Dinoflagellate cyst stratigraphy of the Eocene/Oligocene transition in central Italy

Abstract

Eight dinoflagellate cyst zones based on the Massignano and Monte Cagnero sections in central Italy provide high-resolution control for the Eocene/Oligocene (E/O) transition. Most of these zones have been recognized in the time-equivalent Contessa Highway section and are calibrated against previously established magneto- and biostratigraphies. The invasion of the Mediterranean area by several higher-latitude dinoflagellate taxa marks the E/O boundary as characterized by the last occurrence of the hantkeninids (planktic foraminifers), calibrated against a horizon just above the youngest normal polarity event within Chron C1 3R. Quantitative and qualitative dinoflagellate events across the E/O boundary allow the recognition of warmer and cooler successive intervals of sea surface temperature, in addition to apparent sea-level fluctuations. Our data indicate that latest Eocene warm conditions and a sea-level highstand were rapidly replaced by short-term cooler conditions and a lowstand across the E/O boundary horizon. Following a shortterm warmer interval and a highstand during the earliest Oligocene, a second cool and lowstand episode occurred. This cool interval was of greater magnitude and duration than the one at the E/O boundary horizon and may correspond to the globally recognized cooling event reported from the basal part of Chron C1 3N.