Estratigrafía, anomalías geoquímicas y extinciones de radiolarios del evento anóxico oceánico del Cenomaniense terminal en el Apenino septentrional y en los Alpes meridionales

Resumen

The mid-Cretaceous earth is often referred to as a greenhouse world characterised by high atmospheric CO, levels, reduced temperature gradients and a warm ocean with sea levels extremely high. During the same period, many parts of the world-ocean experienced deposition of sediments rich in organic carbon (oceanic anoxic event) as result of oxygen-deficient conditions in the ocean and high fluxes of organic matter to the sediments. The end-Cenomanian oceanic anoxic event (OAT-2) is the most extensive and best representative of the mid-Cretaceous. In the Italian lithostratigraphy the OAE-2 is known as Bonarelli Horizon, a phosphatic-radiolarian fine-sand/ siltstone developed in pelagic and hemipelagic setting, where neither planktonic nor benthonic microfauna are found, to exception of radiolarians. This paper analyses the relationships between the lithostratigraphy of the Bonarelli Horizon, the geochemical anomalies and the large positive carbon isotope excursion that take place at initial stages o f black shale deposition, and the radiolarian faunal turnover across the end-Cenomanian oceanic anoxic event.