Global Foraminiferal Successions Constrain the Timing and Pattern of Marine Turnover Across the Eocene-Oligocene Transition

The Eocene-Oligocene transition (EOT; ca. 34.1-33.7 Ma) was a major late Paleogene greenhouse-icehouse transition and a key interval for assessing how gradual climate cooling and more abrupt environmental change are recorded in marine successions. Yet the global timing and pattern of marine biotic change across the EOT remain poorly resolved because existing compilations have not been integrated within a consistent stratigraphic framework. Here we compiled ~40,000 occurrence records representing 1,269 species of planktonic, larger benthic, and small benthic foraminifera from 161 sections and sites worldwide, and applied CONOP.EA, a recently developed quantitative stratigraphic algorithm. Using an evolutionary strategy based on mutation, recombination, and selection, CONOP.EA iteratively optimizes composite event sequences built from first and last appearances across many sections, while enforcing basic stratigraphic constraints, to obtain a composite that best matches the observed ranges and coexistences in the source dataset. The optimized framework indicates that marine biotic change across the EOT was staggered among ecological groups rather than concentrated in a single synchronous extinction pulse. In broad terms, planktonic and larger benthic foraminifera changed most strongly near the onset of Antarctic glaciation and sea-level fall, whereas small benthic foraminifera record earlier and more prolonged change. This pattern suggests that shorter-term events near the EOT played out within a longer phase of climatic cooling. The EOT therefore provides a stratigraphically constrained late Paleogene example of how rapid events and longer-term global change are recorded together in marine biotic successions, and a useful reference point for comparison with other greenhouse-icehouse transitions.