Ocean Drilling Program (ODP) Leg 199, "The Paleogene Equatorial Transect" (Sites 1215 through 1222), was designed to study the evolution of the equatorial Pacific current and wind system as the Earth went from maximum Cenozoic warmth to initial Antarctic glaciations. The drilling program was primarily devoted to a transect along 56- to 57-Ma crust, old enough to capture the Paleocene/Eocene boundary in the basal, more carbonate-rich sediments. The Leg 199 transect extends from a paleolatitude of ~4°N–~4°S to encompass a relatively thick lower Eocene sediment section perhaps 8° north of the paleoequator. One drill site (Site 1218) was also drilled on 40-Ma crust to collect a near-equatorial sediment sequence from the middle Eocene–late Eocene in order to investigate the transition in global climate from the Eocene "greenhouse" to Oligocene "icehouse."

The Pacific plate has drifted northward through Cenozoic time, transporting biogenic sediments deposited under the high-productivity equatorial belt into a zone of extremely slow sediment (red clay) accumulation. Thus, the central tropical North Pacific Ocean is an ideal region in which to sample shallowly buried Paleogene sequences of equatorially deposited biogenic sediments. The thin Neogene cover of red clay in the area means that the entire Paleogene sediment section is potentially drillable by ODP advanced piston corer and extended core barrel methods.