Physical properties were measured on unsplit cores and on undisturbed portions of split cores. The MST was used on whole cores for nondestructive measurements of wet bulk density, compressional wave velocity, MS, and natural gamma radiation. Thermal conductivity measurements were made only on unconsolidated whole cores with the exception of Site 1129, where data were collected on consolidated split cores. Undrained shear strength, index properties, and compressional wave velocity (Vp) were measured at discrete intervals on split cores, usually at a frequency of one per section. Figure F9 shows the sequence of physical properties measurements made during Leg 182, and Table T7 lists the average sampling intervals for each of the physical properties data sets collected.
Physical properties measurements on Leg 182 were used to obtain (1) high-resolution records for hole-to-hole correlation, construction of complete stratigraphic sequences, and downhole log calibration; (2) information related to sediment composition, diagenesis, and consolidation history to help constrain the location of unconformities, sediment fracturing, and fluid migration; and (3) data for the calculation of synthetic seismograms (i.e., compressional wave velocity and bulk density) and for the calculation of local heat flow (i.e., thermal conductivity).
To ensure thermal homogeneity for all physical properties measurements, data were collected after equilibrating the cores to ambient room temperature (20°-25°C). Detailed information on the physical principles underlying the sampling methods discussed here can be found in Blum (1997).
The MST consists of an automated track that moves whole-core sections through sensors measuring MS, GRA bulk density, P-wave velocity, and natural gamma radiation (NGR). Whole-round sections designated for shipboard geochemical analyses were removed before scanning.
MS, GRA, and NGR were measured on all cores regardless of collection method (i.e., APC, XCB, and RCB). P-wave velocities were measured only on APC-cored intervals because of the likelihood of discontinuous core, core disturbance, and/or a loss of coupling between the liner and the core with XCB and RCB drilling.
P-wave velocity (Vp) was measured at 4-cm intervals (4-s period) using a 500-kHz compressional wave pulse at a repetition rate of 1 kHz. The transmitting and receiving transducers are horizontally aligned perpendicular to the core axis. A pair of displacement transducers monitors the separation between the compressional wave transducers. Sediments must completely fill the liner for the P-wave logger to provide accurate results.
Magnetic susceptibility was measured using a Bartington Model MS-2 meter with an 80-mm internal diameter sensor loop (88-mm coil diameter), operating at a frequency of 565 Hz and an AF of 80 A/m (0.1 mT) with the sensitivity range set to 1.0 Hz. The sampling interval was 8 cm with a period of 10 s. The long sampling period ensured acceptable readings for the usually low MS of carbonate sediments. The MS-2 meter measures relative susceptibilities, which need to be corrected for volume variations. For core (d) and coil (D) diameters of 66 and 88 mm, respectively, the corresponding correction factor for d/D is 1.48 (Blum, 1997, p. 38). During data reduction the relative susceptibility is converted to the volume-normalized MS by multiplying by 1/(1.48 × 105) or by 0.68 × 10-5 (SI units). Some difficulties occurred when measuring MS on sediments with low susceptibility. In these sediments a trend was seen in which the sediments would appear to have elevated values at the beginning and end of individual sections. Although the problem was not solved, it seems to be related to standardization and data manipulation in the MST software.
NGR is a product of the decay of radioactive atoms, predominantly U, Th, and K. NGR was measured using four scintillation detectors arranged 90° to each other and perpendicular to the core (as outlined by Hoppie et al., 1994). On Leg 182 NGR was measured every 16 cm for a 26-s period. NGR calibration was performed at the beginning of the leg and standards were measured at the end of every site. For the interval at the top of the hole in which pipe remained during downhole logging, the data were used to complete and correct for the attenuation of the gamma-ray wireline log collected through pipe. In open-hole logging sections, the core data were used to calibrate the wireline log.
GRA was used to estimate sediment bulk density. This measurement is based on the principle that the attenuation, mainly by Compton scattering, of a collimated beam of gamma rays (produced by a 137Ce source) passing through a known volume of sediment is related to material density (Boyce, 1976). During Leg 182 the measurement interval was set at 4 cm (4-s period). For each site, GRA and discrete sample bulk densities were compared for repeatability.
