The objective of Ocean Drilling Program (ODP) Leg 199 was to drill a transect of sites across the equator along crust that was created at ~56 Ma. In so doing we endeavored to recover well-preserved sections of Paleogene sediments that would give us a history of the strength of the equatorial divergence, the equatorial currents, and the winds that drove them from mid-Miocene through early Eocene times. Although the calcite compensation depth (CCD) was quite shallow (CCD = ~3300 m) during the Eocene, we hoped that the basal part of the recovered section would contain carbonate material that would allow us to compare radiolarian and calcareous nannofossil stratigraphies. Toward that end we also drilled one site (Site 1218) on ~40-Ma crust in order to recover some upper to middle Eocene sediments containing carbonate. We recovered the sections needed for studying the Paleogene history of the equatorial current system; however, poor preservation of the basal sections prevented a detailed comparison of the calcareous and siliceous stratigraphies. The paleomagnetic stratigraphies developed for these sites (Lanci et al., 2004, in press; Pares et al., 2004) did enable us to establish a robust chronostratigraphy for most of the section recovered. This represents the first time that most of the radiolarian stratigraphic datums of the Paleogene have been tied directly to the paleomagnetic timescale.
The primary focus of this investigation is to precisely quantify the timing and duration of radiolarian events in the sedimentary record. A remarkable number of problems can be addressed with a highly calibrated timescale, from rates of biological evolution to evaluating diachrony of extinction events, to connections between evolution and tectonics. The success depends on the application of a well-calibrated magnetostratigraphy. Development of a high-resolution temporal framework for Paleogene radiolarians will benefit macroevolutionary studies of mass extinctions, post-extinction recoveries, evolutionary radiations, patterns of migration, and diversification.