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doi:10.2204/iodp.proc.336.106.2012 Physical propertiesThe sediment and hard rock from Holes U1382B, U1383D, U1383E, and U1384A were characterized for physical properties as described in the “Methods” chapter (Expedition 336 Scientists, 2012a). All of the sediment cores recovered were processed with the Whole-Round Multisensor Logger (WRMSL) for measurements of gamma ray attenuation (GRA) density, magnetic susceptibility (MS), and P-wave velocity at 1 cm resolution. P-wave velocity was not measured on the WRMSL for the basement contact cores because the samples were small, unsaturated pieces that did not fill the core liner fully. The P-wave sensor on the WRMSL cannot make good contact with such samples. All sediment cores from Holes U1382B, U1383D, and U1384A were analyzed for natural gamma radiation (NGR) total counts and potassium weight percentage on the Natural Gamma Radiation Logger (NGRL); only the uppermost five cores from Hole U1383E were processed for NGR because of time constraints. Core sections shorter than 50 cm were not processed for NGR. Core catcher samples were not analyzed, but they were scanned on the Section Half Imaging Logger (SHIL). Thermal conductivity measurements were attempted on most core sections from Hole U1383D. However, high water content made it impossible for the probe to stabilize; hence, no measurements were successful. Therefore, we did not attempt sediment measurements in any of the other holes. P-wave velocity discrete measurements were taken for all three axes in Hole U1383D samples, but because of time constraints only the x-axis was measured for samples from other holes. A total of 172 discrete samples were taken at a frequency of 1 per core section for moisture and density (MAD) measurements. Electrical conductivity measurements were taken every 10 cm with the exception of cores from Hole U1383E (because of time constraints). These measurements allowed calculation of formation factor. Areas of the core with disturbed sediment, gravel, or sandy textures were avoided because the electrodes could be damaged and the measurements would not give realistic values. Archive core halves were scanned and analyzed for color reflectance and point magnetic susceptibility (MSP) on the Section Half Multisensor Logger (SHMSL). When sediment was too disturbed and watery and could damage the sensors, the section halves were not analyzed for color reflectance and MSP. Core catcher samples were imaged but not analyzed during the core flow. Gamma ray attenuation bulk density
The WRMSL was used to measure MS and GRA bulk density on whole-round cores. GRA measurements are sensitive to underfilled liners. The raw data from this instrument were filtered to remove underestimated data, as described in the “Methods” chapter (Expedition 336 Scientists, 2012a). Sediment cores were considered to have a diameter of ~66 mm, and XCB cores were considered to have a diameter of ~58 mm (e.g., Core 336-U1384A-12X). Hard rock cores generally have a smaller diameter (~58 mm) than the internal diameter of the core liner (66 mm). This can be corrected by multiplying the system output by Magnetic susceptibilityMagnetic susceptibility measurements of whole-round and archive-half cores are summarized in Figures F12, F13, F14, and F15. The raw data obtained from the WRMSL were filtered using the same criteria as those for GRA data because both sensors are installed on the same logger and have a similar range of detection. Magnetic susceptibility data were also corrected for the diameter of the core (58 mm for hard rock [Core 336-U1384A-12X] and 66 mm for sediment) based on the equation given by the manufacturer (see the MS2 Magnetic Susceptibility System operation manual [www.bartington.com/operation-manuals.html]). The correction factor applied was 1.012 for igneous sections and 0.687 for sediment sections. However, this measurement assumes that the core liner is filled, and it does not take into account the disturbance and water content of the core. The MSP sensor is installed on the SHMSL with the color reflectance spectroscopy sensor and was filtered with the same criteria used for color reflectance, as explained in the “Methods” chapter (Expedition 336 Scientists, 2012a). No correction is needed for this measurement. Both whole-round MS and half-core MSP measurements show similar peaks. For all sites, the major peaks are attributed to the presence of rocks, rubble, or sand-sized volcanic clasts. In Hole U1383D (Fig. F12), the two major susceptibility peaks correspond to layers of sand-sized volcanic clasts at ~5 mbsf and sand- to pebble-sized black clasts at ~37 mbsf (absolute maximum value MS = 258 × 10–5 SI; maximum MSP = 1929 × 10–5 SI). Hole U1383E (Fig. F13) has four major peaks, and the maximum values for MSP differ slightly from those of MS (absolute maximum value MS = 167 × 10–5 SI; maximum MSP = 351 × 10–5 SI). Hole U1382B (Fig. F14) has three major areas with peaks for MS and only two major areas for MSP. The shallower peak is absent in the MSP data because these sections were too disturbed and watery to be measured with the MSP sensor. The absolute maximum value of MS is 1660 × 10–5 SI, and the maximum MSP is 2607 × 10–5 SI. The peak area near ~50 mbsf is related to pebble-sized serpentinite clasts. Another secondary area with high values is located at the bottom of the borehole and is probably related to the presence of pebbles. Hole U1384A (Fig. F15) has higher MS and MSP values at the bottom of the borehole, where hard rocks are present. The absolute maxima for