample the drilling slurry between the biscuits in the XCB cores. The presence of biscuits shows that the sediments have been subjected to remolding that can influence the geotechnical parameters. As the sediments become stronger, they probably become more resistant to remolding. The general trend of the shear strength vs. depth plot (Fig. F69) indicates that the shear strength in lithostratigraphic Subunit IIA (63.8-160.1 mbsf) increases from ~50 to ~300 kPa; in Subunit IIB (160.1-254.4 mbsf), the increase is from ~300 to ~500 kPa.
Pocket penetrometer measurements were made only in Unit III down to 457.75 mbsf using a small point as an extension to the tool. Below this depth, the sediment became too hard to be measured. Other shear strength measurements were not possible. The strength of Unit III at 500 mbsf is ~900 kPa.
The shear strength measurements indicate that the sediment column is normally consolidated in the upper 500 m of Hole 1165B and does not have over- or undercompacted layers within this interval. This is shown by the ratio of Cu/p´o (Fig. F70), which generally lies in or below the expected range of 0.25-0.35 (Brooker and Ireland, 1965; Andresen et al., 1979).
Thermal conductivity was measured using both a full-space and a half-space needle probe, as appropriate to the strength of the core recovered (see "Physical Properties" in the "Explanatory Notes" chapter; also see the "Related Leg Data" contents list). Where possible, thermal conductivity was measured twice per core using the full-space probe on APC and XCB cores, usually near the middle of sections. On RCB cores, it was frequently not possible to measure thermal conductivity because there were no pieces in the core long enough to use the half-space needle probe, and the core was too strong to insert the full-space needle probe. Consequently, only a limited number of thermal conductivity measurements were made on cores from below 500 mbsf.
Tables T14 and T15 present the thermal conductivity measurements made at Site 1165. Figure F71 shows the data with a trend line that best represents in situ conditions. The trend line has been intentionally biased toward the higher measurements in the interval 150-500 mbsf for the reasons described below.
The section of the sedimentary column from which XCB cores were taken (147-673 mbsf) was heavily biscuited. Because the full-space needle was inserted into cores before splitting, it was impossible to avoid inserting the needle into the drilling slurry between biscuits. Upon splitting, it was observed not only that the sediment between biscuits was disturbed but also that the water content was often higher than the undisturbed biscuits, the result of the introduction of drilling fluids into the core. Thermal conductivity in fine-grained sediments is, as a first approximation, a linear combination of the conductivities of the grains and the interstitial water. It therefore depends upon porosity or water content and lithology. The thermal conductivity of water is ~0.6 W/(m·°C), whereas the thermal conductivity of most sediment-forming minerals is much higher. Thus, lithology aside, thermal conductivity should decrease as water content increases. The lower values of thermal conductivity measured from 150 to 500 mbsf have been attributed to measurements made in drilling slurry between biscuits and to splitting biscuits during insertion of the needle, allowing the crack to fill with water or air.
Below 500 mbsf, two values at ~700 mbsf (from Sections 188-1165C-3R-4 and 6R-3) represent thin chert layers and lie well above the trend line for the sediment section.
Physical properties generally change at the identified lithostratigraphic boundaries. The physical properties measurements, however, also show a change at 620 mbsf, at which depth there is no identified lithostratigraphic boundary. The change is particularly apparent as a sharp decrease in the porosity from 54% to 44% at 620 mbsf (Fig. F63B) and as an abrupt increase in the P-wave velocity from 1820 to 2120 m/s (Fig. F68). Similar changes are seen at this depth in the downhole logs for natural gamma ray, bulk density, porosity, and photoelectric effect (see "Downhole Measurements"). A reason for this change in the physical properties but not in the lithology may be silica diagenesis (see "Inorganic Geochemistry").