Ocean Drilling Program, United States

The Paleogene Equatorial transect (Leg 199, Fig. 1, Table 1) will 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 will be primarily devoted to a transect along 56- to 57-Ma crust, old enough to capture the late Paleocene thermal maximum event in the basal, more carbonate-rich sediments. One drill site (Site PAT-8C) will also be drilled on 40 Ma crust to collect a near-equatorial sediment sequence from the middle Eocene through the late Eocene transition to glacial conditions in Antarctica. If the plate tectonic model we used for paleopositions is approximately correct, Site PAT-8C is at the equator at 40 Ma. Because the Pacific plate drifts north with time out of the high productivity equatorial region, Paleogene equatorial sediments are overlain by a thin Neogene section of red clays. The youngest biogenic sediments to be drilled will be early Miocene in age. The lack of Neogene sedimentation minimizes burial diagenesis; essentially the entire Paleogene sediment section should be recoverable by advanced piston coring. The Leg 199 transect extends from a paleolatitude of about 11 degrees N to about 5 degrees S and encompasses anomalously thick early Eocene sediments deposited as much as 8 degrees north of the Paleocene equator. The transect will collect continuous sediment sequences to document the evolution of the equatorial current system, equatorial surface-water and deep-water temperature variations, wind patterns, and productivity in the late Paleocene and early Eocene. In addition, one site will specifically be drilled to study the changes in equatorial circulation associated with the transition from the late Eocene to the early Oligocene to the ice-house world.