The objective of the physical properties program at Site 1203 was to assist in interpretation of lithologic variations and correlation with downhole geophysical logs. All cores were run through the multisensor track (MST), which included magnetic susceptibility and gamma ray attenuation (GRA) bulk density measurements for sediment Cores 197-1203A-1R to 17R and natural gamma radiation (NGR) measurements for all cores. Compressional wave velocities were determined from the split cores in the transverse (x-direction) for the soft sediment cores (Cores 197-1203A-1R to Section 17R-3) and for discrete samples of basalt and volcaniclastic sediment without the core liner. Index properties determinations for both sediment and discrete basalt samples included bulk density, moisture content, porosity, and grain density. These were calculated from wet and dry sample masses and dry volumes. Thermal conductivity was also determined for both sediment and basalt samples at a frequency of one per core.
Magnetic susceptibility was determined on Cores 197-1203A-1R through Section 17R-3 at 5-cm intervals (see "Physical Properties" in the "Explanatory Notes" chapter). Values typically ranged between -1 x 10-6 and 100 x 10-6 SI through most of the sedimentary column (300-440 mbsf), but higher values (between ~20 x 10-6 and 1800 x 10-6 SI) were observed in Unit III in the bottom ~15 m (Table T11; Fig. F72A).
Bulk density was measured by the GRA densitometer every 5 cm on whole sections of Cores 197-1203A-1R through Section 17R-3 (see "Physical Properties" in the "Explanatory Notes" chapter), providing a semicontinuous record; discontinuities in the data correspond to regions of reduced core recovery (Table T12; Fig. F72B). The GRA density data offer the potential for direct correlation with downhole bulk density of discrete samples (Fig. F73) and can also be compared with the downhole logging data. Overall, GRA bulk densities show a slight increase downhole through the sediment, from ~1.5 g/cm3 at 300 mbsf to ~ 1.7 g/cm3 at 400 mbsf and ~ 2.3 g/cm3 at the base of the sediment at ~458 mbsf. There appear to be small-scale variations of density with depth (e.g., a peak of ~1.8 g/cm3 at ~324 mbsf followed by a trough of ~1.5 g/cm3 at ~330 mbsf), which are especially pronounced in the upper part of the sediment column. However, there are also considerable nonsystematic variations of ~0.5 g/cm3 between the highest and lowest values at any given depth, making it difficult to draw conclusions about density variations on short spatial scales. A number of sample points show very low GRA bulk densities (<1 g/cm3); these probably represent void spaces or drilling disturbed areas of the core.
NGR was measured every 10 cm on both sediment and basalt cores in Hole 1203A. Total counts are reported here because the corrected counts (which are less by ~16 counts per second [cps]) include negative values, which are physically unreasonable. Data were generally acquired on unsplit sections; however, Cores 197-1203A-24R, 28R, and 33R were split before NGR data were measured, so measurements were taken on the split-half sections.
Gamma ray values are fairly constant in the upper 450 m of the core (Table T13; Fig. F72C), with most values between ~14 and 21 cps; an exception is a positive peak of 28 cps at ~388 mbsf in Subunit IA. The NGR count increases slightly at ~448 mbsf in sedimentary Unit III; this may be due to greater amounts of iron-rich clays in this unit (see "Lithostratigraphy").
For basement rocks (below ~458 mbsf), somewhat higher gamma ray values were measured (Table T13; Fig. F74A). For basalt, measurements generally ranged between ~15 and 25 cps in the depth range 457-690 mbsf and between ~20 and 30 cps in the depth range 690-910 mbsf. Particularly high NGR counts were measured for some of the volcaniclastic units (e.g., ~25-50 cps for basement Units 7, 10, 17, and 28 at ~550, 590, 645, and 867 mbsf, respectively) (see "Physical Volcanology and Igneous Petrology"). A particularly large peak of ~65 cps is seen at ~640-652 mbsf in basement Unit 27, a volcaniclastic sandstone.
All whole-core pieces that could be successfully rotated through 360° were imaged on the Deutsche Montan Technologie (DMT) digital color CoreScan system. Contiguous pieces were imaged together where possible. Pieces too small or uneven to be scanned effectively were also measured, to allow for them in the total core barrel lengths.
In total, >200 m of whole core was scanned using this method. This accounts for ~60% of the material recovered from Hole 1203A. The size and quality of the images varies greatly throughout the core, corresponding closely to core recovery. An example of the core images acquired is shown in Figure F75.
