>During the Jurassic and Cretaceous, global events of widespread low-oxygen conditions (Oceanic Anoxic Events) were recorded in marine strata associated to major perturbations in the carbon cycle. These disturbances were linked to rapid global warming, probably caused by a release of carbon dioxide in the atmosphere due to degassing related to large-scale volcanism, dissociation of methane hydrates and thermogenic methane.

>Many authors have studied the Oceanic Anoxic Events (OAEs) following the original definition by Schlanger and Jenkyns (1976). Nine OAEs are recognized as of global significance and three of them are considered as major events: T-OAE, OAE1a and OAE2. The first, also called Toarcian OAE or Posidonienschiefer event, occurred in the Early Jurassic (~183 Ma) and was first identified by Jenkyns (1980) in northern Europe. The second, also called early Aptian OAE or Selli Event, occurred in the late Early Cretaceous (~120 Ma) and was first observed by Coccioni et al. (1987) in Italy. The third global event, also called Cenomanian – Turonian OAE or Bonarelli Event, occurred in the early Late Cretaceous (~93 Ma) and was noticed by Schlanger and Jenkyns (1976) when comparing subsurface data from the Deep Sea Drilling Project to outcrops; with the most famous being the Livello Bonarelli in the Umbrian Apennines of Italy.

>- The expression of the Oceanic Anoxic Event 2 (OAE2) in the northeast of Brazil (Sergipe-Alagoas Basin)