Physical properties at Site 1222 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 1222A. 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 1222. Gamma ray attenuation (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 T12). The GRA and MAD wet bulk densities are a close match throughout the interval of core recovery in Hole 1222A (Fig. F15), with the exception of the interval from 6.90 to 14.40 mbsf (Sections 199-1222A-2H-2 through 2H-6). This interval contains a recurrence of the electronic artifact in the MST data acquisition that first appeared at Site 1220. The displacement is not present in the Hole 1222B GRA record, and, as at Sites 1220 and 1221, the appearance of Sections 199-1222A-2H-2 through 2H-6 does differ from that of adjacent sediments. Crossplots of wet bulk density and DBD vs. interpolated GRA bulk density, which exclude data from the sections in question, display an excellent correlation between the two bulk density measures (Fig. F16).
The wet bulk density at the top of lithologic Unit I (0-40.5 mbsf) is 1.27 g/cm3. As the clays that comprise the unit compact, wet bulk density increases with depth, reaching a maximum of 1.46 g/cm3 at 31.15 mbsf. The downhole trend of increasing density is interrupted between 16.8 and 20.2 mbsf by an interval of low-density (1.23-1.27 g/cm3) diatom ooze (see "Unit I" in "Lithostratigraphy"). The small-scale variation in bulk density that accompanies alternating lithologies in Subunit IA is demonstrated by low density in diatom-rich sediments and higher density in clayey intervals in Core 199-1222A-3H (Fig. F17). A sharp decrease in wet bulk density to ~1.25 g/cm3 is present in the lowermost part of Subunit IA. The bulk density remains at this level, averaging 1.24 g/cm3, in the radiolarian clay of Subunit IB (40.5-54.9 mbsf). Wet bulk density increases sharply to 1.40 g/cm3 at the top of Unit II (58.7-66.6 mbsf) and remains at roughly this level throughout the nannofossil ooze of this unit. A rapid decrease in bulk density to 1.20 g/cm3 marks the top of lithologic Unit III (58.7-66.6 mbsf), and wet bulk density averages 1.21 g/cm3 for the clays in this unit.
Grain density varies over a wide range (2.21-2.77 g/cm3) at Site 1222 as a result of the combination of different lithologies (Fig. F15). The grain density is roughly 2.60-2.65 g/cm3 at the top of Unit I, reflecting the predominance of clay. Higher grain densities, up to 2.77 g/cm3 at 2.25 mbsf, possibly reflect the presence of manganese oxide and other opaque sediment constituents (see "Unit I" in "Lithostratigraphy"). Grain density decreases downhole to 2.30 g/cm3 at 21.65 mbsf in the clay below the diatom ooze in Subunit IA. Below 21.65 mbsf, grain density increases and is ~2.53 g/cm3 between 25 and 35 mbsf. The density is lower at the base of Subunit IA (2.36 g/cm3) in the transition to the radiolarian clay of Subunit IB. Grain density in Subunit IB ranges from 2.21 to 2.52 g/cm3, with the highest densities at the base of the unit. Grain density in the underlying nannofossil ooze of Unit II varies in a narrow range about an average of 2.65 g/cm3. Grain density decreases in the Unit III clay, ranging from 2.45 to 2.63 g/cm3 and averaging 2.52 g/cm3.
Sediment porosity near the seafloor at Site 1222 is 85%. A downhole trend of decreasing porosity, to 69% at 31.15 mbsf, is interrupted by the high-porosity (85%) diatom ooze between 16.8 and 20.2 mbsf (Fig. F15). Below 31.15 mbsf, porosity in the Unit I clays increases with depth to 84% at 39.15 mbsf. Most of Subunit IB has a porosity of ~86%. The porosity of the radiolarian clays decreases at the base of the unit in the transition to the lower-porosity (~75%) nannofossil ooze of Unit II. Porosity increases sharply to 88% at the top of Unit III and remains roughly at this level throughout the unit.
LAS studies were conducted on sediments from Hole 1222A 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 66.2 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 T13).
Calcite is overestimated throughout Site 1222 because of the lightness of the material (Fig. F18). The high concentrations of zeolites may be contributing to this light color. Overall, the clay intervals show high concentrations of smectite and illite and also correspond to areas of low opal. The illite-smectite transition is found in the upper 10 m of sediment. The diatom ooze (~17 mbsf) shows a large drop in clay and an increase in opal as well as the radiolarian ooze of Subunit IB. The nannofossil ooze of Unit II is associated with the expected high calcite values (up to 80%). Postcruise work will involve a recalculation of these concentrations using better quality standards. This should eliminate the overestimated calcite and the variability in the illite values.
