High-resolution chemostratigraphy of the Bonarelli Level (OAE 2) in the Umbria–Marche Basin (central Italy)

The Bonarelli Level in the Umbria–Marche Basin (Italy) represents the most famous lithological expression of Oceanic Anoxic Event 2 (OAE 2), a major environmental perturbation that occurred ∼94 million years ago. The lack of carbonate prevents the use of carbonate carbon isotopes and the application of calcareous nannofossils and planktonic foraminifera for stratigraphic characterization. This limitation has led to contrasting interpretations of the stratigraphic significance of the unit, affecting correlation with coeval records. Here, we present new high-resolution organic carbon-isotope ratios from two key localities of the Bonarelli Level to compare with equivalent sections elsewhere. The data indicate that the entire OAE 2 interval, as defined by carbon-isotope chemostratigraphy, is potentially preserved in the Bonarelli Level, albeit in condensed form, challenging previous suggestions of a significant hiatus at the top of the unit. High-resolution chemostratigraphy reveals coeval variations in total organic carbon (TOC) and lithological patterns in Umbria–Marche, indicating a basin-wide depositional response with local changes mainly controlled by winnowing and redeposition of radiolarian tests. This framework allows a clearer identification of the timing of the onset and termination of the dominant anoxic to euxinic conditions within the OAE 2 interval in the Umbria–Marche Basin.