- t = 2.54
csg
(ODcsg - IDcsg)/2,
Evaluation of core physical properties at Site 1196 included nondestructive measurements of bulk magnetic susceptibility and natural gamma radiation primarily on split cores using the multisensor track (MST). A small number of full cores were also processed through the MST, although low recovery at Site 1196 limited its use. Additionally, the large diameter of cores recovered with the ADCB (Cores 194-1196B-13Z through 51Z) was too large for MST analysis. P-wave velocity (x-, y-, and z-direction), bulk density, grain density, and porosity were determined from ~9.5-cm3 cubic samples. Thermal conductivity was measured on lithified core samples.
Overall, bulk density ranges between 1.9 and 2.75 g/cm3 and generally increases downhole to ~500 mbsf (Fig. F47). From 500 to 672 mbsf, bulk density values slightly increase to 2.2 g/cm3. Bulk density shows higher scatter throughout the entire interval, and no apparent relation exists between density and the lithologic units. The phosphatic-rich sands of lithologic Unit V at the bottom of Hole 1196A (see "Lithostratigraphy and Sedimentology") have an average bulk density of 2.2 g/cm3.
Grain density values average 2.80 g/cm3 and range between 2.55 and 2.95 g/cm3 (Fig. F47). The downhole variations in grain density are consistent with dolomite abundance (see "Geochemistry") because dolomite has a higher grain density (2.866 g/cm3) than calcite (2.710 g/cm3). Apart from the intervals 480-520 mbsf and 610-630 mbsf and a few outliers, grain density values exceed 2.80 g/cm3 only in dolomite-rich intervals (Fig. F48). This indicates that in these platform carbonates, grain density can be used as a proxy for dolomite content.
The porosity profile mirrors the bulk density profile. Data are extremely scattered and range from 2% to 51%, reflecting the dominant role of local cementation and dissolution in the carbonate rocks (Fig. F47). The highest porosity values are found in dolomite-rich intervals with abundant moldic porosity mainly caused by dissolution of benthic foraminifers (lithologic Units I, III, and IV) (see "Lithostratigraphy and Sedimentology"). Lithologic Unit I is dominated by both intergranular and moldic porosity, and porosity ranges from 10% to 51%. Lower porosity values (2%-23%) occur at the base of lithologic Subunit IIA, which corresponds to a higher natural gamma radiation and higher velocity values (see below). Lithologic Unit III has millimeter-sized lenticular molds (lithologic Subunit IIIB) and centimeter-sized molds that are aligned (lithologic Subunit IIID) (see "Lithostratigraphy and Sedimentology"), and porosity varies between 3% and 38%. The overall porosity profile shows no clear downhole trend, indicating that porosity is mainly controlled by dissolution and dolomitization rather than compaction. Porosity values of lithologic Unit V average 32%.
Compressional wave velocity (x-, y-, and z-direction) for Site 1196 was measured with the PWS3 contact probe system on ~9.5-cm3 samples. Velocity values vary between 2300 and 6600 m/s (Fig. F49). On average, PWS3 velocity is ~1700 m/s higher than velocities derived from sonic logging data and interval velocities from check shot data (see further discussion in "Downhole Measurements"). In lithologic Units I and II, the average velocity is 4600 m/s, which is ~700 m/s lower than in lithologic Units III and IV, indicating a downhole velocity increase. Velocity in lithologic Unit V is low, with an average of 2200 m/s. Anisotropy is significant and ranges from -9% to 14% (Fig. F49). Most of the anisotropy values (71%) are positive, meaning that the velocity in the z-direction is lower than average velocity in the x- and y-directions (see "Core Physical Properties" in the "Explanatory Notes" chapter). This is a common feature in well-bedded sediments, characterized by horizontally aligned grains and pores.
A crossplot of velocity vs. porosity for Site 1196 shows a general inverse relationship (Fig. F50). The measured velocities can be compared with the time-average equation of Wyllie et al. (1956). The abundance of moldic porosity in the platform carbonates can be correlated with the large number of porosity-velocity pairs that have positive deviations from the time-average equation because the pores are integrated in a rigid framework (see "Core Physical Properties" in the "Site 1193" chapter). The phosphatic- and quartz-rich sands of lithologic Unit V deviate negatively from the time-average equation because the velocity of quartz is lower than the velocity of carbonate minerals (Fig. F50).
Thermal conductivity values at Site 1196 show a downhole increasing trend consistent with bulk density and porosity trends (Fig. F51). Values range from ~0.8 to ~3.5 W/(m·K). A direct inverse relationship should exist between porosity and thermal conductivity (see "Core Physical Properties" in the "Explanatory Notes" chapter). The majority of the measured thermal conductivity values lies roughly on the theoretical limestone curve, giving confidence to the measured thermal conductivity (Fig. F52). Three outliers with thermal conductivity values >3.3 W/(m·K) are phosphatic-rich sands from lithologic Unit IV (see "Lithostratigraphy and Sedimentology").
