For the purpose for observing sedimentary structures in detail, slab samples were taken to make X-radiographic prints (Table T1). Some of the slab samples were collected on board ship for visibly distinct sedimentary structures. The other slab samples were collected at the Bremen Core Repository after the cruise. These samples were chosen to investigate the sedimentary structures associated with significant changes in sediment color or magnetic susceptibility in marine isotope Stages 8-10. The slab samples are either 15 cm x 3 cm x 1 cm or 10 cm x 3 cm x 1 cm. The slab samples were taken using thin metal frames. The samples were carefully wrapped in thin transparent plastic to avoid drying and breaking.
X-radiographic prints were made by a "soft" (i.e., relatively long wavelength) X-ray generator, Sofron Type STA-1005 (SOFRON Co. Ltd.), at the Geological Survey of Japan. The plastic-wrapped slab samples were placed directly on an exposure holder that contains photographic printing paper and an intensifying screen (Kyokko SMP-308, Kasei Optonix, Ltd.). Black-and-white photographic printing papers (Fujibro WP FM3, 25.4 cm x 30.5 cm, medium weight, white, glossy, hard paper, Fuji Photo Film Co. Ltd.) were used. The exposure holder, above which a sample was placed, was mounted ~0.6 m below the X-ray source. The X-ray current was 4 mA. Other conditions, such as voltage and exposure time, were controlled for each sample so that the internal sedimentary structures could be observed clearly. These conditions are shown in Table T1. After the X-ray exposure was finished, the photographic printing paper was taken out of the exposure holder and processed in a darkroom like a regular photograph.
Because the X-radiographic prints were made directly onto the photographic printing paper in this procedure, the prints are negative, which means the darker regions represent the more penetrable parts of the sample and the lighter regions the more opaque areas (e.g., Bouma, 1969). High atomic number elements absorb the radiation much more strongly than low atomic number elements, and more dense elements absorb more radiation than those that are less dense (e.g., Young, 1967).
"Results" contains descriptions of the samples and their X-radiographic prints. The sample descriptions, regarding such elements as sediment color (compared with Munsell soil color charts) (Munsell, 1975) and grain size, are based on the visual core descriptions given in the Leg 172 Initial Reports volume (Keigwin, Rio, Acton, et al., 1998). Magnetic susceptibility and color reflectance values are described based on shipboard measurements (Keigwin, Rio, Acton, et al., 1998) when there are significant changes in those values.
Color reflectance was measured using a Minolta spectrophotometer (Minolta CM-2002), and results are expressed in the L*a*b* color system. The L*a*b* system can be visualized as a cylindrical coordinate system in which the axis of the cylinder is the lightness variable L*, ranging from 0% to 100%, and the radii are the chromaticity variables a* and b*. Variable a* is the green (negative) to red (positive) axis, and variable b* is the blue (negative) to yellow (positive) axis (Blum, 1997).