Physical properties at Site 1219 were measured on whole cores, split cores, and discrete samples. MST measurements (bulk density, MS, P-wave velocity, and NGR) 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. LAS analyses were performed on the MAD samples as well as an additional one sample per section (located ~50 cm from the MAD sample). Three in situ temperature measurements were obtained using the Adara tool in Hole 1219B.
Two methods were used to evaluate the wet bulk density at Site 1219. 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 T17). In the radiolarian oozes and clays of lithologic Units I (0-30.0 mbsf) and III (150.6-234.2 mbsf), the MAD wet bulk density is consistently greater than GRA bulk density by 0.05-0.10 g/cm3 (Fig. F28). Despite the offset, the two bulk density measures follow the same general trends. The agreement between the wet bulk density and GRA density is better in the nannofossil ooze of Unit II (30.0-150.6 mbsf), where the two data sets track each other through the alternating lithologies that are expressed as sediment color cycles. A comparison of the GRA density and the digital color image for Core 199-1219A-6H shows that the darker-colored, more radiolarian- and clay-rich intervals are less dense than the lighter-colored, more nannofossil-rich intervals (Fig. F29). Lithologic Unit IV (234.2-244.9 mbsf) was drilled with the XCB, and the limited data that are available display a fair correlation between the discrete sample and GRA densities. Crossplots of wet and DBD vs. interpolated GRA density (Fig. F30) show excellent correlation between the MAD and GRA data for sediments recovered with the APC.
The MAD wet bulk density is nearly constant, with an average of 1.18 g/cm3 in the uppermost 30 m of Hole 1219A. Density increases rapidly at the top of Unit II to 1.54 g/cm3 at 33.25 mbsf. Between 30 and 77 mbsf, Unit II is characterized by highly variable wet bulk density, as a result of alternations between nannofossil ooze and nannofossil ooze with radiolarians and clay. Bulk density in this interval ranges from 1.23 to 1.72 g/cm3. From 77 to 121 mbsf, the variability in bulk density is less than that between 30 and 77 mbsf because the sediment is a more uniform nannofossil ooze with high CaCO3 content (see "Solid-Phase Geochemistry" in "Geochemistry"). The trend for the upper part of Unit II (from 30 to 120 mbsf) is a slight increase in density with depth, from ~1.50 g/cm3 near the top of the unit to 1.66 g/cm3 at 120.75 mbsf. Below 121 mbsf, wet bulk density decreases sharply to 1.39 g/cm3 and the variability of the density increases, which reflects greater abundance of clay and radiolarians in the sediment and alternating lithologies similar to the upper part of Unit II. The general trend for the whole unit is increasing wet bulk density with depth reflecting downhole compaction from increasing overburden. Wet bulk density decreases to 1.23 g/cm3 at the top Unit III, followed by an overall slow increase in density with depth, to 1.31 g/cm3 at 226.27 mbsf. There are two density maxima in the lower part of Unit III, with values of 1.43 and 1.39 g/cm3 at 192.40 and 212.27 mbsf, respectively. The first maximum corresponds to a distinctive nannofossil ooze layer (see "Unit III" in "Lithostratigraphy") and a calcite peak in the LAS analysis. The latter maxima coincides only with an LAS-analysis calcite peak. Wet bulk density increases significantly at the top of Unit IV, followed by a steady decrease in density to the base of the unit. The uppermost sample measured in Unit IV (Sample 199-1219A-26X-1, 42-44 cm) at 234.52 mbsf has a density of 2.16 g/cm3. Qualitatively, the appearance of sediments near the top of Core 199-1219A-26X suggests that they possess even higher densities than the sediment sampled. Wet bulk density decreases steadily toward the base of Unit IV, with a value of 1.81 g/cm3 at 244.38 mbsf.
