Whole-core measurements taken at Site 900 included magnetic susceptibility, Gamma-Ray Attenuation Porosity Evaluator (GRAPE) bulk density, P-wave logger (PWL) compressional-wave velocity, and thermal conductivity. Discrete velocity measurements were obtained in unlithified sediments using the Digital Sound Velocimeter (DSV) on split cores and within the more consolidated units and hard rock using the Hamilton Frame Velocimeter. Undrained shear strength was measured on split sediment cores, and electrical resistivity was measured on split sediment cores and drilled "minicores" from crystalline rock. Index properties were calculated from the wet and dry masses and wet and dry volumes of samples taken from each section of core.
Index properties were determined using gravimetric methods (Table 14; Fig. 38). Based on the nominal uncertainties of the raw mass and volume measurements, the estimated uncertainties for density and porosity are ±0.02 g/cm3 and ±2%, respectively. The sedimentary section at Site 900 yielded fairly smooth downhole trends in bulk density, grain density, and porosity. Minor offsets of these trends may be attributed to changes in lithology and degree of lithification. Gravimetrically determined bulk density increases nearly linearly from 1.7 g/cm3 at the seafloor to about 2.2 g/cm3 at a depth of 620 mbsf, while porosity decreases from about 65% to 32% (Fig. 38). Minor undulations in the trends were observed near 67, 180, and between 370 and 420 mbsf. The first of these corresponds to the boundary between lithostratigraphic Subunits IA and IB, and an associated downhole decrease in carbonate content (see "Lithostratigraphy" section, this chapter). The second corresponds to the boundary between Subunits IC and IIA, which show little difference in composition.
Below 180 mbsf, the sediments gradually become more lithified without major abrupt changes in bulk density and porosity. Minor changes in the downhole trend may be attributed to variations in the lithification state of the sediment. Below about 620 mbsf, the data exhibit considerable scatter with lower bulk density and higher porosity values. The highest bulk density and lowest porosity measurements (several near 0%) are associated with highly cemented calcareous sandstones interbedded with the silty claystones. Grain densities decrease from about 2.8 g/cm3 near the seafloor to about 2.75 g/cm3 at about 200 mbsf. Grain densities increase gradually between 200 and 420 mbsf, and maintain a relatively uniform value of 2.8 g/cm3 below 420 mbsf.
Index properties below 748.9 mbsf reflect sampling of crystalline basement. Bulk density approaches 3.0 g/cm3 (close to the grain density), and porosity is effectively 0%. Grain density increases sharply downward near the top of the crystalline basement, increasing from 2.8 g/cm3 at 748.9 mbsf to about 3.0 g/cm3 at 796.4 mbsf. This increase can be attributed to the downhole decrease in calcite veining and degree of alteration, with the deeper values reflecting the higher grain densities of the fine-grained metamorphosed gabbro (see "Igneous and Metamorphic Petrology and Geochemistry" section, this chapter).
Bulk densities were also estimated from whole-core GRAPE measurements taken in all sections recovered from Hole 900A (see "Explanatory Notes" chapter, this volume). In the sedimentary section, the curve defined by the maximum GRAPE density measurements best fit the corresponding gravimetrically determined bulk density (Boyce, 1973; Gealy, 1971).
The maximum GRAPE density measurements are indicated by the curve in Figure 38. In the sedimentary section, above approximately 300 mbsf, the GRAPE density estimates increase from 1.75 to 1.9 g/cm3. The bulk density increases more rapidly with depth, from about 1.9 g/cm3 near 300 mbsf to 2.2 g/cm3 at 500 mbsf. The high degree of fracturing observed in the lower sedimentary section results in large scatter in the data below 500 mbsf, but the maximum densities are nearly constant at 2.2 g/cm3. In basement cores, GRAPE bulk density increases from about 2.4 to 2.7 g/cm3 at the base of the hole (796.4 mbsf).
Electrical resistivity was measured at intervals of 0.5 to 0.75 m in split cores from the sedimentary section above 655.5 mbsf (Cores 149-900A-2R to -71R), and in drilled minicores in the more lithified rocks in Cores 149-900A-80R to -86R. Formation factors were calculated for the interval down to 620 mbsf (see "Explanatory Notes" chapter, this volume). In the upper 320 mbsf, the formation factor increase linearly with depth from 2.5 to 7.0, although locally between 200 and 250 mbsf larger scattered values up to 12 were observed (Fig. 38). At 320 mbsf, an abrupt increase from 7 to 10 can be seen. Below this depth, the average formation factor increases downhole to 20 at 620 mbsf.
