Sedimentary structures are recognized on 2-D X-ray images, implying that sedimentary rocks (sandstone, siltstone, mudstone, and shale) retain density contrast in spite of decreases in porosity caused by its compaction. X-ray CT is a powerful tool that can reveal important information about structures of consolidated sedimentary rock core samples before splitting, even if only 2-D X-ray imaging is used. X-ray imaging is an efficient method of observing partial sedimentary and postsedimentation structures such as burrows, water escape structures, and small concretions that are often not recognized with split surface observation. CT scanning just after coring may be efficient to describe unstable minerals. Carbonate rocks tend to be unsuitable for X-ray imaging and observation because whole-core cementation often obscures density contrasts, rendering sedimentary structures homogeneous. This is a problem for future studies.
Core imaging from various directions is important for observation of high-angle structures such as trough cross-laminae and intrabed slumps because overlapping structures often prevent clear imaging from a single direction. Hence, it is valuable to construct a system of CT observation and image analysis before core splitting. Core splitting in an appropriate direction will improve accuracy of description and sampling. Because of time constraints inherent in core handling, an effective and efficient X-ray CT procedure must be constructed as a part of the core description process. At a minimum, the procedure should include: (1) 2-D X-ray imaging of the core from several different directions, (2) rough evaluation of sedimentary structures, and (3) determination of the best direction for core splitting.