Variation in grain density corresponds well to the changes in lithology in Hole 1219A (Fig. F28). In Unit I, grain density ranges from 2.33 to 2.57 g/cm3 and averages 2.45 g/cm3. The transition from predominantly siliceous to more calcareous sediments in Unit II is marked by an increase in the magnitude and variability of grain density in the upper part of Unit II. Between 30 and 77 mbsf the grain density ranges from 2.40 to 2.77 g/cm3 and averages 2.63 g/cm3. The more calcareous interval between 77 and 121 mbsf displays relatively uniform grain density, which averages 2.70 g/cm3. In the lower part of Unit II, the transition to the radiolarian ooze and clay of Unit III is marked by greater variability and a decrease in grain density. The pattern of variable and decreasing grain density continues in Unit III. Grain density is 2.51 g/cm3 at 151.45 mbsf, near the top of the unit, and 2.15 g/cm3 at 226.27 mbsf, near the base of the unit. The average grain density for sediments in Unit III is 2.24 g/cm3. A significant increase in grain density to 2.77 g/cm3 is present at the top of Unit IV, marking the change in lithology to nannofossil chalk. At the base of Unit IV, grain density is 2.54 g/cm3.
Porosity and water content vary inversely with wet bulk density (Fig. F28). The high porosity of the clay- and radiolarian-rich sediments of Units I and III are prominent features of the porosity profile. Average porosities for Units I and III are 89% and 80%, respectively. Porosity is nearly constant in Unit I. In Unit III, it decreases with depth, from 86% at 151.45 mbsf to 75% at 226.27 mbsf. In Unit II, porosity trends are similar to those of wet bulk density. Porosity is highly variable between 30 and 77 mbsf in association with the alternating lithologies, relatively uniform in the nannofossil ooze between 77 and 121 mbsf, and more variable and higher at the base of the unit, in the transition to Unit III. Overall, porosity decreases from 79% near the top of the Unit II to 60% at the base of the unit as a result of compaction. The contact between Units III and IV is marked by a substantial decrease in porosity to 34%. At the base of Unit IV, porosity is 48%.
LAS studies were conducted on cores from Hole 1219A 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, smectite, and illite (Table T18). The results of the LAS analyses correlate well with the major lithologic boundaries (Fig. F31).
The radiolarian clay of lithologic Unit I shows clay contents of ~50%, with the dominant clay being smectite. The uppermost sample contains 47% illite and is followed by a drop in illite concentration to near 15%. This transition is believed to correlate with the illite-smectite transition seen at previous sites. Illite concentrations in the interval between 10 and 35 mbsf are higher than expected and may be the result of an increase in metal oxides, which darken the color of the sediment. Opal concentrations in the upper unit average 25% and are consistent with the lithologic description (see "Unit I" in "Lithostratigraphy"). Calcite is overestimated in Unit I compared to the geochemical data (see "Solid-Phase Geochemistry" in "Geochemistry") for reasons unknown. Postcruise research will focus on better calibration of LAS mineralogical calculations.
The carbonate-rich lithologic Unit II has an expected increase in calcite values to ~80%, as well as a corresponding drop in clay content. The clay that is present is mainly smectite, which varies from a low of 0% to a high of ~25%. Between 50 and 75 mbsf, radiolarians increase in abundance, resulting in higher opal concentrations. Likewise, between 125 and 150 mbsf, opal concentrations again rise with increased radiolarian contents (see "Unit II" in "Lithostratigraphy"). Percent silica data show the same trends as LAS percent opal in lithologic Unit II (see "Solid-Phase Geochemistry" in "Geochemistry").
The top of Unit III marks the lithologic transition associated with E/O boundary with a decrease in calcite (an average of 73% in Unit II to an average 17% in Unit III) and an increase in clay (an average of 19% in Unit II to an average of 29% in Unit III) and opal (an average of 7% in Unit II to an average of 53% in Unit III). Between 189 and 196 mbsf, calcite values again increase to an average of 33%, whereas clay and opal values decrease. This increase correlates with the layer of nannofossil ooze (see "Unit III" in "Lithostratigraphy"). The clay in this interval is predominantly smectite, with concentrations averaging 29%.
