During the cruise, individual oriented samples were taken in relatively undisturbed working halves of the cores. A total of 112 samples were taken at ~50- to 80-cm intervals from Unit I (Shipboard Scientific Party, 1998). We collected each sample by pushing a standard ODP sample box (6.06 cm3) until the box was full. We then inserted a sharp knife to cut off and to support the sample during removal. All samples were immediately sealed in plastic bags with wet sponges to protect against drying.
On shore, we measured the anisotropy of magnetic susceptibility (AMS) of each sample with a Kappabridge KLY-3S magnetic susceptibility meter (Table T1). After completing magnetic fabric measurements, we proceeded to SEM observation using the same samples.
Before SEM observation, we fixed wet and fragile samples using a freeze-drying method (e.g., O'Brien, 1970; Gillott, 1975). In this study, we used the t-butyl alcohol freeze-drying method described as follows (Takizawa et al., 1995): After all samples were placed in ethanol, they were dipped into t-butyl alcohol, frozen using liquid nitrogen, and dried in a vacuum evaporator. We selected about 30 specimens for SEM observation. These SEM specimens were investigated by a scanning electron microscope operating at 5 kV. The rest were preserved in a t-butyl bath for future analysis. The reliability of the above procedure was proven in a previous study by Takizawa and Ogawa (1999), who have succeeded in describing microstructure in the scaly fabric portion from the basal décollement zone of the northern Barbados accretionary prism.
To estimate the relative abundance of broken coccolith fragments in a specimen, we basically followed the visual estimation technique (Mazzullo et al., 1988) on a SEM photo by using a standard visual comparison chart. The relative number of fragments were classified into six categories: dominant (>50%-100%), abundant (>20%-50%), common (>5%-20%), present (>1%-5%), rare (>0.1%-1%), and trace (0%-0.1%) in descending order.
To describe a magnetic anisotropy, a Flinn-type diagram has been conventionally used to plot a measure of foliation against that of lineation as this is analogous to the plots of strain or shape ratios commonly used in structural geology (Flinn, 1962, 1965). The eccentricity of the anisotropy ellipsoid can be expressed mainly in terms of the ratios of the axial values. These parameters, i.e., lineation, L, and foliation, F, are given by
where Kmax, Kint, and Kmin are the maximum, intermediate, and minimum axes of the susceptibility ellipsoid, respectively. On this diagram, oblate fabrics plot below the slope of unit gradient and prolate fabrics plot above.