All cores from Section 197-1206A-2R-2 through Core 45R were run through the multisensor track (MST) to measure natural gamma radiation (NGR). Because of the limited amount of sedimentary material recovered, gamma ray attenuation (GRA) bulk density and magnetic susceptibility were only measured on Sections 197-1206A-34R-2 through 36R-2. Index properties (bulk density, grain density, and porosity) and thermal conductivity were determined on one or two discrete samples per core, except for some of the sedimentary units where one sample was collected per section. Compressional wave velocities were measured at a frequency of one or two samples per section.
Volume-normalized magnetic susceptibility was measured at 5-cm intervals on Sections 197-1206A-34R-2 through 36R-2 to assist in interpretation of the lithostratigraphy (Table T12). Magnetic susceptibility values for this section range from 20 x 10-6 to 1480 x 10-6 SI (mean = 605 x 10-6 SI).
Bulk density was measured by the GRA densitometer every 5 cm on Sections 197-1206A-34R-2 through 35R-6 (Table T13). GRA bulk density generally ranges from 0.3 to 2.2 g/cm3 (mean = 1.8 g/cm3) and over the measurement interval varies little with depth. Data points with negative or very low density (<< 1.0 g/cm3) probably represent voids or areas of drilling disturbance.
NGR was measured every 10 cm from Section 197-1206A-2R-2 to Core 45R (Table T14; Fig. F61A). Total counts are reported here because the corrected counts (which are less by ~16 counts per second [cps]) include negative values that are physically unreasonable.
NGR values at Site 1206 range from 12.9 to 34.3 cps (mean = 18.8 cps). In the upper part of the basement section, from ~57 to 99 mbsf, total gamma ray counts decrease slightly with depth from ~19 to ~16.7 cps. This is succeeded by cycles of overall increasing NGR with depth, from 123 to 145.5 and from 145.5 to 246 mbsf. A slight decrease in NGR is observed at 267 mbsf that is succeeded by an increase from ~18 to ~22 cps between 267 and 287 mbsf in the base of basement Unit 17 (see "Physical Volcanology and Igneous Petrology"). An abrupt decrease in NGR occurs at 287 mbsf. Below this depth core sections show a wide range of NGR values; this behavior continues to the base of the recovered sequence. Total NGR counts in basement Units 8 and 19, which contain breccia, tend to be higher than the counts in the basalt units above and below. The highest counts were measured in the sedimentary sandstone, limestone, and soil Units 12, 15,16,18, 20, and 22.
Whole-round core images were taken of cylindrical pieces from the Hole 1206A core. Over 110 m of core images were recorded, representing ~77% of the recovered material. However, because of hole deterioration and wall collapse, downhole logging was not performed at Site 1206; hence, correlation of core image and logging data is not possible at this site.
Thermal conductivity was measured on one or two pieces per core at Site 1206 (Table T15; Fig. F62). Thermal conductivity values of the 30 basalt samples measured ranged between 1.057 and 2.283 W/(m·K) (average = 1.626 W/[m·K]). Five measurements taken on samples from sandstone units in the basement generally gave lower values, between 1.076 and 1.601 W/(m·K) (average = 1.314 W/[m·K]). Five measurements taken on breccia generally gave still lower values, between 0.96 and 1.419 W/(m·K) (average = 1.314 W/[m·K]). One measurement taken on a deeply weathered flow top yielded 1.076 W/(m·K).
At Site 1206, index properties were usually determined on one sample per core. If different lithologies were present in the core, more than one sample per core was taken. Values of wet mass, dry mass, and dry volume of the samples were measured and used to calculate moisture content, bulk density, grain density, and porosity (Table T16; Fig. F61B, F61C, F61D). Basement lava flow units showed considerable variation in bulk density with depth, with values ranging between ~2.0 and 3.0 g/cm3. There is also a corresponding variation in porosity, with values ranging between ~5% and 40%. Grain density of basalt was more uniform, with mean values of ~3.0 g/cm3. Little systematic variation with depth is observed. Units of breccia and fine-grained sedimentary beds both in and above the basement all had a grain density of ~2.8 g/cm3, bulk density of ~2.1 g/cm3, and porosity of ~40%.
Compressional wave velocity measurements were made on discrete samples from Hole 1206A at a frequency of approximately one per section. P-wave velocity was measured in the x- and z-directions for the basement samples. On selected samples, P-wave velocity was also measured in the y-direction.
P-wave velocity varies widely throughout Hole 1206A, ranging from ~2215 to 5820 m/s (mean = ~ 4000 m/s) (Table T17; Fig. F63). Velocities determined in the x-, y-, and z-directions differ by up to 300 m/s, and it is not immediately apparent whether this represents anisotropy or inadequate coupling between sample and transducers as described in previous chapters. As would be expected, higher compressional wave velocity is present in the lava flow units than in the volcaniclastic and sedimentary interbeds. Particularly high compressional wave velocity (>5500 m/s) was recorded in basement Unit 17, a highly olivine-phyric basalt (see "Physical Volcanology and Igneous Petrology").
When plotting P-wave velocity vs. bulk density at the same sampling locations, it is apparent that P-wave velocity and bulk density of basalts are correlated; the lowest densities (~2.4 g/cm3) correspond to the lowest velocities (~3400 m/s), and the highest densities (~2.9 g/cm3) correspond to the highest velocities (~5300 m/s) (Fig. F64). Data points for sediments plotted on the same bulk sound velocity vs. density diagram plot as a separate cluster around 2800 m/s and 2.05 g/cm3.