pw),
that typically occur in marine sediments do not affect the calculations
significantly, and standard seawater values at laboratory conditions were used:Shipboard physical properties measurements provide quantitative information about the composition and lithology of core material and may be used to correlate core data with wireline logging data. All physical properties measurements were taken on the cores after allowing them to equilibrate to room temperature (~25°C). Magnetic susceptibility and natural gamma radiation were measured on whole cores with half liners using the MST. After the cores were split, half-space thermal conductivity measurements were taken on the archive halves of the core. Compressional wave velocity was measured on discrete core samples in one direction. Because no soft sediment was obtained, shear strength was not measured, and only the contact probe system was used in velocity measurements. Finally, wet and dry masses and dry volumes were determined, and water content, bulk density, dry density, grain density, porosity, and void ratio were calculated.
The MST has four physical properties sensors—magnetic susceptibility meter (MSM), gamma-ray attenuation (GRA) densitometer, compressional wave logger (PWL), and natural gamma-radiation (NGR) detector. The quality of the measurements is degraded if the core liner is only partially filled or if the core is disturbed. Because this was the case for many of the cores, the GRA densitometer and PWL were not used. However, the remaining tests were completed on all of the cores that were not extensively fragmented, incomplete, or disturbed, because even inaccurate data can be useful in correlating the cores to well log data and understanding rock property trends. Regardless of the inaccuracies, magnetic susceptibility and NGR values are accessible on the Janus database.
Magnetic susceptibility is the degree to which a material can be magnetized in an external magnetic field. It can be used to help detect variations in magnetic properties caused by lithologic changes or alteration. Tests were run at 2-cm intervals using the 1.0-s integration time range on the Bartington meter (model MS2C), which has an 88-mm coil diameter. Most of the cores were composed of small rock fragments that did not fill the core liner completely. Because of the lower-than-ideal volume, values reported in each chapter generally underestimate the magnetic susceptibility. The data were primarily collected to indicate magnetic trends throughout the core as opposed to gathering exact magnetic susceptibility values. To remove the most inaccurate data, a 0.5-cm interval on either side of the rock fragment dividers was not measured.
The NGR measures the discrete decay of 40K, 232Th, and 238U, which are three long-period isotopes that decay at essentially constant rates within measurable time scales. The operation principles of the NGR system are outlined by Hoppie et al. (1994). Natural gamma-ray emissions were measured every 15 cm on the core for a 30-s interval. The NGR system was calibrated in transit against a thorium source, and sample standards were measured at the end of operations for every site. Similar to the MSM measurements, the quality of NGR measurements is compromised because of the incoherent and incomplete nature of the cores. Again, the data primarily serve as an indicator of where natural gamma-ray emissions are present.
Thermal conductivity is the measure of the rate at which heat flows through a material. It is dependent on the composition, porosity, density, and structure of a material. Thermal conductivity was measured through transient heating of the core with a known heating power and a known geometry and recording the change in temperature with time, using the TK04 system described by Blum (1997). Measurements were made in half-space mode (Vacquier, 1985) at an interval of at least one per lithologic unit. The half-space determinations were made by placing a needle probe in a grooved epoxy block with a relatively low conductivity (Sass et al., 1984; Vacquier, 1985) onto a flat surface of the sample. The measurements were conducted in a seawater bath to keep the samples saturated, to improve the thermal contact between the needle and the sample, and to reduce thermal drift. All samples were allowed to equilibrate to the water temperature before tests were run. At the beginning of each measurement, the TK04 system conducts a self test for calibration. If temperature variations during the test are too high, the test aborts. Data are reported in W/(m·K) units. For each thermal conductivity data point reported, the thermal conductivity was measured at least three times and the values were averaged. If variability was large, additional measurements were taken until consistent values were obtained. Only the consistent measurements were used in the averaged value. If no consistent values could be obtained, the data for that sample were discarded. Thermal conductivity measurements made on a standard of known value were conducted periodically during the cruise to test the accuracy of the system. Measurements were always within 0.05 W/(m·K) of the known value, which is smaller than the analytical uncertainty of the instrument (5%; Blum, 1997). Individual thermal conductivity measurements as well as averaged values are accessible on the Janus database.
Discrete compressional wave velocity measurements were made using the contact probe system (PWS3) with a frequency signal of 500 kHz. Measurements were made approximately once per core in one direction. The core was sampled as 2.54-cm minicores drilled perpendicular to the core. No measurements were made for velocity anisotropy. The top and bottom of each minicore were cut to be parallel to each other and then were polished to improve coupling at the transducer/core interface. Distilled water was applied to the top and bottom transducer to improve the coupling as well.
Minicores were sampled from each lithologic unit where possible. When heterogeneity within a lithologic unit was larger than the scale of a minicore (2.54 cm) or when recovered sections were extremely fragmented, rock fragments were taken in one or more places from the unit to obtain a representative sample. When possible, both minicores and rock fragment samples were taken. In rare cases, the recovery of a particular lithologic unit was too small or unsuitable for index properties sampling.
Wet and dry sample masses and dry volumes were measured and used to calculate water content, bulk density, dry density, grain density, porosity, and void ratio. Sample mass was determined using two Scitech electronic balances. The balances were equipped with a computerized averaging system that corrected for ship accelerations. The sample mass was counterbalanced by a known mass such that the mass differentials were generally <1 g. Sample volumes were measured at least three times, or until consistent readings were obtained, using a helium-displacement Quantachrome Penta-Pycnometer. Instrument accuracy is within 0.1% of the measured mass and within 1% of the measured volume (Blum, 1997). A standard reference volume was included with each group of samples during the measurements and rotated among the cells to check for instrument drift and systematic error. Samples were soaked in seawater for 24 hr before determining wet mass. After the 24-hr soaking period, IC measurements of sulfate content in the seawater used for soaking were conducted to measure the amount of dissolution of anhydrite from the minicore samples. In all cases, the amount of mass lost from the sample was insignificant (<0.02% of sample) as compared to the total sample mass. Then samples were oven-dried at 105° ± 5°C for 24 hr and allowed to cool in a desiccator before measuring dry weights and volumes (Method C in Blum, 1997). The following relationships can be computed from the two mass measurements and dry volume measurements (taken from Blum, 1997). When beakers were used, their mass and volume, which are determined periodically and stored in ODP's computer database, were subtracted from the measured total mass and volume. All measured and calculated values are accessible in the Janus database. The directly measured values are
Variations in pore-water
salinity (s), and density (pw),
that typically occur in marine sediments do not affect the calculations
significantly, and standard seawater values at laboratory conditions were used:
pw
= 1.024 g/cm3.
Pore-water mass (Mpw), mass of solids (Ms), and pore-water volume (Vpw) can then be calculated:
pw
= (Mb - Md)/[(1 - s)pw].
Additional parameters required are the mass and volume of salt (Msalt and Vsalt, respectively) to account for the phase change of pore-water salt during drying (It should be kept in mind that for practical purposes the mass of salt is the same in solution and as a precipitate, whereas the volume of salt in solution is negligible.):
salt
= [(Mb - Md) s/(1 - s)]
/salt
,
where the salt density (salt
= 2.20 g/cm3) is a calculated value for average seawater salt.
Moisture content is the pore-water mass expressed either as a percentage of wet bulk mass or as a percentage of the mass of salt-corrected solids:
Calculations of the volume of solids and bulk volume are as follows:
Bulk density (b),
density of solids or grain density (s),
dry density (d),
porosity (P), and void ratio (e) are then calculated according
to the following equations:
b
= Mb/Vb ,
s
= Ms/Vs ,
d
= Ms/Vb ,