The quality of the magnetic susceptibility (MS) and NGR data at Site 1196 is degraded in RCB sections where the core is disturbed and/or undersized with respect to the inner diameter of the liner (Fig. F53). Generally, these cores are not run through the MST. However, at Site 1196, MST data were used as an aid in the logging interpretation to identify the exact core horizon of peaks detected in hostile environment gamma ray sonde (HNGS) logging data (see "Downhole Measurements"). Because of the change in sample volume, NGR and MS units and amplitudes measured from half cores require some thought. Figure F54 compares NGR and MS measured from both full and half cores. Surprisingly, there is no statistical difference between the full-core and half-core NGR values. This is in contrast to the MS full-core and half-core values, which show a constant offset. The change in sign is unlikely to be real and reflects the inapplicability of the MST calibrations relative to processing half cores. Consequently, no corrections were applied to the NGR amplitudes. This was also the case for the MS data, as these units are not in SI format.
MS ranges from -8 to 5 x 10-6 SI (Fig. F53). A purely diamagnetic interval from 20 to 105 mbsf correlates with most of lithologic Subunit IA, meaning that the carbonates are clean and free from magnetic minerals and bacteria (see "Lithostratigraphy and Sedimentology"). For the remainder of the site, data are too scarce for correlations because of low core recovery.
NGR values range from 0 to 65 counts per second (cps) (Fig. F53), with local maxima at 117 to 126 mbsf and 307 to 318 mbsf. However, NGR data just above and below these intervals are missing, and therefore a comparison with HNGS data was important. Over the first 70 mbsf, logging was performed through the drill pipe, which attenuated the true HNGS reading. The Schlumberger log interpretation chart GR-3 (Schlumberger, 1998) describes the procedure for correcting the amplitude of NGR data measured throughout the drill pipe. A parameter, t, is calculated that represents the sum of density-thickness products for the pipe, any cement sheath, and the borehole fluid (Schlumberger, 1998). Because of the pipe thickness and the lack of casing cement, the Schlumberger equation for t can be simplified to give
csg
(ODcsg - IDcsg)/2,where csg
is the pipe density (7.83 g/cm3), ODcsg is the outer
diameter of the pipe (8.25 in), and IDcsg is the inner diameter of
the pipe (4.125 in). For Sites 1196 and 1199, the t parameter is 41
g/cm2. Using the relationship between the t factor and the
NGR attenuation correction factor as a function of the logging tool diameter
(3.375 in), the correction factor is ~7. Consequently, HNGS values from 0 to 70
mbsf were multiplied by 7 (Fig. F53).
Comparison of the NGR with the corrected HNGS data shows that the maximum NGR
values often follow the trend in the HNGS log. Downhole increasing trends are
visible between 0 and 126 mbsf (~10 to ~60 cps) and between 126 and 318 mbsf
(~10 to ~65 cps). NGR maxima at 117-126 mbsf and 307-318 mbsf match peaks in the
downhole logging data and correspond to the bottom of lithologic Subunit IB and
the bottom of lithologic Subunit IIA (see "Lithostratigraphy
and Sedimentology"). The HNGS peak at 126.5 mbsf logging depth
could be placed at Core 194-1196A-14R (124.3-126.0 mbsf). The two NGR maxima
could be related to either a hardground or an exposure surface, as the rocks are
well-lithified and have high velocity and low porosity.
Evaluation of core physical properties at Site 1199 included nondestructive measurements of bulk MS and natural gamma radiation on whole cores using the MST. Low recovery at Site 1199 limited the use of the MST. P-wave velocity (x-, y-, and z-direction), bulk density, grain density, and porosity were determined from ~9.5-cm3 cubic samples. Thermal conductivity was measured on lithified core samples.
At Site 1199, gamma ray attenuation (GRA) bulk density ranges between 1.3 and 2.4 g/cm3 and moisture and density (MAD) bulk density ranges between 1.4 and 2.7 g/cm3 (Fig. F55). On average, MAD density values are 0.3 g/cm3 higher than the maximum GRA density values. This difference is the result of intracore spaces and undersized cores. MAD density is 2.2 g/cm3 at the top of the hole and increases to 2.7 g/cm3 between 90 and 110 mbsf, which coincides with the bottom 17 m of lithologic Subunit IA and its boundary with lithologic Subunit IB (see "Lithostratigraphy and Sedimentology"). From 110 to 170 mbsf, MAD density decreases to 2.2 g/cm3. Below 170 mbsf, bulk density shows high scatter, and no apparent relation exists between density and the lithologic units.
Grain density values average 2.79 g/cm3, range between 2.70 and 2.85 g/cm3, and do not show any clear downhole trends (Fig. F55). Average grain density is consistent with dolomite abundance (see "Geochemistry") because dolomite has a higher grain density (2.87 g/cm3) than calcite (2.71 g/cm3).