the hole are MS = 133 × 10–5 SI and MSP = 317 × 10–5 SI. Natural gamma radiationNGR was measured for all sediment cores at all sites, with the exception of portions of Hole U1383E that were not measured because of time constraints. Potassium concentrations were only calculated for Hole U1383D. NGR and potassium concentration data for Hole U1383D obtained from the NGRL are summarized in Figure F16. The count time for each core section (30 min for sediment and 2 h for hard rock) was maximized to increase the accuracy of the values obtained. The total counts per second (cps) reflect the concentrations of all radioactive elements. Spectral data were recorded, and the counts per second for each channel indicate the abundance of a particular element. These values were related to a potassium (K) standard with known composition to calculate the K concentration in the core section. Total counts for whole rounds from Hole U1383D range from 0.05 to 77 cps once the background is subtracted (Fig. F16). Potassium concentration was calculated by using GRA bulk density as the effective density for the corrections. No shipboard potassium data were produced by inductively coupled plasma–atomic emission spectrometry due to time constraints, and no downhole logging was conducted in these shallow holes for comparison. Potassium concentrations calculated from NGR range from <0.01 to 1.26 wt%. The peak of potassium observed at ~43.6 mbsf (Section U1383D-6H-1) was cross-checked in the spectral data, and the most prominent signal for this element is present at this depth (Fig. F17). The higher concentrations of potassium near the seafloor may be due to Compton scattering from uranium. This element’s radioactive daughters are relatively abundant in the shallowest section of the hole (see counts per second in Fig. F16). NGR data from all sediment holes present a similar profile, with a peak close to the seafloor and a slight increase at the bottom of the deeper Holes U1382B and U1384A (Fig. F18). Hole U1383E NGR values range from 1.29 to 79 cps. In Hole U1382B, the values range from <1 to 85.6 cps, and in Hole U1384A they range from 0.12 to 76 cps. Formation factorElectrical conductivity was measured for Holes U1383D, U1382B, and U1384A and corrected based on standard measurements of electrical conductivity of the International Association for the Physical Sciences of the Oceans (IAPSO). Disturbed core samples and sandy areas were not measured. Formation factor was calculated for these sites. Hole U1384D formation factors range from 1.76 to 2.77. with two peaks located at ~6.8 and ~24.3 mbsf. Below these peaks, formation factor values decrease with depth to the bottom of the borehole (Fig. F19). Hole U1382B formation factors are lower, varying from 1.79 to 1.96. An increase in formation factor value is observed at ~15.5 mbsf. Below this depth, the values decrease and increase again below ~80 mbsf, reaching another maximum at the bottom of the borehole (Fig. F19). Formation factor values for Hole U1384A range from 1.58 to 2.89. Maximum values correspond to a peak from ~8 to ~12 mbsf. A decrease in formation factor is observed from ~12 to ~34 mbsf. Below this depth, values present no major trend to the bottom of the borehole (Fig. F19). Moisture and densityA summary of bulk density, dry density, grain density, void ratio, and porosity measurements on 172 discrete samples is presented in Table T6. These values were determined using IODP MAD Method C (see “Physical properties” in the “Methods” chapter [Expedition 336 Scientists, 2012a]). Samples were specifically selected to be representative of the core section from which they were taken. The values are consistent within the holes and correlate strongly with GRA bulk density measurements (Figs. F8, F9, F10, F11). All of the holes show a decrease in porosity and void ratio with depth in the top section of the borehole. Compressional P-wave velocityP-wave velocity was measured with the WRMSL on cores from all sites. Additionally, caliper measurements were taken on the cores once they were split for the x-axis. For samples from Hole U1383D, measurements were also taken with the bayonet for the y- and z-axes (Fig. F20). The results of the measurements are presented in Figures F20, F21, F22, and F23. When possible, the P-wave measurements were taken adjacent to the porosity (MAD) samples. In general, x-axis P-wave values are all higher than values obtained from the WRMSL. One reason for this increase could be that manually closing the caliper to take the measurement increased the compression on the sample. The values obtained are relatively close to values for seawater. Some of the intervals recovered did have a high fluid content, as indicated by the porosity values (Table T6). Color reflectance spectroscopyColor reflectance was measured in all areas where the sediment was consolidated enough for the sensor to land. The analyzed sediment at all sites has only positive a* and b* values. The differences in color were mainly detected by changes in the range of the different color parameters and the scatter of the points. Holes U1383D (Fig. F24) and U1383E (Fig. F25) have the most uniform profiles. Holes U1382B (Fig. F26) and U1384A (Fig. F27) show greater variability with depth. The first two sections of Core 336-U1382A-3H were too disturbed and watery for measurements to be made. A summary of the values obtained is given in Table T7. |
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= 1.138 (Jarrard and Kerneklian, 2007). MAD and GRA density measurements have similar values for all of the sections analyzed (Figs.