Site 215 is located at ~5300 mbsl on the western flank of Ninetyeast Ridge far from any continents in the central Indian Ocean (von der Borch, Sclater, et al., 1974). The existing early Paleogene eolian grain-size record for the Southern Hemisphere (Hovan and Rea, 1992) was generated using sediment samples recovered between 83 and 130 meters below seafloor (mbsf). This record (Fig. F1) shows a significant ~6 µm decrease in the median grain size of eolian material near the P/E boundary (~103.3 mbsf), from ~9.6 µm in upper Paleocene sediment (109.37 mbsf) to ~3.8 µm in lower Eocene sediment (84.83 mbsf).
The isolation and analysis of eolian material from marine sediment is a labor-intensive process involving many steps (see the "Appendix"). The subsequent analysis of the extracted component requires reliable measurements. Our first goal, therefore, was to test whether we could reproduce the published eolian grain-size record at Site 215. Ten samples were collected between 85 and 107 mbsf, with most samples taken within 5 cm of those examined by Hovan and Rea (1992).
All Leg 208 sites currently lie well off the continental shelf more than 1200 km away from the African continent and likely were a greater distance in the early Paleogene as a result of a higher sea level. Drilling at Sites 1263 and 1267 recovered lower Paleogene sediment sequences on Walvis Ridge but at much different water depths, both now and in the past. Site 1263 is presently at ~2700 mbsl, whereas Site 1267 is presently at ~4350 mbsl. Near the P/E boundary at ~55 Ma, however, water depths were probably ~1500 m for Site 1263 and ~3200 m for Site 1267 (Zachos et al., 2005).
The P/E boundary has been identified at both Sites 1263 and 1267 (Zachos et al., 2005). Close to this time horizon, ages can be assigned to sediment depths fairly accurately using a model (Zachos et al., 2005) that ties changes in the carbon-isotope composition of carbonate to those observed at ODP Site 690, which has been calibrated using cyclostratigraphy (Rohl et al., 2000). Thus, "time-coincident" sediment samples can be taken from Sites 1263 and 1267 around the P/E boundary. Five such samples were collected from each site. Time-coincidence was emphasized so that potential differences in the delivery of eolian and hemipelagic components to the two sites at similar times could be explored.