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Physical properties

The physical properties program for Site U1360 included routine runs on the Whole-Round Multisensor Logger (WRMSL), which includes GRA bulk density, magnetic susceptibility, and P-wave velocity logger (PWL) sensors, as well as natural gamma radiation (NGR) measurements. P-wave velocity was also analyzed and samples taken for moisture, density, and porosity measurements.

Whole-Round Multisensor Logger measurements

Magnetic susceptibility

Whole-core magnetic susceptibility was measured at 2.5 cm intervals (2 s measurement time). Raw data values range from 6 to 2518 instrument units. However, the majority of values vary between 30 and 320 instrument units (Fig. F9), with peaks in Cores 318-U1360A-5R and 6R where gravel clasts occur. The fining-upward sequence from diamictites at the base (Core 318-U1360A-6R) to claystones at the top (Cores 2R through 3R) (see “Lithostratigraphy”) is also documented in the general decrease in magnetic susceptibility values from the bottom to the top of the hole.

Natural gamma radiation

NGR counts range from 33 to 99 cps, with the majority between 15 and 45 cps, as plotted in Figure F9.

Gamma ray attenuation bulk density

GRA density was measured at 2.5 cm intervals using a 10 s integration time. Variations in GRA density reflect variations in lithology between clast-rich diamictite, sandy mudstone with dispersed clasts, and claystone. The values are as high as 2.48 g/cm3 (Fig. F10).

P-wave velocity

P-wave velocity measurements were made at 5 cm intervals on the PWL on the WRMSL. These measurements range from 1633 to 2767 m/s (Fig. F11). Additionally, split-core P-wave velocity measurements were taken using the Section Half Velocity Gantry. These measurements, taken one per section, range from 1699 to 8658 m/s. In general, all measurements correlate well (Fig. F11).

Moisture and density measurements

Measurements of density, porosity, and grain density were undertaken on five samples taken from cores of Hole U1360A. Dependent on core recovery and quality, one sample was taken per section. These samples were measured for wet mass, dry mass, and dry volume and, using these measurements, porosity, percent water mass, dry density, bulk density, and grain density were calculated.

The bulk densities from discrete samples are plotted in Fig. F10, range from 1.83 to 2.58 g/cm3, and show a slight elevation above the values measured by the GRA densiometer. GRA density results are consistently lower than those measured from discrete samples. We interpret this to be a result of the reduced diameter of the RCB cores. This reduced diameter likely systematically underestimated the bulk density as measured by the GRA density meter.

Calculated porosity ranges from 49% to 17% and generally decreases with depth (Fig. F12). Grain densities range between 2.62 and 2.7 g/cm3. The higher grain density (3.13 g/cm3) in a sample from Core 318-U1360-4R is most likely related to the occurrence of pyrite in the sediment (up to 8%; see “Lithostratigraphy”).