PHYSICAL PROPERTIES

Introduction

Bulk density (GRA), compressional wave velocity (P-wave velocity), MS, and NGR were measured on whole-core sections using the MST. These closely spaced (generally 2-5 cm) measurements are used to characterize lithologic changes and to correlate cores from multiple holes to construct a continuous stratigraphic section (see "Composite Section"). Thermal conductivity measurements using the needle-probe method were taken on whole-core sections at discrete intervals, particularly within intervals where downhole temperature measurements were performed. Heat flow was determined from four to five borehole temperature measurements as well as thermal conductivity measurements on whole cores. After the core was split, further physical properties measurements were made on the working half. These included compressional wave velocity, moisture and density (MAD), and color reflectance measurements using the Minolta CM-2002 spectrophotometer. Samples for MAD measurements normally were extracted at regularly spaced intervals. However, additional samples were taken in thin lithologic units that would have been missed by regular sampling patterns. A detailed description of most of the techniques used is given in the ODP physical properties handbook (Blum, 1997) and are only summarized here.

Multisensor Track

Whole-core sections were run through the MST after they had equilibrated to the ambient laboratory room temperature (21-25C, as measured at the top of the section). The MST data were sampled at the highest sampling rate possible given the time constraints of coring operations. Generally, a 5-cm sampling interval and 4-s sampling periods were the optimal settings.

The quality of core-logging data and the accuracy of the nominal values are degraded if the core liner is not completely filled and/or the core is disturbed. However, general downhole trends may still be used for core-to-core and core-to-well log correlation.

Magnetic Susceptibility

Magnetic susceptibility was measured using a Bartington meter (model MS2C), which has an 80-mm internal-diameter loop and a low-sensitivity setting of 1.0 Hz. The mean value of the 4-s measurements was stored in the database. Wet volume-normalized SI units were calculated from the sensor readings by multiplication with a factor of 0.68 10-5, where the factor is related to the coil-to-diameter ratio (Blum, 1997). This factor is approximate; the true SI value may differ by a constant offset of up to half an order of magnitude, depending upon sediment diameter (e.g., APC and XCB diameters differ), core liner thickness, and liner deformation. Magnetic susceptibility was the most useful record for core-to-core correlation and composite depth construction.

GRA Bulk Density

Estimates of bulk-sediment density were obtained from GRA measurements. These estimates are based on the comparison of the attenuation of gamma rays through the cores with attenuation through calibration standards. These standards consist of an aluminum rod with different diameters within a water-filled core liner (Blum, 1997). This calibration incorporates the lower Compton scattering in water and a correction for the core liner.

Velocity

The P-wave logger (PWL) on the MST transmits a 500-kHz compressional wave pulse through the core. The transmitting and receiving transducers are aligned perpendicular to the long axis of the core (y-direction). A pair of displacement transducers monitors the distance between the compressional wave transducers. The PWL is the MST device most sensitive to core condition and was the first to be turned off if core condition deteriorated. Data quality was assessed by examining arrival times and amplitudes of the received pulses. Calibration of the displacement transducer and measurement of electronic delay within the PWL circuitry were performed using a series of acrylic blocks of known thickness and P-wave traveltime. The validity of the calibration was checked by measuring the P-wave velocity through a section of liner filled with distilled water. However, because of instrument problems, the PWL records are very noisy and need to be specially processed. This will be done postcruise. The data from the PWL are not further discussed in this report but are available from the ODP JANUS database (see the "Related Leg Data" contents list).

Natural Gamma Radiation

The NGR system records the radioactive decay of 40K, 232Th, and 238U. Although 256-channel spectra were recorded, only the total counts were used for shipboard analysis. The four detectors of the NGR device were tuned using a 232Th source at the beginning of the leg. Thorium and K were used about once per week to assign the appropriate channels to their characteristic emission energies. Background radiation was determined by measuring a water-filled core liner.

Thermal Conductivity

Thermal conductivity is the measure of a material's ability to transmit heat by molecular conduction and is required for geothermal heat-flow determinations. Thermal conductivity of soft sediments was measured using the needle-probe method, in full-space configuration (Von Herzen and Maxwell, 1959; Blum, 1997). At least one measurement per core was made, usually near the middle of the core, after the cores had equilibrated to laboratory temperature (~3-4 hr after recovery). Additional thermal conductivity measurements were made in intervals where downhole temperature measurements had been run. Data are reported in units of W/(mK).

