Articles | Volume 12, issue 10
Research article
19 Oct 2016
Research article |  | 19 Oct 2016

Orbital control on the timing of oceanic anoxia in the Late Cretaceous

Sietske J. Batenburg, David De Vleeschouwer, Mario Sprovieri, Frederik J. Hilgen, Andrew S. Gale, Brad S. Singer, Christian Koeberl, Rodolfo Coccioni, Philippe Claeys, and Alessandro Montanari

Abstract. The oceans at the time of the Cenomanian–Turonian transition were abruptly perturbed by a period of bottom-water anoxia. This led to the brief but widespread deposition of black organic-rich shales, such as the Livello Bonarelli in the Umbria–Marche Basin (Italy). Despite intensive studies, the origin and exact timing of this event are still debated. In this study, we assess leading hypotheses about the inception of oceanic anoxia in the Late Cretaceous greenhouse world by providing a 6 Myr long astronomically tuned timescale across the Cenomanian–Turonian boundary. We procure insights into the relationship between orbital forcing and the Late Cretaceous carbon cycle by deciphering the imprint of astronomical cycles on lithologic, physical properties, and stable isotope records, obtained from the Bottaccione, Contessa and Furlo sections in the Umbria–Marche Basin. The deposition of black shales and cherts, as well as the onset of oceanic anoxia, is related to maxima in the 405 kyr cycle of eccentricity-modulated precession. Correlation to radioisotopic ages from the Western Interior (USA) provides unprecedented age control for the studied Italian successions. The most likely tuned age for the base of the Livello Bonarelli is 94.17 ± 0.15 Ma (tuning 1); however, a 405 kyr older age cannot be excluded (tuning 2) due to uncertainties in stratigraphic correlation, radioisotopic dating, and orbital configuration. Our cyclostratigraphic framework suggests that the exact timing of major carbon cycle perturbations during the Cretaceous may be linked to increased variability in seasonality (i.e. a 405 kyr eccentricity maximum) after the prolonged avoidance of seasonal extremes (i.e. a 2.4 Myr eccentricity minimum). Volcanism is probably the ultimate driver of oceanic anoxia, but orbital periodicities determine the exact timing of carbon cycle perturbations in the Late Cretaceous. This unites two leading hypotheses about the inception of oceanic anoxia in the Late Cretaceous greenhouse world.

Short summary
The relative contributions of astronomical forcing and tectonics to ocean anoxia in the Cretaceous are unclear. This study establishes the pacing of Late Cretaceous black cherts and shales. We present a 6-million-year astrochronology from the Furlo and Bottaccione sections in Italy that spans the Cenomanian–Turonian transition and OAE2. Together with a new radioisotopic age for the mid-Cenomanian event, we show that astronomical forcing determined the timing of these carbon cycle perturbations.