At Site 1143, physical properties were measured on whole-round sections, split-core sections, and discrete samples from the latter. Whole-core logging with the multisensor track included GRA bulk density, MS, and NGR on all cores as well as P-wave velocity logging from the top of the holes down to Sections 184-1143A-22X-3, 184-1143B-20X-1, and 184-1143C-21X-1. Sampling intervals were 2 cm for Hole 1143A and 4 cm for Holes 1143B and 1143C (except for Cores 184-1143C-13X and 14X, which were measured at 2-cm intervals). The P-wave logger (PWL) data were bad because of instrument problems and/or cracks or a void in the sediment cores. One to two thermal conductivity measurements per core were also performed on the whole-round sections. Color reflectance (CR) was measured on the archive halves of all split cores, at 2-cm sampling intervals for Holes 1143A and 1143B and at 4-cm intervals for Hole 1143C. Moisture, density, and P-wave velocity (using the P-wave velocity sensors 1, 2, and 3 [PWS1, PWS2, PWS3]) were measured on discrete samples from split-core sections at intervals of one measurement per section (1.5 m) (see "Physical Properties" in the "Explanatory Notes" chapter).
Core physical properties measurements show three first-order features. One is related to the change from APC to XCB coring (201.1 mcd in Hole 1143A, 184.3 mcd in Hole 1143B, and 187 mcd in Hole 1143C). The XCB cores are disturbed significantly by biscuiting, partial remolding, and incorporation of drilling slurry. In addition, XCB cores are reduced in diameter by ~10%. This affects the GRA bulk density and, to a smaller degree, signals from instruments that measure constant volumes such as MS and NGR. This effect is not compensated for because time is not available to perform a careful correction on board ship.
The other two primary features are related to lithologic changes. The first is defined by a downhole change in grain density, a prime indicator of changes in mineralogy, between ~150 and ~190 mcd. The second is marked by repeated inversions in the downhole trend of porosity and related properties that form two apparently anomalous intervals at ~200-300 mcd and ~360-410 mcd. These features are described in more detail in the following sections.
In Hole 1143A, between ~150 and 200 mcd, there is a major change in grain density (Fig. F21) that is compatible with the increase in carbonate over this interval (Fig. F18; see "Organic Geochemistry"). Above this transitional interval, the carbonate mean values and standard deviations are 19 ± 7%, and below the interval they are 45 ± 10 wt%. This compares to grain density values above and below the transition interval of 2.66 ± 0.05 g/cm3 and 2.70 ± 0.04 g/cm3, respectively. A preliminary calculation indicates that the increased carbonate concentration accounts for only half the average increase in grain density. Therefore, the grain density of the noncarbonate component must also increase downhole.
Especially in the interval between 150 and 250 mcd, the GRA bulk density shows cycles that span the lengths of cores (Fig. F22). The lower parts of these core cycles show densities higher by ~0.01 g/cm3 relative to the upper parts. These cycles give us a clear example of how the coring process changes the physical properties of the sediment. With the APC technique, core compression and stretching that result from the coring process probably have the strongest influence on the sediment properties. Cycles in the GRA data, when drilled with the XCB, may represent a function of the time that the sediment had been exposed to drilling vibrations.
Between ~180 and ~190 mcd (the exact position depends on the hole), GRA bulk density shows a sharp decrease resulting from the change to XCB coring (Fig. F22). The effect of the reduced diameter on GRA measurements becomes very clear when compared with the more accurate bulk density data obtained from the moisture and density (MAD) method, which reveal a much smaller offset at that depth. Figure F23 illustrates how GRA and MAD data correlate much better for APC than for XCB cores. In the XCB section, the GRA values are noisy with a bias to lower values because measurements of remolded sediment and drill slurry are included. The highest GRA values, obtained randomly from intact core pieces, are reliable because they correspond to the MAD values obtained from selected, intact core pieces.
Porosity data indicate a compaction trend that varies between two simple envelope trends (Fig. F24). The envelopes are power curve fits to extreme values at a number of depth intervals and represent homogeneous lithology and compaction end-members at Site 1143. The same characteristics are also observed in the MAD bulk density record (Fig. F22), which is largely related to porosity. The uppermost 0-150 m of the section (and the interval between ~300 and ~360 mcd) appear to approach the higher density, lower porosity envelope, whereas the intervals between ~150-300 mcd and 360-420 mcd approach the lower density, higher porosity envelope. The most striking porosity inversion, between 200 and 300 mcd, is also one of the most characteristic features in the wireline logging records of this site (see "Wireline Logging"). The bulk density excursion is as much as 0.2 g/cm3; the porosity inversion, as much as 12%.
