Physical properties measurements of whole-core sections from Hole 1139A using the MST included magnetic susceptibility, gamma-ray attenuation porosity evaluator (GRAPE) bulk density, and natural gamma radiation (NGR) measurements. 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 T14). Downhole trends in index properties show several changes and offsets in slope (Figs. F90, F91), generally corresponding to changes in lithology.
In Subunit IB (19.0-47.5 mbsf), bulk densities vary from 1.5 to 1.7 g/cm3, grain densities range between 2.6 and 2.7 g/cm3, and porosity changes from 60% at the top to 70% at the bottom. This increase in porosity is consistent with an increase in carbonate content and may be related to better sorting of sediments downhole. Lower porosity values at the top of the interval may also result from the hiatus separating Subunits IA and IB. Sediments in this interval consist of middle Miocene foraminifer-bearing nannofossil ooze, and carbonate content of sediments in Unit I vary from 64 wt% CaCO3 at ~5 mbsf to 83 wt% at ~30 mbsf (see "Lithostratigraphy").
Between ~58 and ~153 mbsf in Unit II, bulk densities change little, averaging 1.5 g/cm3. Porosity also remains constant at 70% (Fig. F90C). Grain densities, however, exhibit large scatter in this interval, with values between 1.8 and 3.1 g/cm3. The lithology in this interval changes from foraminifer-bearing nannofossil ooze at the top of the sequence to clay and claystone at the bottom, with a corresponding decrease in carbonate content (from ~60 to ~30 wt% CaCO3) and higher magnetic susceptibility (Fig. F92B; Table T4). The increasing downward proportion of clay may explain the near uniform porosity.
From ~159 to ~242 mbsf in Unit II, bulk density increases slightly, from 1.4 to 1.8 g/cm3. Grain density ranges from 2.6 to 3.0 g/cm3 and averages 2.8 g/cm3. Porosity decreases significantly from 74% to 54% (Fig. F90C). Sediments in this depth interval are mainly calcareous claystone and nannofossil-bearing ooze and chalk. Accordingly, carbonate content increases from ~30 to >60 wt% CaCO3.
Between ~250 and ~330 mbsf in Unit II, bulk and grain densities as well as porosity remain relatively constant, ranging from 1.5 to 1.9 g/cm3, 2.5 to 3.1 g/cm3, and 49% to 70%, respectively. The lithology is dominantly claystone in this interval, and the carbonate content is low, averaging 30 wt% CaCO3. As in the uppermost part of Unit I, the higher clay content in this depth interval may account for the preservation of porosity. Magnetic susceptibility also has higher values in this interval (Fig. F92B).
Between ~333 and ~381 mbsf, still within Unit II, some index properties change significantly. Bulk density gradually increases from ~1.6 to ~2.1 g/cm3, grain density is fairly constant, and porosity gradually decreases from ~66% to ~42% downhole through this interval. Carbonate content increases sharply from ~40 to >90 wt% CaCO3 (see "Lithostratigraphy"). The sediments in this interval are mainly calcareous clay and nannofossil-bearing ooze and chalk.
We only have three data points between ~381.4 and 384.4 mbsf, which spans Units III and IV. Bulk density averages 2.0 g/cm3, grain density maintains a nearly constant value of 2.8 g/cm3, and porosity is ~49% (Unit III) and ~31% (Unit IV). Sediments recovered from this interval are thin layers of brown and red foraminifer nannofossil chalk and sandy packstone. A hiatus (~31-33 Ma) is also present within this zone (see "Biostratigraphy").
Index properties were not determined in Unit V and basement Units 1 and 2. Within basement (below 530 mbsf), all index properties change sharply. In basement Unit 3, which is crystal vitric tuff (see "Physical Volcanology"), bulk density is <2.0 g/cm3, and porosity is questionably high (~50%; see Fig. F91C). Throughout basement Units 4 and 5 (~531-585 mbsf), bulk densities increase to ~2.4 g/cm3. Grain densities gradually increase from 2.6 to 2.7 g/cm3, and porosities vary from 10% to 19%. Lithologies in this interval include oxidized hydrothermally altered trachyte (see "Physical Volcanology").
