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Physical properties

The physical properties program at Site U1358 included routine runs on the Whole-Round Multisensor Logger (WRMSL), which includes GRA bulk density, magnetic susceptibility, and P-wave logger (PWL) sensors and natural gamma radiation (NGR) measurements. P-wave velocity was also analyzed on split cores as well as samples taken for moisture and density (MAD) and porosity analyses.

Whole-Round Multisensor Logger measurements

Magnetic susceptibility

Whole-core magnetic susceptibility was measured at 2.5 cm intervals (2 s measurement time). The raw data values range from 3 to 2834 SI (Fig. F4). However, the majority of measurements vary between 200 and 400 instrument units, with some peaks in Core 318-U1358B-4R representing gravel clasts.

Natural gamma radiation

NGR counts range from 33 to 99 cps, with higher values in the two deeper cores in Hole U1358B. Cores 318-U1358B-3R and 4R show variability on the order of ~50–60 cm, possibly reflecting the alternations of muddy versus sandy diamictites (Fig. F4).

Gamma ray attenuation bulk density

GRA density was measured at 2.5 cm intervals on the WRMSL (using a 10 s integration time). Variations in GRA density reflect variations in the composition of the Pliocene–Pleistocene diamictite that varies between clast-rich muddy and clast-rich sandy lithologies. The GRA density values for the consolidated sediments are as dense as 2.7 g/cm3 (Fig. F5).

P-wave velocity

P-wave velocity measurements were made at 5 cm intervals on the PWL on the WRMSL for Hole U1358B. These measurements range from 1571 to 2867 m/s (Fig. F6). Additionally, split core P-wave velocity measurements were taken using the Section Half Velocity Gantry. These measurements were made once per section and range from 1414 to 6137 m/s. In general, the P-wave measurements on the split cores should be considered more reliable since the reduced diameter of the RCB cores negatively impacted the WRMSL data (Fig. F6).

Moisture and density measurements

Measurements of density, porosity, and grain density were made on seven samples of cores from Hole U1358B. 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, and dry density. Bulk density and grain density were also calculated. The bulk densities (MAD) from discrete samples range from 2.1 to 2.46 g/cm3 (Fig. F5). In the upper two cores of the hole, both the GRA densities and the wet bulk densities on samples (MAD) correlate well. However, from Core 318-U1358B-3R downhole, the GRA density results are consistently lower than those measured from physical samples. We interpret this to be a result of the reduced diameter of the RCB cores. This reduced diameter, especially pronounced in the diamictites recovered at this site, likely systematically underestimated the bulk density as measured by the GRA densiometer (Fig. F5).

The porosity ranges from 35% to 25% (Fig. F7) and overall decreases with depth. Grain densities range from 2.59 to 3.10 g/cm3. These values are slightly higher than expected for the recovered sediment type and are most likely related to the clast abundance and their variable compositions that include basalt, granitic gneiss, quartzite, fine-grained metasediments, and especially the occurrence of pyrite throughout the sediment (up to 4%; see “Lithostratigraphy”).