A volcanic CO2 pulse triggered the Cretaceous oceanic Anoxic event 1a and a biocalcification crisis

• Published in: Geology
• Main Authors: S. Méhay, C. E. Keller, S. M. Bermasconi, H. Weissert, P. A. Hochuli, E. Erba, C. Bottini
• Other Authors: C.E. Keller, S.M. Bermasconi, P.A. Hochuli
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2009
• Subjects: emiliania-huxleyI; organic-matter; carbon; methane; ga; stratigraphy; alkenone; MA; Settore GEO/01 - Paleontologia e Paleoecologia; Methane hydrate
• Online Access: http://hdl.handle.net/2434/430721; https://doi.org/10.1130/G30100A.1

The Aptian Oceanic Anoxic Event 1a (OAE1a, ca.120 Ma ago) is one of the most prominent of a series of geologically brief intervals in the Cretaceous characterized by the deposition of organic carbon-rich sediments. OAEs refl ect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records. However, the triggering mechanisms for OAEs remain controversial. Here we present a bulk-rock and molecular (marine and terrestrial biomarkers) C isotope record at unprecedented time resolution, from the Cismon section of northern Italy, that shows that OAE1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle. The documented sequence of events is most compatible with a trigger associated with increased CO2 emissions, possibly leading to a doubling of pCO2, which in turn caused larger C isotope fractionation in marine and terrestrial organisms, and a major biotic crisis in the calcareous nannoplankton. Our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the OAE1a carbon cycle perturbation.