In the remaining basement Units 6 through 18 (~605 to ~674 mbsf), bulk densities vary widely with a mean of 2.4 g/cm3, grain density approaches a mean of 2.8 g/cm3 and decreases slightly in the deeper rocks, and porosity varies widely from 65% to 3% (Fig. F91). The dominant lithologies are feldspar-phyric basalts with brecciated flow tops and increased vesicularity toward the margins of the flows. Carbonate veins pervade this zone (see "Alteration and Weathering"). In basement Unit 19, grain density averages ~2.7 g/cm3 and is fairly constant. The major minerals are quartz, sanidine, and siderite (see "Alteration and Weathering"). Several samples from the basement Unit 19 exhibited abnormal porosity values >60%, which cannot be explained by a combination of swelling and dehydrating clays alone.
Bulk density was measured by the GRAPE every 4 cm on whole sections of cores recovered from Hole 1139A. GRAPE data offer the potential for direct correlation with downhole bulk density of discrete samples and can be compared with logging data (Fig. F92A). In Units I through IV (from ~19 to ~385 mbsf), the maximum values of GRAPE densities correspond well with wet bulk densities determined from discrete samples and fluctuates similar to shallow resistivity values from the logging data (Fig. F92A) (see "Downhole Measurements" and "Seismic Stratigraphy").
Below ~380 mbsf, bulk densities are much more scattered than in overlying sediments. As previously noted, 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 1139. Gamma-ray values are fairly constant in Unit I (<10 counts per second [cps]) (Fig. F92). NGR count increases distinctly at a depth of ~50 mbsf, corresponding to the boundary between Units I and II. Within Unit II, we observe three positive peaks of >15 cps at depth ranges centered around ~100, ~190, and ~250 mbsf (Fig. F92). These intervals correspond to the darker gray nannofossil-bearing clay (Core 183-1139A-12R), the nannofossil-bearing claystone (Core 183-1139A-20R), and the dark gray claystone (Core 183-1139A-27R), respectively. NGR values reached a peak value of >20 cps at a depth of ~381 mbsf, corresponding to the brown and red foraminifer nannofossil chalk and sandy packstone in Unit III and IV. In Unit V, NGR values are similar to those of Unit II. In Unit VI, values increase downhole, approaching ~60 cps near a depth of 500 mbsf. Between ~518 and ~604 mbsf, in the basement Units 1 to 5, the NGR count fluctuates with a maximum peak near ~538 mbsf, corresponding to the clay-rich coarse green sands from basement Unit 3 (see "Igneous Petrology"). In this interval, NGR values decrease from ~570 to ~600 mbsf, probably reflecting the highly fractured and altered trachyte. Between ~605 and ~694 mbsf, within basement Units 6-17, gamma-ray values increase fairly rapidly downhole, and drop again in basements Units 18 and 19, consisting of sanidine-phyric trachyte (see "Igneous Petrology"). The downhole spectral gamma-ray logging data (see "Downhole Measurements," Fig. F98) reveal fluctuations very similar to those of downhole NGR profile, corroborating the shipboard measurements.
We determined magnetic susceptibility on all cores from Site 1139 (Fig. F92B). The results are discussed in "Paleomagnetism".
At Site 1139, we determined compressional wave velocity from both split-core sections and discrete samples measurements (Figs. F90D, F91D). The compressional wave velocity data for Subunit IB and the upper sequence of Unit II, which consist of foraminifer-bearing diatom and nannofossil ooze, show very little scatter, with a mean value of 1822 m/s (Table T15; Fig. F90). Compressional wave velocity in the lower part of Unit II increase linearly with depth, from 1785 to 4331 m/s. These changes correspond to a decrease in porosity from 75% to 42%, as mentioned above. Four outliers of data points (occurring at 191.61, 287.78, 346.87, and 360.01 mbsf, respectively) display much higher velocity values compared to coeval data at the same depth (Fig. F90D; Table T15). We do not have an explanation for the data point at a depth of 191.61 mbsf, but core photos and the corresponding visual core descriptions reveal that the other three intervals correspond to dark banded layers of volcanic material. In particular, an almost pure basaltic ash layer in Section 183-1139A-38R-4 near ~360 mbsf suggests that such layers account for the observed high velocity values, as opposed to experimental errors.
