Physical properties measurements of whole-core sections from Hole 1140A using the MST included magnetic susceptibility, gamma-ray attenuation porosity evaluator (GRAPE) bulk density, and natural gamma radiation (NGR) data. We determined compressional wave velocities (Vp) from the split cores in transverse x directions for soft sediments in liners and for hard-rock pieces without the liner. Measurements in the longitudinal (z) and transverse (x and y) directions on cut samples of consolidated sediment and hard rock allowed us to investigate velocity anisotropy. We estimated the magnitude of velocity anisotropy by dividing differences between the maximum and minimum velocities (among the three mutually perpendicular directions—x, y, and z) by the mean velocity of the sample. Index properties determinations included bulk density, water content, porosity, and grain density. We calculated index properties from wet and dry sample weights and dry volumes. We also determined thermal conductivity for sediment and basalt.
We determined index properties by using gravimetric methods on discrete samples (Table T10). The general trend exhibited by the index properties data at Site 1140 reflect downhole variations in lithology (Figs. F45, F46).
In Subunit IA (seafloor to 10 mbsf), bulk densities vary from 1.4 to 1.5 g/cm3, grain densities range between 2.2 and 2.4 g/cm3, and porosity changes from 66% to 69%. Sediments in this interval consist of middle Miocene diatom-bearing nannofossil ooze (see "Lithostratigraphy").
Between ~10 and ~75 mbsf in Subunit IB, bulk densities change little, averaging 1.5 g/cm3. Porosity remains constant at 65% (Fig. F45C). Grain densities, however, exhibit large scatter in this interval, with values between 2.3 and 2.6 g/cm3. The lithology in this interval changes from foraminifer-bearing nannofossil ooze at the top of the sequence to semilithified nannofossil chalk at the bottom (the beginning of the ooze-chalk transition zone). The large scatter may reflect the presence of diatoms, which are abundant to 47 mbsf and present until ~200 mbsf. The grain density of sediment consisting of 50% diatoms (opal A) and 50% calcite would be ~2.3 g/cm3.
From 84 to 182 mbsf, still within Subunit IB, bulk density increases slightly from 1.4 to 1.7 g/cm3. Down to ~160 mbsf, grain density is between 2.6 and 2.7 g/cm3, whereas from 160 to 182 mbsf the grain density varies from 2.6 to 2.9 g/cm3. The reason for this scatter is unclear. Porosity decreases from 76% to 62% (Fig. F45C). Sediments in this depth interval become progressively stiffer downhole and are mainly greenish nannofossil-bearing ooze and chalk.
Between 184 and 234 mbsf in Subunit IB, index properties change significantly. Bulk density gradually increases from 1.5 to 2.0 g/cm3, grain density gradually increases from 2.6 to 2.9 g/cm3, and porosity gradually decreases from 74% to 44% downhole through this interval. The sediments in this interval are mainly extensively burrowed nannofossil-bearing ooze and chalk. The increase in grain density downhole corresponds to dolomitization (see "Lithostratigraphy").
At the boundary between Unit II and basement (~235 mbsf), index properties change abruptly (Figs. F45, F46). In basement Unit 1, which consists of pillow and massive basalt (see "Physical Volcanology"), bulk densities increase to ~2.8 g/cm3, grain densities increase to 2.9 g/cm3, and porosities sharply decreases to 6%.
From 278.9 to 279.5 mbsf, within basement Unit 4, a layer of rusty brown to rusty orange dolomite bed was recovered. The corresponding physical properties data clearly reflect this change in lithology. Bulk density sharply decreases to 2.1 g/cm3, grain density decreases to a mean of 2.8 g/cm3, and porosity increases to a mean of 41%. The difference in grain densities reflect the different degree of dolomitization and variable clay content. The dolomite pieces were fragile and tended to disaggregate when saturated in saltwater. This disaggregation may have been caused by swelling of clays. This swelling, followed by dehydration when dried in oven at 110°C, could also cause the lower bulk density and higher porosity observed in this interval.
In the lowermost part of the basement, Units 5 and 6 (287 to 321 mbsf), bulk densities vary from 2.5 to 3.0 g/cm3 with a mean of 2.9 g/cm3, grain density approaches a mean of 3.0 g/cm3, and porosity varies from 22% to 4% (Fig. F46). The lithologies in these units are pillow and massive basalts.
