Carbon-isotope stratigraphy of Cenomanian–Turonian platform carbonates from the southern Apennines (Italy): a chemostratigraphic approach to the problem of correlation between shallow-water and deep-water successions

Abstract

The carbon-isotope record of three sections of shallow-water carbonates from the Upper Cretaceous sequences of the southern Apennines (Italy) shows a pronounced positive excursion of about 4-5‰. Using the upper Cenomanian Cisalveolina fraasi level as a biostratigraphic tie-point we correlate this excursion to the OAE-2 isotopic event. Comparison with the standard reference ä 13 C curve of Eastbourne (England) shows that the overall character of the excursion is clearly reproduced in the shallow-water curves. Chemostratigraphic correlation allows definition of the age of some important shallow-water biostratigraphic events to the precision of an ammonite zone, using the well-established bio-chronostratigraphic framework defined in the Eastbourne section. The onset of the Cenomanian-Turonian isotopic excursion coincides with a transgressive trend, recorded by the occurrence of more open-marine facies and culminating with an incipient drowning in one of the sections studied. Our data suggest that the open-ocean isotopic signal is most faithfully recorded and preserved in shallow-water platform carbonates during transgressive periods, when the effects of meteoric diagenesis and seawater ageing are less severe.

Stepwise extinction of larger foraminifers at the Cenomanian-Turonian boundary: A shallow-water perspective on nutrient fluctuations during Oceanic Anoxic Event 2 (Bonarelli Event)

“…1). Using the upper-Cenomanian largerforaminifer marker Cisalveolina fraasi as a biostratigraphic tie point, this excursion can be correlated with the well-known Cenomanian-Turonian carbon isotope event and can be used to establish a refi ned chronostratigraphic framework for the shallow-water carbonate sections of the southern Apennines (Parente et al, 2007). All carbon isotope curves show an initial rise to a fi rst peak, followed by a return to lower values (so-called trough phase), followed by a rise into another peak (second peak), succeeded by slightly lower, relatively constant but more persistent values (plateau phase) that continue until the beginning of a decay toward background levels: this pattern conforms exactly to the fi ne structure of the δ 13 C excursion at the Cenomanian-Turonian boundary in the European reference section of Eastbourne, England (Paul et al, 1999).…”

Realistic Paleobathymetry of the Cenomanian–Turonian (94 Ma) Boundary Global Ocean

“…This exactly spells out the difference between the two bathymetry dataset and highlights the importance of reconstructing the shelf-slope-wedge. This has special significance especially for the C-T time, as for decades the paleoclimate community has argued for extensive shallow epicontinental seas [36,[62][63][64][65][66][67][68][69][70][71][72][73][74][75][76] for example, to explain oceanic anoxic events. The OES C-T Ocean compared to Modern Ocean, has 4.75% more area (ocean area) less than 1000 m deep (maximum extent of combined euphotic and disphotic zone depth).…”

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

“…In general, shallow-water carbonates are more prone to diagenesis as a result of meteoric-vadose diagenetic overprinting. Nonetheless, the d 13 C records of Cretaceous shallow-water sections have been successfully correlated with well-preserved deep-water sections (Davey & Jenkyns 1999;Parente et al 2007). It has been argued that oxygen isotopes are more sensitive to diagenetic effects that may lead to considerable lowering of d 18 O values (Schrag et al 1995).…”