One triple combo and two FMS-sonic (see Table T7, Fig. F15, both in the "Explanatory Notes" chapter) logging runs were recorded in Hole 1114A (see Table T15). A composite plot of the logs is presented in Figure F53. Natural gamma-ray (HNGS) data were logged downward from 26 m above seafloor in the pipe to locate the mudline, where the string was stopped for 3 min to provide a depth reference for the temperature-logging tool (TLT) temperature log. Upon reaching open hole at 80.5 mbsf, all data except those from the accelerated porosity sonde (APS) were logged during the descent to a total depth of 305 mbsf (about 10 m above where the bit had been released), below which the tool string could not pass. The APS data were not collected because this tool requires activating the formation with the minitron source that would degrade subsequent HNGS runs. An upward log was then recorded at 300 m/hr. The pipe was raised to 74.5 mbsf, and the log was recorded up to mudline, where it was held for ~10 min to run calibrations and to give the TLT log another depth reference.
For the second run, the pipe was lowered again to 80 mbsf and the FMS-sonic string (see Table T7, Fig. F15, both in the "Explanatory Notes" chapter) was lowered. The string reached a depth of 298 mbsf and an upward log was recorded to 96 mbsf (Table T15), although FMS logging was ended at 122 mbsf. The tool string was lowered again, and a second pass was made from 298 to 39 mbsf. The bottom of the pipe was raised to 74.5 mbsf, and FMS logging ended at 107 mbsf. The logging speed for both FMS-sonic runs was 300 m/hr.
The drill-pipe measurement of the mudline was 418.0 meters below rig floor (mbrf). Based on the HNGS log from the triple combo run, the mudline wireline depth was identified at 417.5 mbrf (Fig. F54). This value is used to present data in terms of meters below seafloor. The depth shift for the first and second FMS-sonic runs was 418.25 m and was derived by correlating the natural-gamma spectrometry tool (NGT) from the FMS-sonic tool strings with that of the triple combo run within the intervals between 110 and 120 mbsf (Fig. F55A) and between 215 and 224 mbsf (Fig. F55B). These intervals were chosen for their characteristic large variations.
Log quality is degraded in areas of enlarged diameter and rapidly changing hole diameter (see "Downhole Measurements" in the "Explanatory Notes" chapter). In Hole 1114A the caliper from the triple combo run reached maximum extension in the following intervals: 223-235 mbsf, 241-247 mbsf, 277-280 mbsf, and 288-292 mbsf (Fig. F53A). In addition, the caliper nears full extension between 156 and 166 mbsf.
The relationship between the neutron porosity (APLC) and density porosity (DPHI) measurements was used to distinguish between high clay content and low clay content (clean) lithologies. Relative to Site 1109, the discrepancy between the neutron and density porosities is small, indicating overall lower clay content. Porosity values from both tools are significantly lower than at Hole 1109D. The low porosities (~40%) near the top of the logged interval suggest that these sediments have experienced greater burial than their present depth. With some exceptions, porosity decreases from the top of the logged interval to ~200 mbsf. The porosity data below 200 mbsf are difficult to interpret because of washouts but appear uniform where not washed out. Sonic velocities generally increase from the top of the logged interval (70 mbsf) to 200 mbsf and become more variable from 200 mbsf to the total logged depth of 284 mbsf (Fig. F53B).
In addition to considering the separation between the neutron and density porosities, the definition of log units also considered values from the natural gamma ray and photoelectric effect (PEFL). As was observed in Hole 1109D, uranium content varies little and the total gamma ray seems controlled mainly by the thorium and potassium contents. At previous sites of Leg 180, it has been noted that gamma-ray counts increase within sand layers. This correlation was used in log analysis of Hole 1114A.
A PEFL value greater than 5 barns/e- generally indicates carbonate. However, data from Hole 1114A are surprising in that PEFL values are extremely high, reaching 12 barns/e-. Log analysis defined five logging units (Fig. F56). Distinctive characteristics of each unit are described below.
In this interval, the neutron porosity is larger than the density porosity by ~0.15-0.20, indicating some clay content. This difference decreases downhole, suggesting an upward-fining trend. The PEFL values also increase downhole over this interval, with values reaching 5 barns/e- at 126 mbsf. Gamma-ray values generally range from 26 to 41 GAPI units with the exception of the interval between 113 and 117 mbsf where several peaks range between 50 and 60 GAPI units. Velocities increase from ~1.9 to 2.5 km·s-1 at 116 mbsf, then decrease to ~2.0 km·s-1 at the base of log Unit L1.
Log Unit L1 is correlative with the upper part of lithostratigraphic Unit III, which is interbedded sandstone, siltstone, and claystone (see "Lithostratigraphic Unit III").