Electrical resistivity in the basement rocks (Fig. 39) ranges from 50 to 500 Ωm . Values lower than 100 Ωm were observed in altered breccias (748-755 mbsf) and microbreccias (778 and 782 mbsf; see "Igneous and Metamorphic Petrology and Geochemistry" section, this chapter). Electrical resistivity values higher than 100 Ωm generally were observed in microgabbros and strongly correlate inversely with the degree of veining and directly with the degree of metamorphism. The maximum resistivity (500 Ωm at 787 mbsf) was measured in a metamorphosed microgabbro without any veining.
Undrained shear strength was measured in Cores 149-900A-3R to -20R using the shear vane apparatus (see ""Explanatory Notes" chapter, this volume; Fig. 40). Peak shear strength increases downhole from 18 kPa at 12 mbsf to about 205 kPa at 172 mbsf. Between 12 and 80 mbsf, the measured peak strength oscillates between 15 and 45 kPa, showing only a slight net increase with depth. Below 80 mbsf, the measured values exhibit a much wider variation (possibly reflecting different degrees of lithification), but there appears to be a more pronounced trend of increasing peak strength with depth.
Discrete acoustic velocity was measured in Cores 149-900A-3R to -85R (Table 15). The DSV was used on Cores 149-900A-3R to -18R to measure velocity in sediment from depths shallower than 152 mbsf. The Hamilton Frame Velocimeter was used to measure velocities in more cohesive or indurated sediments and basement samples in Cores 149-900A-18R to -85R. The sedimentary samples were trimmed into cubes, and velocity was measured in three mutually orthogonal directions (see "Explanatory Notes" chapter, this volume). Compressional-wave velocity in basement rock was measured in the horizontal direction in minicores. Repeated measurements of selected samples and calibration standards suggest an accuracy of 2% to 3% for the velocity measurements.
Discrete acoustic velocity measurements in the sedimentary section show a general increase with depth, from about 1490 m/s at 10 mbsf to 2400 m/s at 730 mbsf (Fig. 41). Velocity measured in the vertical direction in the clays, silty clays, and claystones shows a linear trend with a slope of 1.06 s-1 and a correlation coefficient of 0.92. The horizontal velocities show similar downhole variations. Acoustic anisotropy in the intervals 180 to 240 mbsf and 340 to 460 mbsf is significantly higher than the estimated 4% uncertainty in the anisotropy calculation and can generally be attributed to slower propagation in the vertical direction (Table 15). Acoustic anisotropy was not calculated for samples from cores below 550 mbsf (Cores 149-900A-62R to -78R) because horizontal fractures developed during sampling, resulting in an artificially slow velocity in the vertical direction. Velocities measured in the horizontal directions in these samples were not affected by the fracturing and are thought to be representative of the true horizontal velocity of the sample. Velocities greater than 3000 m/s in Figure 41 are from cemented siltstone (the sample at about 400 mbsf) or well-indurated silty claystone (the samples below 630 mbsf).
Compressional-wave velocity also was measured with the PWL in unsplit sections from Cores 149-900A-1R to -18R. This corresponds to the interval in which discrete velocity measurements were taken with the DSV. From 0 to 65 mbsf (Cores 140-900A-1R to -9R), the PWL velocities show a trend consistent with the linear increase in velocity with depth observed in the discrete velocity measurements of the clays and claystones (Fig. 42). The clay velocity gradient derived from the DSV measurements provides an upper bound on the PWL velocities below 110 mbsf (Cores 149-900A-14R to -19R). Average PWL velocities measured in cores from depths between 74 and 103 mbsf (Cores 149-900A-10R to -12R) are significantly lower than the discrete velocity measurements.
Acoustic velocities in the basement rocks show wide scatter that ranges from 3750 to 7600 m/s (Table 15). The velocities show some clustering about 5700 m/s (Fig. 43). No systematic variation of velocity with depth was observed in the basement rocks ("Explanatory Notes").
Magnetic susceptibility was measured at intervals of 3 to 5 cm in all cores collected at Site 900. The results are discussed in the "Paleomagnetism" section (this chapter).
Thermal conductivity for Site 900 was measured in every other section of Cores 149-900A-1R to -60R within the sediments and in the basement Cores 149-900A-80R to -85R (Fig. 44; Table 16). The mean uncertainty associated with these measurements was estimated as ±0.2 W/(m·K). In the sedimentary section, the thermal conductivity values show only a slight increase with depth. Between 0 and 115 mbsf, the average thermal conductivity is 1.2 W/(m·K) (Fig. 44; Table 16). In the interval between 115 and 370 mbsf, the mean value is 1.4 W/(m· K) and a slight increase with depth can be observed. The data points show larger scatter around a mean value of 1.5 W/(m· K) from 370 to 563 mbsf, whereas the crystalline rocks exhibit much higher thermal conductivity values that range between 1.7 and 2.9 W/(m· K) in the depth interval from 749 to 794 mbsf.