Calcareous nannofossil biostratigraphy across the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene transition is characterized by a prominent negative carbon isotope excursion that corresponds to the Paleocene Eocene Thermal Maximum (PETM). The sharp negative shift of stable carbon isotopes has been retained as marker for the Paleocene/Eocene boundary. Although recorded in several oceanic and onland settings, the PETM phases namely the onset, the core of the event and the recovery, are not adequately dated by standard calcareous nannofossils biozonations. Here, we present new biostratigraphic data from Sites 1209 (Shatsky Rise, Tropical Pacific Ocean) and 1263 (Walvis Ridge, South Eastern Atlantic Ocean) in order to precisely assess the succession of biostratigraphic events (first and last occurrences, changes in the assemblage composition), and to anchor them to the independent proxy represented by the δ13Cbulk carb curve. A tidy comparison of our data with nannofossil events from six sections located at different (paleo)latitudes and in different geological settings (open ocean-to-shelf) revealed 26 calcareous nannofossil events across a 250 kyrs long-lasting interval spanning the PETM, and allowed a high-resolution biozonal subdivision of this interval. Calcareous nannofossil events plotted against available δ13Cbulk carb curves show a certain degree of diachroneity, even when considering previously established zonal markers. Also, unconformities occur at the onset of PETM in most oceanic sites, but to a lesser extent in onland sections. We propose here a new biozonation, based on reproducible events at different localities, to obtain a chronostratigraphic subdivision with a high-resolution for this short-lasting hyperthermal event. We define thus four new zones spanning the latest Paleocene and the earliest Eocene that allow correlation of shelf and open-ocean localities, and two subzones mainly useful in shelf environments. These new zones correlate to the main trends of the δ13Cbulk carb curve and define the pre-excursion interval (PE-1), the negative δ13Cbulk carb shift defining the base of the Eocene (PE0), the core of the event, the recovery phase I (PE1) and the recovery phase II intervals (PE2).