Itajaí-Açu Formation

The Itajaí-Açu Formation (Formacão Itajaí-Açu) is a geological formation of the Santos Basin offshore of the Brazilian states of Rio de Janeiro, São Paulo, Paraná and Santa Catarina. The predominantly shale with interbedded turbiditic sandstones formation dates to the Late Cretaceous period; Cenomanian-Maastrichtian epochs and has a maximum thickness of 2000 m. The formation is a reservoir rock of the fields in the Santos Basin.

Etymology
The formation is named after the Itajaí-Açu River, Santa Catarina.

Description
The Itajaí-Açu Formation is 1545 to 2000 m thick, and comprises a thick interval of dark grey clayey rocks, interbedded with the clastics of the Santos and Juréia Formations. Within this formation, the Ilhabela Member includes the turbiditic sandstones occurring along the section. The sedimentary environment is thought to be marine talus to open basin. Biostratigraphic data from palynomorphs, calcareous nannofossils and planktonic foraminifera indicate a Late Cretaceous age (Cenomanian-Maastrichtian).

Petroleum geology
The formation, mainly its Ilhabela Member, is the main post-salt reservoir rock of the Santos Basin. The formation also is the main post-salt source rock and a seal for the post-salt reservoirs.