Intervals of early Pliocene (3.86 Ma; Shipboard Scientific Party, 1997) laminated diatom ooze from Holes 1010C (interval 167-1010C-5H-4, 77-90 cm) and 1010E (interval 167-1010E-5H-2, 22.5-41.5 cm) were identified on board ship. These two intervals were sampled subsequently at the ODP Gulf Coast Repository, using the ODP sediment slab cutters and following the procedure described in Pike and Kemp (1996). Slabs were subsampled and highly polished thin sections prepared for scanning electron microscope (SEM) backscattered electron imagery (BSEI) analysis (Pike and Kemp, 1996).
BSEI is a powerful technique for investigating laminated diatom-rich sediment fabrics (Grimm, 1992; Kemp, 1990; Kemp et al., 1998; Pearce et al., 1998; Pike and Kemp, 1997). When analyzing a polished thin section, the number of backscattered electrons, or backscatter coefficient (recorded as image brightness) of a grain, is principally related to the mean atomic number of that grain; the greater the average atomic number, the brighter the image (Goldstein et al., 1981). Thus, images may be regarded as porosity maps. In the early Pliocene Ethmodiscus ooze from Site 1010, high-porosity sediment rich in Ethmodiscus valve fragments records a dark image (e.g., Fig. 1, Fig. 2, Fig. 3). Low-porosity sediment that is rich in high average atomic number mineral grains (such as quartz) and biogenic debris (such as coccoliths and discoasters) records a bright image (e.g., Fig. 1, Fig. 2, Fig. 4).
Macroscopic core photographs are compared to low-magnification BSEI photomosaics for gross sediment fabric analysis (see Fig. 1, Fig. 2), and higher magnification BSEI photography is used to highlight the characteristic features of the laminated Ethmodiscus ooze intervals (see Fig. 3, Fig. 4).