The physical properties program at Site 1170 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. The Adara tool was deployed once in Hole 1170C for in situ temperature measurements.
All core sections from Holes 1170A, 1170B, 1170C, and 1170D were measured on the MST (for magnetic susceptibility, P-wave velocity, GRA density, and natural gamma ray) at 2-cm intervals. P-wave velocities were recorded at 2-cm intervals in Hole 1170A to a depth of ~163.8 mbsf. P-wave velocities were not recorded in the XCB-cored sections. Natural gamma-ray emission was measured at 20-cm intervals in Hole 1170D only.
The downcore changes in magnetic susceptibility (Fig. F31A) correlate well with the lithostratigraphic units (see "Lithostratigraphy"). The glauconite-rich sediments of Unit IV and Subunit VA have the highest values in the magnetic susceptibility curve. The natural-gamma radiation record (Fig. F31C) also shows a good correlation with the magnetic susceptibility profile (especially for the lithostratigraphic Subunit VB), reflecting the increased terrigenous fraction deeper in the section recovered at Site 1170. Magnetic susceptibility (Fig. F31A) is negatively correlated with GRA and discrete bulk density (Fig. F31B) in both carbonate-rich and clay-rich intervals of the hole, except the lower 120 m of lithostratigraphic Subunit VB.
Discrete and GRA density data correlate well, with both data sets reflecting the sediment compaction and dewatering associated with increased overburden (Fig. F31B). All first-order features of density variations correlate with other physical parameters and lithostratigraphic units. GRA values are higher than discrete density values in carbonate-rich sections (between ~93 and 373 mbsf). The calibration procedure for the GRA density is optimized for mixed sediments and thus overestimates densities in carbonate-rich sediments. GRA density is lower than discrete density in the RCB cores from Hole 1170D (425 mbsf to total depth [TD]). The GRA density data reduction software assumes a full core liner. RCB cores do not generally fill the liner, and thus, the GRA density in RCB cores is underestimated.
The GRA density profile has a good first-order correlation with the P-wave velocities in the upper part of the hole (Fig. F32). P-wave velocity, however, decreases at 120 mbsf and remains particularly low to 300 mbsf (cf. Figs. F31B, F32). This decline in velocity may be a result of the changes from APC to XCB coring and from wire cutting to the sawing of the core. The latter process introduces water into the core, lowering its P-wave velocity. When sediments become more lithified, they are influenced less by additional water from core splitting and values are more representative.
Compressional velocities were obtained on the split-core sections at a sampling interval of one per section in cores from Holes 1170A and 1170D to a depth of ~754 mbsf (PWS3; x-direction) (Figs. F32, F33; Tables T21, T22). Wherever possible, discrete velocity was measured in longitudinal directions (PWS1; z-direction down to ~80 mbsf for Hole 1170A); transverse directions were recorded in some cores only (PWS2; y-direction between 77 and 116 mbsf for Hole 1170A).
A comparison of the continuous MST velocity profile and the discrete values for the interval between 0 and 165 mbsf is shown in Figure F32. All data sets correlate well and reflect the normal increase in density with depth. Within lithostratigraphic Unit I, acoustic velocity increases with depth below seafloor from values slightly higher than seawater velocity to average values of 1600 m/s (PWS1) (Figs. F32, F33). Velocity is variable within Unit I, with high values associated with relatively darker, clay-bearing layers, and low values associated with lighter, carbonate-rich layers. In the upper 200 m of Unit II (Subunits IIA and IIB), velocity increases slightly with depth. Acoustic velocity increases by 150 m/s across the ooze-chalk transition at 300.8 mbsf. Over this transition a slight increase in magnetic susceptibility and a decrease in carbonate content (see "Organic Geochemistry") is also observed. The well-lithified limestone at the base of lithostratigraphic Unit III near the Eocene-Oligocene transition (see "Lithostratigraphy") is characterized by acoustic velocities as high as 3790 m/s. The relatively loose and less lithified glauconite-rich green silts and sands of lithostratigraphic Unit IV (see "Lithostratigraphy") have lower P-wave velocities. Measurements of sediment cubes cut from the limestone horizons within lithostratigraphic Unit V have velocities of ~3900 m/s (Fig. F33).
Thermal conductivity was measured on Section 3 of each core in Hole 1170A to a depth at which induration prevented insertion of the needles (~170 mbsf) (Fig. F34; Table T23). Values generally increase with depth, corresponding to a downhole decrease in porosity (Fig. F35).
The Adara tool was deployed once at Site 1170 and this deployment yielded an acceptable temperature record. The temperature at the seafloor (2.28°C) was determined using the mudline stops. Examination of the penetration temperature records indicates a normal deployment.
The geothermal gradient was determined using the two points of the temperature profile (Fig. F36). Although there are only two control points, the solution of the least-squares regression gives a geothermal gradient of 52°C/km, which is similar to the 58°C/km gradient at Site 1168 (see "Physical Properties" in the "Site 1168" chapter). Data for both sites show higher values than the Cape Sorell No. 1 exploration well (27°C/km) on the continental shelf 100 km to the northeast (Willcox et al., 1989). The average of the thermal conductivities measured from 0 through 180 mbsf in Hole 1170C is 1.083 W/(m·K). Using the average conductivity and the geothermal gradient, a heat flow of 56 mW/m2 is calculated. This heat-flow value is nearly twice that of values reported from sedimentary basins and slopes near western Tasmania (north of the site) 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 in Hole 1170A to the depth at which induration prevented insertion of the vane (~310 mbsf at the ooze-chalk transition). The results are displayed in Figure F37 and Table T24. Undrained shear strength increases with depth in the upper 60 mbsf from 20 to 30 kPa. The shear strength data show an overall increase with depth, but with high variability. In sediments where carbonate controls the deformation behavior (>50 wt% CaCO3; Lee, 1982), shear strength increases with carbonate content. Variations in shear strength between 93 and 310 mbsf reflect the varying carbonate content of the nannofossil oozes with a good overall correlation to the GRA density (Fig. F37).
Bulk density generally increases with depth below seafloor, whereas porosity and water content decrease (Fig. F35; Table T25). These general trends vary in the sediment section with changes in the slope of the property-depth functions that are associated either with changes in sedimentation rates, diagenetic boundaries, or unconformities. The data for the discrete wet bulk density (Fig. F35) correlate very well with the GRA data and can be used to calibrate and correct GRA density (see "Multisensor Track"; Fig. F31B).
Major variations in physical properties were used to assist in defining the lithostratigraphic boundaries. For example, the carbonate-rich lithostratigraphic Unit II is characterized by an upper subunit (IIA) with relatively high density, P-wave velocity, shear strength, and thermal conductivity but low porosity and water content, and a lower subunit (IIB) with low density, P-wave velocity, shear strength, and thermal conductivity but high porosity and water content. The lowermost subunit (IIC) in Unit II is characterized by relatively high density, P-wave velocity, shear strength, and thermal conductivity but lower porosity and water content (cf. Figs. F31A, F33A, F34, F37, F35). Water content and porosity correlate well and mirror the pattern of the magnetic susceptibility curve for the Eocene Subunit VA and for the upper part of Subunit VB.