Porosity values range from 3%-48%. The porosity profile with depth mirrors the bulk density profile. Porosity starts at ~30% at the top of the hole, decreases to 3% between 90 and 110 mbsf, and increases back to 20% at 170 mbsf. Lithologic Unit I is dominated by both intergranular and moldic porosity, and values range from 2% to 33%. Below 170 mbsf, porosity values are scattered between 14% and 48%. (Fig. F55). The highest porosity values are found at the top of lithologic Unit I, which has pronounced moldic porosity (see "Lithostratigraphy and Sedimentology"). The lowest porosity values (2%-12%) exist at the boundary between lithologic Subunits IA and IB (see "Lithostratigraphy and Sedimentology") and correspond to high bulk density values (2.7 g/cm3), local maxima in natural gamma radiation and magnetic susceptibility, and high velocity values (5500 m/s). The overall porosity profile shows no clear downhole trend, suggesting that porosity is mainly controlled by dissolution and dolomitization and not by compaction.
Compressional wave velocity (x-, y-, and z-direction) for Site 1199 was measured with the PWS3 contact probe system on ~9.5-cm3 samples. Velocity mirrors the porosity and bulk density profiles and varies between 3000 and 5500 m/s (Fig. F56). Velocity starts at 4000 m/s at the top of the hole, increases to 5500 m/s between 100 and 110 mbsf, and decreases to 3950 m/s at 170 mbsf. Anisotropy of velocity ranges from -5% to 11% (Fig. F56). Most of the anisotropy values (81%) are positive, meaning that the velocity in the z-direction is lower than average velocity in the x- and y-directions (see "Core Physical Properties" in the "Explanatory Notes" chapter). This is a common feature in well-bedded sediments, characterized by horizontally aligned grains and pores. In Site 1199 sediments, the positive anisotropy is most likely caused by aligned moldic porosity, as no apparent bedding is visible as a result of intense dolomitization. However, Hole 1199A was drilled with an inclination of ~7° (see "Operations"), which may have some effect on the anisotropy.
A crossplot of velocity vs. porosity for Site 1199 shows a general inverse relationship (Fig. F57). The measured velocities can be compared with the time-average equation (Wyllie et al., 1956). The abundance of moldic porosity in the platform carbonates may explain the large number of porosity-velocity pairs that have positive deviations from the time-average equation because the pores are integrated in a rigid framework (see "Core Physical Properties" in the "Site 1193" chapter). Porosity-velocity pairs from the boundary region between lithologic Subunits IA and IB (90-110 mbsf) have the lowest porosity and the highest velocity values and plot below the time-average equation.
Thermal conductivity values at Site 1199 increase downhole (Fig. F58). Values range from ~2.0 to ~3.2 W/(m·K). From 265 to 382 mbsf, thermal conductivity ranges from 1.5 to 2.2 W/(m·K). A direct inverse relationship should exist between porosity and thermal conductivity (see "Core Physical Properties" in the "Explanatory Notes" chapter). The majority of the measured thermal conductivity values lie around the theoretical limestone curve, giving confidence to the measured thermal conductivity (Fig. F59) (Keen and Beaumont, 1990).
The quality of the MS and NGR data at Site 1199 is degraded because the RCB cores are disturbed and/or, in most parts, are undersized with respect to the inner diameter of the liner (Fig. F60).
From 0 to 141 mbsf, MS ranges from -2 to 20 x 10-6 SI and shows no obvious trend with depth (Fig. F60). Most of the values are below 5 x 10-6 SI. Two small spikes of 8 x 10-6 SI exist at 101 and 123 mbsf, and a spike of 22 x 10-6 SI exists at 141 mbsf. Below 141 mbsf, data are too scarce for correlations because of low core recovery.
Natural gamma radiation values range from 0 to 138 cps, with apparent local maxima at ~39 mbsf, from 95 to 114 mbsf, from 132 to 137 mbsf, and at ~170 mbsf (Fig. F60). Over the first 70 mbsf, downhole logging was performed through the drill pipe, which attenuated the HNGS reading (see "Downhole Measurements"). A density-correction factor of 7 was applied to the HNGS data for that interval to correct for the pipe effect (see "Core Physical Properties") (Schlumberger, 1998). A comparison of the NGR data and the corrected HNGS data shows a good correlation. Maximum NGR values often follow the trend in the HNGS log (Fig. F60). Downhole increasing trends are visible between 0 and 40 mbsf (~10 to ~24 cps) and between 40 and 114 mbsf (~10 to ~83 cps). A single NGR spike is visible at 170 mbsf and is part of an interval with high natural gamma radiation in the HNGS data from 160 to 180 mbsf. Downhole logging data show that most of the natural gamma radiation originates from uranium (see "Downhole Measurements"). NGR maxima at 114.06 and 169.65 mbsf can be correlated with the cores and correspond to intervals just above interpreted exposure surfaces (see "Lithostratigraphy and Sedimentology"). This may reflect increased uranium accumulation during initial flooding, which decreases as flooding continues.
