Planktonic foraminifers and environmental changes across the Bonarelli Event (OAE2, latest Cenomanian) in its type area: a high-resolution study from the Tethyan reference Bottacione section (Gubbio, central Italy)

• Published in: The Journal of Foraminiferal Research
• Main Authors: Coccioni R., Luciani V.
• Other Authors: Coccioni, R., Luciani, V.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2004
• Subjects: Cretaceous anoxic event; Bonarelli event; Cenomanian; planktonic foraminifera; Umbria-Marche; paleoecology; paleoceanography; Planktonic foraminifera
• Online Access: http://hdl.handle.net/11392/1204338; https://doi.org/10.2113/0340109

The worldwide latest Cenomanian Oceanic Anoxic Event 2 (OAE2) was investigated for the planktonic foraminiferal assemblages in the type area of its sedimentare expression, the Corg–rich Bonarelli Level (Gubbio, central Italy). The 313 kyr preceding the onset of OAE2 and the 153 kyr following the end of this event were analyzed in the deep-water setting of the Bottaccione section (Umbria-Marche Basin). For the first time, a highresolution approach and quantitative methods were applied.Several events and biotic changes, including the acme and crisis of different genera, were recognized. They provide evidence of a progressive and rapid deterioration of paleoenvironmental conditions, reaching a climax coincident with the Bonarelli Event, and of the subsequent, gradual (although not complete) recovery. Although no major mass extinction in planktonic foraminifera occurred across the Bonarelli Event, the extinction of the most specialized forms, i.e., the rotaliporids, and Globigerinelloides bentonensis, is recorded just bifore its onset. The observed pattern of marked changes in planktonic foraminiferal assemblages indicates five discrete phases of different degrees of environmental perturbation within the marine ecosystem. Phase I (313–55 kyr prior to the onset of OAE2) is characterized by a high planktonic foraminiferal abundance and diversity that imply a relatively stable environment, with different ecological niches occupied and stratified water column. On the other hand, relatively high percentages of hedbergellids and heterohelicids indicate a general meso-eutrophic environment and a well-developed oxygen minimum zone. Episodes of increased eutrophic conditions are indicated by pulses in abundance of radiolarians. A well-developed oxygen minimum zone may be related to a long-term change that precedes the onset of OAE2 (mid-Cenomanian Event). The most dramatic changes took place during Phase II and encompassed the last 55 kyr precedine deposition of the Bonarelli Level. The onset of a highstress environment is ...