Thermal conductivity during Leg 182 was measured using the needle-probe technique with the TK04 system as described by Blum (1997). For whole cores the probe was inserted through an aperture drilled in the core liner mid-depth in the section. After insertion, the probe was heated at 3 or 4 W/m and the temperature rise monitored. The optimal integration time for each conductivity measurement is calculated by an algorithm in the TK04 system for time units of 40-300 s and an evaluation time of 240 s. Thermal conductivity was reported in units of watts per meter degrees centigrade (W/m°C) with an accuracy of 5% and a precision of 2%. Data were collected once per core (usually Section 3), increasing to three per core (Sections 1, 3, and 5) when in situ Adara and Davis-Villinger temperature probe (DVTP) measurements were made. For split cores at Site 1129, thermal conductivity measurements samples were first smoothed with emery paper; then the half-space needle cell was tightly secured to the flat surface of the core with Velcro. The sample was then placed in a water bath. Determinations were made using the TK04 system in half-space mode. Heating power was either 2 or 3 W/m for a period of 80 s. Three replicate determinations were made for each sample.
Moisture and density (MAD) measurements (water content, wet and dry bulk density, and grain density) were routinely measured using ~10-cm3 samples from split cores. Porosity and void ratio were calculated from phase-relation equations. Samples for MAD measurements were collected at a frequency of one per section, taking care to sample undisturbed parts of the core and avoid drilling slurry. Sampling frequency was increased as needed to characterize all significant lithologies.
Immediately after samples were collected, wet sediment mass (Mt) was measured. Samples were then placed in a convection oven for 24 hr at a temperature of 105°± 5°C. After drying, dry sediment mass (Md) and dry sediment volume (Vd) were measured. Sample mass was determined on board ship to a precision of ±0.01 g using two Scientech 202 electronic balances to compensate for the ship's motion. Volumes were determined using a helium Quantachrome Penta-Pycnometer with an approximate precision of ±0.02 cm3. The determination of water content followed the methods of the American Society for Testing and Materials (ASTM) designation (D) 2216 (ASTM, 1989). The recommended equation for the water content calculation, which is the ratio of the pore fluid mass to the dry sediment mass (% dry wt), is as follows:
where Wc is water content reported as a decimal ratio of % dry weight and r is salinity.
Wet bulk density (p) is the density of the total sample including pore fluid. In high-porosity sediment, bulk density was calculated using the following:
where Vt is the total sample volume (10 cm3).
Porosity (ø) was calculated using the equation
where pw is the density of the pore fluid (assuming a salinity of 35).
The grain density (pgrain) was calculated from dry mass and dry volume. Both values were corrected for salt using the equation
where s is salt correction and psalt is the density of salt (2.257 g/cm3, assuming a salinity of 35).
Dry density (pd) is the ratio of Md to Vt, and is used for calculations of mass accumulation. Dry density was calculated using the equation
During Leg 182 GRA densiometry measurements on unconsolidated sediments were commonly higher than discrete density measurements. In addition, GRA density in low-porosity sediments was usually lower, as much as 5%, than discrete density measurements. Three explanations for these differences have been proposed (Shipboard Scientific Party, 1997): (1) the MST software does not include a correction for the attenuation effect in high-porosity sediments (Boyce, 1976; Lloyd and Moran, 1992); (2) air trapped in the sediment-filled beakers (unconsolidated sediments) reduces the relative saturated weight and increases the relative volume measured in the pycnometer, thereby decreasing the resulting bulk density; and (3) low-porosity sediments which are semilithified to lithified have a smaller core diameter, and subsequently a relatively smaller attenuating volume than the calibrated volume, which results in a lower calculated density. To solve the first problem, GRA densities were corrected using the Boyce (1976) equation:
where p is corrected density, pbc is GRA density, pfc is fluid density calculated from gamma counts (1.128 g/cm3), pg is the true grain density of quartz (2.65 g/cm3), pf is the true fluid density (1.024 g/cm3), and pgc is grain density calculated from gamma counts (2.65 g/cm3). It is unclear how to improve the accuracy of the index properties procedure. Therefore, it is assumed that discrete measurements are more accurate, whereas GRA density gives a reliable high-resolution relative density trend.
