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The Eocene-Oligocene transition (between ca. 34 and 33.5 Ma) is the most profound episode of lasting global change to have occurred since the end of the Cretaceous. Diverse geological evidence from around the world indicates cooling, ice growth, sea-level fall, and accelerated extinction at this time. Turnover in the oceanic plankton included the extinction of the foraminifer Family Hantkeninidae, which marks the Eocene-Oligocene boundary in its type section. Another prominent extinction affected larger foraminifera, which resulted in the loss of some of the world's most abundant and widespread shallow-water carbonate-secreting organisms. However, problems of correlation have made it difficult to relate these events to each other and to the global climate transition as widely recorded in oxygen and carbon isotope records from deep-sea cores. Here, we report new paleontological and geochemical data from hemipelagic sediment cores on the African margin of the Indian Ocean (Tanzania Drilling Project Sites 11, 12 and 17). The Eocene-Oligocene boundary is located between two principal steps in the stable-isotope records. The extinction of shallow-water carbonate producers coincided with an extended phase of ecological disruption in the plankton and preceded maximum glacial conditions in the early Oligocene by ∼200 k.y.

Extinction and environmental change across the Eocene-Oligocene boundary in Tanzania