Thermal conductivity was determined at a frequency of one per core for both sediment and basalt from Hole 1203A (Fig. F76; Table T14). In the sedimentary section (Cores 197-1203A-1R through Section 17R-3), thermal conductivity values average ~0.9 W/(m·K), with most values between 0.7 and 1.1 W/(m·K) (Fig. F76A). Values tend to increase with depth; a smooth curve drawn through the data points suggests an increase from ~ 0.7 W/(m·K) at 300 mbsf to 1.1 W/(m·K) at 450 mbsf.
The volcanic basement units generally exhibit higher thermal conductivity values (Fig. F76B). Values for basalt and volcanic breccia generally range between 1.3 and 1.7 W/(m·K) (mean = ~1.5 W/[m·K]). A large positive peak of 2.7 W/(m·K) occurs in basement Unit 11 (see "Physical Volcanology and Igneous Petrology"), which is an olivine-plagioclase-phyric basalt. Values for other basement units range between 0.9 and 1.3 W/(m·K) (mean = ~1.0 W/[m·K]).
The index properties of Hole 1203A were determined with a pycnometer and a Scientech balance. Values of wet mass, dry mass, and dry volume of discrete samples were measured and used to calculate moisture content, bulk density, grain density, and porosity (Table T15; Figs. F73, F74).
In the sedimentary units of Hole 1203A, bulk density shows an overall slight increase with depth, from 1.47 g/cm3 at 300 mbsf to 2.18 g/cm3 at 457 mbsf. At most depths bulk density corresponds well to the GRA density measured on the MST (Fig. F73A, F73B) but tends to be slightly lower (on the order of 10%). Grain density varies very little downhole in the sediment and has a mean value of 2.51 g/cm3. Three samples, at ~320, 372, and 447 mbsf, show considerably lower grain density (<1.00 g/cm3), which does not appear to correlate to any particular lithologic changes. At ~323 mbsf a small positive peak occurs in all three density measurements; this probably represents sampling of a small pyrite nodule located in the sediment at this depth.
In the basement (Fig. F74), the basaltic units correspond to higher bulk density and lower porosity than volcaniclastic sediment. For the basaltic units, bulk density ranges from 2.37 to 2.83 g/cm3 (mean = ~2.6 g/cm3) and porosity ranges from 7% to 26%. Porosity of basalt tends to be higher at greater depth. For the volcaniclastic sediment, bulk density ranges from 1.52 to 2.38 g/cm3 (with the exception of one outlier discussed below) (mean = ~1.9 g/cm3) and tends to slightly increase with depth. Porosity ranges from 19% to 70%, but porosities of >54% only occur in the volcaniclastic siltstone and sandstone units.
Downhole grain density values for the basement units vary little, with a mean of ~ 2.9 g/cm3 (Fig. F74C). At a depth of 626.08 mbsf (basement Unit 15), one sample yields a grain density of 0.51 g/cm3; this unit comprises resedimented and laminated volcanic claystones and sandstones. However, this grain density value is questionable because it is considerably lower than the density values recorded in the overlying soft sediment.
At Site 1203, compressional wave velocity was determined from both split-core sections (Cores 197-1203A-1R through Section 17R-3) and discrete sample measurements. P-wave velocity was measured in the x-, y-, and z-directions using the PWS3 tool (see "Physical Properties" in the "Explanatory Notes" chapter). P-wave velocity was measured only in the x-direction in sediment cores and ranged from 1515 to nearly 1800 m/s (Fig. F77; Table T16).
Paleomagnetic minicore samples of lava and consolidated sediment enabled velocity measurements in the z- and y-, as well as x-directions in hard rock cores. Because of time constraints, y-direction velocity was measured only on Cores 197-1203A-17R through 19R. When possible, hard rock velocity was measured twice per core in the x- and z-directions. The increase in velocity to ~5000 m/s at 462 mbsf coincides with the penetration of submarine basalt flows. Between 489 and 613 mbsf, velocity varies widely from 1770 to nearly 5700 m/s, due to a marine sequence of alternating basalt and volcaniclastic sediment. Subaerially erupted basalt, with velocities >5000 m/s, begin at ~615 mbsf and are interbedded with shallow-marine volcaniclastic rocks. Velocity steadily decreases with depth (<4000 m/s) until ~880 mbsf, where velocity becomes >4000 m/s.
Figure F77 shows that z-direction velocities average ~191 m/s more than x-direction velocities. This apparent anisotropy probably arises from the relatively large amount of water needed to couple the PWS3 transducers with unevenly cut minicores in the x-direction (along the axis of the minicores) to obtain a good signal. Minicore cuts in the z-direction are curved; hence, much less water was needed for z-direction measurements. Consequently, x-direction velocities should be regarded as minimum estimates compared to the more accurate z-direction velocities.