Bulk density was measured by the GRAPE every 4 cm on whole sections of cores recovered from Hole 1140A. In sedimentary Subunits IA and IB (0 to 235 mbsf), the maximum values of GRAPE densities correspond well with wet bulk densities determined from discrete samples. GRAPE densities also show fluctuations that are similar to shallow resistivity values from the logging data (Fig. F47) (see "Downhole Measurements").
Below ~235 mbsf, bulk densities are much more scattered than in overlying sediments. As with other Leg 183 sites, the larger scatter in the GRAPE bulk density data for the deeper units results from empty space between pieces of core and the core's fractured nature, whereas the generally lower maximum GRAPE values are caused by the smaller diameters of the cores.
We measured NGR every 12 cm on unsplit sections of cores from Site 1140. Between seafloor and 10 mbsf, in Subunit IA, the NGR count fluctuates with a maximum peak near the boundary between Subunits IA and IB (~10 mbsf). Within Subunit IB, we observe two positive peaks of >7 counts per s (cps) at depth ranges centered around ~120 and ~215 mbsf (Fig. F47), probably reflecting an increase in clay content. These intervals correspond to the light green chalk (Core 183-1140A-14R) and the light brown nannofossil-bearing chalk (Core 183-1140A-24R), respectively. Gamma-ray values increase to a maximum of 10 cps in basement Units 2 and 3, and to 7 cps in basement Unit 4 (270.5 to 279.7 mbsf). This gamma-ray increase is associated with a decrease in magnetic susceptibility. The remaining basement units have values around 4 cps. The downhole natural gamma-ray profile (MST) exhibit fluctuations very similar to those of downhole spectral gamma-ray logging data (see "Downhole Measurements").
We determined magnetic susceptibility on all cores from Site 1140 (Fig. F47B). The results are discussed in "Paleomagnetism".
We determined compressional wave velocity from both split-core sections and discrete samples (Figs. F45D, F46D). Velocity anisotropy in both sedimentary and basaltic units is negligible, typically <4%. The compressional wave velocity data for Subunit IA and the upper sequence of Subunit IB (0-182 mbsf), which consist of diatom-bearing nannofossil ooze and foraminifer-bearing nannofossil ooze and chalk, show very little scatter, with a mean value of ~1633 m/s (Table T11; Fig. F45D). The compressional wave velocities in the lower part of Unit IB increase gradually with depth, from 1578 to 2018 m/s. These changes correspond to a decrease in porosity from 74% to 44%.
At the boundary between Unit I and basement (~235 mbsf), the compressional wave velocity increases sharply. Velocity in basement Unit 1 varies from 5484 to 6859 m/s. The recovered cores (Cores 183-1140A-26R through 28R) in this unit are pillow and massive basalts. Velocities between ~6000 and 7000 m/s seem high and may be a consequence of the calibration method (see "Velocity Determinations" in "Physical Properties" in the "Explanatory Notes" chapter). Velocities in the bottom of basement Units 5 and 6 typically range from 5099 to 6055 m/s, with few values above 6500 m/s. Velocity, bulk density, and porosity correlate well in Core 183-1140A-34R. Velocity trends correlate with the downhole trends of the sonic log, but discrete velocity values are higher in the basement units.
Thermal conductivity values for sediments from Subunits IA and IB are commonly between 0.7 and 1.1 W/(m·K), with a mean value of 0.9 W/(m·K), and show little scatter (Fig. F48; Table T12). The mean value is similar to values in sedimentary units at other Leg 183 sites. For the basement units, thermal conductivity values vary quite widely, from a low value of 1.1 W/(m·K) to a high value of 2.4 W/(m·K) in the depth interval from ~235 to 321 mbsf, with a mean value of 1.69 W/(m·K). The highest values were in Sections 183-1140A-27R-2 (~243 mbsf) and 183-1140A-34R-4 (~300 mbsf), which are pillow and massive basalts in basement Units 1 and 6, respectively.
Physical properties at Site 1140 vary downhole and correlate with changes in lithology. Index properties data in sedimentary Subunits IA and the upper part of Subunit IB (0-182 mbsf) show insignificant changes, and compressional wave velocity is fairly uniform. Between 184 and 234 mbsf, within Unit IB, physical properties change noticeably because of lithification. Bulk and grain densities as well as compressional wave velocities gradually increase with depth, with a corresponding decrease in porosity.
All index properties abruptly change at the boundary between basement and overlying sedimentary units. Massive pillow basalts in basement Units 1, 5, and 6 have higher density, velocity, and magnetic susceptibility values than those of pillow basalts in basement Units 2 and 3. Basement Units 2 and 3 have the overall highest natural gamma-ray values.