DOWNHOLE MEASUREMENTS

Three different logging runs were successful at Site 1140 (Table T16) (see "Operations"). The first run included the triple combo, consisting of the DITE, the APS, the HLDS, as well as the HNGS and the LDEO-TAP tools. We completed two passes in the basement section; the main log was recorded from 321.2 to 0 mbsf, and a repeat section from 321.2 to 225 mbsf. The tools encountered no ledges or bridges. We attempted to log the seafloor depth, but as at Site 1137, calcareous ooze and seawater showed no contrast in natural gamma radiation. The driller's pipe depth was 2486 meters below rig floor (mbrf), and the logging data recorded the pipe at 2488 mbrf. Instead of shifting the logging data to the driller's seafloor at 2406 mbrf, we shifted the data with respect to the pipe and assumed that the depth of the seafloor was at 2408 mbrf.

For the second run, we deployed the FMS, the LSS, and the NGT tool combination and completed two passes in the basement and one pass in the sedimentary section. Although the tools did not contact the borehole wall through most of the sedimentary section (diameter = >15 in), we continued logging to obtain velocity data.

The third run employed the WST. We used a 300-in³ air gun, which produced good signals into basement. The source offset was 49.0 m. In basement, we chose eight locations clamping the tools every ~10 m. In the sediments, the WST would only clamp at two depths because the hole was too large and/or the tool did not stay in position.

Data from the first two logging runs (Fig. F53) are of good quality. The calipers of the HLDS and the FMS show that the hole was enlarged, >15 in (38 cm) above 227 mbsf, whereas in basement the hole was in excellent condition. Small breakouts in a few discrete intervals correspond to sedimentary interbeds. Unfortunately, all data from the HNGS are not useful. The tool's spectrum was shifted for some reason and gave erroneous counts that cannot be corrected. However, the natural gamma-ray data from the second run are of high quality. Ship heave generally needs to be taken into account because it might have caused shifts between different logging runs.

Discrete core measurements and logged density, compressional wave, and natural gamma-ray data (Fig. F54) agree well both in sediments and basement. In the sediments of lithologic Unit I, all curves show the same trends with no offset or depth mismatch. In igneous basement, recovery was poor and cores should be shifted for a better fit (e.g., low core densities at 278.7-279.2 mbsf [Section 183-1140A-32R-3] were measured in Unit 4 [see "Physical Properties"], which is a sedimentary interlayer [see "Lithostratigraphy"] corresponding to a depth of ~283 mbsf in the logging data). The NGR of the rocks detected by both downhole measurements and the core measurements correlates well in the sedimentary section. In the basement section, the minimum and maximum values correspond generally, but because of the low core recovery, the core data are slightly shifted. The velocity data were corrected for cycle skipping. They agree well with velocities determined from core samples (Fig. F54) (see "Seismic Stratigraphy").

The check-shot survey with the WST yielded excellent data for time-depth conversion (Table T15). For further information, see "Seismic Stratigraphy".

To orient structural measurements of Site 1140 cores (see "Alteration and Weathering") and to determine true thicknesses of lithologic units, we need oriented downhole images. The FMS images show sediment interbeds, fractures, vesicles, and structural features of the pillow lavas. The FMS data are of low quality in the sedimentary section because the FMS pads did not contact the wall of the enlarged borehole. This was as expected based on the caliper data from the first run.

The sediment/igneous basement boundary at 235.8 mbsf is marked by a significant increase in density, resistivity, velocity, and a decrease in porosity (Fig. F55). Logging data help delineate the five lava units and the sedimentary interbeds in basement. The basalts generally have densities of 2.8-3.0 g/cm³, resistivities of 20-200 m, porosities of <20%, and compressional wave velocities of 5-6 km/s. In the sediments, densities are <2.0 g/cm³, resistivities range from 0.5 to 2 m, porosities from 60%-80%, and compressional wave velocities are <4 km/s (Fig. F56A, F56B). Sediments interbedded with lava flows show intermediate physical properties, probably because of greater consolidation compared with sediment overlying basement. Different lithologies identified in the logging data correlate with units identified in the recovered rocks (Table T17).

