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doi:10.2204/iodp.proc.331.104.2011

Physical properties

Physical property measurements were made at Site C0014 to nondestructively characterize lithological units and states of sediment consolidation.

Density and porosity

Bulk density was determined from both gamma ray attenuation (GRA) measurements on whole cores (with the multisensor core logger for whole-round samples [MSCL-W]) and moisture and density (MAD) measurements on discrete samples (see “Physical properties” in Expedition 331 Scientists, 2011b). A total of 208 discrete samples were analyzed for MAD (6, 66, 6, 17, 18, 5, and 90 samples from Holes C0014A, C0014B, C0014C, C0014D, C0014E, C0014F, and C0014G, respectively). Wet bulk density is roughly constant with depth, as determined by both MAD and GRA, although the latter values are generally lower than the former and exhibit more scatter (Fig. F31). This is expected of the GRA-derived density, as GRA measured by the MSCL-W is very sensitive to incompletely filled core liners and the presence of voids and cracks.

Bulk density values are very similar for all holes at this site (Table T17). Average bulk density in Hole C0014G is ~1.7 g/cm³; bulk density lies between 1.2 and 1.6 g/cm³ in the uppermost 60 m of the hole and increases slightly to values between 1.6 and 1.9 g/cm³ between 60 and 130 mbsf. At 127 mbsf bulk density is 2.7 g/cm³.

Grain density was calculated from discrete MAD measurements and is also approximately constant with depth (~2.7–3.1 g/cm³) (Table T17). Lower grain densities (2–2.5 g/cm³) are present between 5 and 15 mbsf. Higher grain densities (>3.25 g/cm³) are present in two intervals, from 20 to 50 mbsf and at ~80 mbsf.

Porosity was calculated from MAD measurements. It is generally quite high (60%–80%) in the shallower holes (C0014A–C0014F) and in the uppermost 60–80 m of Hole C0014G (Fig. F32). Porosity decreases slightly with depth between 80 and 120 mbsf in Hole C0014G to values between 40% and 60%. Porosity decreases sharply at 127 mbsf to 0.13%, consistent with the increase in bulk density.

Density and porosity results from the seven holes at Site C0014 reveal a pattern consistent with the presence of thick water-rich sediments. Only below 127 mbsf is there any indication that sediments have become significantly more lithified. There are no obvious lithological units that can be distinguished based on the density and porosity data.

Electrical resistivity (formation factor)

Formation factor is a measure of the connected pore space within sediments and is used to calculate the bulk sediment diffusion coefficient. Electrical impedance measurements were made at 227 depths (10, 71, 8, 20, 20, 5, and 93 measurements in Holes C0014A, C0014B, C0014C, C0014D, C0014E, C0014F, and C0014G, respectively). Formation factors (a resistivity ratio and thus a unitless parameter) calculated for Hole C0014G range from ~2 to 12 and increase with depth (Fig. F33). The average value for the formation factor at this site was 4.36 ± 1.5 (Table T17). Values for formation factor and the rate of increase in formation factor with depth are similar for all holes at this site.

Discrete P-wave velocity and anisotropy measurements

P-wave velocity and relative anisotropy were measured on samples indurated enough to cut sample polyhedrons, which was rarely the case. P-wave velocity on discrete samples from ~127 mbsf in Hole C0014G range from 3000 to 4000 m/s (data not shown).

Thermal conductivity

Thermal conductivity was measured on whole-round cores. A total of 221 measurements were made (13, 95, 3, 15, 28, 4, and 63 measurements from Holes C0014A, C0014B, C0014C, C0014D, C0014E, C0014F, and C0014G, respectively). Thermal conductivity in Hole C0014G ranged from a low value of ~0.9 W/(m·K) to as high as ~2 W/(m·K) (Fig. F34). Average thermal conductivity for all seven holes is 0.88 ± 0.22 W/(m·K). Thermal conductivity increases slightly with depth and is loosely and inversely correlated with porosity. As porosity decreases, thermal conductivity increases as water is forced from void spaces because thermal conductivity of grains is greater than that of water. Narrow zones of higher thermal conductivity are also roughly coincident with peaks in the MSCL-W P-wave velocity (Fig. F35), where higher velocities should also correspond to regions with less porous, more dense material (data not shown).

In situ temperature

In situ temperature was measured using the advanced piston corer temperature tool (APCT3) (four measurements at 4.2–16 mbsf) and thermoseal strips (three measurements at 38, 47, and 50 mbsf) (Table T18; Fig. F36). For the APCT3, the temperature-time series was recorded at 1 s intervals. The APCT3 was stopped at the mudline for as long as 10 min prior to penetration, and the average of four measurements of apparent bottom water temperature is 4.51° ± 0.17°C (1σ). Temperature-time series for each of the four measurement intervals are shown in Figure F37. Temperature records show significant frictional heating as the coring shoe penetrated the sediment (time = 0), followed by subsequent temperature decay toward the in situ value. For most of the measurements, the probe was kept in the sediment for >5 min, allowing a more accurate extrapolation to the equilibrium formation temperature based on a 1/time approximation (Table T18). All measurements (except perhaps for the one collected from Core 331-C0014D-2H) appear to be reliable, exhibiting good penetration heating and smooth initial decay curves. Equilibrium fits to the temperature-time series are also good and yield the formation temperatures that are plotted versus depth in Figure F36. The temperature recorded during collection of Core 331-C0014D-2H at 16 mbsf was very slightly higher (55.1°C) than the maximum calibration temperature for the APCT3 probe (55°C). Two of the three temperature measurements with thermoseal strips exceeded the range of beads on the strip used and are thus minimum temperature estimates (37.6 and 50.2 mbsf). For the third measurement (46.9 mbsf), the beads for 125°, 130°, and 140°C were blackened but those for 150° and 160°C were not, indicating that the temperature reached or exceeded 140°C but did not reach 150°C. We report this value as 145° ± 5°C. We have not calculated heat flow at this time because of the strongly nonlinear increase in temperature with depth.

MSCL-I and MSCL-C imaging

MSCL-derived core images and color analyses are presented in the visual core descriptions (VCDs).

MSCL-W derived electrical resistivity

MSCL-W–based resistivity data are generally low (<10 Ωm) at depths shallower than 25 mbsf. There are some zones that exhibit increased resistivity where densities are high and porosities are low: >20 Ωm at ~18 mbsf in Hole C0014D, >40 Ωm at ~30 mbsf in Hole C0014E, and as high as 300 Ωm at ~25 mbsf in Hole C0014B. However, there is no obvious relationship with discrete measurements of formation factor (Fig. F38 versus Fig. F33).

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