Physical properties in Hole 1223A were measured on whole cores, split cores, and discrete samples. The MST was used to perform nondestructive measurements of bulk density (GRA bulk density), magnetic susceptibility, compressional wave velocity (as measured by the P-wave logger [PWL] mounted on the MST), and NGR on whole cores. GRA bulk density and magnetic susceptibility were measured every 2.5 cm. Discrete sample measurements were conducted on sediments and hard rock cores. Compressional wave velocity was measured on split cores using the PWS3 contact probe system in the x-direction for soft sediments and in the x-, y-, and z-directions for hard rock cubes. Moisture and density, such as bulk density, water content, porosity, and grain density, were measured on discrete samples. Thermal conductivity was measured on whole cores for soft sediments and on discrete samples for hard rock cores.
Lithologic Units 1 and 2 (0 to ~7 mbsf), which are clay and turbidite layers, show a rapid increase of GRA bulk density, ~1.2 to ~2.0 g/cm3 with increasing depth (Fig. F76A). Unit 4 (between ~8 and ~11 mbsf) corresponds to a black sand layer. The bulk densities for this layer also show a rapid increase from ~2.0 to ~2.2 g/cm3 with increasing depth. Unit 5, a crystal vitric tuff, is one of the key horizons in addressing the generation of the section. The bulk densities of Unit 5 (13-15 mbsf) show a gradual increase from ~1.7 to ~2.0 g/cm3. In Units 8 through 10, bulk densities are scattered around 1.8 ± 0.2 g/cm3, suggesting some heterogeneity. Subunit 11B (between 33 and 37 mbsf) is a palagonitized crystal vitric tuff horizon giving fairly constant bulk densities of ~1.9 g/cm3. Bulk densities for Units 13 and 14 (~37 and 38.7 mbsf) show sudden changes from ~1.3 to ~1.9 g/cm3, corresponding to silty claystone and clayey siltstone, respectively.
Magnetic susceptibilities scatter between ~100 and 600 at depths shallower than ~11 mbsf (Fig. F76B) (all susceptibilities reported here are in raw meter units). In Unit 5, which is the crystal vitric tuff layer, they remain approximately constant at 400-500. In Unit 8, the values rapidly increase from ~170 to 400. In Unit 10 (~23-25 mbsf), the values decrease from ~600 to 300. In Subunit 11B, the palagonitized crystal vitric tuff (~33-37 mbsf) has fairly constant susceptibility values of 300-400. Units 12 and 13 show similar trends as seen in the GRA bulk densities.
Corrected NGR measurements show a quite simple pattern. Unit 1 (0-5 mbsf) shows a rapid decrease from ~15 to a few counts per second (cps) (Fig. F76C). The rest of the units have quite low values that range between 0 and 4 cps.
Five measurements of thermal conductivity were made (Fig. F77; Table T17). In the sedimentary sections shallower than ~12 mbsf (Units 1-4), the two measurements are fairly constant at ~0.8 W/(m·K) (Fig. F77; Table T17). In Units 5 and 10, the values are also similar ~1.0 W/(m·K). Subunit 11B is ~1.2 W/(m·K).
In Hole 1223A, the upper and lower parts of the cored section contain volcanic turbidites and crystal vitric tuffs, respectively. The PWS velocities and bulk densities show similar tendencies to the PWL velocities and GRA bulk densities, respectively. Individual physical property measurements, however, give more precise values in hard rocks, and insight into the microstructure of the cores is provided by the anisotropy of compressional wave velocities.
In general, bulk densities show similar or higher values than dry densities (Fig. F78; Table T18). Grain densities always give higher values than bulk densities. Porosities at this site vary gradually from 80% to 30%, but the porosities for hard volcanic rocks are unusually high. GRA bulk densities match quite well with bulk densities obtained by individual measurements using cubic samples, except for Unit 5, which corresponds to the crystal vitric tuff.
Above 5 mbsf in Unit 1, bulk densities, dry densities, and porosities remain constant at ~1.3 g/cm3, ~0.4 g/cm3, and ~83%, respectively (Fig. F78). In Unit 5, which is the crystal vitric tuff, bulk densities, dry densities, and porosities are ~2.2 g/cm3, ~1.9 g/cm3, and ~35%, respectively, based on three samples. Grain densities range from ~3 to ~2.8 g/cm3. Note that the bulk densities of Unit 5 give significantly larger values (~2.2 g/cm3) than GRA bulk densities (<1.9 g/cm3) (Fig. F79). The reason for this is not well understood. In Units 8 and 10, bulk densities for three samples and dry densities range from 1.6 to 1.95 g/cm3 and from 0.9 to 1.5 g/cm3, respectively. The porosities range from 66% to 47%. Grain densities, however, are constant near ~2.8 g/cm3. In Subunit 11B, which is palagonitized crystal vitric tuff, bulk densities, dry densities, grain densities, and porosities show fairly constant values: ~2.1 g/cm3, ~1.8 g/cm3, ~2.6 g/cm3, and 31%, respectively. The bulk densities and porosities of this vitric tuff have values similar to the crystal vitric tuff in Unit 5. In the deepest horizon, Units 12 to 14, bulk densities and dry densities increase with depth from ~1.6 to ~1.7 g/cm3 and ~1.0 to ~1.2 g/cm3 and porosities decrease from 60% to 50%.
Compressional wave velocities were measured by the MST PWL on whole APC cores and by the PWS on both split-core sections and discrete samples. PWL velocities above 5 mbsf in Unit 1 stay fairly constant at ~1500 m/s (Fig. F80; Table T19). The PWS velocities for this depth range show slightly higher values than PWL velocities. Between 5 and 7 mbsf, the PWL and PWS velocities increase with depth. The values range between 1600 and 1700 m/s. Between 7 and 11 mbsf, only PWL velocities were measured, with values of ~1650 m/s. In Unit 5, the crystal vitric tuff, PWS velocity values are between 3300 and 3400 m/s. Units 8-10 (22 -25 mbsf), which correspond to three different claystones, show quite different velocities ranging from 1900 to 3200 m/s. This suggests a rapid change of petrologic properties among claystones. The velocities for the palagonitized crystal vitric tuff in Subunit 11B are ~4000 m/s and are substantially higher than those for the crystal vitric tuff in Unit 5. This suggests less consolidation in Unit 5 than in Unit 11. PWS velocities in the deepest layer, below 37 mbsf, have values between ~2100 and ~2400 m/s.
Figure F81 compares PWS velocity with bulk density and PWS velocity with porosity. There is a general increase of compressional velocity with increasing bulk density except for the crystal vitric tuff in Unit 5. The crystal vitric tuff in Unit 5 shows very different characteristics from the general trend of the PWS vs. bulk density relation. In contrast, the porosities for this crystal vitric tuff are not drastically different from the general trend of PWS velocity vs. porosity. Visual inspection of the texture of the crystal vitric tuff indicates loosely coupled grains. During the PWS velocity measurements, two samples crumbled to black sand similar to unconsolidated black sand of Unit 4. This occurred after the samples were dried by heating to 100°C for many hours. In the petrological description, these samples were identified as hard rocks, but the samples crumbled when the clay minerals lost their moisture.
The palagonitized crystal vitric tuff in Subunit 11B (33-37 mbsf) shows high velocities around ~4000 m/s with ~5% anisotropy.