The physical properties program at Site 1172 included MST and thermal conductivity measurements of whole-round cores and compressional wave (P-wave) velocity, moisture and density (MAD), and vane shear-strength measurements of split cores. Three in situ temperature measurements were made in Hole 1171B using the Adara tool.
Measurements of magnetic susceptibility, P-wave velocity, and GRA density were taken at 2- to 3-cm intervals in all core sections from Holes 1172A, 1172B, 1172C, and 1172D. P-wave velocities were recorded at 2-cm intervals for Hole 1172A to a depth of ~225 mbsf, but were not taken in the XCB-cored sections.
Downcore variability in magnetic susceptibility (Fig. F30A) correlates well with the lithostratigraphic units (see "Lithostratigraphy"). The glauconite-bearing sediments of the condensed section in Unit II are marked by a prominent increase in magnetic susceptibility. Magnetic susceptibility (Fig. F30A) is negatively correlated with GRA and discrete bulk density (Fig. F30B) in both carbonate-rich and clay-rich intervals of the hole, except in lithostratigraphic Unit IV. The K/T boundary is also characterized by a rapid increase in magnetic susceptibility (see "Lithostratigraphy").
Density generally increases between the seafloor and ~750 mbsf, following a normal compaction and dewatering trend (Fig. F30B). This overall trend is interrupted by an interval of high-porosity diatomaceous silty claystones in lithostratigraphic Unit III. All major features of the GRA density records are also seen in the discrete density data and both data sets correlate well with other physical parameters and lithostratigraphic units. GRA density and discrete density, however, show some offset downcore. GRA values are higher than discrete density values in carbonate-rich sections (between approximately the seafloor and 220 mbsf), because the MST is optimized for mixed sediments. GRA densities are lower than densities from discrete measurements in Hole 1172D (355 mbsf to total depth). This difference in measured density is expected because the RCB cores in Hole 1172D did not fill the core liner.
Compressional ultrasonic velocities were obtained on the split-core sections at a sampling interval of one per section in cores from Holes 1172A and 1172D (PWS3; x-direction) (Figs. F31, F32). When possible, discrete velocity was measured in longitudinal directions (PWS1; z-direction down to ~80 mbsf for Hole 1172A), transverse directions were recorded in some cores only (PWS2; y-direction between the seafloor and 70 mbsf for Hole 1172A).
As expected for the sediment types encountered at this site, average velocities vary between 1550 m/s in the soft-surface sediments and up to 2100 m/s in the more consolidated sediments at 750 mbsf (PWS3; Table T20; Fig. F32). In general, the core velocity corresponds well to the downhole logging data, except within lithostratigraphic Subunit IC, where the combined influence of the XCB coring and the relatively high lithologic variability degrade the core velocity measurements (see "Downhole Measurements").
A comparison of the continuous velocity profile obtained with the MST and the discrete values for the interval between 0 and 230 mbsf is shown in Figure F32. Within lithostratigraphic Unit I, acoustic velocity increases with depth below the seafloor from values slightly higher than seawater velocity to average values of 1.6 km/s (PWS1) (Figs. F31, F32). Velocity is variable within Subunit IC with high values associated with relatively dark clay-bearing layers and low values associated with lighter carbonate-rich layers. At the ooze-chalk transition, which corresponds to the Subunit IB/IC boundary at ~273 mbsf, the acoustic velocity increases by 150 m/s. The limestone at the base of lithostratigraphic Subunit IC near the Eocene-Oligocene transition (see "Lithostratigraphy") is characterized by an acoustic velocity of 2.2 km/s. The relatively porous diatom-silty claystone of lithostratigraphic Unit III (see "Lithostratigraphy") has lower P-wave velocities.
Thermal conductivity was measured on Section 3 of each core from Hole 1172A to a depth at which induration prevented insertion of the needles (~220 mbsf; Fig. F33). Values generally increase with depth, corresponding to a general downhole decrease in porosity (Figs. F33, F34; Table T21).
The Adara tool was deployed three times at Site 1172, and this deployment yielded three acceptable temperature records. The temperature at the seafloor (2.46°C) was determined using the mudline stops. Examination of the penetration temperature records indicates a normal deployment (see "Physical Properties" in the "Site 1168" chapter).
The geothermal gradient was determined using the four points of the temperature profile (Fig. F35). The solution of the least-squares regression gives a geothermal gradient of 46°C/km, which is lower than the 58°C/km at Site 1168 (see "Physical Properties" in the "Site 1168"" chapter) and the 52°C/km at Site 1170 (see "Physical Properties" in the "Site 1170" chapter). Data for all Leg 189 sites show higher values than the Cape Sorell No. 1 exploration well (27°C/km) on the continental shelf 100 km to the northeast of Site 1168 on the western Tasmania margin (Willcox et al., 1989). The average of the thermal conductivities measured from 0 through 89 mbsf in Hole 1172B is 1.182 W/(m·K). Using the average conductivity and the geothermal gradient, a heat flow of 55 mW/m2 is calculated. This heat-flow value is considerably higher than values reported from sedimentary basins and slopes near western Tasmania north of Site 1168 and Mesozoic continental margins in the mid-Atlantic (~40 mW/m2; see "Physical Properties" in the "Site 1168" chapter).
One measurement of vane shear strength was taken per section for Hole 1172A to the depth at which induration prevented insertion of the vane (~270 mbsf; the ooze-chalk transition). The results are displayed in Figure F36 and Table T22. Undrained shear strength increases with depth in the upper 110 mbsf from ~10 to 50 kPa. The data show an overall increase with depth down to 170 mbsf, but with relatively high variability. Variations in shear strength between the seafloor and 130 mbsf correlate well overall with the GRA density (Fig. F36). As already observed in shear strength data from Sites 1168 and 1170, the uppermost Pliocene and upper and lower Miocene are characterized by higher mean values and greater variability and shear strength.
Bulk density generally increases with depth below seafloor, except in Unit III, where a high-porosity diatomaceous claystone is found (Table T23). Water content and porosity mirror the magnetic susceptibility record with the exception of Subunits IVA and IVB. First-order variations in the MAD downcore profiles correspond to the lithostratigraphic units (see "Lithostratigraphy") and with changes in sedimentation rates (see "Biostratigraphy"). The discrete wet bulk density data (Fig. F34) correlate very well with the GRA data and can be used to calibrate and correct GRA density (see "Multisensor Track", Fig. F30B).