Grain density values also mirror these variations to a lesser degree and indicate a lower carbonate content (lower grain density values) in the higher porosity intervals (e.g., 200-300 mcd). This observation is not compatible with the simple assumption that more carbonate increases bulk density and reduces porosity. Higher porosity with increased carbonate could be explained by an increased amount of foraminifers slowing compaction. This hypothesis is supported by the observation of foraminifer turbidite layers, most of which could have been reworked into the sediment by bioturbation and thus would not be accounted for by tabulating preserved sand layers.
Both MS and NGR records show the most significant decrease in values near the transition to XCB coring (Figs. F25, F26). Both measurements are volume specific, and their absolute values are affected by core disturbance that reduces the average bulk density. A good example is that the core-stretching effect at the base of the APC section, shown so well on the GRA record, can also be observed in the NGR data. Much of the general downhole increase in MS and NGR values from 0 to 180 mcd can be accounted for by the overall decrease in porosity.
The change from APC to XCB coring and its effect on the MS and NGR data, however, may well be related to a change in lithologic parameters, such as a pronounced increase in stiffness resulting from the increasing carbonate content. The drop in the MS signal does not occur exactly at the change to XCB cores but ~10 m above. Also, the drop in magnitude from ~25 × 10-5 to ~10 × 10-5 SI in MS, and from ~35 to 25 counts per second (cps) in NGR, cannot be fully explained by the decrease in bulk density as a result of coring disturbance. The decrease in MS and NGR at ~185 mcd, therefore, represents a significant lithologic change at Site 1143.
The NGR, which generally provides a rough estimate of the clay abundance, also shows a slight decrease in values between 130 and 180 mcd (Fig. F26). This cannot be explained either by coring effects and associated porosity changes or by changes in carbonate content, which does not increase until 30 m farther downhole. A decrease in the abundance of the radioactive component (e.g., clays such as illite) may therefore occur in that interval.
The MS shows a number of significant spikes that correspond to observations of volcanic ash layers. The spikes are particularly abundant in the intervals 20-30 and 70-100 mcd (Fig. F25) and also appear between 120 and 190 mcd in the record from Hole 1143A.
The CR data are presented as records of two parameters from the L*a*b* color system: L*, representing the lightness in percent; and a*/b*, the ratio of the two chromaticity parameters (Fig. F27). L* can be used as a first-order approximation of the relative concentration of carbonate. The major increase in carbonate between 150 and 200 mcd is represented by an increase in L* from ~50% to 58%. More subtle trends in carbonate concentration and the L* record appear to correlate as well, although the sampling intervals for carbonate are presently too low for a rigorous analysis of the relationship. The a*/b* ratio is a proxy for color change that can be related to a combination of carbonate or organic matter content, clay mineralogy, oxidation, and so forth. This parameter shows a sharp decrease at ~200 mcd and regains its amplitude at ~280 mcd.
Because of technical problems, the value of the PWL measurements is very limited. A comparison of PWS3 and PWL measurements reveals that the PWL significantly underestimates P-wave velocities. No useful data can be obtained from XCB cores. For these reasons, the PWL data are not shown in this text.
In the uppermost 150 mcd, PWS3 data range from 1600 to 1800 m/s and show little variability (Fig. F28). Below that depth, values increase uniformly to ~1900 m/s at 320 mcd, presumably as a result of compaction and also, perhaps, because of the increase in carbonate content. In the interval between 320 mcd and the bottom of the hole (which comprises many turbidite layers), the P-wave velocity trend is constant around 1900 m/s and shows a much higher scatter of values than above this interval. Individual measurements revealed values >2200 m/s, which were measured on the coarser grained layers of turbidite sequences, whereas the fine-grained turbidite layers showed much lower velocities. Because of an operational error that produced inaccurate transducer displacement measurements, the velocities determined with the PWS3 sensor may be overestimated by ~100-200 m/s.
Thermal conductivity data from the APC and XCB cores range from 0.81 to 1.19 W/(m·K) (Table T14, also in ASCII format; Fig. F29). The values from XCB cores are compromised by poor core quality, particularly in the upper XCB interval. The values from APC cores show a distinct increase around 150 mcd, compatible with the rise in carbonate concentration. Comparison of the APC thermal conductivity and MAD bulk density values interpolated at corresponding depths illustrates the intrinsic relationship between the two properties (Fig. F30).
Four downhole temperature measurements with the APC (Adara) temperature tool were taken in Hole 1143A at depths of 31.4, 59.9, 90.0, and 145.4 mbsf, respectively. In addition, a bottom-water temperature measurement was taken before coring in Hole 1143B (Fig. F31). The objective was to establish the local heat flow. Original temperature records were analyzed using the "Tfit" software to establish the equilibrium temperature at depth. The estimated errors in equilibrium temperature vary from 0.2° to 0.4°C, reflecting the amount of heat introduced by the ship's heave during the 10-min-long measurements. Depth errors are on the order of ±0.5 m. The measurements between 0 and 145.4 mbsf yielded a thermal gradient of 86°C/km (Fig. F32).