On 11 June, wireline logging operations in Hole 1272A began with the deployment of a tool string consisting of the Hostile Environment Gamma Ray Sonde (HNGS), the Hostile Environment Litho-Density Sonde (HLDS), and the Dual Induction Phasor Resistivity Tool (DIT-E). The Accelerator Porosity Sonde (APS) was left out of the standard triple combination (triple combo) configuration because of problems with initialization prior to the beginning of the wireline logging operations. After the first tool string deployment, a tool string composed of the Dipole Sonic Imager (DSI), the Scintillation Gamma Ray Tool (SGT), and FMS was used. Main and repeat passes of the entire logged interval were obtained during both tool string deployments. Wireline logging operations took a total of 10 hr, 50 min from beginning to end.
The water depth was estimated from pipe measurements at 2571 meters below rig floor (mbrf). Drilling operations reached a total depth of 131 mbsf, and the mechanical bit release was used to leaving the rotary core barrel bit at the bottom of the hole. A 20-bbl sepiolite mud sweep was done while finishing the coring operations. After releasing the bit, hole displacement operations consisted of 40 bbl (1264 strokes) of sepiolite mud. The bottom of the BHA was placed at a depth of 41 mbsf.
The wireline logging data were sent to the Borehole Research Group at LDEO via satellite transmission for processing, and the results were returned to the ship within 4 days. All data presented in this chapter have been processed and depth shifted as described in the following section.
All passes reached 125.5 mbsf, or 5.5 m above the maximum penetration. The wireline heave compensator was used to counter ship heave, which was a maximum of 1.7 m at the start of the logging operations and decreased to 1.45 m by the end. The BHA depths are as they appear on the logs after a differential depth shift (see depth shift discussion below) and a depth shift to the seafloor. After processing, there is a discrepancy with the original depths given by the drillers on board. Typical reasons for depth discrepancies are ship heave, use of the wireline heave compensator, and drill string and/or wireline stretch. The location of the BHA on the main passes of both tool string deployments is 38 mbsf.
Depth matching was done by choosing one log as reference (base log) and the features in the equivalent logs from the other runs were manually matched to the reference. The depth adjustments that were required to bring the match log in line with the base log were then applied to all the other logs from the same tool string. The original logs were depth matched to the first pass of the HNGS-HLDS-DIT-E tool string (the reference run) and were then shifted to the seafloor using –2571 m. The HNGS-HLDS-DIT-E pass 2 was matched to the reference run using the spherically focused resistivity (SFLU); the DSI-SGT-FMS pass 1 was matched to the reference run using caliper and gamma- ray logs; and the DSI-SGT-FMS pass 2 was matched to the DSI-SGT-FMS pass 1 using the caliper logs. The seafloor depth was not determined directly because there is no clear step in gamma radiation values, which are very low in this hole. The seafloor depth estimate of the drillers was used.
Bulk density data were recorded at a sampling interval of 2.54 cm. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system on board the JOIDES Resolution. While in normal processing, short-spacing data is smoothed to match the long-spacing values; in enhanced processing this process is reversed. SGT gamma ray measurements were recorded at 15.24- and 5.08-cm sampling intervals.
The HNGS and SGT data were corrected for hole size and the HLDS values were corrected for standoff and hole diameter during the data recording. During the first pass, the DSI tool was run in P- and S-, high-frequency upper dipole, and crossed dipole modes; on the second pass, P- and S-, low-frequency lower dipole, and crossed dipole modes were used. Overall, the compressional wave data are good based on the coherency of the signal; the shear wave data from the second pass are better than those from the first pass.
Hole diameter was recorded with the hydraulic caliper on the HLDS (LCAL) and on the FMS (C1 and C2) tools. The borehole was in good condition, typically 10–13 in wide except for occasional thin washouts, the largest of which is at 95 mbsf (Fig. F72). Additional information about the logs can be found in "Downhole Measurements" in the "Explanatory Notes" chapter.
Electrical resistivity values measured in Hole 1272A are low throughout the entire logged interval. Electrical resistivity values from both passes show deep measurements (IDPH) that range 2.1–4.7 
m, intermediate (IMPH) measurements of 0.9–8.3 m; and shallow (SFLU) measurements that range 1.6–7.2 m (Fig. F72). The SFLU curve shows the widest range of variability, most likely due to changes in fracture intensity and alteration. Several zones with higher resistivity values correlate well with similar changes in density, photoelectric effect (PEF), and velocity (Fig. F72).
High-resolution density measurements show values ranging 1.3–2.7 g/cm3. The average density for the entire logged interval is 2.3 g/cm3, consistent with the overall high degree of serpentinization observed in the peridotites. Densities are especially low in the interval 94–96 mbsf, where a fault zone or large fracture was encountered. In keeping with the HLDS measurements, which show a washout at 95 mbsf, the density values indicate a large standoff (i.e., distance between the tool sensors and the borehole wall). Overall, logging densities correlate well with laboratory measurements (Fig. F72), although densities in rock cubes tend to be lower than the logging densities and laboratory density measurements made on rock chips (see "Porosity, Density, and Seismic Velocity" in "Physical Properties"). The PEF values range 1.5–3.0 barn/e– (mean PEF for the logged interval = 2.45 barn/e–). The relatively low PEF values are also consistent with the high degree of serpentinization (see Table T13, p. 75, in the "Explanatory Notes" chapter), whereas the larger values may reflect the presence of magnetite, as seen in the core magnetic susceptibility logs (see "Magnetic Susceptibility" in "Physical Properties").
