Shipboard physical properties measurements conducted at Hole 1084A included nondestructive, high-resolution measurements of GRAPE density, magnetic susceptibility, P-wave velocity, and natural gamma radiation on most recovered whole-round core sections.
Index properties data (gravimetric wet bulk density, porosity, and moisture content) were collected at discrete locations on split sections. Method C was used at this site (see "Explanatory Notes" chapter, this volume).
Within all APC sections and where sediment properties permitted, such as intact biscuits from XCB cores, undrained vane shear strength was determined.
Compressional (P-wave) velocity measurements were made at a resolution of one or two discrete sampling points per section. For discrete P-wave velocity measurements the modified Hamilton Frame was used on split sections of cores from <38 mbsf.
Thermal conductivity was obtained on every second unsplit section in every core by inserting a thermal probe into the sediment (see "Explanatory Notes" chapter, this volume).
GRAPE density (Fig. 32), P-wave velocity (Fig. 33), and magnetic susceptibility (Figs. 34A, Fig. 35A) were determined every 2 cm between 0 and 98 mbsf. MST data are included on CD-ROM (back pocket, this volume). Below 98 mbsf, the resolution was reduced to 4 cm for all MST sensors. Compressional velocities were recorded at an amplitude threshold of 100 incremental units to avoid erroneous determinations of first-arrival times. The MST P-wave logger did not record any signals below 18 mbsf (Fig. 33), which confirms the very high gas content in the sediments.
Magnetic susceptibility (Figs. 34A, Fig. 35A) and GRAPE density (Fig. 32) show a good correlation over the entire depth range of 600 m. Both profiles correspond well to the identified lithostratigraphic units (see "Lithostratigraphy" section, this chapter).
Index properties wet bulk and GRAPE densities display a high degree of similarity. A majority of discrete wet bulk density values are higher than the GRAPE data. This can be associated with voids and cracks within the recovered sediments, which reduce the effective sediment volume for GRAPE measurements.
All physical properties data sets reveal pronounced cyclicities, which give rise to further detailed analyses after correcting for sediment distortion and combining parallel holes. Intervals of anomalous lithologies will be further studied and compared with results from downhole logging and sediment analyses (see "Lithostratigraphy" and "Downhole Logging" sections, this chapter).
Discrete velocities recorded between 0 and 37 mbsf increase from 1540 to 1570 m/s. The P-wave logger of the MST recorded systematically lower values between 0 and 18 mbsf (Fig. 33). Density and velocity profiles correspond to each other to a certain degree (Fig. 32A, Fig. 33), but because of the high gas content of the sediments (see "Organic Geochemistry" section, this chapter), velocity data are not considered to be very reliable.
Data from discrete measurements of wet bulk density, porosity, and moisture content are displayed in Fig. 36A, Fig. 36B, and Fig. 36C, respectively (also see Table 16 on CD-ROM, back pocket, this volume). The density values vary between 1200 and 1700 kg/m3, with a single peak of almost 5000 kg/m3 at 395 mbsf (not displayed in Fig. 32, Fig. 36A–C).
The overall trend of the wet bulk density profile shows an increase from 5 to 70 mbsf and a decrease downhole to 140 mbsf. Wet bulk density shows very little variation and few excursions between 160 and 380 mbsf. Below 380 mbsf, the data show a higher level of variation and gradually increase because of compaction down to the end of the sampling depth at 585 mbsf. The most prominent changes in wet bulk density coincide with the lithostratigraphic boundaries (see "Lithostratigraphy" section, this chapter).
In general, porosity and moisture profiles are inversely correlated. Porosities decrease from 90% in the top section to 55% at 585 mbsf, indicating the high clay content of these sediments (Fig. 36B). Moisture content varies between 80% at the top of Hole 1084A and 30% at 585 mbsf (Fig. 36C). The overall variation between higher and lower values corresponds to the observed and identified lithostratigraphic units (see "Lithostratigraphy" section, this chapter).
The thermal conductivity profile (Fig. 34B, Fig. 35B) at Hole 1084A was measured in every second core section (see "Explanatory Notes" chapter, this volume). Direct contact with the sediments in the core liner of Hole 1084A was sometimes difficult to establish because of the presence of many voids and cracks, which were difficult to identify through the liner. The profile is similar to wet bulk and GRAPE density profiles over some depth intervals at Hole 1084A (Fig. 32).
In Hole 1084A, the Adara tool was deployed to measure formation temperature. A preliminary analysis provided three data points, which were used to estimate a geothermal gradient of 48 °C/km, but further analyses will be required to confirm this result.
Undrained vane-shear measurements were performed in the bottom part of each core section between 0 and 300 mbsf (Fig. 34D, Fig. 35D). The profile for Hole 1084A shows an overall increase in vane shear strength between 0 and 300 mbsf. Below 255 mbsf, vane-shear data show higher scatter, and local maxima generally decrease.
As noticed at other Leg 175 sites, local maxima in shear strength are usually observed in the middle of each core at Site 1084. Lower shear-strength values coincide mostly with the top and the bottom of each core, where gas expansion may have changed the sediment structure significantly.