Marine biotic signals across a late Eocene impact layer at Massignano, Italy: evidence for long-term environmental perturbations?

The Eocene-Oligocene transition marks the passage from 'greenhouse' conditi ons to an 'icehouse' state, with progressive global cooling starting in the early middle Eocene. The late Eocene presents substantial evidence for ext raterrestrial impacts whose effects on living organisms and climatic change s are still not completely clear. A high-resolution, microfloral and faunal investigation has been carried out in a 4-m-thick segment of the Massignan o Global Stratotype Section and Point for the Eocene-Oligocene boundary. Th e studied interval includes a late Eocene (35.7 +/- 0.4 Myr old) impactocla stic layer containing several cosmic signatures. The impact event recorded at Massignano had no abrupt, dramatic effects on marine biota in terms of e xtinction. However, significant quantitative changes in the calcareous plan kton and dinoflagellate cyst assemblages occurred 60 kyr after the impact e vent. The observed pattern is intepreted as reflecting a long-term re-organ ization of water structure.