The compressional wave velocities for sedimentary Units III and IV increase downhole, with an average value of 3616 m/s. Velocities correlate with changes in lithology, from nannofossil-bearing claystone at the bottom of Unit II to the brownish to pink foraminifer nannofossil chalk in Unit III to sandy packstone in Unit V.
No samples were available for velocity determinations in the uppermost two basement Units. Velocities in basement Unit 3, a crystal-vitric tuff has low velocities, with values between 2590 and 2792 m/s (Fig. F91).
Basement Units 4 and 5 are sanidine-phyric trachytes, their velocities decrease from 4770 m/s in the upper part to 3322 m/s in the lower part. Velocities in the bottom of basement Units 6 to 17 typically range from 3500 to 4600 m/s, with few values >5000 m/s. The trachyandesite and trachyte of the lowermost basement Units 18 and 19 have velocities similar to those of the overlying basalts. However, basement Unit 18 appears to show a trend of decreasing velocity (Fig. F91D), corresponding to the inverse trend in both grain densities and porosity (Fig. F91B, F91C). In the upper half of basement Unit 19, velocities increase from ~4000 to >5000 m/s, whereas grain densities are uniform, suggesting a constant mineralogical composition for the rocks. Discrete velocity determinations generally show higher values than the values obtained from downhole logging (Fig. F98). This is expected at the top of the hole as a result of enlargement caused by the drilling procedure and wiper trip. Below ~575 mbsf, the hole was not logged, but in the basement units above this depth the data somewhat agree (see "Downhole Measurements").
Velocity anisotropy in sedimentary Units I through III is negligible, typically <4%. Two samples from Unit IV, however, exhibit velocity anisotropy as high as 16% (Table T15).
We determined thermal conductivities for soft sediment cores and basement rocks, although we could not determine thermal conductivity in cores recovered in the lower part of Unit II and/or in Units III to V (Fig. F93; Table T16). Thermal conductivity values for sediments from Units I and II are commonly between 0.8 and 1.1 W/(m·K), with a mean value of 0.9 W/(m·K), and show little scatter. For the basement units, thermal conductivity values vary widely, from a low value of 0.7 W/(m·K) to a value as high as 3.7 W/(m·K) (Table T16). We obtained the lowest value (0.7 W/[m·K]) from a highly fractured basalt piece (within Unit 14) in interval 183-1139A-67R-5, 45-55 cm (638.65 mbsf), and the highest value (3.7 W/[m·K]) was in a plagioclase-phyric trachyte in basement Unit 4 in interval 183-1139A-60R-2, 14-26 cm (567.34 mbsf).
Although data are scattered, thermal conductivity values in the basement units appear to have a C-shaped trend, from a relative high value of 1.8 W/(m·K) at a depth of 556.7 mbsf to a low value 0.7 W/(m·K) at ~639 mbsf, followed by an average high value of 2.2 W/(m·K) at ~690 mbsf (Fig. F93). The trend seems to follow the same trend as the natural gamma-ray profile (Fig. F92). Despite the highly variable values, the mean value of thermal conductivity in the basement Units is 1.7 W/(m·K), similar to values in basement rocks at other Leg 183 sites.
Trends in index properties and MST measurements, coupled with changes in compressional wave velocity and thermal conductivity, compare well with the lithologic units and logging data for Hole 1139A. The overall downhole trends in index properties and changes in velocity gradients define several intervals with distinct physical properties. Variations in the physical properties of the sediments and rocks recovered at Site 1139 are the combined result of changes in lithology, depth of burial, diagenesis, and/or alteration.