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doi:10.2204/iodp.proc.334.105.2012

Physical properties

At Site U1380, physical properties measurements provide basic information characterizing lithostratigraphic units. After sediment cores reached thermal equilibrium with ambient temperature at ~20°C, gamma ray attenuation (GRA) density, magnetic susceptibility, and P-wave velocity were measured on whole-round core sections using the Whole-Round Multisensor Logger (WRMSL). After WRMSL scanning, the whole-round sections were logged for natural gamma radiation (NGR). Thermal conductivity was measured using the full-space method on sediment cores and the half-space method on split lithified sediment cores. A photo-image-capture logger and a color spectrophotometer were used to collect images of the split surfaces of the archive-half cores on the Section Half Image Logger and Section Half Multisensor Logger (SHMSL), respectively. Discrete P-wave measurements were made on cubes subsampled from split sediment cores on the Section Half Measurement Gantry (SHMG). Moisture and density (MAD) were measured on discrete subsamples collected from the working halves of the split sediment cores.

Density and porosity

Bulk density values at Site U1380 were determined from both GRA measurements on whole cores and mass/volume measurements on discrete samples from the working halves of split cores (see “Physical properties” in the “Methods” chapter [Expedition 334 Scientists, 2012a]). Samples were chosen from relatively undisturbed portions and preferentially from clay sediments rather than silty or sandier sections. A total of 38 discrete samples were analyzed for MAD.

In general, wet bulk density values determined from whole-round GRA measurements agree with measurements from discrete samples (Fig. F10A). Wet bulk density values are relatively constant through the cored interval. The mean and standard deviation are 1.87 and 0.05 g/cm³, respectively.

Grain density measurements were determined from mass/volume measurements on discrete samples. Values are relatively constant with depth, with an average value of 2.69 g/cm³ and increasing variability with depth (Fig. F10B). The mean and standard deviation are 2.67 and 0.08 g/cm³, respectively. These values suggest a terrigenous composition.

Porosity values (see “Physical properties” in the “Methods” chapter [Expedition 334 Scientists, 2012a]) were determined from mass/volume measurements on discrete samples using MAD Method C. Porosity is relatively constant through the cored interval at 49% (Fig. F10C).

Magnetic susceptibility

Volumetric magnetic susceptibilities were measured using the WRMSL and point measurements were made on the SHMSL for all recovered cores from Site U1380. Uncorrected values of magnetic susceptibility are presented in Figure F11. Magnetic susceptibility values measured with these two methods are in good agreement, although point measurements show much greater scatter. In general, magnetic susceptibility in the sedimentary sequence is low, indicating an abundance of non-iron-bearing clays. Whole-core magnetic susceptibility values are relatively constant through the cored interval, with a mean value of 0.028 SI.

Natural gamma radiation

NGR results are reported in counts per second (cps; Fig. F12). NGR counting intervals were ~10 min per whole-core interval. Despite the short counting time, NGR counts are considered reliable and have a mean and standard deviation of 19 and 3 cps, respectively.

P-wave velocity

Unconfined measurements of P-wave velocity at Site U1380 were determined from measurements on sediment whole cores and on discrete samples from the working halves of sediment split cores (see “Physical properties” in the “Methods” chapter [Expedition 334 Scientists, 2012a]). No reliable whole-core P-wave velocity measurements were made (Fig. F13). Only three reliable discrete sample measurements of P-wave velocity were made with the SHMG along the z-axis. The mean of these values is 1581 m/s. Based on visual inspection of the cores, the unreliable measurements are attributed to the low water content of the clays. The P-wave signal does not seem to penetrate through relatively dry clays. Comparisons between these measurements and empty core liners suggest that the signal travels within the plastic liner around the core instead of through the recovered material, resulting in unrealistically low velocities.

Thermal conductivity

Thermal conductivity measurements were conducted on split cores using the half-space method (see “Physical properties” in the “Methods” chapter [Expedition 334 Scientists, 2012a]). Thermal conductivity is relatively constant through the cored interval, with a mean and standard deviation of 1.05 and 0.22 W/(m·K), respectively (Fig. F14).

Color spectroscopy

Color reflectance measurement results are presented in Figure F15. L* values are generally between 10 and 50. a* and b* values are inversely correlated. a* values are generally between –5 and 5 and those of b* generally vary from –10 to 5.

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