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X-ray CT has proven to be a relatively quick method to reveal 3-D internal structures of core samples and 3-D distribution of coral fragments, dropstones, and pebbles and their relationship to the surrounding host sediments without any disturbance to samples. CT scanning immediately after coring and before splitting may be efficient to avoid degradation of cores.

Sedimentary and coring structures are clearly recognized in X-ray CT images (see 20–90 cm in Fig. F6A, F6B), implying that these structures retain density contrasts. X-ray imaging is also efficient for observing dropstones and pebbles. However, Shirai et al. (2007) suggested that carbonate rocks might be unsuitable for X-ray imaging because cementation often obscures density contrasts, rendering sedimentary structures homogeneous. When CT numbers are selected in narrower ranges, which is more suitable for observation of sedimentary structures, coral fragments can be clearly distinguished on CT images (Fig. F12).

Changes in point of view are conspicuous in some features. Ashi (1997) and Shirai et al. (2007) suggest that some lamina sets drastically change in visibility according to changes in observation direction. 3-D imaging with an X-ray CT system can be observed from any angle. Figure F12 shows the 3-D distribution of CT numbers of Section 307-U1316A-7H-1 (Fig. F11) from the viewpoint at an azimuth of 210° and elevation of 60°. Once X-ray CT data are obtained, such a representation is easily available.

Information on X-ray CT images, coupled with shipboard measurements, is useful to estimate some physical properties. For example, Ashi (1997) obtained 3-D density distributions on unsplit cores using a medical X-ray CT scanner. The same method is possible using data obtained in this study and may give a spatially precise map of density variation in the core compared with GRA density profile and magnetic susceptibility at 5 cm intervals (Fig. F13).

Effective and efficient use of the X-ray CT system represents the possibility for rapid systematic characterization of 3-D structural features and may improve subsampling and core processing procedures.