Physical properties at Site 1221 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 undisturbed section in Hole 1221A. Samples from cores in Holes 1221B and 1221C were used to supplement intervals that were disturbed by drilling or not recovered in Hole 1221A. Light absorption spectroscopy (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 1221. 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 T13). The GRA and MAD wet bulk densities are a close match in the clays and nannofossil oozes of lithologic Unit I (0-1.12 mbsf) and Unit II (1.12-7.40 mbsf), but the MAD densities are consistently 0.10 g/cm3 greater than the GRA density in the radiolarian ooze of Subunit IIIA (7.40-112.00 mbsf) (Fig. F17). The GRA bulk density was the primary density measurement made on the P/E boundary sections contained in Cores 199-1221C-11X and 199-1221D-4X (see "Sediment of the P/E Boundary Interval" in "Lithostratigraphy"). In both Holes 1221C and 1221D, the calcareous chalk above and below the boundary is characterized by bulk densities of ~1.60 to 1.75 g/cm3 (Fig. F18). In Hole 1221C, the GRA bulk densities of the multicolored clays directly above the boundary are ~0.30 g/cm3 lower (~1.40 g/cm3) than the densities above and below the clays. In Hole 1221D, the bulk density in the multicolored clays, which ranges from 1.20 to 1.40 g/cm3, is lower and less uniform than in Hole 1221C. Section 199-1221D-4X-2 contains a chert nodule at 151.93 mbsf that has a bulk density of 2.13 g/cm3. The two low density spikes in the section, at 152.52 and 152.56 mbsf, coincide with small voids in the core.
GRA bulk densities for Cores 199-1221A-4H and 5H (28.5-47.5 mbsf) appear to be displaced to values 0.10-0.15 g/cm3 greater than adjacent GRA densities (Fig. F17). As at Site 1220, where GRA densities display a similar displacement over short intervals, the offset is an electronic artifact in the MST data acquisition. The correlation between the MAD and GRA densities (excluding the questionable GRA data from Cores 199-1221A-4H and 5H) is not as strong at Site 1221 as it is at other Leg 199 sites because of the limited range in densities (Fig. F19). In both the regression of GRA density with wet bulk density and GRA density with DBD, the regression coefficients are 0.86.
The MAD wet bulk density varies over a narrow range for sediments at Site 1221 (Fig. F17). Bulk density of the clay and radiolarian ooze in Unit I is 1.10 g/cm3 at 0.75 mbsf. Density increases in Unit II to a maximum of 1.38 g/cm3 at 2.25 mbsf in an interval of nannofossil ooze. Below this depth, density decreases in conjunction with LAS-indicated increasing opal content (Fig. F20). The highest wet bulk density in Unit III (1.32 g/cm3) is at 8.25 mbsf, near the clay-rich top of the unit. Density decreases as the clay content of the sediment rapidly decreases downhole. The average density for the radiolarian ooze of Subunit IIIA is 1.14 g/cm3. The nannofossil chalk of lithologic Unit IV (150.50-156.00 mbsf) was sampled at 150.88 mbsf and has a wet bulk density of 1.81 g/cm3.
Grain density is low for most of the interval cored at Site 1221, reflecting the abundance of radiolarians. The highest grain density (2.78 g/cm3) occurs in the nannofossil ooze at 2.25 mbsf in Unit II. At the top of Subunit IIIA, grain density rapidly decreases to 2.20 g/cm3 at 18.86 mbsf as a result of the decrease in nannofossils. The high concentration of radiolarians in Subunit IIIA is reflected by the low average grain density for the unit (2.17 g/cm3). Grain density of the Unit IV nannofossil chalk is 2.72 g/cm3.
The porosity near the seafloor (0.75 mbsf) is 94%. It decreases rapidly to 80% in the nannofossil ooze at 2.25 mbsf. Porosity then increases slightly downhole as radiolarian content increases. The average porosity for the radiolarian ooze of Subunit IIIA is 84%. Porosity of the nannofossil chalk at 150.88 mbsf in Unit IV is 54%.
LAS studies were conducted on sediments from Cores 199-1221A-1H through 11H and Sections 199-1221B-1H-1 through 1H-3 at a frequency of two samples per undisturbed section (see Vanden Berg and Jarrard, this volume, for a discussion of the LAS technique). Samples were not collected below 105 mbsf because of poor core recovery. Semiquantitative mineral concentrations were calculated from the collected spectra, assuming a four-component system: calcite, opal, smectite, and illite (Table T14). The results of the LAS analyses correlate well with the major lithologic boundaries (Fig. F20) and are described below in terms of lithologic units.
The upper 8 cm of Site 1221 contains an illite-rich (60%) clay, which abruptly changes to radiolarian ooze that characterizes the rest of lithologic Unit I below 0.08 mbsf. Unit II contains calcite-rich (75%) nannofossil ooze between 1.7 and 2.3 mbsf, an interval of opal-rich (48%) radiolarian and diatom ooze between 3.2 and 6.8 mbsf, and a lower thin interval of calcite-rich (65%) nannofossil ooze between 7.7 and 8.3 mbsf. The upper 4.3 m of lithologic Unit III is a smectite-rich (75%-90%) clay layer, which overlies 100.7 m of opal-rich radiolarian ooze. Opal and smectite concentrations average 58% and 37%, respectively, throughout Unit III (excluding the upper clay layer). The illite-smectite transition at this site is difficult to determine precisely with LAS because of the high concentrations of biogenic material in the uppermost sediments.
