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

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

doi:10.5194/cp-12-1995-2016

Abstract

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.

Highlights

The organic-rich Livello Bonarelli formed as a result of oxygen deficiency and carbonate dissolution in the oceans duringPublished by Copernicus Publications on behalf of the European Geosciences Union.S
Occurring black cherts and shales below the Livello Bonarelli demonstrate that oceanic conditions in the Umbria–Marche Basin were punctuated by episodes of regional anoxia from the mid-Cenomanian onwards
The proxy records from the Bottaccione, Contessa and Furlo sections are all presented on the same height scale, using the recent height scale for the Cretaceous Umbria– Marche Basin, introduced by Sprovieri et al (2013)

Summary

Introduction

During Oceanic Anoxic Event 2 (OAE 2), a combination of factors caused increased productivity, incomplete decomposition of organic matter and widespread deposition of black shales These sediments have been intensively studied, the exact extent, cause, timing and duration of oceanic anoxia are debated (Sinton and Duncan, 1997; Mitchell et al, 2008). Occurring black cherts and shales below the Livello Bonarelli demonstrate that oceanic conditions in the Umbria–Marche Basin were punctuated by episodes of regional anoxia from the mid-Cenomanian onwards Their hierarchical stacking pattern suggests an orbital control on the deposition of organic-rich horizons (Mitchell et al, 2008; Lanci et al, 2010). We investigate the role of orbital forcing on climate and the carbon cycle and, on organic-rich sedimentation prior to, during, and after OAE 2

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Results

Conclusion