Physical properties were measured on unsplit cores and on the undisturbed parts of split cores. The MST was used for nondestructive measurements of wet bulk density, P-wave velocity, magnetic susceptibility, and natural gamma radiation on unsplit cores. Thermal conductivity measurements were also conducted on unsplit sediment cores and split rock cores. Undrained shear strength was measured on unlithified sediment cores, and three-directional P-wave velocities were measured on both soft and lithified sediment cores. Portions of split cores that were undisturbed by drilling, sampling, gas expansion, bioturbation, cracking, and large voids were used to obtain specimens for moisture and density measurements and calculations (wet bulk density, grain density, dry bulk density, water content, void ratio, and porosity).
Physical properties measurements were conducted after the cores had equilibrated to near ambient room temperature (i.e., 22°-24°C) after ~2-4 hr. A summary of each of the physical properties measurement procedures for Leg 190 is outlined below; more detailed descriptions are provided by Blum (1997).
The first measurement station was the MST, which combines four sensors on an automated track to measure magnetic susceptibility, bulk density, P-wave velocity, and natural gamma-ray emission on whole-core sections. The four MST sensors are the magnetic susceptibility meter, the gamma-ray attenuation (GRA) bulk densiometer, the P-wave logger (PWL), and the natural gamma-ray (NGR) detector. Magnetic susceptibility, bulk density, and natural gamma-ray emission were generally measured on all cores indiscriminately of coring method, (i.e., APC, XCB, or RCB). P-wave velocities were measured on undisturbed APC cores. MST measurement of P-wave velocities on XCB and RCB cores is not usually recommended because there is incomplete coupling between the liner and the core. MST data were sampled at discrete intervals, with the sampling rate chosen to optimize the data resolution and the time needed to run each core section through the device.
Magnetic susceptibility was measured with a Bartington meter MS2 using an 80-mm internal diameter sensor loop (88-mm coil diameter) operating at a frequency of 565 Hz and an alternating field of 80 A/m (0.1 mT). The sensitivity range was set to the low sensitivity setting (1.0 Hz). The sample period and interval were set to 2 s and 4 cm, respectively, unless noted otherwise. The mean raw value of the measurements was calculated and stored automatically. The quality of these results degrades in XCB and RCB cores, where the core may be undersized and/or disturbed. Nevertheless, general downhole trends are useful for stratigraphic correlations. The MS2 meter measures relative susceptibilities, which have not been corrected for the differences between core and coil diameters.
Bulk density was estimated for unsplit core sections as they passed through the GRA bulk densiometer using sampling periods and intervals of 2 s and 4 cm, respectively, unless noted otherwise. The gamma-ray source was 137Cs. For each site, the GRA bulk densities and the bulk densities measured on discrete samples were compared.
P-wave velocity was measured at 4-cm intervals and 2-s periods with the high-resolution PWL. The PWL measured P-wave velocity across the unsplit core sections. In order to determine the P-wave velocity, the PWL transmits 500-kHz P-wave pulses through the core at a frequency of 1 kHz. The transmitting and receiving transducers are aligned perpendicular to the core axis while a pair of displacement transducers monitors the separation between the P-wave transducers. Variations in the outer diameter of the liner do not degrade the accuracy of the velocities, but the unconsolidated sediment or rock core must completely fill the liner for the PWL to provide accurate results.
Natural gamma-ray emission analysis is a function of the random and discrete decay of radioactive atoms and is measured through scintillating detectors as outlined by Hoppie et al. (1994). During Leg 190, NGR was measured for 20 s for each 20-cm length of core unless noted otherwise. NGR calibration was performed at the beginning of the leg, and sample standards were measured at the end of every site.
Unconsolidated sediment and rock samples were measured for thermal conductivity in the shipboard laboratory using the TK04 system described by Blum (1997). This system employs a single-needle probe (von Herzen and Maxwell, 1959) heated continuously, in "full-space configuration" for soft sediments and in "half-space configuration" for lithified sediments. Under conditions of moderate to full recovery, thermal conductivity measurements were conducted at a frequency of two per core.
Thermal conductivity was measured on unsplit-core unconsolidated sediment sections using a full-space single-needle probe TeKa (Berlin) TK04 unit. A hole was drilled in the outer core liner, and the 2-mm-diameter temperature probe was inserted into the working half of the core section. For lithified samples, a smooth surface was prepared on ~5-cm-long split-core specimens that had been placed in a water bath for a minimum of 15 min. The half-space needle probe was secured onto the flat surface of the half core. At the beginning of each half- and full-space measurement, temperatures in the samples were monitored automatically, without applying a heater current, until the background thermal drift was determined to be <0.04°C/min. The heater circuit was then closed and the temperature increase in the probe was recorded.
The reported thermal conductivity measurement for each sample is the average of three and four repeated measurements for the full- and half-space methods, respectively. Data are reported in W/(m·°C) with a stated error of ~5%. The choice of measurement interval and assessment of thermal stability are automatic with the TK04 meter, which does not require shipboard calibration.