Compressional wave velocity was measured by the P-wave logger (PWL) on all whole cores from Holes 1221A and 1221B and Cores 199-1221C-1H through 6X. The contact probe system was used to measure velocities on split cores from Hole 1221A and Sections 199-1221B-1H-1 through 1H-3, 199-1221C-6X-1 through 6X-3, and 199-1221C-11X-1 (Table T15). Agreement between PWL and split-core velocities is poor, and the two data sets show an offset of ~30 m/s (Fig. F21). Velocities in Unit I decrease from 1531 m/s at the seafloor to 1488 m/s at 1.3 mbsf. This low-velocity interval correlates with a thin layer of nannofossil ooze as recorded in the LAS mineralogy data (Fig. F20). Below 1.3 mbsf, velocities increase to 1525 m/s in the radiolarian and diatom oozes of Unit II before decreasing again to ~1500 m/s between 9.3 and 12.4 mbsf in a clayey interval. In the radiolarian ooze between 12.4 and 114.0 mbsf, velocities gradually increase downcore from ~1530 to ~1550 m/s. A velocity of 1610 m/s was measured in the nannofossil chalk of Unit IV at 150.89 mbsf.
Thermal conductivity was measured on the third section of all undisturbed cores from Hole 1221A and Cores 199-1221B-1H and 2H (Table T16). The conductivity was only measured on cores in lithologic Unit II and Subunit IIIA. The average thermal conductivity for these units is 0.73 W/(m·K). This value is comparable to the other high-porosity (80%-90%) radiolarian oozes cored during Leg 199. The conductivity does not vary as a function of porosity or display a trend in variation downhole at Site 1221.
Natural gamma radiation was measured on all whole cores in Holes 1221A, 1221B, 1221C, and 1221D (Fig. F22). The highest NGR value (38 counts per second [cps]) is present in clay-rich lithologic Unit I. NGR values rapidly decrease downhole in the radiolarian ooze of Unit III, coinciding with a downhole decrease in clay content. The values are essentially at zero below 25 mbsf. In the P/E boundary section in Sections 199-1221C-11X-3 and 199-1221D-4X-2 (see "Sediment of the P/E Boundary Interval" in "Lithostratigraphy"), NGR values rise from background levels in the calcareous chalk to 17 cps in the multicolored clay above the boundary.
Whole-core MS measurements were made on all cores from Holes 1221A, 1221B, 1221C, and 1221D (Fig. F23). MS for lithologic Unit I is 25 x 10-6 SI at the seafloor and decreases to 9 x 10-6 SI at the base of the unit. Unit II is characterized by a small increase in susceptibility to 18 x 10-6 SI at 3.4 mbsf and another decrease to values of 9 x 10-6 SI at 4.2 mbsf. The susceptibility minima in Units I and II correspond to intervals of calcite-rich nannofossil ooze, whereas the maxima correspond to regions of more clay- and radiolarian-rich sediments (see "Unit I" and "Unit II," both in "Lithostratigraphy").
The top of Lithologic Unit III is marked by an increase in susceptibility to ~72 x 10-6 SI. The high MS correlates with a region of clay-rich sediments between 7.4 and 11.7 mbsf. This interval is also characterized by higher NGR values and low porosities and velocities. Between 9.8 and 114.2 mbsf in the radiolarian-rich Unit III, MS decreases to an average of 17 x 10-6 SI. The lower susceptibility values (~6 x 10-6 SI at 69.1 mbsf) correlate with the lowest grain densities in Unit III.
The P/E boundary sections, Sections 199-1221C-11X-3 and 199-1221D-4X-2, were well documented by the MS detector (Fig. F18). The transition from nannofossil chalk to the metal oxide-rich clay is marked by an increase from ~25 x 10-6 SI to 119 x 10-6 SI at 154.02 mbsf in Hole 1221C and 25 x 10-6 SI to 92 x 10-6 SI at 152.32 mbsf in Hole 1221D. This difference is comparable to the change at the boundary between the radiolarian ooze of Unit II and the upper clay interval of Unit III but occurs over a much narrower interval. Below this peak, susceptibility decreases to minima of 53 x 10-6 SI in Hole 1221C and 38 x 10-6 SI in Hole 1221D, which coincides with the reddish brown layer (154.16 mbsf in Hole 1221C and 152.56 mbsf in Hole 1221D). In Hole 1221C, a second broad susceptibility peak of 112 x 10-6 SI at 154.26 mbsf lies just above the P/E boundary (Fig. F18). Hole 1221D is characterized by the same broad peak (94 x 10-6 SI at 152.69 mbsf) but fails to return to the same low values as in Hole 1221C. Susceptibility and GRA bulk density in the three recovered P/E boundary sections (two from Site 1221 and one from Site 1220) correlate well with one another. The susceptibility peaks also correlate well with zones of metal enrichment, as seen in the geochemical analyses (see "P/E Boundary" in "Geochemistry").