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doi:10.2204/iodp.proc.318.107.2011

Physical properties

The physical properties program for Site U1359 included routine runs on the WRMSL, which includes the GRA bulk density, magnetic susceptibility, and PWL sensors, as well as NGR measurements. P-wave velocity was also analyzed and samples taken for moisture, density, and porosity measurements of cores from Hole U1359A, Hole U1359B, and Hole U1359D. Thermal conductivity measurements were taken in cores from all holes.

Whole-Round Multisensor Logger and Special Task Multisensor Logger measurements

All Site U1359 cores were measured on the WRMSL (Figs. F41, F42, F43, F44, F45, F46, F47, F48) except for Core 318-U1359B-2H (intensive whole-round samples) and 318-U1359C-2H (no recovery).

Starting with Core 318-U1359B-3H, all cores from Holes U1359B and U1359C (except Core 318-U1359C-2H) were first run through the Special Task Multisensor Logger (STMSL) with the overall strategy to use these data for quick correlation to the Hole U1359A data to evaluate the offset during drilling of Holes U1359B and U1359C. Afterward, the core sections were allowed to equilibrate to room temperature and then run through the WRMSL. Hole U1359D cores were only run through the WRMSL.

Magnetic susceptibility

Whole-core magnetic susceptibility was measured at 2.5 cm intervals (2 s measurement time). The raw data values are as high as 1168 instrument units, with the peaks representing gravel clasts throughout the section (Figs. F41, F43, F45). The most prominent features in the magnetic susceptibility data are the two intervals of relatively low values (<20 instrument units) between 94 and 123 mbsf (95 and 124 m CCSF-A), as well as between 220 and 278 mbsf (230 and 295 m CCSF-A). In the intervals where the magnetic susceptibility is between 40 and ~100 instrument units, we observe a cyclicity at several scales throughout the section.

Natural gamma radiation

The total counts per second ranged from 3 to 101 cps, with the peaks representing dispersed gravel clasts (Figs. F41, F42, F43, F44, F45). However, the majority of measurements fall between 15 and 65 cps, and the values show an especially pronounced cyclicity. The NGR, magnetic susceptibility, and the GRA density data were used to correlate the four holes drilled at Site U1359 and to define a composite record (see “Stratigraphic correlation and composite section”).

Gamma ray attenuation bulk density

GRA bulk density was measured at 5 cm intervals on the STMSL (5 s integration time) and at 2.5 cm intervals at the WRMSL (10 s integration time). Measured values are as high as 2.57 g/cm³. The variations in GRA density reflect the regular fluctuations in lithology and porosity at Site U1359 (Figs. F46, F47, F48). We observe especially pronounced lower density values between 50 and 65 mbsf (50 and 65 mcd; below the lithostratigraphic Unit I–II transition) and a sudden drop at ~99.5 mbsf (~101 mcd) that coincides with the lithologic change from diatom-bearing to diatom-rich silty clays (lithostratigraphic Subunit IIa–IIb transition) as well as a shift to slightly lower values at ~248 mbsf (~264 mcd) (lithostratigraphic Unit II/III boundary).

P-wave velocity

P-wave velocity measurements were made at 5 cm intervals on the WRMSL for all cores. The raw values are as high as 2770 m/s, including data from dispersed gravel clasts (Figs. F49, F50).

Additionally, discrete measurements of P-wave velocity were made on the working halves in Holes U1359A and U1359D. One measurement per section was targeted, however, because of the composition and expansion of the sediment, the Section Half Velocity Gantry could hardly obtain any valid measurements below 135 mbsf in Hole U1359A. However, discrete P-wave velocity measurements were successful in most cases in Hole U1359D cores, especially on sediment cubes taken below 450 m CCSF-A. These multiaxis measurements exhibit an anisotropy between the x-axis (perpendicular to the split-core surface) and the y-axis (parallel to the split-core surface) with generally higher velocities (Fig. F50). Because of the poor quality of the sediment cubes, in many cases we were not able to get readings along the z-axis (perpendicular to both x- and y-axes).

Because of the high water content and poor consolidation, the upper four cores in Hole U1359A (lithostratigraphic Unit I), a poor correlation between the PWL velocities and the discrete velocities measured on the split core (Fig. F49) is present. Overall, velocities slightly increase with depth from ~1650 m/s at 142 mbsf (150 mcd) to ~1730 m/s at 463 mbsf (480 mcd). Below 463 mbsf (480 mcd), about the level of Core 318-U1359-36R, the rise in velocity is much steeper (Fig. F50).

Moisture and density measurements

Moisture and density (MAD) measurements were undertaken on 105 samples taken of cores from Hole U1359A (Cores 318-U1359A-1H through 22X), 40 samples from Hole U1359B (318-U1359B-16H through 26X), and 157 samples from Hole U1359D (Cores 318-U1359D-7R through 48R). Depending on core recovery and quality, one sample was taken per section. These samples were carefully selected to cover the representative lithology of each core section and were taken in undisturbed sediments whenever possible. 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 wet bulk densities (MAD) from discrete samples range from 1.36 to 1.99 g/cm³ in Holes U1359A and U1359B (Figs. F46, F47) and from 1.46 to 1.93 g/cm³ in Hole U1359D (Figs. F46, F48). In the upper 248 mbsf (264 mcd) of the hole, both the GRA densities and the wet bulk densities on samples (MAD) are in good agreement. However, starting below 248 mbsf (264 mcd), and even more pronounced below 463 mbsf (480 mcd), the 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 recovered in the lower, more lithified portions of Hole U1359D. This reduced diameter likely systematically underestimated the bulk density as measured by the GRA densiometer and is especially noticeable in the bioturbated diatom-bearing silty clays and silty clays with millimeter-scale laminations of lithostratigraphic Unit III (248–593 mbsf; 264–610 mcd).

All MAD parameters reflect the overall cyclic variations in the record (Figs. F46, F47, F48, F51, F52, F53) and also especially exhibit the lower density interval between 50 and 65 mbsf, as well as a relatively sudden change at ~100 mbsf. Grain density values are in the expected range of clayey to silty sediments (~2.6–2.7 g/cm³), and the values slightly decrease with depth to 463 mbsf (~480 mcd) but are stronger below (Figs. F46, F48). Porosity ranges from 75% to 55%, and these values only slightly decrease with depth (Figs. F51, F52, F53). Bulk density fluctuates between 1.4 and 1.8 g/cm³, and dry density varies between 0.8 and 1.2 g/cm³ (Figs. F54, F55, F56). Moisture content and void ratio show similar trends to porosity, as expected (Figs. F57, F58, F59).

Thermal conductivity

Thirty-two measurements were made on full cores in Holes U1359A, U1359B, and U1359C and 30 measurements on cores in Hole U1359D (Fig. F60). The thermal conductivity data slightly decrease with depth and are discussed in more detail in relation to downhole temperature measurements for calculating heat flow (see “Downhole measurements”).

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