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doi:10.2204/iodp.proc.329.105.2011

Physical properties

At Site U1367, physical property measurements were made to provide basic information characterizing lithologic 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 with the Whole-Round Multisensor Logger (WRMSL) on whole-round core sections. After WRMSL scanning, the whole-round sections were logged for NGR. Thermal conductivity was measured using the full-space method on sediment cores. Discrete P-wave measurements were made on split sediment cores using 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. Additional discrete measurements of electrical resistivity were made on the split sediment sections to calculate formation factor. The Section Half Image Logger and Section Half Multisensor Logger (SHMSL) were used to collect images and color spectrometry of the split surfaces of the archive-half cores. Four holes targeted the sedimentary cover, Holes U1367B–U1367E, and are relatively complete. The most complete hole for logging physical properties was Hole U1367B. Hole U1367F targeted basement but contains a few meters of sediment above basement. Sediment holes have not been correlated and offsets exist. Basalt recovered from Hole U1367F consists of pieces too small for WRMSL and NGR logging.

Density and porosity

Sedimentary bulk density values at Site U1367 were determined from both GRA density 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 329 Scientists, 2011a]). A total of 39 discrete samples were analyzed for MAD, 8 samples from Hole U1367B, 8 samples from Hole U1367C, 10 samples from Hole U1367D, 12 samples from Hole U1367E, and 1 sample from Hole U1367F.

In general, wet bulk density values determined from whole-round GRA measurements and measurements from discrete samples agree well (Fig. F19A). The most conspicuous feature of the bulk density measurements is the relatively abrupt shift from ~1.3 to 1.6 g/cm³ at ~6 mbsf. This shift corresponds to a lithologic change between lithologic Units I and II.

Grain density measurements were determined from mass/volume measurements on discrete samples (Fig. 19B). The mean and standard deviation of grain density is 2.8 and 0.2 g/cm³, respectively. No depth-dependent variation is observed.

Porosity measurements (see “Physical properties” in the “Methods” chapter [Expedition 329 Scientists, 2011a]) were determined from mass/volume measurements on discrete samples. Porosity in lithologic Unit I is >80% and drops abruptly to 64% in Unit II. No depth-dependent trend is observed in Unit II. The decrease in porosity is attributed to the diagenetic precipitation of calcite (Hamilton, 1976) (see “Lithostratigraphy”).

Magnetic susceptibility

Volumetric magnetic susceptibilities were measured using the WRMSL and point measurements were made on the SHMSL on all recovered cores from Site U1367. Uncorrected values of magnetic susceptibility are presented for Holes U1367B–U1367E (Fig. F20). The spatial resolution of the WRMSL magnetic susceptibility loop is ~5 cm, and the observed “ringing” in Holes U1367C–U1367E is due to edge effects.

Magnetic susceptibility values show the greatest variability in lithologic Unit I and peak at ~2 mbsf. These values decrease rapidly to the boundary between Units I and II. Magnetic susceptibility values in Unit II are more consistent than those in Unit I and increase with depth.

Natural gamma radiation

NGR results are reported in counts per second (cps) (Fig. F21). NGR counting intervals were ~1 h per whole-core interval for Hole U1367B but decreased to 0.5 h per whole-core interval for Holes U1367C–U1367E. NGR counts are considered reliable. NGR at the tops of all holes is high, indicating that the sediment/water interface was sampled.

In general, NGR counts decrease with depth to ~10 mbsf but then increase with greater depth. A prominent but local peak is observed at 7 mbsf in Hole U1367B and at ~10 mbsf in Hole U1367E. Ringing is more prevalent in cores from Holes U1367C and U1367D because only short core pieces remained after whole-round sampling prior to NGR measurements.

P-wave velocity

P-wave velocity at Site U1367 was determined from measurements on sediment whole cores and mass/volume measurements on discrete samples from the working halves of sediment split cores (see “Physical properties” in the “Methods” chapter [Expedition 329 Scientists, 2011a]). In general, discrete measurements are similar to whole-core measurements (Fig. F22). The mean value is ~1525 m/s, which is close to the compressional velocity of water (Fig. F22B). In all holes, there is a shift to higher values in lithologic Unit II relative to Unit I. In Holes U1367C–U1367E, the greater apparent scatter is an artifact caused by edge effects as these measurements were made after whole-round sampling for chemistry and microbiology.

Formation factor

Electrical conductivity was measured on working halves of the split sediment cores from Hole U1367B. Measurements in Hole U1367B were made at a nominal interval of 10 cm. For each measurement, the temperature of the section was also noted. Surface seawater was used as a standard and measured at least twice per section (Table T7), normally prior to making measurements for that section and then around the 75 cm offset of each section. These measurements were used to compute the drift (Fig. F23). The temperature dependence of electrical conductivity was corrected and all reported measurements correspond to a temperature of 20°C. Electrical conductivity measurements were transformed to a dimensionless formation factor by dividing the measurements for the drift (Table T8).

Within lithologic Unit I, the formation factor is generally <2 and generally increases with depth (Fig. F24). Formation factor values in Unit II are generally offset from those in Unit I and are >2. This pattern inversely mimics the difference in observed porosity between the two units (Fig. F19C).

Thermal conductivity

Thermal conductivity measurements were made on sediment whole-round cores using the needle-probe method. Many of the needle-probe measurements in lithologic Unit I are considered unreliable because temperature-time series of these measurements indicate that the measurements caused fluid to convect within the samples. Convection leads to unreasonably low estimates of thermal conductivity by causing the thermal response to heating to depart from the theoretical prediction. Convection appears to be less of an issue in Unit II, where decreased porosity may be inhibiting convection, but the scatter is large. Thermal conductivity values of material from a piston core collected during the KNOX-02RR site survey cruise indicate a thermal conductivity value of 0.7 W/(m·K) for Unit I (R. Harris, unpubl. data) (Fig. F25). Thermal conductivity values in Unit II are higher than in Unit I but also show increased scatter. The mean and standard deviation of values in Unit II are 1.0 and 0.2 W/(m·K), respectively.

Color spectrometry

Results from color reflectance measurements are presented in Figures F26, F27, and F28. L* values are ~35, with some clusters of higher values at ~275. The majority of a* and b* values are ~5–10 and 7–19, respectively. A slight offset in these color reflectance parameters exists between lithologic Units I and II. There is an additional break in b* values at ~15 mbsf. All parameters decrease slightly with depth in Unit II.

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