Lithologic Unit IV is a calcareous chalk and correlates with an increase in calcite concentrations to an average of 73%. Opal and illite concentrations are negligible in this unit, and smectite concentrations average 27%. These data correlate well with the percent silica and percent calcium concentrations (see "Solid-Phase Geochemistry" in "Geochemistry").
Compressional wave velocity was measured by the P-wave logger (PWL) on whole cores from Holes 1219A and 1219B and the insertion and contact probe systems on split cores from Hole 1219A (Table T19). For XCB cores, cube samples were cut with the dual-bladed rock saw, allowing determination of velocities in the y- and z-directions with the contact probe system. The match between the whole-core and split-core measurements is relatively good for the insertion and contact probe systems, with only a few anomalous points (Fig. F32).
Downhole trends in velocity approximate changes in lithology and bulk properties. Velocity (transverse) increases slightly with depth in Unit I, from ~1500 m/s near the seafloor to 1524 m/s at ~30 mbsf. The sharp increase in density and decrease in porosity that occurs at the boundary between Units I and II is not seen in the velocity profile. Overall, there is a gradual increase in velocity with depth in Unit II. Small variations in velocity most likely reflect alternations in lithology and porosity (Fig. F29). Unit III is marked by a jump to higher velocity values, from an average of 1534 m/s in Unit II to an average of 1570 m/s in Unit III. Lower velocities at 192 and 210 mbsf correlate with regions of higher LAS calcite concentrations (Fig. F31). Below 212 mbsf, velocity continues to increase downhole. Velocities from Unit IV were determined on three cut samples and record much higher values compared to the rest of the hole, averaging 1901 m/s. These high velocities are consistent with the high densities and low porosities in this interval.
The lack of simple downhole velocity trends in Hole 1219A is partly explained by the crossplot of velocity and wet bulk density (Fig. F33). The nannofossil ooze of Unit II is characterized by a general increase in velocity with increasing density. The radiolarian clays of Units I and III differ from the calcareous sediment in their relationship with bulk density. In Units I and III, there is either no relation or a weak increase in velocity with decreasing density. This pattern results from the stiff sediment framework created by the shape of radiolarians and their interlocking spines. This stiffness produces a higher shear modulus and velocities higher than expected for the high porosity of the sediment. The difference in the trends of velocity with bulk density for the calcareous and siliceous sediments explains the lack of a prominent change in velocity at the boundary between radiolarian clay of Unit I and the nannofossil ooze of Unit II.
Inconsistencies in the relationship between velocity and bulk density also are present at the core scale (Fig. F29). Sections 199-1219A-6H-2 and 6H-3 contain dark-colored, clay- and radiolarian-rich intervals with low bulk density, high MS, and high velocity and light-colored, more calcareous intervals of higher density, lower susceptibility, and lower velocity. In Sections 199-1219A-6H-4 through 6H-6, the pattern is reversed, with light-colored intervals displaying higher velocity than the dark layers.
Velocity anisotropy was calculated from longitudinal (z-direction) and transverse (y-direction) measurements provided by the insertion probe system and the cut samples measured with the contact probe system (Table T19). The sediments of Hole 1219A are essentially isotropic and do not show effects of particle realignment that accompany compaction of clayey sediments. The anisotropy ranges from 1.0% to 1.5% and averages 1.3% for the insertion probe system (upper 18 m of Hole 1219A). Anisotropy also was determined on the three cut samples from below 234 mbsf, with an average of 1.7%.