The top of the igneous basement consists of both pillows and massive basalts producing distinguishable FMS images. The pillow contacts with wider (>40 cm) voids show clearly in density, resistivity, and porosity logs. The thicknesses and relative positions of the pillowed and massive lavas correlate with the rocks recovered from basement Unit 1 in Cores 183-1140A-25R to 28R. At the bottom of basement Unit 1, in the portion not recovered in cores, a 2.4-m-thick zone with both pillows and pods of sediments appears in the FMS data. This might indicate that basement Unit 1 flowed over the underlying sediments and partially sank into them. The lack of thick sediment fill between the pillows above this points argues against sediments infilling after the pillows were emplaced. The sediments from 253.4 to 255.5 mbsf appear homogeneous in the FMS data; we assume that they separate basement Units 1 and 2 (Fig. F55).

Only 1.27 m of pillow basalts was recovered from basement Unit 2, but the downhole measurements show that this unit is 10.9 m thick and includes a 1.3-m-thick massive lava (Fig F55). Basement Unit 2 lavas are the most phenocryst rich at Site 1140, but this did not produce any significant change in the physical properties of the lava. However, natural gamma-ray intensity is elevated compared to basement Unit 1 (Fig. F55), which is related to the primary composition of the lava (see "Igneous Petrology and Geochemistry"). The FMS images of basement Unit 2 show the pillowed character of the lava flows (Fig. F57).

The top of basement Unit 3 consists of a small piece of greenish sediment in the recovered core (see "Lithostratigraphy"). In the logging data, this sedimentary layer is 2.4 m thick (Fig F55). The FMS image appears speckled; this could be caused by mottles, burrows, coarse sediment grains, or concretions (Fig. F58). The sediments are also characterized by low total gamma-ray signature (SGR) values (~12 gAPI), increased porosity and low density, resistivity, and velocity values, comparable to the ranges in the calcareous sediments above basement (Fig F55). This minimizes the possibility that the sediment is dominantly hyaloclastite. Furthermore, caliper measurements indicate that the hole was in good condition in this interval, suggesting very competent sediment.

The lava in basement Unit 3 consists solely of pillows, and, therefore, its physical properties vary widely. The marginally lower resistivity and density might be related to the slightly higher vesicularity of this unit (see "Physical Volcanology"). The elevated total gamma-ray readings are caused by increased potassium and thorium values (Fig. F53), which are related to the primary composition of the lavas (see "Igneous Petrology and Geochemistry").

Below basement Unit 3, a thin package of lava is sandwiched between two sediment layers (Fig. F59). The upper sediment layer probably corresponds to basement Unit 4, which consists of dolomite and dolomitic nannofossil chalk (see "Lithostratigraphy"). In the FMS data, we see no pillow structures within the sandwiched lava. This lava might have been recovered as the altered (orange) uppermost lava in basement Unit 5 (Section 183-1140A-33R-1) (see "Alteration and Weathering") (Fig. F10; Table T17). Caliper measurements show an enlarged hole in the lower sediment layer (Fig. F59), which suggests that it is soft, thus explaining why it was not recovered.

Beneath the sediment layers, basement Unit 5 is massive lava with relatively homogeneous physical properties. This correlates with the thick, massive lowermost lobe recovered in core (see "Physical Volcanology"). Near the base of basement Unit 5, planar fractures are well imaged by the FMS (Fig. F60). These fractures all dip in a direction of ~240°. We interpret vertical features to be pipe vesicles or fingers of late-stage segregations seen in Section 183-1140A-34R-3 (see "Alteration and Weathering" and "Physical Volcanology").

The logging data show that the small piece of orange dolomite between basement Units 5 and 6 is from a ~1-m-thick sediment layer (Fig. F60). Although the FMS data essentially cover the entire drilled interval of basement Unit 6, not all instruments were able to reach the bottom of the hole. We acquired no data from the natural gamma-ray tool within basement Unit 6. The FMS images show that basement Unit 6 is a mix of pillowed and massive basalt. The 3-m-thick massive portion of basement Unit 6 is also seen in the recovered core.

Comparing the different lava units, we find that gamma-ray values are lowest in the basalts of basement Units 1 and 5. This is related to primary geochemical differences. This observation is consistent with XRF analyses, in which the highest potassium values were detected in basement Units 2 and 3 (see "Igneous Petrology and Geochemistry"). In general recovery of massive lava was somewhat better than that of pillows (45%-100% vs. 12%-79%).