To free the pipe at the conclusion of drilling at Hole 1130C, the bit was released and, accordingly, no wiper trip was possible before logging. Hole preparation was limited to circulating with seawater. The lower limit of the BHA was placed at 108 mbsf. The WHC was used throughout logging and generally coped well with the moderate heave conditions.
Three different logging strings were deployed in the following order: (1) triple combo, (2) FMS/sonic, and (3) WST (Table T18; see "Downhole Measurements" in the "Explanatory Notes" chapter). To increase the maximum depth of logging with the triple combo, and thereby increase the chances of logging across the carbonate/siliciclastic boundary at the base of the hole, the Lamont-Doherty Earth Observatory high-resolution temperature/acceleration/pressure tool was not deployed. Three passes with the triple combo were made. The first was a short quality-control run from 239.5 to 179.5 mbsf, with the accelerator porosity sonde (APS) switched off. A main pass was initiated at the base of the hole (371.5 mbsf); however, the WHC failed because of overheating caused by a water-pump failure when the triple combo was ~20 m off bottom. As a result, the WHC had to be closed down. The logging speed was then doubled to 550 m/hr to protect the tools, and the hole was logged to mudline without the WHC. A second full run of the triple combo with the WHC working was made from 322.5 mbsf to the mudline. Two passes of the FMS/sonic were made at Site 1130. The first pass was from 368.5 to 152.5 mbsf. For the second FMS run, the BHA was raised by 10 m, and the hole was logged from 367.5 to 132.5 mbsf. Eight check-shot stations (stacks of seven shots), spaced ~30 m apart, were recorded with the WST between 358 and 140 mbsf, adjacent to significant boundaries indicated by acquired logs and potential seismic sequence boundaries. As a result of the shallow water depth, the generator-injector (GI) gun pressure was lowered to the minimum level of 600 psi to avoid saturating the WST geophone.
Conditions in Hole 1130C were good, despite the minimal hole preparation. The borehole diameter indicated by the caliper log identified only slight rugosity, with a maximum diameter of ~38 cm in the interval from 300 to 335 mbsf (Figs. F25, F26). Data from the first pass of the triple combo was of poor quality above 342.5 mbsf as a result of the high logging speed and significant tool heave after the WHC failed. The second pass with the operational WHC and normal logging speed produced good quality data in the open-hole interval between 322.5 mbsf and 107 mbsf. Neutron loading of the formation by the APS from the first triple combo significantly degraded gamma-ray measurements through pipe during the second pass, but not in the open-hole interval. The uniform hole diameter produced good quality FMS logs on both passes, with heave effects largely removed by shipboard processing. The sonic log was of high quality, even for the analog channels. Check-shot data were generally of good quality, although the last four stations clipped slightly on the first arrival, despite the GI being run at minimum pressure. The low gun pressure reduced the bubble-suppression benefits of the GI gun, causing multiples to appear in the signal.
Comparison of logging data to physical properties measurements (see "Physical Properties") shows good agreement between the gamma-ray log (standard [total] gamma ray [HSGR] from the hostile environment natural gamma-ray sonde [HNGS]) and NGR from core, although there seem to be small depth discrepancies possibly caused by heave, poor core recovery, and/or core expansion (Fig. F27). Downhole sediment density and GRA bulk density measured from core also correlate well (Fig. F27). Downhole sonic velocity shows a greater increase with depth when compared to discreet P-wave velocity measurements from cores. This difference occurs because discrete P-wave velocities are not measured under in situ pressure. In addition, discrete velocity measurements from cores show higher amplitude excursions than measurements seen in the sonic log (Fig. F27), probably as a result of the limited vertical resolution of the sonic digital tool.
Three logging units were defined at Site 1130, primarily from variations in NGR (Figs. F25, F26, F28). Boundaries between the defined logging units are characterized by abrupt shifts in gamma-ray, suggesting sharp boundaries between distinct lithostratigraphic units as observed in the recovered core (see "Lithostratigraphy").
The upper portion of Unit 1 that was logged through pipe (0-108 mbsf) is characterized by very low gamma-ray levels (Fig. F28), whereas the open-hole logged interval has distinct cyclic variations in gamma radiation, with excursions of as much as 45 American Petroleum Institute (API) units (Fig. F25). The frequency of this cyclicity increases near 173 mbsf. Uranium is the dominant source of gamma radiation throughout Unit 1 (Figs. F25, F28). Sonic velocity (1.9-2.3 km/s) and sediment density (1.8-2.0 g/cm3) increase linearly with depth in Unit 1, consistent with a normal compaction profile. Photoelectric effect (PEF) increases slightly downhole from 4.4 barn/e- at the top to 4.7 barn/e- at the base of the unit. These values are characteristic of calcium carbonate-rich sediments. The slight positive separation of the porosity and density curves may result from the increased magnesium carbonates in this part of the section, as confirmed by XRD analyses (see "Inorganic Geochemistry"). The base of Unit 1 is defined at an abrupt drop in uranium gamma radiation and a decrease in the slope of the sonic velocity profile (Fig. F26). This boundary roughly correlates to lithostratigraphic Unit I.
Unit 2 is characterized by nearly constant values of all parameters measured (Fig. F26). The lower gamma-ray values in this unit relative to Unit 1 reflect a decrease in uranium content (Fig. F25). The separation between the porosity and density logs is less than in Unit 1 and is characteristic of a clean calcium carbonate (see "Lithostratigraphy"). Several low-porosity peaks, crossing over the density curve, may indicate the occurrence of partially silicified beds within this unit. The reduced gradient in sonic velocity within logging Unit 2 (Fig. F26) may indicate slight fluid overpressure of this unit. Some degree of overpressure is also indicated by the large difference between in situ velocities and velocities measured on the recovered core (Fig. F27). The base of Unit 2 is defined by an abrupt decrease in NGR (Fig. F25). This boundary is clearly identified on FMS images (Fig. F29) and correlates to the base of lithostratigraphic Unit II.
Unit 3 is characterized by low gamma-ray values compared with overlying units (Fig. F25), and the PEF log displays increased variability. The jagged appearance of both shallow-resistivity and sonic logs indicates a thinly bedded (1-2 m) succession of varying lithification (Fig. F26). This is confirmed by limited core recovery (see "Lithostratigraphy") and FMS images that indicate a sequence of highly resistive thin chert beds (~20 cm) alternating with 1- to 3-m intervals of more conductive chalk or ooze (Fig. F29).