At Site 1166, natural gamma-ray (NGR) activity was measured at intervals of 12 cm. Magnetic susceptibility (MS) and gamma-ray attenuation (GRA) bulk density were measured at 4-cm intervals. All measurements were taken on whole-round samples (see "Physical Properties" in the "Explanatory Notes" chapter). No P-wave measurements were made on the cores because of the many air gaps in the whole-core sections.
Because of the low recovery, only a few cores were available for multisensor track (MST) measurement. For information on available raw data, see the "Related Leg Data" contents list. The quality of the MST measurements was degraded by incompletely filled core liners that were a result of the RCB drilling method, and direct interpretation of the raw GRA and MS data is not possible at this stage. General trends might be inferred from the NGR data. Extensive postcruise work is needed to carefully edit the data. For higher quality continuous physical properties data, refer to "Downhole Measurements".
The core recovery was such that an insufficient number of measurements were taken to allow reliable binned NGR spectra to be produced. The NGR data do, however, show a trend similar to the mineralogy values (Fig. F32). The number of NGR counts indicates the relative concentration of the total clay-mineral content plus the K-feldspars. Lithostratigraphic Subunits IC and ID and Unit II have a somewhat higher NGR activity than the diamicts of Subunits IA and IB and the sands in Unit III, which indicates that Subunits IC and ID probably have a higher total clay content plus K-feldspars than those units above and below. Unit IV has a high mica content (see "Lithostratigraphy"), a mineral that contributes significantly to the potassium content (and therefore to the content of radioactive 40K) in the sediments.
Gravimetric and volumetric determinations of moisture and density were made for 56 samples from Hole 1166A (Cores 188-1166A-1R through 40R). One sample was taken, where possible, from each section of each core. Wet mass, dry mass, and dry volume were measured; 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 for available raw data).
The grain densities measured at Site 1166 are shown in Figure F33. Twenty-one determinations of grain density were obtained from lithostratigraphic Unit I (0-135.41 mbsf), giving an average value of 2.70 g/cm3, with a range of 2.60-2.75 g/cm3. Within Unit I, the measured values show three decreasing-downward cycles: 0-66, 75-117, and 124-135 mbsf. The lowermost cycle (124-135 mbsf) corresponds to lithostratigraphic Subunit ID. One possible reason for the decreasing-downward trend in each cycle may be a decreasing clay/quartz ratio, although the NGR data (see "Multisensor Track" and "Downhole Measurements") do not show a corresponding variation. The cycles also suggest a cyclic depositional history and may represent three advances and retreats of the continental ice sheet. Further explanation of these cycles requires postcruise investigation.
Fourteen determinations of grain density were made in lithostratigraphic Unit II (135.63-156.62 mbsf). The mean value is 2.61 g/cm3, with a range of 2.48-2.73 g/cm3. Unit II has a relatively lower grain density than either the unit above or below, probably because of a higher content of diatomaceous material (see "Lithostratigraphy"). Siliceous tests of diatoms have a density of 2.0-2.25 g/cm3 (Klein and Hurlbut, 1977), and the addition of 10%-20% diatomaceous material to a predominantly clay material would explain the measured grain densities.
Within lithostratigraphic Unit III (156.62-267.17 mbsf), 14 determinations of grain density were made, giving an average value of 2.68 g/cm3, with a range of 2.65-2.74 g/cm3. The measured values are relatively uniform with depth, showing no particular trend.
Within lithostratigraphic Unit IV (156.62-267.17 mbsf), seven determinations of grain density were made, giving an average value of 2.72 g/cm3, with a range of 2.51-3.48 g/cm3. The measurement of 3.48 g/cm3 at 297.75 mbsf was made on a nodule of siderite (see "Lithostratigraphy"), which was present only sporadically in the section and was therefore not plotted on Figure F33. If that measurement is excluded, then the average grain density within Unit IV is 2.59 g/cm3. The measurements show a relatively broad scatter (2.51-2.67 g/cm3), within which there is no apparent trend. The generally lower values of grain density in Unit IV than in Unit III are likely traceable to the higher OC content in Unit IV (1.6%-9.3%) (see "Organic Geochemistry") than in Unit III (<0.5%).
The porosities measured at Site 1166 are shown in Figure F33B. A total of 21 determinations of porosity were made in lithostratigraphic Unit I. The average porosity value is 30.6%, with a range of 22.8%-57.5%. The values show no trend with depth within the unit, except that lithostratigraphic Subunit ID contains a cluster of values with an average value of 23.8%, which ranges from 124.19 to 133.25 mbsf.