Moisture and density (MAD) measurements were determined by measuring wet mass, dry mass, and dry volume of specimens from split cores. Samples were collected at a frequency of two per section. Where a whole-round sample was taken from a section, one of the two MAD samples was taken adjacent to it. Care was taken to sample undisturbed parts of the core and to avoid drilling slurry.
Immediately after the samples were collected, wet sediment mass (Mwet) was measured. Dry sediment mass (Mdry) and dry sediment volume (Vdry) were determined after the samples had dried in a convection oven for 24 hr at a temperature of 105° ± 5°C. Wet and dry masses were determined using electronic balances, which compensated for the ship's motion, and dry volume was measured using a gas pycnometer.
Moisture content, grain density, bulk density, and porosity were calculated from the measured wet mass, dry mass, and dry volume as described by Blum (1997). Corrections were made for the mass and volume of evaporated seawater using a seawater density of 1.024 g/cm3 and a salt density of 2.20 g/cm3.
The method chosen for P-wave velocity measurements (VP) was dependent on the degree of sediment consolidation. For unconsolidated sediments, the P-wave sensors 1 and 2 (PWS1 and PWS2) insertion probe system was used to measure the transverse and longitudinal (i.e., along the core axis) P-wave velocity. In semilithified sediments, only the modified Hamilton frame velocimeter (PWS3) contact probe system, described by Boyce (1976), could be employed. Where sediments were sufficiently indurated for cutting with a saw, velocity measurements were made on ~8-cm3 oriented cubes. If core recovery permitted, two to three velocity measurements were conducted per core.
The PWS1 and PWS2 probe system calculates P-wave velocity based on a fixed distance and measured traveltime. Anisotropy was calculated by the following equation:
where VPt is the transverse P-wave velocity and VPl is the longitudinal velocity. The velocity meter was calibrated by measuring VP in water.
In addition to traveltime, the PWS3 system measures sample thickness with a digital micrometer. Measurements were generally taken two to three times per core, with more measurements taken in sections characterized by varying lithology. In cores that were too consolidated for the PWS1 and PWS2 insertion probes but too soft or friable to cut into cubes, the PWS3 system was used to measure P-wave velocity in the x-direction. In hard rock, cubes were oriented, cut, and then rotated so that the PWS3 system could measure velocities in the x-, y-, and z-directions.
Electrical conductivity was measured with two different methods, both using the Wayne-Kerr component analyzer in the 10-KHz to 30-kHz range. With samples saturated with saline pore water, polarization effects are minimal in this frequency range, and the measured conductivity is largely independent of frequency. In soft sediment cores (APC cores), a Wenner needle array was used. Four electrodes 1 cm long and spaced ~1 cm apart were inserted into the working half. The two outer electrodes inject an alternating current while the two inner electrodes measure the resulting potential difference. The apparent resistance (R) is inversely proportional to the conductivity of the medium. Calibration was performed after each measurement by immersion of the electrode array in seawater. The conductivity of seawater (cw) as a function of temperature is computed from the formula
The formation factor is then
This definition of the formation factor does not take into account surface conductivity effects but is convenient for correction of temperature effects and for comparison with porosity data. Ambient temperature ranged from 23° to 28°C, and the temperature difference between core temperature and calibration temperature was usually <2°C. Measurements were performed both along and across the core axis and often yielded an anisotropy of a few percent. This anisotropy may be caused at least in part by cracking perpendicular to the core axis and was not reported on the graph. When the cores were lithified enough to cut cubic samples, cubes were placed between two stainless steel electrodes, and impedance, which is a complex number, was measured with the Wayne-Kerr component analyzer. To assure good contact between sample and electrodes, filter papers were thoroughly soaked in seawater and care was taken to avoid trapped gas bubbles and to remove excess water dripping on the sides of the sample. Residual contact impedance was obtained from measurements of two seawater-saturated filter papers with no sample.
For correction, the contact impedance was subtracted from the impedance measured on samples. The nonreal part of the complex impedance was small and was generally accounted for by the contact impedance. Sample conductivity (c11) was computed from the three dimensions of the cube (L1 = length between the electrodes, and L2 and L3 = lengths in the other directions) and from the real impedance (R) as
Sample dimensions were obtained with the PWS3 system during P-wave velocity measurements. Measurements in all three directions (cxx, cyy, and czz) were performed when possible. Horizontal and vertical electrical conductivity anisotropy are defined as for the P-wave velocity anisotropy:
Anisotropyh (%) = 200 (cxx - cyy)/(cxx + cyy), and
The formation factor in each direction is computed as
where cw varies with temperature as described above.
Undrained shear strength (Su) was measured using a motorized miniature vane shear apparatus that was inserted into soft sediment and rotated until the sediment failed, following the ASTM D4648-87 procedure (ASTM, 1989). The difference in rotational strain between the top and bottom of the vane shear spring was measured digitally, and the peak shear strength was recorded. Shear strength measurements by this apparatus are reliable to a threshold of 100-150 kPa.