Thermal conductivity was measured on the third section of all APC-recovered cores from Holes 1219A and 1219B (Table T20). The thermal conductivity shows a strong dependence on lithology (Fig. F34) and porosity (Fig. F35). The radiolarian oozes and clays of Units I and III display a nearly constant conductivity, which averages 0.73 W/(m·K). Thermal conductivity increases sharply to 0.93 W/(m·K) at the top of Unit II. Between 30 and 120 mbsf, conductivity values are scattered but display a general increase with depth, with a maximum of 1.22 W/(m·K). Thermal conductivity gradually decreases between 120 and 150 mbsf and sharply declines to 0.71 W/(m·K) at the top of Unit III. The expected inverse relationship between thermal conductivity and porosity is displayed by the nannofossil ooze of Unit II but is lacking for the radiolarian oozes and clays of Units I and III (Fig. F35). The lack of a relationship results from the high porosity of the sediment and the poor heat conduction in the biogenic silica that comprises the radiolarians.
In situ temperature measurements were taken using the Adara tool with three cores in Hole 1219B. Borehole temperatures range from 5.72°C at 49.50 mbsf to 9.34°C at 116.00 mbsf, with an average seafloor temperature of 1.45°C (Table T21; Fig. F36).
Heat flow at Site 1219 was determined according to the procedure of Pribnow et al. (2000). The laboratory-determined thermal conductivity was used to estimate in situ thermal conductivity (see "Heat Flow Calculation" in "Physical Properties" in the "Explanatory Notes" chapter). The thermal resistance was calculated assuming a constant conductivity for Unit I (0-30 mbsf) and a linear fit through conductivity values between 30 and 125 mbsf in Unit II (Fig. F36). Thermal resistance was estimated for the depths of the temperature measurements, and the heat flow was obtained from the inverse of the linear fit for the crossplot of temperature and thermal resistance (Fig. F36). The heat flow estimate for Site 1219 is 66 mW/m2, which essentially is the same as the heat flow calculated for Site 1218 (67 mW/m2). The value of 66 mW/m2 compares favorably to the heat flow of 62 mW/m2 at the point (9°0.0´N, 163°48.2´W) in the global heat flow data set (Pollack et al., 1993) that is closest to Site 1219.
Natural gamma radiation was measured on all whole cores at Site 1219 (Fig. F37). The highest natural gamma radiation values occur in the clay-rich lithologic Unit I, where they decrease downcore from 68.7 counts per second (cps) at the seafloor to ~1.0 cps (near background levels) at 30 mbsf. Below 30 mbsf, values drop to zero in the carbonate-rich Unit II and remain at this level to a depth of 150 mbsf. There is a slight increase in natural gamma radiation values (average = 0.84 cps) in lithologic Unit III, which correlates with an increase in clay content over the E/O boundary.
Whole-core MS measurements correlate well with the major differences in lithology and to changes in other bulk physical properties. MS values in Unit I, are relatively high, averaging 26 x 10-6 SI. The MS record (Fig. F38) contains significant variation that is not present in the more uniform GRA bulk density profile (Fig. F28), although there is a match between the general trends of both data sets.
A significant decrease in susceptibility marks the top of the carbonate-rich Unit II at 30 mbsf. MS values in the interval between 30 and 95 mbsf average 11 x 10-6 SI, and the variation that is present corresponds with alternations between nannofossil ooze (lower MS) and nannofossil ooze with radiolarian ooze and clay (higher MS) (Fig. F29). Between 95 and 122 mbsf, MS values decrease to an average of 8 x 10-6 SI, which suggests that this interval contains the greatest amounts of calcite. Other data sets (percent calcium, grain density, and porosity) show a thicker interval (between 70 and 122 mbsf) of high calcite content. MS values increase between 122 and 150 mbsf, averaging 12 x 10-6 SI, correlating to small increases in LAS clay and opal contents (Fig. F31).
An increase in susceptibility marks the boundary between Units II and III as the clay content increases. MS values then decrease downhole to near zero in the nannofossil ooze at 192 mbsf and increase below 195 mbsf as clay content increases. Lower MS values at 212 mbsf correlate with higher calcite concentrations present in the LAS mineralogy data (Fig. F31). The large spike at the bottom of Subunit IIIA most likely reflects the presence of a chert bed. Data from Subunit IIIB and Unit IV are not representative because of poor core condition.