Physical properties measurements of whole-core sections from Site 1149 using the multisensor track (MST) included gamma-ray attenuation porosity evaluator (GRAPE), magnetic susceptibility meter (MSM), and natural gamma radiation (NGR). P-wave velocity logging (PWL) data were measured only in soft sediments in APC cores. We determined P-wave velocities from split cores in liners in the transverse x direction within both sediment and hard rock using contact probe systems PWS3, and in the transverse (x and y) and longitudinal (z) directions using PWS1, PWS2, and PWS3 on soft sediments. Velocity measurements were also obtained for cut cubes and minicores in the transverse (x and y) and longitudinal (z) directions using PWS3. Index properties on discrete samples, including wet bulk density, grain density, porosity, void ratio, and water content were calculated from measurements of wet mass, dry mass, and dry volume. We also measured thermal conductivity on whole-round or split cores and obtained shear- strength data on split cores of soft sediments.
We obtained index properties data using gravimetric methods on 189 samples from Site 1149. The results are presented in Table T16 and displayed in Figure F68. The average wet bulk density, porosity, and velocity of each lithologic unit and each lithology are listed in Table T17. From the seafloor to 100 mbsf in lithologic Unit I (ash- and diatom/radiolarian-bearing clay) (see "Unit I"), the wet bulk density and grain density have almost constant values with averages of 1.42 and 2.62 g/cm3, respectively. The porosity and water content decrease slightly with depth, and the averages are 75.5% and 54.8%, respectively. The porosity and water content slightly decrease at 38, 65, and 92 mbsf without apparent lithologic changes. Between 100 and 118.2 mbsf in lithologic Unit I, the wet bulk density decreases with depth, and the porosity and water content increase. At 118.2 mbsf, there is an abrupt change in most of the index properties (Fig. F68). This boundary corresponds to the lithologic contact between ash- and diatom/radiolarian-bearing clay (Unit I) and dark brown pelagic clay (Subunit IIA) (see "Subunit IIA"). Between 118.2 and 149.5 mbsf in Subunit IIA (dark brown pelagic clay with ash), the wet bulk density is slightly lower than that of Unit I, with an average of 1.38 g/cm3; however, the porosity and water content are significantly lower than those of Unit I, with averages of 67.1% and 49.9%, respectively. A second large contrast in index properties occurs at the lithologic Unit II/Unit III boundary where the average value of wet bulk density increases to 2.20 g/cm3 and porosity and water content decrease to 14.57% and 7.46%, respectively. Some of these large contrasts in average values are due to the preferential recovery and measurement of chert and porcelanite rather than the zeolite-bearing clay component of Unit III. The change in average index property values is much less dramatic across the Unit III/Unit IV boundary. Averages of wet bulk density and grain density increase slightly to 2.28 and 2.63 g/cm3, respectively, whereas porosity and water content averages decrease to 21.7% and 11.9%, respectively.
Index properties that require volume measurements were not obtained for most samples from Subunit IIB because the pyncnometer could not attain a stable helium pressure. We speculate that helium continued to be absorbed within what must be extremely small-scale porosity in the clay structure.
The relationship between the wet bulk density and porosity is displayed in Figure F69 and indicates the expected negative linear correlation. Chert and some marl samples have relatively high wet bulk density and low porosity. Intermediate values are measured for some cherts, porcelanite, marl, and chalk, whereas clay in Unit I, Subunits IIA and IIB, and nannochalk has the lowest density and highest porosity.
Wet bulk density was measured by the GRAPE every 4 cm for 4 s on unsplit sections of core from Site 1149. These data are shown in Figure F70. The continuous GRAPE density measurements can be compared to discrete samples of wet bulk density in Table T16. In Unit I, these densities show quite similar patterns and values, with an average of 1.42 g/cm3. GRAPE bulk density values are generally lower than those of gravimetric measurements in hard rock (Units III, IV, and basement) because of the effects from the discontinuous core with fractures and open space between core and liner. The GRAPE and gravimetric wet bulk density averages are 1.40 and 2.19 g/cm3 in Unit III and 1.37 and 2.28 g/cm3 in Unit IV, respectively. However, the GRAPE bulk densities are higher than the gravimetric values in Subunits IIA and IIB (pelagic clay). The GRAPE and gravimetric density averages are 1.46 and 1.38 g/cm3 in Subunit IIA and 1.56 and 1.40 g/cm3 in Subunit IIB, respectively. Shore-based investigation of microscale texture and composition within clay minerals in Unit I and Subunits IIA and IIB may reveal why GRAPE density values are higher in this unusual interval.
Magnetic susceptibility was measured every 4 cm for 4 s on unsplit sections of core from Site 1149. The data are shown in Figure F70. Magnetic susceptibility in Unit I and Subunits IIA and IIB displays semiperiodic variations punctuated with distinct peaks, which may correlate with discrete ash layers. Magnetic susceptibility is very low in chert/chalk/marl samples and abruptly jumps to maximum values in altered basalt encountered at ~410 mbsf.
