The FMS logging tool applies four pads, each with an array of electrodes, against the formation to produce a continuous oriented map of the electrical microconductivity of the borehole wall (Pezard et al., 1990; Shipboard Scientific Party, 1999b). The FMS calipers indicate the values of two perpendicular diameters of the borehole. The maximum extension of the FMS pads is 15 in, and, if the borehole diameter is larger, the pad contact is poor and the image quality drops.
Two passes of the FMS tool were run in Hole 1114A in an attempt to provide greater coverage of the borehole wall. However, the two images overlie each other over much of the logged interval, as is often the case in noncircular holes. As a consequence, only the second pass, which logged a longer interval, is presented here.
Two types of images were constructed: a dynamic image, where the color equalization is done on a moving 2-m-long window, and a static image, where the color equalization is done for the whole borehole. The FMS images are presented at three different scales, together with the tadpole representation of the structural measurements. First, a synthetic view is provided by whole borehole images at 1/1000 vertical scale (Fig. F4). Only the static image is shown because the 2-m equalization window makes the dynamic images uniform at this scale. The resistivity variations in this static image are related to the lithologic variations. Second, full borehole images at the scale of 1/200 are given in the "Appendix" for more detailed analysis because this scale is sufficiently small for the borehole image to be limited to a few pages and sufficiently large for the dynamic image to start displaying some character; the color equalization window of 2 m is represented by 1 cm. Finally, close ups of selected intervals at 1/60 to 1/5 scales, which are closer to the typical 1/20 to 1/10 interpretation scales, will illustrate the discussion. The full set of available images and corresponding depth intervals and lithologic units is summarized in Table T1.
The structure of both the sedimentary sequence and the underlying tectonic breccia is almost continuously imaged through a 200-m-long vertical section (105-297 mbsf), with the exception of two large washout zones at 223-234 and 241-247 mbsf (Fig. F4).
The FMS data interval (105-297 mbsf) corresponds, from top to bottom, to lithologic Units III-VII and logging Units L1-L5. Characteristic images facies corresponding to these various units are illustrated. Resistive beds with sharp boundaries are seen within logging Unit L1 (80-126 mbsf) in the upper part of lithologic Unit III (intercalated sandstone, siltstone, and claystone; 55-238 mbsf) (Fig. F5). The increased carbonate content suggested by the higher photoelectric effect of logging Unit L2 (126-146 mbsf) and observed in the calcareous sandstone of Subunit IIIA (123-142 mbsf) corresponds to a zone of higher resistivity in the static image (Fig. F6). A resistive layer with an intricate structure best seen on the static image at 178-180 mbsf (Fig. F7) corresponds to the conglomerate of Subunit IIIB (180-181 mbsf). The lower part (146-238 mbsf) of Unit III shows well-contrasted resistive beds within a more conductive background (Fig. F8).
Within lithologic Unit IV (sandstones; 238-276 mbsf), resistivity is lower than in carbonates and no bedding structure is apparent (Fig. F9). Unit V (silty claystone; 276-286 mbsf), Unit VI (tectonic breccia; 286-287 mbsf), and Unit VII (metadolerite; 287-353 mbsf) FMS facies are shown on Fig. F10, which are degraded by a large washout at 287-292 mbsf.