Fourteen determinations of porosity were made in lithostratigraphic Unit II. Within the unit, the average porosity value is 49.5%, with a range of 33.5%-57.9%. A possible explanation for the relatively higher porosity of Unit II compared to Units I and III is the higher biogenic silica content of the unit, which could inhibit compaction as described by Bryant and Rack (1990). Within lithostratigraphic Unit III, 14 determinations of porosity were calculated. Within the unit, the average value of porosity is 24.5%, with a range of 18.0%-31.6%. Neither Unit II nor Unit III displays any trend in porosity with depth.
Seven determinations of porosity were made in lithostratigraphic Unit IV. Within the unit, the average value of porosity is 31.6%, with a range of 4.8%-45.2%. The measurement of 4.8% was made on a nodule of siderite at 297.75 mbsf (see "Lithostratigraphy"). If that measurement is excluded, then the average porosity within Unit IV is 36.0%. The measurements appear to show a downward increase in the upper portion of Unit IV, but this may be simply an artifact of scatter in the few data points available for the unit. The porosity of Unit IV is higher than that of Unit III, which may be related to the higher OC content of Unit IV (1.6%-9.3%, as compared to <0.5% in Unit III) (see "Organic Geochemistry").
No measurements of grain density were made in lithostratigraphic Unit V.
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 F34. A total of 56 determinations of bulk and dry density were made on samples from Hole 1166A. Through lithostratigraphic Unit I, the average is 2.19 g/cm3. In Unit II, the value of bulk density drops abruptly to 1.83 g/cm3. The relatively low value of bulk density of Unit II is a function of the low grain density (2.5-2.6 g/cm3) and high porosity (50%-60%), both of which are attributed to the diatom-bearing claystones found in the unit (see "Lithostratigraphy"). The bulk density rises abruptly to 2.28 g/cm3 in Unit III. Excluding the measurement on the siderite nodule at 297.75 mbsf, the average value of bulk density in lithostratigraphic Unit IV is 2.0 g/cm3. In Unit IV, there is relatively more scatter in the measurements than in the other units, giving a range in Unit IV of 1.91-2.33 g/cm3.
Water content (as a percentage of dry mass corrected for salt content) and void ratio are presented in Figure F35. These plots show trends similar to those observed in the porosity data.
At Site 1166, P-wave velocities on split cores were measured at a frequency of one measurement per recovered section. The velocity probes P-wave sensor (PWS1 and PWS2), which allow measurements in z- and y-directions in soft sediments, were used only on Core 188-1166A-1R. Below this core, the sediments became too stiff to insert the probes, and P-wave velocities were measured in the x-direction (through the core liner) using probe PWS3. In some intervals, the sediments were consolidated or lithified enough to cut out blocks and measure the P-wave velocity in x-, y-, and z-directions using PWS3. The laboratory velocity measurements presented here (Fig. F36) were not corrected to in situ temperature and pressure conditions. Velocity data are compiled in Table T7 (see the "Related Leg Data" contents list).
At Site 1166, a velocity of 1792 m/s (z-direction) was measured at 3 mbsf in lithostratigraphic Subunit IA (Fig. F36). From 20 to 123 mbsf (lithostratigraphic Unit I), velocities range from 2000 to 2150 m/s. Within this zone, an interval of greenish gray clayey silt at 113-114 mbsf (lithostratigraphic Subunit IC) is characterized by a much lower velocity of ~1640 m/s. At the base of Unit I (114-136 mbsf), velocities display a steep increase from 1980 to 2395 m/s. Velocities then decrease abruptly back to ~2000 m/s (x-direction) in lithostratigraphic Unit II (136-157 mbsf). Furthermore, the dark greenish gray claystone found in Unit II displays a velocity anisotropy with velocities in the x-direction ~5% higher than the corresponding velocities in the z-direction, which is most likely caused by the alignment of clay minerals parallel to the bedding plane. Because core recovery was poor, only a few velocity measurements cover lithostratigraphic Unit III (157-267 mbsf). The coarse sands in this unit have velocities ranging from 2100 to 2400 m/s with values increasing downhole. Below 267 mbsf, an abrupt decrease in velocity to values of ~1850 m/s is associated with a change in lithology from coarse sand to black claystone. Within lithostratigraphic Unit IV (276-315 mbsf), several highly lithified thin layers of siderite with velocities of up to 5740 m/s (not shown in Fig. F36) were found.