In most of the logs, this unit is similar in character to log Unit L1. The primary difference is that gamma-ray values step up to between 44 and 79 GAPI units. Generally, neutron porosity is greater than density porosity, but this difference rarely exceeds 0.10, suggesting a cleaner (lower clay content) formation than log Unit L1. The PEFL values range between 4 and 5 barns/e-, which would typically be considered consistent with a carbonate-bearing lithology. However, carbonate content in this interval is <6 wt% (see "Organic Geochemistry"); therefore, other minerals may be responsible for the PEFL values here (see discussion in "Log Unit L3"). Log Unit L2 coincides with lithostratigraphic Subunit IIIA, which consists of calcite-cemented siltstone, sandstone, and bioclastic packstone (see "Lithostratigraphic Subunit IIIA").
This unit is defined by its PEFL values, which are consistently greater than 5 barns/e- and reach peak values of 10-12 barns/e-. These high values suggest the presence of iron-bearing minerals. The density and neutron porosities are very similar in this unit, indicating low clay content. Gamma-ray values range between 59 and 82 GAPI units. Below 178 mbsf, resistivity values step up, but this change is not accompanied by significant variations in any other logs.
Log Unit L3 lies within lithostratigraphic Unit III, including Subunit IIIB (see "Lithostratigraphic Unit III"). Low recovery within this interval makes it difficult to assess the source of the elevated PEFL values. Pyrite is commonly noted within the core descriptions and may contribute to the elevated PEFL values that characterize this unit. The top boundary of lithostratigraphic Unit IIIB containing conglomerate and coarse sandstone may correlate with the step increase in resistivity noted at 178 mbsf. However, the increased resistivity persists to a depth of ~220 mbsf, whereas lithostratigraphic Subunit IIIB was determined to extend only to ~190 mbsf.
In log Unit L4 the hole is frequently enlarged, thereby affecting log quality (Fig. F53A). Two of the washout intervals (at 223-235 mbsf and 288-292 mbsf) coincide with increased incidence of pervasive scaly fabrics noted in core description (see "Structural Geology"). In much of log Unit L4 the neutron porosities are larger than the density porosities by ~0.05, suggesting some clay content. The difference reaches as high as 0.20 in thin (several meter) intervals, suggesting increased clay content, and meter-scale zones exist where neutron porosity falls below density porosity, suggesting clean units. Between 198 and 250 mbsf, the PEFL values decrease downhole from 5 to 3 barns/e-. From 250 mbsf to the bottom of log Unit L4, PEFL values remain ~4 barns/e-, with two distinct drops to ~3 barns/e- at 278 and 290 mbsf. Gamma-ray values show large variation between 198 and 235 mbsf. A peak in gamma-ray values occurs at 210 mbsf and coincides with a peak in resistivity. Below 235 mbsf, gamma-ray data show less variation, generally ranging from 60 to 70 GAPI units.
Log Unit L4 overlaps lithostratigraphic Units IV, V, and VI, which consist of sandstone, silty claystone, and a tectonic breccia, respectively (see "Lithostratigraphic Unit IV," "Lithostratigraphic Unit V," and "Lithostratigraphic Unit VI"). These units are not distinguishable on the logs because of both washouts and lack of coverage by the upper tools of the triple combo tool string.
This unit and its contact with overlying log Unit L4 are shown most clearly on the FMS images, which are described in "Borehole Geometry, Magnetic Field, and FMS Dynamics." The upper boundary of log Unit L5 was selected as the bottom of the washouts. It is highly resistive and corresponds to the metadolerite (see "Igneous and Metamorphic Petrology").
The accelerometer data of the FMS-sonic run show that the hole deviation increases from 0.5° near the top of the borehole to more than 2° near the bottom of the logged interval (Fig. F57). Acceleration magnitudes indicate scatter in tool movement, which represents some tool sticking during the passes. The azimuth data of Pad 1 from the two FMS passes indicates a 90° difference for most of the passes (Fig. F58). Consequently, the second pass directly underlies the first for most of the logged interval. The FMS caliper data indicate loss of pad contact for both calipers at depths of 223-235 mbsf, 240-247 mbsf, and 288-292 mbsf (Fig. F59). Between 156 and 167 mbsf, one reading is near the maximum while the other caliper indicates a hole size of 28-30 cm. In general, the hole is very elliptical between 135 and 200 mbsf, with the larger diameter trending 50°. This direction is consistent with the strike of bedding noted in the FMS images. It is important to note that FMS-based data are oriented relative to geographic north.
The magnetometer measurement yields both inclination and magnitude of the total field. These measurements are strongly influenced by the pipe when approaching it. Although magnitudes of magnetic intensity show a consistent offset between Pass 1 and Pass 2, the character of the logs is very similar. The magnetic intensities increase downhole until 210 mbsf and then remain relatively constant (Fig. F60). Magnetic inclination decreases from -29.7° at the top of the logged section to -30.3° at the bottom (Fig. F60).
Two passes of the FMS tool were run in Hole 1114A in an effort to provide greater coverage of the borehole wall (Table T15). However, the two images overlie each other over much of the logged interval despite rotation of the tool between passes. Good quality FMS images were acquired between ~105 and 298 mbsf with the exception of large, frequent washouts as shown in the caliper log (Fig. F59). The FMS processing steps included speed correction, depth shifting, and static and dynamic normalization using a 1-m window. The first-pass FMS images were depth shifted an additional 0.1 m to correct a constant vertical offset observed between the two images. Remaining vertical offsets (<0.05 m) between the two images vary throughout the logged interval and appear to be caused by differential accelerations caused by sticking, which will be corrected by further processing postcruise.
