)
of the nonplatform sediments of Site 1193 can be related to depth (z)
using an exponential functionEvaluation of core physical properties at Site 1193 included nondestructive measurements of bulk density, bulk magnetic susceptibility (MS), natural gamma radiation (NGR), and P-wave velocity on whole cores using the multisensor track (MST). P-wave velocity (x-, y-, and z-direction) and moisture and density (MAD) were measured on split cores and on core samples. Low recovery in Cores 194-1193A-6X through 40X, 194-1193A-63X through 83X, and throughout Hole 1193C limited the use of the MST. The large diameter of cores recovered with the ADCB (Cores 194-1193B-3Z through 21Z) prohibited MST analysis. Thermal conductivity was measured on whole cores and on semilithified and lithified core samples.
Bulk density at Site 1193 was computed from gamma ray attenuation (GRA) measurements conducted on unsplit cores and from MAD measurements conducted on samples from split cores. The two independently derived bulk density data sets indicate the same general trend over most intervals (Fig. F46A). The similarity is best displayed in the interval from 0 to 35 mbsf, recovered using the APC. Samples from cores recovered with the XCB and the RCB and ADCB data (35-540 mbsf) have MAD density values that are on average 0.1 to 0.2 g/cm3 higher than the GRA values. The largest bulk density difference occurs between 340 and 360 mbsf, where the MAD density is 0.4 g/cm3 higher than the GRA density. Most likely, this is the result of reduced core diameter and a decrease in sample integrity that results from XCB and RCB core disturbance affecting GRA measurements.
Overall, bulk density ranges between 1.5 and 2.6 g/cm3 (Fig. F46A). The data show a general increasing trend downhole to a depth of 540 mbsf. Bulk density averages 1.67 g/cm3 in the upper 35 m at Hole 1193A, the interval corresponding to lithologic Units I and II (Fig. F46A). At 35 mbsf, the top of the carbonate platform, density increases to 1.75 g/cm3. The lithified platform sediments of Unit III (35-229 mbsf) (see "Lithostratigraphy and Sedimentology") are exceptions to the general downhole trend and have density values between 1.95 and 2.65 g/cm3 with a slightly decreasing trend with depth. Below 35 mbsf, local maxima can be observed at 220, 249, 365, and 385 mbsf (Fig. F46A). The maxima at 249 and 385 correspond to the top and bottom of lithologic Unit V.
Grain density averages 2.77 g/cm3 and shows broad scatter throughout most of Site 1193 (Fig. F46B). Approximately constant values of grain density exist between 35 and 130 mbsf, where the average grain density is 2.73 g/cm3. This interval corresponds to the upper part of the carbonate platform (lithologic Subunit IIIA) (see "Lithostratigraphy and Sedimentology"). Values increase slightly with depth from 2.5 g/cm3 at 50 mbsf to 2.9 g/cm3 at 505 mbsf. Below that interval, a slight decrease occurs to ~2.65 g/cm3. Suspect grain density values >3.0 g/cm3, possibly due to grain volume measurement error, have been identified in Figure F46B.
The porosity profile
mirrors the bulk density profile, with minor differences caused by variations in
grain density, indicating that bulk density variations are consistently
controlled by porosity (Fig. F46C).
Porosity at Site 1193 shows a general decrease with depth, except within the
platform sediments (35-229 mbsf). Porosity is relatively low at the seafloor
(55% to 70%) and decreases gradually to 30%- 40% at a depth of 500 mbsf (Fig. F46C).
The platform interval shows the most scatter with values ranging from 10% to
45%, reflecting the various degrees of cementation in the carbonate rocks. In
general, porosity increases slightly downhole within the platform interval.
Porosity ()
of the nonplatform sediments of Site 1193 can be related to depth (z)
using an exponential function
(z)
= o
e-kz,
where o
is the seafloor porosity, and k describes the rate of porosity decay
with depth (Athy, 1930). A least-squares fit to this equation yields 0
= 61.2% and k = 0.001 m-1 (correlation coefficient = 0.60)
(Fig. F46C).
P-wave velocity was measured with the PWS3 contact probe system on split cores (within the core liner) and ~10 cm3 samples of semilithified and lithified sediments. The P-wave logger was not used at Site 1193. From Cores 194-1193A-1H through 4H, velocity measurements were only taken in the x-direction. From Cores 194-1193A-6X through 79X and for Holes 1193B and 1193C, x-, y-, and z-direction velocity was routinely measured using sample cubes prepared from indurated sediment.
