Physical properties at Site 1216 were measured on whole cores, split cores, and discrete samples. MST measurements (bulk density, MS, P-wave velocity, and natural gamma radiation) and thermal conductivity comprised the whole-core measurements. Compressional wave velocity measurements on split cores and moisture and density (MAD) analyses on discrete core samples were made at a frequency of one per section. Because the first three sections of Core 199-1216A-1H were significantly disturbed, the corresponding interval in Hole 1216B was sampled. LAS analyses were performed on the MAD samples as well as an additional one sample per section (located ~50 cm from the MAD sample).
Two methods were used to evaluate the wet bulk density at Site 1216. GRA provided an estimate from whole cores. MAD samples gave a second, independent measure of wet bulk density, along with providing DBD, grain density, water content, and porosity from discrete samples (Table T11). MAD wet bulk densities trend ~0.05 g/cm3 higher than the GRA estimated densities in the uppermost 30 m at Site 1216 (Fig. F13). Below 30 mbsf the two bulk density measures coincide more closely. Crossplots of wet bulk densities and DBD vs. interpolated GRA density (Fig. F14) show that despite the offset in the upper section of the site, the overall match between the data sets is very good.
Wet bulk density values are nearly constant about a mean of 1.41 g/cm3 from the seafloor to 30 mbsf. Between 30 and 35 mbsf, wet bulk density decreases uniformly to 1.19 g/cm3. This shift in density corresponds to the transition from illite-rich to smectite-rich clays as indicated by the LAS analyses. Below 35 mbsf, wet bulk density is more variable and ranges from 1.21 to 1.32 g/cm3. Grain densities are ~2.6 g/cm3 in the uppermost 20 m at Site 1216. Within the interval of 20-29 mbsf, grain density increases downcore to a maximum of ~2.9 g/cm3. This increase may be the result of higher concentrations of Fe and Mn in sediments (see "Geochemistry"). Below 30 mbsf, there is a large decrease in grain density that is consistent with a change from illite to smectite dominance in the sediment (as indicated by LAS analyses). Omitting an anomalous value of 2.57 g/cm3 at 39.30 mbsf, grain density averages 2.16 g/cm3 in this interval (smectite has a grain density of ~2.2 g/cm3). Porosity is ~75% from the seafloor to 25 mbsf. From 25 to 32 mbsf, it increases to 83%. Below 32 mbsf, porosity remains high, averaging 82%.
LAS studies were conducted on cores from Hole 1216A 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/silica, smectite, and illite (Table T12). LAS-derived mineralogical data (Fig. F15) show that illite decreases downhole while smectite increases. The illite-smectite transition near 25 mbsf may be the same transition that occurs at 10 mbsf in Hole 1215A. Estimated opal/silica concentrations probably reflect other minerals, such as zeolites, because very little biogenic opal was present at this site (see "Biostratigraphy"). Calcite is probably overestimated because the clays are barren of calcareous microfossils (see ""Biostratigraphy") and Ca contents measured by ICP-AES analyses are relatively low (see "Geochemistry").
Compressional wave velocity was measured by the P-wave logger (PWL) on whole cores from Holes 1216A and 1216B and by the insertion and contact probe systems on split cores from Hole 1216A and Hole 1216B (Table T13). Measurements with the insertion probe system were restricted to soft sediments in the uppermost 38 m at Site 1216. The match between the whole-core and split-core measurements is relatively good (Fig. F16). The discrete values either coincide with the PWL velocities or are up to 15 m/s higher than whole-core measurements. The general trends in the velocities are an increase from 1485 m/s near the seafloor to 1520 m/s at 23 mbsf, a decrease to ~1505 m/s at 32 mbsf, and higher, more variable velocities below 32 mbsf.
Velocity anisotropy was calculated from longitudinal (z-direction) and transverse (y-direction) measurements provided by the insertion probe system to evaluate burial-induced changes in sediment fabric. The anisotropy ranges from -0.7% to 1.8% (Table T13) and averages 0.9%, with no consistent trend with depth.
Thermal conductivity was measured on the third section of cores from Site 1216 (Table T14). The thermal conductivity averages 0.77 W/(m·K). As is the case at Site 1215, there is a general inverse relation relationship between thermal conductivity and porosity at Site 1216.
NGR was measured on all whole-cores at Site 1216 and displays trends similar to the other physical properties (Fig. F17). Between the seafloor and 24 mbsf, NGR values are high, 20 to 32 counts per second (cps), coinciding with the illite-rich pelagic clay. The NGR values decrease to ~2 cps at 35 mbsf and remain at this level to the bottom of Hole 1216A. This change is consistent with the transition to more smectite-rich clay.
Whole-core MS measurements display greater variability than other properties and do not follow the identified changes in lithology (Fig. F18). The susceptibility increases from 75 x 10-6 SI at the seafloor to approximately 200 x 10-6 SI at 10 mbsf. Between 10 and 20 mbsf, MS values are more uniform in a range of 125 to 165 x 10-6 SI. Below 20 mbsf, the susceptibility is more variable and increases to 215 x 10-6 SI at 28 mbsf. A variable, but consistent decrease to 75 x 10-6 SI coincides with the proposed transition to more smectite-rich clay between 30 and 40 mbsf. Below this depth, measurements are few as a result of coring disturbance and the MS values are ~75 x 10-6 SI.