Physical properties at Site 1215 were measured on whole cores, split cores, and discrete samples. MST measurements (GRA bulk density, MS, P-wave velocity, and natural gamma ray radiation [NGR]) and thermal conductivity comprised the measurements on whole cores from Holes 1215A and 1215B. Compressional wave velocity measurements on split cores and moisture and density (MAD) analyses on discrete core samples were made at a frequency of one sample per section. LAS analyses were performed on the MAD samples as well as an additional one sample per section (located ~50 cm from the MAD sample). One in situ temperature measurement was obtained using the Adara tool in Core 199-1215A-4H.
Two methods were used to evaluate the bulk density at Site 1215. GRA provided an estimate of bulk density from whole cores. MAD samples gave a second, independent measure of wet bulk density, as well as providing DBD, grain density, water content, and porosity from discrete samples (Table T14). Throughout Hole 1215A, the MAD values closely match the GRA values (Fig. F16). The high degree of correlation of the data sets is shown in cross-plots of dry and wet bulk density vs. interpolated GRA density (Fig. F17).
Bulk density values decrease downhole in the upper red-clay unit (lithologic Unit I; 0-25.8 mbsf). Bulk density is 1.48 g/cm3 at the seafloor and decreases to a minimum value of 1.13 g/cm3 at the bottom of the red clay. Bulk density values increase from 25.8 to 67.2 mbsf in lithologic Unit II (nannofossil clay and clayey nannofossil ooze). At the top of the nannofossil ooze, the bulk density is 1.26 g/cm3 and increases to a maximum of 1.75 g/cm3 at 67.2 mbsf. Lithologic Unit III, 67.2 to 69.3 mbsf, is a metalliferous oxide ooze with an average wet bulk density of 1.39 g/cm3.
Grain density (Fig. F16) for lithologic Unit I sediments averages 2.50 g/cm3 and ranges from 1.97 to 2.92 g/cm3. The illite-rich section, above ~10.0 mbsf, shows less scatter than the smectite-rich section (~10.0-25.8 mbsf). Lithologic Unit II sediments have an average grain density of 2.71 g/cm3, and values range from 2.63 to 2.79 g/cm3. One sample was analyzed from lithologic Unit III, and it has a grain density of 3.12 g/cm3. This high value reflects the enrichment of manganese and other metal oxides in these sediments.
Porosity values (Fig. F16) increase with depth in the red clays (lithologic Unit I). Near the seafloor, porosity is 73.3% and increases to 91.3% at the bottom of the red-clay unit (25.8 mbsf). Porosity values in lithologic Unit II sediments decrease from 86.1% at the top of the unit (26.9 mbsf) to a value of 58.0% at the bottom (67.2 mbsf). The one sample analyzed from lithologic Unit III has a porosity of 82.4%.
LAS studies were conducted on cores from Hole 1215A at a frequency of two samples per section (see Vanden Berg and Jarrard, this volume, for a discussion of the LAS technique). Semiquantitative mineral concentrations were calculated from the collected spectra, assuming a four-component system: calcite, opal (not present at this site), smectite, and illite. LAS-derived mineralogical data (Fig. F18; Table T15) show a distinct transition at 25.8 mbsf from the red clays of lithologic Unit I (illite and smectite rich) to the calcite-rich, clayey nannofossil oozes of lithologic Unit II. Also, a gradual transition downcore from illite-rich clay to smectite-rich clay is seen between 5 and 10 mbsf. This change marks the Neogene transition from wind-blown eolian dust originating in Asia (illite rich) to wind-blown dust derived mainly from the Americas (smectite rich) (Rea, 1994).
Compressional wave velocity was measured by the P-wave logger (PWL) on whole cores from Holes 1215A and 1215B and by the insertion and contact probe systems on split cores from Hole 1215A (Table T16). Measurements with the insertion probe system were restricted to soft sediments in the uppermost 50 m of Hole 1215A. The downhole trends recorded by the PWL compare well with the trends of the discrete measurements. However, the insertion probe velocities trend 10-20 m/s lower than the PWL values, and the contact probe velocities are on the order of 10-40 m/s higher than the PWL measurements (Fig. F19). Differences between the whole-core and split-core measurements possibly reflect the presence of water in the space between the core liner and sediment in the whole cores and the slight compaction of the sediment in the contact probe technique. A consistent relationship between increasing burial depth and velocity is not present at Site 1215, suggesting that differences in sediment composition in addition to dewatering are affecting the velocity. In Hole 1215A, with the exception of the uppermost 8 m, the PWL velocity follows the same downhole trends as the GRA bulk density (Fig. F16). The PWL velocity displays a broad peak between 5 and 15 mbsf, with values reaching ~1550 m/s. Between 15 and 60 mbsf, the velocity values average ~1475 m/s before increasing to 1550 m/s below 60 mbsf.
Velocity anisotropy was calculated from longitudinal (z-direction) and transverse (x-direction) measurements provided by the insertion probe system (Table T16) to evaluate burial-induced changes in sediment fabric. Sediments in Hole 1215A are nearly isotropic, with most values in the range of -0.6% to 0.4%. There is a general decrease in anisotropy from the seafloor to 12.96 mbsf (Table F12). Below this depth, there is greater variability with no consistent trend.
Thermal conductivity was measured on the third section of cores from Hole 1215A and from Core 199-1215B-1H (Table T17). The thermal conductivity is inversely correlated with porosity (Fig. F20). This decrease in conductivity with increasing porosity occurs as increased interstitial spacing attenuates the applied current.
One in situ temperature measurement of 3.19°C at 29.70 mbsf was obtained with the Adara tool in Hole 1215A. An attempt to obtain a second temperature in Hole 1215B failed when the Adara tool was damaged by striking chert.
MS values average 49.8 x 10-6 SI, but many spikes to higher values are present (Fig. F21). Lithologic Unit I records the highest MS values, displaying a broad peak with a maximum of ~155 x 10-6 SI between 10 and 12 mbsf. Values for the carbonate-rich lithologic Unit II are much lower (15 to 50 x 10-6 SI), with spikes to values of ~125 x 10-6, most likely the consequence of chert nodules present in the core. MS values increase slightly from 75 to 100 x 10-6 SI in lithologic Unit III as a result of the increase in clay and metalliferous material.
NGR values show trends similar to susceptibility trends (Fig. F21). The highest counts (~20-30 counts per second [cps]) occur in the upper 10 m of Hole 1215A in the illite-rich section of lithologic Unit I. The NGR counts decrease by almost half (~5-10 cps) as the clays become more smectite rich with increasing depth in the hole. NGR counts in lithologic Unit II are low (~1-5 cps) but increase in lithologic Unit III (~10 cps) as a result of the higher metal content in this unit.