Oligocene foraminiferal δ18O records suggest the development of ice caps (= inferred glacio–eustatic falls) at ca. 36, 31, and 25 Ma. Biostratigraphic analyses of wells from the United States east coast and Irish continental margins consistently show that upper Oligocene sediments overlie a diachronous erosional surface, underlain by lower Oligocene to Eocene strata. At the minimum, the hiatus extends between ca. 34 and 30 Ma. We speculate that erosion during a glacio–eustatic fall near the early/late Oligocene boundary (ca. 32–31 Ma) developed (1) an unconformity on the margins, (2) numerous canyons noted in seismic profiles from the margins of the North Atlantic, and (3) a coastal offlap event. Using δ18O data, we apply a model for eustatic changes and margin response that explains the relationships of sea level, unconformities, and coastal onlap/offlap events.

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