Velocity averages ~1600 m/s from 0 to 35 mbsf (lithologic Units I and II) (Fig. F47). From 35 to 165 mbsf (lithologic Subunit IIIA), velocity values are scattered from 1600 to 5200 m/s without a clear trend. In a third interval, from 229 to 415 mbsf, a distinct downhole-increasing velocity trend is visible. Velocity values in this interval start at 1600-1700 m/s and increase downhole to nearly 2700 m/s. Velocity in the top of the acoustic basement is low (1960 m/s at 540 mbsf).
A crossplot of velocity vs. porosity for Site 1193 shows a distinct inverse trend (Fig. F48). The measured velocities can be compared with the time-average equation of Wyllie et al. (1956):
)/Vmatrix
+ /Vfluid.
This empirical equation states that the traveltime of an acoustic signal through rock is the sum of the traveltime through the solid and the fluid phases. For Site 1193, the matrix was assumed to be calcite (Vmatrix = 6530 m/s), and the pore fluid was assumed to be seawater (Vfluid = 1500 m/s). Often, the time-average equation provides a lower envelope for carbonate sediments. Deviations from the time-average equation are explained by different kinds of pore types (Anselmetti and Eberli, 1993). Moldic porosity shows a positive deviation from the time-average equation because the pores are integrated in a rigid framework. This type of porosity is common in the platform carbonates of Site 1193 (see "Lithostratigraphy and Sedimentology"). Platform velocity values plot almost entirely above the time-average equation (Fig. F48). The time-average equation for dolomite (Vmatrix = 7000 m/s) shows that the positive deviation cannot uniquely be explained by mineralogy (Fig. F48). Three velocity clusters can be clearly separated from each other in terms of lithology:
The negative deviations of upper-slope sediments from the time-average equation range from 600 to 1000 m/s, which is high for these types of rocks and might be explained by interparticle porosity and micrite cement.
Thermal conductivity
values of the carbonate platform rocks at Site 1193 differ greatly from those of
the remainder of the section (Fig. F49).
From 40 to 130 mbsf, platform values decrease from 2.7 to 1.6 W/(m·K). Below
230 mbsf, in lithologic Units IV-VI, thermal conductivity increases with depth,
ranging from ~1.1-2.0 W/(m·K). Variations in thermal conductivity are
consistent with those in bulk density and porosity. A direct inverse
relationship should exist between porosity ()
and thermal conductivity because of the power law dependence of bulk thermal
conductivity (Kbulk) on the solid matrix grain thermal
conductivity (Kgrain) and the thermal conductivity of the
interstitial fluid (Kw) (Keen and Beaumont, 1990). This
equation can be expressed as
· Kgrain(1-
).
The observed relationship between the thermal conductivity and porosity can be compared with calculated bulk thermal conductivity using the measured porosity values and grain thermal conductivity values summarized in Table T6 in the "Explanatory Notes" chapter (Keen and Beaumont, 1990). The majority of the measured thermal conductivity values lie between the theoretical shale and sandstone curves, giving confidence in the measured thermal conductivity (Fig. F50). Given the predominance of carbonate through the various sections, the observed thermal conductivity is consistent with mixed siliciclastic/carbonate and clay/carbonate sediments.
The quality of the MS and NGR data at Site 1193 is degraded in XCB sections where the core is undersized with respect to the liner inner diameter and/or is disturbed (Fig. F51).
Downhole trends for MS and NGR are similar to that of the GRA bulk density in the first 35 mbsf (Fig. F52). All three data sets show a transition at 5.5 mbsf, which is best detected in the NGR with a downhole decrease from 50 to 5 cps (Fig. F52C). The MS data displays a positive spike at 5.5 mbsf, which is likely explained by the presence of framboidal pyrite found at this level (see "Site 1193 Visual Core Descriptions"). This transition coincides with a change in texture from grainstone to packstone and correlates with a hiatus (see "Age Model"). Below, the data show two distinct intervals with downhole-increasing NGR with a length of ~13 m (Fig. F52C). At 35 mbsf, the values of all three data sets increase sharply in response to the hardground at the top of the carbonate platform (lithologic Unit III) (see "Lithostratigraphy and Sedimentology"). Below the hardground, NGR values range from 0 to 35 cps. However, from 35 to 540 mbsf, low recovery prevented observations of cyclicity in NGR. An MS spike of 1500 x 10-6 SI occurs at the top of acoustic basement, which is likely caused by the presence of volcaniclastics (see "Lithostratigraphy and Sedimentology").