The measured undrained shear strengths are tabulated in Table T8 and plotted in Figure F37. The shear strengths of the sediments show a firm upper part (Subunit IA) with a shear strength (Cu) of 53 kPa, underlain by a harder Subunit IB with shear strengths of at least 400 kPa (Fig. F37). Shear strengths through Subunit IB all have about the same value. The scatter in the measured values increases downcore into Subunit IC but indicates a trend of increasing shear strengths that continues down through the underlying units into the top of Unit II. In Unit II, the values exceed 900 kPa, the upper limit for the measurement tools on the ship.
The recorded depths of the cores (in mbsf) are 6.7 m too shallow, a result of missing the initial 6.7 m of the mudline sediments with the first RCB core (see "Operations"). Effective overburden stresses were computed to account for this missing portion of the sediment column. The shear strengths of normally consolidated clays normalized by the effective overburden pressure (p´0) are expected to give Cu/p´0 ratios of between 0.25 and 0.35 (Brooker and Ireland, 1965; Andresen et al., 1979). Figure F38 shows that for Site 1166, this value is exceeded for nearly all the measurements made. The uppermost sample, 2.63 mbsf, falls within the range expected for normally consolidated marine sediments. The upper few meters of marine sediments experiences a small degree of overconsolidation due to the same interparticle bonds that cause flocculation.
The Cu/p´0 ratios (1.3-1.9) for the sample from 20.5 mbsf are the result of loading by an overburden greater than that of the present. Empirical relationships (Brooker and Ireland, 1965; Andresen et al., 1979) show that this previous load was 7-12 times the current overburden stress (295 kPa). Similarly, the values at 38.8 mbsf give a total previous overburden stress 3.5 times the present. The decreasing trend of Cu/p´0 ratio with depth indicates that one previous load applied above 20 mbsf can account for the overconsolidation/compaction profile in Subunit IB. The normalized shear strengths (Fig. F38) exhibit another possible downhole increase into Subunit IC. This shows a possible second horizon at ~100 mbsf on which loading of ~3700 kPa, or three times the present overburden stress, has occurred and below which the sediments are further overcompacted.
The shear strengths in the upper 150 mbsf thus reveal a depositional history that includes at least one or two periods during which the sediments were compacted either by a thicker sediment column (removed by erosion), a glacier, or a combination of both. The loads needed are equivalent to ~2950 kPa at 20.5 mbsf (which corresponds to a sediment column 250 m thick or 330 m of nonbuoyant ice) and 3700 kPa at 100 mbsf (which corresponds to a sediment column 300 m thick or 420 m of nonbuoyant ice). It should also be noted that the stress history that can be deduced from sediment properties is limited to the maximum load that the sediment has experienced in the past. Therefore, the normalized shear strength profile (Fig. F38) does not exclude compaction episodes in the interval between 20 and 100 mbsf (e.g., at the breaks in the grain density vs. depth profile). It does, however, limit the past effective load to one less than or equal to that of the episode at 20 mbsf and thereby the corresponding thickness of eroded sediments or nonbuoyant ice.
Thermal conductivity was measured using both a full-space and a half-space needle probe, as appropriate to the strength of the core recovered. Measurements were made only on selected sections because of limited core recovery and core disturbance. 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 (see "Physical Properties" in the "Explanatory Notes" chapter; also see the "Related Leg Data" contents list).
Table T9 presents the thermal conductivity measurements made at Site 1166, and Figure F39 shows the data plotted against depth. Eleven thermal conductivity measurements were made. The average thermal conductivity is 1.423 W/(m·°C), with a range of 0.938-2.159 W/(m·°C). There is no discernible difference in the thermal conductivities measured in lithostratigraphic Units I and II nor is there any trend with depth.
The measured values of thermal conductivity are in the range expected for soils (0.25-2.5 W/[m·°C]; Mitchell, 1993). Thermal conductivity in 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 bulk density and lithology. The thermal conductivity of water is ~0.6 W/(m·°C) and is much higher for most sediment-forming minerals. Thus, thermal conductivity should increase as dry density increases. The covariance of thermal conductivity and dry density is illustrated in Figure F39, where dry density is plotted with the measured thermal conductivities. The lower values of thermal conductivity measured at 115 and 146 mbsf are clearly reflected in the lower values of dry density measured at the same depths.