Umbria–Marche revisited: A refined magnetostratigraphic calibration of dinoflagellate cyst events for the Oligocene of the Western Tethys

In order to contribute to the improvement of biostratigraphic age control for the Oligocene of the Western Tethys, we have carried out a high-resolution study of dinoflagellate cysts from three outcrop sections in the Umbria–Marche Basin of Central Italy. All three sections investigated (Contessa Barbetti Road, Monte Cagnero and Pieve d'Accinelli) have magnetostratigraphic age control, thus allowing us to firmly tie the identified dinoflagellate cyst bioevents to the global geomagnetic polarity timescale.The Oligocene succession of the Umbria–Marche Basin is marked by recurrent acmes of Chiropteridium spp., Lingulodinium machaerophorum and Deflandrea spp. that can be correlated between the sections studied. These acmes originate from long-distance transport from near-shore environments into the pelagic setting represented by the sections studied, probably triggered by eustatic sea-level variations. Four formal dinoflagellate cyst zones of Wilpshaar et al. (1996; Journal of the Geological Society, London 153, 553-561), viz the Hpu, Clo, Dbi, and Ebu zones are revised. Furthermore we propose two new subzones for the Dbi zone. The new taxon Oligokolpoma galeottii is formally described.