The Eocene-Oligocene transition (between ca. 34 and 33.5 Ma)is the most profound episode of lasting global change to haveoccurred since the end of the Cretaceous. Diverse geologicalevidence from around the world indicates cooling, ice growth,sea-level fall, and accelerated extinction at this time. Turnoverin the oceanic plankton included the extinction of the foraminiferFamily Hantkeninidae, which marks the Eocene-Oligocene boundaryin its type section. Another prominent extinction affected largerforaminifera, which resulted in the loss of some of the world'smost abundant and widespread shallow-water carbonate-secretingorganisms. However, problems of correlation have made it difficultto relate these events to each other and to the global climatetransition as widely recorded in oxygen and carbon isotope recordsfrom deep-sea cores. Here, we report new paleontological andgeochemical data from hemipelagic sediment cores on the Africanmargin of the Indian Ocean (Tanzania Drilling Project Sites11, 12 and 17). The Eocene-Oligocene boundary is located betweentwo principal steps in the stable-isotope records. The extinctionof shallow-water carbonate producers coincided with an extendedphase of ecological disruption in the plankton and precededmaximum glacial conditions in the early Oligocene by 200 k.y.