Planktonic Foraminifera and Environmental Changes Across the Bonarelli Event (Oae2, Latest Cenomanian) in Its Type Area: A High-Resolution Study From the Tethyan Reference Bottaccione Section (Gubbio, Central Italy)

Abstract

The worldwide latest Cenomanian Oceanic Anoxic Event 2 (OAE2) was investigated for the planktonic foraminiferal assemblages in the type area of its sedimentary expression, the C org -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 before 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 preceding deposition of the Bonarelli Level. The onset of a highstress environment is clearly shown by the shift to a distinctly unstable planktonic foraminiferal structure, characterized by low species diversity and marked foraminiferal changes and events. Some of these took place at the same time (the rotaliporid crisis, the heterohelicid decline, the Hedbergella-Schackoina shift, the onset of the 'large form eclipse' when Ͼ 150 m forms temporarily disappeared) followed by other sequential events (onset of dwarfism, schackoinid acme, and hedbergellid acme). The above-mentioned changes and events indicate for Phase II an increased surface productivity, enhanced oxygen minimum zone, and marked rapid changes of ecological parameters (e.g., temperature, salinity, trace metals). These marked foraminiferal changes culminate at the base of the Bonarelli Level with the temporary disappearance of all planktonic foraminifera. Phase III (100-900 kyr) coincides with the Bonarelli Level deposition and is characterized by highly eutrophic conditions, as indicated by radiolarian proliferation. Phase IV ...

Biostratigraphy of the Cenomanian-Turonian boundary in the Eastern Carpathians (Dâmboviţa Valley): preliminary observations

“…The Cenomanian/Turonian boundary interval is barren of foraminifera in most of the studied sites from the North Atlantic and Europe (Kuhnt, 1992;Coccioni and Luciani, 2004;Scopelliti et al, 2004;Bak, 2006 among others), but in the Ganuza section, Spain and the deepest sites of Demerara Rise, ODP Leg 207, a benthic extinction is not evident, only low diversity and poor assemblages occur as result of low oxygen levels represented by this interval (Peryt, 2004;Friedrich et al, 2006).…”

Iterative evolution of digitate planktonic foraminifera

“…1). Unusually diverse assemblages have been found in association with organic-rich sediments preserved on continental margins that are the hallmark of Cretaceous oceanic anoxic events (OAEs) (e.g., Magniez-Jannin 1998;Aguado et al 1999;Cobianchi et al 1999;Luciani et al 2001;Leckie et al 2002;Verga and Premoli Silva 2002;Luciani 2004, 2005;Coccioni et al 2006). OAEs involved severe per-turbations to the marine carbon system and pelagic ecosystems and in some cases were accompanied by extinction of many surface-living planktonic foraminifera (Leckie et al 2002;Coccioni et al 2006).…”

Cretaceous Oceanic Anoxic Event 2 in the Arobes section, northern Spain: nannofossil fluctuations and isotope events

“…For instance, the record of benthic and planktonic foraminiferal diversity from the Rehkogelgraben of Upper Austria during OAE2 is much higher than elsewhere, possibly due to the palaeogeography of the Penninic Ocean, a semi-enclosed basin that could represent a refuge during the biotic and palaeoenvironmental crisis (Gebhardt et al 2010). In contrast, in the Botaccione section (Gubbio, Italy), Coccioni & Luciani (2004) assumed the instauration of an extremely stressed environment during OAE2, characterized by a significantly developed oxygen minimum zone and high eutrophic surface waters that significantly impacted the biota. The OAE2 is not characterized everywhere by an anoxic event, and this may explain differences from one site to another.…”