Beginning with Site 1129,
problems were encountered with the pycnometer used for volume measurements. The
instrument showed a drift in the volume calibration of individual cells that
limited the precision achievable, and duplicate analyses for actual samples
showed differences of as much as 10% (e.g., for beaker 547, three determinations
gave volumes of 11.39, 12.27, and 11.65 cm3). Calculated grain
densities were also very much lower than would be expected for carbonate
sediments (average 2.0 ± 0.15 g/cm3; expected density 
2.8). The cause of this problem is not known, although it may have arisen from
an error in calibration of the pycnometer reference cell, or some other
malfunction. Index properties measurements at Sites 1129, 1130, 1131, and 1132
(Hole 1132D only) were also affected (see "Physical Properties" in
relevant site chapters).
The choice of method and sampling frequency of discrete compressional wave velocity measurements (Vp) was dependent on the degree of consolidation of the sediments.
1. Unconsolidated sediments: Vp was measured using two pairs of perpendicularly oriented digital sound velocimeters (PWS). One pair is aligned vertical to bedding (PWS1; z-direction) and the other is aligned horizontally (PWS2; y-direction) to determine sediment anisotropy. The transducer pairs have a fixed spacing of 7 cm (vertical) and 3.5 cm (horizontal) and were inserted into the split cores of soft sediment. An acoustic signal of 500 kHz was emitted and received by the two transducers. This signal was then digitized by an oscilloscope so that the first-arrival waveform could be manually picked and velocity calculated. Anisotropy could then be determined by the difference between the horizontal and vertical velocity using the following:
where Vpt is the transverse compressional wave velocity and Vpl, the longitudinal velocity. The velocity meter was calibrated by measuring Vp in distilled water. In unconsolidated sediments, at least two P-wave velocity measurements per section were made using either or both PWS1 and PWS2.
Vp in unconsolidated sediments was also measured through the split core (PWS3; x-direction) using vertically oriented transducer pairs (500 kHz), with the upper transducer pressed against the split surface and the lower pressed against the core liner. These data were recorded, digitized, and transferred to a computer as for PWS1 and -2. Core thickness was measured using a digital caliper that was directly mounted on the transducer pair. Zero traveltimes for the velocity transducers were measured using a series of polycarbonate standards of known length. The axial pressure applied between sample and transducer was monitored by a pressure cell. To improve the coupling between transducer and sample, distilled water was applied to the transducer head. Measurements were corrected for the additional traveltime passing through the core liner. In unconsolidated sediments two PWS3 measurements were made per section.
2. Semilithified and consolidated sediments: If sediments were too hard for the PWS1 and -2 transducers to be inserted, only PWS3 data were collected at a frequency of four or more per section.
During the measurements for Site 1127, the pressure cell of PWS3 ceased to operate. No replacement pressure cell was available; thus, an alternate apparatus was constructed that consisted of a pneumatic platform that raised the lower PWS3 transducer a predetermined distance to press the sediment surface against the upper PWS3 transducer. Because there was no way to ensure that the pressure was constant between the transducers and the split core for different samples, pressure differences were minimized by lowering the upper transducer until it made initial contact with the core surface, at which time the lower cell was raised. Despite careful attention to consistency of measurement, there are likely to be slight pressure differences between samples that would result in greater than normal errors in P-wave velocity. Thus, the data from Site 1126 may not be directly comparable to those of subsequent Leg 182 sites. As the new apparatus was being constructed only limited PWS3 measurements could be made at Site 1127, which resulted in a minimal PWS3 data set at this site.