The TK04 (Teka, Berlin) was used for the thermal conductivity measurements. A needle probe (#V00594), containing a heater wire and a calibrated thermistor, was inserted into the sediment through a small hole drilled in the core liner. Three measuring cycles were automatically performed at each location. At the beginning of each cycle, a self-test, which included a drift study, was conducted. Once the samples were equilibrated, the heater circuit was closed, and the temperature rise in the probes was recorded. Thermal conductivities were calculated from the rate of temperature rise while the heater current was flowing. Temperatures measured during the first 150 s of the heating cycle were fitted to an approximate solution of a constantly heated line source (Kristiansen, 1982; see Blum, 1997, for details). Errors are between 5% and 10%. Corrections were not attempted for in situ temperature or pressure effects.

Moisture and Density

Bulk density, grain density, water content, porosity, dry density, and void ratio were calculated from measurements of wet and dry masses and dry volumes. Samples of ~10 cm3 were taken from split cores at sampling intervals of 1.5 m. However, where frequent lithologic changes occurred, denser sampling was done to ensure measurements from all lithologies throughout the core.

Sample mass was determined using a Scientech electronic balance. The sample mass was counterbalanced by a known mass, so that only mass differences of usually <2 g were measured. The balance was also equipped with a computer-averaging system that corrected for ship accelerations. Dry mass was measured from samples oven-dried at 110C 5C for 24 hr and cooled in a desiccator for 2 hr.

Dry volumes were determined using a helium-displacement Quantachrome Penta-Pycnometer. Sample volume measurements were repeated up to three times until the last three measurements had <0.01% standard deviation. A purge time of 3-5 min was used before each run. A reference sphere of known volume was run with each group of four samples during all the measurements. The standard was rotated systematically among cells to check for errors.

Compressional Wave (P-wave) Velocity on Split Cores

In addition to the velocity measurements taken with the PWL on the MST, compressional wave velocity was measured on split-core sections.

For soft sediments, the P-wave velocity was determined with the PWS (P-wave velocity sensor)1 in z-direction and PWS2 in y-direction. Two transducer pairs were inserted manually into the sediment and the traveltime of a sonic signal between the sensors was measured. P-wave velocity is calculated using the measured traveltime and the distance between the transducers. Calibration of the system was performed according to Blum (1997).

An external digital thermometer was used to record core temperature. The values are stored in the database but are not used for shipboard reporting.

The PWS3 contact probe system measured the traveltime of a 500-kHz signal in two modes depending on the sediment consistency. In the split-core mode, the section liner rests on the bottom transducer, and the upper transducer is lowered manually onto the core surface. P-wave velocity is measured parallel to the sediment bedding (x-direction). In the specimen mode (for hard sediments), the oriented sample is placed directly between the transducers in the desired orientation (x-, y-, or z-direction; ODP definitions of directions are illustrated in Blum, 1997). Sample thickness was measured directly by a digital multimeter. Measurement frequency was the same as that used for MAD samples.

Delay times for the velocity transducers were estimated by linear regression of traveltime vs. distance for a series of aluminum and lucite standards. Velocity data recorded in the JANUS database are uncorrected for in situ temperature and pressure (such corrections can be made using relationships in Wyllie et al., 1956).

Only after completion of Site 1145 was it discovered that, because of an operational error, the distance between the transducers had been measured incorrectly. Therefore, PWS3 velocity values are not correct for Sites 1143 and 1145 and can only be regarded with extreme caution. (At Site 1144, no P-wave velocities could be measured because of the core conditions.) The problem was discovered and fixed at Site 1146 and all PWS3 values for Sites 1146, 1147, and 1148 are correct.

Color Reflectance

Quantitative estimates of sediment diffuse spectral reflectance and sediment color were generated by the shipboard sedimentologists using a handheld Minolta CM-2002 spectrophotometer. The new AMST core logger was not usable because of software problems. The archive halves were wrapped in GladWrap plastic film to protect the spectrophotometer opening. The CM-2002 was operated and calibrated according to the Minolta CM-2002 users' manual (Minolta Camera Co., 1991). The Minolta color data are presented in uncorrected form in this volume and are available from the ODP JANUS database (see the "Related Leg Data" contents list).

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