Compressional wave velocity was measured by the P-wave logger (PWL) on all whole cores from Holes 1222A and 1222B. The insertion and contact probe systems were used to measure velocities on split cores from Hole 1222A (Table T14). Agreement between PWL and split-core velocities is good, typically displaying offsets of <10 m/s (Fig. F19). The difference between the whole-core and split-core velocities is greater in the radiolarian clay between 50 and 52 mbsf, where contact probe velocities are ~30 m/s higher than the PWL velocities. This disparity in velocities in radiolarian clay and ooze is present at other Leg 199 sites and possibly results from dewatering of the radiolarian-rich sediment after core splitting.
Velocity varies with lithology at Site 1222 (Fig. F19). In the Subunit IA clay, transverse velocity is 1510 m/s near the seafloor and is at a maximum of 1558 m/s in the diatom ooze at 20.11 mbsf. The velocity variation that accompanies alternating lithologies in Subunit IA is displayed in the PWL record for Core 199-1222A-3H (Fig. F17), in which peaks in velocity correspond to layers of laminated diatom ooze and lower velocities are present in clay intervals. Velocity increases slightly with depth in Subunit IA and is ~1520 m/s at the base of the unit. In Subunit IB velocity is 1512 m/s at 40.66 mbsf and rapidly increases to 1563 m/s at 45.66 mbsf. Below this depth, velocity decreases downhole and is 1524 m/s at the base of the unit. Overall, the average velocity for the radiolarian clay of Subunit IB is 1543 m/s. The downhole decrease in velocity continues in the nannofossil ooze of Unit II. The average velocity for this unit is 1519 m/s. Velocity sharply increases to 1543 m/s at the top Unit III. It decreases with depth in the clay of Unit III to 1519 m/s at 66.16 mbsf, just above the base of the unit.
Velocity anisotropy was determined with the contact probe system to evaluate changes in fabric that might accompany sediment burial. The clays of Subunit IA are nearly isotropic with a range in anisotropy from 0.6% to 2.0% without a downhole trend, suggesting that little particle reorientation has occurred (Table T14).
Thermal conductivity was measured on the third section of all undisturbed cores from Holes 1222A and 1222B (Table T15). Overall, the conductivity of sediments recovered at Site 1222 is low, ranging from 0.69 to 0.82 W/(m·K). Near the top of Subunit IA, thermal conductivity is 0.72 W/(m·K) (Fig. F20). It increases downhole in the clay to 0.82 W/(m·K) at 28.16 m/s. This increase accompanies the downhole decrease in porosity. Thermal conductivity decreases to 0.73 W/(m·K) near the base of Subunit IA as porosity increases in transition to the radiolarian clay of Subunit IB. The high-porosity radiolarian clay of Subunit IB has the lowest conductivity at Site 1222, averaging 0.71 W/(m·K). Below the radiolarian clay, thermal conductivity increases to an average of 0.78 W/(m·K) in the nannofossil ooze of Unit II. As porosity increases in the clay of Unit III, thermal conductivity decreases to 0.71 W/(m·K) at 66.16 mbsf.
Natural gamma radiation was measured on all whole cores from Holes 1222A and 1222B (Fig. F21). The NGR values are as high as 137.1 counts per second (cps) at 1.0 mbsf before they decrease to an average of 19.8 cps for the rest of Subunit IA. Between 16.8 and 20.2 mbsf, natural gamma radiation values decrease to an average of 8.0 cps in the interval of diatom-rich sediments. Within this interval, thin layers of laminated diatom ooze are present, which record minima in NGR values (Fig. F17). In the upper radiolarian-rich part of Subunit IB (40.5-52.1 mbsf), NGR values decrease to an average of 5.4 cps. The lower section of Subunit IB (52.6-56.5 mbsf) records a rise in values to an average of 12.6 cps and correlates to an interval of more clay-rich sediments. Below 56.5 mbsf, NGR values decrease downcore to near background levels.
Whole-core MS measurements were made on all cores from Holes 1222A and 1222B (Fig. F22) and correlate well with other physical property measurements. MS values in the upper section of Subunit IA (0.0-16.8 mbsf) average 40 x 10-6 SI, followed by a decrease between 16.8 and 20.4 mbsf to an average of 24 x 10-6 SI. This low-susceptibility interval correlates with the zone of diatom-rich sediments. Within this interval, lower than average susceptibility (as low as 3 x 10-6 SI) correlates with thin layers of laminated diatom ooze (Fig. F17). The lower part of Subunit IA (20.4-40.5 mbsf) is characterized by a broad peak in susceptibility, with values as high as 202 x 10-6 SI at 31.5 mbsf. Between 40.5 and 52.1 mbsf in the radiolarian-rich interval of Subunit IB, susceptibility decreases to an average of 45 x 10-6 SI before increasing again to an average of 73 x 10-6 SI in the clay-rich interval at the base of Subunit IB and the top of Unit II (52.1-56.5 mbsf) (see "Subunit IB" and "Unit II," both in "Lithostratigraphy"). Between 56.5 and 59.9 mbsf, MS decreases to an of average 29 x 10-6 SI in the nannofossil ooze. The clay-rich Unit III and top of Unit IV mark an increase in susceptibility to an average of 64 x 10-6 SI.