X-radiographic prints of the slab samples from Leg 172 show the following features.
In general, (1) the images become lighter as the amount of nannofossils increases and (2) coarser sediments result in lighter images.
For samples containing visible, distinct structures (Group I), the radiograph images reveal more detailed, fine structures such as (1) distinct sharp lines indicating plane beds; (2) gradation from light to dark uphole, indicating fining-upward structures; (3) ripple cross-laminae; (4) erosional surfaces sometimes associated with small scours; and (5) very rare bioturbation. These structures indicate fairly intense flows, such as turbidity currents and contour currents, that are especially strengthened by some phenomena (i.e., benthic storms) that occur at these sites and deposit sediments over short periods. Group II samples, which contain visible color changes or changes in magnetic susceptibility but not visibly distinct structures as in Group I, are characterized by (1) bioturbated, gradual contacts; (2) homogeneous images; (3) sharp hairline structures associated with the contacts between the different colors; and (4) obscure line structures that are sometimes bioturbated. It is notable that the sharp peaks in magnetic susceptibility do not disappear even where the interval is intensely bioturbated. It should be noted that the change in color or magnetic susceptibility could be accompanied by some degree of intense flow that could make these line structures in Group II, even though they are not recognized in visual inspections. Although further investigation is needed to discover the intensity of these flows, it is suggested that these changes in flow conditions occur commonly in Deep Western Boundary Currents in these areas, resulting in these kind of structures and the high sedimentation rates seen in our samples. The features observed here would aid our understanding of sedimentation in these areas when linked with studies of other factors, such as isotopes and grain sizes.