The Radiolarian biotic response during OAE2. A high-resolution study across the Bonarelli level at Bottaccione (Gubbio, Italy)

Abstract

In order to improve our understanding of the radiolarian biotic response and the palaeoceanographic changes associated with the Late Cenomanian oceanic anoxic event (OAE2), a high-resolution radiolarian study was carried out across the Bonarelli level at its typical locality (Bottaccione section, central Italy). Our results confirm that a drastic radiolarian faunal change took place during the OAE2. The radiolarian turnover took place within the median part of the Bonarelli level, associated with an interval of high organic matter preservation, but relatively low values of silica. Therefore, this part constitutes a critical period in the evolutionary history of Radiolaria. A synthesis of all data available in the Umbria-Marche basin suggests that the lower part of the Bonarelli level (and underlying limestones) records mainly radiolarian extinctions ( ca. 41%), while its upper part (and overlying limestones) records mainly first occurrences ( ca. 35%). Our results improve understanding of the paleoecology of the family Saturnalidae, which would seem to prefer oligotrophic environments.