Compressional wave velocities from both passes range 2.1–5.2 km/s (mean = 3.0 km/s). In general, these compressional wave velocities are lower than expected values for lower oceanic crust and upper mantle and may reflect the high degree of serpentinization and/or the fractured nature of the rocks recovered from this hole. Compressional wave velocities correlate well with laboratory measurements made at ambient pressure (Fig. F72). Shear wave velocities are generally low, ranging 0.5–3.1 km/s (mean = 1.2 km/s). Postcruise processing and detailed analysis of the shipboard slowness time coherence processing and cross-dipole measurements will determine any potential velocity anisotropy or shear wave splitting associated with structural features imaged with the FMS.
The General Purpose Inclinometry Tool (GPIT) run in conjunction with the FMS, contains a triaxial fluxgate magnetometer (see "Downhole Measurements" in the "Explanatory Notes" chapter) that can provide information on the intensity and direction of magnetization in the formation (Fig. F73). In the simple case of a uniformly magnetized, horizontally layered medium, the vertical anomaly measured in the borehole will have the opposite sign from the vertical component of the formation magnetization (e.g., Ito et al., 1995; Gallet and Courtillot, 1989). Moreover, for a normal polarity magnetization formed in the Northern Hemisphere, the horizontal anomaly will be 180° out of phase with respect to the vertical anomaly. The relative amplitudes of the horizontal and vertical anomalies are dictated by the inclination of the formation magnetization.
Magnetic data for peridotite samples (lithologic Unit II) from Hole 1272A reveal a normal polarity remanence with an average inclination of ~45° (see "Paleomagnetism"). Initial inspection of the magnetic anomaly data from Hole 1272A reveal that both horizontal and vertical anomalies are positive, apparently at odds with the pattern expected from the paleomagnetic data from samples at this site. Two factors contribute to this discrepancy. First, the strong magnetization of the drill pipe generates a positive vertical anomaly for a significant distance below the end of the pipe. Second, the calibration of the fluxgate sensors is apparently inaccurate, leading to an offset, particularly in the vertical anomaly. The offset in the vertical fluxgate sensor is poorly constrained by the data from Hole 1272A, but an estimate of the possible calibration error can be obtained from FMS logging results from Leg 197 (Tarduno, Duncan, Scholl, et al., 2002). Here, the vertical component of the ambient field measured >100 m from the drill pipe in weakly magnetized sediments is 1000–2000 nT larger than the true value.
To partially compensate for these effects, we removed an estimate of the anomaly associated with the drill pipe (Fig. F74A) from the vertical anomaly measured in the borehole. An offset of 1000 nT inferred from Leg 197 data was assumed for the vertical fluxgate (the base level of the modeled drill pipe signal), although the Leg 197 results suggest that this value could be larger. The resulting magnetic anomaly pattern more closely corresponds to the expected pattern (Fig. F74B). Below ~60 mbsf, the vertical and horizontal anomalies show similar amplitude patterns that are 180° out of phase. Notably, the anomalies at ~90 mbsf are consistent with the presence of a highly magnetized (normal polarity) zone, presumably reflecting ~1 m thickness for the oxide-rich gabbroic rocks recovered in this interval. Additional calibration postcruise studies on the GPIT will be required onshore to validate these initial results.
FMS images show many zones that are characterized by high fracture density and deformation. Fault gouge samples recovered from Section 209-1272A-19R-1 correlate with an interval with high resistivity contrast interpreted to represent a highly fractured interval between 89.5 and 93 mbsf (Fig. F75). Oxide gabbro samples from this core could be responsible for the dark resistive bands found in interval 90.2–90.9 mbsf (Fig. F75). The interval 94.2–95.9 mbsf also corresponds to a zone where fault gouge samples were recovered in Section 209-1272A-19R-2 (Fig. F76). The interval with resistivity contrast most indicative of intense faulting is 100.5–101.9 mbsf (Fig. F77). This interval is characterized by thick, sharp-bounded conductive zones and defining the top and bottom contacts, a series of resistive clasts (white round features) that suggest brecciation, and some faint high-angle features that suggest either additional fracturing or veining episodes. A total of 2.1 m was recovered from a 5-m cored interval that corresponds to Core 209-1272A-21R, including a soapstone (interval 21R-1, 67–70 cm).
Preliminary structural analyses of fracture patterns show 78 features striking roughly northwest–southeast and dipping mostly northeast (Fig. F78). Dip magnitudes range between 10° and close to 90°, with most the dips ranging 40°–60°. Highly fractured and brecciated intervals interpreted from FMS images and correlated with fault gouge recovered in core strike in a general northwest–southeast direction and dip northeast–southwest (Fig. F79). The general northwest–southeast strike of most of the identified features indicates that faults and fractures are oblique to both the fracture zone and the Mid-Atlantic rift valley. These orientations are consistent with orientations of serpentine veins and fractures measured on the core face and rotated into a geographical reference frame using paleomagnetic data (see "Structures in Peridotite and Gabbroic Intrusions" in "Mantle Upwelling, Melt Transport, and Igneous Crustal Accretion" in the "Leg 209 Summary" chapter).
Formation natural radioactivity was measured during each run with two different tools. The SGT measured total gamma counts, whereas the HNGS provided spectral measurements. The different gamma ray tools show the same general patterns throughout the logged interval. The high-resolution total counts curve from the SGT and spectral data from the HNGS are shown in Figure F80 for simplicity. The SGT curve has low values (0.0–6.4 gAPI). The spectral gamma ray measurements also show very low values that in many instances are below the tool detection limits for Th (0.7 ppm), U (0.35 ppm), and K (0.18 wt%). The spectral data show a general inverse relationship between thorium and uranium as well as a general increase in potassium with depth.