NGR was measured every 10 cm for 20 s on unsplit sections of core from Site 1149. The data are shown in Figure F70. High NGR counts occurred just below the seafloor (0-5 mbsf) in lithologic Unit I and from 160 to180 mbsf in Subunit IIB (pelagic clay without ash). The NGR profile above 180 mbsf (above chert) exhibits fluctuations and general trends that are matched by those observed in the downhole spectral gamma-ray logging data (see "Natural Radioactivity"). In Units III and IV the NGR counts are relatively low (<20 cps) compared to those of Unit I and Subunits IIA and IIB because of chert and carbonate dilution of clay. NGR counts appear to generally decrease downsection in Unit IV. NGR remains below 20 cps in the igneous basement section with slightly higher values than in Unit VI.
Compressional wave velocity (P-wave velocity) was measured using two instruments, the P-wave logger (PWL) on the MST (y direction) and PWS1 (z direction), PWS2 (y direction), and the PWS3 (x direction) on split cores. The PWL was used only in soft sediments in APC cores. We also determined P-wave velocities from split cores in liners in the transverse x direction within both sediment and hard rock and on cube and minicore samples in x, y, and z directions of chert, chalk, and marl. The soft sediments in Hole 1149A, measured by PWS1, PWS2, and PWS3, are listed in Table T18 and displayed in Figure F71. The PWL data from Hole 1149A are compared with other MST data in Figure F70. The sediments and rocks recovered in Holes 1149B, 1149C, and 1149D were measured by PWS3 (x direction) in split core and discrete cube or minicore samples (Table T18; Fig. F71). In Unit I (0-118.2 mbsf) P-wave velocities range from 1480 to 1589 m/s and average 1520 m/s. In Subunits IIA and IIB (118.2-180 mbsf) usually only velocity in the x direction was measured by PWS3 because most split cores were too stiff to penetrate using the probes of PWS1 and PWS2. These values range from 1492 to 1544 m/s and the average of x-direction velocity in Subunits IIA and IIB is 1520 and 1515 m/s, respectively. These velocities are similar to those measured in situ by downhole logging tools (see "Seismic Velocity"). In Units III and IV (180-398.4 mbsf), the velocities are much higher than those of Unit I and Subunits IIA and IIB. In Unit III (180-282.9 mbsf), insufficient quantities of the soft interbedded pelagic clay were recovered; therefore, velocities were measured only on radiolarian chert and porcelanite samples in split core liners. Velocities range from 2540 to 6382 m/s, and the average velocity of radiolarian chert is 5167 m/s; that of porcelanite is 3429 m/s. In Unit IV (282.9-398.4 mbsf) recovered lithologies are classified as chert, chalk, and marl (see "Unit IV"). The P-wave velocity of radiolarian cherts ranges from 4439 to 5493 m/s, and the average is 4958 m/s. The average values of siliceous nannofossil chalk and marl are 2280 and 2676 m/s, respectively. Igneous basement samples range in velocity from 3408 m/s in a hyaloclastite sample to 5647 m/s in aphyric basalt. The average velocity from all samples (aphyric basalt, hyaloclastites, breccia) in the igneous section is 4821 m/s.
Relationships among the wet bulk density, porosity, and velocity are shown in Figure F69. The average velocity displays the expected positive linear correlation with wet bulk density and negative linear correlation with porosity. Samples of radiolarian chert have the highest velocity and density and lowest porosity. The velocities of pelagic clay from Unit I and Subunits IIA and IIB are nearly constant at ~1520 m/s, with no apparent relation to porosity and wet bulk density. The average P-wave velocity of each lithology calculated from x-direction data from Site 1149 is listed in Table T17.
Thermal conductivity measurements were taken once per core on either a whole round section or split section. The results are listed in Table T19 and plotted with depth in Figure F68. The values in Unit I and Subunits IIA and IIB are almost constant, and the average is 0.85 W/(m·K). Measurements were not obtained in Units III and IV because of the poor recovery.
Measurements of shear strength, using a mechanical vane, were made on split cores from Holes 1149A and 1149B. The results are listed in Table T20 and plotted with depth in Figure F68. Between the seafloor and 150 mbsf, the values gradually increase with increasing burial depth and range from 20.4 to 147.2 kPa. Undrained shear strength of soft sediments is generally related to their consolidation state, which is partly controlled by overburden pressure, which is in turn influenced by burial depth. It seems unusual, therefore, that shear strength values rapidly decrease between 150 and 180 mbsf in Subunit IIB. This zone corresponds to the dark brown pelagic clay of Subunit IIB, which is associated with the highest NGR counts, the presence of palygorskite clay, and a minimum in chloride concentration in interstitial waters, as well as collapsing hole conditions (see "Authigenic Clay Formation: Unit II" and "Subunit IIB").
Physical properties are clearly related to changes in the primary lithologies recovered at Site 1149. There is a general gradient of increasing velocity and density and decreasing porosity in the primary lithologies from pelagic clay to chalk to marl, porcelanite, and finally to basalt and chert. Even though recovery within Units III and IV was poor, representative samples were taken that will allow a correlation between core and continuous downhole log data.
Distinct physical and chemical properties mark the brown pelagic clay of Subunit IIB, including relatively low shear strength, the highest NGR counts, anomalous behavior in the pyncnometer, the occurrence of palygorskite clay, and a minimum in chloride concentration in interstitial waters, as well as collapsing hole conditions.