The peak undrained and residual shear strength of unconsolidated sediment was measured at an interval of one per section using a Wykeham Farrance motorized vane shear apparatus following the procedures of Boyce (1977). The vane rotation rate was set to 90° per min, and the vane used for all measurements had a 1:1 blade ratio with a dimension of 1.28 cm. This instrument measures the torque and strain at the vane shaft using a torque transducer and potentiometer, respectively. Output for torque and strain were recorded on a Hewlett-Packard X-Y recorder in volts. The shear strength reported was the peak strength determined from the torque vs. strain plot.
In the interpretation of shear vane measurements, a cylinder of sediment is assumed to be uniformly sheared around the axis of the vane in an undrained condition, with cohesion as the principal contributor to shear strength. Departures from this assumption include progressive cracking within and outside of the failing specimen, uplift of the failing core cylinder, drainage of local pore pressures, and stick-slip behavior.
In situ temperature measurements were made either using an Adara or DVTP temperature tool. The Adara tool fits directly into the coring shoe of the APC and consists of a battery pack, data logger, and a platinum resistance-temperature device calibrated over a temperature range from 0° to 30°C. Before entering the borehole, the tool was first briefly stopped at the mudline to thermally equilibrate with bottom water. After the APC penetrated the sediment, it was held in place for 10 min as the Adara instrument recorded the temperature of the cutting shoe every 5 s. Initially, there was an instantaneous temperature rise from frictional heating caused by APC penetration. This heat gradually dissipated into the surrounding sediments, and the equilibrium temperature of the sediments was then estimated by applying a mathematical heat-conduction model to the temperature decay record (Horai and Von Herzen, 1985). Additional information on the Adara tool can be found in previous Initial Reports volumes (Shipboard Scientific Party, 1992, 1994).
The DVTP tool is used in semilithified sediments in which the APC cannot penetrate and, unlike the Adara, the DVTP requires a separate wireline run. This tool measures formation temperature using a probe that is pushed into the top of the sediment section. The probe is conical with two thermistors, one located 1 cm from the tip of the probe and the other 12 cm above the tip. A third thermistor, referred to as the internal thermistor, is located in the electronics package. Thermistor sensitivity is 1 mK in an operating range from -5° to 20°C, and the total operating range is -5° to 100°C. The thermistors were calibrated at the factory and on the laboratory bench before installation in the probe. In addition to the thermistors, the probe contains an accelerometer sensitive to 0.98 m/s2. Both peak and mean acceleration are recorded by the logger. The accelerometer data are used to track disturbances to the instrument package during the equilibration interval.
In a DVTP deployment, mudline temperatures are measured for 10 min on the first run within each hole and 2 min for subsequent runs before descent into the hole for a 10-min equilibration interval in the bottom. Mudline temperatures are also collected for at least 2 min on ascent. Data from the probe tip thermistor were used for estimation of in situ temperatures.
For shallow-water sites a longer mudline stop was required to ensure that the temperature tools had sufficient time to equilibrate to bottom-water temperatures. At deeper sites this time was reduced as the tools are able to thermally equilibrate during descent through deeper waters with very low thermal gradients. This problem is less serious with the DVTP because it has a lower heat capacity and a thermal time constant that is less than the Adara temperature shoe.
Data reduction procedures are similar for both temperature tools. The synthetic thermal decay curves for the Adara tool and DVTP are a function of the geometry and thermal properties of the probe and the sediments (Bullard, 1954; Horai and von Herzen, 1985). However, it is never possible to obtain a perfect match between the synthetic curves and the data because (1) the probe never reaches thermal equilibrium during the penetration period; (2) contrary to theory, the frictional pulse upon insertion is never instantaneous; and (3) temperature data are sampled at discrete intervals, meaning that the exact time of penetration is always uncertain. Thus, both the effective penetration time and equilibrium temperature must be estimated by applying a fitting procedure, which involves shifting the synthetic curves in time to obtain a match with the recorded data. The data collected >20-50 s after penetration usually provide a reliable estimate of equilibrium temperature. However, where the APC has not achieved a full stroke, leakage of drilling fluid into the formation may occur and results are not considered reliable.