The FMS interpretation is organized according to log units defined in this section (Fig. F56). Hole 1114A is generally characterized by thin (~10 cm), moderately resistive beds that are heavily fractured. Bed dips throughout Hole 1114A average 38° with a mean northwestward dip direction of 320° (Figs. F61, F62, F63). Fractures show two prominent dip distributions in Hole 1114A. Above ~260 mbsf, fractures dip 68° with a northward dip direction of 355° (Figs. F61, F62, F63). Below 280 mbsf (i.e., within the fault zone), fractures dip 65° with a southwestward dip direction of 230°, which is consistent with the south-southwest-dipping normal fault orientation determined from the seismic reflection data.
Log Unit L1 is characterized by moderately resistive beds interpreted as clayey layers occasionally interlayered with 10- to 15-cm-thick, highly resistive beds, which are inferred to be sand and possibly calcium-carbonate-rich layers (Fig. F64). Beds are cut by numerous thin conductive fractures that are occasionally observed to be filled with resistive material, which is consistent with calcite cement. Bed dips increase with depth within this short unit from ~20° to 45°, whereas dip directions are consistently to the northwest (Fig. F63). Fractures dip 40° -60° to the northwest; however, minor fractures dipping 60° to the east-northeast are also observed to crosscut the northwest-dipping beds.
Calcium carbonate-rich sediments of lithostratigraphic Subunit IIIA correlate with the more highly resistive layers of log Unit L2 (see "Subunit IIIA"). Beds show a slight change in dip direction to the west-northwest with dips between 35° and 55° (Fig. F63). Fractures are poorly defined within this unit. Image quality is degraded throughout much of this interval because of poor pad contact with the borehole wall.
The upper portion of log Unit L3 displays overall low resistivity above 178 mbsf, which is likely related to clays as well as heavy (i.e., conductive) mineral content indicated by the PEFL (Figs. F53B, F65). Pyrite recognized in the core samples is suggested to be the dominant conductive mineral in this unit (see "Lithostratigraphy"). A distinct increase in large-scale resistivity begins at 179 mbsf with the top of a 1.5-m-thick highly resistive layer (Fig. F66). Below 170 mbsf, both bed and fracture dip directions verge northward with depth and steadily increase in dip from 30° to 50° and 35° to 80°, respectively (Fig. F63).
Large washouts and borehole irregularities commonly degrade FMS image quality within this unit. Between 208 and 216 mbsf, however, image quality is very good and the two FMS images do not overlap (Fig. F67). Log Unit L4 displays overall low resistivity, which suggests increased conductive mineral content. The trend of increasing bed and fracture dips and northward verging dip direction observed in Unit L3 (see "Log Unit L3") continues within Unit L4 as far as 215 mbsf (Fig. F63), below which large washouts preclude image interpretation. As shown in Figure F67, steep 80°-dipping fractures cut more shallow 40°-dipping beds, and both beds and fractures display north-northwestward dip directions.
Below ~292 mbsf, highly resistive material continues to the base of the FMS log. The top of log Unit L5 is defined by steep (65°) southwestward-dipping, fracture-bounded beds, whereas below 293 mbsf it appears relatively structureless with few well-defined, continuous fractures. The tectonic breccia-metadolerite contact described in cores correlates in depth approximately with the top of log Unit L5 (see "Lithostratigraphic Unit VI" and "Lithostratigraphic Unit VII," and "Igneous and Metamorphic Petrology").
It is difficult to select
the boundary between the tectonically brecciated metadolerite and the
metadolerite basement. Although FMS images above 292 mbsf are partially obscured
by poor pad contact, a coarse-textured, highly resistive 1-m-thick bed appears
at 290.5 mbsf. Based on the strong resemblance in both structure and
microresistivity response to the material below 292 mbsf, this bed is
interpreted to be similar material to that of log Unit L5 (Fig. F68).
Below this 1-m-thick layer a relatively thin (
1-m-thick)
layer is washed out with the exception of a small portion of the borehole
between 240° and 360°, which suggests continuity between the beds above and
below. It is reasonable to infer that the partially washed-out interval above
~292 mbsf consists of metadolerite that has been brecciated to various extents.
The TLT data reveal the temperature profile within the pipe (Fig. F69) and in open hole (Fig. F70) where 23.4°C is reached at 304 mbsf. The tool string was held on bottom for a few minutes, and warming of the bottom hole is evident. However, the data record was not long enough to extrapolate in situ temperatures. Although the tool was held at mudline for ~10 min, the temperature continued to decrease and a stable temperature was not reached. The lowest recorded value was 15.0°C. No in situ temperature measurements were possible at Site 1114. Based on the TLT data, we estimate that a lower limit for the thermal gradient is 0.03°C·m-1. The actual gradient is probably significantly higher.
